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256 Cards in this Set
- Front
- Back
- 3rd side (hint)
What is the nucleus?
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The control center of the cell
A membrane bound organelle found in eukaryotic cells |
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What are the contents of the nucleus?
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1. Nuclear lamina
2. Nucleolus 3. Chromatin 4. Enzymes needed for DNA replication, repair, and transcription |
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What is the function of the nucleus?
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Site of DNA replication and transcription
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What is the nuclear envelope?
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A double membrane containing pores surrounding the nucleus
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How many membranes does the nuclear envelope have?
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2 lipid bilayers
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What is the nuclear envelope continuos with?
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The outer membrane of the nuclear envelope is continuos with the rough endoplasmic reticulum
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What is the nuclear lamina?
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An interlaced network of proteins
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What is the function of the nuclear lamina?
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1. Attach chromatin to the inner membrane of the nuclear envelope
2. Participate in the breakdown and reformation of the nuclear envelope during cell division |
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What is the role of the nuclear lamina during mitosis?
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During prophase, the phosphorylation of the nuclear lamina (by lamin kinase) initiates the disassembly of nuclear components
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"Phosporylation of the nuclear lamina (by lamin kinase) during prophase of mitosis initiates nuclear dissasembly into small vesicles" in bold!
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Why is breakdown of nuclear components important during mitosis?
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It allows the mitotic spindle to interact with the chromosomes
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What is the nucleolus?
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A non-membrane bound structure located inside the nucleus
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What are the contents of the nucleolus?
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Fibrils and granules rich in RNA
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What is the function of the nucleolus?
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Site of rRNA synthesis and assembly
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A cell having big/multiple nucleolus indicates what?
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The cell is making lots of proteins
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What are the three zones of the nucleolus?
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1. Granular Zone
2. Fibrillar Zone 3. Fibrillar Center |
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Describe the granular zone of the nucleolus
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Found at the periphery
Contains ribosomal precursor particles being assembled |
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Describe the fibrillar zone of the nucleolus
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Centrally located
Contains ribonuclear protein fibrils |
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Describe the fibrillar center of the nucleolus
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Contains DNA that is not being transcribed
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What is chromatin?
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A complex of DNA, histone proteins, and non-histone proteins
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What is DNA?
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A double stranded helical molecule
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What is the function of DNA?
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Carries the genetic information of the cell
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What forms does DNA exists in?
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A DNA
B DNA Z DNA |
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What are histone proteins?
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Positively charged proteins enriched with Arginine and Lysine residues
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What is the function of histone proteins?
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Important in forming two types of structures in chromatin:
1. Nucleosome 2. Solenoid fibers |
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What is a nucleosome?
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The nucleosomes are the basic repeating units of the chromatin fiber, having a diameter of 10nm
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"The nucleosomes are the basic repeating units of the chromatin fiber, having a diameter of 10nm" in bold!
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Solenoid fiber is a
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30 nm fiber
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Which fiber is more condensed, the nucleosome or the solenoid?
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The solenoid fiber
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What are non-histone proteins?
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Acidic or neutral proteins
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What are the functions of non-histone proteins?
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They are involved in nuclear functions such as:
1. Replication 2. Transcription 3. DNA repair 4. Regulation of chromatin function |
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What two forms does chromatin exists in?
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Euchromatin
Heterochromatin |
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What is euchromatin?
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The dispersed, extended chromatin
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What does euchromatin contain?
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The portion of the genome truly being transcribed
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"Transcriptionally active" in bold!
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What percentage of total chromatin does euchromatin account for?
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90%
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Euchromatin is represented by
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The 10 nm fiber
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How does euchromatin stain?
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Light
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What is heterochromatin?
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The condensed, tightly coiled chromatin
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What does heterochromatin contain?
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The portion of the genome which is transcriptionally inactive
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"Transcriptionally inactive" in bold!
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What percentage of total chromatin does heterochromatin account for?
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10%
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How does heterochromatin stain?
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Dark
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Heterochromatin is represented by
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The 30 nm fiber
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What are two examples of heterochromatin?
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1. Mitotic chromosomes
2. Barr body in females: Inactive X chromosome condensed to heterochromatin |
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What are ribosomes?
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Small cytoplasmic granules containing rRNA
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What is the function of ribosomes?
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Use mRNA to direct the assembly of proteins
Protein making factory |
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What are ribosomes composed of?
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Ribosomal RNA (rRNA) and protein
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What are the two parts of a ribosome?
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Ribosomes are composed of two pieces or subunits:
1. The large subunit: 60s 2. The small subunit: 40s |
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Where are ribosomes assembled?
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In the nucleus, and transported to the cytoplasm thru the nuclear pores
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Where is the large ribosomal subunit synthesized?
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In the nucleolus
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Where is the small ribosomal subunit synthesized?
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In the nucleus
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What are polysomes?
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A single mRNA being translated by several ribosomes at the same time
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How do the ribosomal subunits interact?
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The two ribosomal subunits associate on the mRNA with the small subunit binding first
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"The two ribosomal subunits associate on the mRNA with the small subunit binding first" in bold!
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How do ribosomes move on the mRNA?
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From the 5' end to the 3' end
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"The ribosomes move on the mRNA from the 5' end to the 3' end" in bold!
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What two forms do ribosomes exist in?
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1. Free ribosomes
2. Membrane associated ribosomes |
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What is the function of free ribosomes?
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Site of synthesis for proteins destined for the cell's own use (for the nucleus, peroxisomes, or mitochondria)
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If a cell has a lot of free ribosomes....
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It is not a secretory cell
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What is the function of membrane associated ribosomes?
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Site of synthesis of secretory proteins, membrane proteins and lysosomal enzymes
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What structure are the membrane associated ribosomes associated with?
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RER
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What is the endoplasmic reticulum?
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An extensive system of interconnected membrane bound cavities that are continuos with the nuclear membrane
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What are the two types of endoplasmic reticulum?
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Rough endoplasmic reticulum
Smooth endoplasmic reticulum |
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What is the rough endoplasmic reticulum?
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A single lipid bilayer continuos with the outer nuclear membrane
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What does the RER contain?
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Ribosomes
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How is the RER organized?
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It's organized into stacks of large flattened sacs called cisternae that are studded with ribosomes on the cytoplasmic side
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What are the functions of the RER?
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Site of protein synthesis for:
1. Secretory proteins (secretory vesicles or granules), proteins to be exported out of the cell by exocytosis 2. Lysosomal proteins (lysosomes), acid hydrolases 3. Integral proteins for the cell membrane |
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Where do proteins go after they are made in the RER?
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Newly synthesized proteins leave the RER in small transfer vesicles that go to the Golgi Apparatus for further modification, packaging, and distribution
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In what cells is the RER very prominent?
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In cells that are specialized in the synthesis of proteins destined for secretion
Secretory cells |
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Example of a cell with a prominent RER
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Pancreatic acinar cells
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What is the smooth endoplasmic reticulum?
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A network of membranous sacs, vesicles, and tubules continuos with the RER but lacking ribosomes
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What does the SER contain?
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The enzymes for the synthesis of lipids and cholesterol derived compounds (phospholipids, triglycerides, and sterols)
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In what cells is the SER very prominent?
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In cells that secrete lipids, lipoproteins, or steroid hormones
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Why does the mRNA bind to the small subunit of the ribosome first?
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Because the small subunit has a nucleotide sequence exposed on its surface (leader region) where the mRNA binds
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Example of a cell with a prominent SER
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Liver cells, where it's involved in the removal of toxins, lipid soluble drugs (barbiturates), and alcohol from the blood
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What are the functions of the SER?
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1. Steroid synthesis: production of testosterone and glucocorticoids
2. Detoxification reactions: drug detoxification by hepatocytes 3. Glycogen degradation and gluconeogenesis 4. Reactions in lipid metabolism 5. Sequestration and release of Calcium ions in skeletal muscle |
Review Question
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Which detoxification reactions take place in the SER?
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Hydroxylation reactions
Conjugation reactions |
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What molecules are involved in the hydroxylation reaction taking place in the SER?
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Occur by way of hydroxylase complexes containing cytochrome p450, a flavoprotein, and a non-heme iron protein
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Describe the conjugation reaction taking place in the SER
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The transfer of polar groups (i.e. glucoronic acid) from the active carrier UDP-glucoronic acid to the toxic water insoluble molecule
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What is the role of the SER in glycogen degradation and gluconeogenesis?
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The enzyme glucose-6-phosphatase, an integral membrane protein of the SER, removes the phosphate group from glucose-6-phosphate.
This controls the formation of free glucose from glycogen and via gluconeogenesis |
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What reactions related to lipid metabolism take place in the SER?
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Lipolysis
Lipoprotein assembly |
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What reaction related to calcium in striated muscle takes place in the SER?
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The sequestration and release of Calcium ions takes place in the Sarcoplasmic Reticulum (SER in muscle)
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What is the golgi apparatus?
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It's the primary center for recycling, packaging, and distributing of membranes and segregated proteins
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What does the golgi consist of?
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A stack of flattened membranous sacs and vesicles.
Disc shaped cisternae assembled in stacks and associated with numerous small membrane bound vesicles |
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What are the two faces of the golgi apparatus?
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1. The cis (forming) face: associated with the RER
2. The trans (maturing) face: associated with the cell membrane |
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Where does the golgi like to be?
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Around the nucleus
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What are the key functions of the golgi apparatus?
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1. Chemical modification of proteins (addition of carbohydrates to proteins)
2. Packaging and distribution of secretory proteins to form secretory vesicles, and hydrolytic enzymes to form lysosomes 3. Distribution and recycling depot for the various kinds of membranes on the cell |
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What is the relationship between proteins & lipids and the golgi apparatus?
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The golgi apparatus is the site of post-translational modification and sorting of newly synthesized proteins and lipids
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What is the relationship between glycoproteins and the golgi apparatus?
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Modification of the carbohydrate portion of a glycoprotein produces complex and hybrid oligosacharide chains.
This modification determines which proteins remain in the golgi or leave the golgi to become secretory proteins, lysosomal proteins, or part of the plasma membrane. So modification of glycoproteins in the golgi apparatus marks them for their final destination |
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What diseases are caused when glycoproteins are not modified and marked in the golgi apparatus?
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Two diseases are caused by the breakdown of the process of modification and marking in the golgi apparatus:
1. I cell disease 2. Hyperproinsulinemia |
Clinical Correlation
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What causes hyperproinsulinemia?
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It's characterized by elevated levels of pro-insulin in the serum resulting from the failure of a peptidase to cleave pro-insulin to insulin and C-peptide in the golgi apparatus
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What are the clinical manisfestations of hyperproinsulinemia?
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Similar to those seen in patients with non-insulin dependent diabetes
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What causes I-cell disease?
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A deficiency in N-acetylglucosamine phosphotransferase
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What is another name for I-cell disease?
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Mucolipidosis II
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What goes wrong in I-cell disease?
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1. Proteins in the golgi apparatus need to be sent away to their proper destinations
2. Proteins are targeted/marked in the golgi so that the golgi knows where to send them 3. Phosphorylation of mannose targets/marks proteins to go to the lysosomes 4. Phosphorylation of mannose needs an enzyme: N-acetylglucosamine-phosphotransferase 5. If this enzyme is defficient, no phosphorylation, proteins are not marked, and are sent to the wrong destination 6. Lysosomes did not get the proteins/enzymes that they need to do their job, and are thereby not functional 7. Since lysosomes can't degrade things, inclusion bodies accumulate |
Clinical Correlation
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Where does lipolyisis take place?
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In the SER with the release of a fatty acid from a triglyceride
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What is acidophilic?
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Tissue components that stain with an acid dye
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Name an acid dye
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Eosin
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What color is eosin?
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Pink/orange
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Which cellular components are acidophillic?
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Cytoplasm
Mitochondria Collagen fibers Bone matrix RBC's Some secretory and lysosomal granules |
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What is basophilic?
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Tissue components that stain with a basic dye
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Name a basic dye
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Hematoxylin
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What color is hematoxylin?
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Blue/purple
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Which cellular components are basophillic?
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Organelles with substantial amounts of DNA and RNA:
Nucleus Nucleolus Ribosomes RER Some secretory and lysosomal granules |
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In terms of H&E staining, what should be the appearance of the nucleus?
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Should be basophilic due to the presence of RNA and DNA
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Nucleous and chromatin stain with?
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Hematoxylin (hence basophilic)
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What are the two descriptive terms used to describe the activity in the nucleus?
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Heterochromatic (dark): inactive
Euchromatic (light): active |
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In terms of H&E staining, what should be the appearance of the cytoplasm?
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Should be lightly acidophilic in most cells
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Which structures in large amounts would result in a more acidophilic cytoplasm?
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1. Mitochondria (cell needs lots of energy)
2. Secretory vesicles that stain with eosin (may appear grainy) 3. Lysosomal vesicles that stain with eosin (eosinophils) |
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Which structures in large amounts would result in a basophilic cytoplasm?
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1. Ribosomes
- Free or in small clusters (cell makes lots of in-house proteins) - Attached to RER (cell makes lots of secretory proteins) 2. Secretory vesicles that stain with hematoxylin |
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What material in large amounts would result in an empty or clear cytoplasm?
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Cells with a large amount of:
1. Lipid: in droplets (adipose cells) or in membranous organelles (SER, golgi) 2. Glycogen 3. Mucus |
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What are frozen tissue sections used for?
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Surgical biopsies
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What are smears or whole mounts used for?
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To examine blood, bone marrow, and cervical cells (Pap smears)
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What is a lysosome?
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A membrane bound bag of hydrolytic enzymes
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What do lysosomes contain?
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Enzymes required for intracellular digestion
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Why do acid hydrolases have to be segregated by a membrane?
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Because they are capable of degrading almost all the constituents of the cell
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How many lysosomes does a cell have?
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It varies from a few lysosomes to hundreds of lysosomes in specialized cells
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What can cause the rupture of lysosomes within the cell?
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Low oxygen
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Where are lysosomal enzymes synthesized?
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RER
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Review Question
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Where are lysosomal enzymes packaged as primary lysosomes?
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In the golgi apparatus
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Where can lysosomes destroy material?
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Inside and outside the cell
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Which cells have lysosomes that can destroy material outside of the cell?
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Osteoclasts and eosinophils
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What are the two forms of a lysosome?
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Primary lysosome
Secondary lysosome |
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What is a primary lysosome?
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A newly formed, virgin lysosome that has not yet acquired the materials to be digested
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How are primary lysosomes formed?
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By budding from the trans side of the golgi apparatus
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What is a secondary lysosome?
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A vesicle formed after fusion of the primary lysosome with the membrane bound material to be destroyed
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How are secondary lysosomes formed?
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By the fusion of the primary lysosome with the substrate to be degraded
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What do secondary lysosomes contain?
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Contents in various stages of degradation
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What is a residual body?
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Left over material after destruction by the lysosome
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What happens to a residual body?
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It can slowly dissolve, be exocytosed, or remain inside the cell (lipofuschin granules)
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How may hydrolytic enzymes do lysosomes contain?
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Approximately 60
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What hydrolytic enzymes are present in lysosomes?
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1. Nucleases for degrading DNA and RNA
2. Lipases for degrading lipids 3. Glycosides for degrading glycoconjugates 4. Proteases and peptidases for degrading proteins 5. Phosphatases |
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All lysosomal enzymes are...
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Acid hydrolases
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What is the optimal pH for lysosomes?
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pH 5
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In I-cell disease, where are the missing lysosomal enzymes found?
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In plasma and other body fluids
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What is the main characteristic of I-cell disease?
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Huge inclusion bodies are found in cells caused by the accumulation of undegraded glycoconjugates in lysosomes missing the hydrolases that normally degrade these macromolecules
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What is the effect of the absence of mannose-6-phosphate on hydrolases?
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The absence of mannose-6-phosphate results in the secretion of hydrolases instead of their incorporation into lysosomes
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What are the clinical manisfestations of I-cell disease?
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1. Skeletal abnormalities
2. Coarse features 3. Restricted joint movements 4. Psychomotor retardation |
I-cell think Inclusion bodies affecting joInts.... and bones
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When are the symptoms for I-cell disease generally noted?
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At birth
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What is the life expectancy of somebody diagnosed with I-cell disease?
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Less than 10 years
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What is the name of the less severe form of I-cell disease?
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Pseudo-Hurler polydystrophy
Adult onset Potential survival |
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What is the treatment for I-cell disease?
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There is no treatment for I-cell disease (early or late onset), but prenatal diagnosis is available
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What are peroxisomes?
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Vesicles similar to lysosomes containing oxidative enzymes and catalase
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In what organ are peroxisomes particularly important?
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In the liver, where they perform the oxidation of fatty acids
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What do peroxisomes contain?
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Oxidative enzymes and catalase
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What are oxidative enzymes?
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Enzymes that transfer hydrogen atoms from organic substrates (urate, D-amino acids, and very long chain fatty acids) to molecular oxygen, with the formation of hydrogen peroxide
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What is the major peroxisomal protein?
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Catalase
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What is the function of catalase?
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Degrades hydrogen peroxide and water to oxygen
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Where are peroxisomes synthesized?
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On free ribosomes
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Where do peroxisomal enzymes go after being translated on free ribosomes?
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After translation the enzymes are incorporated directly into peroxisomes
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What are the functions of peroxisomes?
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1. Synthesis and degradation of hydrogen peroxide
2. Beta oxidation of very long chain fatty acids (C>24) 3. Phospholipid exchange 4. Bile acid synthesis |
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What are the four more common disorders associated with peroxisome deficiency?
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1. Zellweger (cerebrohepatorenal) syndrome
2. Neonatal adrenoleukodystrophy 3. Infantile Refsum disease 4. Hyperpipecolatemia |
Clinical Correlation
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What happens in patients with peroxisome deficiency?
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Impairment or absence of peroxisomes causes the patient to fail to oxidize very long chain fatty acids and accumulate bile acid precursors
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What is the mitochondria?
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Large, motile organelles with two membranes, with the inner membrane highly folded into shelves (cristae)
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What are some special characteristics of mitochondria?
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1. They are self replicating, having their own double stranded circular DNA
2. They have their own membrane bound enzymes 3. They make their own proteins 4. They have several compartments |
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What is the function of mitochondria?
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Synthesize ATP
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How do mitochondria generate energy in the form of ATP?
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Thru oxidative phosphorylation
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A metabolically active cell may have how many mitochondria?
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Over 1000, with more inner folds in order to increase the surface area for substrates
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How do mitochondria stain?
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Acidophilic (pink)
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How is the outer membrane of the mitochondria?
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Smooth, continuos, and highly permeable
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What does the outer membrane of the mitochondria contain?
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An abundance of porins, an integral membrane protein that forms channels in the outer membrane thru which molecules less than 10kD can pass
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How is the inner membrane of the mitochondria?
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Impermeable to most small ions (Na, K, H) and small molecules (ATP, ADP, pyruvate)
Has numerous foldings called cristae |
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Why is the inner membrane of the mitochondria impermeable?
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Due to the high content of the lipid cardiolipin
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What is the purpose of cristae in the mitochondria's inner membrane?
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To increase the total surface area
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What does the cristae in the inner mitochondrial membrane contain?
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The enzymes for electron transport and oxidative phosphorylation
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"The cristae contain the enzymes for the electron transport and oxidative phosphorylation" in bold!
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The number of mitochondria and the number of cristae is proportional to...
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The metabolic activity of the cell in which they reside
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What is the intermembrane compartment in the mitochondria?
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The space between the inner and outer membrane
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What does the intermembrane compartment contain?
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The enzymes that use ATP to phosphorylate other nucleotides (creatine phosphokinase and adenylate kinase)
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Where is the mitochondrial matrix?
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It's enclosed by the inner membrane
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What does the mitochondrial matrix contain?
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1. Dehydrogenases
2. Double stranded circular DNA genome 3. RNA, proteins, and ribosomes 4. Intramitochondrial granules |
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What is the function of the dehydrogenases present in the mitochondrial matrix?
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They oxidize many of the substrates in the cell (pyruvate, amino acids, fatty acids) generating NADH, and FADH for use by the electron transport chain and energy generation
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How is mitochondrial DNA inherited?
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Always inherited from the mother, resulting in the maternal transmission of diseases of energy metabolism
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"Mitochondrial DNA is always inherited from the mother, resulting in the maternal transmission of diseases of energy metabolism" in bold!
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How are diseases of energy metabolism inherited?
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Thru maternal transmission of the mitochondrial DNA
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Where are mitochondrial proteins made?
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Most mitochondrial proteins are made in the cytoplasm of the cell and then transferred into the mitochondria
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"Most mitochondrial proteins are made in the cytoplasm of the cell and then transferred into the mitochondria"in bold!
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What do intramitochondrial granules contain?
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Calcium and magnesium
May represent a storage site for calcium |
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What is the cytoskeleton?
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The supporting framework of the cell that consists of a variety of proteins assembled into minute filaments and tubules
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What is the function of the cytoskeleton?
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Cell support, shape, movement of the cell, and movement of materials within the cell
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How do filaments and tubules stain?
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Acidophilic
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What components make up the cytoskeleton?
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1. Microtubules
2. Intermediate filaments 3. Microfilaments |
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What are microtubules?
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Hollw tubules formed by a repeating helical arrangement of tubulin that undergo rapid assembly and disassembly
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What are some of the cellular specializations containing microtubules?
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1. Centriole
2. Mitotic spindle 3. Cilia and flagella |
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What is the major component of microtubules?
|
Tubulin, a protein dimer composed of two different polypeptides: alpha and beta tubulin
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How are microtubules formed?
|
Polymerization of tubulin to form microtubules is accomplished by:
1. Microtubule organizing centers 2. Two types of accesory proteins: tau proteins and microtubule associated proteins |
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How do microtubules grow?
|
From the organizing centers
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What ion can affect the polymerization of microtubules?
|
Calcium ions can block or reverse polymerization of microtubules
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What are the functions of microtubules?
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1. Chromosomal movement during meiosis and mitosis
2. Mitotic spindle formation 3. Intracellular vesicle and organelle transport 4. Ciliary and flagellar movement |
"Microtubule assembly is an important event in spindle formation" in bold!
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What micritubule-dependent ATPases are involved in generating the force that drives intracellular transport?
|
Kinesin and dynein
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In bold!
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What disease results from a defect in microtubule polymerization?
|
Chediak-Higashi Syndrome
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Clinical Correlation
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What are the main features of Chediak-Higashi syndrome?
|
This disease causes disordered intracellular traficking
Defect in microtubule polymerization leads to defects in cytoplasmic granules activity including: 1. Delayed fusion of phagosomes with lysosomes, thus preventing the phagocytosis of bacteria 2. Increased fusion of melanosomes in melanocytes, leading to albinism 3. Granular defects in natural killer cells and platelets |
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What is the function of intermediate filaments?
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Function primarily in structural roles
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What types of proteins do intermediate filaments contain?
|
Intermediate filaments contain several tissue specific proteins:
1. Cytokeratins: found in epithelial tissues 2. Desmin: found in smooth muscle, Z discs of skeletal and cardiac muscle 3. Vimentin: found in cells of mesechemyal origin (endothelium, fibroblasts, chondroblasts, vascular smooth muscle) 4. Neurofilaments: found in neurons 5. Glial fibrillary acidic protein (GFA): found in astrocytes |
Review Question: know where each is found
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What are microfilaments composed of?
|
Actin
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How is the structure of an actin filament?
|
Each actin filament (F actin) consists of two strands of actin twisted into a helical pattern with 13.5 molecules of globular actin (G actin) per turn of the helix
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What are microfilaments?
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Tiny rods made of actin, found in all cells
Called thin filaments in muscle |
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What is an intermediate filament?
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A heterogeneous class of filaments especially important in cell support and shape
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Where are intermediate filaments present?
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In adhering type of cell junctions
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How does the composition of intermediate filaments vary among cells?
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The composition of intermediate filaments is specific for different cell types
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How can intermediate filaments be useful to the clinician in terms of diagnosis?
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Identification of the exact type of intermediate filaments present in a tumor can sometimes be used to ID the primary source of the cancer
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What type of movements are associated with microfilaments?
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1. Local movements (polymerization and depolymerization of microfilaments)
2. Sliding filament movement (interaction of actin filaments with myosin filaments) |
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Name a cellular specialization containing microfilaments
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Microvilli
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What is the basement membrane?
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Multilayer, acellular, fibrous sheet that attaches epithelia, adipose, muscle, and schwann cells to the underlying connective tissue
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What is the function of the basement membrane?
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1. Flexible support that anchors the epithelia to the connective tissue
2. Acts as a barrier or filter of material passing between the epithelium and the connective tissue 3. Epithelial cells must be attached to the basal lamina to maintain normal function 4. Serves as scaffold or guide during regeneration after injury |
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What is the structure of the basement membramne?
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It consists of multiple layers:
1. Basal lamina 1.1 Lamina lucida (electron-lucent layer) 1.2 Lamina densa (electron-dense layer) 2. Reticular lamina |
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What is the composition of the basal lamina?
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1. Type 4 collagen
2. Glycoproteins (laminin) 3. Proteoglycans (heparin sulfate) |
Review Question
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Which cells secrete the basal lamina?
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Epithelial cells
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Which cells secrete the reticular lamina?
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Fibroblasts in the connective tissue
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What is the function of heparin sulfate in the basal lamina?
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To filter material by charge
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Review Question
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What molecules bind the cell membrane to the basal lamina?
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Laminin
Entactin |
Review Question
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What is the composition of the reticular lamina?
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Type 3 collagen fibrils (reticular fibers)
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What are the lateral surface specializations present in cells?
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1. Zonula occludens (tight junctions)
2. Zonula adherens (intermediate junction) 3. Macula adherens (desmosome) 4. Gap junctions (nexus junction) |
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What is the zonula occludens (tight junction)?
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An area of complete fusion between adjacent cell membranes
Completely encircles the cell |
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How is the zonula occludens formed?
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By the fusion of opposed cell membranes
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What is the function of the zonula occludens?
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1. Completely block the passage of molecules between cells
2. Seals the intercellular clefts from contact with the outside environment |
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Which cell junction constitutes the anatomic component of many barriers in the body?
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The zonula occludens (tight junctions)
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Which cell junction is the basis of the blood-brain barrier?
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Zonula occludens (tight junctions)
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What is the zonula adherens?
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A band-like junction that serves in the attachment of adjacent epithelial cells
It's a dense area with actin filaments |
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What is the function of the zonula adherens?
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Anchors actin filaments to the cell membrane (cardiac muscle)
Stabilizes cytoskeleton |
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Where is the zonula adherens normally found?
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It often lies basal below the zonula occludens
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What is a desmosome (macula adherens)?
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Intermediate filaments inserted into electron dense plaques
Strong spot attachment Intermediate filaments curl back and forth radiating from the plaques |
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What does zonula mean?
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Belt
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What does macula mean?
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Spot
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What are the functions of a desmosome?
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1. To provide strong cell to cell attachment
2. Keeps neighboring cells from pulling apart 3. Attaches cells to the basal lamina 4. Considered the spot welds that hold cells together |
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How is a desmosome formed?
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It's formed by the juxtaposition of two disk-shaped plaques contained within the cytoplasm of each adjacent cell
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Where are desmosomes most common?
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In lining membranes
They are subject to wear and tear |
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What are gap junctions?
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An area of communication between adjacent cells that allows the passage of very small particles and ions across a small intercellular gap within the junction
Spot communicating junction |
Review Question
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How are gap junctions formed?
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Neighboring cell membranes form small channels or bridges between cells
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What are the functions of gap junctions?
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1. Permits the movement of small molecules between cells
2. Participates in the metabolic and electrical coupling of the cell |
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In what tissues are desmosomes and gap junctions common?
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Smooth muscle
Cardiac muscle |
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In what tissues are gap junctions common?
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Embryonic cells
Osteocytes |
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How is the structure of a gap junction and how are they formed?
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It consists of a hexagonal lattice of tubular protein subunits called connexons, which form hydrophilic channels connecting the cytoplasm of adjacent cells
Tubular proteins (connexons) form hydrophilic channels connecting cells |
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Which cellular junction allows for the conduction of electrical impulses?
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Gap junctions allow the direct passage of ions and small molecules between cells to conduct electrical impulses
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"Allow the direct passage of ions and small molecules between cells to conduct electrical impulses" in bold!
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Name the apical surface specializations present in cells
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Cilia
Microvilli |
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What are cillia?
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They are apical (free) cell surface projections of the cell membrane that contain microtubules
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How are cilia formed?
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They are formed from centriole-like basal bodies present below
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Describe the structure of cilia
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Cilia contain 2 central microtubules surrounded by a circle of 9 peripheral microtubules doublets
9+2 doublets in shaft 9 triplets in basal body Think of cross section drawing |
"9 peripheral microtubules doublets" in bold!
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What is the function of cilia?
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Movement of material
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In what organs is cilia particularly important?
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1. Respiratory system: transport mucus
2. Female reproductive system: transports ovum |
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Name a structure that is a modified cilium
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The flagellum of sperm
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What are microvilli?
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Apical cell surface evaginations of cell membranes that function to increase the surface area available for absorption
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What covers microvilli?
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A thick glycocalyx coat
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What are microvilli composed of?
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Actin microfilaments
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What are microvilli anchored to?
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The core of each microvilli is anchored in the apical cell cytoplasm to the terminal web, which itself is anchored to the zonula adherens of the cell membrane
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What are stereocilia?
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Extremely long microvilli
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Where is stereocilia found?
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At the apices of cells lining the:
1. Epididymis 2. Ductus deferens 3. Hair cells of the inner ear where they play a role in auditory sensation |
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Which structure is longer: flagella or cilia?
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Flagella is longer, but both have the same structure
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What is the function of acting-binding drugs?
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They can interfere with the polymerization-depolymerization cycle of microfilaments in order to inhibit processes such as endocytosis, phagocytosis, cytokinesis, and cytoplasmic movements
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Clinical Correlation
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Name one actin-binding drugs
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Cytochalasin B
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How do cilia move?
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Cilia move back and forth to propel fluid and particles in one direction
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What role do dynein arms play in cilia?
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The dynein arms bind to ATP and rearrange themselves to allow movement to occur
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What defect is present in in Kartagener syndrome?
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Absent or aberrant dynein arms in the cilia and flagella resulting in immotile cilia syndrome
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Clinical Correlation
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How is the outer mitochondrial membrane?
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Smooth, continuos, and highly permeable
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What are lysosomal storage diseases?
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Hereditary diseases caused by a lack of a particular enzyme
This results in the buildup of toxic materials in the cell |
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Name two specific microtubule-dependent ATPases
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Kinesin
Dynein |
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What is the function of kinesin and dynein?
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They are involved in generating the force that drives intracellular transport
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Patients with deficient dynein arms have
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Immotile cilia and flagella (sperm)
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Clinical Correlation
Review Question |
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Patients with immotile cilia syndrome have
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Chronic sinusitis
Bronchiectasis Infertility Situs Inversus |
Clinical Correlation
Review Question |
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What is kinesin?
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The ATPase motor protein used in anterograde axonal transport
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Clinical Correlation
Review Question |
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Defects in the production of kinesin results in
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The inability of axons to transport substances in the anterograde direction
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Clinical Correlation
Review Question |
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What is the site of initial N-glycosylation of proteins?
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RER
The addition of sugars to proteins begins in the RER and is completed in the golgi apparatus |
Review Question
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Which glycoprotein functions to bind cells at a hemidesmosome to an underlying basal lamina?
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Integrin
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Review Question
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Which lateral surface specialization functions in the metabolic coupling between adjacent cells?
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Gap junctions
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Review Question
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