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256 Cards in this Set

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What is the nucleus?
The control center of the cell

A membrane bound organelle found in eukaryotic cells
What are the contents of the nucleus?
1. Nuclear lamina

2. Nucleolus

3. Chromatin

4. Enzymes needed for DNA replication, repair, and transcription
What is the function of the nucleus?
Site of DNA replication and transcription
What is the nuclear envelope?
A double membrane containing pores surrounding the nucleus
How many membranes does the nuclear envelope have?
2 lipid bilayers
What is the nuclear envelope continuos with?
The outer membrane of the nuclear envelope is continuos with the rough endoplasmic reticulum
What is the nuclear lamina?
An interlaced network of proteins
What is the function of the nuclear lamina?
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
What is the role of the nuclear lamina during mitosis?
During prophase, the phosphorylation of the nuclear lamina (by lamin kinase) initiates the disassembly of nuclear components
"Phosporylation of the nuclear lamina (by lamin kinase) during prophase of mitosis initiates nuclear dissasembly into small vesicles" in bold!
Why is breakdown of nuclear components important during mitosis?
It allows the mitotic spindle to interact with the chromosomes
What is the nucleolus?
A non-membrane bound structure located inside the nucleus
What are the contents of the nucleolus?
Fibrils and granules rich in RNA
What is the function of the nucleolus?
Site of rRNA synthesis and assembly
A cell having big/multiple nucleolus indicates what?
The cell is making lots of proteins
What are the three zones of the nucleolus?
1. Granular Zone

2. Fibrillar Zone

3. Fibrillar Center
Describe the granular zone of the nucleolus
Found at the periphery

Contains ribosomal precursor particles being assembled
Describe the fibrillar zone of the nucleolus
Centrally located

Contains ribonuclear protein fibrils
Describe the fibrillar center of the nucleolus
Contains DNA that is not being transcribed
What is chromatin?
A complex of DNA, histone proteins, and non-histone proteins
What is DNA?
A double stranded helical molecule
What is the function of DNA?
Carries the genetic information of the cell
What forms does DNA exists in?
A DNA

B DNA

Z DNA
What are histone proteins?
Positively charged proteins enriched with Arginine and Lysine residues
What is the function of histone proteins?
Important in forming two types of structures in chromatin:

1. Nucleosome

2. Solenoid fibers
What is a nucleosome?
The nucleosomes are the basic repeating units of the chromatin fiber, having a diameter of 10nm
"The nucleosomes are the basic repeating units of the chromatin fiber, having a diameter of 10nm" in bold!
Solenoid fiber is a
30 nm fiber
Which fiber is more condensed, the nucleosome or the solenoid?
The solenoid fiber
What are non-histone proteins?
Acidic or neutral proteins
What are the functions of non-histone proteins?
They are involved in nuclear functions such as:

1. Replication

2. Transcription

3. DNA repair

4. Regulation of chromatin function
What two forms does chromatin exists in?
Euchromatin

Heterochromatin
What is euchromatin?
The dispersed, extended chromatin
What does euchromatin contain?
The portion of the genome truly being transcribed
"Transcriptionally active" in bold!
What percentage of total chromatin does euchromatin account for?
90%
Euchromatin is represented by
The 10 nm fiber
How does euchromatin stain?
Light
What is heterochromatin?
The condensed, tightly coiled chromatin
What does heterochromatin contain?
The portion of the genome which is transcriptionally inactive
"Transcriptionally inactive" in bold!
What percentage of total chromatin does heterochromatin account for?
10%
How does heterochromatin stain?
Dark
Heterochromatin is represented by
The 30 nm fiber
What are two examples of heterochromatin?
1. Mitotic chromosomes

2. Barr body in females: Inactive X chromosome condensed to heterochromatin
What are ribosomes?
Small cytoplasmic granules containing rRNA
What is the function of ribosomes?
Use mRNA to direct the assembly of proteins

Protein making factory
What are ribosomes composed of?
Ribosomal RNA (rRNA) and protein
What are the two parts of a ribosome?
Ribosomes are composed of two pieces or subunits:

1. The large subunit: 60s

2. The small subunit: 40s
Where are ribosomes assembled?
In the nucleus, and transported to the cytoplasm thru the nuclear pores
Where is the large ribosomal subunit synthesized?
In the nucleolus
Where is the small ribosomal subunit synthesized?
In the nucleus
What are polysomes?
A single mRNA being translated by several ribosomes at the same time
How do the ribosomal subunits interact?
The two ribosomal subunits associate on the mRNA with the small subunit binding first
"The two ribosomal subunits associate on the mRNA with the small subunit binding first" in bold!
How do ribosomes move on the mRNA?
From the 5' end to the 3' end
"The ribosomes move on the mRNA from the 5' end to the 3' end" in bold!
What two forms do ribosomes exist in?
1. Free ribosomes

2. Membrane associated ribosomes
What is the function of free ribosomes?
Site of synthesis for proteins destined for the cell's own use (for the nucleus, peroxisomes, or mitochondria)
If a cell has a lot of free ribosomes....
It is not a secretory cell
What is the function of membrane associated ribosomes?
Site of synthesis of secretory proteins, membrane proteins and lysosomal enzymes
What structure are the membrane associated ribosomes associated with?
RER
What is the endoplasmic reticulum?
An extensive system of interconnected membrane bound cavities that are continuos with the nuclear membrane
What are the two types of endoplasmic reticulum?
Rough endoplasmic reticulum

Smooth endoplasmic reticulum
What is the rough endoplasmic reticulum?
A single lipid bilayer continuos with the outer nuclear membrane
What does the RER contain?
Ribosomes
How is the RER organized?
It's organized into stacks of large flattened sacs called cisternae that are studded with ribosomes on the cytoplasmic side
What are the functions of the RER?
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
Where do proteins go after they are made in the RER?
Newly synthesized proteins leave the RER in small transfer vesicles that go to the Golgi Apparatus for further modification, packaging, and distribution
In what cells is the RER very prominent?
In cells that are specialized in the synthesis of proteins destined for secretion

Secretory cells
Example of a cell with a prominent RER
Pancreatic acinar cells
What is the smooth endoplasmic reticulum?
A network of membranous sacs, vesicles, and tubules continuos with the RER but lacking ribosomes
What does the SER contain?
The enzymes for the synthesis of lipids and cholesterol derived compounds (phospholipids, triglycerides, and sterols)
In what cells is the SER very prominent?
In cells that secrete lipids, lipoproteins, or steroid hormones
Why does the mRNA bind to the small subunit of the ribosome first?
Because the small subunit has a nucleotide sequence exposed on its surface (leader region) where the mRNA binds
Example of a cell with a prominent SER
Liver cells, where it's involved in the removal of toxins, lipid soluble drugs (barbiturates), and alcohol from the blood
What are the functions of the SER?
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
Which detoxification reactions take place in the SER?
Hydroxylation reactions

Conjugation reactions
What molecules are involved in the hydroxylation reaction taking place in the SER?
Occur by way of hydroxylase complexes containing cytochrome p450, a flavoprotein, and a non-heme iron protein
Describe the conjugation reaction taking place in the SER
The transfer of polar groups (i.e. glucoronic acid) from the active carrier UDP-glucoronic acid to the toxic water insoluble molecule
What is the role of the SER in glycogen degradation and gluconeogenesis?
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
What reactions related to lipid metabolism take place in the SER?
Lipolysis

Lipoprotein assembly
What reaction related to calcium in striated muscle takes place in the SER?
The sequestration and release of Calcium ions takes place in the Sarcoplasmic Reticulum (SER in muscle)
What is the golgi apparatus?
It's the primary center for recycling, packaging, and distributing of membranes and segregated proteins
What does the golgi consist of?
A stack of flattened membranous sacs and vesicles.

Disc shaped cisternae assembled in stacks and associated with numerous small membrane bound vesicles
What are the two faces of the golgi apparatus?
1. The cis (forming) face: associated with the RER

2. The trans (maturing) face: associated with the cell membrane
Where does the golgi like to be?
Around the nucleus
What are the key functions of the golgi apparatus?
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
What is the relationship between proteins & lipids and the golgi apparatus?
The golgi apparatus is the site of post-translational modification and sorting of newly synthesized proteins and lipids
What is the relationship between glycoproteins and the golgi apparatus?
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
What diseases are caused when glycoproteins are not modified and marked in the golgi apparatus?
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
What causes hyperproinsulinemia?
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
What are the clinical manisfestations of hyperproinsulinemia?
Similar to those seen in patients with non-insulin dependent diabetes
What causes I-cell disease?
A deficiency in N-acetylglucosamine phosphotransferase
What is another name for I-cell disease?
Mucolipidosis II
What goes wrong in I-cell disease?
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
Where does lipolyisis take place?
In the SER with the release of a fatty acid from a triglyceride
What is acidophilic?
Tissue components that stain with an acid dye
Name an acid dye
Eosin
What color is eosin?
Pink/orange
Which cellular components are acidophillic?
Cytoplasm

Mitochondria

Collagen fibers

Bone matrix

RBC's

Some secretory and lysosomal granules
What is basophilic?
Tissue components that stain with a basic dye
Name a basic dye
Hematoxylin
What color is hematoxylin?
Blue/purple
Which cellular components are basophillic?
Organelles with substantial amounts of DNA and RNA:

Nucleus

Nucleolus

Ribosomes

RER

Some secretory and lysosomal granules
In terms of H&E staining, what should be the appearance of the nucleus?
Should be basophilic due to the presence of RNA and DNA
Nucleous and chromatin stain with?
Hematoxylin (hence basophilic)
What are the two descriptive terms used to describe the activity in the nucleus?
Heterochromatic (dark): inactive

Euchromatic (light): active
In terms of H&E staining, what should be the appearance of the cytoplasm?
Should be lightly acidophilic in most cells
Which structures in large amounts would result in a more acidophilic cytoplasm?
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)
Which structures in large amounts would result in a basophilic cytoplasm?
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
What material in large amounts would result in an empty or clear cytoplasm?
Cells with a large amount of:

1. Lipid: in droplets (adipose cells) or in membranous organelles (SER, golgi)

2. Glycogen

3. Mucus
What are frozen tissue sections used for?
Surgical biopsies
What are smears or whole mounts used for?
To examine blood, bone marrow, and cervical cells (Pap smears)
What is a lysosome?
A membrane bound bag of hydrolytic enzymes
What do lysosomes contain?
Enzymes required for intracellular digestion
Why do acid hydrolases have to be segregated by a membrane?
Because they are capable of degrading almost all the constituents of the cell
How many lysosomes does a cell have?
It varies from a few lysosomes to hundreds of lysosomes in specialized cells
What can cause the rupture of lysosomes within the cell?
Low oxygen
Where are lysosomal enzymes synthesized?
RER
Review Question
Where are lysosomal enzymes packaged as primary lysosomes?
In the golgi apparatus
Where can lysosomes destroy material?
Inside and outside the cell
Which cells have lysosomes that can destroy material outside of the cell?
Osteoclasts and eosinophils
What are the two forms of a lysosome?
Primary lysosome

Secondary lysosome
What is a primary lysosome?
A newly formed, virgin lysosome that has not yet acquired the materials to be digested
How are primary lysosomes formed?
By budding from the trans side of the golgi apparatus
What is a secondary lysosome?
A vesicle formed after fusion of the primary lysosome with the membrane bound material to be destroyed
How are secondary lysosomes formed?
By the fusion of the primary lysosome with the substrate to be degraded
What do secondary lysosomes contain?
Contents in various stages of degradation
What is a residual body?
Left over material after destruction by the lysosome
What happens to a residual body?
It can slowly dissolve, be exocytosed, or remain inside the cell (lipofuschin granules)
How may hydrolytic enzymes do lysosomes contain?
Approximately 60
What hydrolytic enzymes are present in lysosomes?
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
All lysosomal enzymes are...
Acid hydrolases
What is the optimal pH for lysosomes?
pH 5
In I-cell disease, where are the missing lysosomal enzymes found?
In plasma and other body fluids
What is the main characteristic of I-cell disease?
Huge inclusion bodies are found in cells caused by the accumulation of undegraded glycoconjugates in lysosomes missing the hydrolases that normally degrade these macromolecules
What is the effect of the absence of mannose-6-phosphate on hydrolases?
The absence of mannose-6-phosphate results in the secretion of hydrolases instead of their incorporation into lysosomes
What are the clinical manisfestations of I-cell disease?
1. Skeletal abnormalities

2. Coarse features

3. Restricted joint movements

4. Psychomotor retardation
I-cell think Inclusion bodies affecting joInts.... and bones
When are the symptoms for I-cell disease generally noted?
At birth
What is the life expectancy of somebody diagnosed with I-cell disease?
Less than 10 years
What is the name of the less severe form of I-cell disease?
Pseudo-Hurler polydystrophy

Adult onset

Potential survival
What is the treatment for I-cell disease?
There is no treatment for I-cell disease (early or late onset), but prenatal diagnosis is available
What are peroxisomes?
Vesicles similar to lysosomes containing oxidative enzymes and catalase
In what organ are peroxisomes particularly important?
In the liver, where they perform the oxidation of fatty acids
What do peroxisomes contain?
Oxidative enzymes and catalase
What are oxidative enzymes?
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
What is the major peroxisomal protein?
Catalase
What is the function of catalase?
Degrades hydrogen peroxide and water to oxygen
Where are peroxisomes synthesized?
On free ribosomes
Where do peroxisomal enzymes go after being translated on free ribosomes?
After translation the enzymes are incorporated directly into peroxisomes
What are the functions of peroxisomes?
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
What are the four more common disorders associated with peroxisome deficiency?
1. Zellweger (cerebrohepatorenal) syndrome

2. Neonatal adrenoleukodystrophy

3. Infantile Refsum disease

4. Hyperpipecolatemia
Clinical Correlation
What happens in patients with peroxisome deficiency?
Impairment or absence of peroxisomes causes the patient to fail to oxidize very long chain fatty acids and accumulate bile acid precursors
What is the mitochondria?
Large, motile organelles with two membranes, with the inner membrane highly folded into shelves (cristae)
What are some special characteristics of mitochondria?
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
What is the function of mitochondria?
Synthesize ATP
How do mitochondria generate energy in the form of ATP?
Thru oxidative phosphorylation
A metabolically active cell may have how many mitochondria?
Over 1000, with more inner folds in order to increase the surface area for substrates
How do mitochondria stain?
Acidophilic (pink)
How is the outer membrane of the mitochondria?
Smooth, continuos, and highly permeable
What does the outer membrane of the mitochondria contain?
An abundance of porins, an integral membrane protein that forms channels in the outer membrane thru which molecules less than 10kD can pass
How is the inner membrane of the mitochondria?
Impermeable to most small ions (Na, K, H) and small molecules (ATP, ADP, pyruvate)

Has numerous foldings called cristae
Why is the inner membrane of the mitochondria impermeable?
Due to the high content of the lipid cardiolipin
What is the purpose of cristae in the mitochondria's inner membrane?
To increase the total surface area
What does the cristae in the inner mitochondrial membrane contain?
The enzymes for electron transport and oxidative phosphorylation
"The cristae contain the enzymes for the electron transport and oxidative phosphorylation" in bold!
The number of mitochondria and the number of cristae is proportional to...
The metabolic activity of the cell in which they reside
What is the intermembrane compartment in the mitochondria?
The space between the inner and outer membrane
What does the intermembrane compartment contain?
The enzymes that use ATP to phosphorylate other nucleotides (creatine phosphokinase and adenylate kinase)
Where is the mitochondrial matrix?
It's enclosed by the inner membrane
What does the mitochondrial matrix contain?
1. Dehydrogenases

2. Double stranded circular DNA genome

3. RNA, proteins, and ribosomes

4. Intramitochondrial granules
What is the function of the dehydrogenases present in the mitochondrial matrix?
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
How is mitochondrial DNA inherited?
Always inherited from the mother, resulting in the maternal transmission of diseases of energy metabolism
"Mitochondrial DNA is always inherited from the mother, resulting in the maternal transmission of diseases of energy metabolism" in bold!
How are diseases of energy metabolism inherited?
Thru maternal transmission of the mitochondrial DNA
Where are mitochondrial proteins made?
Most mitochondrial proteins are made in the cytoplasm of the cell and then transferred into the mitochondria
"Most mitochondrial proteins are made in the cytoplasm of the cell and then transferred into the mitochondria"in bold!
What do intramitochondrial granules contain?
Calcium and magnesium

May represent a storage site for calcium
What is the cytoskeleton?
The supporting framework of the cell that consists of a variety of proteins assembled into minute filaments and tubules
What is the function of the cytoskeleton?
Cell support, shape, movement of the cell, and movement of materials within the cell
How do filaments and tubules stain?
Acidophilic
What components make up the cytoskeleton?
1. Microtubules

2. Intermediate filaments

3. Microfilaments
What are microtubules?
Hollw tubules formed by a repeating helical arrangement of tubulin that undergo rapid assembly and disassembly
What are some of the cellular specializations containing microtubules?
1. Centriole

2. Mitotic spindle

3. Cilia and flagella
What is the major component of microtubules?
Tubulin, a protein dimer composed of two different polypeptides: alpha and beta tubulin
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
How do microtubules grow?
From the organizing centers
What ion can affect the polymerization of microtubules?
Calcium ions can block or reverse polymerization of microtubules
What are the functions of microtubules?
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!
What micritubule-dependent ATPases are involved in generating the force that drives intracellular transport?
Kinesin and dynein
In bold!
What disease results from a defect in microtubule polymerization?
Chediak-Higashi Syndrome
Clinical Correlation
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
What is the function of intermediate filaments?
Function primarily in structural roles
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
What are microfilaments composed of?
Actin
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
What are microfilaments?
Tiny rods made of actin, found in all cells

Called thin filaments in muscle
What is an intermediate filament?
A heterogeneous class of filaments especially important in cell support and shape
Where are intermediate filaments present?
In adhering type of cell junctions
How does the composition of intermediate filaments vary among cells?
The composition of intermediate filaments is specific for different cell types
How can intermediate filaments be useful to the clinician in terms of diagnosis?
Identification of the exact type of intermediate filaments present in a tumor can sometimes be used to ID the primary source of the cancer
What type of movements are associated with microfilaments?
1. Local movements (polymerization and depolymerization of microfilaments)

2. Sliding filament movement (interaction of actin filaments with myosin filaments)
Name a cellular specialization containing microfilaments
Microvilli
What is the basement membrane?
Multilayer, acellular, fibrous sheet that attaches epithelia, adipose, muscle, and schwann cells to the underlying connective tissue
What is the function of the basement membrane?
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
What is the structure of the basement membramne?
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
What is the composition of the basal lamina?
1. Type 4 collagen

2. Glycoproteins (laminin)

3. Proteoglycans (heparin sulfate)
Review Question
Which cells secrete the basal lamina?
Epithelial cells
Which cells secrete the reticular lamina?
Fibroblasts in the connective tissue
What is the function of heparin sulfate in the basal lamina?
To filter material by charge
Review Question
What molecules bind the cell membrane to the basal lamina?
Laminin

Entactin
Review Question
What is the composition of the reticular lamina?
Type 3 collagen fibrils (reticular fibers)
What are the lateral surface specializations present in cells?
1. Zonula occludens (tight junctions)

2. Zonula adherens (intermediate junction)

3. Macula adherens (desmosome)

4. Gap junctions (nexus junction)
What is the zonula occludens (tight junction)?
An area of complete fusion between adjacent cell membranes

Completely encircles the cell
How is the zonula occludens formed?
By the fusion of opposed cell membranes
What is the function of the zonula occludens?
1. Completely block the passage of molecules between cells

2. Seals the intercellular clefts from contact with the outside environment
Which cell junction constitutes the anatomic component of many barriers in the body?
The zonula occludens (tight junctions)
Which cell junction is the basis of the blood-brain barrier?
Zonula occludens (tight junctions)
What is the zonula adherens?
A band-like junction that serves in the attachment of adjacent epithelial cells

It's a dense area with actin filaments
What is the function of the zonula adherens?
Anchors actin filaments to the cell membrane (cardiac muscle)

Stabilizes cytoskeleton
Where is the zonula adherens normally found?
It often lies basal below the zonula occludens
What is a desmosome (macula adherens)?
Intermediate filaments inserted into electron dense plaques

Strong spot attachment

Intermediate filaments curl back and forth radiating from the plaques
What does zonula mean?
Belt
What does macula mean?
Spot
What are the functions of a desmosome?
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
How is a desmosome formed?
It's formed by the juxtaposition of two disk-shaped plaques contained within the cytoplasm of each adjacent cell
Where are desmosomes most common?
In lining membranes

They are subject to wear and tear
What are gap junctions?
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
How are gap junctions formed?
Neighboring cell membranes form small channels or bridges between cells
What are the functions of gap junctions?
1. Permits the movement of small molecules between cells

2. Participates in the metabolic and electrical coupling of the cell
In what tissues are desmosomes and gap junctions common?
Smooth muscle

Cardiac muscle
In what tissues are gap junctions common?
Embryonic cells

Osteocytes
How is the structure of a gap junction and how are they formed?
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
Which cellular junction allows for the conduction of electrical impulses?
Gap junctions allow the direct passage of ions and small molecules between cells to conduct electrical impulses
"Allow the direct passage of ions and small molecules between cells to conduct electrical impulses" in bold!
Name the apical surface specializations present in cells
Cilia

Microvilli
What are cillia?
They are apical (free) cell surface projections of the cell membrane that contain microtubules
How are cilia formed?
They are formed from centriole-like basal bodies present below
Describe the structure of cilia
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!
What is the function of cilia?
Movement of material
In what organs is cilia particularly important?
1. Respiratory system: transport mucus

2. Female reproductive system: transports ovum
Name a structure that is a modified cilium
The flagellum of sperm
What are microvilli?
Apical cell surface evaginations of cell membranes that function to increase the surface area available for absorption
What covers microvilli?
A thick glycocalyx coat
What are microvilli composed of?
Actin microfilaments
What are microvilli anchored to?
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
What are stereocilia?
Extremely long microvilli
Where is stereocilia found?
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
Which structure is longer: flagella or cilia?
Flagella is longer, but both have the same structure
What is the function of acting-binding drugs?
They can interfere with the polymerization-depolymerization cycle of microfilaments in order to inhibit processes such as endocytosis, phagocytosis, cytokinesis, and cytoplasmic movements
Clinical Correlation
Name one actin-binding drugs
Cytochalasin B
How do cilia move?
Cilia move back and forth to propel fluid and particles in one direction
What role do dynein arms play in cilia?
The dynein arms bind to ATP and rearrange themselves to allow movement to occur
What defect is present in in Kartagener syndrome?
Absent or aberrant dynein arms in the cilia and flagella resulting in immotile cilia syndrome
Clinical Correlation
How is the outer mitochondrial membrane?
Smooth, continuos, and highly permeable
What are lysosomal storage diseases?
Hereditary diseases caused by a lack of a particular enzyme

This results in the buildup of toxic materials in the cell
Name two specific microtubule-dependent ATPases
Kinesin

Dynein
What is the function of kinesin and dynein?
They are involved in generating the force that drives intracellular transport
Patients with deficient dynein arms have
Immotile cilia and flagella (sperm)
Clinical Correlation

Review Question
Patients with immotile cilia syndrome have
Chronic sinusitis

Bronchiectasis

Infertility

Situs Inversus
Clinical Correlation

Review Question
What is kinesin?
The ATPase motor protein used in anterograde axonal transport
Clinical Correlation

Review Question
Defects in the production of kinesin results in
The inability of axons to transport substances in the anterograde direction
Clinical Correlation

Review Question
What is the site of initial N-glycosylation of proteins?
RER

The addition of sugars to proteins begins in the RER and is completed in the golgi apparatus
Review Question
Which glycoprotein functions to bind cells at a hemidesmosome to an underlying basal lamina?
Integrin
Review Question
Which lateral surface specialization functions in the metabolic coupling between adjacent cells?
Gap junctions
Review Question