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72 Cards in this Set
- Front
- Back
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Ribosomes are (basophilic/neutrophilic)? How do you know?
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They're basophilic -- they contain RNA
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What dye could you use to stain a ribosome?
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hematoxylin
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Describe the structure of a ribosome
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-initially formed in the nucleolus
-initially the rRNA is transcribed as a single chain (45s) and then cut into three smaller fragments (32 --> 28s and 18s) which form the framework of the ribosomal subunits to which proteins bind -consists of a large and small subunit, both of which contain both protein and rRNA * the major function of the proteins is to stabilize the structure of the RNA The final subunit sizes are 60s (large) and 40s (small) -- this is from 28s and 28s of pure RNA |
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Describe the functions of the ribosome
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-the ribosome complex is responsible for the translation of mRNA into protein
-acts as a ribozyme (RNA responsible for enzymatic activity) -mRNA is bound to the ribosome by the capped sequence and protein synthesis is begun at a specific initiation sequence (AUG --> Met) -Protein synthesis continues until a specific stop sequence is encountered |
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How big is a ribosome?
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25 nm
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Polyribosome
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aka polysome
-consist of a single mRNA molecule associated with a number of ribosome along its length -the longer the mRNA, the greater the number of ribosomes -2 forms, Free and membrane bound |
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How does the mRNA chain grow in a ribosome?
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chain grows by addition of aa bound to tRNA. tRNA .. each one recognizes a specifc amino acid. another part recognizes a specific codon on MRNA and it docks w that codon and adds aa to the growing protein chain
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Free ribosomes
what kind of proteins are synthesized on them?? |
-in the cytoplasm
-synthesize soluble proteins for the cytoplasm and nucleus -used to synthesize small proteins that DO NOT need to be post translationally modified |
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Membrane bound polyribosome
what kind of proteins are synthesized on them? |
-associated with rough endoplasmic reticulum * membrane bound polysomes/polyribosome involved in synthesis of proteins that need to be further modified. 1st site of modification is in ER.
-the proteins made by these ribosomes include: 1. secreted proteins 2. membrane proteins 3. those targeted for specific organelles |
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What recognizes the 5' cap of mRNA?
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note 5' cap of mRNA which recognized components of the eIF = eukaryotic initiation factor
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Vectoral discharge
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process by which peptides are shuttled to the RER and translated into the RER lumen
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Endoplasmic reticulum (general characteristics)
total % of cell volume? major types? |
-only visible by EM
-composed of a single continuous membrane which encloses a single sac or ER lumen -this lumen forms a compartment separated from the rest of the cytoplasm -the ER lumen may comprise 10% of the total cell volume -the ER can be separated into two major types: Rough and Smooth ER |
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Smooth ER characteristics
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-membrane LACKING ribosomes **no protein synthesis in or on this ER
-continuous with the rough ER -often in the form of FINE TUBULES -particularly prominent in cells which carry out lipid metabolism (eg. secrete steroid hormones) |
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Functions of the smooth ER?
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1. Carbohydrate metabolism -- glycogen synthesis AND breakdown
2. detoxification of drugs 3. Regulation of muscle contraction -- the lumen can SEQUESTER Ca2+ AND RELEASE IT under the appropriate conditions -- the levels of Ca2+ in the cytoplasm controls contraction 4. Synthesis of phospholipids and cholestrol |
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Rough ER structure
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-associated with ribosomes giving it a rough appearance under EM
-ribosomes always on cytoplasmic side, never on the lumen side -often in the form of flattened sacs called cisternae -Rough ER is particularly prominent in protein secreting cells |
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Rough ER function
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-involved in the
1. synthesis 2. processing 3. segregation of membrane proteins and those which are targeted for specific organelles or for secretion |
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Transfer (transport) vesicles can be termed COATED or UNCOATED depending on the presence or absence of WHAT?
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an electron dense layer on the surface
coated vesicles from the ER are surrounded by a protein termed COPII |
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Coated vesicles from the ER are surrounded by?
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A protein termed COPII
COPII can polymerize to form a polygonal structure |
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Give examples of proteins that coat vesicles
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Clathrin
COPI COPII |
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What is the point of the coat proteins? How do they work?
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-Vesicle with coat protein is formed.
-Coat protein prevents vesicle once its budded off the ER from refusing with the membrane where it was formed, essentially allows 1 DIRECTIONAL TRANSPORT -Once vesicle is fully formed and separated, coat proteins (COP1, COP2, clatherin) come off and vesicle finds target, fuses with target and releases protein at its target organelle. |
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Clatherin
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coat protein used in transport of vesicles from golgi --> LYSOSOMES
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How do transfer vesicles know where to go? What is this process called?
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-The surfaces of the transfer vesicles have proteins (called v-SNAREs) on their surfaces which determine what they will fuse with.
-Each V snare recognizes its spectic T snare in its target organelle CALLED VESICULAR SORTING |
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Golgi complex -- general characteristics
-location in cell -# per cell |
-Present in most if not all nucleated cells
-Generally located near the nucleus -1-100 golgi complexes per cell depending on the cell type |
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Golgi structure
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-consists of a series of disk-shaped cisternae arranged in a stack (also called the golgi stack)
-in general there about 6 cisternae per stack but this number may vary -the stack is polarized: cis/forming face + trans/maturing face -different enzymes are restricted to the different cisterna of the stack so that modifications can be done in the appropriate sequence |
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Vesicles from ER enter Golgi on __ face and exit on __ face
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Enter on cis/forming face
exit on trans/maturing face |
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Cis face
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aka forming face of golgi comples
-closely associated with the transitional portion of the ER |
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Trans face
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aka maturing face
-often directed towards the plasma membrane -associated with condensing and secretory vesicles |
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Where can cargo from the golgi go?
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1. constitutive secretion (outside cell)
2. Regulated secretion -- vesicles need to receive signal before secretory signals fuse and release constituents 3. Lysosomes ** clatherin coat ** mannose 6 |
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Functions of golgi?
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1. Biochemical modification of biological material
1A. Carbohydrate core of glycoproteins is elaborated upon by a number of different enzymes 1B. Sulfation of glycosaminoglycans 1C. Cleavage of peptide chain pro-proteins to the mature form of the protein 2. Director of molecular traffic -once all the modificatinos on the proteins have been completed, they are then packaged for export -the proteins destined for a particular destination are concentrated in CONDENSING vacoules in a specific region of the Golgi termed the TRANS GOLGI NETWORK -the vacoules then buds off the membrane to form a secretory vesicle -the mechanism by which proteins are concentrated is unknown -The cytoplasmic side of the transport vesicles probably have docking markers which determine their final destination |
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Cisternal maturation model
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New cis cisternae continually form and migrate to the trans- face, while the Golgi resident enzymes are maintained in their correct cisternae by retrograde flow in vesicles
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Vesicular sorting
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sorting procedure which allows vesicles from point a to recognize target organelle at point b whether its from one portion of golgi to another or from transgolgi network and final target organelle. This is how these vesicles get their protein cargo where it is needed
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What signals will get you from the golgi to a lysosome?
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On the Protein -- mannose-6-phosphate
*recognized by proteins in the trans golgi network that package these proteins into transport vesicles that give rise to lysosomes On the Vesicle - clatherin coat |
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General characteristics of lysosomes
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-present in all eukaryotic cells
-arise from the trans golgi network -proteins --> lysosomes have the mannose-6-phosphate residue |
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Structure of lysosomes
pH? |
-various shapes and sizes
-contain a large number of acid hydrolases which break down a variety of molecules -have an optimal enzymatic activity at pH 5 ****this protects cytoplasmic structures if the enzymes are accidentally released -- the enzymes wont work at pH 7.2-7.4, the pH of the cytosol |
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What types of lysosomes are there?
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A. Primary lysosomes
B. Secondary lysosomes B1.Digestive vacuoles B2. Late endosomes B3. Autophagic vacoules B4. Multivesicular bodies |
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Autophagy
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-a process that occurs under austere conditions in the cell
-when there are no other sources of energy in the cell, the cell can survive by phagocytozing some of its own organelles and then using them to generate energy **can be important in cancer development as a survival mechanism |
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Describe the process whereby lysosomes are formed
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-In cis face: mannose is phosphorylated in the 6 position to form mannose6phosphate, then protein in further modified as it is transported through golgi.
-It then enters into a vesicle in the transgolgi network. This vesicle has a MANNOSE-6-PHOSPHATE RECEPTOR. -The vesicle is then coated with a particular coat protein -- CLATHERIN. -The coat protein dissociates and you have transport vesicle with lysosomal enzyme bound to m6p-receptor. -m6p-receptor is recognized by receptor on lysosome, fuses and releases content into lysosomes -phosphate from m6p is removed and the protein is released into lysosome |
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Peroxisomes - general characteristics
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-present in most cells
-proteins are selectively imported from the cytoplasm -are thought to be a very primitive organelle predating mitochondria |
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How is the pH of the lysosome maintained?
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-The membrane contains a proton pump which maintains the internal pH around 5
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Primary lysosome
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-newly formed as buddings of the trans golgi network
-appears to be homogeneous under the electron microscope |
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Secondary lysosomes
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-contain injested substances
-small fragments of difested material enter the cytoplasm and can be reused -older lysosomes containing the remnants of digested material are called residual bodies -in some cells there are large quantities of residual bodies referred to as lipofuscin A. digestive vacuoles B. late endosome C. autophagic vacuole D. multivesicular bodies |
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Residual bodies
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older lysosomes containing the remnants of digested material
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Digestive vacuoles
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-resulting from the phagocytosis of large particles such as bacteria
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Late endosomes
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-cells take up material through process of endocytosis into an early endosome
-this may be passed on to a late endosome that takes on lysosomal enzymes |
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Autophagic vacuoles
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-contain intracellular organelles such as mitochondria
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Multivesicular bodies
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-contain numerous vesicles
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Function of lysosomes?
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-Purpose is to degrade substances within the cell
-The lysosome fuses with the target material and then digests it with hydrolytic enzymes |
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Peroxisome structure and function
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Structure:
-small packets of oxidative enzymes surrounded by a single membrane Function: -produce H2O2 -H202 is utilized by catalase to oxidize fatty acids and metabolize drugs -detoxifies alcohol! -can divide by fission to make daughter lysosomes |
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Microbodies
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peroxisomes
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Catalase
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utilized H202 in the peroxisome to oxidize fatty acids and detoxify substances
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Where is alcohol detoxified?
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Peroxisomes
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Mitochondria general characteristics
# per cell, etc |
-powerhouse of the cell
-number vary depending upon the cell type -most numerous in cells requiring large amounts of energy -thought to have evolved from energy producing bacterium (purple photosynthetic bacteria) which took up residence in the cytoplasm of the primitive eukaryotic cell -contain the material necessary to carry out protein synthesis (DNA mRNA tRNA and ribosomes), all of which more closely resemble that of bacteria than of eukaryotic cells -divide by FISSION |
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What are mitochondria thought to have evolved from?
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-thought to have evolved from energy producing bacterium (purple photosynthetic bacteria) which took up residence in the cytoplasm of the primitive eukaryotic cell
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Outer mitochondrial membrane
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contains channel-forming proteins which make the membrane permeable to small molecule
similar to the endoplasmic reticulum |
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mitochondrial intermembrane space
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-chemically equivalent to cytosol with respect to small molecules
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inner mitochondrial membrane
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-contains special lipids that make it relatively impermeable to ions and small molecules
-highly folded to form cristae which INCREASE SURFACE AREA -shape and number of cristae vary depending upon the cell -contains: 1. transport proteins to make the membrane selectively permeable to certain substances (like atp) 2. proteins of the electron transport system (respiratory chain) 3. elementary (or f1) particles |
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Elementary (or F1) particles
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-knob like structures on the inner side of the inner mitochondrial membrane
-contain ATP synthase activity |
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mitochondrial matrix
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-highly concentrated material inside the inner membrane
-contains various metabolic enzymes including those of the citric acid cycle -also contain the material necessary to carry out protein synthesis (DNA, mRNA, tRNA and ribosomes) -a small fraction of the mitochondrial proteins are made in the matrix -dense granules composed of precipitated calcium salts are also present |
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process by which atp is formed in mitochondria?
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oxidative phosphorylation
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Function of mitochondria?
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Production of energy
-carries out oxidative phosphorylation (ie. requires O2) in which NADH produced by various metabolic reactions is converted into ATP -this is done through the chemiosmotic mechanism |
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Chemiosmotic mechanism
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1. The citric acid cycle results in the production of NADH in the matrix
2. NADH donates an electron to the electron transport system (respiratory chain) which is located in the inner mitochondrial membrane -through a series of steps, the electron is eventually combined with O2 to form H20 -in this process, protons are pumped out of the matrix INTO the intermembrane space 3. Since the inner mitochondrial membrane is impermeable to H+, a proton gradient is formed between the matrix and the intermembrane space 4. The H+ can enter the matrix by passing through a hole in the F1 particle -this passage causes the head group to rotate (converting chemical energy into mechanical energy) -This mechanical energy is then used by the complex to catalyze the formation of ATP from ADP and P (mechanical energy converted back to chemical energy) 5. The ATP can then leave the matrix through a specific membrane carrier and enter the cytoplasm where it is used -A single molecule of ATP/ADP may go in and out of the mitochondria several times a minute |
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What level of ATP:ADP does the mitochondria maintain for the cell?
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10 ATP : 1 ADP
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How many complexes are in the electron transport system (respiratory chain)? What's at the end?
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Total of 4 complexes.
Eventually e- donated to O2 to form water |
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Types of cytoplasmic inclusions:
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1. Pigment Granules
a. Melanosomes b. Lipofuscin 2. Glycogen 3. Lipid note that some inclusions have membranes, others do not melanosomes have membranes initially liposomes have membranes (i think) glycogen DOES NOT HAVE A MEMBRANE lipid inclusions usually dont have membranes |
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Melanosomes
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-melanin produced and accumulates in melanosomes. Melanosomes have the enzymes necessary to synthesize melanin and give cells their pigmentation
-found in the epidermis -when initially formed, they are surrounded by a membrane -as they mature, the outer membrane may be lost |
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Lipofuscin
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-older secondary lysosomes containing the remnants of digested material (residual bodies)
-accumulates PIGMENT ASSOCIATED WITH AGING -- accumulates in a person's cells as they age |
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how do you stain for glycogen?
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Light microscope: periodic acid-shiff reagent (PAS)
EM: stain with lead |
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glycogen
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-large branched polymer of glucose
-acts as storage for glucose -particularly large amounts found in LIVER AND MUSCLES -often closely associated with the smooth ER ** NO MEMBRANES** (must have said it like 10x) |
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Approximate diameter of a glycogen molecule?
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35 nm
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Lipid vacoules
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-serve as local storage of stores of energy
-particularly abundant in cells that secrete lipid hormones and adipose cells *mammary tissue has a lot of lipid vacoules -often associated with the smooth ER and mitochondria |
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Histochemical appearance of lipid vacoules
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A. often lost from tissue during routine preparation -- lipid soluble in organic solvents used in processing tissue
B. Can be stained in frozen sections by a fat soluble dye C. Fixation with OSMIUM preserves the lipid - under the EM there is a gradient of density from the outside to the inside reflecting the diffusino of the osmium -most droplets are NOT SURROUNDED BY A UNIT MEMBRANE |
