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104 Cards in this Set

  • Front
  • Back
This organelle is a network of membrane tubules and sheets in the cytoplasm.
ER.
How does the ER lumen compare to the rest of cell size-wise?
It takes up maybe 10% of the cell's volume, and the lumen may be continuous.
Why do we say the ER is self-replicating?
It produces its own lipids and transmembrane proteins--many of which go into the Golgi and PM.
Where all do products of the ER go?
To itself, to other organelles in the cell, to the PM, and for export outside of cell.
What does flippase do?
It's an enzyme found on the cytosolic side of the ER that transfers newly made phospholipids to the cisternal side of the ER. This is an important mechanism the ER has in making its own bilayer.
Name three places where SER is abundant.
Cells that detoxify drugs (liver...where cytochrome 450 oxidizes drugs), muscle cells (think Ca), and cells that make steroid hormones (like the adrenal...SER makes cholesterol and uses it to synthesize steroids).
How is polyspermy prevented?
Ca is released from the SER of an oocyte after fertilization.
Which proteins do RER ribosomes translate?
Proteins of the ER, Golgi, PM, lysosome, endosome, and cell exterior.
What's a polyribosome?
Several ribosomes on one mRNA.
What proteins do free ribosomes translate?
Proteins of the cytosol, mitochondria, and nuclei. Some peroxisomal proteins (RER makes the rest).
T/F: One pool of ribosomes supplies ribosomal subunits to both cytosolic ribosomes and ER ribosomes.
True. The subunits can go back and forth.
What is the ER signal sequence?
A 16-30 AA chain at the beginning (N terminus) of a nascent protein that binds to a signal recognition particle.
During translation in the ER, what does the signal recognition particle do?
It halts translation of the growing protein until the SRP + ribosome complex can bind to the SRP receptor on the ER membrane. The growing protein then passes through a channel in the ER membrane called the protein translocator.
What happens as soon as a growing protein passes through the protein translocator in the RER?
As soon as it enters the ER cisterna, a signal peptidase removes the ER signal sequence. This is called "cotranslational" entry into the ER, since it occurs during translation.
What is posttranslational entry?
Entry of a protein translated on cytosolic ribosomes into organelles after translation has ended.
What does the ER do with misfolded proteins?
It exports them to the cytosol and they are broken down in proteasomes.
How do transmembrane proteins get correctly inserted into the ER membrane?
They have a stop-transfer signal. It's a hydrophobic alpha helix about 20 AAs long. It anchors the protein into the membrane.
When would oligosaccharides get attached to new proteins in the ER that are destined to become ER resident proteins?
Once inside the ER cisterna. This is where the new proteins fold as well.
T/F. Most proteins made on RER ribosomes stay in the ER.
False. Most go elsewhere--Golgi, lysosomes, PM, cell exterior.
What protein forms a coat around a newly formed vesicle?
Clathrin.
How does clathrin associate with a cargo molecule?
Via another protein called adaptin. Adaptin binds the cargo receptor; Clathrin binds adaptin. Order from inside to outside is cargo-cargo receptor-adaptin-clathrin.
What makes the membrane form the coated pit?
Clathrin.
How does the coated pit pinch off from the PM?
A protein called dynamin.
What's the difference between v- and t-SNAREs?
v-SNAREs are located on vesicles; they recognize and attach to t-SNAREs on the target membrane.
What catalyzes the union of v- and t-SNAREs?
GTPases called Rab proteins.
With regard to the vesicle/target membrane, what kind of protein are SNAREs?
Transmembrane.
What is the source of glycocalyx on the PM?
It comes from proteins that were glycosylated in the ER. Many proteins are glycosylated in the ER.
What's the difference between COP vesicles and clathrin-formed vesicles?
COPs are in the ER; clathrin acts in the Golgi.
COPII vesicles transport proteins and lipid components from ____ to ____.
RER; cis Golgi.
COPI-coated vesicles transport material from ____ to ____ to ____.
Cis; medial; trans Golgi.
Which way do COPI vesicles take vesicles?
Cis-medial-trans Golgi, or retrograde the other way.
What's the purpose of retrograde transport in the Golgi?
It returns both membranes and ER resident proteins.
Why do ER resident proteins leave the ER in the first place?
They're soluble, and don't have much of a choice.
What's KDEL? How does it work?
A retention signal on ER resident proteins. It enables them to bind to receptors in Golgi cisternae and to be returned to the ER in COPI vesicles.
Which way do COPII vesicles go?
Only from ER to cis Golgi. They can't go backwards.
On ER resident proteins, where is the KDEL signal located?
On their carboxyl end.
Why does the Golgi need multiple components (cis, etc.)?
They compartments have different enzymes and, therefore, different functions. Sugars that were added to proteins in the ER may be removed. Conversely, sugars may be added in the Golgi. The compartments modify, package, and sort.
What are the 3 main pathways a protein secreted from the Golgi can follow?
Signal-mediated diversion to lysosomes; the regulated secretory pathway; and the constitutive secretory pathway.
In the signal-mediated diversion to lysosomes pathway, how do proteins get to lysosomes?
They are tagged, while in the cis Golgi, with a mannose-6-phosphate. This tag binds to mannose-6-phosphate receptors in the trans Golgi which directs the proteins to lysosomes.
What's an important example of the regulated secretory pathway? How does it work?
Beta cells in the pancreas producing insulin. These Golgi products are stored in vesicles which are rapidly released in response to hormonal or neural stimuli.
In the regulated secretory pathway, where are proteins packaged into vesicles? How do they get to the right vesicle?
It occurs in the trans Golgi network (TGN). Signal patches on them ensure they get in the right vesicle.
In the regulated secretory pathway, what triggers secretion of a vesicle?
Some stimuli, often a hormone. The mechanism may involve influx of Ca into a cell which causes the membrane of the vesicle to fuse with the PM.
In the regulated secretory pathway, what happens (to both the vesicle contents and the vesicle itself) once the vesicle has fused with the PM?
Contents are secreted upon proper stimulus. The vesicle often becomes part of the PM. Often, the vesicle is taken back into the cell by endocytosis.
What's the identifying characteristic of the constitutive secretory pathway? Where does this usually happen?
Golgi products are immediately discharged at the cell surface. Usually, this involves production of ECM material.
Where is procollagen made, where does it end up, and which secretory pathway does it use to get there?
It's made in the RER, ends up as collagen in the ECM as part of a larger collagen fibril, and gets there through the constitutive secretory pathway.
What parasite uses phagocytosis to its advantage?
Leishmania. It prevents the vacuoles that phagocytosed it from fusing with lysosomes.
What's actin's role in phagocytosis?
It forms the pseudopods that engulf the particle, cell, etc.
What are two chief characteristics of pinocytosis?
It's non-selective; it uses small vesicles (<150nm diameter).
What are the three possible fates of molecules (ligands) taken in by receptor-mediated endocytosis?
1) May end up in lysosomes and get digested.
2) May remain in the cytoplasm (yolk proteins).
3) May pass unchanged through the cell (maternal antibodies).
What's clathrin's role in receptor-mediated endocytosis?
Once the ligand binds to the receptor, clathrin forms the coated pit. Then, dynamin/GTP pinches it off to form a coated vesicle (50-100nm diameter).
In receptor-mediated endocytosis, when do clathrin vesicles lose their coats?
Once they have entered the cell. An uncoating enzyme removes it, and the clathrin is recycled to the PM. The vesicle then fuses with an endosome.
List the 5 steps of receptor-mediated endocytosis.
1) Ligands bind externally to transmembrane receptor proteins which are attached to clathrin molecules immediately inside the PM.
2) Clathrin, dynamin, and GTP form a coated vesicle and enter the cell.
3) The coat falls off and the vesicle is now termed an endosome.
4) Low pH interior causes some ligands to dissociate from their receptors; a vesicle rich in receptors buds off to recycle receptors to the PM.
5) The endosome containing ligand fuses with a lysosome and ligands are broken down.
How many enzymes do lysosomes have?
40.
What's optimal pH for lysosomes?
5.
How are lysosomal enzymes protected against autolytic protease digestion?
They are glycosylated.
What method do lysosomes use to acquire molecules/cells/cell fragments to digest?
Receptor-mediated endocytosis and phagocytosis.
What's autophagy?
A term describing lysosomal digestion of old cell components from within the lysosome's own cell.
How do the end products of lysosomal digestion get back out of the lysosome?
Transport proteins in the lysosomal membrane.
How can lysosomes be identified by cytochemistry?
Phosphatase (the defining enzyme) in lysosomes causes Pb to be precipitated on the lysosome.
How are lysosomal enzymes made? How are they transported to lysosomes?
Made in RER, where oligosaccharides are added to the amino end. Once in cis Golgi, they are recognized by a signal patch of AAs. Enzymes then add M6P to the oligosaccharides. At trans Golgi, M6P binds to transmembrane M6P receptors. A clathrin-coated vesicle is then formed. The vesicle leaves the Golgi, loses its coat, and fuses with an endosome. The low pH removes the M6P receptor, and P is removed from the M6P on the enzyme to prevent re-attachment to the receptor. The receptor is recycled to trans Golgi, and the endosome has become a lysosome.
What are lysosomal storage diseases?
When enzymes aren't targeted correctly to lysosomes or the enzymes themselves are defective. A buildup of enzyme ensues. Major diseases are I-Cell and Tay-Sachs disease.
What is I-cell disease?
AKA ML II (mucolipidosis). An inherited lysosomal storage disorder caused by deficiency of an enzyme responsible for adding P to M6 to form M6P. These enzymes aren't targeted right and end up in the extracellular fluid. The buildup of mucolipids and mucopolysaccharides causes the symptoms: coarse facial features, skeletal abnormalities, & mental retardation.
What is Tay-Sachs disease?
A genetic lysosomal storage disorder. Causes ganglioside accumulation in the brain resulting in mental retardation, blindness and death by early childhood.
How do silica and asbestos fibers do their damage?
They're endocytosed and end up in lysosomes, where they puncture the lysosomal membrane.
What's another name for peroxisomes?
Microbodies.
How big are peroxisomes?
0.2 to 1.0 micron diameter.
What kind of enzymes are in peroxisomes?
Ones that produce and break down H2O2 (Catalase breaks it down).
Where do you find catalase and what does it do that's useful?
It's in peroxisomes. It breaks down excess H2O2 and inactivates toxic organic molecules by oxidizing them using H2O2. Abundant in liver cells.
What dietary macronutrient do peroxisomes help break down?
They help break down fatty acids.
What appearance characterizes peroxisomes?
Spherical, single membrane, with a granular matrix. Peroxisomal enzymes can be so concentrated that they form crystals.
Where do peroxisomes acquire all of their proteins? Why is this obvious?
They get all of them from the cytosol. It's obvious because peroxisomes don't contain nucleic acid.
What is Zellweger's Syndrome?
When protein import into peroxisomes fails. Since they don't have the right enzymes, buildup of toxic molecules occurs. Leads to hepatomegaly and high Fe and Cu in the blood. Fatal during infancy.
What is neonatal adrenoleukodystrophy?
Occurs when very long chain FAs can't be oxidized and so accumulate in the brain. They destroy myelin sheaths. In the adrenal gland they cause a deficiency of adrenal steroid hormones. Occurs because peroxisomes in the CNS can't import enzymes for beta-oxidation to occur.
Where do peroxisomal precursors come from?
RER.
These enzyme-rich organelles are capable of dividing into daughters.
Peroxisomes.
Describe what kind of oxidation peroxisomes do to FAs.
Beta-oxidation. They remove 2 carbon atoms at a time and use them to make acetyl CoA, which is exported to the cytosol.
Describe key components of the IMM.
Invaginated to form cristae. Contains enzymes for oxidation rxns and 10nm stalked particles called ATP synthases--there are 2000 to 4000 ATP synthases per square micron of IMM.
Describe key components of the Mitochondrial Matrix.
ATP synthases extend from the IMM into the matrix. Matrix contains enzymes of the Krebs cycle and enzymes for oxidation of pyruvate and FAs. Contains miDNA, ribosomes, and tRNAs.
In mitochondria, where do protons accumulate?
Intermembrane space.
Would you find more cristae in a muscle cell or a fat cell? Explain.
More in muscle. More cristae means more surface area of IMM means more ATP synthases means more ATP production.
ATP Production: What happens in the cytosol?
One glucose is glycolysed into 2 pyruvates with a net gain of 2 ATP, and reduction of 2 molecules of NAD+ to NADH.
ATP Production: What happens right after glycolysis?
In the matrix, pyruvate and FAs are converted into acetyl CoA which enters the TCA cycle.
ATP Production: What happens in the Krebs cycle?
A cyclic series of rxns that release CO2, produce small amounts of GTP, and pass electrons to NAD+ and FAD, creating NADH and FADH2.
ATP Production: What happens right after the Krebs cycle?
The high energy electrons in FADH2 and NADH pass along the ETC in the IMM, pumping protons from the matrix into the intermembrane space. The proton gradient pushes protons through ATP synthases, turning ADP into ATP.
ATP Production: What's the final step (final e acceptor)?
Electrons are passed to oxygen and protons at cytochrome oxidase c and water is formed.
ATP Production: what does glycolysis yield?
2 ATP, 2 NADH
ATP Production: what does pyruvate processing yield?
2 CO2, 2 NADH
ATP Production: What do 2 turns of the TCA cycle yield?
4 CO2, 2 GTP, 6 NADH, 2 FADH2
ATP Production: How many ATPs can NADH make?
3 ATPs per NADH molecule.
ATP Production: How many ATPs can FADH2 make?
2 ATPs per FADH2 molecule.
What's the total yield of OXPHOS?
30-38 molecules of ATP/GTP per glucose molecule.
How does brown fat affect ATP production?
Thermogenin in brown fat in babies allows protons to re-enter the matrix without ATP synthesis. The energy is released as heat.
Describe miDNA.
Appears as 2-3 nm diameter fibrils. A double helix with no histones. It's circular and about 5 microns long. Has 16,569 base pairs. There are 2-10 DNAs in every mitochondrion.
Most mitochondrial proteins are encoded by DNA from where?
Nuclear DNA, not miDNA.
What does UGA code for in miDNA?
Tryptophan.
What does miDNA code for?
It encodes 37 genes, 13 of which are involved in OXPHOS (most OXPHOS genes are from nuclear DNA, though).
What is Leber's Hereditary Optic Neuropathy?
A miDNA defect. Caused by a single base change in NADH dehydrogenase; leads to blindness.
Compare mitochondrial ribosomes to cytosolic ribosomes.
They're smaller and they respond to antibiotics in similar ways to bacteria. Therefore, mitochondrial ribosomes are sensitive to chloramphenicol and insensitive to cycloheximide. Non-mitochondrial ribosomes act the opposite to these antibiotics.
What is heteroplasmy in miDNA?
When some mitochondria have normal DNA and some have mutated DNA. If too many have mutated DNA, then cell damage or death occurs.
What mitochondria does Leber's Hereditary Optic Neuropathy affect?
Mitos in optic nerve cells.
What role does hsp70 play in importing proteins from cytosol to mitochondria?
It's a chaperone and there are two--one outside the mito (cytosolic hsp70) and one inside (mito hsp70). Prevents proteins from folding until they have gotten through the TOM and TIM complexes.
When a protein is entering a mitochondrion, when is it finally free to fold into its 3D shape?
After mito hsp70 is detached, and after its import signal sequence is removed by a signal peptidase inside the matrix.
What additional chaperone is needed by many mitochondrial proteins?
hsp60, which helps fold the protein after hsp70 has detached.
What drives newly made proteins through the IMM?
ATP and a proton gradient.