MCB 305 Exam 2 Overview

What are the 4 major functions of the cytoskeleton?

- Shape (structural support for cell shape) - Internal organization (internal framework to organize organelles within the cell) - Transport (direct movement of materials within the cell) - Cellular mobility (force-generating apparatus for cellular locomotion)

What are the 3 functions of the smooth endoplasmic reticulum?

- Synthesize steroid hormones - Detox in liver - Sequester calcium ions

how does actin contribute to cell movement individually and in interaction with myosin?

- actin branching form lamellipodium (leading edge) - actin interactions with myosin allow for cell contraction forward

What is the KDEL sequence?

- amino acid sequence that functions as a retrieval signal - specific receptors (KDEL receptors) capture molecules with the sequence, bring them to the ER - part of protein targeting

What is GMP-PNP? What is it used for?

- can bind in the place of GTP, but cannot be hydrolyzed to GDP - acts as a block of normal GTPase in experiments

Describe the cisternal maturation model of the Golgi

- cisternae form at the cis end of the Golgi stack - cisternae physically move from cis to trans end of Golgi stack - vesicles carry enzymes between cisternae of different maturity, altering the enzyme composition of the cisternae

Describe the transport model of the Golgi

- cisternae of golgi stack are stable compartments -enzyme composition differs by cisternae, but remains constant within an individual cisternae - vesicles carry cargo between cisternae

What are the two component subunits of Maturation Promoting Factors (MPFs)?

- cyclin-dependent kinase -cyclin

What are the 4 kinds of proteins made at free ribosomes in the cytoplasm?

- cytoplasm proteins - peripheral membrane proteins - nucleus proteins - proteins to go to organelles outside the endomembrane system

What are SNARES?

- engage vesicles in docking - t- and v- snares pull vesicle towards membrane causing fusion between the two lipid bilayers

What is the function of centrioles?

- initiate microtubules

How do microtubules function in the spindle checkpoint in cell division?

- microtubules provide force and spatial organization to align and separate chromosomes in two daughter cells - there needs to be tension on all chromosomes (from microtubule binding) for mitosis to proceed - Dynamic instability allows microtubules to make multiple "grabs" to locate chromosomes

How do microtubules and the actin cytoskeleton each play a part in cell division?

- microtubules pull apart chromosomes and spatially organize the shape of the daughter cells - actin interacts with myosin provides contractile force to split cells

what are 4 general functions of myosin?

- molecular motor for actin - pull actin filaments together - involved in cell contraction during cytokinesis

What are rabs?

- proteins that mediate tethering vesicles to target compartments - specific rab associations with membrane proteins confer specificity to membrane tethering interactions - part of recognition feature of protein transport

What are the 4 kinds of proteins made at the surface of the rough ER?

- secreted proteins - integral membrane proteins - ER proteins - Golgi proteins

Describe the process by which cells move via actin

- signal binds membrane receptor - receptor forms ARP2/3 complex that facilitates actin polymerization - protrusion of actin-filled lamellipodium - gripping of surface at lamellipodium via integrin - contractile forces (generated via actin/myosin interactions) pull cell body forward - rear of cell released from substratum and pulled forward

What does taxol do? how does it affect cells?

- stabilizes microtubules, preventing microtubule depolymerization - treated cells fail to form normal spindle during mitosis, chromosomes fail to separate normally

How do Low-density lipoproteins (LDLs) affect the body?

- taken up by RME - taken to the lysosomes - results in the release of cholesterol into the cell

how do high-density lipoproteins (HDLs) affect the body?

- transport cholesterol from tissue to livers for excretion

What is the main symptom of familial hypercholesterolemia? What causes this?

- unable to control cholesterol biosynthesis in response to low-density lipoproteins -result of defect in receptor-mediated endocytosis

What is the purpose of cyclins?

-regulate entry/exit of different cell cycle stages - made and degraded throughout the cell cycle

Describe the 4 steps of getting protein secreted

1) Protein synthesis at the ER 2) Vesicle sorting in the Endoplasmic Reticulumm Golgi Intermediate Compartment (ERGIC) 3) Processing through Golgi 4) Receptor-mediated endocytosis

Name the 5 component parts of the endomembrane system

1. ER 2. Golgi 3. Endosomes 4. Lysosomes 5. Vacuoles

describe the 4 steps of microtubule formation and disassembly that make up the dynamic instability model

1. GTP-tubulin added to tip (+ end) of microtubule 2. Tubulin hydrolyzes GTP 3. If tubulin GTP hydrolysis is faster than addition of GTP-tubulin to growing end, loose GTP-tubulin cap 4. Catastrophe, microtubule disassemble

Describe the 7 steps by which ribosomes are targeted to the ER surface and proteins are synthesized

1. Signal sequence at N-terminus of nascent polypeptide attaches to signal reception particle (SRP) 2. SRP receptor (at surface of ER) recognizes SRP 3. SRP released, ribosome binds translocon 4. Polypeptide moves into ER cisternal space through pore in translocon (ribosome released and translocon pore closed) 5. upon entering RER lumen, signal sequence is cleaved by signal peptidase 6. Carbohydrates added to protein 7. Chaperones in ER assist in folding

Microtubule organizing centers (MTOCs) control microtubule:

1. abundance 2. polarity 3. structure

What are the 3 functions of the golgi complex?

1. assembly of carbohydrates 2. incorporate sugars into oligosaccharides 3. synthesis of polysaccharides

What are the 4 steps of receptor-mediated endocytosis (RME)

1. cargo binds to coated pit membrane receptors 2. clathrin-coated regions invaginate into the cytoplasm 3. clathrin coat disassembled 4. vesicle fuses with endosome

What are the 3 component parts of clathrin coats pits/ clathrin-coated vesicles? what do they do?

1. clathrin (invaginates pit into cells, pinches off to form vesicle, support adapters at surface of pit) 2. adapter (support membrane receptors at surface of vesicle membrane) 3. membrane receptors (carry cargo)

describe the structure of microtubules

1. hollow, cylindrical structures 2. arranged in rows of protofilaments 3. have a minus and a plus end

Describe the 6 steps of neurotransmission at the synaptic cleft?

1. import of neurotransmitter into vesicle 2. movement of vesicle into active zone 3. vesicle docking at plasma membrane 4. exocytosis of neurotransmitter triggered by influx of Ca 2+ 5. reuptake of neurotransmitter 6. recovery of synaptic vesicles via endocytosis

Mice are treated with a high dose of Prozac, which blocks reuptake of serotonin from the synaptic cleft, or with a control solution. Sections of brain from both set of animals are prepared and immuno-gold electron microscopy is performed using an antibody against serotonin (a neurotransmitter). Use the following model to answer the following question. What would you predict to see in your experimental results?

A greater number of uncoated vesicles filled with serotonin in the control-treated compared to the Prozac treated

(?) is an example of a protein that aids in the selective packaging of certain molecules into vesicles. (?) is an example of a protein that aids vesicles in recognizing (or selectively interacting with) a target compartment.

AP2; Rab

Which of the following statements about cyclin is FALSE? A) Cyclin is a component of MPF B) Cyclin degradation is necessary to trigger the transition from G2 to mitosis C) Cyclin binding regulates the activity of CDK D) Cyclin levels fluctuate during the cell cycle E) Both A and C are FALSE

B (Cyclin degradation is necessary to trigger the transition from G2 to mitosis)

Which of the following occurs when DNA damage is detected? A) Ubiquitylation of p53. B) Phosphorylation of p53. C) Synthesis of p53. D) Exclusion of p53 from the nucleus.

B (phosphorylation of p53)

Which coated vesicles move materials in a retrograde direction from the ERGIC and Golgi stack backwards toward the ER?

COPI-coated vesicles

Why can mutations in both copies of p53 lead to cancer?

Cells do not stall in the cell cycle when there is DNA damage

Which of the following experimental results directly linked cyclins to entry of cells into M phase? A) Radio-labeled proteins were found in fertilized sea urchin eggs that were not found in unfertilized eggs, by polyacrylamide gel electrophoresis. B) Progesterone treatment induced frog oocytes to undergo mitosis. C) Cytoplasm collected from frog oocytes which were treated with progesterone and then incubated for over 12 hours could induce unstimulated cells to undergo mitosis when injected into these naive cells. D) Injection of synthetic cyclin mRNA into frog oocytes led to mitosis on a time scale similar to progesterone treatment

D (Injection of synthetic cyclin mRNA into frog oocytes led to mitosis on a time scale similar to progesterone treatment)

Which of the following proteins would NOT be synthesized at the surface of the ER? A) A G protein coupled receptor B) Collagen C) KDEL receptor D) A transcription factor E) A golgi enzyme

D (a transcription factor)

When the rate of loss of actin subunits from the pointed end of an actin filament is balanced by the rate of their addition to the barbed end A) the filaments are said to be in steady state B) the length of the filaments remains the same C) treadmilling occurs D) A and B are correct E) All of the above are correct

E (all of the above)

Which of the following nonmuscle cell activities involves actin filaments often working in concert with myosin motors? A) cytoplasmic streaming B) phagocytosis C) cell-substratum interactions D) cell locomotion E) all of the above

E (all of the above)

The cis end of the golgi stack faces the (?)

ER

The KDEL receptor is responsible for recognizing an ER retention signal on ER proteins. What would happen if yeast cells contained a mutation that made the KDEL receptor non-functional?

ER enzymes would be secreted from the cell rather than stored in the ER

What was the primary phenotype of the JD patient?

His cells were able to bind but not internalize LDL.

Why is retinoblastoma more common in individuals who have inherited the RB deletion and have the genetic predisposition for retinoblastoma?

If the RB gene is already mutated or deleted on one of the homologous chromosomes, only one hit rather than two is needed to cause development of retinoblastoma; thus the probability is higher.

What do cyclin-dependent kinases do?

Phosphorylate downstream targets when bound to cyclins

Cancer is a genetic disease in that it can be traced to alterations within specific genes, but, in most cases, it is not an inherited disease. Why is that the case?

The genetic alterations in most cancers arise mostly in the DNA of somatic cells during the lifetime of the affected individual

Which of the following steps in the synthesis of a secreted protein would happen FIRST? A) The ribosome binds the mRNA. B) The SRP binds the signal sequence. C) The signal sequence is synthesized. D) The SRP binds the SRP receptor. E) The ribosome binds the translocon.

The ribosome binds the mRNA

When a microtubule is growing, the plus end is present as an open sheet to which GTP-dimers are added. A cap of GTP-dimers can often form on the growing microtubules during rapid growth periods. How does this cap form?

Tubulin dimers are added to the microtubule faster than the GTP is hydrolyzed

A "catastrophy" happens when:

When tubulin throughout an entire microtubule is bound to GDP, instead of GTP

What causes the rapid drop in Cdk activity that leads to the exit from mitosis and the entry into G1 typically exhibited by cells as they finish division?

a plunge in mitotic cyclin concentration

What is the purpose of the endomembrane system?

allows materials to be shuttled around the cell

What are the units that make up microtubules?

alpha- and beta- tubulin dimers

Vesicles that move through the Golgi complex from the cis-cisternae to the trans-cisternae are said to move in a(n) (?) direction.

anterograde

COPII coated vesicles move in a(n) (?) direction from the (?) to the (?)

anterograde; ER, golgi complex

What do chaperone proteins do?

bind to unfolded/misfolded proteins to correct structure

How does the protein coat differ between budding and fusing vesicles?

budding vesicles have a protein coat (allows for targeting of vesicle to cellular compartment) vesicles must disassemble protein coat in order to fuse

Which of the following activities in higher vertebrates does not involve cell locomotion? A) tissue and organ development B) axon development C) cleavage in the early embryo D) wound healing E) metastasis

c (cleavage in the early embryo)

the trans end of the golgi stack faces the (?)

cell membrane

Which model suggests that the Golgi cisternae are transient structures that form at the cis face of the stack by fusion of membranous carriers from the ER and ERGIC and that each cisterna travels through the Golgi complex from the cis to the trans end of the stack, changing in composition as it progresses?

cisternal maturation model

What is the role of COP proteins in the endomembrane system?

coat proteins that help to promote vesicle formation

The regulatory subunit of maturation-promoting factor is called (?) because (?)

cyclin; its concentration rises and falls predictably as the cell cycle progresses

What are the two sites within a cell at which protein synthesis is generally thought to occur?

cytosolic surface of RER and free ribosomes

What protein is common to all MTOCs?

gamma-tubulin

LDLs are associated with (?) blood cholesterol while HDLs are associated with (?) blood cholesterol.

high; low

how are molecular motors able to move?

hydrolysis of ATP generates mechanical force / conformation change

LDL receptors are found mostly on the outer surface of cells even in the absence of ligand. Where specifically on the cell surface are they found?

in the coated pits

The extracellular portion of an integral membrane protein locates to the (inside/outside) of the ER membrane upon location

inside (in the lumen)

what kind of motor protein moves cargo along axons?

kinesins

what are the 2 motor proteins that move along microtubules?

kinesins and dyneins

What are microsomes?

large vesicle-like pieces of the ER

temperature sensitive mutants have normal phenotype at (?), permissive temperatures and abnormal phenotype at (?) restrictive temperatures due to (?)

low; high; slight protein misfolding

The endomembrane system when homogenized is broken up into vesicles, which are heterogeneous but similar in size. These vesicles can be purified and, after purification, often retain their biological activity. They are collectively referred to as (?)

microsomes

dyneins are (?) end directed

minus

Which directed do non-conventional kinesins move along microtubules?

minus end

Profilin is a protein that binds to actin-ATP monomers. It was once thought to be a (?) protein, but new evidence suggests that it probably (?) actin filament growth by catalyzing the dissociation of its bound (?).

monomer-sequestering; promotes; ADP

kinesins are (?) end directed

mostly plus (some are minus-end directed)

Define chemotaxis

movement of cell towards or away from chemical signal

what kind of motor protein is Ncd?

non-conventional kinesin

In experiments by Brown and Goldstein, what was a key difference between normal cultured cells and those from individuals with familial hypercholesterolemia?

only normal cells could bind significant LDL

Microtubules grow on which end?

plus end

actin filaments grow from the (?) end and shrink from the (?) end

plus end; minus end

What does cofilin do?

promotes depolymerization of actin filament

What does profilin do?

promotes dissociation of ADP from actin, prompts formation of actin-ATP

What effect does the binding of the SRP to the growing polypeptide chain and the ribosome have on protein synthesis?

protein synthesis ceases temporarily

What kind(s) of modifications are made in proteins as they move through the Golgi complex?

protein's carbohydrates are modified by a series of stepwise enzymatic reactions

COPI coated vesicles move in a(n) (?) direction from the (?) to the (?)

retrograde; golgi complex; ER

What is IgG?

secreted protein normally made at the surface of the ER

What molecules do the AP2 adaptors of the clathrin coat connect?

the cytoplasmic tails of specific membrane receptors and clathrin molecules

To which end of microtubules are tubulin subunits primarily added in vitro?

the plus end

Blöbel, Sabatini and Dobberstein proposed that the site of protein synthesis is determined by information contained in the N-terminal portion of the protein, the first part to emerge from the ribosome. What did they call their proposal?

the signal hypothesis

What allows smooth and rough vesicles (microsomes) to be readily separated by density gradient centrifugation?

their differences in density

What happened to COPI-coated vesicles within the cell when the cell was treated with GTP analogues that could not be hydrolyzed?

they accumulated in the cytoplasm (GTP hydrolysis necessary for protein coat disassembly)

In order to study the origin of the J D phenotype, the authors of the Davis et. al. paper:

transfected cultured cells with normal LDL receptor or an LDL receptor with a point mutation.

How are integral membrane proteins thought to enter the lipid bilayer?

translocon channel has gate that continuously opens and closes, allowing nascent polypeptide to move into lipid bilayer

The steady state of actin in which the plus end is growing at the same rate as the minus end is shrinking is called what?

treadmilling

Is Rb an oncogene or tumor suppressor?

tumor suppressor

define phagocytosis

uptake of a solid particle into a cell by engulfing the particle

motor proteins direct movement of:

vesicles, organelles, mRNA, and other proteins