Exam 2 Questions

G1 to S checkpoints?

-is there any DNA damage? -is the environment favorable?

What is the function of stable microtubules in the cell?

-support flagella and cilia -provide constant pathway for motor proteins -highly organizing cell -attach to chromosome

______________________1. Inhibition of G1 CDK ______________________2. Degradation of S cyclins ______________________3. Inhibition of a phosphatase that targets the CDK/cyclin complex ______________________4. Loss of function mutation in a mitogen receptor ______________________5. Degradation of CDC6 ______________________6. Gain of function mutation in p53 activity ______________________7. Degradation of G1 cyclins ______________________8. Degradation of M cyclins ______________________9. Activate an inhibitory kinase that targets a CDK/cyclin complex ______________________10. Inhibit M CDK

1. Slow progression through G1 2. Slow progression from G1-->S 3. Slow progression through all 4. Slow progression through all 5. Slow progression through G1 6. Slow progression from G1-->S 7. Slow progression through G1 8. Slow progression from G2-->M 9. Slow progression through all 10. Slow progression from G2-->M

#4. Which of the following is true of the protein called p53? A. It regulates the expression of p21 B. It promotes DNA synthesis C. It activates G1/S CDKs D. All of the above

A

Compared to the normal situation, in which actin monomers carry ATP, what do you predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments? A. Actin filaments would grow longer. B. Actin filaments would grow shorter because depolymerization would be enhanced. C. Actin filaments would grow shorter because new monomers could not be added to the filaments. D. No change, as addition of monomers binding nonhydrolyzable ATP would not affect actin filament length.

A

Cortisol is a hormone made in the cells of the adrenal gland that affects the metabolism of proteins, carbohydrates, and lipids in most tissues of the body. What type of signaling molecule is cortisol? A- Endocrine B- Paracrine C- Autocrine D- Contact dependent

A

Which is likely to occur more rapidly in response to an extracellular signal. A. changes in protein phosphorylation B. changes in proteins being synthesized

A

Which is likely to occur more rapidly in response to an extracellular signal? A. Changes in protein phosphorylation B. Changes in proteins being synthesized

A

Which of the following statements about the function of the centrosome is false? A. Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome. B. Centrosomes contain hundreds of copies of the γ-tubulin ring complex important for microtubule nucleation. C. Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules. D. Centrosomes are the major microtubule-organizing center in animal cells.

A

Which of the situations below will enhance microtubule shrinkage? A. addition of a drug that inhibits GTP exchange on free tubulin dimers B. addition of a drug that inhibits hydrolysis of the GTP carried by tubulin dimers C. addition of a drug that increases the affinity of tubulin molecules carrying GDP for other tubulin molecules D. addition of a drug that blocks the ability of a tubulin dimer to bind to γ-tubulin

A

2. G-protein coupled receptors (GPCRs) are a very common type of switch used to control signal transduction. GPCRs activate G-proteins. An α-subunit of a G-protein bound to GDP is inactive, but becomes active when the GDP is replaced by GTP. This releases the ß and γ subunits, which are involved in activating signaling pathways within the cell. a. What process would be involved in turning a G-proteins off (GTP -> GDP)? b. Describe how a GPCR might be involved in these processes: • Signal relay: • Amplification of signal: • Integration of multiple signals:

A. A phosphorylase could dephosphorylate the GTP bound to the G-protein, reverting the G-protein to its inactive form (bound to GDP). B. i. GPCRs process extracellular signals and relay them to signaling pathways within the cell. ii. A single GPCR can activate multiple proteins within the cell before it is inactivated. Think in terms of the G-protein; as long as it's active (bound to GTP) it can interact with multiple downstream target proteins, therefore amplifying the signal. iii. GPCRs can work in conjunction with other signaling molecules to induce a joint change in the cell. Think about multiple GPCRs receiving individual signals, but then the downstream target proteins in both of those pathways interacting later to produce one cellular effect.

1. NO signals from the blood vessels cause smooth muscles to relax; however, these signals can only cross a short distance as NO will be converted to more stable forms if exposed in the extracellular space. a. What type of signaling is this? b. If a smooth muscle cell culture were exposed to an environment rich in NO, what would be the result? Would you expect different results if this experiment was conducted in a culture plate vs a large flask?

A. Paracrine (short distance diffusion). B. In an NO rich environment, we expect smooth muscle cells to relax. This effect would be greater in a smaller vessel, such as a plate, whereas larger distances would be difficult for the NO to cross without converting to more stable forms so you would see much lower levels of relaxation.

What makes a good activated carrier?

Activated carriers are small molecules and contain easily exchangeable energy

#2. What is the role of a CDK in the cell? A. Dephosphorylate proteins involved in cell division and cell growth B. Phosphorylate proteins involved in cell division and cell growth

B

#5. What is the function of a mitogen? A. Phosphorylate cyclins B. Stimulate synthesis of G1 cyclins C. Inhibit cell cycle progression D. All of the above

B

Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal.. A. True B. False

B

Consider the mechanism by which actin and tubulin polymerize. Which of the items below does not describe something similar about the polymerization mechanisms of actin and microtubules? A. Although both filaments can grow from both ends, the growth rate is faster at the plus ends. B. Depolymerization initiates at the plus ends of filaments. C. Nucleotide hydrolysis promotes depolymerization of filaments. D. Free subunits (actin and tubulin) carry nucleoside triphosphates.

B

NADH pills can be purchased over the counter, and are often taken by sufferers of chronic fatigue syndrome (CFS). How might these pills benefit a CFS patient? A) They would increase energy by creating more FADH2. B) They would decrease the rate of glycolysis. C) They would increase the number of electrons provided to the electron transport chain. D) They would decrease the rate of alcoholic fermentation

C

The following happens when a G-protein-coupled receptor activates a G protein. A. The β subunit exchanges its bound GDP for GTP. B. The GDP bound to the α subunit is phosphorylated to form bound GTP. C. The α subunit exchanges its bound GDP for GTP. D. It activates the α subunit and inactivates the βγ complex.

C

The growth factor Superchick stimulates the proliferation of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken tumor cell lines have mutations in the gene that encodes this receptor. Which of the following types of mutation would be expected to promote uncontrolled cell proliferation? A. a mutation that prevents dimerization of the receptor B. a mutation that destroys the kinase activity of the receptor C. a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor D. a mutation that prevents the binding of the normal extracellular signal to the receptor

C

The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true? A. Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells. B. Glial cells do not have a receptor for QGF. C. QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed. D. Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF.

C

Which of the following happens when a G-protein-coupled receptor activates a G protein? A- The β subunit exchanges its bound GDP for GTP B- The GDP bound to the α subunit is phosphorylated to form bound GTP C- The α subunit exchanges its bound GDP for GTP D- It activates the α subunit and inactivates the βγ subunit

C

Which of the following statements about the cytoskeleton is false? A. The cytoskeleton is made up of three types of protein filaments. B. The cytoskeleton controls the location of organelles in eukaryotic cells. C. Covalent bonds between protein monomers hold together cytoskeletal filaments. D. The cytoskeleton of a cell can change in response to the environment.

C

Which of the following statements is correct? Kinesins and dyneins ____________________. A. have tails that bind to the filaments. B. move along both microtubules and actin filaments. C. often move in opposite directions to each other. D. derive their energy from GTP hydrolysis.

C

#3. Which of the following proteins are regulated by cyclin? A. mitogens B. The anaphase promoting complex C. p53 D. CDK E. DNA helicase

D

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in ________ signaling. A. endocrine B. paracrine C. neuronal D. contact-dependent

D

For both actin and microtubule polymerization, nucleotide hydrolysis is important for ______. A. stabilizing the filaments once they are formed. B. increasing the rate at which subunits are added to the filaments. C. promoting nucleation of filaments. D. decreasing the binding strength between subunits on filaments.

D

The hydrolysis of GTP to GDP carried out by tubulin molecules ________________. A. provides the energy needed for tubulin to polymerize. B. occurs because the pool of free GDP has run out. C. tips the balance in favor of microtubule assembly. D. allows the behavior of microtubules called dynamic instability.

D

#1. Which of the following questions does the cell ask itself as it transitions from G1 to S phase A. Is DNA replicated? B. Is all DNA damage repaired? C. Are chromosomes properly attached to the mitotic spindle? D. Is the environment favorable? E. More than one of the above are correct

E

In an experiment to test the physiological effects of caffeine on aerobic respiration, you plan to measure the amount of radioactively labeled CO2 expelled from mice exercising on a wheel. Which atom and in which molecule will you label that will allow you to carry out this experiment? A) Oxygen atoms in glucose B) Atmospheric oxygen atoms C) Carbon atoms in glucose D) A or B E) A or C

E

Which of the following is a shared characteristic of both GPCRs and enzyme coupled receptors? A. Cytoplasmic domains act as enzymes B. Cytoplasmic domains phosphorylate downstream target proteins directly C. Display ligand binding domain on the inner surface of the plasma membrane D. Multiple transmembrane segments E. None of the above

E

What is the first law of thermodynamics?

Energy is neither created nor destroyed, but may be transformed to other forms of energy

Because hormones like cortisol are broadcast throughout the body, all cells will respond to them. True or False?

F

1. Explain how ATP production in the mitochondria follows the First Law of Thermodynamics.

First law says energy can be neither created nor destroyed ATP production in mitochondria mostly happens in the ETC, a system that utilizes a gradient (potential energy) of protons to oxidize hydrogen. This oxidation generates the energy that ATP synthase relies on to add a phosphate to ADP to make ATP, in a process referred to as oxidative phosphorylation

How are GTP binding proteins regulated by GTP hydrolysis?

GTPase activity tends to switch off GTP binding proteins

How could inhibition be a good thing (sometimes)?

Gives the cell more time to grow Lets the cell ensure the DNA has no errors/fix those errors Lets the cell wait until extracellular conditions are favorable for division

how do protein kinases and protein phosphatases switch proteins on and off?

ISMs are often switched ON by phosphorylation via a KINASE and OFF by dephosphorylation via a phosphatase

G2 to M checkpoints?

Is DNA damaged? Is DNA replicated properly?

Predict the outcome of: A mutation in Gα that prevents the dissociation of GDP A mutation in Gα that significantly increased its affinity for GTP but reduced its affinity for GDP. A disease causing bacterium that produces a toxin that prevents Gα from hydrolyzing bound GTP

No activation of Gα --> no downstream signaling Constitutive activation of Gα --> increase in downstream signaling Constitutive activation of Gα --> increase in downstream signaling

Do signaling pathways always regulate the function of proteins already present in the cell? Defend your answer.

No, sometimes they regulate gene expression some cAMP pathways do this

Are microtubules always growing and shrinking? If not, how are microtubules stabilized in cells?

No; by interactions with cell structures and molecules, other proteins (+ end proteins that bind with + end)

3. Generate a list of 3 favorable reactions (exergonic) involved in cellular respiration.

Oxidation reactions ATP ADP Glucose pyruvate acetyl CoA NADH NAD+ FADH FAD

2. What are the 2 ways in which cells produce ATP? Where do they occur? (NOT aerobic and anaerobic)

Oxidative phosphorylation in the mitochondria Substrate level, as in glycolysis, in the cytoplasm

The endothelial cells that line blood vessels release nitric oxide (NO) locally to neighboring cells of the smooth muscle. What type of signal molecule is NO?

Paracrine

What does the activity of Cyclin-CDK complexes depend on??

Phosphorylation and dephosphorylation cyclins must be bound to the CDKs --> but these complexes tend to switch on abruptly at the appropriate time and then get switched off just as quickly --> the complex has inhibitory phosphatases --> to become active, the Cdk must be dephosphorylated by a protein phosphatase --> to become inactive, it can be phosphorylated by a protein kinase could also block activity by Cdk inhibitor proteins binding the complex to maintain CDks in an active state to dely progression into the next phase

A mutant form of constitutively active Ras was originally identified in cancer cells. How do you think mutant Ras function differs from wild-type Ras function in cancer cells and why would this lead to uncontrolled cell division? Would this be a gain or loss of function mutation in Ras?

Ras remains bound to GTP (never hydrolyzed), overactive cell division, constant downstream signaling to transcription regulator gain of function

What is the 2nd law of Thermodynamics?

The amount of entropy/disorder increases over time

Intracellular signaling pathways take MANY years, many scientists, and MANY experiments to map out. How do scientists piece together complex signaling pathways?

They... screen for mutants in which signaling pathways are not functional determine the order in which proteins act in a pathway identify protein-protein interactions.

Cell biologists have phospho-antibodies that allow them to detect phosphorylated versions of their favorite proteins.  You have a mutant with a missense mutation that you hypothesize alters the single amino acid that is phosphorylated in wild-type cells. Design an experiment that would allow you to determine if this amino acid is indeed phosphorylated.

Western Blot--> detect presence of phosphorylated protein, visualized fluor; 2ndary antibody conjugated to phospho-antibody bu=ind can use immunofluorescence

Can cargo be transferred between motor proteins? Does John always take the same route through the cell? What happens when kinesin gets to the very end of the + end? What happens when dynein gets to the very end of the - end?

YES! NO! It is taken to the minus end by dynein which moves toward the minus end of microtubules It is taken to the plus end by kinesin which moves toward the plus end of microtubules

We can determine the mitotic phase of a cell by looking at the cyclins which are present at a given time. We hypothesize that cancer cells proceed through G1 quickly. a. What checkpoint is being skipped by these cancer cells? b. What could cause the increase in G1 cyclins? Try to come up with at 2 different ways. How would you test them?

a. G1/s- so the cell is not verifying that the environment is appropriate, causing it to divide detrimentally b. Degradation is prevented: tag ubiquitin and cyclins to see if they co-localize in the degredation complexes OR affinity chromatography to verify that they aren't interacting increased transcription caused by an increase in mitogens: western of mutant vs wild type to compare band sizes

The binding of adrenaline to the GPCR shown here promotes an interaction between Gα and adenylyl cyclase. What is the role of cyclic AMP in this pathway? What is the function of PKA and how is this function related to that of phosphorylase kinase?

cAMP is a secondary messenger molecule that amplifies the signal and activates PKA It activates phosphorylase kinase via phosphorylation

What regulates CDKs (3)?

cyclins p27 inactive M-CDK

During Mitosis checkpoints?

duplicated chromosomes are attached to mitotic spindle

how can activation energy be diminished?

enzymes

How can you find out if a protein acts upstream or downstream of Ras? You find that cells DO proliferate, does this suggest that unknown protein X acts upstream or downstream of Ras?

express constitutively active Ras in mutant #2 Protein X acts upstream of Ras

Why might cancer cells lower mitochondrial respiration?

fewer blood vessels reach these due to tumors, prevent O2 from entering mitochondria cancer cells only go through glycolysis

do you think all proteins have just a single site of phosphorylation?

no

does phosphorylation always activate proteins?

no

Do cells (does life) violate the laws of thermodynamics?

no they don't