Final Exam Short Answer Questions

Question 1

We covered many proteins in lecture and discussed their wide diversity in cellular function. For each category below, name a specific protein and briefly describe its function and a unique structural feature. You must use a different protein for each of the 10 categories and use proteins covered in lecture.

1.An enzyme important in cellular respiration

2.A molecular switch (or allosteric protein)

3.A plasma membrane transmembrane protein

4.A protein with a nuclear localization sequence

5.A protein involved in the signaling pathway activated by epinephrine in liver cells

6.A protein found in the cytoskeleton

7.A motor protein

8.A protein that can function as an ion channel

9.A protein found in coated vesicles

10.A protein that contains disulfide bonds

Answer 1

1.An enzyme important in cellular respiration
Hexokinase – involved in first step of glycolysis, catalyzes the conversion of glucose to glucose-6-phosphate, which traps glucose inside the cell and primes it for further metabolic reactions
2.A molecular switch (or allosteric protein)
Hemoglobin – binding of oxygen to one subunit induces conformational changes that enhance the binding of subsequent oxygen molecules
3.A plasma membrane transmembrane protein
GLUT1 transporters – transmembrane proteins responsible for the facilitated diffusion of glucose into cells
4.A protein with a nuclear localization sequence
P53 – tumor suppressor protein has an NLS that allows it to translocate into the nucleus to activate target genes involved in cell cycle control and DNA repair
5.A protein involved in the signaling pathway activated by epinephrine in liver cells
Glycogen Phosphorylase – breaks down glycogen to be released into the bloodstream (glycogenolysis)
6.A protein found in the cytoskeleton
Actin
7.A motor protein
Kinesin – move along microtubules carrying cargo
8.A protein that can function as an ion channel
Na/K Pump
9.A protein found in coated vesicles
COP I
10.A protein that contains disulfide bonds
Insulin – these contribute to its stable and functional conformation

Question 2

We have discussed several energy-dependent cellular functions that rely on GTP or ATP.

Describe five specific examples of cellular functions driven by either GTP or ATP. You must choose examples we covered in lecture this semester. Be sure to provide details regarding how other molecules are involved and specify whether the function uses GTP or ATP in your answer.

Answer 2

1. Muscle Contraction - the addition of ATP allows for the myosin head to release from the actin binding site within a sarcomere as it binds to the myosin. ATP is hydrolyzed into ADP and Pi which release the energy necessary to allow for the myosin to form a cross bridge again, ready to perform another powerstroke.
2. Active Transport - certain membrane transporters require ATP to transport molecules in and out of a cell. The Na/K is an example of this where the hydrolysis of ATP allows for the 3 bound Na ions to exit the cell while allowing 2 K ions in, both against their concentration gradient
3. Glycolysis - in preparation for the breakdown of glucose into two pyruvate molecules, Steps 1 & 3 phosphorylates the glucose molecule (hexokinase converts it into glucose 6-phosphate; then glucose 1.6-phosphate), which requires an input of 1 ATP each. This is essential as the “investment phase” for glycolysis eventually pays off with a net 2 ATP at the end.
4. GPCR Signaling - in the example of epinephrine, when the signal binds to a GPCR, a G Protein that is activated through GTP further allows for the activation of adenyl-cyclase, which is able to synthesize cAMP with ATP. This under further activations allows for glycogen phosphorylase to breakdown glycogen for this response.
5. Growing/Shrinking Microtubule - The tubulin protein subunits, which make up microtubules, bind GTP. GTP-bound tubulin promotes microtubule polymerization, while GTP hydrolysis to GDP allows for microtubule disassembly or dynamic instability

Question 3

Cellular processes are often a target of plant toxins and animal venoms.

Describe 5 examples, discussed in class, of how chemical compounds negatively impact cellular function. In your answer give details about the specific targets of the toxin/venom, the problems that develop within the cell, and the resulting affects on the organism. Each example must be taken from a different textbook chapter.

Answer 3

1. Latrotoxin (widow spiders)
   -within the axon of a neuron, this toxin causes a complete axon terminal release of ACh (uncontrolled exocytosis)
   -severe muscle cramping and pain
2. Tremetol (milk poisoning)
   -inhibits citric synthase within the Krebs Cycle
   -cannot make ATP from Krebs, which leads to breakdown of fatty acids as the energy source
   -higher ketone levels (fruity breath), more acidic pH of bloodstream

3 DNP
-acts as an “uncoupler” where the energy from the proton gradient of the ETC runs through it rather than ATP Synthase, discharging it as heat and lowering ATP synthesis
-leads to major symptoms of high body temperature, which can be problematic in denaturing proteins

4. Phalloidins (mushroom toxin)
   -binds tightly to actin filaments and inhibits their depolymerization
   -damages and inhibits function of cells in the liver
5. Botulinum Toxin
   -inhibits voltage-gated sodium channels from allowing for the creation of an action potential and further muscle contraction
   -flaccid paralysis of muscle (seen in botox)

Question 4

Give 3 examples of the regulation of glucose use in cells. One example should involve glucose uptake, one example should involve glucose metabolism (such as glycolysis), and one from its use in storage (or liberation from storage) as glycogen. For each example, describe the role of proteins involved in the regulatory events

Answer 4

Glucose Uptake: GLUT4
Insulin promotes the translocation of GLUT4 from intracellular vesicles to the plasma membrane. This allows increased glucose uptake into cells, aiding in glucose clearance from the bloodstream

Glucose Metabolism: PFK
ATP and citrate inhibit PFK-1 activity and slow down glycolysis. This feedback inhibition helps prevent excessive glucose metabolism when energy and metabolic needs are met.

Glucose Storage: Glycogen Phosphorylase