short answer questions

Question 1

What is meant by a membrane’s transition temperature?

Answer 1

The temp required to induce change in the lipid physical state from the ordered gel phase, where the hydrocarbon chains are fully extended and closely packed , to the disordered liquid crystalline phase, where the hydrocarbon chains are randomly oriented and fluid

Question 2

How will the transition temperature of a membrane be affected if
the amount of unsaturated lipids is increased?

Answer 2

fluidity will increase and the temp will decrease

Question 3

What property of transmembrane domains allows them to remain embedded in a lipid bilayer?

Answer 3

the hydrophobic regions anchor them to the hydrophobic core of the phospholipid bilayer

Question 4

Thinking about the Na+/K+ pump, how many ATP molecules are
required to transport 10 K+ ions into a cell?

Answer 4

for every cycle of ATP binding and hydrolysis, the na+/K+ pump brings in 2 K+ ions. to transport 10 K+ ions, 5 ATP molecules are required.

Question 5

Explain how chemiosmotic mechanisms are used in mitochondria and chloroplasts.

Answer 5

both cell organelles possess an electron transport chain in their membrane that establishes a proton gradient.

Question 6

How can GFP be used to track the movement of membrane
proteins?

Answer 6

GFP can be fused with cellular proteins (add GFP to N or C terminus of protein). These fused proteins can be expressed in cells and the fluorescent colouring can be detected with a fluorescence microscopy.

Question 7

How are proteins selectively moved from one compartment to another?

Answer 7

vesicular transport.

Question 8

Where in chloroplast and mitochondria are the highest
concentrations of protons found?

Answer 8

chloroplast = thylakoid space or thylakoid lumen
mitochondria = the intermembrane space

Question 9

Where is cytochrome c protein normally found and
what does it mean when it is present in the
cytoplasm?

Answer 9

cytochrome c protein normally found in the inner membrane of the mitochondrion where it plays a critical role in cellular respiration. When cytochrome c is found in the cytoplasm it means that apoptosis (cell death) is being triggered.

Question 10

The N-terminus of an integral membrane protein is in
the RER lumen. If GFP is fused to the N-terminus of
this protein, which side of the plasma membrane
glows green?

Answer 10

the extracellular side

Question 11

Where does all protein synthesis initiate?

Answer 11

Ribosomes are the sites in a cell in which protein synthesis takes place.

Question 12

Which of the following statements regarding the intrinsic pathway of
apoptosis are not correct?
a) It can be triggered by hypoxia
b) Bax protein binds to the mitochondria inner membrane
c) Cytochrome c leaks out into the cytosol
d) Executioner caspases are activated
e) Nuclear lamins break down

Answer 12

b) Bax protein binds to the mitochondria inner membrane

Question 13

Transition of a plasma membrane from a liquid crystal state to a
crystalline gel state:
a) Occurs more readily at higher temperatures
b) Requires cholesterol
c) Is aided by phospholipid bilayers embedded with glycoprotein
d) Is favoured when there are more saturated lipids
e) Does not occur in the membranes of Listeria monocytogenes

Answer 13

d) Is favoured when there are more saturated lipids

Question 14

A mutation in the gene encoding the BiP chaperone protein might:
a) Cause the Golgi complex to form incorrectly
b) Produce Transport Vesicles with no ribosomes
c) Cause ER lumen proteins to exit to the cytosol
d) Redirect COP II coated vesicles to the ER
e) Result in misfolded proteins in the ER lumen

Answer 14

e) Result in misfolded proteins in the ER lumen

Question 15

Which of the following properties are different between prokaryotic and
eukaryotic cells?
a) The presence of a membrane-bound nucleus
b) The presence of membranes consisting of lipid bilayers
c) The presence of ribosomes to produce proteins
d) The presence of DNA
e) Susceptibility to viruses

Answer 15

a) The presence of a membrane-bound nucleus

Question 16

COP I and COP II proteins:
a) Are synthesized in the ER lumen
b) Direct vesicle traffic in opposite directions
c) Move cargo vesicles from ER to the cis Golgi Network (CGN)
d) Are excreted from the cell
e) Integrate into the Extracellular Matrix (ECM)

Answer 16

b) Direct vesicle traffic in opposite directions

Question 17

The synthesis of a plasma membrane receptor protein begins:
a) In the ER lumen
b) Between the mitochondrial IMM and OMM
c) In the cytoplasm
d) Inside the ER translocon
e) In a transport vesicle

Answer 17

c) In the cytoplasm

Question 18

What is the initial energy source that drives ATP production via
photophosphorylation

Answer 18

light

Question 19

What are the major morphological differences between
RER and SER? What are the major differences in their
functions?

Answer 19

RER has ribosomes on surface, SER don’t. RER important for co-translational
import, SER has enzymes important for detoxification or store Ca++

Question 20

A toxin from toadstools called garafraxin, when added to nerve cells,
prevents Na+ ion movement from higher to lower concentrations. A
possible explanation for this might be:
a) the toxin enters and blocks Na+ channels
b) garafraxin binds acetylcholine and changes membrane potential
c) garafraxin antagonizes the ligand that activates Na+ channels
d) the toxin deactivates the Sodium/Potassium ATPase pump
e) both ‘a’ and ‘c’ could be correct

Answer 20

e) both ‘a’ and ‘c’ could be correct

Question 21

What are 3 lines of evidence supporting the endosymbiont
theory?

Answer 21

mitochondria and chloroplast have 1) double membranes 2) divide by fission like bacteria 3) have their own genomes (circular)

Question 22

Describe the cotranslation process for a protein destined for the ER
lumen?

Answer 22

-SRP binds to signal sequence and halts translation
-SRP binds to receptor on the ER membrane
-Receptor brings ribosome to transmembrane channel
-SRP dissociates and protein synthesis resumes
-Protein ends up in the ER lumen to be secreted or transported

Question 23

Which of the following properties represent as difference between
prokaryotic and eukaryotic cells?
a. The presence of a membrane-bound nucleus
b. The presence of membranes consisting of lipid bilayers
c. The presence of ribosomes to produce proteins
d. The presence of DNA
e. Susceptibility to viruse

Answer 23

a. The presence of a membrane-bound nucleus

Question 24

The synthesis of a plasma membrane receptor protein begins:
a. On free ribosomes in the ER lumen
b. Between the mitochondrial IMM and OMM
c. On free ribosomes in the cytoplasm
d. Inside the ER translocon
e. On Rough ER-bound ribosome

Answer 24

c. On free ribosomes in the cytoplasm

Question 25

What happens to the signal sequence after a protein is
synthesized in the ER lumen?

Answer 25

It is cleaved off by signal peptidase

Question 26

What proteins are critical for vesicle docking at a recipient
compartment?

Answer 26

SNAREs (v-SNARE and t-SNARE)

Question 27

Describe how information intrinsic to a protein is required for insertion of that protein into the ER membrane.

Answer 27

Signal sequence interacts with SRP and targets to translocon in RER
Hydrophobic amino acids of transmembrane domain (TMD) specifies it will insert into membrane

Question 28

The sequence below that best describes the order of
cotranslational import are:
a. SER - lysosome - RER -vacuole
b. cytosol - translocon - RER - lumen
c. COPII-coated vesicle - lysosome - RER - lumen
d. Translocon - cytosol - chaperone
e. Nucleus - cytosol - SRP

Answer 28

b. cytosol - translocon - RER - lumen

Question 29

Which statement about the SER is true?
a. It is continuous with the Golgi complex
b. Has ribosomes on the cytosolic side of membrane
c. Has an important role in detoxification
d. Is the site of cotranslational import
e. It is present at high levels in chondrocytes

Answer 29

c. Has an important role in detoxification

Question 30

Which of the following statements about the Golgi complex is incorrect:
a. it modifies proteins and lipids by adding carbohydrates
b. it does not have ribosomes on its membrane surface
c. it receives and sends off vesicles
d. it does not send vesicles back to the RER
e. it is present in eukaryotic cells only

Answer 30

d. it does not send vesicles back to the RER

Question 31

Cellular compartments with the lowest pH are:
a. nucleoplasm and transport vesicles
b. RER lumen and SER lumen
c. cytosol and endosomes
d. lysosomes and vacuoles
e. mitochondria intermembrane space and Golgi lumen

Answer 31

d. lysosomes and vacuoles

Question 32

What type of cytoskeletal structural components are found in the
nucleus of animal cells?
a. F-actin
b. microtubules
c. keratin monomer protein
d. Intermediate Filaments
e. kinesin

Answer 32

d. Intermediate Filaments

Question 33

Where is the large ribosomal subunit assembled?
a. in the nucleolus
b. in the ER lumen
c. in the nucleoplasm
d. at the nuclear pore
e. they are not assembled - they are one protein

Answer 33

a. in the nucleolus

Question 34

Which of the following cytoskeletal subunit proteins might have a
Nuclear Localization Signal (NLS)?
a. G-actin
b. beta tubulin
c. gamma tubulin
d. keratin monomer
e. lamin

Answer 34

e. lamin

Question 35

Explain how the fluidity of the membranes would theoretically change in the cells of a frog
between summer (hot temperatures) and winter (cold temperatures)

Answer 35

The fluidity of a frog’s membranes changes between summer and winter due to temperature differences. In summer, the membranes become more fluid due to the rapid movement of phospholipids, allowing for better flexibility and dynamic interactions. In winter, the membranes become less fluid due to slower phospholipid movement, preventing stiffness and maintaining integrity.

Question 36

What are 2
mechanisms used by the cell to maintain membrane fluidity despite temperature?

Answer 36

Cells maintain membrane fluidity through two mechanisms: desaturation of lipids and exchange of lipid chains. Unsaturated fatty acids introduce kinks in fatty acid chains, preventing phospholipids from packing tightly together. Cells can also exchange lipid chains between different phospholipids, regulating membrane fluidity.

Question 37

How could cholesterol help stabilize the membrane in both summer and winter conditions?

Answer 37

In hot temperatures, cholesterol raises the membrane’s melting point, preventing it from becoming too fluid. In cold temperatures, cholesterol intercalates between phospholipids, increasing fluidity and preventing stiffness.

Question 38

Explain how kidney cells maintain a balanced pH

Answer 38

the sodium-proton exchanger (Na+/H+ exchanger) in the nephron of the kidney (transports sodium ions (Na+) into the cell (down concentration gradient) and protons (H+) out of the cell (against concentration gradient)). Protons are acidic; removing them helps to maintain a balanced pH. No energy is used; passive transport.

Question 39

How do kidney cells absorb glucose from the blood stream despite having a high concentration
of glucose within the cell? Why is it important?

Answer 39

Kidney cells need to absorb glucose from the bloodstream, as the concentration in the blood is typically higher than the concentration inside the cell. Reabsorbing glucose in kidney cells after blood filtration helps prevent the loss of glucose through urine. To transport glucose against its concentration gradient, kidney cells rely on the chemical gradient of sodium ions (Na+). The Na+-glucose symporter is a carrier protein that binds two Na+ ions and one glucose molecule, causing a conformational change that allows the glucose molecule to enter the cell.

Question 40

You spot a GIANT spider; this activates your fight or flight response which causes your adrenal
glands to release adrenaline into your bloodstream and travels to your liver (and elsewhere).
Explain the pathway of how adrenaline works on your liver cells to cause the mobilization of
glucose.

Answer 40

• Adrenaline is released from the adrenal glands
• Adrenaline circulates in the bloodstream and binds to specific receptors on the surface of liver cells
• Adrenaline signals the liver cells to break down glycogen into glucose
• The glucose that is produced from the breakdown of glycogen is released into the bloodstream.

Question 41

You get on a bus and sit in a seat, unknown to you, the previous occupant of the seat was
infected with influenza, they sneezed and transferred viral particles onto the seat that now
transfer to your hands when you touch the seat. 1) what are these viral particles called?
2) Is this virus enveloped or naked?
3)Do these particles infect you through your epidermal
cells on your hands? Briefly explain.

Answer 41

1) influenza viruses
2) Influenza viruses are enveloped. This means they have an outer lipid membrane derived from the host cell membrane, which surrounds their genetic material and proteins.
3)The primary route of infection for influenza is through the respiratory system, not through the skin.the risk of infection would be more related to touching your face (nose, mouth, or eyes) with contaminated hands rather than through direct infection of epidermal cells on your hands.

Question 42

When looking at photosynthesis, Briefly, explain the processes that take place during the light-
dependent reactions

Answer 42

1) Light Absorption:
Chlorophyll and other pigments in the thylakoid membrane absorb sunlight. This energy is used to excite electrons in the chlorophyll molecules.
2) Water Splitting (Photolysis):
The absorbed light energy is used to split water molecules into oxygen, protons (H⁺), and electrons. This process is known as photolysis and releases oxygen as a byproduct.
3) Electron Transport Chain:
The energized electrons from water are passed through a series of proteins embedded in the thylakoid membrane called the electron transport chain. As electrons move through this chain, energy is released and used to actively transport protons (H⁺) from the stroma into the thylakoid space.
4) ATP Synthesis:
The proton gradient created across the thylakoid membrane results in a concentration difference of protons, known as a proton motive force. This force is harnessed by ATP synthase, an enzyme complex, to produce ATP (adenosine triphosphate) from adenosine diphosphate (ADP) and inorganic phosphate (Pi).
5) NADPH Formation:
Simultaneously, electrons from the electron transport chain combine with protons and NADP⁺ (nicotinamide adenine dinucleotide phosphate) to form NADPH.

Question 43

A cell senses DNA damage, it tries to repair the damage but it seems it is irreparable, so the cell
needs to trigger apoptosis what are the steps in point form that will lead to apoptosis

Answer 43

1) shrinkage of cell
2) fragmentation of DNA and nucleus
3) blabbing of the plasma membrane
4) loss of attachment to other cells
5) engulfment by phagocytosis

Question 44

Explain in point form, how an integral membrane protein is translated, start from where the
ribosome binds to the translocon on the RER and translation resumes.

Answer 44

• ribosome binding to the translocon
• recognition of a signal sequence
• translocation of the polypeptide chain into the endoplasmic reticulum
• membrane insertion
• folding
• potential glycosylation
• vesicle formation
• futher processing in the Golgi apparatus
• final packaging and transport to its destination

Question 45

Explain how a soluble protein that needs to secreted from the cell via exocytosis is translated.
Use point form and start from the beginning. (5

Answer 45

• transcription
• translation
• recognition of a signal sequence
• translocation to the endoplasmic reticulum
• transfer to golgi apparatus
• protein folding and modification
• vesicle formation
• exocytosis to release the secreted protein outside the cell