Biology SAQ's (final) Flashcards
1) Explain how the fluidity of the membranes would theoretically change in the cells of a frog between summer (hot temperatures) and winter (cold temperatures) (1 mark). What are 2 mechanisms used by the cell to maintain membrane fluidity despite temperature (2 marks)? How could cholesterol help stabilize the membrane in both summer and winter conditions (2 marks)?
In summer: fluidity would increase (liquid crystal)
In winter: fluidity would decrease (crystalline gel)
2 mechanisms to control fluidity:
- cholesterol
- nature of lipids in membrane; unsaturated increases fluidity, saturated decreases fluidity - desaturation of lipids, exchange of lipid chains
cholesterol stabilizing membrane:
- in liquid crystal, it decreases fluidity : in crystalline gel, it increases fluidity
(bidirectional regulator of membrane fluidity)
- stabilizes the membrane and raises its melting
point at HT
- intercalates between the phospholipids and
prevents them from clustering together and stiffening at LT
2) Explain how kidney cells maintain a balanced pH (3 marks).
- Na+/H+ (proton) antiporter
- If pH is high in the cell exchanger moves H+ down its gradient into the cell, using this it pumps Na+ against its gradient out of the cell
- If the pH is low in the cell the exchanger moves Na+ down its gradient into the cell, using this is pumps H+ against its gradient out of the cell
3) How do kidney cells absorb glucose from the blood stream despite having a high concentration of glucose within the cell? Why is it important? (4 marks)
NA+-GLUCOSE SYMPORTER
*if not absorbed, glucose lost to urine
- both molecules transported in same direction
- Simultaneous binding of 2 Na+ and 1 glucose to the transporter with outward-facing binding sites.
- This cause a conformational change in the transporter (occluded conformation).
- Eventually the transporter adopts an inward-facing conformation that allows
- the dissociation of the two Na+ molecules in the cytosol. As a result, the glucose molecule gets pushed-in as well.
- Return to the outward-facing conformation to repeat the cycle
4) 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.
GLYCOGENESIS
- adrenaline made in adrenal glands
- adrenaline binds to receptor cells (hepatocyte)
- Active receptor will recruit G-protein and allow the binding of GTP to turn it ON.
- A subunit of the G-protein will then dissociate and turn ON an enzyme called adenyl cyclase. This will cause accumulation of cAMP (second messenger) inside the cells, activating PKA
- PKA activates phosphorylase-P (enzyme) that will release glucose units. (glycogen to glucose)
1) 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. A) what are these viral particles called? (1 mark) Is this virus enveloped or naked? (1 mark)
Do these particles infect you through your epidermal cells on your hands? Briefly explain. (2 marks)
A) Virions (infective form of a virus outside a host cell, with a core of RNA or DNA and a capsid)
B) envelopped
C) NO
- first layer of skin is first layer of defense against diseases
- viruses bind to cell surface via specific cell proteins and then enter cell
- it has a narrow host range: infects epithelial cells of human respiratory system
- lytic cells (Production of virus particles ruptures (and kills) host cell)
2) When looking at photosynthesis, Briefly, explain the processes that take place during the light-dependent reactions (4 marks).
*in thylakoid membrane
- Light energy is absorbed by chlorophyll in Photosystem II (PSII) and Photosystem I (PSI), exciting electrons.
- Excited electrons move through an electron transport chain, releasing energy that pumps protons into the thylakoid lumen.
- Proton gradient formation drives ATP synthesis via ATP synthase in a process called photophosphorylation.
- Electrons from PSI reduce NADP+ to NADPH, serving as energy carriers for the Calvin cycle and subsequent carbon fixation.
*products are ATP and NADPH
3) 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 (4 marks)
1- DNA damage triggers apoptosis pathway
2- leads to the activation of Bax
3- Bax forms pores in outer MM- cytochrome C leaks from intermembrane space of mitochondria into cytosol
4- Cyto C in cytosol leads to activation of initiator caspase and assembly of apoptosome
5- Active initiator caspase cleaves and activates executioner caspases
4) 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. (4 marks)
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? (1 mark)
- begins on free ribosomes (not associated with ER), completed on either free or bound ribosomes
1. After translation of SIGNAL SEQUENCE, a Signal Recognition Particle (SRP) binds to signal sequence and STOPS the translation process.
2. SRP binds SRP receptor to target the whole translation complex to ER (SRP + ribosome + mRNA + new polypeptide).
3. SRP is released and ribosome binds to translocon. Once this is done, protein synthesis resumes.
4. Polypeptide enters the ER (through the translocon) as it is translated. In the end, the signal peptide is cleaved off and chaperone folds the protein - extracellular side
5) 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 marks)
-* To the plasma membrane via biosynthetic/secretory pathway *
-Start protein synthesized on a ribosome
- moved from RER to the ER lumen to cis Golgi network to trans Golgi network to a secretory vesicle
- secreted out through the plasma membrane
- You are a genetic counsellor, a baby has been diagnosed with cystic fibrosis and you are tasked with explaining things to their family and answering their questions.
A) What is the most likely mutation that their baby is affected by? (1 mark)
B) How does this mutation result in the mucus surrounding the lungs being dehydrated? (start at how it affects protein structure and what that leads to) (3 marks)
A) delta F508 (deleted)
- CFTR gene
B)
- changes a protein (CFTR) that regulates the movement of salt in/out of cells (domains do not fit together)- cannot make chloride channels regulate salt/water at cell surface
- movement of fluid/salt changing causes the mucus to thicken
- thickened mucus causes clogged organs: lungs, pancreas, intenstines leading to other issues (ex: respiratory infections)
- Explain how LDL particles are brought into the cell and broken down into its components. (5 marks)
1-LDL particles are recognized+ bound by LDL receptors on liver cell membranes, initiating uptake via endocytosis
2- Once internalized, LDL particles are enclosed in vesicles and transport to late endosomes within cell.
3- Within late endosome, LDL particle is released, and its components (amino acids, fatty acids, and cholesterol) break down by lysosomal enzymes.
4- breakdown products are utilized by cell for various purposes-> synthesizing molecules / building cellular structures.
5- After releasing LDL particle, LDL receptor undergoes conformational change triggered by pH change, preventing immediate rebinding- receptor recycled back to the cell membrane to participate in further LDL uptake
- The mitochondria in a cell is not working properly and the cell has “decided” it needs to be degraded.
A) What is this process called? (general or specific name is fine) (1 mark)
B) Briefly explain how this happens. (3 marks)
A) autophagy/mitophagy
- Isolation membrane derived from ER engulf target organelles to form an autophagosome
- Lysosome fuses with ER-derived autophagic vesicle to form an autolysosome.
- Content of autolysosome is enzymatically digested and released
- The cytoskeleton is made up of 3 components, name them and order them from smallest to largest (3 marks).
Which of them are associated with movement within the cell? (1 mark)
Microtubules > intermediate filaments > actin filaments
Microtubules
- A zebrafish can camouflage into itself environment by moving pigment molecules using the cytoskeleton. Based on the diagram below what is labelled with the following letters (0.5 each, 2 marks)
Label the plus and minus end of the microtubule on the diagram, which end is more dynamic? (2 marks)
A- Mtoc
B- kinesin
C- myosin va
D- microtubules
- right end is plus, left end is minus
- plus end is more dynamic
- Lamins are a type of intermediate filament, where in the cell are they found? (1 mark)
What type of localization sequence would be found on the Lamin protein? (1 mark)
What is the main function of the Lamin protein? (1 mark)
- nucleus of animal cells
- NLS
- provides structural support and mechanical strength; support nuclear envelope
