VCE Biology Question Thread

[Sine]

In a chemical reaction, 1,3-bisphosphoglycerate + ADP yields 3-phosphoglycerate plus ATP. What is the delta G for this reaction?
A greater than zero
B equal to zero
C less than zero
D cannot be determined

Why is this c can someone explain

2 ways to solve this quesiton

1) Have memorised which glycolysis reactions are favourable and which ones aren't (A delta G < 0 means the reaction is favourable and occurs spontaneously). Not expected of anyone in highschool.
2) Understand that when ATP production occurs in glycolysis ADP + Pi -> ATP it is linked to a highly favourable reaction (delta G <0) resulting in a overall delta G < 0. for then conversions involving ATP production.

[Chocolatepistachio]

The model for DNA structure put forward by Watson, crick and Wilkins can explain many characteristics of the genetic material. However, it fails to help explain:
A why certain characteristics are passed on from generation to generation without change
B how DNA determines the order of nucleotides in mRNA
C why different proteins are active at different times in a cell
D how DNA molecules replicate themselves

Would this be c

[Billuminati]

The model for DNA structure put forward by Watson, crick and Wilkins can explain many characteristics of the genetic material. However, it fails to help explain:
A why certain characteristics are passed on from generation to generation without change
B how DNA determines the order of nucleotides in mRNA
C why different proteins are active at different times in a cell
D how DNA molecules replicate themselves

Would this be c

Yes it's C. Although you know the structure of DNA from their model (which they stole/plagiarised from a lady), it doesn't tell you how gene expression is regulated by transcription factors and chromatin remodelling proteins.

[Bluebird]

Hi AN,

What exactly does it mean when a caspase 'cleaves' specific proteins?

Thank you

[Billuminati]

Hi AN,

What exactly does it mean when a caspase 'cleaves' specific proteins?

Thank you

Cleave= a molecule making a cut in another molecule. The effector caspases (eg caspase 3) which directly destroy the cell by cleaving its proteins etc are actually activated by an initiator caspase (caspase 8 or 9) cleaving them.

[Bluebird]

Cleave= a molecule making a cut in another molecule. The effector caspases (eg caspase 3) which directly destroy the cell by cleaving its proteins etc are actually activated by an initiator caspase (caspase 8 or 9) cleaving them.

Thank you

[Chocolatepistachio]

What is the predicted energy yield of the Krebs cycle per molecule of glucose in eukaryotic cells? Consider that 1 NADH yields 3 atp and 1 FADH2 yields 2ATP
A 2 ATP
B 24 atp
C 18 ATP
D 30 ATP

Would this be a but if 1NADH  yields 3 then wouldn’t it be 20

[Billuminati]

What is the predicted energy yield of the Krebs cycle per molecule of glucose in eukaryotic cells? Consider that 1 NADH yields 3 atp and 1 FADH2 yields 2ATP
A 2 ATP
B 24 atp
C 18 ATP
D 30 ATP

Would this be a but if 1NADH  yields 3 then wouldn’t it be 20

You're correct that it's only 2 ATP. Remember that glycolysis only produces a net of 2 ATP while it generates NADH as well, the ATP generated by NADH are attributed to the electron transport chain because that's where NADH deposit the H+s for a proton gradient to spin the the ATP synthase turbine. FYI, Kreb's cycle doesn't generate ATP directly, it actually generates GTP which is converted to ATP.

[Chocolatepistachio]

Can someone explain anaerobic respiration in detail this is what I have for fermentation but it’s missing details
In alcohol fermentation pyruvate is converted to ethanol in two steps. First pyruvate is converted to a two carbon compound acetaldehyde by the removal of co2. Then acetaldehyde is reduced by NADH to ethanol.

[Billuminati]

Can someone explain anaerobic respiration in detail this is what I have for fermentation but it’s missing details
In alcohol fermentation pyruvate is converted to ethanol in two steps. First pyruvate is converted to a two carbon compound acetaldehyde by the removal of co2. Then acetaldehyde is reduced by NADH to ethanol.

That's pretty accurate, except you may need to say NAD+ is regenerated after ethanal was reduced to ethanol as well as the ATP yield. You don't need to know the specific enzymes for VCE, but I think it's good to be aware that these reactions require enzymes. You also need to know the different types of fermentation, lactate fermentation occurs in animals  whereas ethanol fermentation is for plants and yeasts (fungi).

[Chocolatepistachio]

Can someone explain it like all the specific enzymes and reactions

With lactate fermentation is pyruvate reduced to lactate or lactic acid

[Billuminati]

Can someone explain it like all the specific enzymes and reactions

With lactate fermentation is pyruvate reduced to lactate or lactic acid

You have the reaction glucose —>pyruvate. This requires all the glycolytic enzymes and produces NADH and ATP (the desired end product). However, the NADH is unable to enter the mitochondria for the electron transport chain (and be oxidised to NAD+) in anaerobic conditions, so it stays in the cytosol. You need to regenerate NAD+ somehow.

Meanwhile pyruvate will be converted to ethanal by pyruvate decarboxylase (removal of a carboxyl= releases CO2).

Ethanal will be reduced to ethanol by NADH (NADH unloads its proton to ethanal and is oxidised to NAD+, which is required for glycolysis).

Lactate and lactic acid are used interchangeably. Lactate is the deprotonated form of lactic acid (with a negative charge) ie its conjugate base. The enzyme that converts pyruvate to lactate is called lactate dehydrogenase.

[Chocolatepistachio]

Thanks
what happens to the 2H+ and the 2H20 that are produced in glycolysis are they used in fermentation

with the electron transport chain why is it 1/2O2 combining with 2H+ to form water

[Billuminati]

Thanks
what happens to the 2H+ and the 2H20 that are produced in glycolysis are they used in fermentation

with the electron transport chain why is it 1/2O2 combining with 2H+ to form water

The H+s produced will be taken up by NAD+ to form NADH, and they will be delivered to an ethanal molecule to form ethanol during fermentation. H2O on the other hand won’t participate in fermentation and will sit around as a byproduct.

I personally don’t like fractional coefficients in chemical equations (you see this in New Zealand textbooks according to my chem professors who also complain about this). To help you see the stoichiometry, the balanced reduction half equation in the ETC should be O2 + 4H+ + 4e- —> 2H2O. If you half everything you get the fractional form you mentioned above.

[Chocolatepistachio]

Water is formed during oxidative phosphorylation when oxygen combines with electrons and protons. Where does the oxygen come from?
A  molecular oxygen diffuses into the cell and then into the mitochondrion
B chemiosmosis
C electron transport chain
D glycolysis

Would this be a