VCE Biology Question Thread

[katiesaliba]

Can the products of an enzyme-mediated reaction act as non-competitive inhibitors of the enzyme?

Feedback inhibition is normally non-competitive.

[Vicbelgaus]

In regards to the first question, denaturation involves un-folding the protein's secondary, tertiary or quaternary structure.
So if the quaternary structure of an enzyme is destroyed, it is indeed denatured.

[Rishi97]

I have a biology sac tomorrow on the prac that we did. Basically, to measure effects on enzymes, we had different concentrations of protease in each test tube. We then put a bit of photographic film in there and had to time how long it took for each film in each test tube to go clear.
Does anyone have a good aim and hypothesis for this prac?
Thanks

[Jason12]

what is the purpose of a control in an experiment?

for the experiment boiled liver was placed in a test tube and H202 added to breakdown the enzyme catalase inside the liver.

- one group of students recorded a breakdown of hydrogen peroxide in the sample using boiled liver. suggest a possible explanation for this result?

also how exactly do enzymes lower the activation energy required to start a reaction?

[Tyleralp1]

Three questions:
1) If the quaternary structure of an enzyme is destroyed, does an enzyme denature or does denaturation specifically concern the destruction of the tertiary structure?
2) Concerning photosynthesis and cellular respiration, do we ACTUALLY only need to know the outputs and inputs? Teachers always tell us this, but that seems too simple. Do we at least need to know the exact reaction that results in, for example, the oxidation of ATP into ADP? So for glycolysis, the expenditure of ATP occurs during step 1 and step 3. Is that complex enough, or do I need to know the specific names of the enzymes?
3) ATP synthase harnesses the energy from the proton gradient to catalyse the anabolism of ATP from ADP and Pi. HOWEVER, I read somewhere that free e- are also used to help 'fuel' ATP synthase, so to speak. Is this true?

Thank you!!

1. As mentioned earlier on, the quaternary does indeed effect enzyme functioning. If the enzyme is disrupted on this level, the enzyme is denatured as it's specific 3D shape will have changed. Therefore, it won't be able to bind to its specific substrate to catalyse reactions.

2. It is true in the sense that we only need to know the inputs and outputs for each section. However, VCAA can test on the knowledge of whether a specific reaction is endergonic or exergonic, catabolic or anabolic. Also, it won't hurt to have a general understanding of what is happening, and where. You must definitely don't know to know the specific names of enzymes , or proteins involved.

3. Doesn't hydrogen ions move from the matrix into the inner membrane space, and then comes back in via ATP Synthase along the cristae and combines with ADP + Pi to form ATP?

[Tyleralp1]

what is the purpose of a control in an experiment?

for the experiment boiled liver was placed in a test tube and H202 added to breakdown the enzyme catalase inside the liver.

- one group of students recorded a breakdown of hydrogen peroxide in the sample using boiled liver. suggest a possible explanation for this result?

also how exactly do enzymes lower the activation energy required to start a reaction?

1. The purpose of a control group is provide a basis of comparison of which to compare the effects of your experimental (independent) variable.

2. The liver sample contained the enzyme catalase. When in contact with the hydrogen peroxide, a catabolic reaction occurred to break it down as H2O2 is a complimentary fit to the active site of catalase. The increased temperature due to the boiling, caused an increased rate of reaction due to more kinetic energy thus resulting in more enzyme-substrate collisions in a given time.

3. I believe...The complimentary fitting of substrates aids with this. With combined with an enzyme, two individual substrates are within close proximity for a bond to be formed. If it is a larger molecule to be broken down, the bond is being weakened by the enzyme.

[alchemy]

what is the purpose of a control in an experiment?

for the experiment boiled liver was placed in a test tube and H202 added to breakdown the enzyme catalase inside the liver.

- one group of students recorded a breakdown of hydrogen peroxide in the sample using boiled liver. suggest a possible explanation for this result?

also how exactly do enzymes lower the activation energy required to start a reaction?

1) To ensure that the dependent variable isn't affected by any other factors other than the independent variable.
2) I haven't done this prac, so I'd have to take a guess. The liver may not have been boiled adequately by the group, meaning the enzyme catalase had not been denatured. Thus, catalse would have still been able to catalyse the breakdown of hydrogen peroxide into water and oxygen.
3) Substrates bind to an enzyme's active site, in the presence of a coenzyme or cofactor, allowing the enzyme to catalyze a reaction.

[alchemy]

2. The liver sample contained the enzyme catalase. When in contact with the hydrogen peroxide, a catabolic reaction occurred to break it down as H2O2 is a complimentary fit to the active site of catalase. The increased temperature due to the boiling, caused an increased rate of reaction due to more kinetic energy thus resulting in more enzyme-substrate collisions in a given time.

Sorry, but I don't think this is really correct. Although I haven't done the experiment, I'm sure it'd be safe to assume that they added a piece of pre-boiled liver into the test tube hydrogen peroxide (as opposed to boiling the liver in Hydrogen peroxide like I think you mean).

[Tyleralp1]

Aha sorry for the confusion..

I interpreted that as a boiled liver piece, hence being a higher temperature than a room temperature liver piece.

[nerdmmb]

What's the difference between NADH and FADH₂

I know that they're both acceptor molecules but can one difference be that FAD accepts two hydrogen molecules?

Also, in regards to cellular respiration, do we need to know about the chemical composition of pyruvate molecules,etc?

And when glucose is converted into two pyruvate molecules, what happens to the water molecules (6H20) and oxygen (602) ?

Thanks heaps!

[alchemy]

What's the difference between NADH and FADH₂

I know that they're both acceptor molecules but can one difference be that FAD accepts two hydrogen molecules?

Also, in regards to cellular respiration, do we need to know about the chemical composition of pyruvate molecules,etc?

And when glucose is converted into two pyruvate molecules, what happens to the water molecules (6H20) and oxygen (602) ?

Thanks heaps!

1) You just need to know they're two acceptor molecules basically.
2) You don't need to know the chemical composition of pyruvate, other than it being 3C compound with 2 phosphate groups.
3) The Hydrogen atoms from the splitting of water are accepted NAD+. Oxygen is only required for aerobic respiration, so I'm guessing it passes to the next stage (Kreb's Cycle), since we don't release it into the atmosphere.

[alchemy]

^On a similar note, the StudyOn book says that this is the equation for Aerobic respiration: C6H12O6 + 6O2 + 6H2O ---> 6CO2 + 12H2O + Energy
This is the first time I've seen it written this way. In fact, I can't really seem to find this form mentioned anywhere on the internet either! Can someone verify, or explain the reason why it's written like so?

[nerdmmb]

^On a similar note, the StudyOn book says that this is the equation for Aerobic respiration: C6H12O6 + 6O2 + 6H2O ---> 6CO2 + 12H2O + Energy
This is the first time I've seen it written this way. In fact, I can't really seem to find this form mentioned anywhere on the internet either! Can someone verify, or explain the reason why it's written like so?

Yes it actually is that. I was told by two examiners as well that the 6H20 molecules which many people are not taught is metabolic water that then diffuses into the cytoplasm. So yes, you are correct.

[alchemy]

Yes it actually is that. I was told by two examiners as well that the 6H20 molecules which many people are not taught is metabolic water that then diffuses into the cytoplasm. So yes, you are correct.

Phew! So I didn't get it wrong on the SAC! Thanks for that too nerdmmb! 

[nerdmmb]

Was a bit confused about the FADH₂

In the ETC, does it mean that an FADH₂ gives off 2 hydrogen atoms?