Biology Unit 3 Questions Megathread

[dooodyo]

Thaaaanks heaps ! 

[shinny]

ah okay thankyou, so STOP is not an amino acid? like methionine is a 'start?"

Also for chemical pathways if

A->B -> C is the reaction
but A - B enzyme is messed up, how does the body get past this? I'm not sure if in your answer you meant

A->B or A -> C
I'm not sure exactly how it works

is it just by chance that there is another enzyme that turns it into the product? or does every product have more than 1 possible pathway?

Yeh stop isn't one. And I meant A->B and A->C, so if A->B doesn't work, C will increase. Did you mean getting the same product through a different pathway? But if there was something like A->B1->C and A->B2->C, a decrease in one pathway will cause a compensatory increase in the other just by principle. A possible example would be something like the production of glucose in the body, where there's many possible sources (fats, glycogen, proteins etc) involved.

[WhoTookMyUsername]

The exact question is


The follwoing diagram represents a biochemical pathway in a living organism. The final product, substance T, is essential for the life of the organism


P -> (enzyme P) Q -> (enzyme q) R -> (enzyme r) S -> (enzyme s) T

The organism involved undergoes a mutation and is no longer able to produce enzyme r. It is reasonable to predict that:

A. The organism will be able to compensate for the lack of enzyme r by using an alternative pathway

B Substance Q will tend to accumulate

D the lack okf enzyme r will be fatal for this organism

I said D but the answer is A.

It seems to suggest alternative pathways are quite common in a case like this?


EDIT: Also, no proteins have no tertiary structure... right?
Engage Education exam says fibrin is a 'secondary protein' not a 'tertiary protein'

[HERculina]

i would have said d too  
wat was option c btw

[shinny]

I don't agree with that answer. Alternative pathways aren't really that common as far as I can tell. You also shouldn't be expected to know that in Bio 3/4 anyhow. It really isn't reasonable to assume that at all I would think - going from what they've given, D is far more justifiable.

[HERculina]

oh ok. my teacher sed STAV doesn't have good solutions, i havent done these ones yet.

[Kaille]

if there is a decrease in water concentration in the blood, what would be the receptor for this situation? Would it be the osmoregulator in the hypothalamus or the mechanorecpetors in the blood that detect blood pressure?

[WhoTookMyUsername]

osmoregulator, as change in water conc. may not result in change in BP

[dooodyo]

Hey guys,

Whats the difference between glycocalyx and oligosaccharides?

From what I decipher it seems that oligosaccharides are short carbohydrate chains attached to proteins or
lipid molecules on the membrance and according to wikipedia they seem to have a similar function. 

[Russ]

oligo is part of the numbering/naming system:
mono = one
di = two
oligo = several
poly = many

So an oligosaccharide is just several sugar molecules linked together.

Glycocalyx is slightly more complicated. It's a layer around the outside of a cell, designed for adhesion and (to some extent) protection. Bacterial cells often use certain types of glycocalyces called "capsules" to hide from the immune system and stick to your cells (eg plaque deposits in your mouth)

[WhoTookMyUsername]

highly doubt that knowledge is necessary though

[WhoTookMyUsername]

What is the difference between Natural Killer Cells and Cytotoxic C Cells if they both kill virus infected cells?


Also, are all cells of the immune system, e.g. B cells, T cells WBC's?

[Russ]

I would be fairly confident at VCE level that all cells are considered WBCs ("leucocytes").
There might be a bit of debate about dendritic cells but i don't think it's an important distinction.

RE: NK and Cytotoxic T Cells (typo?)

NK cells are basically highly specialized antiviral cells with some other functions. Cytotoxic T Lympocytes (CTLs) are a subset of T cells that are responsible for killing infected or abnormal cells. Cells can be infected by viruses but also by various other pathogens (eg Salmonella).

So CTLs have a much broader spectrum of action. There are a lot of fine more specific differences but they're definitely not going to be assessed.

[WhoTookMyUsername]

Thanks Russ! That makes sense C was a typo

This is a series of questionable questions and answers from TSFX 2010
Could someone please explain the answers.

1)
The roles of cholestrol include:

A) Acting as a a precurser molecule to steroid hormones such as testoseron and adrenalin.
D) Assisting in membrane stability at 37 C

2)

Rate of reaction could be further increased by

B) adding more substrate
C) adding more enzyme

3)
During photosynthesis, rubisco is the enzyme responsible for grabbing C02 in the atmosphere in

A) CAM
B) C3
C) C4

plants

Do we need to know this
?


4) A water soluble hormone includes

B) The thyroid amino acid derivate thyroxin
A) The peptide hormone insulin
D The neurotarnsmitter acetylcholine

15)
Endorphins are neurotransmitters which reduce the chances of impulses traveeling along pain pathways. Their effect ois to

A) Hyperpolarise the membrane of the post - synaptic cell (not even in textbook?)
C) Attach to excitatory neurotransmittors before the reach the post - synaptic membrane

20)
Unlike most proteins, prions

C) Do not denature when superheated
D) Contain nucleotide side chains

I got 18/25 in MC. In every other exam i've done so far i've gotten 23- 25 (8 exams) in MC, so i think possibly many of these things we don't need to know?

[Russ]

1. Cholesterol plays an important role in membrane stability, not sure if it's important at 37 degrees though. Adrenaline also isn't a steroid hormone.

2. I would have thought either, based on circumstances. Hmmmm...

4. ACh at a guess, based on structure/size

15. Both plausible, no idea. Based on the question stem, A, since that will prevent all impulses.

20. C but if you weren't taught it I doubt it's going to be asked. One of the great virulence problems with prions is they're so resilient.