Hey guys!
I just had some questions from the 2009 exam 1.
1c.
I said that the function of cholesterol is to maintain fluidity in the cell membrane. Is this correct? VCAA said that cholesterol increases the fluidity of the cell in colder temperatures.
Cholesterol does maintain the fluidity of the cell membrane (increasing fluidity at low temps + decreasing fluidity at high temps). I personally don't think you would be marked wrong for this, but perhaps it would help if you specified the specific changes in fluidity in higher/lower temperatures.
2 c i
Is it correct if I say tRNA is found at the ribosome?
tRNA can be found occasionally at the ribosome during translation, however, the better response would be in the cytoplasm/cytosol where it hangs about waiting to bind to mRNA at the ribosome.
2 c ii
In translation, is it correct to say that tRNA carries a complementary amino acid to the codon on the mRNA? Also, would it be correct to say that tRNA carried a complementary anticodon? Like can we use anticodon and amino acid interchangeable when referring to translation? Like, aren't they referring to the same thing? Do we have to talk about amino acids and anticodons?
tRNA does carry a complementary amino acid to the ribosome. tRNA doesn't carry an anticodon as such - tRNA has site known as the anticodon which is complementary to a specific codon. This complementarity between the anticodon and the codon facilitates the binding of the tRNA to the mRNA and this allows for specific amino acids to be delivered to the ribosome as dictated by the codons of the mRNA.
- the amino acid is the molecule that the tRNA carries (each tRNA is specific to an amino acid)
- the anticodon is a region on the tRNA composed of 3 nucleotides complementary to a specific mRNA codon
3 c
The question asked for what was the purpose of additional pigments and I said that it is able to trap and absorb different coloured light and VCAA said to 'trap and absorb different wavelengths of light'? Is my answer correct?
You might get the mark for this, but I think it might be best to use the term wavelength in the future.
3 e
So, according to the graph provided, does high light intensity along with high temperature denature enzymes? Does this mean that high temperature and low light intensity does not denature enzymes? This is referring to photosynthesis by the way.
This question is wanting you to identify different limiting factors of the rate of photosynthesis. For the low light intensity plants, the rate of photosynthesis remained relatively low and constant, not because enzymes were denatured, but because the rate of photosynthesis was limited by the low light intensity itself. You can still see that as the temperature approached 40 degrees, the rate dropped sharply, indicating that denaturation of enzymes did still occur.
In the case of the plants with the higher light intensity, the lower temperatures acted as a limiting factor initially (reducing the frequency of collisions) and as the temperature increases, the rate of photosynthesis increased until denaturation occurred.
Remember that denaturation will occur regardless of light intensity.
7 e
In autoimmune response, is it basically the same as normal immune response with pathogen except autoantibodies are produced instead? Like does agglutination still occur and the B cells being activated by T helper cells and self antigen being presented to T helper cell by antigen presenting cell?
Autoimmune responses are the exact same.
While not in the course (sadly - as it is fascinating), your body produces immune cells (B and T cells) that can mount immune responses to essentially any convincible protein, however in normal individuals, the immune cells that respond to self-antigens are killed during their development (to put it simply) and only the immune cells that respond to foreign antigens remain. However, in the case of autoimmune disorders, this process doesn't occur properly and some immune cells that respond to self-antigens survive and mount immune responses against self in just the same way a normal immune cell would respond to a foreign antigen. You DO NOT need to know this, however it might help understand a bit about autoimmune diseases.
8 a
B cells mature in the bone marrow
B cells are produced in the bone marrow.
Do these two statements mean the same thing?
No.
While you don't really need to understand the maturation process, you need to be able to state that B cells are produced in the bone marrow and mature within the bone marrow also. By contrast, T cells are produced in the bone marrow but migrate to and mature in the Thymus.
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I'm fairly sure that BMP4 is indeed a structural gene, and the level at which it is expressed is controlled by other regulatory genes. So, for instance, in the case of the Galápagos finches, the gene coding BMP4 isn't different between the different finches, but rather what differs between them is the rate at which BMP4 is translated, so the mutation occurs a regulatory gene that contributes to that rate of synthesis.
There are many others on here that know much more than I do, so if anything I've said is wrong, please correct!
Just to correct this a little bit, BMP4 is, in fact, a regulatory gene, coding for the protein BMP4, which is a signalling molecule which alters gene expression. In Galapagos finches, the quantity and timing of BMP4 expression determine the size and shape of the finches beaks formed.
The precise description (relative to the Galapagos finches and cichlid fish) given by VCAA from the 2018 Examiner's report is:
Galápagos finches: The BMP4 gene is a gene for a signalling protein that is responsible for
beak formation in Galápagos finches. The longer the gene is expressed in the embryo, the more
BMP4 and the larger the beak that develops. This allowed diversity in beak shape and length in
populations of finches and different phenotypes for natural selection.
African cichlid fish: The BMP4 gene is responsible for jaw formation in African cichlid fish. When
BMP4 is overexpressed in the embryo, it can change the jaw shape. This allowed diversity in
jaw shape and length in populations of cichlids and different phenotypes for natural selection.