VCE Biology Question Thread

[IndefatigableLover]

Thanks IL! <3

Can someone help me out with protein structure please? This was one of my major loss in the prac exam
How can you define primary structure of proteins? Is it okay to just say that it is the linear sequence of amino acids?
Also secondary structure is the both alpha helices and beta pleated sheets. How do these form? How does a protein go from it's primary structure to the secondary structure?

Thank you!

Haha no worries

As for your protein questions:

Your answer for primary structure of proteins should consist of the word "specific" since it is a sequence of amino acids but it's specific since order matters!
A primary structure protein will go to a secondary structure due to the hydrogen bonds between nearby peptide groups. As a result, these will cause a change in structure such as coiling or folding of segments in the polypeptide chain (in order for it to help stabilise the structure as it is now 3-D). The effect of the hydrogen bonds will cause the primary structure to turn into alpha helices (if it coils), beta-pleated sheets (if it is segmented) or random coils if it doesn't fit either shape

[tiff_tiff]

heyy,
i have a question:
In the human gas exchange system,
A. the lungs and airways are completely collapsed after a forceful exhalation.

B. exhalation is driven by contraction of the diaphragm.

C. the PO2 of the blood leaving the lungs is greater than that of the exhaled air.

D. the amount of air that is moved per breath during normal, at-rest breathing is termed the total lung capacity.

E. PCO2 in the air reaching the alveoli during inhalation is close to zero, as it is in the outside air.
I know the answer is out of option c or e)

The back of the book says the answer is e) which I reasoned as because nothing has been done to that air yet once it just reaches the alveoli sacs therefore it can still be considered as being the same as outside air, and thus PCO2 is regarded as 0 relative to the air outside of body?

But why can’t c be correct. Isn’t there more oxygen in the blood that leaves the lungs after it has been oxygenated and therefore has a higher P02 than the exhaled air which I presume would contain more CO2 than O2, as the oxygen has been used up by body tissue?

[jyodesh.com]

heyy,
i have a question:
In the human gas exchange system,
A. the lungs and airways are completely collapsed after a forceful exhalation.

B. exhalation is driven by contraction of the diaphragm.

C. the PO2 of the blood leaving the lungs is greater than that of the exhaled air.

D. the amount of air that is moved per breath during normal, at-rest breathing is termed the total lung capacity.

E. PCO2 in the air reaching the alveoli during inhalation is close to zero, as it is in the outside air.
I know the answer is out of option c or e)

The back of the book says the answer is e) which I reasoned as because nothing has been done to that air yet once it just reaches the alveoli sacs therefore it can still be considered as being the same as outside air, and thus PCO2 is regarded as 0 relative to the air outside of body?

But why can’t c be correct. Isn’t there more oxygen in the blood that leaves the lungs after it has been oxygenated and therefore has a higher P02 than the exhaled air which I presume would contain more CO2 than O2, as the oxygen has been used up by body tissue?

A. Lungs have residual volume.
B. Contraction of diaphragm = inhalation
C. Not possible. Gases diffuse across the across the alveolar membrane from a region of high concentration to a region of low concentration. Thus the PO2 in the alveolar capillaries can never be higher than the PO2 in the air of the lungs. If it was then O2 would be transported the wrong way across the alveoli.
D. Whats described is tidal volume. Total lung capacity is is vital capacity + residual volume
E. Not really because again the lungs have residual volume and this residual volume of air will have a higher PCO2 than the inhaled air. Thus during inhalation, the PCO2 at the alveoli will be higher than the PCO2 in the outside air. How much of an impact this makes on PCO2 or whether PCO2 is close to zero im not sure because i dont have the numbers.

If i may ask, whats this for anyway? I dont remember having to do this much detail in VCE, in fact this is what im doing now for physiology in uni.

[biy]

Haha no worries

As for your protein questions:

Your answer for primary structure of proteins should consist of the word "specific" since it is a sequence of amino acids but it's specific since order matters!
A primary structure protein will go to a secondary structure due to the hydrogen bonds between nearby peptide groups. As a result, these will cause a change in structure such as coiling or folding of segments in the polypeptide chain (in order for it to help stabilise the structure as it is now 3-D). The effect of the hydrogen bonds will cause the primary structure to turn into alpha helices (if it coils), beta-pleated sheets (if it is segmented) or random coils if it doesn't fit either shape

By this do you mean the same polypeptide chain, or other polypeptide chains? So basically primary structure is the specific amino acid sequence, and the secondary is determined by the hydrogen bonds that occur between the peptide groups. What do you mean by peptide groups?

Thanks IL <3

Also you said you did some practice exams for bio and chem, what scores were you getting for biology, if you don't mind?

[IndefatigableLover]

By this do you mean the same polypeptide chain, or other polypeptide chains? So basically primary structure is the specific amino acid sequence, and the secondary is determined by the hydrogen bonds that occur between the peptide groups. What do you mean by peptide groups?

Thanks IL <3

Also you said you did some practice exams for bio and chem, what scores were you getting for biology, if you don't mind?

Well it's the same polypeptide chain but lots of them joined together essentially  
As for peptide groups, I'm probably digressing into Chemistry here but basically if you look at two amino acids and see how they join, you'll see that the linkage between the two is known as a peptide bond/group. This has the opportunity to form hydrogen bonds (where the Hydrogen in the N forms a bond with the oxygen in the carboxyl group) when they are adjacent to each other.

As for practice exams, I've only done the one so far (Insight 2011) and scored ~75% (including questions outside the SD like C3/C4 plants) so definitely some work that needs to be done alright!

[KingDrogba]

Do you suggest a book of errors for exams? Also, what scores are needed for a 50 in bio??

[cosine]

Was doing some practice questions, encountered this.

It showed a diagram of aquaporin, and then the question stated what type of biomolecule would it be, obviously protein. But then it asked what type of diffusion would occur when water passed through the aquaporin, i said facilitated. Also correct. But then it asked state another type of diffusion that could occur when water is transported along the membrane, answer says simple diffusion. Why so? How can water diffuse simply through the membrane, is it because of it's small size?

Also so does water generally get transported through aquaporins or just through the membrane? Or is it both? If so, would it be best to just say water diffuses across membranes, instead of being specific as we don't know which type of diffusion, facilitated or simple?

Thanks guys

[cosine]

Do viruses actually enter the cell? Because the answers I was reading stated that the virus entered the cell, and coded the cell's DNA to produce a protein to promote the expansion of plasmodesmata. I thought viruses attach to the cell membrane, and inject their viral DNA/RNA into the cell, and that nucleic acid is responsible for the reproduction of viral particles, which then assemble and upon lysing of the cell, are released.

Can this viral DNA/RNA injected into the cell actually produce other proteins besides complement proteins and the viral particles?

Cheers.

[HighTide]

Was doing some practice questions, encountered this.

It showed a diagram of aquaporin, and then the question stated what type of biomolecule would it be, obviously protein. But then it asked what type of diffusion would occur when water passed through the aquaporin, i said facilitated. Also correct. But then it asked state another type of diffusion that could occur when water is transported along the membrane, answer says simple diffusion. Why so? How can water diffuse simply through the membrane, is it because of it's small size?

Also so does water generally get transported through aquaporins or just through the membrane? Or is it both? If so, would it be best to just say water diffuses across membranes, instead of being specific as we don't know which type of diffusion, facilitated or simple?

Thanks guys

Yes, small amounts of water can pass through the plasma membrane via simple diffusion. This occurs in osmosis as well where the water passes through the semi-permeable layer (plasma membrane) down its concentration gradient. This is because of the concentration gradient and also due to the small size of water molecules, thereby enabling it to fit through pores.
From what I've learnt, the aquaporin can enable large amounts of water to pass through, because the plasma membrane, itself, cannot. Aquaporins, however, are special proteins though. For example, they are found in the nephrons in the collecting ducts as large amounts of water must be reabsorbed by the body. So basically, it can pass through either simple or facilitated, but, simple occurs with small amounts of water, whilst facilitated occurs with large amounts, and also cells with specialized integral proteins.

Do viruses actually enter the cell? Because the answers I was reading stated that the virus entered the cell, and coded the cell's DNA to produce a protein to promote the expansion of plasmodesmata. I thought viruses attach to the cell membrane, and inject their viral DNA/RNA into the cell, and that nucleic acid is responsible for the reproduction of viral particles, which then assemble and upon lysing of the cell, are released.

Can this viral DNA/RNA injected into the cell actually produce other proteins besides complement proteins and the viral particles?

Cheers.

Viruses can enter the cell, and they do enter the cell. When they bind to the surface receptors on eukaryotic cells, they are taken in by receptor mediated endocytosis. I think you may have been mixed up with bacteriophages. Bacteriophages attach to the cell membrane and inject their viral genome into the cell, which then results in infection, and so so. These are viruses that infect bacteria.

If by that question you mean, can a virus change an organisms genome or the proteins it may create, I think it can. For example, the HIV virus caries the enzyme reverse transcriptase which creates viral DNA from viral RNA and then incorporates it into the genome of the organism, such that it produces the viral proteins.
Hope this helps 

[cosine]

Yes, small amounts of water can pass through the plasma membrane via simple diffusion. This occurs in osmosis as well where the water passes through the semi-permeable layer (plasma membrane) down its concentration gradient. This is because of the concentration gradient and also due to the small size of water molecules, thereby enabling it to fit through pores.
From what I've learnt, the aquaporin can enable large amounts of water to pass through, because the plasma membrane, itself, cannot. Aquaporins, however, are special proteins though. For example, they are found in the nephrons in the collecting ducts as large amounts of water must be reabsorbed by the body. So basically, it can pass through either simple or facilitated, but, simple occurs with small amounts of water, whilst facilitated occurs with large amounts, and also cells with specialized integral proteins.
Viruses can enter the cell, and they do enter the cell. When they bind to the surface receptors on eukaryotic cells, they are taken in by receptor mediated endocytosis. I think you may have been mixed up with bacteriophages. Bacteriophages attach to the cell membrane and inject their viral genome into the cell, which then results in infection, and so so. These are viruses that infect bacteria.

If by that question you mean, can a virus change an organisms genome or the proteins it may create, I think it can. For example, the HIV virus caries the enzyme reverse transcriptase which creates viral DNA from viral RNA and then incorporates it into the genome of the organism, such that it produces the viral proteins.
Hope this helps 

Thanks HighTide

DO you guys know which commercial biology exams are the hardest? And which are the easiest? Where can I get some for free, or is it all for $$ these days?

[faso]

Thanks HighTide

DO you guys know which commercial biology exams are the hardest? And which are the easiest? Where can I get some for free, or is it all for $$ these days?

I heaps of STAV NEAP trial exams.

[cosine]

Following a transplant, describe the process of tissue rejection that may occur in Jane after recognition of non-self cells has occurred.

Answer says: t-cell mediated rejection response occurs and macrophage presents antigen from transplanted kidney on its surface and releases cytokine to attract helper T cells to activate cytotoxic T cells to destroy the no self cells.


I understand this all, but how/when do macrophages engulf antigens from these transplanted organs? Since when did organs have antigens? If antigens are involved, doesn't it mean it's Humoral immunity and not cell mediated? In my answer I just said the macrophages detect foreign MHC markers and engulf the transplanted cells. Is this wrong ?


Thanks guys

[cosine]

Are foreign MHC markers considered antigens?

[HighTide]

Are foreign MHC markers considered antigens?

Antigen is a foreign substance that causes an immune response in an organism. Transplanted organs are from other individuals. As such, there will be two types of MHC complexes present: MHC of the host's cells, MHC of the donor's cells, given that the donor is not an identical twin as they share the same DNA. Now... MHC markers enable an organism to distinguish between self and non-self. As non-self cells are attacked by the immune system, they are called an antigen, as they result in an immune response. MHC are a type of antigen. There are self antigens and non-self antigens. To stress this, they are also called Human Leukocytic Antigens (HLA). Any foreign MHC marker can be attacked by the immune system as it is recognized as non-self, thus transplanted cells are usually non-self and have to be transplanted with an induced immunosuppressant drug.

Following a transplant, describe the process of tissue rejection that may occur in Jane after recognition of non-self cells has occurred.

Answer says: t-cell mediated rejection response occurs and macrophage presents antigen from transplanted kidney on its surface and releases cytokine to attract helper T cells to activate cytotoxic T cells to destroy the no self cells.


I understand this all, but how/when do macrophages engulf antigens from these transplanted organs? Since when did organs have antigens? If antigens are involved, doesn't it mean it's Humoral immunity and not cell mediated? In my answer I just said the macrophages detect foreign MHC markers and engulf the transplanted cells. Is this wrong ?


Thanks guys

Organs have many cells, and these cells have MHC markers aka Human leukocytic antigens. If antigens are involved, it does not always have to be humoral immunity. Both cell-mediated and humoral will work together to create the specific immunity, which attacks the specific antigen.
You are on the right track. Macrophages detect the foreign MHC's and engulf the cells. They present the antigenic epitopes on the MHC Class II markers. In the case of transplanted markers, it is the cytotoxic T cells that are mostly working. This is because, cytotoxic T cells control the cells of the body by differentiating between self and non-self and attacking the non-self cells. When the macrophage presents the antigenic epitope, it will secrete Interleukin I to alert and stimulate T Helper Cells. These will then secrete Interleukin II to proliferate cytotoxic T cells. These cytotoxic T cells will recognize that the macrophage presents the foreign antigen, and will kill it via apoptosis. Alternatively, it can also attack the non-self cells.
Hope this helps 

[IndefatigableLover]

Thanks HighTide

DO you guys know which commercial biology exams are the hardest? And which are the easiest? Where can I get some for free, or is it all for $$ these days?

I asked this question a while back which alchemy answered!

Neap and STAV were quite good from memory. Neap was the hardest in terms of difficulty I found.
Insight was on the easier side, but still good.
Lisachem wasn't all that great tbh....

Just ask your school for practice exams otherwise go through VCAA papers since they're nicely separated into Unit 3/4 (making sure to omit anything not on the study design as such).

I'm not too sure how good they are as well but Engage has some free ones here: http://engageeducation.org.au/practice-exams/biology