VCE Biology Question Thread

[BakedDwarf]

In the 2015 STAV exam, an MC question states
In vertebrates the pathway of a nervous impulse is in one direction only because:
A. (obviously wrong answer)
B. the action potential can only jump across the synapse in one direction
C. neurotransmitter receptors are only found on the post-synaptic membranes
D. (obviously wrong answer)

I reasoned that C cannot be the answer (hence circled B) because I thought neurotransmitter receptors are found in both post and pre synaptic membranes. This is because the receptors in the:
- postsynaptic membranes open up the sodium channels
- presynaptic membranes to prevent the release of further neurotransmitters

bumperino.

Bangaloki told me why the answer cannot be B. But how is C correct?

[Biology24123]

bumperino.

Bangaloki told me why the answer cannot be B. But how is C correct?
[/quote

Why would there be neurotransmitter receptors on the pre- synaptic membrane

[BakedDwarf]

Why would there be neurotransmitter receptors on the pre- synaptic membrane

This is some copypasta from wikipedia:
Neurotransmitter receptors are present on both postsynaptic neurons and presynaptic neurons with the former being used to receive neurotransmitters and the latter for the purpose of preventing further release of a given neurotransmitter.

[vox nihili]

Will think of that from now on

I'm glad, because that is what I fucked up on the MCQs on the unit 4 exam.

This is some copypasta from wikipedia:
Neurotransmitter receptors are present on both postsynaptic neurons and presynaptic neurons with the former being used to receive neurotransmitters and the latter for the purpose of preventing further release of a given neurotransmitter.

Translation: negative feedback basically

[Biology24123]

I'm glad, because that is what I fucked up on the MCQs on the unit 4 exam.

Translation: negative feedback basically

So in both DNA replication and transcription, DNA is read in the  3' to 5' direction but the new strand grows in the 5' to 3' direction?

[kimmytaaa]

Hey guys,
How do I define evolution? Because on my sac, I define evolution as the permanent genetic change in population of individuals, but my friend told me, my answer is too generic  and that I haven't rote learn how to answer the question properly. When I asked my friend, my friend said the question is too vague and it should have asked whether its biological, technological or cultural. Is that correct?

[cosine]

So in both DNA replication and transcription, DNA is read in the  3' to 5' direction but the new strand grows in the 5' to 3' direction?

Correct, just remember any polymerase READS the DNA strand from the 3'-5' direction.

[StupidProdigy]

So with dna polymerase, does it join opposite/complementary nucleotides and ligase joins the phosphate backbone of the new strand?

[cosine]

So with dna polymerase, does it join opposite/complementary nucleotides and ligase joins the phosphate backbone of the new strand?

Don't say opposite, say complementary
And it's not ligase, it's DNA Ligase (specifics are my death on this upcoming exam).

And in which process are you talking about for the i). addition of nucleotides and ii). DNA ligase functioning?

[StupidProdigy]

Don't say opposite, say complementary
And it's not ligase, it's DNA Ligase (specifics are my death on this upcoming exam).

And in which process are you talking about for the i). addition of nucleotides and ii). DNA ligase functioning?

Gotta be specific  uhm just replication of dna in general, as the dna polymerase elongates the strand does it just make complementary nucleotides (like the hydrogen bonds in between) form and dna ligase functioning in replication by joining the adjacent (not complementary) nucleotides. That's how I understand it, is it wrong? Thankyou!

[cosine]

Gotta be specific  uhm just replication of dna in general, as the dna polymerase elongates the strand does it just make complementary nucleotides (like the hydrogen bonds in between) form and dna ligase functioning in replication by joining the adjacent (not complementary) nucleotides. That's how I understand it, is it wrong? Thankyou!

Well during DNA replication there are two strands of the daughter strands - leading and lagging strand.

The first step of DNA replication involves the DNA unwinding, with the aid of DNA helicase, and as the DNA double helix unwinds, primers attach to the 3' end of both single strands. Now, due to DNA's antiparallel nature, the primer that attaches to the opposite end of the replication fork will allow DNA polymerase to synthesise the leading strand in the 5'-3' and move along with DNA helicase so synthesise it smoothly. However, the other strand is the lagging strand, so primers are continuously attached to the 3' end of the DNA strand as it keeps unwinding, and then DNA polymerase synthesises in the 5-3' direction. So this means that when the replication is complete, the lagging strand will have fragments of DNA that are not bonded together, known as Okazaki fragments, and so DNA ligase comes along and seals these gaps by forming phosphodiester bonds within the backbone of the fragments.

In short: DNA ligase is only used on the lagging strand, because the leading strand is continuously being synthesised and there is no gaps within the nucleotides.

[Sine]

Well during DNA replication there are two strands of the daughter strands - leading and lagging strand.

The first step of DNA replication involves the DNA unwinding, with the aid of DNA helicase, and as the DNA double helix unwinds, primers attach to the 3' end of both single strands. Now, due to DNA's antiparallel nature, the primer that attaches to the opposite end of the replication fork will allow DNA polymerase to synthesise the leading strand in the 5'-3' and move along with DNA helicase so synthesise it smoothly. However, the other strand is the lagging strand, so primers are continuously attached to the 3' end of the DNA strand as it keeps unwinding, and then DNA polymerase synthesises in the 5-3' direction. So this means that when the replication is complete, the lagging strand will have fragments of DNA that are not bonded together, known as Okazaki fragments, and so DNA ligase comes along and seals these gaps by forming phosphodiester bonds within the backbone of the fragments.

In short: DNA ligase is only used on the lagging strand, because the leading strand is continuously being synthesised and there is no gaps within the nucleotides.

DNA ligase is actually used in the leading strand as the primers are added by RNA primase and thus are RNA nucleotides which are later replaced by DNA nucleotides by DNA polymerase so the primers(which are actually the new DNA nucleotides which replace the RNA primer) need to be joined with the newly synthesised strand(leading strand).

How would one link biological, cultural & technological evolution?

[cosine]

DNA ligase is actually used in the leading strand as the primers are added by RNA primase and thus are RNA nucleotides which are later replaced by DNA nucleotides by DNA polymerase so the primers(which are actually the new DNA nucleotides which replace the RNA primer) need to be joined with the newly synthesised strand(leading strand).

How would one link biological, cultural & technological evolution?

One needs to relax within the boundaries of the 3/4 Biology thread

[Sine]

How would one link biological, cultural & technological evolution?

Also B-cells  have antibodies on their surface but how exactly do they present antigen that they encounter, do they first engulf it and then express the relevant antigens on antibodies or kinda just bind the antibody with the antigens without internalising it?

Can someone run through what we need to know about the lymphatic system?
From what I understand it's a fluid transport system containing B & T cells which initiate specific immune response, but what exactly occurs at the lymph nodes, is it the detection of antigenic material or is it stimulation of B & Tc cells?

[cosine]

Also B-cells  have antibodies on their surface but how exactly do they present antigen that they encounter, do they first engulf it and then express the relevant antigens on antibodies or kinda just bind the antibody with the antigens without internalising it?

Can someone run through what we need to know about the lymphatic system?
From what I understand it's a fluid transport system containing B & T cells which initiate specific immune response, but what exactly occurs at the lymph nodes, is it the detection of antigenic material or is it stimulation of B & Tc cells?

B cells engulf the antigen and present them on their MHC II markers to that T-Helper cells can activate them to proliferate.

Lymphatic system is the system that is responsible for the lymphocytes of the immune system, production of B and T cells. At lymph nodes are B and T cells sitting there, waiting for either the Helper T cells to come along and activate them, or as B cells require interaction with the antigen, wait for the pathogen to come in the lymph nodes and be engulfed by the B cell. So it's technically both - detection of antigenic material and stimulation/activation of B and Tc cells.