AQA BIOL5 Biology Unit 5 Exam - 22nd June 2011

Reply 1920

KingMessi

19

Original post by angel1992

why does fsh need to be lowered by negative feedback in the first section of the oestrous cycle?

Because otherwise it would stimulate excessive growth of the follicles? :confused:

Reply 1921

emmaaa65

Original post by KingMessi

You don't use primers in DNA sequencing? :confused:

yeahhhh you do, they can be radioactively/fluorescently labbelled and they are needed so the dna polymerase can attach and add nucleotides! :tongue:

Reply 1922

KingMessi

19

Original post by Sparkly-Star

You do, according to NT book.

Ah, yes, you do...well, the primers are used to start DNA synthesis? Only thing that I can think of?

Reply 1923

slapyoself

Someone please explain the key points i need to know for locating and sequencing genes! Please i will positive rep !

Reply 1924

percy93

Original post by emmaaa65

yeahhhh you do, they can be radioactively/fluorescently labbelled and they are needed so the dna polymerase can attach and add nucleotides! :tongue:

don't think you use primers, you use probes

Reply 1925

laura123

Original post by Abby :)

Can someone explain the whole antibitiotic resistance thing in identifying if Vectors have been taken up. o.O

I really really dont understand how the textbook explains it.
All i know is there is something involving tetracycling and acetyl or something
And if the vector is still apparent then it has taken the vector up?

-.- Hehe

Basically, you just have to imagine that the vector you are using (in this case a plasmid) contains two genes for antibiotic resistance, one for an antibiotic called ampicillin and one for tetracycline. When you insert the DNA fragment into the vector using DNA ligase, the tetracyclin gene is cut - essentially this means that the plasmid no longer contains the gene for resistance to tetracycline, however it still contains the gene for resistance to ampicillin.
NB/ Some of the plasmids will close up before the desired gene can be inserted into it. When the recombinant DNA is mixed with the plasmids (with calcium ions and heat shock etc) some of the plasmids will be taken up by the bacteria. In order so see whether the bacteria has taken up the plasmid containing the DNA fragment, you need to treat it with antibiotics (in this case ampicillin and tetracycline)
Bacteria that have taken up plasmids will contain the gene for ampicillin resistance, so they will break down the ampicillin and survive - this doesn't mean however that they contain the DNA fragment. Bacteria that don't contain the plasmid will die.
The cells that survive are then cultured, to produce a genetically identical colony. A tiny sample from each colony is transferred onto a replica plate, in the same position as it was on the original plate. The replica plate is then treated by tetracycline, the colonies that are killed must be the ones that contain the DNA fragment, as the gene for the resistance to tetracycline was cut when the DNA fragment was inserted. The colonies in exactly the same position on the original plate are the ones that possess the required gene - these are the bacteria cells that have been transformed.

PHEW! Glad I got that off my chest.

Reply 1926

KingMessi

19

Original post by Sparkly-Star

Sorry for re-post, do we need to know the method of genetic screening?

Yeah, I reckon so...I'll give this a go.

The order of nucleotides in the mutated gene is sequenced using DNA sequencing. DNA fragments are made that have bases complementary to the bases on the mutated gene. A probe is made by radioactively labelling these fragments. Multiple copies of the probe are made using PCR techniques. If the person has the mutated gene, the probe will bind to the complementary bases on the mutated gene; these fragments can then be identified using X-Ray film; if the person has complementary fragments, the probe will be taken up and the fragments will be exposed using X-Ray film...if the person does not have the gene, complementary fragments will not be present, the probe will not be taken up and exposed by radioactive film? Correct?

Reply 1927

fretter778

14

Wrote 4 essays today. Bring it on, Bill!

Reply 1928

feelbetter

Original post by percy93

don't think you use primers, you use probes

In the NT book it says radioactively labelled primers, but it could be a probe too? weird

Reply 1929

percy93

Original post by feelbetter

In the NT book it says radioactively labelled primers, but it could be a probe too? weird

oh right, i don't get it. are primers and probes the same thing?

Reply 1930

paintedsmile

does anyone know if the plant hormone IAA is a protein like insulin or is it something else?

Reply 1931

Abby :)

8

Original post by laura123

Basically, you just have to imagine that the vector you are using (in this case a plasmid) contains two genes for antibiotic resistance, one for an antibiotic called ampicillin and one for tetracycline. When you insert the DNA fragment into the vector using DNA ligase, the tetracyclin gene is cut - essentially this means that the plasmid no longer contains the gene for resistance to tetracycline, however it still contains the gene for resistance to ampicillin.
NB/ Some of the plasmids will close up before the desired gene can be inserted into it. When the recombinant DNA is mixed with the plasmids (with calcium ions and heat shock etc) some of the plasmids will be taken up by the bacteria. In order so see whether the bacteria has taken up the plasmid containing the DNA fragment, you need to treat it with antibiotics (in this case ampicillin and tetracycline)
Bacteria that have taken up plasmids will contain the gene for ampicillin resistance, so they will break down the ampicillin and survive - this doesn't mean however that they contain the DNA fragment. Bacteria that don't contain the plasmid will die.
The cells that survive are then cultured, to produce a genetically identical colony. A tiny sample from each colony is transferred onto a replica plate, in the same position as it was on the original plate. The replica plate is then treated by tetracycline, the colonies that are killed must be the ones that contain the DNA fragment, as the gene for the resistance to tetracycline was cut when the DNA fragment was inserted. The colonies in exactly the same position on the original plate are the ones that possess the required gene - these are the bacteria cells that have been transformed.

PHEW! Glad I got that off my chest.

Wow, thank you so much <3 <3

Is this the same EVERY time. In every case does it cut into the tetracycline??
Or will it state what it was inserted into in the exam question? :smile:

But thank you, i get it now. Youre a life saver!

Reply 1932

Aiboz

Original post by Jeshiii

Hello there guys, does anyone have some notes or tips on remembering the stuff for the control of the heartbeat? The book i've got doesn't explain it that well and I forgot to ask my teacher about it earlier :/

Well how I remember is it that we have two ways - increase of a heartbeat and slowing of a heartbeat.

So when we exercise there is an increase in metabolic/muscular activity, this increases the rate of respiration and thereby increase the level of carbon dioxide in the blood. When carbon dioxide is dissolved in solution it becomes acidic. So this increased level of carbon dioxide lowers the pH level. The chemoreceptors in the walls of the carotid arteries (the arteries that serve the brain) detect this and send signals to the medualla oblongata in the brain. The centre in the medulla oblongata that increases heart rate increases the frequency of impulses to the sinoatrial node via the sympathetic system. The sinoatrial node increases the heart beat. This causes increased blood flow, which removes the carbon dioxide from the lungs faster. This means carbon dioxide levels decrease back to normal.

If this helps, quote me. I will then explain the control in slowing down the heartbeat and pressure receptors.

Reply 1933

laura123

Original post by Abby :)

Wow, thank you so much <3 <3

Is this the same EVERY time. In every case does it cut into the tetracycline??
Or will it state what it was inserted into in the exam question? :smile:

But thank you, i get it now. Youre a life saver!

Hmmmm that's a good question, I don't know.. but that's the example that they gave us in the text book, so it would be really unfair if they expected us to know anything else! I'm sure they'd provide more info in the question if it wasn't that exact technique :smile:

Reply 1934

feelbetter

Original post by percy93

oh right, i don't get it. are primers and probes the same thing?

A DNA probe is a short, singled stranded radioactively/fluorescently labelled DNA, a primer is a short single strand of DNA used needed to for polymerase chain reaction, they're not labelled inPCR to work but IDK if they're the same thing:/

(edited 12 years ago)

Reply 1935

Aiboz

Original post by paintedsmile

does anyone know if the plant hormone IAA is a protein like insulin or is it something else?

All I know is that its a growth factor, an auxin.

Reply 1936

KingMessi

19

Original post by slapyoself

Someone please explain the key points i need to know for locating and sequencing genes! Please i will positive rep !

-Use the Sanger method to sequence genes. This involves putting the fragments into test tubes, of which there are four, one of which containing each base. Each test tube contains terminator nucleotides that stop DNA synthesis as they cannot attach to the next base in the sequence. The test tubes also contain primers to start DNA synthesis, and DNA polymerase to catalyse DNA synthesis. The binding of nucleotides to a complementary strand of DNA is a random process, and therefore the binding of a terminator nucleotide or a normal nucleotide is equally likely. The fragments in each test tube can be identified because the primer attached to the other end of the DNA section is labelled radioactively, and all of the ones in each test tube will end in the same base.

Once you have obtained fragments, you can separate them using gel electrophoresis. The fragments are placed onto an agar gel and a voltage is applied across it. The fragments are of different lengths, and therefore will move different distances in different lengths of time. This means that smaller fragments move further than larger fragments, and this means that you can identify the sequence of the fragments.

You then use a DNA probe that is radioactively labelled to locate the gene, because it has complementary fragments to the mutated portion of the gene.

:biggrin:

Reply 1937

laura123

Original post by paintedsmile

does anyone know if the plant hormone IAA is a protein like insulin or is it something else?

It's just a chemical in plants, not a protein I don't think...

Reply 1938

BackDoorEntry

Original post by feelbetter

A DNA probe is a short, singled stranded radioactively/fluorescently labelled DNA, a probe is a short single strand of DNA used needed to for polymerase chain reaction, they're not labelled inPCR to work but IDK if they're the same thing:/