[Fatima0065]

(Original post by walkbesideme)
Added a few things here and there

NO problemo lol its good to know extra stuff...btw i reckon ur gona ace this exam cuz uv revysd evrything with detail

[The Illuminati]

(Original post by Robpattinsonxxx)
Is anyone going to answer this? What if it comes up, you will regret it

Outline the role of acetylcholine and acetylcholinesterase in synapses. State where they are found [2], what type of molecule they are [2] and what they do [6. 3 each]

ACh is a neurotransmitter, transmits impulse from presynaptic neurone to post synaptic neurone
ACh found in the presynaptic knob
ACHEase is an enzyme found at the junction
ACHEase breaks down ACh which diffuses across the synapse back to the presynaptic membrane to be reformed

[walkbesideme]

(Original post by Robpattinsonxxx)
Is anyone going to answer this? What if it comes up, you will regret it

Outline the role of acetylcholine and acetylcholinesterase in synapses. State where they are found [2], what type of molecule they are [2] and what they do [6. 3 each]

Acetylcholine is found in vesicles present in the pre-syanaptic neurone
Acetylcholinesterase is found attached to the post-synaptic membrane in the synaptic cleft.

Acetylcholine is a neurotransmitter
Acetylcholinesterase is an enzyme

Acetylcholine is expelled from the presynaptic neurone (via exocytosis of the vesicles upon an influx of Ca2+ into the cell), the acetlychoine then diffusses across the synaptic cleft and binds to complementary receptors on the post-synaptic membrane hence causing the opening of associated Na+ ion channels therefore leading to an action potential in the post-synaptic neurone (upon generator potential reaching the threshold value of -55mV)

Acetylcholinesterase hydrolyses the Acetylcholine (to choline and acetate) in the synaptic cleft. This prevents overstimulation and potential damage of the neurone by ensuring the Acetylcholine only has a limited period in which it can bind to complmentary receptors before it is hydrolysed. This effect also ensure that the acetlycholine can be replaced as the choline and acetate then diffuse back into the pre-synaptic neurone (down the concentration gradient) and are reformed back into acetylcholine ready for release should another nervous impulse arrive.

[The Illuminati]

(Original post by DoctorVertigo)
Somewhere on this thread, there's hundreds of questions.

where.

[walkbesideme]

(Original post by DoctorVertigo)
How do you sequence a genome? (9)

Gonna recycle this to see whether you agree

1) the genome is mapped out using previously known information such as the location of microsatellites and is then mechanically sheared into lots of smaller fragments of approx 100000bp's in length

2) the sheared fragments are then inserted into bacterial artificial chromosomes (BAC's) which are then in turn implanted into E-coli cells. These cells are then cultured and kept as a 'clonal-library'

3) Specific E-coli cells known to contain specific BACs (hence specific fragments) are taken and cultured to produced a large number of copies of the desired fragment. The BAC is then extracted from all of these cells.

4) The Fragments are then treated with a mixture of many different restriction enzymes to produce a large number of smaller, different and 'overlapping' fragments.

5) These smaller fragments are then arranged into size order via Gel Electrophoresis.

6) Once arranged into size order the fragments are placed in a reaction mixture containing the following components: Free DNA nucleotides, Free modified (fluroescently marked) nucleotides, DNA primers and DNA polymerase.

7) The Free Nucleotides, modified nucleotides and primers (anneals to 3' end) anneal to the exposed complementary bases on the fragments. DNA polymerase then attaches at the primer and moves along the fragment bonding the adjacent nucleotides together (froming sugar-phospahte backbone), this continues until the DNA polymerase reaches a modified nucleotide at which point it drops off therefore the nucleotide chain terminates. This process is known as interrupted PCR. This process occurs many times produing a very large number of DNA fragments with modified nucleotides at many different places along the fragments.

8) The fragments are now transferred to a specialised electrophoresis machine which has a laser at one end that makes the modified nucleotides fluoresce. Each modified nucleotide (A, C, G and T) fluoresce a different colour therefore a computer programme can read this data and from this, along with the map of the genome, sequence the genome in its entirity.

[ds4143]

(Original post by DoctorVertigo)
Has anyone done the Hentrietta Barnett school questions? Are they all from our syllabus cause i'm looking at these genetics questions and thinking if this is real life?!

Ive got a whole bunch of biotech questions from that school...its so muchhhh! I need to do them ugh!

This was posted from The Student Room's Android App on my HTC Desire HD A9191

[SS*]

(Original post by DoctorVertigo)
How do you sequence a genome? (9)

This is a toughy to remember...

1. First, the genome has to be cut into smaller fragments using restriction enzymes. This is because the chain termination method can only be used to sequence DNA fragments that are up to 750 base pairs long.
2. The fragments are then inserted into bacterial artificial chromosomes (BACs) which are man made plasmids. A different DNA fragment is inserted into each BAC.
3. The BACs are then inserted into bacterial cells.
4. The bacteria divide, creating colonies of cells that each contain the DNA fragment from the original cell.
5. The different colonies make a complete genomic DNA library.
   DNA is extracted from each colony, and cut up using restriction enzymes producing overlapping pieces of DNA. This overlapping increases the accuracy of the sequencing.
6. Now, each fragment can be sequenced using the chain termination method.
7. A mixture is set up for each fragment which contains the single stranded DNA fragment to be sequenced, the enzyme DNA polymerase, primers and free DNA nucleotide bases. Some of these bases have a fluorescent tag attached to them and have also been modified to 'throw off' the DNA polymerase enzyme when they are added to the growing chain. Once they are added, the chain can no longer be extended by the DNA polymerase. Each of the 4 different nucleotide bases are tagged with a different fluorescent colour.
8. The primers anneal at the 3' end of the template strand allowing DNA polymerase to attach.
9. DNA polymerase extends the double stranded chain until a modified nucleotide base is added which throws it off and prevents the chain from growing.
10. The result is many copies of the DNA that are lots of different lengths - each ends in a base with a coloured tag attached to it.
11. If there are enough pieces of DNA, every base will be tagged.
12. The mixture of the different lengths of DNA is pulled along a capillary tube by electrophoresis. The shorter the lengths of the fragments, the quicker they pass along the tube.
13. At the end of a tube is a laser light that shines on each fragment and the tagged colour for each length of DNA is recorded.
14. A computer records the sequence of the colours. Because each of the 4 nucleotide bases has a different colour, the DNA base sequence can hence be established.
15. The chain termination method is carried out for each DNA fragment from the genome, and the computer analyses all the information to give the complete genomic sequence.

[DoctorVertigo]

(Original post by walkbesideme)
Gonna recycle this to see whether you agree

1) the genome is mapped out using previously known information such as the location of microsatellites and is then mechanically sheared into lots of smaller fragments of approx 100000bp's in length

2) the sheared fragments are then inserted into bacterial artificial chromosomes (BAC's) which are then in turn implanted into E-coli cells. These cells are then cultured and kept as a 'clonal-library'

3) Specific E-coli cells known to contain specific BACs (hence specific fragments) are taken and cultured to produced a large number of copies of the desired fragment. The BAC is then extracted from all of these cells.

4) The Fragments are then treated with a mixture of many different restriction enzymes to produce a large number of smaller, different and 'overlapping' fragments.

5) These smaller fragments are then arranged into size order via Gel Electrophoresis.

6) Once arranged into size order the fragments are placed in a reaction mixture containing the following components: Free DNA nucleotides, Free modified (fluroescently marked) nucleotides, DNA primers and DNA polymerase.

7) The Free Nucleotides, modified nucleotides and primers (anneals to 3' end) anneal to the exposed complementary bases on the fragments. DNA polymerase then attaches at the primer and moves along the fragment bonding the adjacent nucleotides together (froming sugar-phospahte backbone), this continues until the DNA polymerase reaches a modified nucleotide at which point it drops off therefore the nucleotide chain terminates. This process is known as interrupted PCR. This process occurs many times produing a very large number of DNA fragments with modified nucleotides at many different places along the fragments.

8) The fragments are now transferred to a specialised electrophoresis machine which has a laser at one end that makes the modified nucleotides fluoresce. Each modified nucleotide (A, C, G and T) fluoresce a different colour therefore a computer programme can read this data and from this, along with the map of the genome, sequence the genome in its entirity.

Looks good to me!

[Lalaa]

im sorta confused....

when sequencing a genome.. people have wirtten, add primers, nucleotides lalaaa... THEN do PCR, but dont you add those things during PCR..

[walkbesideme]

(Original post by Lalaa)
im sorta confused....

when sequencing a genome.. people have wirtten, add primers, nucleotides lalaaa... THEN do PCR, but dont you add those things during PCR..

I'm not sure the order would matter

[SS*]

(Original post by Lalaa)
im sorta confused....

when sequencing a genome.. people have wirtten, add primers, nucleotides lalaaa... THEN do PCR, but dont you add those things during PCR..

There is no PCR for genome sequence. I think you're mixing it up with the chain termination method

[Lalaa]

(Original post by walkbesideme)
I'm not sure the order would matter

hopefully!

(Original post by SS*)
There is no PCR for genome sequence. I think you're mixing it up with the chain termination method

okay.. sorry not to be a pain.. if you have the purple book can u direct me to the chain termination and sequencing pleasee..

[ds4143]

(Original post by Lalaa)
im sorta confused....

when sequencing a genome.. people have wirtten, add primers, nucleotides lalaaa... THEN do PCR, but dont you add those things during PCR..

Me too, ahh

This was posted from The Student Room's Android App on my HTC Desire HD A9191

[SS*]

(Original post by Lalaa)
hopefully!



okay.. sorry not to be a pain.. if you have the purple book can u direct me to the chain termination and sequencing pleasee..

Which purple book? "Advanced Biology" or "OCR biology"?

[Lalaa]

(Original post by SS*)
Which purple book? "Advanced Biology" or "OCR biology"?

ocr biology.. i have both .. but purples better.. thanks soo muchhh!

[The Illuminati]

(Original post by SS*)
There is no PCR for genome sequence. I think you're mixing it up with the chain termination method

It's based on PCR (the textbook doesnt call it chain termination though, that's in the revision guide)

[SS*]

(Original post by Lalaa)
ocr biology.. i have both .. but purples better.. thanks soo muchhh!

On page 172 it mentions that the reaction mixture is similar to the one for PCR and that the way the chain grows is like PCR - the full PCR method doesnt actually take place.

[SS*]

(Original post by The Illuminati)
It's based on PCR (the textbook doesnt call it chain termination though, that's in the revision guide)

Oui oui, based but not the same.

[Lalaa]

(Original post by SS*)
On page 172 it mentions that the reaction mixture is similar to the one for PCR and that the way the chain grows is like PCR - the full PCR method doesnt actually take place.

thanks.. so page 172.. is chain termination.. and sequencing genome.. is the BAC thing =S

OR

as The Illuminati said, that the chain termination is PCR and genome sequencing is 172

WOOOW CONFUSIINGG =O!

[The Illuminati]

(Original post by Lalaa)
thanks.. so page 172.. is chain termination.. and sequencing genome.. is the BAC thing =S

OR

as The Illuminati said, that the chain termination is PCR and genome sequencing is 172

WOOOW CONFUSIINGG =O!

I said it's based on it (the reaction mixture in both contain primers, free nuclotides, single strands of the DNA to be copied etc) not that they are the same thing.