F215 - Revision thread 13th June 2011

If you want me to work it out, PM me your module UMS and what you got in your practical /40 this year and I can tell you

Can you convert raw marks from the practical into UMS? I thought they changed that every year Please could you tell me what 34/40 would be?

34/40 is usually the mark for an A so 80% therefore 48/60 ums
Hope i helped!

Ahh I see, that makes sense. I guess you'd have to do PCR a LOT in order to replicate it, so a lot of effort.

Yeah, was just trying to get my head around it. Because in the 'outline DNA sequencing' it had the use of BAC's. So when is PCR used? Replicating DNA when searching for genetic diseases? I hate all this stuff!

Lol i know wot u mean every1 has somehting they hate and cant get in unit 5 (for me its some of the genetics)

PCR is basically the copying the DNA sample. Ill beak it down into points:
1. DNA molecule is mixed with DNA polymerase (Taq polymerase), primers and free dna nucleotides.
2. the mixture is heated (to 95degrees), breaking the hydrogen bonds between the DNA molecule, thus we are left with two DNA single strands.
3. the heat is bought down to 60 degrees, enables primers to now bind (anneal) to its complementary sequence on a specific part of the strands. this forms double strands on part of the dna single-strand.
4. the heat is bought upto 75degrees, now the Taq polymerase (special as it is able to work in high temps) can now bind to double strands on the DNA strand and use free dna nucleotides to continue the double strand.
5. thus we are left with two DNA double strands which are identical to the original DNA molecule we started with.
6. This process can be repeated with these two new DNA molecules, thus we get 4 DNA molecules after the 2nd cycle, repeat PCR for these 4 we get 8 etc.

Thats PCR, now Genome Sequencing is:
1. sample of dna is denatured to reveal two DNA single strands.
2. these are then mixed with DNA polymerase, free NTPs (nuleoside triphosphate), ddNTP (dedioxynucleoside triphostphate) and primers.
3. primers anneal to the dna strands via specific complementary binding.
4. dna polymerase then binds to sites with primers (as thats wer the double strands are). dna polymerase builds the double strand by using the free NTPs and ddNTPs. (the ddNTPs lack a hydroxy group, thus if they bind to a chain, they stop that chain as the gydrocy group is required to make a bond with the next nucleoside).
5. due to the ddNTP, different lengths of DNA fragments are produced in a mixture.
This process (1 to 5) is genome sequencing, from step 5 we go onto electrophoresis.

Where does BAC come into this? well the above genome sequencing is for small genomes only (100,000 bases). for the HUMAN GENOME (which has loads of bases) it undergoes another first step before the above. What happens is that the genome is treated with restriction enzymes, thus cutting down the genome into smaller fragments. the same restriction enzymes (used for each cut) are used on a 'Bacteria Artifical Chromosome' (aka, BAC) this is basically a man-made plasmid. The complementary sticky ends of the two (dna fragment and BAC) forms a recombinant DNA (rDNA). Now each rDNA contains a different part of the human genome. As you will notice we now have a smaller genome (around 100,000 bases) so we can carry out genome sequencing on each separately (so steps 1 to 5). After this is done, to recreate/recombine the human genome a very clever computer is used which does it.

AND THAT IS IT! loool long i know, but ive summarised 3 processes. I would answer the exam questions with these personally as they cover what the book goes over and a bit more, thus covering all the marks for tht particular question.
(btw i did this from memory without looking at books etc so if i have missed a step out let me knw!!)

so sequencing genome is same as sequencing and copying DNA.... coz i am a bit confused.... bcoz when you talked about genome sequencing..you described DNA sequencing

How come everyone is getting different answers for sequencing of a genome? What's the answer?

My teacher said we don't need to know about BAC's but everyones talking about them!

Anyone summarise Meiosis? Looking through past papers for topics applicable to F215...there could be an essay on Meiosis...

34/40 is usually the mark for an A so 80% therefore 48/60 ums
Hope i helped!

yeah you're right

Thank you

Hai Iby! hows it goin (if you remember me :P)

Also for you guys...

Module 4 Notes that I made last year (hopefully not much/nothings changed in that content).

http://www.mediafire.com/file/qit5izu1zyt/bio%20notes.doc

good luck, hope you nail these exams

I was going through some past paper question and there couple of questions on Sterile Hybrid... just wondering do we need to know about that as the book does not talk about it anywhere

Lol i know wot u mean every1 has somehting they hate and cant get in unit 5 (for me its some of the genetics)

PCR is basically the copying the DNA sample. Ill beak it down into points:
1. DNA molecule is mixed with DNA polymerase (Taq polymerase), primers and free dna nucleotides.
2. the mixture is heated (to 95degrees), breaking the hydrogen bonds between the DNA molecule, thus we are left with two DNA single strands.
3. the heat is bought down to 60 degrees, enables primers to now bind (anneal) to its complementary sequence on a specific part of the strands. this forms double strands on part of the dna single-strand.
4. the heat is bought upto 75degrees, now the Taq polymerase (special as it is able to work in high temps) can now bind to double strands on the DNA strand and use free dna nucleotides to continue the double strand.
5. thus we are left with two DNA double strands which are identical to the original DNA molecule we started with.
6. This process can be repeated with these two new DNA molecules, thus we get 4 DNA molecules after the 2nd cycle, repeat PCR for these 4 we get 8 etc.

Thats PCR, now Genome Sequencing is:
1. sample of dna is denatured to reveal two DNA single strands.
2. these are then mixed with DNA polymerase, free NTPs (nuleoside triphosphate), ddNTP (dedioxynucleoside triphostphate) and primers.
3. primers anneal to the dna strands via specific complementary binding.
4. dna polymerase then binds to sites with primers (as thats wer the double strands are). dna polymerase builds the double strand by using the free NTPs and ddNTPs. (the ddNTPs lack a hydroxy group, thus if they bind to a chain, they stop that chain as the gydrocy group is required to make a bond with the next nucleoside).
5. due to the ddNTP, different lengths of DNA fragments are produced in a mixture.
This process (1 to 5) is genome sequencing, from step 5 we go onto electrophoresis.

Where does BAC come into this? well the above genome sequencing is for small genomes only (100,000 bases). for the HUMAN GENOME (which has loads of bases) it undergoes another first step before the above. What happens is that the genome is treated with restriction enzymes, thus cutting down the genome into smaller fragments. the same restriction enzymes (used for each cut) are used on a 'Bacteria Artifical Chromosome' (aka, BAC) this is basically a man-made plasmid. The complementary sticky ends of the two (dna fragment and BAC) forms a recombinant DNA (rDNA). Now each rDNA contains a different part of the human genome. As you will notice we now have a smaller genome (around 100,000 bases) so we can carry out genome sequencing on each separately (so steps 1 to 5). After this is done, to recreate/recombine the human genome a very clever computer is used which does it.

AND THAT IS IT! loool long i know, but ive summarised 3 processes. I would answer the exam questions with these personally as they cover what the book goes over and a bit more, thus covering all the marks for tht particular question.
(btw i did this from memory without looking at books etc so if i have missed a step out let me knw!!)

I was going through some past paper question and there couple of questions on Sterile Hybrid... just wondering do we need to know about that as the book does not talk about it anywhere