[d_94]

(Original post by VRS)
Can some one explain

Gel Electrophoresis

and

PCR - Polymerase Chain Reaction

Please

Here you go. These are ah-mazing. But somehow detailed. But they're very good. It helped me alooooott

[sceptic_medic]

(Original post by SimpleGirl)
DNA is made up of both introns and exons.
Introns - Non coding regions
Exons - Coding regions.
After transcription takes place, a strand of mRNA is made. This strand is then expressed during translation and proteins are synthesised. Only exons, the coding regions, can be expressed; therefore, the introns (the non coding regions) are removed after transcription as they are not needed. This leaves a strand of mRNA consisting of only exons (only sections of coding regions that can now be expressed).

When mRNA is spliced, all introns are removed and the exons are spliced together. When they are spliced together, there are a number of different combinations in which they can form a sequence. That's why several proteins can be made with just one strand of mRNA. The exons of that one strand can be spliced together in different ways, creating different combinations hence resulting in a different sequence being translated and giving the end protein.

For example (from the textbook, page 120):

pre-mRNA: (just after transcription, and before splicing has taken place)
Exon 1; Intron 1; Exon 2; Intron 2; Exon 3

Introns are removed and the exons can be spliced together to form different sequences:
Exon 1; Exon 2; Exon 3
Exon 1; Exon 3
Exon 2, Exon 3
Exon 1, Exon 2

The original strand of mRNA can produce these 4 different sequences meaning that many different proteins can be synthesised from just a single strand.

It's important to clarify that the exons cannot be rearranged in a different order to produce different proteins. All that can happen is that sometimes introns are left in which changes the sequence or sometimes some exons are also taken out along with the introns, again changing the sequence. This is the basis of post-transcriptional changes. (Post translational changes also happen but you don't have to worry about these)


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[SimpleGirl]

(Original post by VRS)
Can some one explain

Gel Electrophoresis

and

PCR - Polymerase Chain Reaction

Please

PCR - Polymerase Chain Reaction
This is used in order to make copies of the DNA. It's helpful for evidence found at a crime scene that may only be present in very small amounts so they use PCR to make several copies which can then be used for testing.

The sample of DNA, free nucleotides, primers and DNA polymerase are put together in a reaction tube.
Primers are short sections of DNA that are complementary to the bases adjacent to the fragment you want to amplify. The primers anneal (stick to) the start of the section so that DNA polymerase can begin complementary-base-pairing from there.
In simple terms, primers are like markers that attach to the beginning of the DNA so that the DNA polymerase knows where to start .

The mixture is heated at 3 different temperatures:
First at 95°C - In order to break the hydrogen bonds between the two strands of the DNA.
Then at 55°C - This is optimum temperature for primers to bind to the beginning of the desired fragment (STR).
Finally at 70°C - This is optimum temperature for the enzyme, DNA polymerase, to work at.

The DNA polymerase then attaches to where the primers have highlighted and it will move along the strand, lining up the free nulceotides and creating a new strand.

The one stand put into the PCR machine has now been copied into two. These two strands are then put back into the machine and the whole process is repeated and four strands will be made at the end. However many strands are put in at the beginning will be doubled by the end of the PCR process.

Gel Electrophoresis

The DNA can now be separated out according to length.
The DNA is placed on a slab of gel (usually agarose) which is covered in a buffer solution. The buffer solution is present as it conducts electricity; therefore, when the gel is connected to electrodes, a potential difference will be created across the gel.

The electric current then passes through the gel and causes the negatively charged DNA fragments to migrate (move towards) the positive electrode.

The smaller fragments move faster, allowing the bands to separate depending on size. This is what creates a series of bands on the profile.

Southern blotting (a staining technique) is used to highlight the bands. The DNA is transferred to a nylon membrane. The nylon membrane is then incubated with DNA probe .
Then finally, by using UV light, you can shine it over the membrane and the bands can be visualised.

Profiles are created and the bands are compared between them to identify the similiarity of the individuals.
(Used for matching DNA at crime scene with potential suspect's DNA profile or matching a child's DNA profile with the father's DNA profile for paternity testing)

[VRS]

(Original post by SimpleGirl)
PCR - Polymerase Chain Reaction
This is used in order to make copies of the DNA. It's helpful for evidence found at a crime scene that may only be present in very small amounts so they use PCR to make several copies which can be then be used for testing.

The sample of DNA, free nucleotides, primers and DNA polymerase are put together in a reaction tube.
Primers are short sections of DNA that are complementary to the bases adjacent to the fragment you want to amplify. The primers anneal (stick to) the start of the section so that DNA polymerase can begin complementary-base-pairing from there.
In simple terms, primers are like markers that attach to the beginning of the DNA so that the DNA polymerase knows where to start .

The mixture is heated at 3 different temperatures:
First at 95°C - In order to break the hydrogen bonds between the two strands of the DNA.
Then at 55°C - This is optimum temperature for primers to bind to the beginning of the desired fragment (STR).
Finally at 70°C - This is optimum temperature for the enzyme, DNA polymerase, to work at.

The DNA polymerase then attaches to where the primers have highlighted and it will move along the strand, lining up the free nulceotides and creating a new strand.

The one stand put into the PCR machine has now been copied into two. These two strands are then put back into the machine and the whole process is repeated and four strands will be made at the end. However many strands are put in at the beginning will be doubled by the end of the PCR process.

Gel Electrophoresis

The DNA can now be separated out according to length.
The DNA is placed on a slab of gel (usually agarose) which is covered in a buffer solution. The buffer solution is present as it conducts electricity; therefore, when the gel is connected to electrodes, a potential difference will be created across the gel.

The electric current then passes through the gel and causes the negatively charged DNA fragments to migrate (move towards) the positive electrode.

The smaller fragments move faster, allowing the bands to separate depending on size. This is what creates a series of bands on the profile.

Southern blotting (a staining technique) is used to highlight the bands. The DNA is transferred to a nylon membrane. The nylon membrane is then incubated with DNA probe .
Then finally, by using UV light, you can shine it over the membrane and the bands can be visualised.

Profiles are created and the bands are compared between them to identify the similiarity of the individuals.
(Used for matching DNA at crime scene with potential suspect's DNA or matching a child's DNA profile with the father's DNA profile for paternity testing)

Thanks a million!!!!!


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[VRS]

(Original post by d_94)
Here you go. These are ah-mazing. But somehow detailed. But they're very good. It helped me alooooott

Thanks a lot - appreciate it


This was posted from The Student Room's iPhone/iPad App

[M Kh]

Do we have to know the similarities between the structure of bacteria and viruses?

Do we have to know the names and exact colours of the different pigments making up chlorophyll?

Also what enzymes are involved in each stage of protein synthesis?

I can't think of enough points for this -> How does reforestation and using biofuels reduce atmospheric levels of Carbon dioxide?

How do we calculate the efficiency of energy transfer between trophic levels?
Do we calculate efficiency of energy transfer from the higher trophic level to the lower one or vice versa?

Why is a climax community stable?
What is a plagioclimax community?
What is the difference between a climax community and a plagioclimax community?
Are there any othe types of climax communties other than plagioclimax community?

What is a suitable control for: the antibiotic core practical, effect of temperature on seedling growth rate core prac, effect of temperature on brine shrimp hatch rate core prac?

I know how to write up an investigation report on the effect of temperature on brine shrimp hatch rate but not the investigation on THE EFFECT OF TEMPERATURE ON SEEDLING GROWTH RATE. Can someone please clear up this one for me?

How does analysing ice cores give evidence of global warming?

What is thee exact difference between correlation and causal relationship?
And, what synoptic questions do you guys think could come up?

[SimpleGirl]

(Original post by marc_h94)
It's important to clarify that the exons cannot be rearranged in a different order to produce different proteins. All that can happen is that sometimes introns are left in which changes the sequence or sometimes some exons are also taken out along with the introns, again changing the sequence.

Really? I didn't know that
I thought that all introns are removed.

[alexsasg]

Is everyone on this thread doing the context-based, SNAB approach? Or are some doing the content-based approach? Because that would explain why stuff I've never heard of (humoral responses etc) has been mentioned.

And thanks, SimpleGirl I think I get splicing now.

[This Honest]

(Original post by Jasmine_777)
sry, what does 'prevent antigen processing' mean?

Basically, when a t helper cell gets infected, it presents the anitgens on its surface to activate other t helper cells to help fight the infection
If anitgen processing doesn't occur, t helper cells are not activated so they can't activate t killer and b cells...after all of the symptoms and diseases...death will come.

[aqua05]

(Original post by arnab)
sorry i never answered your question about splicing but i have been on and off ( doing papers in between) but i guess you know it no

Guys what could your answer be to this question :

Foxes are territorial animals. Rural foxes commonly have territories between
two and six km2 (200 to 600 hectares) in size. Urban foxes have a much smaller
territory of less than 0.6 km2. Explain how this could affect the population of
foxes in urban areas.

I thought the answer was this :

- smaller area, hence less food available
- Lower area, hence less "space" to find a good nesting/breeding site
- More competition due to smaller area
- hence population will decrease

Can that be right?

from what paper is this question from?

[This Honest]

(Original post by SimpleGirl)
DNA is made up of both introns and exons.
Introns - Non coding regions
Exons - Coding regions.
After transcription takes place, a strand of mRNA is made. This strand is then expressed during translation and proteins are synthesised. Only exons, the coding regions, can be expressed; therefore, the introns (the non coding regions) are removed after transcription as they are not needed. This leaves a strand of mRNA consisting of only exons (only sections of coding regions that can now be expressed).

When mRNA is spliced, all introns are removed and the exons are spliced together. When they are spliced together, there are a number of different combinations in which they can form a sequence. That's why several proteins can be made with just one strand of mRNA. The exons of that one strand can be spliced together in different ways, creating different combinations hence resulting in a different sequence being translated and giving the end protein.

For example (from the textbook, page 120):

pre-mRNA: (just after transcription, and before splicing has taken place)
Exon 1; Intron 1; Exon 2; Intron 2; Exon 3

Introns are removed and the exons can be spliced together to form different sequences:
Exon 1; Exon 2; Exon 3
Exon 1; Exon 3
Exon 2, Exon 3
Exon 1, Exon 2

The original strand of mRNA can produce these 4 different sequences meaning that many different proteins can be synthesised from just a single strand.

Excellent response
I already kinda know it but you've just settle the doubts

[This Honest]

(Original post by arnab)
sorry i never answered your question about splicing but i have been on and off ( doing papers in between) but i guess you know it no

Guys what could your answer be to this question :

Foxes are territorial animals. Rural foxes commonly have territories between
two and six km2 (200 to 600 hectares) in size. Urban foxes have a much smaller
territory of less than 0.6 km2. Explain how this could affect the population of
foxes in urban areas.

I thought the answer was this :

- smaller area, hence less food available
- Lower area, hence less "space" to find a good nesting/breeding site
- More competition due to smaller area
- hence population will decrease

Can that be right?

Seems right.
I would say intraspecific competition occurs to make it more technical
you know how edexcel biology is like

[arnab]

(Original post by aqua05)
from what paper is this question from?

http://www.xtremepapers.com/papers/E...%20Unit-5B.PDF

Q5c, part 1

The mark scheme does not make sense to me at all

[arnab]

(Original post by This Honest)
Seems right.
I would say intraspecific competition occurs to make it more technical
you know how edexcel biology is like

yhh well the mark scheme says the exact opposite of me

EDIT : here is the answer if anyone is wondering why i am saying i am wrong



Uploaded with ImageShack.us


CAN SOME ONE EXPLAIN IT TO ME??????????

[arnab]

guys how does virus, such HIV, infect cells and cause disease?

[aqua05]

(Original post by arnab)
yhh well the mark scheme says the exact opposite of me

EDIT : here is the answer if anyone is wondering why i am saying i am wrong



Uploaded with ImageShack.us


CAN SOME ONE EXPLAIN IT TO ME??????????

oh my i was thinking your answer was rightt :O

[19941994]

Hey does anyone knownof the SNAB revision guide has all information needed for this exam? And is there additional information that isnt in the exam in the snab booklet? Because i dont remember doing the 5 different kingdoms :s


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[alexsasg]

(Original post by 19941994)
Hey does anyone knownof the SNAB revision guide has all information needed for this exam? And is there additional information that isnt in the exam in the snab booklet? Because i dont remember doing the 5 different kingdoms :s


This was posted from The Student Room's iPhone/iPad App

I don't think we have to know the five kingdoms for this exam? I thought that was more topic 4, from last year. And this unit isn't the synoptic one.

[wam-bam]

(Original post by d_94)
.

(Original post by This Honest)
.

QUERY FROM JUNE 10 ( Q.1b)

Hi i've attached the question and the paper, for the mark scheme does anyone understand how point 2, how have they calculated that 60% of the data lies within 1 SD of the mean???

Thanks in advance

[d_94]

(Original post by wam-bam)
QUERY FROM JUNE 10 ( Q.1b)

Hi i've attached the question and the paper, for the mark scheme does anyone understand how point 2, how have they calculated that 60% of the data lies within 1 SD of the mean???

Thanks in advance

I saw the markscheme. But I could open the qp, could you re-upload it again?


*Ohh. Never mind. Opened the question too. LOL
Yeaa. I got confused. I'm sorry I don't know how they got 60%
Did you get the other points?