Edexcel GCSE Biology | 1) DNA
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DNA It’s structure and practical Edexcell GCSE gcsepresentations
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From the Edexcel GCSE additional science specification for biology. Talks about
Transcript of Edexcel GCSE Biology | 1) DNA
DNAIt’s structure and practicalEdexcell GCSE
gcsepresentations
*BASICS* !
DNA is fundamental for all life - it contains genes (short sections of DNA), which code for making different proteins, the building
blocks of life. !
DNA is what you find, tightly coiled up, inside all 46 chromosomes in every nucleus in every single human diploid body cell.
!It consists of two strands coiled together with a double helix
structure and just 4 base pairs:!!
A (adenine) <—> T (thymine)!
C (cytosine) <—> G (guanine)
*FRANKLIN & WILKINS* !
Franklin and Wilkins were the brains behind DNA and it’s structure:!
They emitted X-Rays at the crystallised DNA and recorded the patterns of the reflected rays onto a screen.
!From this they discovered the DNA’s helical structure
!
*WATSON & CRICK* !
Watson and Crick used information of the double helix !
and that the amount of A + G was equal to the amount of C + T to make a model of DNA with the paired bases.
*PRACTICAL EXPERIMENT* !
This practical shows DNA as a stringy white substance, which proves that there is DNA in cells of living organisms.
*STEP 1* !
Chop a big juicy fresh onion into tiny pieces.!
Put it into a beaker.
*STEP 2* !
Add salt and detergent to the onions and stir.!!!!!!!!!!!
The detergent will help to break down the cell membranes;!
The salt helps to make the DNA stick together.
*STEP 3* !
Put the beaker into a water bath.!!!!!!!!!!!
Set the water to 60 celsius for 15 minutes and then remove the solution.
*STEP 4* !
Cool the solution with ice.!!!!!!!!!!!
This stops the DNA from breaking down.
*STEP 5* !
Blend the mixture.!!!!!!!!!!!
To open the cell walls and reelase the DNA.
*STEP 6* !
Cool the solution with ice.!!!!!!!!!!!
This stops the DNA from breaking down.
*STEP 6* !
Filter the mixture.!!!!!!!!!!!
Removing any big parts of cell and stop froth.
*STEP 6* !
Add ice cold alcohol to the solution.!!!!!!!!!!!
Do this slowly, and you should see the DNA separating from the cells as a white stringy substance, which can be removed with a glass rod.
DNA
