Paper 2

Question 1

What are types of stem cells

Answer 1

Totipotent - can divide into any type of cell
Pluripotent - can differentiate into almost any cell
Multipotent - can differentiate into a few types of specialised cells
- bone marrow can produce any type of blood cell
Unipotent - can only differentiate into one type of cell (cardiomyocyte)

Question 2

How does oestrogen influence transcription?

Answer 2

Oestrogen increases expression of particular genes
- Oestrogen is lipid soluble (derived from cholesterol) so can diffuse across the membrane
- Oestrogen specifically binds to the RECEPTOR PROTIEN of transcription factor and changes it’s shape
- Transcription factor enters the nucleus
- Transcription factor binds to the specific promotor region of the DNA
This allows RNA polymerase can bind and start transcription

Question 3

Describe myelination

Answer 3

• A methyl group (CH3) attaches to a to a promoter region
  
  • cytosine base when it is next to guanine (CpG site - p = phosphate between the 2 bases) the DNA sequence of a gene

Increased methylation inhibits transcription by preventing the binding of transcription factors to the promoter sequence so that the gene is not expressed.

Question 4

Describe acetylation

Answer 4

Binding of acetyl to histones makes chromatin less condensed so genes are accessible to transcription factors

Question 5

Describe gel electrophoresis

Answer 5

• DNA is placed in wells at the negatively charged end and the negatively shared DNA fragments move towards the positive electrode
  
  • Separates DNA fragments as smaller fragments travel faster and therefore further when an electric change is applied
  • After gel electrophoresis fragments are transferred to a nylon membrane then radioactively labelled DNA probes area added
  • This is placed under Xray or photographic film so the position of the labelled fragments show as dark bands (autoradiography)

Question 6

Is DNA +/-?

Answer 6

Negative!!!

Question 7

Describe the production of complimentary (cDNA)

Answer 7

• mRNA transcribed from genes is removed
  
  • mRNA used as a template to produce required fragment
  • mRNA is mixed with free nucleotides and reverse transcriptase
  • Free DNA nucleotides align next to their complementary bases on the mRNA template
  • Reverse transcriptase joins the DNA nucleotides together to produce a fragment of DNA (gene)
    The DNA strand produced by this technique is known as complementary DNA (cDNA)
    Double-stranded DNA is produced from this cDNA using DNA nucleotides and the enzyme DNA polymerase
    The absence of introns means these fragments can be transcribed by bacteria

Question 8

Describe the production of a recombinant plasmid

Answer 8

Recombinant plasmid
- Plasmid is cut using the same restriction endonuclease used to cut the gene
- Plasmid and DNA join by complimentary base paring due to ‘sticky ends’
- Ligase used to form phosphodiester bonds
- Plasmid is added to a culture of bacteria and the take up is called transformation

Question 9

Describe the light independent reaction

Answer 9

Carbon dioxide cobines with RuBP (in the presence of rubisco) to form 2 GP.
Using energy from ATP and reduced NADP GP is reduced into trisphosphate
Using ATP Triosphosphate is converted into RuBP with one carbon attom converted into an organic substance like glucose