Outline the process of DNA replication (6)
- semi-conservative
- DNA helicase breaks Hydrogen bonds between nitrogenous bases
- DNA strands seperate
- Complimentary DNA nucleotides base pair to template strand
- DNA polymerase joins adjacent nucleotides
- by catalysing a phosphodiester bond
Define: semi conservative replication (2)
- each new DNA molecule contains one strand from Original DNA template Strand and one new strand
Explain how results from other generations provides evidence to show that DNA replication is semi-conservative (2)
- tube gen1 and gen 2 show new DNA
Describe 3 differences b/w the process of replication & transcription of DNA (3)
1 - replication uses DNA nucleotides
transcription uses RNA nucleotides
2 - replication uses DNA polymerase
transcription uses RNA polymerase
3 - replication makes double helix DNA
transcription makes single strand mRNA
Explain why meselson and stahl accepted one of the models for DNA replication and rejected the other (4)
- semi-conservative Model accepted
- gen1 = single band b/w 14 and 15N
- bcs DNA strand has one strand containing 15N and one containing 14N
- further gens would have a band halfway b/w 14 and 15N
Suggest how gene therapy could allow lungs to function normally in ppl with cystic fibrosis (4)
- insert functional gene that codes for CFTR protein
- CFTR protein made via transcription
- allows chloride ions to leave cell
- mucus is less sticky
Suggest why rhythmical tapping of chest during physiotherapy can relieve symptoms of cystic fibrosis (2)
- loosens mucus
- mucus expelled from lungs more easily
Explain why people with cystic fibrosis can have breathing difficulties (4)
- produces thicker mucus
- blocking airways
- cilia unable to move mucus out of lungs
- reduced air flow to alveoli
Define: recessive allele (3)
- diff. form of gene
- diff. base sequence
- both alleles need to be present for recessive phenotype to be expressed
Explain how a frame shift mutation could result in production of leptin with a variety of shorter primary structures (2)
- introduces new stop codon
- coding for shorter sequence of amino acid
