meselson&stahl

Question 1

describe structure of DNA

Answer 1

Double stranded
deoxyribose mononucleotides through condensation reactions

Question 2

How does DNA form double stranded helix

Answer 2

Bases form hydrogen bonds with each other holding two strands together
Stacking many mononucleotides results in a helix shape

Question 3

Describe RNA structure

Answer 3

Ribose sugar
Single stranded
Uracil instead of T base

Question 4

Outline transcription process

Answer 4

1. Dna helicase breaks hydrogen bonds between two strands
2. mRNA is built using complementary base pairing w RNA polymerase. mRNA is identical to non template strand.
3. It leaves nucleus though nuclear pores into cytoplasm

Question 5

Outline translation

Answer 5

1. In cytoplasm, the mRNA attaches to ribosome
2. Anti codon of tRNA attaches complementary to the three mRNA sequence )
3. Amino acids bonded to tRNA form polypeptide chain, through peptide bonds between the amino acids, until stop codon reaches
4. Process requires ATP

Question 6

Featured for genetic code

Answer 6

• triplet if bases
• non overlapping ( each triplet only read once)
  Degenerate more than one triplet codes for same amino acids
  -

Question 7

What’s a gene

Answer 7

Sequence of bases on DNA molecule that codes for specific sequence of amino acids

Question 8

Summarise dna REPLICQTION

Answer 8

1. Double helix unwinds & hydrogen bonds break cataylised by DNA helicasw
2. Complementary base pairing between template strand and free nucleotides
3. Nucleotides joined by phoshidiester binds catalysed by DNA polymerase

Question 9

How did Meselson and stahl( experimental DNA) prove seninconservative

Answer 9

15N culture showed one band at the bottom becuase it’s dense and heavier
Second round of replication in 14N was more lighter at the top
Third round ( noe containing 14n and 15n bases) shows two bands showing there was lighter bases and heavier bases.
This proved semi conservative becuase if it was conservative the first round would have showed two bands

Question 10

Genetic screening

Answer 10

Determining if individual DNA contains certain allele usually one that may result in genetic disorder

Question 11

CVS?

Answer 11

Sample of embryonic tissue taken from placenta at 8-12 / 11-14 weeks
1-2% risk of miscarriage
Screened for disorders
Results available quickly

Question 12

Amniocentesis

Answer 12

Another form of orental testing

I blocked removing cells from amniotic fluid using fine needle which contains foetal DNA
carried around15-20 weeks of pregnancy
1% miscarriage risk