DNA Flashcards
Describe the process of DNA replication
- Helicase breaks down hydrogen bonds between dna bases forming two separate strands
- Abundant nucleotides in the nucleus form hydrogen bonds with the complimentary bases
- DNA polymerase joins the new nucleotides together with phosphodiester bonds creating a sugar phosphate backbone
Explain how Meselson and Stahl’s experiment provides evidence for the semi-conservative model of DNA replication
They cultivated bacteria colonies in one growth medium containing heavy nitrogen (N-15) and one growth medium containing light nitrogen (N-14).
they then extracted dna from the bacteria from both growth mediums and put them into separate vials. they spun these vials in a centrifuge.
The dna cultivated in the heavy nitrogen settled low down in its vial, whereas the dna cultivated in the light nitrogen settled high up in its vial.
The scientists then transferred some of the bacteria that had been cultivated in the heavy nitrogen into a growth medium containing light nitrogen. they let the bacteria grow for 1 generation and then extracted the dna from it.
They spun this dna in a centrifuge and it settled halfway between where the n-14 and n-15 dna settled.
They let the bacteria grow in the n-14 growth medium for another generation, and spun it in the centrifuge. They repeated this for 5 generations. They found that after the second generation, the amount of dna that settled at the midpoint stayed the same, but an increasing number of dna molecules began to settle at the N-14 line again.
This provided evidence for the semi conservative model as it shows that after the first generation, each dna molecule was made of a split of heavy and light nitrogen as the dna settled at the halfway point between heavy and light, which disproved the conservative theory.
It also provided evidence for the semi conservative model as each increasing generation began to gather at the light nitrogen line, while the number of dna molecules at the midpoint stayed the same. This shows that each generation conserves the strand of heavy nitrogen dna along with producing new strands of dna using the light nitrogen from the growth medium.
Explain how Meselson and Stahl’s experiment refuted the conservative model of DNA replication
The dna settled at a midpoint in the centrifuge rather than having an even split between n-14 and n-15
Explain how Meselson and Stahl’s experiment refuted the dispersive model of DNA replication
Later generations of the dna had a split between n14 dna and midpoint dna, and the n14 one increased steadily.
Describe the process of transcription
DNA helicase breaks hydrogen bonds between nucleotides
mRNA nucleotides will form hydrogen bonds with the exposed DNA bases via complimentary base pairing
RNA polymerase catalyses reaction between sugar groups and phosphate groups in the mRNA strand forming a sugar phosphate backbone
DNA helicase breaks hydrogen bonds between DNA molecule and mRNA molecule, mRNA diffuses away
hydrogen bonds reform between strands of DNA, creating double helix structure
Describe the process of translation
mRNA moves to ribosome
tRNA with complimentary anticodons bind to the first codon on the mRNA strand by complimentary base pairing.
Define the terms codon and anticodon
codon: triplet of three bases attached to an mRNA strand
anticodon: triplet of three bases attached to a tRNA strand
Describe the nature of the genetic code by defining the following:
a) degenerate
b) triplet code
c) non-overlapping
a) degenerate: amino acid with more than one codon that relates to it
b) a triplet code is a set of 3 bases that codes for an amino acid
c) non overlapping means that each base is only read once
Give the definition of a mutation
A mutation is an error that occurs when dna is replicated that causes a change in the order of bases in the chain.
Explain why accurate DNA replication is important for protein synthesis
a change in the dna base order will change the order of amino acids which will affect the primary structure of the protein.
Explain the impact of a silent mutation on protein structure
No impact on protein structure
Explain the impact of a missense mutation on protein structure
a change in one amino acid as one base is replaced with another, which will have very little effect on overall protein structure.
Explain the impact of a nonsense mutation on protein structure
introduction of a stop codon in the middle of the base sequence causes protein to be shorter which means no protein is produced
Explain the impact of a frameshift mutation on protein structure
alters order of all amino acids down stream which creates a non functional protein.
Explain the impact of a frameshift mutation on protein structure
