DNA REPLICATION Flashcards
Explain the process of DNA replication?
The DNA double helix unwinds. The hydrogen bonds between the 2 polynucleotide strands are broken. This is done by DNA - Helicase which leads to 2 seperated stands with exposed bases.
New DNA monomers are attracted to the exposed bases due to comp. Base pair rulings. Each strand acts as a template and hydrogen bonds form between the comp. base pairs. the new DNA nucleotides join together. Phosphodiester bonds are reformed in the sugar - phosphate backbone. DNA polymerase join the nucleotides back together by condensation.
Semi conservative Replication means that each new double strand of DNA has one old strand and one newly synthesized strand
What is the role of DNA?
It carries genetic information which codes for proteins
How many hydrogen bonds form between A-T
2
How many hydrogen bonds form between C-G?
3
What is different about an RNA nucleotide?
The pentose sugar is Ribose instead of Deoxyribose
What is the role of RNA?
It transfers genetic code from DNA (in the nucleus) to ribosomes in the cytoplasm
Which enzyme unwinds the DNA double helix?
DNA helicase
How does DNA helicase work?
By breaking hydrogen bonds between complimentary bases
What happens to both strands once they are separated?
They act as templates
Which enzyme forms phosphodiester bonds?
DNA polymerase
What happens to the template strands?
They attract free nucleotides
How does DNA polymerase work?
It joins free nucleotides by catalysing the condensation reaction that forms phosphodiester bonds
Why is DNA replication semi-conservative?
New DNA contains one original strand and one new strand
How do the DNA strands run?
Antiparallel
How can it be proved that DNA replication is semi-conservative?
A population of bacteria are cultured in a growth medium where the only nitrogen available is heavy nitrogen (N15) so that when centrifuged only one (heavy) band is observed. The cells are then transferred to a medium with only light nitrogen (N14). After one replication the DNA strand will be an intermediate containing 1/2 (N14) and 1/2 (N15) and will appear as one band double the width. After two replications in a light nitrogen (N14) environment two intermediate bands (as seen in 1st rep|) will be observed and two light bands which contain only light nitrogen (N14)
