Central Dogma of Molecular Biology Flashcards
process names of
DNA -> DNA
DNA -> RNA
RNA -> Protein
replication
transcription
translation
what is DNA made from
2 polynucleotide chains
strands held together by hydrogen bonds
sugar phosphate backbone
What is a nucleotide composed of
5 carbon sugar
phosphate group
N containing base (eg A, G, T, C, U)
What is required in DNA replication
dNTPs
Template strand
Primer
Enzyme DNA polymerase catalyses reaction adding corresponding dNTP to the chain.
What is semi conservative replication
DNA strands come apart and each serve as a template for replication
Parts of the replication fork
- bubble opens
- Leading strand
- lagging strand
what happens at the leading strand
DNA replication occurs in the 5’ to 3’ direction, widening the fork in the process
what happens at the lagging strand
replication occurs in 5’ to 3’ direction, running antiparallel to leading strand. Therefore have to keep landing primers to continue replication as fork opens.
Okazaki fragments then have to be stitched together by ligase
what happens to ensure there aren’t any mistakes in replication
Mismatch repair
a specific protein scans along checking for bulges where there is a mismatch. When identified it cuts it out and a new polymerase will later fill the gap
Difference between DNA replication in the body and PCR (polymerase chain reaction)
- different polymerase - Taq polymerase
used as it can withstand high temperatures required to separate strands. Used so don’t have to add more polymerase every cycle of replication
Why does the cell use RNA instead of DNA in protein synthesis
The intermediary RNA ensures that the DNA is protected in the nucleus
Differences between RNA and DNA
- shorter, single strand
- U instead of T
What is the promoter
How does it work
The region of DNA where transcription is initiated
Sigma factor with the RNA polymerase identifies the promotor and binds to it. When reaches terminator, it falls off and signals both polymerase and RNA to be released
Steps of transcription
- RNA polymerase binds to promotor
- separates strands so ~9 are exposed
- matching rNTP covalently bonded by dehydration reaction
- moves along and repeats until reaches terminator
Where does the energy for DNA replication and RNA transcription come from
The breaking off of 2 of the phosphates from the triphosphate group in the nucleotides, forming a phosphodiester bond between the 5’ and 3’ carbon atoms
what is a phosphodiester bond
chemical bond between 2 nucleotides in a polynucleotide
what is a codon
triplet code of genes that encode for a specific amino acid
redundancy = multiple codons code for same AA (third different)
what codon starts translation and why
AUG
so that the same reading frame is set every time, otherwise there would be 3 options for each mRNA which would encode different AAs
what is a tRNA and what does it do
transfer RNA
binds to both AA and codon on mRNA by comp.base pairing with its anticodon
what organelle is involved in translation
ribosome
describe process of translation
- starts at AUG codon
- tRNA comp.base pairs anticodons in A-site of ribosome
- new AA covalently bond to form chain
- moves along mRNA repeating
- terminator protein binds and hydrolysis reaction releases protein
How are eukaryote and prokaryote DNA different
- linear chromosomes vs circular
What’s the problem with eukaryote having long linear chromosomes
What’s the solution
A primer cannot be landed at the end of the DNA strand in replication, leaving the new stand too short.
Telomeres of specific sequence are added to the end of every strand to keep it the same length
When does RNA -> DNA occur
In viruses that use reverse transcriptase once inside a host cell
Retroviruses can insert DNA into host
