Wk4 Storage And Retrieval Of Genetic Information Flashcards
What is the central dogma of molecular biology ?
Passage of genetic information - 1 way process
Why is dna stored in eukaryotic nucleus?
Stores sequence for proteins to be expresssed
What is the only thing to reverse transcription?
Reverse transcriptase (retrovirus)
DNA vs RNA
Both have phosphate backbones DNA double-stranded high molecular weight Uses T Stable
RNA
single-stranded - intra-molecular base pairing (RNA can form hydrogen bonds)
heterogeneous in size
Has an OH group at ribose C2 that DNA doesn’t have
Uses U
Unstable
DNA summary
- Bases pair because of hydrogen bonding
- There is room for 1 purine + 1 pyrimidine inside the helix
- The base sequence of one strand determines the sequence of the other strand
What makes up the genome?
Genes = <5%
- ‘Promoter’ & ‘enhancer’ elements
- 5’ (upstream) and 3’ (downstream) of gene
- Typically several per gene
- Can be ~450kB from gene
What is non-coding DNA?
Even genes are broken up by stretches of non-coding DNA
Exons = coding DNA (they are ‘Expressed’)
Introns = non-coding DNA (they are ‘intervening’)
Introns removed from primary RNA by ‘splicing’ machinery
What are repeated elements?
Common
Derived from virus
- Most common repeats are LINE & SINE families
- Vary in size
- Represent ~25% of our DNA
- Can be used to detect polymorphisms (‘DNA fingerprinting’)
What is DNA replication?
Turning it into 2 copies
What is semi-conservative replication?
DNA helix that contains one strand from helix it was copied from
What are the building blocks of DNA synthesis?
Deoxynucleoside triphosphates
What direction does DNA synthesis occur?
5’ to 3’
DNA polymerase
Proceeds in a 5’ to 3’ direction
Adds 1000 bases /second to the chain
Require dNTPs
Must have a template and an RNA primer
What does DNA polymerase do?
- DNA is pulled apart and copies of both stands made
- Top stand = leading strands
- DNA polymerase keeps on a 5-3 point direction, copying leading strand continuously
- Logging strand leaves a gap that must be filled but DNA polymerase cannot go backwards
- So instead it binds in different points in gaps - making little DNA fragments (Okazaki fragments) to form a continuous DNA strand
DNA to RNA transcription
- RNA synthesis needs DNA template
- building blocks: nucleoside triphosphates
- RNA is synthesised in a 5 to 3 direction
- only one strand is copied
- RNA polymerase adds 50 bases per second
What is the spliceosome?
The primary RNA transcript binds proteins involved in RNA processing
Local DNA melting produces ~30bp bubble
As the bubble moves along the DNA, the RNA chain extends
What are ribosomes?
Complexed that assemble strings of amino acids (proteins) as instructed by the mRNA sequence
What is tRNA?
An adaptor molecule
- 3 hairpin stem loop structures
- stabilised by base pairing
- distinctive functional region
- responsible for recognising sequence on mRNA and recognising specific amino acid
- structure reinforced by hydrogen bonds
The genetic code
- read in groups of 3 bases
- read in a 5’ to 3’ direction
- 3 possible reading frames
- each amino acid is coded for by a codon
- some amino acids have more than one codon
- some have only one codon
- 3 codons do not encode amino acids