Genetic code and transcription Flashcards
What are the 4 nucleotides that make up amino acids?
Adenine (A), Cytosine (C), Guanine (G) and Thymine (T)
What is a reading frame?
A sequence of codons starting with ATG (methionine)
What is a frame-shift mutation?
Code shifts by one letter causing the wrong amino acid to be read
What does the genetic code not apply to?
Chromosomes and mitochondria in some eukaryotes
Gene expression
Information stored in a gene is made into a functional product
Gene regulation
The ability of a cell to control the expression of each gene
What is transcription?
DNA is copied into RNA using RNA polymerase (enzyme) to go from a gene to mRNA
What is DNA separated into?
Coding strand and template strand
Coding strand
Contains codons
Template strand
Copied by RNA polymerase
What are the 3 classes of RNA transcriptions in eukaryotes?
- Ribosomal RNA (rRNA)
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
What is the promoter?
Encourages RNA polymerase to synthesise to DNA
Non-coding DNA
Junk RNA
Coding DNA
Important RNA (information)
Why is transcription termination needed?
Because RNA can become elongated causing problems for RNA synthesising with DNA
How is RNA synthesis prevented in prokaryotes?
The RNA forms a hairpin loop and a uracil poly-tail
How else can RNA synthesis be prevented?
A protein termination factor (Rho) in the cytosol
How is RNA synthesis prevented in eukaryotes?
Transcripts are cleaved and poly-tail is added in the nucleus and cytosol
What is post-transcriptional gene silencing (PTGS)?
Triggers production of small RNA fragments of gene to be suppressed and induces mechanism to destroy complimentary RNA.
What are transgenes?
Genes which are artificially introduced into the genome of another organism
What is the purpose of transfer RNA (tRNA)?
Carries specific amino acids and decodes codons
Structure of tRNA
4 arms (only 2 are important): acceptor arm (attaches to amino acid) and anticodon arm (carries 3 nucleotides)
Eukaryotic translation
Requires mRNAs, ribosomes and tRNAs
Why are ribosomes needed in translation?
tRNAs can’t make proteins without them
What is a Svedberg (S)?
A unit of weight
What is the eukaryotic mRNA structure?
5’cap, 5’ UTR, coding region, 3’ UTR and a poly tail
What is the UTR?
The untranslated region where RNA bases pair up
What occurs in the translocation phase?
Charged tRNAs enter at the A site, then shift to the P site, and then finally to the E site for removal
What occurs in the termination phase?
Translation is ended via the release of mRNA from the ribosome
Control of translation
Rapid method of altering protein levels in the cell
