Sesh 8: Gene Expression Flashcards
DNA to mRNA is _____________, and mRNA to protein is ____________.
- Transcription
2. Translation
Transcription occurs in the _______ and translation occurs in the _________.
- Nucleus
2. Cytoplasm
What is a gene?
A stretch of DNA at a specific chromosomal locus, coding for a specific protein.
What direction is a polypeptide elongated in?
N to C terminus.
What are the 3 stages of DNA replication, transcription and translation?
- Initiation
- Elongation
- Termination
What 3 general components are needed to make DNA, RNA and proteins?
- Enzymes
- Activated substrates
- A template
What is a TATA BOX?
A sequence within the promoter sequence of a gene that is recognised by transcription factors, to set the direction of transcription.
What do transcription factors do?
Bind the promoter sequence of a gene, to set the direction of transcription, and recruit RNA polymerase.
RNA polymerase binds 1 nucleotide __________ of where transcription begins.
Upstream.
Pre-mRNA is synthesised from the _________ strand, and made in the __ to __ direction.
- Template/ non-coding
- 5’
- 3’
RNA polymerase reads the template DNA strand in the __ to __ direction.
- 3’
- 5’
To make mRNA in 5’ to 3’ direction.
What 3 types of RNA processing occur?
- Capping
- Polyadenylation
- Splicing
What is RNA capping?
A 7-methylguanosine cap is added to the 5’ end of pre-mRNA via a 5’ to 5’ triphosphate link.
Protects against degradation and has a role in translation.
How does polyadenylation of pre-mRNA occur?
- Endonuclease recognises a specific polyA site, which then cleaves the RNA- ‘falls off’ the DNA
- PolyA polymerase then adds ~200 adenylate residues to the 3’ end
What subunits make up a eukaryotic ribosome?
40S+60S–> 80S ribosome
What is the most abundant type of RNA in the body?
Ribosomal RNA (rRNA)=~80%
What is the adaptor molecule for translation?
tRNA
What is meant by the degenerate nature of the genetic code?
Some amino acids are coded for by >1 triplet code….due to ‘wobble’ base.
What is the start/initiation codon, and what amino acid does it code for?
AUG codes for Methionine. At N-terminus of all proteins unless cleaved off after translation.
What are tRNA stem loops?
Loops formed by H bonds between anti-parallel complementary sequences, from a single-stranded structure.
Which part of the tRNA does an amino acid bind to?
The 3’OH end.
A charged tRNA is referred to as an…….?
Aminoacyl tRNA
A tRNA anticodon of 5’CAU would recognise the mRNA codon_____?
5’AUG- Met
Anticodon needs to be in 3’ to 5’ =UAC=complementary to AUG.
How is translation initiated?
A ‘special’ methionyl tRNA recognises 5’ cap of mRNA & moves along until reaches start codon (AUG). Ribosome 40S subunit is also associated.
Once the tRNA anticodon has recognised this, the 60S ribosome subunit associates to form a fully functional ribosome.
Which ribosome site will the ‘special’ methionyl tRNA move in to?
The P site. Another charged tRNA will then move into the adjacent A site.
What enzyme moves an amino acid from the ribosome P site to on top of an amino acid in the A site, allowing the ribosome to translocate?
Peptidyl transferase.
tRNA in P site becomes uncharged, is released, so ribosome can move along.
The final tRNA to occupy the P site during translation is called………….?
Peptidyl tRNA (has peptide on top).
What breaks the bond between peptidyl tRNA and the polypeptide?
Water and another tRNA.
Allows tRNA, ribosome and polypeptide to be released.
