12 - Gene Expression Flashcards
What are the three stages of making a polynucleotide/polypeptide and what things are needed?
- Initiation
- Elongation
- Termination
- Enzyme
- Activated substrates
- Template
What are the three things needed to make DNA?
- DNA Polymerase
- dNTP’s
- Template of DNA
What are the three things needed to make RNA?
- RNA Polymerase
- NTPs
- Template of DNA
What are the three things needed to make a polypeptide?
- Ribosome
- Activated amino acids
- mRNA template
In DNA replication, what terminates replication?
When the replication forks meet
How does transcription occur?
- RNA polymerase binds to a promotor region at the start of a gene with the aid of transcription factors
- DNA double helix separated and the 3’ to 5’ acts as a template strand, whilst the 5’ to 3’ which the promoter is on, is the coding strand
- RNA nucleotides match up with complementary bases on DNA and RNA polymerase joins them together in 5’ to 3’ direction
- Termination sequence reached and pre-mRNA released, with same code as 5’ to 3’
What is the promoter sequence?
- Sequence on DNA that is recognised by a transcription factor and marks the start of transcription
- TATAAA box upstream or at 5’ of gene
What does upstream and downstream mean?
Downstream is the direction of the gene (+1)
Upstream is behind the gene (-1)
THERE IS NO ZERO
How is pre-mRNA modified?
- Capping (5’)
- Tailing (3’)
- Splicing
What is the point of capping and tailing?
- Prevent degradation by polynucleases
- Increase stability of mRNA
- 5’ to 5’ Cap with methylguanine
- Poly A tail at 3’ using polyA polymerase
Why is mRNA a bit longer than it should be before the polyA tail is added?
- Transcription termination sequence is further down than polyadenylation sequence
- Endonucleases cleave off chain after polyadenylation sequence before polyA polymerase adds polyA tail
What is splicing?
- Removing introns from pre-mRNA by splicing at specific intron sites
- Stick exons together
- If mutation in 5’ and 3’ ends of intron sites some introns may not be spliced out
What is a polyribosome/polysome?
- Lots of ribosomes on a single mRNA all making individual proteins
What are ribosomes made up of?
Why is their more than one type of RNA polymerase?
- 3 types to make different types of RNA
- e.g polymerase II makes mRNA, I makes rRNA
Why are there so many different types of mRNA?
- pre-mRNA can be spliced in lots of different ways
- 20,000 genes and different mRNA for each gene
What are the three characteristics of the genetic code?
- Degenerate
- Non-overlapping
- Triplet
What are the initiation and termination sequences for translation?
Start codon (Met) - AUG
Stop codon (no aa) - UAA, UAG, UGA
How many nucleotides long is a polypeptide with 300 amino acids?
300 x 3 = 900
900 + 3 = 903
ADD THREE FOR THE STOP CODON AS THIS DOESNT CODE FOR AN AA
What is the structure of tRNA?
- Single stranded
- Clover
- Stem loops
- Anticodon
- A at 3’ end that amino acids bind to
What is the relevance of the anticodon?
- Recognises codon on mRNA
- Amino acid bound to tRNA has complementary sequence to 3’ to 5’ anticodon
How does one tRNA molecule recognise multiple codons?
- Wobble position
- Contains an I at the 5’ end of the anticodon, and I can bind to C, A and U
How are amino acids for translation activated?
LOTS OF ENZYMES NEEDED FOR TRANSLATION
What are the stages of translation?
1. Initiation:
- Methionyl tRNA recognises 5’ cap
- Small ribosome subunit binds to cap using GTP
- When AUG reached, large ribosome subunit attaches using ATP and ready to translate
2. Elongation:
- AUG moved from A site to P site
- Ribosome reads next codon in A site and tRNA with complementary anticodon enters
- Peptide bond forms between two amino acids by peptidyl transferase
- Translocation of ribosome so first tRNA molecule leaves and another tRNA enters
- Continues
3. Termination
- Stop codon enters A site
- Release factors enter P-site and cause enzymes forming peptide bonds to add water to amino-acyl tRNA causing release of peptide and tRNA
