Translation Flashcards
LOOK AT TRANSCRIPTION NOTES
What does mRNA look like?
- looks like a series of nucleotides
How is mRNA read?
- its read as three letter words - codons
What do codons relate to?
- relate to a specific amino acid
What will AUG encode when its translated?
- it will encode methionine (Met/M) amino acid
What will AUA encode for when its translated?
- it will encode for the amino acid = isoleucine (IIe/I)
How many amino acids are encoded in an eukaryote?
- 20 amino acids are encoded in eukaryotes
In a eukaryote how many amino acid possibilities are there, how many nucleotides and how long is a codon?
- there are 64 possibilities with 4 nucleotides and a three letter codon
Can amino acids be encoded by more than one codon?
- yes some amino acids are encoded by more than one codon - redundancy not ambiguity
What are the commonly similar codons?
- same 1st and 2nd position but different 3rd position
If there is a mutation in the coding region does this lead to changes in the amino acid?
- it may not lead to any changes in the amino acid
How does one base change in a genome effect a protein?
- one base change in a a genome can have dramatic effects on a protein or none at all
Why is it important to know what a change in base pairs does - how does it affect horses?
- major role in some breeds gait
- DMRT3 (a transcription factor) - premature stop codon introduction - caused by a SNP C>A
Deletion or insertion can have an even more dramatic effect on an amino acid - why?
- this can change the reading frame
- if a base is inserted or deleted the reading frame gets shifted and what is being read is different so can change the amino acid
What recognises the three letter codons in the mRNA?
- transfer RNAs (tRNAs)
What does tRNAs lead to the production of?
- leads to the production of proteins
- but they themselves are RNAs not proteins
Describe the structure of tRNAs and what this allows them to do?
- tRNAs are RNAs folded in a cross structure
- at one end they have the amino acid that will turn into a protein
- they have an anti-codon at the other end which is the thing that recognises the code on the mRNA and is complementary so the three letter codon
What do tRNA’s create?
- create the proteins in the ribosome
Where do tRNAs encounter mRNAs?
- at ribosomes
Where are ribosomes present and what are they attached to?
- present in the cytoplasm
- also present free in the cytoplasm
- attached to ER (rough endoplasmic reticulum)
Why do cells have millions of ribosomes?
- due to all the proteins that need to be made
What are ribosomes made up of?
- rRNA subunits
- Ribosomal proteins
What are rRNA subunits?
- subunits are another non-coding RNA that function as the RNA they don’t need to turn into a protein to be functional
Eukaryotic ribosomes have two subunits - What are these?
- 60 S subunit (large ribosomal subunit) mase up of additional small ribosomal RNA’s
- 40 S subunit (small ribosomal subunit)
What are both ribosomal subunits in a eukaryote required for?
- both required for translation
40 S - is a subunit of a ribosome - what is the S?
- S - refers to the measurement, to do with hie they sediment in a centrifuge, how they spin down
How are mitochondria different in translation?
- mitochondria have their own different ribosomes and translation machinery
What do mitochondria ribosomes relate to?
- relate to bacterial origins of mitochondria but diverge
What are the subunits for eukaryotic cytosolic ribosomes?
- 60 S subunit
- 40 S subunit
What are the subunits for mitochondrial ribosomes?
- 39 S subunit
- 28 S subunit
What subunits do prokaryotic ribosomes have?
- 50 S subunit
- 30 S subunit
Why does knowing what the difference in ribosome subunits matter?
- for antibiotic treatments as they heavily target ribosomes and target translation of proteins in the bacteria
- because there is a difference between eukaryotic and prokaryotic ribosomes it allows for the drug to be specific enough and lead to very few side effects
What does the macrolide class (e.g. erythromycin) target?
- 50S ribosomal subunit activity in prokaryotes
What does the Tetracycline class (e.g. doxycycline) target?
- 30 S ribosomal subunit activity
How do antibiotics effect bacteria?
- they lead to bactericidal activities as the bacteria need proteins to stay alive so have powerful affects against bacteria
Some antibiotics lead to side effects including impairment of mitochondria why?
- this is due to the slight similarity between mitochondrial ribosomes with prokaryotes
Where is the place of translation?
- the ribosomes
What is the first thing that must happen in order for messenger RNA to be translated?
- The messenger RNA will have left the nucleus through a nuclear pore (a regulated entrance and exit) and go into the ribosome to be translated
What must bind in order to initiate translation?
- Large and small ribosomal subunits bind to the 5’ of mRNA
What is the key part if initiation of translation?
- the starting codon
What is always the starting codon for encoding a methionine - Met?
- always ATG
What is the start codon for DNA?
- ATG
What is the start codon is mRNA?
- AUG
Commonly the start codon is not just ATG its part of a Kozak sequence such as RNNATGG - why is it part of a Kozak sequence?
- the sequence is something that can be recognised by the ribosomes translation machinery to signal the start at ATG is not specific enough and could happen by chance
In a kozak sequence what does R = (or A or a G)?
= a purine
What is the structure of mRNA before the starting codon?
- there is a cap region at the start and there should be an untranslated region, a bit of nucleotides that are not translated rather they are part of the mRNA before the start codon
What are the key molecules that recognises sequences on mRNA during the imitation of translation?
- Eukaryotic initiation factor - eIF1 A
-eIF2alpha - tRNA-Met
= all present already in the small subunit
Why do vets need to know what recognises sequences on mRNA?
- aids in vaccinations and how they work
What are the four main binding sites that are critical for the elongation of a polypeptide chain?
- mRNA binding site
- A-site - Aminoacyl-tRNA
- P-site - Peptidyl-tRNA
- E-site - exit - so end of the process
(this is read right to left so A, P, E)
What is elongation?
- where you add more and more amino acids onto the chain to lead to a protein
What is the mRNA binding site?
- where the mRNA sits which is in the small ribosomal subunit
What is the specific enzyme leading to peptide synthesis and how does it do this?
- Peptidyl transferase which covalently bonds amino acids together, contained in the large ribosomal subunit
- N terminal to C terminal
Termination - how is the end of protein synthesis signalled?
- its signalled by the stop codon on the mRNA
- codons that are not leading to an amino acid being added
What are the stop codons?
- UGA
- UAA
- UAG
What is a stop codon not recognised by?
What is a stop codon recognised by instead?
- not recognised by a tRNA
- recognised by a protein that has a similar shape and charge to tRNA’s so it can still fit into A part of ribosome
How does termination of translation occur?
- Translation release factor (eRF1) bind to ribosome with a stop codon positioned in the A site
- this changes the activity of the Peptidyl transferase to stop amino acids being added
What does transferase add so the synthesized protein can be released from the ribosome?
- adds a water molecule NOT an amino acid
Once a water molecule has been added and the synthesised protein has been released from the ribosome what then happens?
- Ribosome and other molecules then dissociate and will later reassociate
You can ger multiple ribosomes working on the same mRNA at the same time - what does this vastly increase?
- increases the amount of protein output
You can have more than one ribosome reading the same mRNA so ling at its sufficiently what and what does this lead to?
- so long as its sufficiently long
- this leads to 2 proteins being produced out of one mRNA
Does translation have to be sequential?
- no translation on the next ribosome can be started before the end of the first
mRNA will degrade but can produce what?
- can produce multiple protein monomers
