Proteins + Translation

- Can be very simple or very complex
- Side chain determines type of amino acid
- Side chain determines if amino acid is charged (acidic or basic) or non charged (apolair or polair)

They have a positively & negatively charged side which cancel eachother out so the net charge of the molecule = 0

Placing it in acid makes it acidic
Placing it in an alkali solution makes it basic

The pH at which the molecule will have no charge

a sequence of three nucleotides that together form a unit of genetic code in a DNA or RNA molecule. 1 codon codes for 1 amino acid

Start: AUG
Stop: UGA, UAG, UAA

When tRNA binds to a codon on the mRNA strand that doesn't exactly complement the anticodon on the tRNA.
- Allows same tRNA anticodon with same amino acid to bind to several different mRNA codons

1. Amino acid & ATP bind to aminoacyl transferase enzyme
2. Enzyme catalyses them to bind creating aminoacyl-amp complex (2 phosphates released)
3. specific uncharged tRNA binds to complex
4. Enzyme catalyses the amino acid to bind to the tRNA & the AMP to be released
5. charged tRNA released
6. Enzyme recycled

C-C-A, Amino acid will bind to the A

AGGAG, binding point on mRNA sequence for the small ribosomal subunit to bind

1. Shine Dalgarno sequence (AGGAG) on mRNA recognised by small ribosomal subunit & binds
2. tRNA with formyl Methionine amino acid binds to P site of small ribosomal subunit
3. Large ribosomal subunit binds to methionine & to small subunit
4. Next codon read by ribosome & complementary tRNA recruited into A-site

Eukaryotes: Methionine
Prokaryotes: Formyl Methionine

1. Peptide bond formed between amino acid in A & P site (condensation reaction)
2. amino acid released from tRNA in P site (deacylated) - tRNA in A site carries polypeptide chain
3. A site tRNA moves to P site, P site tRNA moves to E site & new tRNA accepted at A site
4. tRNA at E site is ejected and sent to get re-charged

Peptidyl transferase is RNA, whereas all other enzymes are proteins

Elongation carries on till it reaches a stop codon
1. Stop codon recognised by ribosome
2. Release factor (RF 1 or 2) binds to ribosome at A site
3. Peptidyl transferase removes polypeptide chain from ribosome
4. Release factor 3 bound to GDP tells RF1 (at A site) to remove itself
5. Ribosomal recycling factor moves into A site
6. EFG factor bound to GTP introduced & GTP converted to GDP to create energy for translocation
7. Translocation: Last uncharged tRNA moves to E-site, Ribosome recycling factors move to P-site, EFG + GDP move to A-site
8. Whole complex disassembles - mRNA broken down, Ribosome reused

Eukaryotes only have 1 release factor for all stop codons, prokaryotes have 2

1. Initiation factors bind to 5' cap, which connects it to Poly-A-tail forming a stable loop
2. Loop is binding site for small ribosomal subunit
3. Small ribosomal subunit scans mRNA till it reaches AUG start codon (in the kozak sequence) - it binds
4. tRNA with Methionine binds to start codon
5. Initiation factors (IF1,2,3) released - allows large ribosomal subunit to bind

Allows for multiple variations of similar protein to be made from 1 mRNA strand even though the strand is monocistronic and only has gene for 1 protein. - only some parts of gene sequence used

Possible because mRNA can have several start codons & ribosomes can start at any

Several ribosomal complexes on one mRNA strand.

mRNA scanned for mistakes. Mistakes often result in premature stop codons - UPF proteins sense if a stop codon is in the wrong place, if a mistake is found it directs mRNA to be degraded by endonucleases

- can inhibit initiation
- can cause ribosome to fall off prematurely
- can slow/stall elongation
- can cause proteins to degrade during translation
- can cause de-adenylation (poly-a-tail removal)
- can cause mRNA to degrade
- can bind to mRNA & move it to sequestration sites for storage