7.3 translation Flashcards
ribosome remains free and unattached IF
the protein is targeted for INTRACELLULAR use within the CYTOSOL
what do bound ribosomes synthesize proteins for
secretion or use in lysosomes (enzyme-containing organelle)
ribosome synthesizing protein targeted for secretion is…
BOUND to the ER
protein destination after translation is determined by…
presence or absence of an INITIAL SIGNAL SEQUENCE
what does the presecne of an initial signal sequence do
recruitment of a SIGNAL RECOGNITION PARTICLE (SRP) that halts translation
what happens to a SRP-ribosome complex in translation
it docks at a receptor on the ER membrane – forms rough ER
tranlation is RE-INITIATED, polypeptide chain cont growing
after translation is reinitiated wher does the polypeptide chain grow like whats happening there babe where does the thing go
grows via a transport channel into lumen of the ER
- synth protein transported via vesicle to Golgi complex (secretion) or the lysosome
- proteins for membrane fixation – embedded into ER membrane
what happens when the polypeptide has been fully synthesized within the lumen of the ER
signal sequence is cleaved – SRP recycled
how is translation initiated
assembly of 3 components: mRNA, tRNA, ribosome
define polysome / polyribosome
grp of 2 or more ribosomes translating an mRNA sequence simultaneously (beads on a string)
whats up with polysomes in prokaryotes
polysomes may form while mRNA is still being transcribed from the DNA template
they really goin in for it huh not even a break. anyways eukaryotes have the nucleus and cytoplasm thing and the whole nuclear membrane cock block so they cant be this efficient :(
which end of the polysome cluster (lotsa ribosomes on the same mRNA strand) has longer polypeptide chains
3’ end has LONGER than 5’
idk why lol
what are ribosomes made out of + structure
protein (stability) and ribosomal RNA (catalytic activity)
- a large and small subunit
small = mRNA binding site
large = 3 tRNA binding sites – aminoacyl (A), peptidyl (P), exit (E) APE
ribosomes in prokaryotes vs eukaryotes
70S vs 80S
structure of tRNA molecules (strucutre + 4 regions)
TRANSFER RNA
- fold into cloverleaf strcutre, 4 regions
1. acceptor stem (carries AA)
2. anticodon (complementary with the mRNA codon)
3. T arm – associates with ribosome
4. D arm – associates with tRNA activating enzyme
4 stages of translation
- initiation
- elongation
- translocation
- termination
initaition of translation 3 steps (got the big and samll bits of the ribosoe yeah)
- small ribosomal subunit binds to the 5’-end of the mRNA and moves along it until it reaches the start codon (AUG)
- The appropriate tRNA molecule binds to codon via its anticodon
- large ribosomal subunit aligns itself to the tRNA molecule at the P site (peptidyl) and forms a complex with the small subunit
elongation part 2 of translation steps 3
- A second tRNA molecule pairs with the next codon in the ribosomal A site
- The amino acid in the P site is covalently attached via a peptide bond (condensation reaction) to the amino acid in the A site
- The tRNA in the P site is now deacylated (no amino acid), while the tRNA in the A site carries the peptide chain
translocation steps in translation 3
- The ribosome moves along the mRNA strand by one codon position (in a 5’ → 3’ direction)
- The deacylated tRNA moves into the E site and is released, while the tRNA carrying the peptide chain moves to the P site
- Another tRNA molecules attaches to the next codon in the now unoccupied A site and the process is repeated
termination of translation
- disassembly of the components
- release of a polypeptide chain
elongation and translocation cont repeating until stop codon
steps to termination of translation
- Ribosome reaches the stop codon
- A Release factor is recruited – signals for translation to stop
- The polypeptide is released, ribosome disassembles back into its two independent subunits
translation in eukaryotes vs prokaryotes
e
- ribosomes seperated from genetic mat. by nucleus
- aft transcription, mRNA transcrived needs to be transported from nucleus via nuclear pores
- requires modification to RNA (capping, polyadenylation, splicing)
p
- lack compartmentalised structures
- being translating RNA while still being transcribed
- possible bc both transcription and translation occur in 5’ –> 3’ direction
e for eukaryotes and p for prokaryotes. e p ? eepy im eepy hi eep y im eepy
tRNA activating enzyme does what
catalyses tRNA molecules binding w specific AA in cytoplasm – each AA recog by specific enzyme
2 steps to binding AA to tRNA receptor stem
- The enzyme binds ATP!!! to the amino acid to form an amino acid–AMP complex linked by a high energy bond (PP released)
- The amino acid is then coupled to tRNA and the AMP is released – the tRNA molecule is now “charged” and ready for use
function of phosphorylation of tRNA
ATP creates high energy bond, transferred to tRNA molecule
- stored energy provides majority of energy req for peptide bond formation during translation
what is the primary structure of a polypeptide
- order/sequence of AA that compormise the pp chain
- formed by COVALENT PEPTIDE BONDS
- controls all subsequent levels of protein organisation (Determines nature of R grps)
secondary structure of polypeptides
- pp folds in repeating arrangement – forms alpha helices and beta pleated sheets (Wtf????)
- hydrogen bonding btw non adjacent AAs (provides mechanical stability)
- those not in A or B are just random coils
tertiary structure of polypeptide
- pp chain coils, forms complex molecular shape
- caused by interactionbetw R grps (H-bonds, disulfide bridges, ionic bonds etc)
- relative AA positions impt
- impt for function of protein
quaternary structure of polypeptide/protein
Multiple polypeptides or prosthetic groups (inorganic compounds) may interact to form a single, larger, biologically active protein
- incl prostetic grp = conjugated protein (eg haemoglobin)
- held tgt by variety of bonds
what is a conjugated protein
a protein with a quaternary structure containing a prosthetic group
5 ways protein expression is controlled
- transcriptional control (trans factors, reg proteins)
- RNA processing control (reg. formation of mature mRNA, CPS)
- RNA transport control (out of the nucleus)
- translational control (inhibiting ribosomal subunit assembly, or targeting mRNA for degradation)
- protein activity control (expression patterns affected by rate of protein degradation)
