mRNA translation Flashcards
translation
RNA to protein
protein function
metabolism
organisation
structure
development
condensation reaction
peptide bond requires a lot of energy forming polymers
location of synthesis
cytoplasm in ribosomes
in 5’ to 3’ direction and in N to C direction
ribosome contain
RNA and protein - complex enzymes
function of ribosome
read mRNA and translate = amino acid sequence and assemble them to form polymer
eukaryotic ribosomes
80s containing 60s and 40s
60s
> 49 proteins and 3 rRNA
40s
> 33 proteins and 1 rRNA
prokaryotic ribosomes
70s containing 50s and 30s
50s
34 proteins and 2 rRNA
30s
21 proteins and 1 rRNA
catalysis for ribosomes
rRNA components such as ribozymes
tRNA
75 nucleotides long
adopt folded structure with internal base pairing
Ribosome structure
E-site - exiting of mRNA
P-site - transcription occurs
A-site - mRNA enters
small ribosomal subunit
has mRNA binding site
inactive proteins
when one or two bases are added in RNA
active protein
adding 3 bases in the RNA
singlet code
only gives 4 possibilities
doublet code
gives 16 (4(2)) combination
triplet code
64 combination (4(3))
quartet code
256 combination (4(4))
cracking genetic code in in vitro translation
polyu - polyphenylalanine
dinucleotide
alternating e.g. UAUAUAUA
either be UAU or AUA
trinucleotide
AAGAAGAAG
could be AAG or AGA or GAA
tetranucleotide
UAUCUAUCUAUCUAUC
could be UAU, AUC, UCU, CUA
experimenting on cracking genetic code
if have 76% U and 24% G
started at random
8 possibilities
UUU, UUG, UGU, GUU, GUG, GGU, UGG, GGG
likelihood of UUU is 0.760.760.76 = 44%
code - triplet
degenerate, non-overlapping
and no punctuation
code of life - table
universal with few exception
translation in mitochondria
uses specific ribosomes and different sets of tRNA genes
similar system as chloroplast
protein synthesis - initiation in bacteria
ribosome binding site
has shine-Dalgarno sequence complementary 3’ end of 16s rRNA
protein synthesis - initiation in eukaryotes
starts AUG from 5’ has good context ; gcc (A/G)ccAUGG
adaptor molecule
amino acids linked to tRNA
first amino acid
methionine AUG
anticodon
complementary to codon triplet on mRNA
charging of tRNA
activation of amino acids
formation of aminoacyl-tRNA
activation of amino acid
ATP + amino acid -> amoniacyl adenylate +PPi
formation of aminoacyl-tRNA
aminoacyl adenylate + tRNA -> aminoacyl-tRNA + AMP
aminoacyl-tRNA synthases
ensure fidelity of addition
addition of further amino acid - elongation
translocation
peptidyl-transferase activity
transfers next amino acid onto growing peptide by condensation reaction
translocation
movement of triplets to triplets
peptidyl-transferase activity
transferring of the next amino acid
mRNA decorating
with many ribosomes (polysomes)
move along message at different points of protein synthesis
transcription and translation in bacteria
coupled - occur at the same time
transcription and translation in eukaryotes
compartmentalised and then mRNA exported to cytoplasm
termination of protein synthesis
stop codons
completes polypeptide chain - released
ribosomal subunit after termination
dissociate and go on new round of initiation
stop codons
UAA, UAG, UGA
mutation missense
change of one base but able to get away with it
nonsense
change in base to a stop codon - producing shorter protein
silent mutation
change in base but no change in amino acid
frameshift base deletion
base deleted - affecting the rest of the chain
disrupting - streptomycin
freeze initiation complex and cause misreading of mRNA
tetracycline
prevent binding of incoming aminoacyl-tRNA
chloramphenicol
inhibits peptidyl transferase
erytromucin
binds to 50s and inhibits translocation
puromycin
mimics terminals of aminoacyl-tRNA
added onto growing chain causing premature termination
one disrupting protein synthesis effect our cells as well
puromycin
