Unit 3B Translation RNA -> protein Flashcards
if four letters how many possible combinations?
what can be concluded from that?
4^3 = 64 possible codons but 20 AA
we have more possible codes than AA either some aren’t used or some are specified by more than one code
what is true for most amino acids
what is genetic code
more than one triplet code specifies for them, for AA with multiple codons, third base is most variable
genetic code is almost universal, same codons assigned to same AA and the same START and STOP signals in vast majority of living things (exceptions some fungi, and protoza, mitochondria)
What are exceptions in genetic code
common exception to assign some of the three STOP codons to AA
excpetions in mitochondria: mitch from animal cell use UGA to encode tryptophan (rather than STOP) - has implications for transferring of mitochondrial genes to nuclear genome
How does mRNA codon specify an AA?
Francis Crick proposed that adapter molecule help AA in place while interacting directly and specifically with a codon in mRNA
tRNA + AA = aminoacyl tRNA (the adapter)
loaded tRNA covalently bonded to a particular site to the tRNA
each AA has its own aminoacyl tRNA
how does redundancy relate to the specificity of tRNAs
some AA have more than one tRNA
some tRNA need accurate base-pairing at only the first two bases of a codon (can tolerate mismatching)
wobble hypothesis
anticodon of tRNAs can still bind successfully to codon whose third position requires a nonstandard base pairing
how does tRNA attach with AA
enzymes work by bringing reactants close together so that rxn is more likely to happen
ATP bound to active site of enzyme, going to use hydrolysis to drive building reaction
combined action of tRNA and synthetases ensures that each mRNA codon is matched to correct AA
anticodon loop at bottom also has to match
at this point charging or loading tRNA
txt 733
What are ribosomes made of
macromolecular structures composed of RNA and proteins
large subunit is 3 RNA bunch of protein, small subunit 1 RNA bunch of protein
main jobs or large and small ribosomes
small matching codons and anticodons
large creating peptide bonds
translation begins and ends
begins when anticodon of charged tRNA binds to codon in mRNA
ends when AA forms ppt bond with growing chain
A, P, E sites
A site - acceptor site for aminoacyl tRNA
P site - where pepride bond forms that adds AA to growing polypeptide chain
E site - where tRNAs no longer bound to an AA exit the ribosome
= once translation ongoing, 2 of the three binding sites within ribosome are occupied bu a tRNA at any given time
Ribosomal machine start
what starts translation
translation always begins with AUG and gets recognized by initiator tRNA always combined with methianine
find the cap, initiator going to scan until AUG
small ribosomal subunit joins attracts large ribosomal subunit
now joined together looks like regular translation
if its a fit 1st ppt bond forms
Ribosomal machine end
what terminates translation
presence of STOP codon in mRNA
STOP codon binds release factor and alters catalytic activity causing addition of H2O instead of forming ppt bond creating end of pptide
frees carboxyl
Ribosome of enzyme
is catalytic activity provided by its RNA or protein components
A, P, E sites are primarily rRNA
catalytic sites where ppt bond is formed between P and A sites in large subunits formed entirely by RNA, not protein
ribosomal proteins are mostly on surface, helping create and maintain shape of RNA core
Ribozyme
RNA molecule whith a well defined tertiary structure that enables it to catalyze a chemical reaction
