notes- February 6

II. Overview of translation
a. Initiation- steps where mRNA, 1st tRNA, ribosome connect
b. Elongation-repeated steps where tRNA with a.a.s are lined up with mRNA codons. a.a.s linked into a chain
c. Termination- Ribosome detached from mRNA, releases new polypeptide (protein) - a chain of amino acids chained together

III. Initiation (fig. 10.21 in textbook)
a. prokaryotes - small subunit of ribosome (rRNA) base-pairs with mRNA sequence (Shine-Dalgarno sequence). once mRNA base pairs with rRNA at Shine-Dalgarno sequence, tRNA formylmethionine binds to small subunit of ribisome recuits large subunit of ribosome.

i. Shine-Dalgarno sequence- sequence that rRNA base pair with.
ii. open reading frames - prokaryotes transcribe ORFs transcript of lots of different genes (usually related function ) transcript then translated into different proteins ( Polycisttronic mRNA)

1.Polycistronic mRNA- genes on polycistronic mRNA transcript because they each have a start codon (AUG) that is close and slightly downstream of a shine-dalgarno sequence.
- mRNA that contains many different genes that can be translated differently
ex: arabinose operon and GFP

b. Eukaryotes = have a nucleus, DNA is in nucleus so transcribed mRNA is in nucleus, must be shipped out to be transcribed or translated.
i. shipping of mRNA out of nucleus via nuclear pores - mRNA shipped out of nucleus to cytoplasm
ii. 5' methylated guanine cap - EIF4 family of elongation factors bind to cap, recruit ribosome small subunit.
iii. mRNA scanning - small ribosome subunit moves down mRNA in 3' direction until reaches AUG
look at fig. 10.21 for diagram

IV. Elongation = when small subunit of ribosome reaches AUG, small ribosome subunit binds charged methiomine and RNA to that codon complementary pairing between mRNA codon and tRNA anticodon.
-tRNA, small ribosome subunit AUG interaction, then recruitment of large ribosome subunits
a. Elongation factors - EF1 alpha and EF2 active when bound to GTP. elongation factors use energy from breaking GTP to GDP + P to fuel bond formation in polypeptide chain.
b. ribosome large subunit sites - large subunit of ribosome recruited - met- tRNA in peptidyl site.
when bond formed between amino acids in P and A sites, tRNA is free o diffuse into cytoplasm where aminoacyl - tRNA synthase will replace amino acid. then amino acid from P site moves to E site amino acid in A site moves to P site and ribosome moves in 3' direction 1 codon.
fig. 10.24 shows a diagram of this

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