Making Proteins: Synthesis
TRANSCRIPTION
- DNA in nucleus
- RNA polymerase binds to promoter region on sense strand of DNA
- DNA strands unwind ahead of RNA polymerase & separate (break H bonds)
- [template is "antisense" strand]
- [RNA nucleotides float into position and match with DNA complements on the template]
- [RNA polmerase binds RNA nucleotides to each other in 5' -> 3' direction]
- [RNA stops building at end of gene sequence when it reaches "terminator"]
- RNA processing (to produce mature RNA):
- Introns are cut OUT of RNA sequence....
- Exons are re-attached together
- Cap and Tail are added to RNA
- mRNA released into cytoplasm from nucleus
TRANSLATION
general overview
- Translation include initiation, elongation, termination
- mRNA translated in 5' --> 3' direction
- tRNA have an anticodon which is complementary to codon on mRNA -AND- they carry cooresponding amino acid.
- in cytoplasm, special enzymes attach correct amino acid to each tRNA
- tRNA with appropriate amino acid attached is called "activated tRNA"
- mRNA released into cytoplasm from nucleus
Initiation
- initiating tRNA (carrying methionine) binds to small ribosomal subunit
- Small ribosomal subunit/tRNA complex binds to mRNA
- ... complex moves along mRNA until it reaches start codon (AUG)
- large ribosomal subunit binds to small ribosomal subunit / mRNA /tRNA complex
- Ribosome has 2 working sites: P site and A site ; tRNA is in P-site
- 2nd tRNA with antiocodon complementary to second codon, fits into A site
Elongation
[occurs in 5' --> 3' direction]
- next tRNA complementary the next codon (and carries the amino acid for that codon) fits into the A site
- ribosome catalyzes peptide bond formation between two amino acids
- this requires energy in form of GTP
- SIMULTANEOUSLY - the ribosome/mRNA shift so that the second tRNA shifts to P site.
- SIMULTANEOUSLY - the first tRNA shifted into E site
- SIMULTANEOUSLY - tRNA in E site releases the first amino acid (now bonded to amino acid on tRNA in the P site)
- SIMULTANEOUSLY - tRNA in E site is released from mRNA and leaves to recharge in cytoplasm
- SIMULTANEOUSLY - the polypeptide coils up to form 3-D shape
- [SIMULTANEOUSLY - other ribosomes can be decoding the SAME mRNA!!!!]
- When STOP codon enters site 2, ribosome splits into its two subunits and drifts away.
- ie. the come in to riboStart codon of mRNA attracts anti-codon of tRNA
Termination
- next asdf
- as
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