Unit 3--Lecture 14 (Transcription and Translation) Flashcards
Modern Central Dogma
Replication – Transcription – Translation – Modification
Polymerization reactions
Replication, Transcription, and Translation
Repetitive processes
—-build polymers of nucleotides or amino acids
Three Major Steps:
Initiation
—-bind polymerizing machine, first monomer to template
—-DNA polymerase, RNA polymerase, ribosome
Elongation
—-read template, add next monomer
—-DNA, RNA, Protein
Termination
—-release machinery and completed product
Replication
Template: DNA
Product: DNA
Monomers: dA, dC, dG, dT
Enzyme: DNA polymerase III
Direction: 5’ –> 3’
Start: oriC
End: Ter
Transcription
Template: DNA
Product: mRNA
Monomers: A, C, G, U
Enzyme: RNA polymerase
Direction: 5’ –> 3’
Start: Promoter
End: Terminator
Translation
Template: mRNA
Product: Protein
Monomers: Amino Acids (A, C, D, E, F, G, H, I, K, L, M, N, P, R, S, T, V, W, Y)
Enzyme: Ribosome
Direction: N –> C
Start: Shine Dalgarno
End: Stop Codon
RNA Polymerase
RNA Polymerase is a large molecular machine
4 proteins in one complex
—-alpha (a)
—-beta (B)
—-beta prime (B’)
—-omega (w)
Binds DNA and reads sequence
—-binds to sigma factor
Polymerizes RNA
Sigma Factor
Where RNA polymerase binds to DNA
Smaller protein
Guides RNA polymerase to target DNA sequence
—-promoter
Sigma-32 RpoH
Heat shock response
Transcription Elongation
Core polymerase adds RNA to 3’ end
Added base is complementary to template strand
mRNA has same sequence as non-template
Transcription Termination
Rho-dependent Termination
—-Rho factor binds to mRNA
—-slides along mRNA up to the polymerase
—-breaks polymerase, mRNA off of DNA
Rho-independent Termination
—-series of U residues downstream of pause site
—-DNA-RNA UA base pairs are least stable
—-mRNA breaks off of DNA, polymerase released
Operon Structure
Eukaryotes are monocystronic
Bacteria are polycystronic
Promoter–5’ Leader–Gene 1–Gene 2–Gene 3–Transcription Terminator
Types of RNA
mRNA: messenger codes for peptides
rRNA: ribosomal structure and function
tRNA: transfers amino acids to ribosome
snRNA: small nuclear (splicing of message)
miRNA: microRNAs (regulate expression)
CRISPR: a prokaryotic “immune system”
Genetic Code
Consists of nucleotide triplets called codons
64 possible codons:
—-61 specify amino acids (includes start codon)
—-3 are stop codons
The code is degenerate or redundant
—-multiple codons can encode the same amino acid
tRNA
Set of tRNAs bind individual amino acid
tRNAs have a specific shape and a 3-base anticodon
—-base pair to codon in mRNA
Proteins add amino acid to tRNA
—-aminoacyl-tRNA transferase
Ribosome Active Site
The 70S ribosome harbors 3 binding sites for tRNA:
A (acceptor) site: binds incoming aminoacyl-tRNA
P (peptidyl-tRNA) site: harbors the tRNA with the growing polypeptide chain
E (exit) site: binds a tRNA recently stripped of its polypeptide
