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Learn about the processes of transcription and translation in biochemistry, including DNA-binding motifs, amino acids, initiation, elongation, termination, and gene organization.
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PRS Which of the following is not an example of a DNA-binding motif in proteins? • Beta Sheet • Helix-turn-Helix • Zinc Finger • Leu Zipper
PRS • Which amino acid contains a hydroxyl in its side chain? • Threonine • Methionine • Aspartic Acid • Phenylalanine
Transcription Transcription is the process by which RNA is producedfrom a DNA template. • Initiation • Elongation • Termination Steps involved intranscription
Transcription DNA has to separate at the position where transcription occurs. Fig. 26-3
Transcription Sense Strand 5’-…GATCCGTAGGTC…-3’ 3’-…CTAGGCATCCAG…-5’ Antisense Strand(template) Newly synthesizedRNA has the same general sequence as the sense strand; U in RNA, T in DNA 5’-…GATCCGTAGGTC…-3’ 5’----GAUCCGUAGGUC…3’ 3’-…CTAGGCATCCAG…-5’
Transcription Initiates at Promoter Sequences What is a gene? Example of E.coli Lactose Operon Organization Fig. 26-4 P: Promoter O: Operator I: Inhibitor
Structural genes follow promotersequences In E. coli, the lactose operon consists of 3 structural genes: • Beta-Galactosidase (Z) • Galactoside Permease (Y) • Thiogalactoside Transacetylase (A)
E. coli Promoter Sequences Notice how sequence is numbered! Usuallysingle purine
= sigma factor Prokaryotic RNA Polymerases The sigma factor bindsspecifically to the promoter.Core enzyme affinity to DNA ~5x10-12 M. Core enzyme Holoenzyme
Elongation: RNA Chain Growth 3’-OH group acts as a nucleophile, attacking the alpha phosphate group, with subsequent release of inorganic pyrophosphate.
DNA Supercoiling Negativesupercoiling Positivesupercoiling RNA polymerase is processive Once an RNAP has moved from the promoter, another can bind Transcription is fast: constitutive enzymes vs. inducible enzymes
Termination of Transcription Because the newly synthesized RNA is single-stranded,hairpin structures can easily form from the termination sequence.
Hairpin Structure in RNA What happens when a known terminator sequence is missing? G-C richbp region Poly-U tail
Termination: Rho Factor Helicase: RNA-RNA and RNA-DNA complex unwinding.
Transcription in Eukaryotes • RNA Polymerase I • Precursors to rRNA • RNA Polymerase II • Precursors to mRNA • RNA Polymerase III • Precursors to 5S rRNA, tRNA • Precursors to other small RNA’s
Eukaryotic Transcription Factors Transcription factors are req’d to initiate transcription,and facilitate elongation in eukaryotes. Eukaryotic Termination: Not well understood
Portion of the Genetic Code Wobble
Translation: Protein Synthesis • Messenger RNA • Template • Transfer RNA • Carries amino acids • Ribosomal RNA • Aids protein synthesis
tRNA Structures 3D 2D
tRNA’s have modified bases Be able to name, draw, recognize structures fromFigure 27-4.
Aminoacyl tRNA Synthetases Aminoacyl tRNA synthetases add aa’s to tRNA. Step 1.
Aminoacyl tRNA Synthetases Step 2. +tRNA
Sites in the Ribosome A Aminoacyl PPeptidyl EExit E P A
Chain Initiation in Translation Start Codon: AUG Methionine
Shine-Dalgarno Sequence upstream downstream
Translation: Polypeptide Synthesis PeptidylTransferaseActivity
Administrative Updates • Exam 1 on Thursday, 4-5 pm • 20 questions • Short answers and Multiple Choice • Closed-book • Calculators allowed • No cell phones, blackberries, etc. • Office Hours: M, T, R 2-4 pm