Biology 102Biology 102

Gene Regulation and ExpressionGene Regulation and Expression

Part 2Part 2

Lecture outlineLecture outline

1.1. TranslationTranslation Review of what translation isReview of what translation is Types of RNA and their functionsTypes of RNA and their functions Overview of translationOverview of translation Details of translationDetails of translation

2.2. Information flow through cellInformation flow through cell

Review: Information FlowReview: Information FlowDNA=>mRNA=>ProteinDNA=>mRNA=>Protein

11 22

catalytic site

tRNA docking sites

Attached amino acidTransfer RNA

Smallsubunit

Ribosomecontains rRNA

Largesubunit

CC

AA

GG

AA

UU

GG

GG

AA

GG

UU

UU

AA

UU

GG

GG

mRNAmRNA

AA GG UU

Met

anticodon

Three Types of RNA (review)Three Types of RNA (review)

Translation: An OverviewTranslation: An Overview

Translation: Initiation Translation: Initiation A tRNA with an attached methionine amino acid A tRNA with an attached methionine amino acid

binds to a small ribosomal subunit, forming an binds to a small ribosomal subunit, forming an initiation complex.initiation complex.

Translation: Initiation (2)Translation: Initiation (2) The initiation complex The initiation complex

binds to end of mRNA binds to end of mRNA and travels down until it and travels down until it encounters an AUG encounters an AUG codon in the mRNA. codon in the mRNA.

The anticodon of the The anticodon of the tRNA in the initiation tRNA in the initiation complex forms base complex forms base pairs with the AUG pairs with the AUG codon.codon.

Translation: Initiation (3)Translation: Initiation (3) The large The large

ribosomal subunit ribosomal subunit binds to the small binds to the small subunit, with the subunit, with the mRNA between the mRNA between the two subunits.two subunits.

The methionine The methionine tRNA is in the first tRNA is in the first tRNA site on the tRNA site on the large subunit. large subunit.

Translation: Elongation 1Translation: Elongation 1 The second tRNA enters The second tRNA enters

the second tRNA sitethe second tRNA site

The tRNA that binds must The tRNA that binds must be able to match its be able to match its anticodon (CAA in this anticodon (CAA in this example) to base pair with example) to base pair with the codon (GUU in this the codon (GUU in this example) in the mRNA.example) in the mRNA.

tRNAs with a CAA tRNAs with a CAA anticodon carry an anticodon carry an attached valine amino attached valine amino acid, which was added to it acid, which was added to it by enzymes in the by enzymes in the cytoplasm.cytoplasm.

Translation: Elongation 2Translation: Elongation 2

The catalytic site The catalytic site on the large on the large subunit catalyzes subunit catalyzes the formation of a the formation of a peptide bond peptide bond linking the amino linking the amino acidsacids

The two amino The two amino acids are now acids are now attached to the attached to the tRNA in the second tRNA in the second binding position.binding position.

Translation:Translation:Elongation 3Elongation 3

The "empty" tRNA is The "empty" tRNA is released and the released and the ribosome moves ribosome moves down the mRNA, one down the mRNA, one codon to the right.codon to the right.

The tRNA that is The tRNA that is attached to the two attached to the two amino acids is now in amino acids is now in the first tRNA binding the first tRNA binding site and the second site and the second tRNA binding site is tRNA binding site is empty.empty.

Translation: Elongation 4Translation: Elongation 4

Another tRNA enters the Another tRNA enters the second tRNA binding site second tRNA binding site carrying its attached amino carrying its attached amino acid.acid.

The tRNA has an anticodon The tRNA has an anticodon that pairs with the codon. that pairs with the codon. (Here, the CAU mRNA codon (Here, the CAU mRNA codon pairs with a GUA tRNA pairs with a GUA tRNA anticodon.)anticodon.)

The tRNA molecule carries The tRNA molecule carries the amino acid histidine the amino acid histidine (his).(his).

Translation: Elongation 5Translation: Elongation 5 The catalytic site forms The catalytic site forms

a new peptide bond, in a new peptide bond, in this example, between this example, between the valine and the the valine and the histidine.histidine.

A three-amino acid A three-amino acid chain is now attached to chain is now attached to the tRNA in the second the tRNA in the second tRNA binding site.tRNA binding site.

The empty tRNA in the The empty tRNA in the first site is released and first site is released and the ribosome moves one the ribosome moves one codon to the right.codon to the right.

Translation:Translation:TerminationTermination

Binding of tRNAs, & Binding of tRNAs, & formation of peptide bonds formation of peptide bonds continues.continues.

Ribosome reaches STOP Ribosome reaches STOP codon (UAG).codon (UAG).

Protein "release factors" Protein "release factors" signal the ribosome to signal the ribosome to release the protein.release the protein.

The mRNA is also released The mRNA is also released and large & small subunits and large & small subunits separate.separate.

GG GG GG AA GG CC GG AA UU UU UU

CC AA AA CC AA UU CC CC UU

Methionine Glycine Valine etc.

GG GG GG AA GG TT TT CC TT GG AA

templateDNA strand

(a) complementaryDNA strand

(b) mRNA

(c) tRNA

(d) protein

amino acids

anticodons

codons

gene

etc.

etc.

etc.

etc.

GG TT CC CC CC CC AA AA AA TT CC

Review: From DNA to amino acid chainReview: From DNA to amino acid chain

AminoAminoAcidsAcids

ActiveActiveProteinProtein

Overview ofOverview ofInformation Flow within Information Flow within

the cellthe cell

InactiveInactiveProteinProtein

(Cytoplasm)(Cytoplasm)

DNADNA(Nucleus)(Nucleus)

rRNArRNA tRNAtRNA1 TranscriptionTranscription

+ Proteins+ Proteins

RibosomesRibosomestRNAtRNA

tRNA-AAtRNA-AA

mRNAmRNA

mRNAmRNA

2 TranslationTranslation

3 ModificationModification

ProductProductSubstrateSubstrate4 DegradationDegradation

The EndThe End