© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

PowerPoint Lectures forCampbell Biology: Concepts & Connections, Seventh EditionReece, Taylor, Simon, and Dickey

Chapter 10Chapter 10 Molecular Biology of the Gene

FROM DNA TO PROTEIN -

Part 2:

Translation

© 2012 Pearson Education, Inc.

Genes Determine the Production of RNA and Proteins

Gene = a DNA sequence that specifies an RNA or protein sequence

Transcription is the synthesis of RNA under the direction of DNA.

DNA mRNA (recipe for protein’s amino acid seq)

DNA tRNA

DNA rRNA

Translation is the synthesis of proteins under the direction of RNA.

© 2012 Pearson Education, Inc.

Used in translation of mRNA

Figure 10.7

DNAmolecule

Gene 1

Gene 2

Gene 3

A

Transcription

RNA

Translation Codon

Polypeptide

Aminoacid

A A C C G G C A A A A

U U G G C C G U U U U

DNA

U

10.15 Review: The flow of genetic information in the cell is DNA RNA protein

Transcription is the synthesis of RNA from a DNA template. In eukaryotic cells,

– transcription occurs in the nucleus and

– the mRNA must travel from the nucleus to the cytoplasm.

© 2012 Pearson Education, Inc.

10.15 Review: The flow of genetic information in the cell is DNA RNA protein

Translation can be divided into four steps, all of which occur in the cytoplasm:

1. amino acid attachment,

2. initiation of polypeptide synthesis,

3. elongation, and

4. termination.

© 2012 Pearson Education, Inc.

Figure 10.8A

Second base

Th

ird

bas

e

Fir

st b

ase

Transfer RNA (tRNA) match appropriate amino acid with codon in mRNA

Amino acidattachment site

Hydrogen bond

RNA polynucleotidechain

Anticodon

A simplifiedschematic of a tRNA

A tRNA molecule, showingits polynucleotide strandand hydrogen bonding

Anticodon is group of 3 nucleotides complementary to codon in mRNA

DNA: 3’-TAC-5’mRNA: 5’-AUG-3’tRNA: 3’-UAC-5’

Figure 10.11B

Enzyme

tRNA

ATP

Protein synthesis takes a lot of ATP!

Figure 10.15_2

Translation

Amino acid

Enzyme

CYTOPLASM

Amino acidattachment

2

tRNA

ATP

Anticodon

Initiation ofpolypeptide synthesis

Largeribosomalsubunit

InitiatortRNA

Start Codon Smallribosomalsubunit

mRNA

2 3

Ribosomes build proteins

Translation occurs on the surface of the ribosome.

– Ribosomes bring together mRNA and tRNA and catalyze attachment of each amino acid in protein.

© 2012 Pearson Education, Inc.

tRNA binding sites

mRNA binding site

Large subunit

Small subunit

Psite

Asite

Ribosomes have two subunits: small and large.

–Each subunit is composed of rRNA and proteins.

Details of Translation

Initiation

– Small subunit of ribosome binds mRNA

– tRNA-Met binds to first AUG codon

– Large subunit sits down - placing tRNA-Met at P site

© 2012 Pearson Education, Inc.

InitiatortRNA

mRNA

Start codon

Smallribosomalsubunit

Largeribosomalsubunit

Psite

Asite

Met

A U G

U A C

2

A U G

U A C

1

Met

Animation: Translation

Figure 10.13A

Start of genetic message

Cap

End

Tail

Remember - AUG marks start of proteinStop codon marks end!

Polypeptide

mRNA

Codon recognition

Anticodon

Aminoacid

Codons

Psite

Asite

1

Codon recognition: The anticodon of an incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon in the A site of the ribosome

Elongation

Polypeptide

mRNA

Codon recognition

Anticodon

Aminoacid

Codons

Psite

Asite

1

Peptide bond2

formation

Elongation

Peptide bond formation: The new amino acid is joined to the chain.

Polypeptide

mRNA

Codon recognition

Anticodon

Aminoacid

Codons

Psite

Asite

1

Peptide bond2

formation

Translocation3

Newpeptidebond

Elongation

Translocation: tRNA is released from the P site and the ribosome moves tRNA from the A site into the P site

Polypeptide

mRNA

Codon recognition

Anticodon

Aminoacid

Codons

Psite

Asite

1

Peptide bond2

formation

Translocation3

Newpeptidebond

Stopcodon

mRNAmovement

Elongation

Translocation: tRNA is released from the P site and the ribosome moves tRNA from the A site into the P site

Ribosome reaches a stop codon,– the completed protein is freed from the last tRNA, and

– the ribosome splits back into its separate subunits.

Termination

© 2012 Pearson Education, Inc.

Figure 10.15_3

4 Elongation

Growingpolypeptide

New peptidebond forming

Codons

mRNA

Polypeptide

Termination

Stop codon

5

Mutations can change the meaning of genes A mutation is any change in the nucleotide sequence of

DNA.

Single nucleotide substitution One nucleotide changed for another

Silent - no effect in protein sequence

Missense - amino acid change

Nonsense - stop codon introduced

© 2012 Pearson Education, Inc.

Normal hemoglobin DNA Mutant hemoglobin DNA

mRNA mRNA

Sickle-cell hemoglobinNormal hemoglobin

Glu Val

C T T

G A A

C T

G A

A

U

Mutations can change the meaning of genes

© 2012 Pearson Education, Inc.

Nucleotide Addition or Deletion (Frameshift)

Alters reading frame

Sequence of every amino acid altered after mutation.

Figure 10.16B

Normalgene

Nucleotidesubstitution

Nucleotidedeletion

Nucleotideinsertion

Inserted

Deleted

mRNAProtein Met

Met

Lys Phe

Lys Phe

Ala

Ala

Gly

Ser

A U G A A G U U U G G C G C A

G C G C AAG U U UA U G A A

Met Lys Ala HisLeu

G U UA U G A A G G C G C A U

U

Met Lys Ala HisLeu

G U UA U G A A G G CU G G C