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Chapter 10
Molecular Biology of the Gene
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
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
Used in translation of mRNA
 Translation is the synthesis of proteins under the
direction of RNA.
© 2012 Pearson Education, Inc.
Figure 10.7
DNA
molecule
Gene 1
Gene 2
Gene 3
DNA
A A A C C G G C A A A A
Transcription
RNA
Translation
U U
U G G C
Codon
Polypeptide
Amino
acid
C G U
U
U 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
Third base
First base
Second base
Transfer RNA (tRNA) match appropriate amino
acid with codon in mRNA
Amino acid
attachment site
Anticodon is group of
3 nucleotides
complementary to
codon in mRNA
Hydrogen bond
RNA polynucleotide
chain
Anticodon
A tRNA molecule, showing
its polynucleotide strand
and hydrogen bonding
A simplified
schematic of a tRNA
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
CYTOPLASM
Translation
Amino acid
Amino acid
attachment
2
Enzyme
tRNA
ATP
Anticodon
Initiator
tRNA
Large
ribosomal
subunit
Start Codon
mRNA
Small
ribosomal
subunit
Initiation of
polypeptide synthesis
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.
tRNA binding sites
Ribosomes have two
subunits: small and
large.
–Each subunit is
composed of rRNA and
proteins.
Large
subunit
P A
site site
Small
subunit
mRNA binding site
© 2012 Pearson Education, Inc.
Details of Translation
 Initiation
Animation: Translation
– Small subunit of ribosome binds mRNA
– tRNA-Met binds to first AUG codon
– Large subunit sits down - placing tRNA-Met at P site
Large
ribosomal
subunit
Initiator
tRNA
U A C
A U G
U A C
A U G
Start codon
1
© 2012 Pearson Education, Inc.
A
site
P
site
mRNA
Small
ribosomal
subunit
2
Figure 10.13A
Start of genetic message
Cap
Remember - AUG marks
start of protein
Stop codon marks end!
End
Tail
Elongation
Polypeptide
P
site
mRNA
Amino
acid
A
site
Anticodon
Codons
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
Codon recognition
Elongation
Polypeptide
P
site
mRNA
Amino
acid
A
site
Anticodon
Codons
1
Codon recognition
Peptide bond formation: The new
amino acid is joined to the chain.
2
Peptide bond
formation
Elongation
Polypeptide
P
site
mRNA
Amino
acid
A
site
Anticodon
Codons
1
Codon recognition
Translocation: tRNA is
released from the P site and
the ribosome moves tRNA
from the A site into the P site
2
New
peptide
bond
3
Translocation
Peptide bond
formation
Elongation
Polypeptide
P
site
mRNA
Amino
acid
A
site
Anticodon
Codons
1
Codon recognition
mRNA
movement
Translocation: tRNA
is released from the
P site and the
ribosome moves
tRNA from the A site
into the P site
3
Translocation
Stop
codon
2
New
peptide
bond
Peptide bond
formation
Termination
 Ribosome reaches a stop codon,
– the completed protein is freed from the last tRNA, and
– the ribosome splits back into its separate subunits.
© 2012 Pearson Education, Inc.
Figure 10.15_3
New peptide
bond forming
Growing
polypeptide
4
Elongation
Codons
mRNA
Polypeptide
5
Stop codon
Termination
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
Normal hemoglobin DNA
Mutant hemoglobin DNA
C A T
C T T
mRNA
mRNA
G A A
Normal hemoglobin
Glu
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G U A
Sickle-cell hemoglobin
Val
Mutations can change the meaning of genes
 Nucleotide Addition or Deletion (Frameshift)
 Alters reading frame
 Sequence of every amino acid altered after mutation.
© 2012 Pearson Education, Inc.
Figure 10.16B
Normal
gene
mRNA
Protein
Nucleotide
substitution
A
U G A A G U
Met
A U G A
Met
Lys
U
U G G C G
C
Phe
Gly
Ala
U A G C
A G U U
Lys
Phe
Ser
G C
A
A
Ala
U Deleted
Nucleotide
deletion
A U G A A G
Met
U
U G G C G
Ala
Leu
Lys
C A
U
His
Inserted
Nucleotide
insertion
A U G A A G
Met
Lys
U
U G
Leu
U G G
C G C
Ala
His