© 2012 pearson education, inc. lecture by edward j. zalisko powerpoint lectures for campbell...
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© 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
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.
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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.
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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.
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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 10.15_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.
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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
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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
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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
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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
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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
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