1. Mutations are changes in the genetic material of a cell or virus
Concept 17.5: Point mutations can affect protein structure and function
Mutations are changes in the genetic material of a cell or virus
Point mutations are chemical changes in just one base pair of a gene
The change of a single nucleotide in a DNA template strand can lead to the production of an abnormal protein
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2. Wild-type hemoglobin DNA Mutant hemoglobin DNA 3 C T T 5 3 C A T 5
Fig
Wild-type hemoglobin DNA
Mutant hemoglobin DNA 3 C T T 5 3 C A T 5 5 G A A 3 5 G T A 3
mRNA
mRNA 5 G A A 3 5 G U A 3
Figure The molecular basis of sickle-cell disease: a point mutation
Normal hemoglobin
Sickle-cell hemoglobin
Glu
Val

3. Types of Point Mutations
Point mutations within a gene can be divided into two general categories
Base-pair substitutions
Base-pair insertions or deletions
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4. Figure 17.23 Types of point mutations
Wild-type
DNA template strand 3 5 5 3
mRNA 5 3
Protein
Stop
Amino end
Carboxyl end
A instead of G
Extra A 3 5 3 5 5 3 5 3
U instead of C
Extra U 5 3 5 3
Stop
Stop
Silent (no effect on amino acid sequence)
Frameshift causing immediate nonsense (1 base-pair insertion)
T instead of C
missing 3 5 3 5 5 3 5 3
A instead of G
missing 5 3 5 3
Stop
Figure Types of point mutations
Missense
Frameshift causing extensive missense (1 base-pair deletion)
A instead of T
missing 3 5 3 5 5 3 5 3
U instead of A
missing 5 3 5 3
Stop
Stop
Nonsense
No frameshift, but one amino acid missing (3 base-pair deletion)
(a) Base-pair substitution
(b) Base-pair insertion or deletion

5. Silent (no effect on amino acid sequence)
Fig a
Wild type
DNA template
strand 3 5 5 3
mRNA 5 3
Protein
Stop
Amino end
Carboxyl end
A instead of G 3 5 5 3
Figure Types of point mutations
U instead of C 5 3
Stop
Silent (no effect on amino acid sequence)

6. Wild type DNA template strand 3 5 5 3 mRNA 5 3 Protein Stop
Fig b
Wild type
DNA template
strand 3 5 5 3
mRNA 5 3
Protein
Stop
Amino end
Carboxyl end
T instead of C 3 5 5 3
Figure Types of point mutations
A instead of G 5 3
Stop
Missense

7. Wild type DNA template strand 3 5 5 3 mRNA 5 3 Protein Stop
Fig c
Wild type
DNA template
strand 3 5 5 3
mRNA 5 3
Protein
Stop
Amino end
Carboxyl end
A instead of T 3 5 5 3
Figure Types of point mutations
U instead of A 5 3
Stop
Nonsense

8. Frameshift causing immediate nonsense (1 base-pair insertion)
Fig d
Wild type
DNA template
strand 3 5 5 3
mRNA 5 3
Protein
Stop
Amino end
Carboxyl end
Extra A 3 5 5 3
Figure Types of point mutations
Extra U 5 3
Stop
Frameshift causing immediate nonsense (1 base-pair insertion)

9. Frameshift causing extensive missense (1 base-pair deletion)
Fig e
Wild type
DNA template
strand 3 5 5 3
mRNA 5 3
Protein
Stop
Amino end
Carboxyl end
missing 3 5 5 3
Figure Types of point mutations
missing 5 3
Frameshift causing extensive missense (1 base-pair deletion)

10. Wild type DNA template strand 3 5 5 3 mRNA 5 3 Protein Stop
Fig f
Wild type
DNA template
strand 3 5 5 3
mRNA 5 3
Protein
Stop
Amino end
Carboxyl end
missing 3 5 5 3
Figure Types of point mutations
missing 5 3
Stop
No frameshift, but one amino acid missing (3 base-pair deletion)

11. Substitutions
A base-pair substitution replaces one nucleotide and its partner with another pair of nucleotides
Silent mutations have no effect on the amino acid produced by a codon because of redundancy in the genetic code
Missense mutations still code for an amino acid, but not necessarily the right amino acid
Nonsense mutations change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
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12. Insertions and Deletions
Insertions and deletions are additions or losses of nucleotide pairs in a gene
These mutations have a disastrous effect on the resulting protein more often than substitutions do
Insertion or deletion of nucleotides may alter the reading frame, producing a frameshift mutation
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13. Mutagens are physical or chemical agents that can cause mutations
Spontaneous mutations can occur during DNA replication, recombination, or repair
Mutagens are physical or chemical agents that can cause mutations
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14. Concept 17.6: While gene expression differs among the domains of life, the concept of a gene is universal
Archaea are prokaryotes, but share many features of gene expression with eukaryotes
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15. Comparing Gene Expression in Bacteria, Archaea, and Eukarya
Bacteria and eukarya differ in their RNA polymerases, termination of transcription and ribosomes; archaea tend to resemble eukarya in these respects
Bacteria can simultaneously transcribe and translate the same gene
In eukarya, transcription and translation are separated by the nuclear envelope
In archaea, transcription and translation are likely coupled
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16. RNA polymerase DNA mRNA Polyribosome Direction of 0.25 µm
Fig
RNA polymerase
DNA
mRNA
Polyribosome
Direction of
transcription
0.25 µm
RNA
polymerase
DNA
Figure Coupled transcription and translation in bacteria
Polyribosome
Polypeptide
(amino end)
Ribosome
mRNA (5 end)

17. What Is a Gene? Revisiting the Question
The idea of the gene itself is a unifying concept of life
We have considered a gene as:
A discrete unit of inheritance
A region of specific nucleotide sequence in a chromosome
A DNA sequence that codes for a specific polypeptide chain
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18. Fig
DNA
TRANSCRIPTION 3
Poly-A
RNA
polymerase 5
RNA
transcript
RNA PROCESSING
Exon
RNA transcript
(pre-mRNA)
Intron
Aminoacyl-tRNA
synthetase
Poly-A
NUCLEUS
Amino
acid
AMINO ACID ACTIVATION
CYTOPLASM
tRNA
mRNA
Growing
polypeptide
Cap 3 A
Activated
amino acid
Poly-A P
Ribosomal
subunits
Figure A summary of transcription and translation in a eukaryotic cell E
Cap 5
TRANSLATION E A
Anticodon
Codon
Ribosome

19. In summary, a gene can be defined as a region of DNA that can be expressed to produce a final functional product, either a polypeptide or an RNA molecule
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