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Ch 10
Structure of Genetic Material
Inheritance
• To be heritable
• The genetic material must be able to copy itself.
• The genetic material must be able to direct the
expression of an organisms phenotype.
• The genetic material must generate variation in
some manner.
DNA & RNA
Sugar-phosphate backbone
Phosphate group
A
C
Nitrogenous base
A
Sugar
DNA nucleotide
Thymine (T)
C
Nitrogenous base
(A, G, C, or T)
Phosphate
group
O
H3C
C
O
T
T
O
P
O
CH2
O–
G
G
C
H
C
N
N
C
O
C H
H C
H C
C H
O
H
Sugar
(deoxyribose)
T
T
DNA nucleotide
DNA polynucleotide
H
O
DNA
H
O
H3C
H
C
C
C
N
N
C
H
H
H
O
N
C
C
C
N
H
H
N
C
H
O
H
H
Thymine (T)
N
C
N
C
C
N
C
N
H
O
N
C
H
H
H
Twist
N
C
C
C
N
N
C
Guanine (G)
Purines
Pyrimidines
C
H
Adenine (A)
Cytosine (C)
N
H
N
H
H
Base Pairing
RNA
Key
Hydrogen atom
Carbon atom
Nitrogen atom
Oxygen atom
Phosphorus atom
DNA Replication
• Semi conservative model
Enzymes
• Helicase- unwinds the helix
• Primase- synthesizes a primer for polymerase
to start on
• Polymerase- adds nucleotides
• Ligase- seals gaps in the strand
Unwinding the Helix
Replication
Replication
Flow of Genetic Information
• Gene Expression
– Information in a gene becomes converted to an
RNA or protein product
• Transcription
• Translation
Genetic Flow
Genetic Flow
The genetic code
Creating RNA
Transcription
RNA nucleotides
RNA
polymerase
T
C
C
A
A
U
C
C
A
T
A
G
G
T
Direction of
transcription
Figure 10.9A
Newly made RNA
A
T
T
A
Template
Strand of DNA
Transcription
• Initiation
• Elongation
• Termination
Introns
Exon Intron
Exon
Intron
Exon
DNA
Transcription
Addition of cap and tail
Cap
RNA
transcript
with cap
and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
Nucleus
Cytoplasm
Translation
Translation
Proteins synthesized at ribosomes
tRNA-binding sites
Large
subunit
Next amino acid
to be added to
polypeptide
Growing
polypeptide
tRNA
mRNAbinding site
mRNA
Small
subunit
Codons
Figure 10.12B, C
Initiation Codon
Start of genetic message
End
Figure 10.13A
mRNA
mRNA, a specific tRNA, and the
ribosome subunits assemble
during initiation
Met
Met
Large
ribosomal
subunit
Initiator tRNA
P site
U
A C
A U G
U
A C
AUG
Start
codon
1
mRNA
Figure 10.13B
A site
Small ribosomal
subunit
2
Translation
So what is all of the noncoding “junk” in the genome?
• Now that the complete sequence of the human
genome is available we know what makes up most of
the 98.5% that does not code for proteins, rRNAs, or
tRNAs
Exons (regions of genes coding
for protein, rRNA, tRNA) (1.5%)
Repetitive
DNA that
includes
transposable
elements
and related
sequences
(44%)
Figure 19.14
Serial repeats
Alu
elements
(10%)
Simple sequence
DNA (3%)
Repetitive
DNA
unrelated to
transposable
elements
(about 15%)
Introns and
regulatory
sequences
(24%)
Unique
noncoding
DNA (15%)
Large-segment
duplications (5-6%)
Inhibitory RNA
Bacteria
• Bacteria replicate DNA and use binary fission
to reproduce
– How to they produce new gene combinations?
Bacteria
DNA enters
cell
• Transformation
Fragment of
DNA from
another
bacterial cell
Bacterial chromosome
(DNA)
• Transduction
Phage
Fragment of
DNA from
another
bacterial cell
(former phage
host)
Bacteria
Mating bridge
• Conjugation
Sex pili
Donor cell
(“male”)
Recipient cell
(“female”)
Mutations
– Changes in the DNA base sequence
– Substituting, inserting, or deleting nucleotides alters a
gene with varying effects on the organism
The similarity in the amino acid sequences of the
various globin proteins supports this model of
gene duplication and mutation
Table 19.1
Evolution of Genes with Novel
Functions
• The copies of some duplicated genes have
diverged so much during evolutionary time that
the functions of their encoded proteins are now
substantially different
• A particular exon within a gene could be
duplicated on one chromosome and deleted
from the homologous chromosome
In exon shuffling errors in meiotic recombination lead to
the occasional mixing and matching of different exons
either within a gene or between two nonallelic genes
EGF
EGF
EGF
EGF
Epidermal growth
factor gene with multiple
EGF exons (green)
F
F
F
Fibronectin gene with multiple
“finger” exons (orange)
F
Exon
shuffling
F
Exon
duplication
EGF
K
Plasminogen gene with a
“kfingle” exon (blue)
Figure 19.20
Portions of ancestral genes
Exon
shuffling
TPA gene as it exists today
K
K
• http://www.youtube.com/watch?v=4jtmOZaIv
S0
• http://www.youtube.com/watch?v=5bLEDdPSTQ&feature=related