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1. DNA, RNA structure
2. DNA replication
3. Transcription, translation
DNA and RNA are polymers of nucleotides
• DNA is a nucleic acid, made of long chains of
nucleotides
Phosphate
group
Nitrogenous
base
Sugar
Phosphate
group
Nitrogenous base
(A, G, C, or T)
Nucleotide
Thymine (T)
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate backbone
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Figure 10.2A
• DNA has four kinds of bases, A, T, C, and G
Thymine (T)
Cytosine (C)
Pyrimidines
Adenine (A)
Guanine (G)
Purines
Figure 10.2B
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• RNA is also a nucleic acid
– different sugar
– U instead of T
– Single strand, usually
Nitrogenous base
(A, G, C, or U)
Phosphate
group
Uracil (U)
Sugar
(ribose)
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Figure 10.2C, D
DNA is a double-stranded helix
• James Watson and Francis Crick worked out
the three-dimensional structure of DNA, based
on work by Rosalind Franklin
Figure 10.3A, B
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• Hydrogen bonds between bases hold the
strands together: A and T, C and G
Hydrogen bond
Ribbon model
Partial chemical structure
Computer model
Figure 10.3D
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Untwisting and replication of DNA
• each strand is a template for a new strand
helicase
DNA polymerase
Figure 10.4B
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How can entire chromosomes be replicated during S phase?
• DNA replication begins at many specific sites
Origin of replication
Parental strand
Daughter strand
Bubble
Two daughter DNA molecules
Figure 10.5A
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• Each strand of the
double helix is
oriented in the
opposite direction
5 end
3 end
P
P
P
P
P
P
P
P
Figure 10.5B
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3 end
5 end
• DNA
polymerase
works in
only one
direction
• Telomere
sequences
are lost
with each
replication.
DNA polymerase
molecule
5 end
Daughter strand
synthesized
continuously
Parental DNA
5
3
Daughter
strand
synthesized
in pieces
3
5
P
5
3
• Cancer,
aging
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
3
5
P
telomeres
DNA ligase
Overall direction of replication
Figure 10.5C
• The information constituting an organism’s
genotype is carried in its sequence of bases
– The DNA is transcribed into RNA, which is
translated into the polypeptide
DNA
TRANSCRIPTION
RNA
TRANSLATION
Protein
Figure 10.6A
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Transcription produces genetic messages in the
form of mRNA
RNA
polymerase
RNA nucleotide
Direction of
transcription
Template
strand of DNA
Figure 10.9A
Newly made RNA
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RNA polymerase
• In transcription,
DNA helix unzips
DNA of gene
Promoter
DNA
– RNA nucleotides line
up along one strand
of DNA, following the
base-pairing rules
– single-stranded
messenger RNA peels
away and DNA
strands rejoin
Initiation
Elongation
Terminator
DNA
Area shown
in Figure 10.9A
Termination
Growing
RNA
Completed RNA
Figure 10.9B
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RNA
polymerase
Eukaryotic RNA is processed before leaving
the nucleus
• Noncoding
segments,
introns, are
spliced out
Exon Intron
Exon
Intron
Exon
DNA
Cap
RNA
transcript
with cap
and tail
• A cap and a tail
are added to
the ends
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
NUCLEUS
CYTOPLASM
Figure 10.10
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Translation of nucleic acids into amino acids
• The “words” of the DNA “language” are triplets
of bases called codons
– The codons in a gene specify the amino acid
sequence of a polypeptide
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Gene 1
Gene 3
DNA molecule
Gene 2
DNA strand
TRANSCRIPTION
RNA
Codon
TRANSLATION
Polypeptide
Figure 10.7
Amino acid
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Virtually all organisms share the same genetic code
“unity of life”
Second Base
C
U
UUU
UUC
UUA
UUG
C
CUU
CUC
CUA
CUG
A
AUU
AUC
ile
AUA
AUG met (start)
ACU
ACC
ACA
ACG
G
GUU
GUC
GUA
GUG
GCU
GCC
GCA
GCG
phe
leu
leu
val
UCU
UCC
UCA
UCG
CCU
CCC
CCA
CCG
A
ser
UAU
UAC
UAA
UAG
pro
CAU
CAC
CAA
CAG
thr
AAU
AAC
AAA
AAG
ala
GAU
GAC
GAA
GAG
G
tyr
stop
stop
his
gln
asn
lys
asp
glu
UGU
UGC
UGA
UGG
CGU
CGC
CGA
CGG
AGU
AGC
AGA
AGG
GGU
GGC
GGA
GGG
cys
stop
trp
arg
ser
arg
gly
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
Third Base
First Base
U
• An exercise in translating the genetic code
Transcribed strand
DNA
Transcription
RNA
Start
codon
Polypeptide
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Translation
Stop
codon
Figure 10.8B
Transfer RNA molecules serve as interpreters
during translation
• In the cytoplasm, a
ribosome attaches
to the mRNA and
translates its
message into a
polypeptide
• The process is aided
by transfer RNAs
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
Figure 10.11A
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• Each tRNA molecule has a triplet anticodon on
one end and an amino acid attachment site on
the other
Amino acid
attachment
site
Anticodon
Figure 10.11B, C
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Ribosomes build polypeptides
Next amino acid
to be added to
polypeptide
Growing
polypeptide
tRNA
molecules
P site
A site
Growing
polypeptide
Large
subunit
tRNA
P
A
mRNA
mRNA
binding
site
Codons
mRNA
Small
subunit
Figure 10.12A-C
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An initiation codon marks the start of an
mRNA message
AUG = methionine
Start of genetic message
End
Figure 10.13A
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• mRNA, a specific tRNA, and the ribosome
subunits assemble during initiation
Large
ribosomal
subunit
Initiator tRNA
P site
A site
Start
codon
mRNA
Small ribosomal
subunit
1
Figure 10.13B
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2
Elongation
• The mRNA moves a codon at a time relative to
the ribosome
– A tRNA pairs with each codon, adding an amino
acid to the growing polypeptide
– A STOP codon causes the mRNA-ribosome
complex to fall apart
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Amino acid
Polypeptide
A
site
P site
Anticodon
mRNA
1
Codon recognition
mRNA
movement
Stop
codon
New
peptide
bond
3
Translocation
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2
Peptide bond
formation
Figure 10.14
b
a
Red object = ?
What molecules are present
in this photo?
Table 14.2
Types of RNA
Type of RNA
Functions in
Messenger RNA
(mRNA)
Nucleus,
migrates
to ribosomes
in cytoplasm
Transfer RNA
(tRNA)
Cytoplasm
Provides linkage
between mRNA
and amino acids;
transfers amino
acids to ribosomes
Ribosomal RNA
(rRNA)
Cytoplasm
Structural
component
of ribosomes
Function
Carries DNA
sequence
information to
ribosomes
Review: The flow of genetic information in the cell
is DNARNAprotein
• The sequence of codons in DNA spells out the
primary structure of a polypeptide
– Polypeptides form proteins that cells and
organisms use
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Mutations can change the meaning of genes
• Mutations are changes in the DNA base
sequence
– caused by errors in DNA replication or by
mutagens
– change of a single DNA nucleotide causes
sickle-cell disease
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Normal hemoglobin DNA
mRNA
Mutant hemoglobin DNA
mRNA
Normal hemoglobin
Sickle-cell hemoglobin
Glu
Val
Figure 10.16A
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• Types of mutations
NORMAL GENE
mRNA
Protein
Met
Lys
Phe
Gly
Ala
Lys
Phe
Ser
Ala
BASE SUBSTITUTION
Met
Missing
BASE DELETION
Met
Lys
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Leu
Ala
His
Figure 10.16B
•Chromosomal changes can be large or small
Deletion
Homologous
chromosomes
Duplication
Inversion
Reciprocal
translocation
Nonhomologous
chromosomes
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Figure 8.23A, B
• Summary of
transcription
and
translation
TRANSCRIPTION
DNA
mRNA
RNA
polymerase
Stage 1 mRNA is
transcribed from a
DNA template.
Amino acid
TRANSLATION
Enzyme
Stage 2 Each amino
acid attaches to its
proper tRNA with the
help of a specific
enzyme and ATP.
tRNA
Initiator
tRNA
mRNA
Figure 10.15
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Anticodon
Large
ribosomal
subunit
Start
Codon
Small
ribosomal
subunit
Stage 3 Initiation of
polypeptide synthesis
The mRNA, the first
tRNA, and the
ribosomal subunits
come together.
New
peptide
bond
forming
Growing
polypeptide
Codons
Stage 4 Elongation
A succession of tRNAs
add their amino acids to
the polypeptide chain as
the mRNA is moved
through the ribosome,
one codon at a time.
mRNA
Polypeptide
Stop Codon
Figure 10.15 (continued)
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Stage 5 Termination
The ribosome recognizes
a stop codon. The polypeptide is terminated and
released.