1. DNA, RNA structure

2. DNA replication

3. Transcription, translation

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•

DNA is a nucleic acid, made of long
chains of nucleotides

DNA and RNA are polymers of

nucleotides

Figure

10.2A

Nucleotide

Phosphate

group

Nitrogenou

s

base

Sugar

Polynucleotide

Sugar-phosphate backbone

DNA nucleotide

Phosphate

group

Nitrogenous base

(A, G, C, or T)

Thymine (T)

Sugar

(deoxyribose)

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•

DNA has four kinds of bases, A, T,
C, and G

Figure

10.2B

Pyrimidines

Thymine (T)

Cytosine (C)

Purines

Adenine (A)

Guanine (G)

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•

RNA is also a nucleic acid

–

different sugar

–

U instead of T

–

Single strand, usually

Figure

10.2C, D

Phosphate

group

Nitrogenous base

(A, G, C, or U)

Uracil (U)

Sugar

(ribose)

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•

James Watson and Francis Crick
worked out the three-dimensional
structure of DNA, based on work by
Rosalind Franklin

DNA is a double-stranded helix

Figure 10.3A, B

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•

Hydrogen bonds between bases hold
the strands together: A and T, C
and G

Figure

10.3D

Ribbon model

Partial chemical structure

Computer model

Hydrogen bond

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Untwisting and replication of DNA

•

each strand is a template for a new
strand

Figure

10.4B

helicase

DNA polymerase

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•

DNA replication begins at many
specific sites

How can entire chromosomes be replicated during S phase?

Figure

10.5A

Parental strand

Origin of replication

Bubble

Two daughter DNA molecules

Daughter strand

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•

Each strand of
the double helix
is oriented in
the opposite
direction

Figure

10.5B

5 end

3 end

3 end

5 end

P

P

P

P

P

P

P

P

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•

DNA
polymera
se works
in only
one
directio
n

5 end

P

P

Parental DNA

Figure

10.5C

DNA polymerase

molecule

5
3

3
5

3
5

Daughter strand

synthesized

continuously

Daughter

strand

synthesiz

ed

in pieces

DNA

ligase

Overall direction of replication

5
3

•

Telomere
sequence
s are
lost
with
each
replicat
ion.

•

Cancer,
aging

telomeres

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–

The DNA is transcribed into RNA,
which is translated into the
polypeptide

Figure
10.6A

DNA

RNA

Protein

TRANSCRIPTION

TRANSLATION

•

The information constituting an
organism’s genotype is carried in
its sequence of bases

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Transcription produces genetic

messages in the form of mRNA

Figure

10.9A

RNA

polymerase

RNA nucleotide

Direction of

transcription

Newly made RNA

Template

strand of DNA

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•

In
transcription,
DNA helix
unzips

–

RNA nucleotides
line up along
one strand of
DNA, following
the base-pairing
rules

–

single-stranded
messenger RNA
peels away and
DNA strands
rejoin

RNA polymerase

DNA of gene

Promoter

DNA

Terminator

DNA

Initiation

Elongation

Termination

Area shown

in Figure 10.9A

Growing

RNA

RNA

polymerase

Completed RNA

Figure

10.9B

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RNA transcripts of DNA

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•

Noncoding
segments,
introns,
are spliced
out

•

A cap and a
tail are
added to
the ends

Eukaryotic RNA is processed

before leaving the nucleus

Figure

10.10

DNA

RNA

transcript

with cap

and tail

mRNA

Exon Intron

Intron

Exon

Exon

Transcription

Addition of cap and tail

Introns removed

Exons spliced together

Coding sequence

NUCLEUS

CYTOPLASM

Tail

Cap

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•

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

Translation of nucleic acids

into amino acids

Copyright © 2003 Pearson Education, Inc. publishing
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Figure

10.7

DNA

molecule

Gene 1

Gene 2

Gene 3

DNA strand

TRANSCRIPTION

RNA

Polypeptide

TRANSLATION

Codon

Amino acid

U

C

A

G

U

C

A

G

G

A

C

U

G

A

C

U

G

A

C

U

G

A

C

U

U

U

U

U

U

C

U

U

A

U

U

G

C

U

U

C

U

C

C

U

A

C

U

G

A

U

U

A

U

C

A

U

A

A

U

G

G

U

U

G

U

C

G

U

A

G

U

G

phe

leu

leu

ile

met (start)

val

U

C

U

U

C

C

U

C

A

U

C

G

C

C

U

C

C

C

C

C

A

C

C

G

A

C

U

A

C

C

A

C

A

A

C

G

G

C

U

G

C

C

G

C

A

G

C

G

ser

pro

thr

ala

U

A

U

U

A

C

U

A

A

U

A

G

C

A

U

C

A

C

C

A

A

C

A

G

A

A

U

A

A

C

A

A

G

A

A

A

G

A

U

G

A

C

G

A

A

G

A

G

tyr

stop
stop

his

gln

asn

lys

asp

glu

U

G

U

U

G

C

U

G

A

U

G

G

C

G

U

C

G

C

C

G

A

C

G

G

A

G

U

A

G

C

A

G

A

A

G

G

G

G

U

G

G

C

G

G

A

G

G

G

cys

stop

trp

arg

ser

arg

gly

F

i

r

s

t

B

a

s

e

T

h

i

r

d

B

a

s

e

Second Base

Virtually all organisms share the

same genetic code “unity of life”

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•

An exercise in translating the
genetic code

Figure
10.8B

Start

codon

RNA

Transcribed strand

Stop

codon

Translation

Transcription

DNA

Polypeptide

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as Benjamin Cummings

•

In the
cytoplasm, a
ribosome
attaches to
the mRNA and
translates its
message into a
polypeptide

•

The process is
aided by
transfer RNAs

Transfer RNA molecules serve as

interpreters during translation

Figure
10.11A

Hydrogen bond

Amino acid attachment site

RNA polynucleotide chain

Anticodon

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•

Each tRNA molecule has a triplet
anticodon on one end and an amino
acid attachment site on the other

Figure

10.11B, C

Anticodon

Amino acid

attachment

site

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Ribosomes build polypeptides

Figure 10.12A-C

Codons

tRNA

molecules

mRNA

Growing

polypeptide

Large

subunit

Small

subunit

mRNA

mRNA

binding

site

P site

A site

P

A

Growing

polypeptide

tRNA

Next amino acid

to be added to

polypeptide

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An initiation codon marks the

start of an mRNA message

Figure
10.13A

End

Start of genetic message

AUG = methionine

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•

mRNA, a specific tRNA, and the
ribosome subunits assemble during
initiation

Figure
10.13B

1

Initiator tRNA

mRNA

Start

codon

Small ribosomal

subunit

2

P site

Large

ribosomal

subunit

A site

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•

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

Elongation

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Figure 10.14

1

Codon recognition

Amino acid

Anticodon

A

sit

e

P

site

Polypeptide

2

Peptide bond

formation

3

Translocation

New

peptide

bond

mRNA

movement

mRNA

Stop

codon

b

a

Red object = ?

What molecules are
present in this
photo?

Table 14.2

Types of RNA

Type of RNA

Functions in

Function

Messenger RNA

(mRNA)

Nucleus,

migrates

to ribosomes

in cytoplasm

Carries DNA

sequence

information to

ribosomes

Transfer RNA

(tRNA)

Cytoplasm

Provides linkage

between mRNA

and amino acids;

transfers amino

acids to ribosomes

Ribosomal RNA

(rRNA)

Cytoplasm

Structural

component

of ribosomes

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•

The sequence of codons in DNA
spells out the primary structure of
a polypeptide

–

Polypeptides form proteins that
cells and organisms use

Review: The flow of genetic

information in the cell is

DNARNAprotein

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•

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

Mutations can change the meaning of

genes

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Figure 10.16A

Normal hemoglobin DNA

mRNA

Normal hemoglobin

Glu

Mutant hemoglobin DNA

mRNA

Sickle-cell hemoglobin

Val

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•

Types of mutations

Figure
10.16B

mRNA

NORMAL GENE

BASE SUBSTITUTION

BASE DELETION

Protein

Met

Lys

Phe

Gly

Ala

Met

Lys

Phe

Ser

Ala

Met

Lys

Leu

Ala

His

Missing

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Figure 8.23A,

B

Deletion

Duplicati

on

Inversio

n

Homologous

chromosomes

Reciprocal

translocat

ion

Nonhomologous

chromosomes

•

Chromosomal changes can be large or small

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•

Summary of
transcript
ion and
translatio
n

Figure
10.15

1

Stage mRNA is
transcribed from a
DNA template.

Anticodon

DNA

mRNA

RNA

polymerase

TRANSLATION

Enzyme

Amino acid

tRNA

Initiator

tRNA

Large

ribosoma

l

subunit

Small

ribosoma

l

subunit

mRNA

Start

Codon

2

Stage Each
amino acid attaches
to its proper tRNA
with the help of a
specific enzyme and
ATP.

3

Stage
Initiation of
polypeptide
synthesis

The mRNA, the
first tRNA, and
the ribosomal
subunits come
together.

TRANSCRIPTION

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Figure 10.15
(continued)

4

Stage
Elongation

Growing

polypeptid

e

Codons

5

Stage
Termination

mRNA

New

peptid

e

bond

formin

g

Stop

Codon

The ribosome

recognizes a stop

codon. The poly-

peptide is terminated

and released.

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.

Polypeptide