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Chapter 26 Nucleic Acids and
Protein Synthesis
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Nucleic Acids
Nucleic acids are:
„ Molecules that store information for cellular
growth and reproduction.
„ Deoxyribonucleic acid (DNA) and ribonucleic
acid (RNA).
„ Large molecules consisting of long chains of
monomers called nucleotides.
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Nucleic Acids
„
„
„
„
Nucleic acids are:
Made from Nucleotides
Nucleotides are made from Nucleosides
Nucleosides are made from Nitrogen
bases and pentose (five-carbon) sugar.
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Nucleosides and nucleotides
HO
Nucleoside
Nucleotide
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The nucleotides adenosine 5´-monophosphate (AMP) and
deoxycytidine 5´-monophosphate (dCMP) are shown below.
Nucleotides are formed from nucleosides by
1.
2.
3.
4.
addition of a heterocyclic nitrogen base to a sugar.
changing the heterocyclic nitrogen base.
changing the monsaccharide.
conversion of an alcohol functional group on the
monosaccharide to a phosphate ester.
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The nucleotides adenosine 5´-monophosphate (AMP) and
deoxycytidine 5´-monophosphate (dCMP) are shown below.
Nucleotides are formed from nucleosides by
1.
2.
3.
4.
addition of a heterocyclic nitrogen base to a sugar.
changing the heterocyclic nitrogen base.
changing the monsaccharide.
conversion of an alcohol functional group on the
monosaccharide to a phosphate ester.
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Nitrogen Bases
„
„
The nitrogen bases in
nucleic acids consist
of the:
Pyrimidines C, T,
and U
And purines A and
G.
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The hetereocyclic nitrogen base in the nucleotide
shown below is the
1.
2.
3.
4.
purine base adenine.
purine base cytosine.
pyrimidine base
adenine.
pyrimidine base
cytosine.
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The hetereocyclic nitrogen base in the nucleotide
shown below is the
1.
2.
3.
4.
purine base adenine.
purine base cytosine.
pyrimidine base
adenine.
pyrimidine base
cytosine.
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Pentose Sugars
„
„
„
The pentose (fivecarbon) sugar:
In RNA is ribose.
In DNA is
deoxyribose.
Has carbon atoms
numbered with
primes to distinguish
them from the
nitrogen bases.
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Nucleosides
A nucleoside:
„ Has a nitrogen base
linked by a glycosidic
bond to C1’ of a ribose
or deoxyribose.
„ Is named by changing
the nitrogen base
ending to -osine for
purines and –idine for
pyrimidines
HO
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Nucleotides
A nucleotide:
„ Is a nucleoside that forms
a phosphate ester with
the C5’ OH group of
ribose or deoxyribose.
„ Is named using the name
of the nucleoside
followed
by 5’-monophosphate.
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Nucleic acids are polynucleotides. Nucleic acids are
classified as either DNA or RNA. The nucleotide
shown below might be found in
1.
2.
3.
4.
either DNA or RNA.
neither DNA nor
RNA.
only DNA.
only RNA.
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Nucleic acids are polynucleotides. Nucleic acids are
classified as either DNA or RNA. The nucleotide
shown below might be found in
1.
2.
3.
4.
either DNA or RNA.
neither DNA nor
RNA.
only DNA.
only RNA.
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Names of Nucleosides and
Nucleotides
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DNA and RNA differ in the nature of the
monsaccharide unit and the nature of the
heterocyclic base. In a nucleic acid, which
heterocyclic base is never combined with the sugar
shown below?
1.
2.
3.
4.
Adenine
Guanine
Thymine
Uracil
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DNA and RNA differ in the nature of the
monsaccharide unit and the nature of the
heterocyclic base. In a nucleic acid, which
heterocyclic base is never combined with the sugar
shown below?
1.
2.
3.
4.
Adenine
Guanine
Thymine
Uracil
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Nucleosides and Nucleotides with
Purines
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Nucleosides and Nucleotides with
Pyrimidines
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AMP, ADP, and ATP
„
Adding
phosphate
groups to
AMP forms
the
diphosphate
ADP and the
triphosphate
ATP.
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Learning Check
Give the name and abbreviation for the
following and list its nitrogen base and sugar:
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Solution
Guanosine 5’-monophosphate; GMP
nitrogen base: guanine sugar: ribose
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Primary Structure of Nucleic
Acids
In the primary structure of nucleic acids:
„ Nucleotides are joined by phosphodiester
bonds.
„ The 3’-OH group of the sugar in one
nucleotide forms an ester bond to the
phosphate group on the 5’-carbon of the
sugar of the next nucleotide.
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Primary Structure of Nucleic
Acids
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Structure of Nucleic Acids
A nucleic acid polymer:
„ Has a free 5’-phosphate
group at one end and a
free 3’-OH group at the
other end.
„ Is read from the free 5’end using the letters of
the bases.
„ This example reads
5’—A—C—G—T—3’.
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Example of RNA
„
In RNA, A, C,
G, and U are
linked by 3’-5’
ester bonds
between ribose
and phosphate.
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Example of DNA
„
In DNA, A, C,
G, and T are
linked by 3’-5’
ester bonds
between
deoxyribose
and
phosphate.
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DNA Double Helix
In DNA:
„ There are two strands of nucleotides that wind
together in a double helix.
„ Two hydrogen bonds form between the
complementary base pairs A-T.
„ Three hydrogen bonds form between the
complementary base pairs G-C.
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DNA Double Helix Structure
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How many hydrogen bonds link the two
complementary strands of DNA shown below?
1.
2.
3.
4.
10
11
12
13
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How many hydrogen bonds link the two
complementary strands of DNA shown below?
1.
2.
3.
4.
10
11
12
13
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Learning Check
Write the complementary base sequence for the
matching strand in the following DNA section:
5’—A—G—T—C—C —A—A—T—C— 3’
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Solution
Write the complementary base sequence for the
matching strand in the following DNA section:
5’—A—G—T—C—C—A—A—T—C—3’
3’—T—C—A—G—G—T—T—A—G—5’
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What is the sequence of the DNA strand on the rightside of the picture below?
1.
2.
3.
4.
A–G–T–C
C–T–G–A
G–A–C–T
T–C–A–G
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What is the sequence of the DNA strand on the rightside of the picture below?
1.
2.
3.
4.
A–G–T–C
C–T–G–A
G–A–C–T
T–C–A–G
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Animation_26.1
DNA Replication
DNA replication involves:
„ Unwinding the DNA
„ Pairing the bases in each
strand with new bases to
form new complementary
strands.
„ Producing two new DNA
strands that exactly
duplicate the original DNA.
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Hydrolysis Energy
„
Energy from the
hydrolysis of
each nucleoside
triphosphate
adding to the
complementary
strand is used to
form the
phosphodiester
bond.
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Direction of Replication
„
„
„
„
During replication, helicase unwinds the parent
DNA at several sections.
At each open DNA section called a replication fork,
DNA polymerase catalyzes the formation of
5’-3’ester bonds of the leading strand.
The lagging strand, which grows in the 3’-5’
direction, is synthesized in short sections called
Okazaki fragments.
The Okazaki fragments are joined by DNA ligase
to give a single 3’-5’ DNA strand.
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Direction of Replication
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Learning Check
Match the following:
1) helicase
2) DNA polymerase
3) replication fork
4) Okazaki fragments
A. Short segments formed by the lagging strand.
B. The starting point for synthesis in unwound
DNA sections.
C. The enzyme the unwinds the DNA double helix.
D. The enzyme the catalyzes the formation of
phosphodiester bonds of complementary bases.
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Solution
Match the following:
1) helicase
2) DNA polymerase
3) replication fork
4) Okazaki fragments
A. 4 Short segments formed by the lagging strand.
B. 3 The starting point for synthesis in unwound
DNA sections.
C. 1 The enzyme the unwinds the DNA double helix.
D. 2 The enzyme the catalyzes the formation of
phosphodiester bonds of complementary bases.
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26.7 DNA and RNA
„
The three differences in structure between
DNA and RNA are
„
„
„
DNA bases are A, G, C, and T; the RNA bases
are A, G, C, and U
the sugar in DNA is 2-deoxy-D-ribose;
ribose in RNA
it is D-ribose
DNA is always double stranded;
stranded there are
several kinds of RNA, all of which are singlestranded
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Animation_26.10
Transfer RNA and Protein Synthesis
„
„
„
The following two processes are involved in transfer, and
use of genetic information:
Transcription: The process by which the genetic
messages contained in DNA are read and copied.
Translation: The process by which the genetic
messages carried by RNA are decoded and used to build
proteins.
Animation_26.10.1
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26.7 Structure and Function of
RNA
RNA is similar to DNA – both are sugarphosphate polymers and both have nitrogencontaining bases attached – but there are
differences between them.
„DNA has only one kind of function-storing
genetic information. By contrast, the different
kinds of RNA perform different functions.
„
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The following three RNA make it possible for
the encoded information carried by the DNA to
be put to use in the synthesis of proteins.
„Ribosome RNA: The granular organelles in the
cell where protein synthesis takes place. These
organelles are composed of protein and
ribosomal RNA (rRNA).
„Messenger RNA (mRNA): The RNA that
carries the code transcribed from DNA and
directs protein synthesis.
„
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Transfer RNA (tRNA): The smaller RNA that
delivers amino acids one by one to protein chains
growing at ribosomes. Each tRNA recognizes
and carries only one amino acid.
„
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26.8 Transcription: RNA Synthesis
„
„
RNA are synthesized in the cell nucleus.
Before leaving the nucleus, all types of RNA
are modified in the various ways needed for
their various functions.
In transcription, a small section of the DNA
double helix unwinds, the bases on the two
strands are exposed, and one by one the
complementary nucleotides are attached.
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„
„
„
rRNA, tRNA, and mRNA are all synthesized
in essentially the same manner. Only one of
the two DNA strands is transcribed during
RNA synthesis.
The DNA strand that is transcribed is the
template strand; while the its complementary
strand is the informational strand.
The messenger RNA produced is a duplicate
of the DNA informational strand, but with U
base wherever the DNA has a T base.
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The process of forming mRNA from DNA is called
1.
2.
3.
4.
reduction.
replication.
transcription.
translation.
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The process of forming mRNA from DNA is called
1.
2.
3.
4.
reduction.
replication.
transcription.
translation.
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26.9 The Genetic Code
„
„
The ribonucleotide sequence in an mRNA
chain is like a coded sentence that species
the order in which amino acid residues
should be joined to form a protein.
Each word, or codon in the mRNA
sentence is a series of three ribonucleotides
that code for a specific amino acid.
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„
„
For example, the series uracil-uracil-guanine
(UUG) on an mRNA chain is a codon
directing incorporation of the amino acid
leucine into a growing protein chain.
Of the 64 possible three-base combinations
in RNA, 61 code for specific amino acids
and 3 code for chain termination.
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26.10 Translation: Transfer RNA and
Protein Synthesis
„
„
The synthesis of proteins
occur at ribosomes,
which are outside the
nucleus and within the
cytoplasm of cells.
The mRNA connects
with the ribosome, and
the amino acids attached
to transfer RNA (tRNA)
are delivered one by one.
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Three stages in protein
Synthesis are initiation,
elongation,
and
termination. A diagram
of translation is shown
in the Fig 26.8.
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Chapter Summary
„
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Nucleic acids are polymers of nucleotides.
Each nucleotide contains a sugar, a base, and a
phosphate group.
The sugar is D-ribose in ribonucleic acid (RNA) and
2-deoxy-D-ribose in deoxyribonucleic acid (DNA).
A nucleoside contains a sugar and a base, but not the
phosphate group.
The DNA in each chromosome consists of two
polynucleotides strands twisted together in a double
helix.
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Chapter Summary Contd.
„
„
„
The bases on the two strands are
complementary – opposite every thimine is an
adenine, opposite every guanine is a cytisine.
The base pairs are connected by hydrogen
bonds – two between T and A; three between
G and C.
Messenger RNA (mRNA) carries the genetic
information out of the nucleus to the ribosomes
where protein synthesis occurs.
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Chapter Summary Contd.
„
„
„
„
Transfer RNA (tRNA) bond to amino acids that
they deliver to protein synthesis.
Ribosomal RNA (rRNA) are incorporated into
ribosomes.
In transcription, one strand of the DNA is copied
(the template) and the other is the informational
strand, and is not copied.
The genetic information is read as a sequence of
codons-triplets of bases in DNA that give the
sequence of amino acids in a protein.
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„
End of Chapter 26
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Animations
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http://www.lewport.wnyric.org/JWANAM
AKER/animations/Protein%20Synthesis%2
0-%20long.html
http://highered.mcgrawhill.com/sites/0072437316/student_view0/c
hapter15/animations.html
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