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Anatomy and Physiology I
Protein Synthesis and the
Genetic Code
Instructor: Mary Holman
Proteins
• Every cell contains large numbers of
diverse proteins
• The proteins determine the physical
and chemical characteristics of
cells
• Much of cellular machinery is devoted
to synthesizing proteins
• Instructions for making proteins are
contained primarily in the DNA in
the nucleus of the cell
Organic Compounds
Proteins
• More complex than carbohydrates and lipids
• Have a larger range of functions :
structural material, energy source,
hormones, receptors, enzymes,
antibodies
• Contain N as well as C, H, and O and some contain S
• Amino acids are the building blocks (monomers)
of proteins
• There are twenty (20) different amino acids
• Amino acids bind together by forming peptide bonds
General structure of an amino acid
R
Fig. 2.17a
H
N
C
C
H
H
O
OH
The portion common to all amino acids
is within the oval.
It includes the amino group (—NH2)
and the carboxyl group (—COOH).
The "R" group, or the "rest of the molecule,"
is what makes each amino acid unique.
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Fig. 2.17b
H
C
H
C
C
H
H
C
C
H
H
S
H
C
H
C
H
N
C
C
H
H
O
OH
(b) Cysteine. Cysteine has an
R group that contains sulfur.
H
H
C
H
N
C
C
H
H
O
OH
Phenylalanine. Phenylalanine
has a complex R group.
Improper metabolism of
phenylalanine occurs in the
disease phenylketonuria.
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Fig. 2.18
H
N
H
A Peptide Bond
H
O
C
C
R
R
N
C
H
H
O
C
(H2O)
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OH
Primary Structure of Proteins
Fig.
2.19a
Amino acids
Polypeptide chain
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Secondary Structure
Tertiary Structure
R
H
C
H
H
C
H
Pleated
structure
C
Coiled
structure
N
H
O
H O
N
C
N
C
C
R
C
HO
R
N
R
C
H
R
C
H
C
N
Three-dimensional folding
Quaternary Structure
R
C
H
H
R
H
N
C
H
O
C
H
C
H
H
R
C
C
N
O
O
N
C
H
C
N
H
O
C
Two or more folded chains may connect and fold together
Ex:
Hemoglobin molecule
Nucleic Acids
• Huge molecules that contain C, H, O, N and P
• Building blocks (monomers ) are nucleotides
• Nucleic acids are of two varieties
• Deoxyribonucleic acid (DNA)
• Ribonucleic acid (RNA)
Fig. 2.20
Basic Structure of a Nucleotide
P
Base
Sugar
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Fig. 2.22
Different sugar groups of DNA and RNA
O
HOCH2
C
H
OH
H
H
C
C
O
HOCH2
C
C
H
H
H
H
C
C
OH
Ribose
OH
H
Deoxyribose
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C
H
Nitrogenous Bases
• The two types of nitrogenous
bases in nucleotides:
• Purines - structure of two joined
organic rings
• Pyrimidines - have a single organic
ring
Nitrogenous bases of DNA
The Five Nitrogenous Bases
DNA
App. D Pg. 937
RNA
App. D pg 937
The Molecular Structure of DNA
Fig. 4.19a
(a)
Hydrogen
bonds
P
P
CC
Fig. 4.19a
Guanine (G)
P
TT
CC
GG
P
G
C
P
A
P
Cytosine (C)
P
P
Adenine (A)
P
P
Thymine (T)
P
P
DNA
P
G
G
C
A
Nucleotide strand
Nucleotide
strand
G
C
T
C
G
A
Segment
Segment
of DNA
of DNA
molecule
molecule
Fig. 4.19b
The Double Helix Structure of DNA
Fig. 4.19b
Globular
histone
proteins
Chromatin
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Fig. 4.19c
DNA as condensed Chromosome during Mitosis
Metaphase
chromosome
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Fig 4.20 (partial)
DNA Replication prior to Mitosis
A
T
C
G
Fig. 4.20b
G
C
C
G
C
Original
DNA
molecule
G
C
G
A
C
T
G
A
T
G
C
C
Region of
replication
G
A
G
C
C
C
G
G
G
T
Newly formed
DNA molecules
C
G
G
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Fig. 2.21
P
B
P
B
P
B
P
B
P
B
P
B
S
RNA
B
B
B
B
B
B
P
S
P
S
P
S
P
S
S
P
B
B
S
S
S
P
B
P
S
S
P
B
S
S
S
P
B
S
S
P
B
P
S
DNA
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
S
P
Fig. 4.21
RNA Differences from DNA
S
A
P
S
U
P
S
G
P
S
G
P
S
C
P
S
A
P
S
U
P
S
U
P
S
G
P
S
U
P
• RNA is single stranded
• contains ribose instead
of deoxyribose
• contains uracil instead
of thymine
• there are different
types of RNA - all with
unique roles
Steps in Relaying the Genetic Information
Stored in DNA to Proteins to be
Synthesized
• Transcription - in nucleus
mRNA copies the DNA sequence
• mRNA enters cytoplasm and arrives at a
ribosome
• Translation - on ribosome in cytoplasm
tRNA matches its anticodon to codons on
mRNA and delivers the corresponding
amino acid.
• The polypeptide chain of a new protein is
assembled on the ribosome
Fig. 4.22
Transcription by RNA from DNA bases
DNA
mRNA
S
P
A
U
P
Direction of “reading” code
S
S
P
T
A
P
S
S
P
G
C
P
S
S
P
C
G
P
S
S
P
G
C
S
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P
Fig.
4.23a
T
Nucleus
T
A
G
C
T A
G
C G
T
A
G
C
A
A
C
T
G C
T
G
T A
C G
T
A
G
C
A
G C
T
A
C
T A
T
G
C
A
T
G C
T
A
DNA
strands
pulled
apart
2
A
G
C
A
Transcription
Cytoplasm
DNA
double
helix
T
A
T
G
G
G
C
T
C
C
G
C
A
A
C
G
G
C
A
G
G
C
T
C
C
A
T
G
A
C
G
T
U
2 mRNA leaves
the nucleus
Messenger and attaches
to a ribosome
RNA
A
G C
G C
G C
C G
U A
C G
C G
C G
C G
A
T
A
T
C G
G C
G C
C G
A
T
G C
G C
C G
U A
C G
C G
A T
U A
G C
A T
C G
C
Nuclear
pore
1 DNA
information
is copied, or
transcribed,
into mRNA
following
complementary
base pairing
T
A
G
DNA
strand
Messenger
RNA
C G
C
Transcription
(in nucleus)
G
C
C
G
A
T
G
C
C
G
C
U
C
G
A
G
1
Fig 4.23b
3
Translation
Fig. 4.23b
Translation begins as tRNA anticodons
recognize complementary mRNA codons,
thus bringing the correct amino acids into
position on the growing polypeptide chain
leaves
2 mRNA
the nucleus
Amino acids
attached to tRNA
6
Polypeptide
chain
and attaches
to a ribosome
5
At the end of the mRNA,
the ribosome releases
the new protein
Cytoplasm
4
tRNA molecules
can pick up another
molecule of the
same amino acid
and be reused
As the ribosome
moves along the
mRNA, more amino
acids are added
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Fig. 4.24a
1
1
2
Growing
The transfer RNA molecule
polypeptide
for the last amino acid added
chain
holds the growing polypeptide
Anticodon
chain and is attached to its
complementary codon on mRNA.A U G G G C U
1
2
3
4
Next amino acid
5
6
Transfer
RNA
U G C C G U
C C G C A A C G G C A G G C A A G C G U
3
4
5
Codons
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6
7
Messenger
RNA
Fig. 4.24b
Peptide bond
1
2
A second tRNA binds
2 complementarily to the
Growing
polypeptide
next codon, and in doing
chain
so brings the next amino
Anticodon
acid into position on the ribosome.
A U G G G C U
A peptide bond forms, linking
the new amino acid to the
growing polypeptide chain.
1
2
3
4
Next amino acid
5
6
Transfer
RNA
U G C C G U
C C G C A A C G G C A G G C A A G C G U
3
4
5
Codons
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6
7
Messenger
RNA
Fig. 4.24c
1
2
3
The tRNA molecule that
brought the last amino acid
to the ribosome is released
to the cytoplasm, and will be
used again. The ribosome
moves to a new position at
the next codon on mRNA.
3
4
7
5
Next
amino acid
6
Transfer
RNA
C G U
A U G G G C U C C G C A A C G G C A G G C A A G C G U
1
2
3
4
5
6
7
Ribosome
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Messenger
RNA
Fig. 4.24d
Alanine
Glycine
Methionine
Alanine
Glycine
Serine
1
2
4
3
A new tRNA complementary to
the next codon on mRNA brings
the next amino acid to be added
to the growing polypeptide chain.
4
5
6
7
Next
amino acid
Transfer
RNA
C G U C C G
A U G G G C U C C G C A A C G G C A G G C A A G C G U
1
2
3
4
5
6
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7
Messenger
RNA
Step 1
Amino acids
represented
mRNA
A
U
Fig.
4.23c
Codon
1 Methionine
G
G
G
Codon 2
Glycine
Codon 3
Serine
Codon 4
Alanine
Codon 5
Threonine
Codon 6
Alanine
Codon 7
Glycine
C
U
C
C
G
C
A
A
C
G
G
C
A
G
G
C
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Fig. 4.25
A single base Mutation
Direction of “reading” code
DNA
Code for
Glutamic
acid
P
T
DNA
Mutation
P
S
P
P
S
A
S
C
P
S
(a)
T
S
T
P
Code for
valine
C
S
(b)
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Fig. 4.26
STARTING MATERIALS
Enzyme #1
Resulting Conditions
INTERMEDIATE #1
Consequences
of mutations in
enzymes in the
synthesis of
Heme
Enzyme #2
ALA dehydratase deficiency
INTERMEDIATE #2
Enzyme #3
acute intermittent porphyria
INTERMEDIATE #3
Enzyme #4
congenital erythropoietic
porphyria
INTERMEDIATE #4
Enzyme #5
porphyria cutanea tarda
INTERMEDIATE #5
Enzyme #6
coproporphyria
INTERMEDIATE #6
Enzyme #7
porphyria variegata
INTERMEDIATE #7
Enzyme #8
HEME
erythropoietic protoporphyria