Anatomy and Physiology I Protein Synthesis and the Genetic Code Instructor: Mary Holman.

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 CompoundsProteins

• 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

Fig. 2.17aH N

H

C

H

C

O

OH

R

The portion common to all amino acidsis 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.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

General structure of an amino acid

Fig. 2.17b

S

C

H

HH

H N

H

C

H

C

O

OH

C

C

C

H

H

C H

C H

H

CH

CH

H N

H

C

H

C

O

OH

(b) Cysteine. Cysteine has anR group that contains sulfur.

Phenylalanine. Phenylalaninehas a complex R group.Improper metabolism ofphenylalanine occurs in thedisease phenylketonuria.


Fig. 2.18

O

OHCNCCN C

ROHH

HHHR


A Peptide Bond

(H2O)

Fig. 2.19a

Amino acids


Primary Structure of Proteins

Polypeptide chain

Pleatedstructure

Coiledstructure

N

N

N

NN

HH

HH

C

CC

C

OCC

C

CC

OC

O

H

NN

H

O

O

C

CC

C

N

NHO

CC

H OC

H

R

H

R

R

H

R

H

R

H

R

H

R

H

R

H

CH

CH

Secondary Structure

Three-dimensional folding

Tertiary Structure

Quaternary Structure

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)

Sugar

P Base


Basic Structure of a NucleotideFig. 2.20

OH

HH

HOCH2

H

C C

O

HC C

H

HH

HOCH2 OH

H

C C

O

HC

OH

C

Ribose Deoxyribose


Fig. 2.22

Different sugar groups of DNA and RNA

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

DNA RNA

App. D Pg. 937

The Five Nitrogenous Bases

The Molecular Structure of DNAApp. D pg 937

Fig. 4.19a

G C

G

G

A

T

C

C

A

P

G C P

TP

P

C G

P

G

P

C P

A

P

P

P

Thymine (T)

Cytosine (C)

Adenine (A)

Guanine (G)

Nucleotide strand

Segmentof DNAmolecule

(a)

G C

G

G

A

T

C

C

A

P

G C P

TP

P

C G

P

G

P

C P

A

P

P

P

Thymine (T)

Cytosine (C)

Adenine (A)

Guanine (G)

Hydrogenbonds

Nucleotide strand

Segmentof DNAmolecule

Fig. 4.19a

DNA

Fig. 4.19b

Globularhistoneproteins

Chromatin


Fig. 4.19b The Double Helix Structure of DNA

Fig. 4.19c

Metaphasechromosome


DNA as condensed Chromosome during Mitosis

Fig. 4.20b

C

C

A T

C

C G

G

C

C

G

CG

A

A

T

T

C G

C

A T

Newly formedDNA molecules

Region ofreplication

Original DNAmolecule

G

G

G

G

G

G

GG

G

C C

C

C

C G


DNA Replication prior to MitosisFig 4.20 (partial)

S

P

S

P

S

P

S

P

S

P

S

P

B

B

B

B

B

B

S

P

S

P

S

P

S

P

S

P

S

P

B

B

B

B

B

B

S

S

S

S

S

S

P

P

P

P

P

P

B

B

B

B

B

B


Fig. 2.21

RNA DNA

Fig. 4.21

SC

S

S

S

S

G

G

G

U

A

U

U

P

P

P

P

S

S

S

SA

P

P

US

P

P

P

PRNA Differences from DNA

• 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 InformationStored 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 cytoplasmtRNA 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


DNA mRNA

SG

SC

S

S

S

S

C

G

T

A

S

S

S

S

G

C

A

U

Dir

ecti

on

of

“rea

din

g”

cod

e

P

P

P

P

P

P

P

P

P

P

Transcription by RNA from DNA bases

Fig. 4.23a

1

2

CytoplasmDNAdoublehelix Nucleus

MessengerRNA

AT

A

A

T

T

T

A T

A T

A T

A T

A T

U A

U A

U A

G C

C

G C

G C

G C

G C

G C

G C

G

G

C

C

G C

C G

U AC GC

G

G

GG

G

G

G

G

G

G

C

CC

C

C

C

C

C

C

C

A

A

A

A

A

T

T A

A T

A T

A T

A T

C G

G C

G C

G C

T A

T A

T A

C G

A T

G C

T A

C G

T A

C G

C G

G C

A T

T A

C G

G C

T

T

G

C G

C G

C G

C G

C G

C G

C G

C G

DNAstrandspulledapart

MessengerRNA

DNAinformationis copied, ortranscribed,into mRNAfollowingcomplementarybase pairing

Nuclearpore

mRNA leavesthe nucleusand attachesto a ribosome

Transcription (in nucleus)

DNAstrand

G C

C G

A

G

G

C

U

C

T

C

C

G

A

G

Transcription

1

2

Fig. 4.23b

mRNA leavesthe nucleusand attachesto a ribosome

Translation begins as tRNA anticodonsrecognize complementary mRNA codons,thus bringing the correct amino acids intoposition on the growing polypeptide chain

As the ribosomemoves along themRNA, more aminoacids are added

At the end of the mRNA,the ribosome releasesthe new protein

tRNA moleculescan pick up anothermolecule of thesame amino acidand be reused

Polypeptidechain


3

2

4

5

6

Amino acidsattached to tRNA

Fig 4.23bTranslation

Cytoplasm

Fig. 4.24a

MessengerRNA

TransferRNA

Next amino acid

Anticodon

Codons

Growingpolypeptidechain

1

1

2

2

3

3

4

4

5

5

6

6

7

CU G C G U

UCG GA AA A A AG G G G G G G GC C C C C C CU U

The transfer RNA moleculefor the last amino acid addedholds the growing polypeptidechain and is attached to itscomplementary codon on mRNA.

1


Fig. 4.24b

MessengerRNA

TransferRNA

Next amino acid

Anticodon

Codons

1

1

2

2

3

3

4

4

5

5

6

6

7

CU G C G U

Peptide bond


2A second tRNA bindscomplementarily to thenext codon, and in doingso brings the next aminoacid into position on the ribosome.A peptide bond forms, linkingthe new amino acid to thegrowing polypeptide chain.

Growingpolypeptidechain


Fig. 4.24c

CU G G

Messenger RNA

Transfer RNA

Nextamino acid

Ribosome

1

1

2

2

3

37

4

4

5

5

6 7

CC

C G U

6


The tRNA molecule thatbrought the last amino acidto the ribosome is releasedto the cytoplasm, and will beused again. The ribosomemoves to a new position atthe next codon on mRNA.

3


Fig. 4.24d

C CG C GU

Messenger RNA

Transfer RNA

Next amino acid

1

1

2

2

3

3

4

4

5

5

6 7

6 7


A new tRNA complementary tothe next codon on mRNA bringsthe next amino acid to be addedto the growing polypeptide chain.

4


AlanineAlanine

Glycine

Glycine

SerineMethionine

Step 1

Fig. 4.23c


C

Codon 1

Codon 2

Codon 3

Codon 4

Codon 5

Codon 6

Codon 7

G

G

G

G

G

A

A

A

U

U

C

C

C

C

C

C

G

G

G

A

Methionine

Glycine

Amino acidsrepresented

Serine

Alanine

Threonine

Alanine

Glycine

mRNA

Fig. 4.25

Code forGlutamicacid

Mutation

Dir

ecti

on

of

“rea

din

g”

cod

e

Code for valine

(a) (b)

S

S

S

C

T

A

P

P

P

S

S

S

C

T

T

P

P

P


A single base MutationDNA DNA

Fig. 4.26 STARTING MATERIALS

INTERMEDIATE #1

Enzyme #1

Enzyme #2

Enzyme #3

Enzyme #4

Enzyme #5

Enzyme #6

Enzyme #8

HEME

Enzyme #7

ALA dehydratase deficiency

acute intermittent porphyria

congenital erythropoietic porphyria

porphyria cutanea tarda

coproporphyria

erythropoietic protoporphyria

porphyria variegata

INTERMEDIATE #2

INTERMEDIATE #3

INTERMEDIATE #4

INTERMEDIATE #5

INTERMEDIATE #6

INTERMEDIATE #7

Resulting Conditions

Consequencesof mutations in enzymes in thesynthesis of Heme

Anatomy and Physiology I Protein Synthesis and the Genetic Code Instructor: Mary Holman.

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