Fig. 17-5Second mRNA base

Firs

t mRN

A ba

se (5

end

of c

odon

)

Third

mRN

A ba

se (3

end

of c

odon

)

Polypeptide

Ribosome

Aminoacids

tRNA withamino acidattached

tRNA

Anticodon

Trp

Phe Gly

Codons 35

mRNA

the mechanism of translation

Fig. 17-14

Amino acidattachment site

3

5

Hydrogenbonds

Anticodon

(a) Two-dimensional structure

Amino acidattachment site

5

3

Hydrogenbonds

3 5AnticodonAnticodon

(c) Symbol used in this book(b) Three-dimensional structure

Amino acid Aminoacyl-tRNAsynthetase (enzyme)

ATP

AdenosineP P P

AdenosineP

PP i

PPi

i

tRNA

tRNA

Aminoacyl-tRNAsynthetase

Computer modelAMPAdenosineP

Aminoacyl-tRNA(“charged tRNA”)

Attaching amino acids to tRNAs:Amino-acyl tRNA synthases

-20 different synthases-Require ATP-Each must be specific to the right amino acid and tRNA(s)

tRNAGLN

Aminoacyl-tRNA synthase(ATSGLN)

Adenylated Glutamine

Fig. 17-16b

P site (Peptidyl-tRNAbinding site) A site (Aminoacyl-

tRNA binding site)E site(Exit site)

mRNAbinding site

Largesubunit

Smallsubunit

(b) Schematic model showing binding sites

Next amino acidto be added topolypeptide chain

Amino end Growing polypeptide

mRNAtRNA

E P A

E

Codons

(c) Schematic model with mRNA and tRNA

5

3

The Ribosome

LSU

SSU

Fig. 17-18-1

Amino endof polypeptide

mRNA

5

3E

Psite

Asite

Fig. 17-18-2

Amino endof polypeptide

mRNA

5

3E

Psite

Asite

GTP

GDP

E

P A

Fig. 17-18-3

Amino endof polypeptide

mRNA

5

3E

Psite

Asite

GTP

GDP

E

P A

E

P A

Peptide bond formation- Transfer of growing chain from tRNA in P site to tRNA in A site

Fig. 17-18-3

Amino endof polypeptide

mRNA

5

3E

Psite

Asite

GTP

GDP

E

P A

E

P A

Fig. 17-18-4

Amino endof polypeptide

mRNA

5

3E

Psite

Asite

GTP

GDP

E

P A

E

P A

GDPGTP

Ribosome ready fornext aminoacyl tRNA

E

P A

Fig. 17-17

3355U

UA

ACGMet

GTP GDPInitiator

tRNA

mRNA5 3

Start codon

mRNA binding siteSmallribosomalsubunit

5

P site

Translation initiation complex

3

E A

Met

Largeribosomalsubunit

Initiating translation

Fig. 17-19-1

Releasefactor

3

5Stop codon(UAG, UAA, or UGA)

Terminating translation

Fig. 17-19-2

Releasefactor

3

5Stop codon(UAG, UAA, or UGA)

5

32

Freepolypeptide

2 GDP

GTP

Terminating translation

Fig. 17-19-3

Releasefactor

3

5Stop codon(UAG, UAA, or UGA)

5

32

Freepolypeptide

2 GDP

GTP

5

3

Terminating translation

Fig. 17-20

Growingpolypeptides

Completedpolypeptide

Incomingribosomalsubunits

Start ofmRNA(5 end)

PolyribosomeEnd ofmRNA(3 end)

(a)

Ribosomes

mRNA

(b) 0.1 µm

Second mRNA base

Firs

t mRN

A ba

se (5

end

of c

odon

)

Third

mRN

A ba

se (3

end

of c

odon

)

The genetic code:-read in triplet codons

-once a start codon is specified, codons are read in order (5’ to 3) until a “stop” codon is read

-redundant

-unambiguous

-universal*

DNA sequence

RNA sequence

Amino acid sequence

Protein structure and function

tRNAGLN

Aminoacyl-tRNA synthase(ATSGLN)

Adenylated Glutamine

tRNAGLN

Aminoacyl-tRNA synthase(ATSGLN)

Adenylated Glutamine

Altered DNA sequence

Altered RNA sequence

Altered (?) Amino acid sequence

Altered (?) Protein structure and function

Fig. 5-17Nonpolar

Glycine(Gly or G)

Alanine(Ala or A)

Valine(Val or V)

Leucine(Leu or L)

Isoleucine(Ile or I)

Methionine(Met or M)

Phenylalanine(Phe or F)

Trypotphan(Trp or W)

Proline(Pro or P)

Polar

Serine(Ser or S)

Threonine(Thr or T)

Cysteine(Cys or C)

Tyrosine(Tyr or Y)

Asparagine(Asn or N)

Glutamine(Gln or Q)

Electricallycharged

Acidic Basic

Aspartic acid(Asp or D)

Glutamic acid(Glu or E)

Lysine(Lys or K)

Arginine(Arg or R)

Histidine(His or H)

The 20 amino acids

Fig. 17-23a

Wild type

3DNA templatestrand

3

355

5mRNA

Protein

Amino endStop

Carboxyl end

A instead of G

33

3

U instead of C

55

5

Stop

Silent (no effect on amino acid sequence)

Fig. 17-23a

Wild type

3DNA templatestrand

3

355

5mRNA

Protein

Amino endStop

Carboxyl end

A instead of G

33

3

U instead of C

55

5

Stop

Silent (no effect on amino acid sequence)

Fig. 17-23b

Wild type

DNA templatestrand

35

mRNA

Protein

5

Amino endStop

Carboxyl end

53

3

T instead of C

A instead of G

33

3

5

5

5

Stop

Missense

Fig. 17-22

Wild-type hemoglobin DNA

mRNA

Mutant hemoglobin DNA

mRNA

33

3

3

3

3

55

5

55

5

C CT T TTG GA A AA

A A AGG U

Normal hemoglobin Sickle-cell hemoglobin

Glu Val

Fig. 17-23cWild type

DNA templatestrand

35

mRNA

Protein

5

Amino endStop

Carboxyl end

53

3

A instead of T

U instead of A

33

3

5

5

5

Stop

Nonsense

Fig. 17-23e

Wild type

DNA templatestrand

35

mRNA

Protein

5

Amino end

Stop

Carboxyl end

53

3

missing

missing

33

3

5

5

5

Frameshift causing extensive missense (1 base-pair deletion)