Chapter 17:From Gene to Protein

Figure 17-01

LE 17-2

Class IMutants(mutationIn gene A)Wild type

Class IIMutants(mutationIn gene B)

Class IIIMutants(mutationIn gene C)

Precursor

Ornithine

AEnzyme

A

Citrulline

Arginine

Gene A

Gene B

Gene C

Precursor Precursor Precursor

AA

B B B

Ornithine Ornithine OrnithineEnzyme

B

EnzymeC

Arginine Arginine ArginineC C C

Citrulline Citrulline Citrulline

MinimalMedium(MM)(control)

Wild typeClass IMutants

Class IIMutants

Class IIIMutants

MM +Ornithine

MM +Citrulline

MM +arginine(control)

LE 17-4

DNAmolecule

Gene 1

Gene 2

Gene 3

DNA strand(template)

3

TRANSCRIPTION

Codon

mRNA

TRANSLATION

Protein

Amino acid

35

5

DNA vs. RNA(review from chapter 5)

Activity: (16) DNA and RNA Structure

LE 17-3-2

TRANSCRIPTIONDNA

Prokaryotic cellRibosome

Polypeptide

mRNA

Prokaryotic cell

Activity: Overview of Protein Synthesis

20 amino acids

LE 17-5Second mRNA base

Firs

t mR

NA

bas

e (5

end

)

Third

mR

NA

bas

e (3

end

)

LE 17-7

Elongation Non-templatestrand of DNA

RNApolymerase

RNA nucleotides

3 end3

5

5

Newly madeRNA

Templatestrand of DNA

Direction of transcription(“downstream”)

Promoter

53

RNA polymeraseStart point

DNA

Transcription unit

35

53

35

UnwoundDNA

RNAtran-script

Template strandof DNA

Initiation

Elongation

Termination

53

35

53

35

35

RewoundDNA

RNAtranscript

5

Completed RNA transcript

Activity: Transcription

Transcription

LE 17-7a-1

Promoter Transcription unit

RNA polymeraseStart point DNA

53

35

DNAi.org

LE 17-9

5Protein-coding segment

5 Start codon Stop codon Poly-A tail

Polyadenylation signal

5 3Cap UTR UTR

Activity: RNA Processing

mRNA processing (eukaryotes only)

LE 17-10

5 Exon Intron Exon Intron Exon 3Pre-mRNA

1 30 31 104 105 146

Codingsegment

Introns cut out andexons spliced together

1 1465Cap

5Cap

Poly-A tail

Poly-A tail

5 3UTR UTR

LE 17-11

Exon 15

Intron Exon 2

Other proteinsProtein

snRNA

snRNPs

RNA transcript (pre-mRNA)

Spliceosome

5

Spliceosomecomponents

Cut-outintron

mRNA

Exon 1 Exon 25

LE 17-12

Gene

Transcription

RNA processing

Translation

Domain 2

Domain 3

Domain 1

Polypeptide

Exon 1 Intron Exon 2 Intron Exon 3

DNA

Activity: Overview of Protein Synthesis

Protein Synthesis

Polypeptide

tRNA withamino acidattached

Ribosome

tRNA

Anticodon

35

mRNA

Aminoacids

Codons

LE 17-14a

Amino acidattachment site

Hydrogenbonds

3

5

Two-dimensional structureAnticodon

Amino acidattachment site

35

Hydrogenbonds

Anticodon Anticodon

Symbol used in this bookThree-dimensional structure

3 5

tRNA

LE 17-15Amino acid Aminoacyl-tRNA

synthetase (enzyme)

Pyrophosphate

Phosphates

tRNA

AMP

Aminoacyl tRNA(an “activatedamino acid”)

LE 17-16

Amino end

mRNA

5

3

Growing polypeptide

Next amino acidto be added topolypeptide chain

tRNA

Schematic model with mRNA and tRNA

Computer model of functioning ribosome

5 3

E

Codons

Schematic model showing binding sites

Smallsubunit

Largesubunit

A site (Aminoacyl-tRNA binding site)E site

(Exit site)E P A

mRNAbinding site

P site (Peptidyl-tRNAbinding site)

Smallsubunit

Largesubunit

Exit tunnelGrowingpolypeptidetRNA

molecules

E P A

mRNA

Activity: Translation

LE 17-17

Met

GTPInitiator tRNA

mRNA

5 3

mRNA binding site

Smallribosomalsubunit

Start codon

P site

5 3

Translation initiation complex

E A

Largeribosomalsubunit

GDP

Met

Translation: Initiation

LE 17-18

Ribosome ready fornext aminoacyl tRNA

mRNA

5

Amino endof polypeptide

E

Psite

Asite

3

2

2 GDP

E

P A

GTP

GTP

GDP

E

P A

E

P A

Elongation

LE 17-5Second mRNA base

Firs

t mR

NA

bas

e (5

end

)

Third

mR

NA

bas

e (3

end

)

LE 17-19

Releasefactor

Stop codon(UAG, UAA, or UGA)

5

3

5

3

5

Freepolypeptide

3

When a ribosome reaches a stopcodon on mRNA, the A site of theribosome accepts a protein calleda release factor instead of tRNA.

The release factor hydrolyzes thebond between the tRNA in theP site and the last amino acid of thepolypeptide chain. The polypeptideis thus freed from the ribosome.

The two ribosomal subunitsand the other componentsof the assembly dissociate.

Termination

DNAi.org

LE 17-20

Ribosomes

mRNA

This micrograph shows a large polyribosome in a prokaryotic cell (TEM).

An mRNA molecule is generally translated simultaneouslyby several ribosomes in clusters called polyribosomes.

Incomingribosomalsubunits

Growingpolypeptides

End ofmRNA(3 end)

Start ofmRNA(5 end)

Polyribosome

Completedpolypeptides

m0.1

LE 17-21

Ribosomes

mRNASignalpeptide

Signal-recognitionparticle(SRP)

SRPreceptorprotein

CYTOSOL

ER LUMEN Translocationcomplex

Signalpeptideremoved

ERmembrane

Protein

LE 17-22

RNA polymerase

DNA

Polyribosome

RNApolymerase

Direction oftranscription

mRNA

0.25

DNA

Polyribosome

Polypeptide(amino end)

Ribosome

mRNA (5 end)

m

LE 17-23

Wild-type hemoglobin DNA

mRNA

3 5 53

5 3 35

Mutant hemoglobin DNA

mRNA

Normal hemoglobin Sickle-cell hemoglobin

LE 17-24

Base-pair substitution

No effect on amino acid sequenceU instead of C

MissenseA instead of G

NonsenseU instead of A

Stop

Amino end

Protein5 3

Carboxyl end

Stop

Stop

Stop

mRNA

Wild type

LE 17-25

Base-pair insertion or deletion

Frameshift causing immediate nonsense

Extra U

MissingFrameshift causingextensive missense

Insertion or deletion of 3 nucleotides:no frameshift but extra or missing amino acid

Missing

Stop

Stop

Amino end Carboxyl endStop

Wild type

mRNAProtein

5 3

LE 17-26

TRANSCRIPTION

RNA PROCESSING

RNAtranscript5

Exon

NUCLEUS

FORMATION OFINITIATION COMPLEX

CYTOPLASM

3

DNA

RNApolymerase

RNA transcript(pre-mRNA)

Intron

Aminoacyl-tRNAsynthetase

AminoacidtRNA

AMINO ACID ACTIVATION

3

mRNA

A

P

E Ribosomalsubunits

5

Growingpolypeptide

E A

Activatedamino acid

Anticodon

TRANSLATION

Codon

Ribosome

Noncoding segments…

Follow up to the Unseen Genome: Gems Among the Junk

ENCODE