Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings THE FLOW OF GENETIC...

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEINA specific gene specifies a polypeptide

– The DNA is transcribed into RNA, which is translated into the polypeptide

DNA

TRANSCRIPTION

RNA

TRANSLATION

Protein


• The “words” of the DNA “language” are triplets of bases called codons

– The codons in a gene specify the amino acid sequence of a polypeptide

CODONS


Figure 10.7

DNA molecule

Gene 1

Gene 2

Gene 3

DNA strand

TRANSCRIPTION

RNA

Polypeptide

TRANSLATIONCodon

Amino acid


• Virtually all organisms share the same genetic code

• 64 Codons total (4 x 4 x 4)

• AUG = Start (Met)

• 3 Stops

• Redundant, but NOT ambiguous

CODON TRANSLATION

Figure 10.8A


• An exercise in translating the genetic code

Figure 10.8B

Startcodon

RNA

Transcribed strand

StopcodonTranslation

Transcription

DNA

Polypeptide


Where does RNA come from: TRANSCRIPTION

Figure 10.9A

RNApolymerase

RNA nucleotide

Direction oftranscription

Newly made RNA

Templatestrand of DNA


• In transcription, the DNA helix unzips– Promoter: turns a

gene on/off

– RNA nucleotides line up along one strand of the DNA following the base-pairing rules

– The single-stranded messenger RNA peels away and the DNA strands rejoin

RNA polymerase

DNA of gene

PromoterDNA Terminator

DNAInitiation

Elongation

Termination

Area shownin Figure 10.9A

GrowingRNA

RNApolymerase

Completed RNA

Figure 10.9B


• Noncoding segments called introns are spliced out

• A cap and a tail are added to the ends

RNA Processing: Splicing Exons & Discarding Introns

Figure 10.10

DNA

RNAtranscriptwith capand tail

mRNA

Exon Intron IntronExon Exon

TranscriptionAddition of cap and tail

Introns removed

Exons spliced together

Coding sequence

NUCLEUS

CYTOPLASM

Tail

Cap


• In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide

• The process is aided by transfer RNAs

TRANSLATION: tRNA helps assemble the polypeptide chain (amino acids)

Figure 10.11A

Hydrogen bond

Amino acid attachment site

RNA polynucleotide chain

Anticodon


• Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other

Figure 10.11B, C

Anticodon

Amino acidattachment site


Ribosomes build polypeptides

Figure 10.12A-C

Codons

tRNAmolecules

mRNA

Growingpolypeptide

Largesubunit

Smallsubunit

mRNA

mRNAbindingsite

P site A site

P A

Growingpolypeptide

tRNA

Next amino acidto be added topolypeptide


• mRNA, a specific tRNA, and the ribosome

Figure 10.13B

1

Initiator tRNA

mRNA

Startcodon Small ribosomal

subunit

2

P site

Largeribosomalsubunit

A site


• The mRNA moves a codon at a time

• A tRNA pairs with each codon, adding an amino acid to the growing polypeptide

Amino acids are added to the polypeptide chain until a stop Codon is reached


Figure 10.14

1 Codon recognition

Amino acid

Anticodon

AsiteP site

Polypeptide

2 Peptide bond formation

3 Translocation

Newpeptidebond

mRNAmovement

mRNA

Stopcodon


• The sequence of codons in DNA spells out the primary structure of a polypeptide

– Polypeptides form proteins that cells and organisms use

Review: The flow of genetic information in the cell is DNARNAprotein


• Summary of transcription and translation

Figure 10.15

1Stage mRNA istranscribed from aDNA template.

Anticodon

DNA

mRNARNApolymerase

TRANSLATION

Enzyme

Amino acid

tRNA

InitiatortRNA

Largeribosomalsubunit

Smallribosomalsubunit

mRNA

Start Codon

2Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP.

3Stage Initiation of polypeptide synthesis

The mRNA, the first tRNA, and the ribosomal subunits come together.

TRANSCRIPTION


Figure 10.15 (continued)

4Stage ElongationGrowingpolypeptide

Codons

5Stage Termination

mRNA

Newpeptidebondforming

Stop Codon

The ribosome recognizes a stop codon. The poly-peptide is terminated and released.

A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time.

Polypeptide


• Mutations are changes in the DNA base sequence

– These are caused by errors in DNA replication or by mutagens

– The change of a single DNA nucleotide causes sickle-cell disease

Mutations can change the meaning of genes


Figure 10.16A

Normal hemoglobin DNA

mRNA

Normal hemoglobin

Glu

Mutant hemoglobin DNA

mRNA

Sickle-cell hemoglobin

Val


• Types of mutations

Figure 10.16B

mRNA

NORMAL GENE

BASE SUBSTITUTION

BASE DELETION

Protein Met Lys Phe Gly Ala

Met Lys Phe Ser Ala

Met Lys Leu Ala His

Missing

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings THE FLOW OF GENETIC...

Documents

Transcript of Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings THE FLOW OF GENETIC...