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CHAPTER 10 Molecular Biology of the Gene. Modules 10.6 – 10.16. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN. 10.6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits.

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slide2

THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN

10.6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits
  • The information constituting an organism’s genotype is carried in its sequence of bases
slide3

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

  • A specific gene specifies a polypeptide

DNA

TRANSCRIPTION

RNA

TRANSLATION

Protein

Figure 10.6A

slide4

1950’s

Protein

RNA

DNA

Phosphorylation

Glycosylation

Methylation

Acetylation

Splicing

1980’s

DNA

RNA

Poly-

peptide

Alternative

Splicing

Histone

modifications

MicroRNAs

Editing

Conformational

Isomers

Phosphorylation

Glycosylation

Methylation

Acetylation

Other

Splicing

Today

DNA

RNA

Poly-

peptide

Alternative

Splicing

Other epigenetic

factors

Other catalytic

regulator RNAs

The Evolution of Crick’s Central Dogma from the 1950s to today

10 7 genetic information written in codons is translated into amino acid sequences
10.7 Genetic information written in codons is translated into amino acid sequences
  • 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
slide6

Gene 1

Gene 3

DNA molecule

Gene 2

DNA strand

TRANSCRIPTION

RNA

Codon

TRANSLATION

Polypeptide

Amino acid

Figure 10.7

10 8 the genetic code is the rosetta stone of life
10.8 The genetic code is the Rosetta stone of life
  • Virtually all organisms share the same genetic code

Figure 10.8A

slide8

Template strand

or antisense - strand

Transcribed strand

  • An exercise in translating the genetic code

DNA

Coding Strand or

Sense + strand

Transcription

RNA

Startcodon

Stopcodon

Translation

Polypeptide

Figure 10.8B

10 9 transcription produces genetic messages in the form of rna
10.9 Transcription produces genetic messages in the form of RNA

In eukaryotes, RNA poly 1

Synthesizes rRNA, II synthesizes

mRNA, and III synthesizes

tRNA. RNA poly. Has 5

Subunits: 2 alpha bind reg-

ulatory subunits,

1 beta binds the

DNA template,

1 beta binds the

nucleosides, and

one sigma

recognizes the promoter

and initiates synthesis.

RNA nucleotide

RNApolymerase

Direction oftranscription

Templatestrand of DNA

Newly made RNA

Figure 10.9A

slide10

The enzymes of transcription

RNA polymerase I is responsible for transcribing

RNA that becomes structural components of the

ribosome. Pol 1 synthesizes a pre-rRNA 45S, which

matures into 28S, 18S and 5.8S rRNAs which will form

the major RNA sections of the ribosome.

RNA polymerase II transcribes protein-encoding

genes, or messenger RNAs, which are the RNAs

that get translated into proteins. Also, most snRNA (splicing)

and microRNAs (RNAi). This is the most studied type, and

due to the high level of control required over

transcription a range of transcription factors are

required for its binding to promoters.

RNA polymerase III transcribes a different structural

region of the ribosome (5s), transfer RNAs,

which are also involved the translation process, as

well as non-protein encoding RNAs.

slide11

RNA polymerase

DNA of gene

  • RNA nucleotides line up along one strand of the DNA following the base-pairing rules at the promoter. A regulatory protein binds at -25 binds the TATAAAA box.
  • This either allows the Polymerase to transcribe or not. Many other protein factors comprise the transcription complex.
  • 50 nucleotides/sec
  • 12 bases in the bubble
  • No proofreading enzymes like DNA
  • The single-stranded messenger RNA peels away and the DNA strands rejoin after GC hairpin forming region.

Promoter

DNA

Terminator

DNA

Initiation

  • In transcription, the DNA helix unzips

Elongation

Area shownin Figure 10.9A

Termination

GrowingRNA

Completed RNA

http://www.johnkyrk.com/DNAtranscription.html

RNApolymerase

Figure 10.9B

10 10 eukaryotic rna hnrna is processed before leaving the nucleus
10.10 Eukaryotic RNA (hnRNA) is processed before leaving the nucleus

Exon

Intron

Exon

Intron

Exon

DNA

TranscriptionAddition of cap and tail

  • Noncoding segments called introns are spliced out
  • A cap and a tail are added to the ends
  • 5” cap is a guanosine nucleotide connected to the mRNA via an unusual 5' to 5' triphosphate linkage. This guanosine is methylated on the 7' position directly after capping in vivo by a methyl transferase.
  • The addition of adenine nucleotides to the 3′ end of messenger ribonucleic acid molecules during posttranscriptional modification

Cap

RNAtranscriptwith capand tail

Introns removed

Tail

Exons spliced together

mRNA

Coding sequence

NUCLEUS

CYTOPLASM

Figure 10.10

10 11 transfer rna molecules serve as interpreters during translation
10.11 Transfer RNA molecules serve as interpreters during translation

Amino acid attachment site

  • In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide
  • The process is aided by transfer RNAs

Hydrogen bond

RNA polynucleotide chain

Anticodon

Figure 10.11A

slide15
Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other

Amino acidattachment site

Anticodon

Figure 10.11B, C

10 12 ribosomes build polypeptides
10.12 Ribosomes build polypeptides

Next amino acidto be added topolypeptide

Growingpolypeptide

tRNA

molecules

P site

A site

Growingpolypeptide

Largesubunit

tRNA

P

A

mRNA

mRNAbindingsite

Codons

mRNA

Smallsubunit

Figure 10.12A-C

10 13 an initiation codon marks the start of an mrna message
10.13 An initiation codon marks the start of an mRNA message

Start of genetic message

End

Figure 10.13A

slide18
mRNA, a specific tRNA, and the ribosome subunits assemble during initiation

Largeribosomalsubunit

Initiator tRNA

P site

A site

Startcodon

Small ribosomalsubunit

mRNA

1

2

Figure 10.13B

slide19
10.14 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
  • The mRNA moves a codon at a time relative to the ribosome
    • A tRNA pairs with each codon, adding an amino acid to the growing polypeptide
slide20

Amino acid

Polypeptide

Asite

P site

Anticodon

mRNA

1

Codon recognition

mRNAmovement

Stopcodon

Newpeptidebond

2

Peptide bond formation

3

Translocation

Figure 10.14

10 15 review the flow of genetic information in the cell is dna rna protein
10.15 Review: The flow of genetic information in the cell is DNARNAprotein
  • The sequence of codons in DNA spells out the primary structure of a polypeptide
    • Polypeptides form proteins that cells and organisms use
slide23

TRANSCRIPTION

DNA

Stage mRNA istranscribed from aDNA template.

1

mRNA

RNApolymerase

  • Summary of transcription and translation

Amino acid

TRANSLATION

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

2

Enzyme

tRNA

Initiator

tRNA

Anticodon

Stage Initiation of polypeptide synthesis

3

Largeribosomalsubunit

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

Start Codon

Smallribosomalsubunit

mRNA

Figure 10.15

slide24

Newpeptidebondforming

Growing

polypeptide

Stage Elongation

4

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.

Codons

mRNA

Polypeptide

Stage Termination

5

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

Stop

Codon

Figure 10.15 (continued)

10 16 mutations can change the meaning of genes
10.16 Mutations can change the meaning of genes
  • 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
slide26

Normal hemoglobin DNA

Mutant hemoglobin DNA

mRNA

mRNA

Normal hemoglobin

Sickle-cell hemoglobin

Glu

Val

Figure 10.16A

slide27

Missense-mutation causing a change in aa.

Nonsense-mutation causing a premature stop codon

  • Types of mutations

mRNA

NORMAL GENE

Protein

Met

Phe

Gly

Ala

Lys

BASE SUBSTITUTION

Met

Lys

Phe

Ser

Ala

Causes a “frame shift”

Missing

BASE DELETION

Met

Lys

Leu

Ala

His

Figure 10.16B