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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. - PowerPoint PPT Presentation
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BIOLOGYCONCEPTS & CONNECTIONS
Fourth Edition
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
From PowerPoint® Lectures for Biology: Concepts & Connections
CHAPTER 10Molecular Biology of the Gene
Modules 10.6 – 10.16
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The information constituting an organism’s genotype is carried in its sequence of bases
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• A specific gene specifies a polypeptide
– The DNA is transcribed into RNA, which is translated into the polypeptide
Figure 10.6A
DNA
RNA
Protein
TRANSCRIPTION
TRANSLATION
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Evolution of Crick’s Central Dogma from the 1950s to today
1950’s DNA RNA Protein
DNA RNA Poly-peptide
Splicing
AlternativeSplicing
Phosphorylation
Glycosylation
Methylation
Acetylation
1980’s
DNA RNA Poly-peptide
SplicingAlternative
SplicingOther catalyticregulator RNAs
MicroRNAsEditing
ConformationalIsomers
Phosphorylation
Glycosylation
Methylation
Acetylation
Other
Histonemodifications
Other epigeneticfactors
Today
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
10.7 Genetic information written in codons is translated into amino acid sequences
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.7
DNA molecule
Gene 1
Gene 2
Gene 3
DNA strand
TRANSCRIPTION
RNA
Polypeptide
TRANSLATIONCodon
Amino acid
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• Virtually all organisms share the same genetic code
10.8 The genetic code is the Rosetta stone of life
Figure 10.8A
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• An exercise in translating the genetic code
Figure 10.8B
Startcodon
RNA
Transcribed strand
StopcodonTranslation
Transcription
DNA
Polypeptide
Template strand or antisense - strand
Coding Strand orSense + strand
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
10.9 Transcription produces genetic messages in the form of RNA
Figure 10.9A
RNApolymerase
RNA nucleotide
Direction oftranscription
Newly made RNA
Templatestrand of DNA
In eukaryotes, RNA poly 1Synthesizes rRNA, II synthesizes mRNA, and III synthesizestRNA. RNA poly. Has 5Subunits: 2 alpha bind reg-ulatory subunits, 1 beta binds the DNA template,1 beta binds thenucleosides, and one sigmarecognizes the promoterand initiates synthesis.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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.
The enzymes of transcription
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• In transcription, the DNA helix unzips
– 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.
RNA polymerase
DNA of gene
PromoterDNA Terminator
DNAInitiation
Elongation
Termination
Area shownin Figure 10.9A
GrowingRNA
RNApolymerase
Completed RNA
Figure 10.9Bhttp://www.johnkyrk.com/DNAtranscription.html
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
10.10 Eukaryotic RNA (hnRNA) is processed before leaving the nucleus
Figure 10.10
DNA
RNAtranscriptwith capand tail
mRNA
Exon Intron IntronExon Exon
TranscriptionAddition of cap and tail
Introns removed
Exons spliced together
Coding sequenceNUCLEUS
CYTOPLASM
Tail
Cap
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Alternative splicing
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide
• The process is aided by transfer RNAs
10.11 Transfer RNA molecules serve as interpreters during translation
Figure 10.11A
Hydrogen bond
Amino acid attachment site
RNA polynucleotide chain
Anticodon
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• 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
10.12 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
10.13 An initiation codon marks the start of an mRNA message
Figure 10.13A
End
Start of genetic message
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• mRNA, a specific tRNA, and the ribosome subunits assemble during initiation
Figure 10.13B
1
Initiator tRNA
mRNA
Startcodon Small ribosomal
subunit
2
P site
Largeribosomalsubunit
A site
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
10.14 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.14
1 Codon recognition
Amino acid
Anticodon
AsiteP site
Polypeptide
2 Peptide bond formation
3 Translocation
Newpeptidebond
mRNAmovement
mRNA
Stopcodon
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
1. Initiation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The sequence of codons in DNA spells out the primary structure of a polypeptide
– Polypeptides form proteins that cells and organisms use
10.15 Review: The flow of genetic information in the cell is DNARNAprotein
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Summary of transcription and translation
Figure 10.15
1Stage mRNA istranscribed from aDNA template.
Anticodon
DNA
mRNARNApolymerase
TRANSLATION
Enzyme
Amino acid
tRNA
InitiatortRNA
Largeribosomalsubunit
SmallribosomalsubunitmRNA
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
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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
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• 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
10.16 Mutations can change the meaning of genes
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Figure 10.16A
Normal hemoglobin DNA
mRNA
Normal hemoglobin
Glu
Mutant hemoglobin DNA
mRNA
Sickle-cell hemoglobin
Val
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Types of mutations
Figure 10.16B
mRNANORMAL GENE
BASE SUBSTITUTION
BASE DELETION
Protein Met Lys Phe Gly Ala
Met Lys Phe Ser Ala
Met Lys Leu Ala His
Missing
Missense-mutation causing a change in aa.Nonsense-mutation causing a premature stop codon
Causes a “frame shift”
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