chapter 10 protein synthesis
DESCRIPTION
CHAPTER 10 Protein Synthesis. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN. 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 the sequence of bases in DNA - PowerPoint PPT PresentationTRANSCRIPT
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 10Protein Synthesis
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The information constituting an organism’s genotype is carried in the sequence of bases in DNA
• The flow of information is from DNA to RNA to protein
THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN
The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits
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• 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
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• Studies of inherited metabolic disorders first suggested that phenotype is expressed through proteins• Studies of the bread mold Neurospora crassa led to the one gene-one polypeptide hypothesis
Figure 10.6B
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Mutate wild type fungus
*Supply all mutant isolates with complete media
*Grow purified mutants with minimal media
to find nutritional mutants
*Determine what is the nutritional limitation find mutation
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There for the gene used to produce an enzyme that helps cells manufacture Arginine amino acid
was mutated in that fungal strain
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Transcription produces genetic messages in the form of RNA
Figure 10.9A
RNApolymerase
RNA nucleotide
Direction oftranscription
Newly made RNA
Templatestrand of DNA
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RNA Transcription
• Process in which the genetic information on DNA is transferred to RNA
• During transcription only 1 DNA stand serves as the template or pattern from which RNA is formed.
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• In transcription, the DNA helix unzips– 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 10.9Bhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf
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RNA Transcription
1. Initiation
• The enzyme RNA polymerase attaches to the promoter site on the DNA
• Promoter – a sequence of nucleotides that is found on one of the DNA strands
– tells RNA polymerase to start transcription and which of the two DNA strands to transcribe
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RNA Transcription
2. Elongation
• RNA nucleotides attach to the free DNA nucleotides by hydrogen bonds one at a time
• As RNA synthesis continues the growing RNA strand peels away from the DNA and the DNA strands rejoin
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RNA Transcription
3. Termination
• RNA polymerase reaches the terminator.
• Terminator – a sequence of bases on DNA that signals the end of the gene
• The RNA polymerase detaches from the DNA and the RNA molecule is complete
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• Noncoding segments called introns are spliced out
• The coding segments called exons are joined together
• A cap and a tail are added to the ends
10.10 Eukaryotic RNA 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 sequence
NUCLEUS
CYTOPLASM
Tail
Cap
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• 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
Genetic information written in codons is translated into amino acid sequences
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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
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
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Translation
• The process in which a polypeptide is synthesized using the genetic information encoded on an mRNA molecule
• The following are needed for translation to occur
1. mRNA
- Contains the instructions for the assembly of proteins
- Codon – a sequence of 3 bases on mRNA that specifies a specific amino acid that will be added to the polypeptide chain
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• In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide
• The process is aided by transfer RNAs
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
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Translation
2. tRNA (transfer RNA)
• Carries an amino acid to the ribosome
• A tRNA molecule is composed of
– A single strand of RNA (about 80 nucleotides)
– A loop at one end that contains the anticodon
– Anticodon – a sequence of 3 bases on tRNA that are complementary to the bases on mRNA
– At the opposite end of the loop is a site where an amino acit can attach
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Translation
3. Amino acids
• Located in the cytoplasm
• Synthesized from other chemicals or obtained from food
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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
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Translation
4. Ribosomes
• Organelles where protein synthesis occurs
• Consists of 2 subunits each made up of proteins and ribosomal RNA (rRNA)
– Small subunit – has binding site for mRNA
– Large subunit – has binding site for tRNA
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An initiation codon marks the start of an mRNA message
Figure 10.13A
End
Start of genetic message
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• 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
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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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• 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
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Figure 10.14
1 Codon recognition
Amino acid
Anticodon
AsiteP site
Polypeptide
2 Peptide bond formation
3 Translocation
Newpeptidebond
mRNAmovement
mRNA
Stopcodon
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Steps of Translation
1. Initiation
• mRNA binds to the ribosome
• The start codon (AUG) is reached
• The first amino acid (methionine) is brought to the ribosome by the tRNA
2. Elongation
• Amino acids are added one by one to a growing polypeptide chain
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Steps of Translation
3. Termination
• The stop codon is reached
• The completed polypeptide is released
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Modification of the polypeptide
Endoplasmic reticulum
• Collects proteins made by the ribosomes
• Packages them into vesicles which move to the Golgi apparatus
Golgi apparatus
• Proteins are altered, packaged into vesicles, and transported to different parts of the cell or exported out of the cell
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• 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
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• 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
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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
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
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• 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
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Types of Mutations
There are 2 general categories of mutations:
1. Base substitution
• The replacement of one nucleotide with another
• Can result in no change in the protein
• An insignificant change
– The altered amino acid has no effect on the function of the protein
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Types of Mutations
• A change that is crucial to life of the organism
– The altered amino acid has an effect on the function of the protein
2. Base insertions or deletions
• One or more bases are added or deleted from the DNA
• Often have disastrous effects
– The nucleotide sequence following the change alters the genetic message (reading frame)
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Mutations are Useful
Mutations are useful because they
1. Provide diversity that allows evolution by natural selection to occur
2. Essential tool for geneticists
• Create different alleles needed for genetic research