Chapter 14 From DNA to Protein. Ricin – comes from the castor oil plant Inactivates ribosomes,...
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Transcript of Chapter 14 From DNA to Protein. Ricin – comes from the castor oil plant Inactivates ribosomes,...
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Chapter 14Chapter 14
From DNA to ProteinFrom DNA to Protein
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Ricin – comes from the castor oil plant Ricin – comes from the castor oil plant
Inactivates ribosomes, the protein-building Inactivates ribosomes, the protein-building machinery of all cellsmachinery of all cells
Impacts, Issues: Impacts, Issues: Ricin and Your Ricin and Your RibosomesRibosomes
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Marvelous Mussel AdhesiveMarvelous Mussel Adhesive
Mussel binds itself to rocks with threads Mussel binds itself to rocks with threads
coated with the protein bysusscoated with the protein bysuss
Gene for bysuss has been put into yeastGene for bysuss has been put into yeast
Yeast synthesize the protein based on the Yeast synthesize the protein based on the
instructions in the mussel DNAinstructions in the mussel DNA
WHY IS THIS POSSIBLE?WHY IS THIS POSSIBLE?
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Central DogmaCentral Dogma
DNA RNA PROTEIN
TRANSCRIPTION TRANSLATION
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Same two steps produce all proteins:Same two steps produce all proteins:
1) DNA is transcribed to form RNA1) DNA is transcribed to form RNA Occurs in the nucleusOccurs in the nucleus RNA moves into cytoplasmRNA moves into cytoplasm
2) RNA is translated to form polypeptide 2) RNA is translated to form polypeptide chains, which fold to form proteinschains, which fold to form proteins
Steps from DNA to ProteinsSteps from DNA to Proteins
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Three Classes of RNAsThree Classes of RNAs
Messenger RNAMessenger RNA Carries protein-building instructionCarries protein-building instruction
Ribosomal RNARibosomal RNA Major component of ribosomesMajor component of ribosomes
Transfer RNATransfer RNA Delivers amino acids to ribosomes Delivers amino acids to ribosomes
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A Nucleotide Subunit of RNAA Nucleotide Subunit of RNA
phosphate group
sugar (ribose)
uracil (base)
Fig. 14-2, p. 220
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base pairing during transcription
DNA
RNA
DNA
DNA
base pairing during DNAreplication
Fig. 14-2c, p.220
Base Pairing during
Transcription
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Transcription & DNA ReplicationTranscription & DNA Replication
Like DNA replicationLike DNA replication Nucleotides added in 5’ to 3’ directionNucleotides added in 5’ to 3’ direction
Unlike DNA replicationUnlike DNA replication Only small stretch is templateOnly small stretch is template RNA polymerase catalyzes nucleotide RNA polymerase catalyzes nucleotide
additionaddition Product is a single strand of RNAProduct is a single strand of RNA
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PromoterPromoter
A base sequence in the DNA that A base sequence in the DNA that signals the start of a genesignals the start of a gene
For transcription to occur, RNA For transcription to occur, RNA polymerase must first bind to a polymerase must first bind to a promoter (Initiation)promoter (Initiation)
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InitiationInitiation
promoter region
RNA polymerase, the enzyme that catalyzes transcription
a RNA polymerase initiates transcription at a promoter region in DNA. It recognizes a base sequence located next to the promoter as a template. It will link the nucleotides adenine, cytosine, guanine, and uracil into a strand of RNA, in the order specified by DNA.
Fig. 14-3a, p.220
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newly forming RNA transcript
DNA template unwindingDNA template winding up
DNA template at selected transcription site
b All through transcription, the DNA double helix becomes unwound in front of the RNA polymerase. Short lengths of the newly forming RNA strand briefly wind up with its DNA template strand. New stretches of RNA unwind from the template (and the two DNA strands wind up again).
Fig. 14-3b, p.220
Elongation
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direction of transcription3´
growing RNA transcript
5´
5´ 3´
c What happened at the assembly site? RNA polymerase catalyzed the assembly of ribonucleotides, one after another, into an RNA strand, using exposed bases on the DNA as a template. Many other proteins assist this process.
Fig. 14-3c, p.221
Adding Nucleotides
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d At the end of the gene region, the last stretch of the new transcript is unwound and released from the DNA template. Shown below is a model for a transcribed strand of RNA.
Fig. 14-3d, p.221
Termination
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unit of transcription in a DNA strand
exon intron
mature mRNA transcript
poly-A tail
snipped out snipped out
exon exonintron
cap
transcription into pre-mRNA
Fig. 14-4, p.221
Transcript Modification
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mRNA ModificationmRNA Modification
5' cap – modified guanine cap5' cap – modified guanine cap 3' poly-A tail3' poly-A tail Introns = interuptionsIntrons = interuptions Exits = exitExits = exit Alternative splicingAlternative splicing
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mature mRNA transcript
5’ 3’
3’
poly-A tail
5’
snipped out snipped out
cap
transcription into pre-mRNA
unit of transcription in a DNA strand
exon intron exon exonintron3’ 5’
Stepped Art
Fig. 14-4, p.221
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Conference AssignmentConference Assignment
Response paper:Response paper: Find an article that relates to the conference.Find an article that relates to the conference.
• You will turn a copy of this in.You will turn a copy of this in. Basically a five paragraph essay:Basically a five paragraph essay:
• Summarize the articleSummarize the article• How does this topic relate to the conferenceHow does this topic relate to the conference• Your response to this topic (why is it important, Your response to this topic (why is it important,
etc)etc)
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Genetic CodeGenetic Code Set of 64 base Set of 64 base
tripletstriplets CodonsCodons 61 specify amino 61 specify amino
acidsacids 3 stop translation3 stop translation High conservedHigh conserved
Fig. 14-6, p.222
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DNA
mRNA
mRNAcodons
threonine proline glutamate glutamate lysine
amino acids
Fig. 14-5, p.222
Genetic Code
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tRNA StructuretRNA Structure
codon in mRNA
anticodon
amino acid OH
amino-acidattachment site
Figure 14.7Page 223
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tRNA StructuretRNA Structure
aa attachment siteaa attachment site Attached by activating enzymesAttached by activating enzymes
There are 45 tRNA, not 64 as the genetic There are 45 tRNA, not 64 as the genetic code would suggest, WHY?code would suggest, WHY? Wobble effectWobble effect
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funnel
small ribosomal subunit
large ribosomal subunit
intact ribosome+Fig. 14-8, p.223
Ribosomes
2 units of rRNA and protein2 units of rRNA and protein Large and small units converge when Large and small units converge when
translatingtranslating Built in nucleus (nucleosome)Built in nucleus (nucleosome)
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Three Stages of TranslationThree Stages of TranslationOROR
Gum Drop Protein SynthesisGum Drop Protein Synthesis
InitiationInitiation
ElongationElongation
TerminationTermination
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OverviewOverview
Transcription
Translation
mRNA rRNA tRNA
Mature mRNA transcripts
ribosomal subunits
mature tRNA
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InitiationInitiation
Initiator tRNA binds to small Initiator tRNA binds to small ribosomal subunitribosomal subunit
Small subunit/tRNA Small subunit/tRNA complex attaches to mRNA complex attaches to mRNA and moves along it to an and moves along it to an AUG “start” codonAUG “start” codon
Large ribosomal subunit Large ribosomal subunit joins complexjoins complex
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Binding Sites Binding Sites
binding site for mRNA
P (first binding site for tRNA)
A (second binding site for tRNA)
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ElongationElongation
mRNA passes through ribosomal subunits mRNA passes through ribosomal subunits tRNAs deliver amino acids to the tRNAs deliver amino acids to the
ribosomal binding site in the order ribosomal binding site in the order specified by the mRNAspecified by the mRNA
Peptide bonds form between the amino Peptide bonds form between the amino acids and the polypeptide chain growsacids and the polypeptide chain grows
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ElongationElongation
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TerminationTermination
Stop codon into placeStop codon into place No tRNA with anticodonNo tRNA with anticodon Release factors bind to Release factors bind to
the ribosomethe ribosome mRNA and polypeptide mRNA and polypeptide
are releasedare released
new polypeptide chain
mRNA
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What Happens to the What Happens to the New Polypeptides?New Polypeptides?
Some just enter the cytoplasmSome just enter the cytoplasm
Many enter the endoplasmic reticulum and Many enter the endoplasmic reticulum and move through the cytomembrane system move through the cytomembrane system where they are modifiedwhere they are modified
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Gene MutationsGene Mutations
Base-Pair Substitutions or Point Base-Pair Substitutions or Point
MutationsMutations InsertionsInsertions DeletionsDeletions
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Base-Pair SubstitutionBase-Pair Substitution
original base triplet in a DNA strand
During replication, proofreading enzymes make a substitution
a base substitution within the triplet (red)
original, unmutated sequence
a gene mutation
possible outcomes:
or
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Frameshift MutationsFrameshift Mutations
InsertionInsertion Extra base added into gene regionExtra base added into gene region
DeletionDeletion Base removed from gene regionBase removed from gene region
Both shift the reading frameBoth shift the reading frame
Result in many wrong amino acids Result in many wrong amino acids
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THREONINE PROLINE GLUTAMATE GLUTAMATE LYSINE
THREONINE PROLINE VALINE GLUTAMATE LYSINE
THREONINE PROLINE GLYCINE ARGININE
part of DNA template
mRNA transcribed from DNA
resulting amino acid sequence
base substitution in DNA
altered mRNA
altered amino acid sequence
deletion in DNA
altered mRNA
altered amino acid sequence
Fig. 14-10, p.226
Frameshift Mutation
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TransposonsTransposons
DNA segments that move DNA segments that move spontaneously about the genomespontaneously about the genome
When they insert into a gene region, When they insert into a gene region, they usually inactivate that genethey usually inactivate that gene
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TransposonsTransposons
Barbara McClintockBarbara McClintock
Nonuniform coloration of kernels in strains Nonuniform coloration of kernels in strains of indian cornof indian corn
Fig. 14-11, p.227
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Mutation Rates Mutation Rates
Each gene has a characteristic mutation Each gene has a characteristic mutation rate rate Can be used as a molecular clock for Can be used as a molecular clock for
evolutionevolution Average rate for eukaryotes is between Average rate for eukaryotes is between
1010-4-4 and 10 and 10-6-6 per gene per generation per gene per generation Only mutations that arise in germ cells can Only mutations that arise in germ cells can
be passed on to next generationbe passed on to next generation
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MutagensMutagens
Ionizing radiation (X Ionizing radiation (X
rays)rays)
Nonionizing radiation Nonionizing radiation
(UV)(UV)
Natural and synthetic Natural and synthetic
chemicalschemicals
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How can you explain the occurrence of How can you explain the occurrence of birth defects (caused by altered genes) in birth defects (caused by altered genes) in children and grandchildren of the victims of children and grandchildren of the victims of the atomic bombs that destroyed Hiroshima the atomic bombs that destroyed Hiroshima and Nagasaki, Japan, when the victims and Nagasaki, Japan, when the victims themselves were only mildly affected?themselves were only mildly affected?
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Euk vs Prok Protein SynthesisEuk vs Prok Protein Synthesis
Most have intronsMost have introns mRNA must be mRNA must be
completely formed completely formed and pass thru and pass thru nuclear membranenuclear membrane
mRNA modified mRNA modified before translationbefore translation
Larger ribosomesLarger ribosomes
None (w/ None (w/ exceptions)exceptions)
Often start Often start translation before translation before transcription is donetranscription is done
Begin at AUG but Begin at AUG but proceeded by a proceeded by a special sequencespecial sequence
Small ribosomesSmall ribosomes