fill in ap paper and then make a chart enzyme role in what process? helicase dna polymerase...
TRANSCRIPT
Fill in AP paper and thenmake a chart
Enzyme Role In what process?
HelicaseDNA polymeraseTopoisomerasePrimaseLigaseNucleaseTelomeraseRNA polymerasesnRNA
DNA Replication: A Closer Look
• The copying of DNA is remarkable in its speed and accuracy
• More than a dozen enzymes and other proteins participate in DNA replication
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Origins of ReplicationVideo
• At the end of each replication bubble is a replication fork, a Y-shaped region where new DNA strands are elongating
• Helicases are enzymes that untwist the double helix at the replication forks
• Single-strand binding protein binds to and stabilizes single-stranded DNA until it can be used as a template
• Topoisomerase corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands
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Fig. 16-13
Topoisomerase
Helicase
PrimaseSingle-strand binding proteins
RNA primer
55
5 3
3
3
DNA Polymerase
3’ 5’
3’5’ Pol
Pol
Leading and Lagging Strands
5’
5’
3’
3’
Leading Strand
Lagging Strand
Pol
3’
5’
Okazaki FragmentsRNAPrimer
Video
Other Proteins at Replication Fork
Pol
5’
5’
3’
3’
Leading Strand
Lagging Strand
Pol
3’
5’
Okazaki Fragments
Helicase
Single StrandedBinding Proteins
Primase
DNA Pol I
Ligase
DNA Pol III
Fig. 16-16 Overview
Origin of replication
Leading strand
Leading strand
Lagging strand
Lagging strand
Overall directions of replication
Template strand
RNA primer
Okazaki fragment
Overall direction of replication
12
3
2
1
1
1
1
2
2
51
3
3
3
3
3
3
3
3
3
5
5
5
5
5
5
5
5
5
5
53
3
Damaged DNA Nuclease Excision Repair
Nuclease
DNA Polymerase
Ligase
Replicating the Ends of DNA Molecules
• Limitations of DNA polymerase create problems for the linear DNA of eukaryotic chromosomes
• The usual replication machinery provides no way to complete the 5 ends, so repeated rounds of replication produce shorter DNA molecules
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Replicating Ends of Linear Chromosomes
Fig. 16-19Ends of parental DNA strands
Leading strand
Lagging strand
Lagging strand
Last fragment Previous fragment
Parental strand
RNA primer
Removal of primers and replacement with DNA where a 3 end is available
Second round of replication
New leading strand
New lagging strand
Further rounds of replication
Shorter and shorter daughter molecules
5
3
3
3
3
3
5
5
5
5
• If chromosomes of germ cells became shorter in every cell cycle, essential genes would eventually be missing from the gametes they produce
• An enzyme called telomerase catalyzes the lengthening of telomeres in germ cells
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Telomerase
Central Dogma of Molecular Biology
Gene Structure
Promoter Terminator
Transcribed Region
RNA( )Open Reading Frame5’UTR 3’UTR
Three Parts to Transcription• Transcriptional Initiation –
– RNA polymerase binds to promoter– DNA strands separate– RNA synthesis begins as ribonucleotides complementary to template
strand are linked• Transcriptional Elongation
– RNA polymerase moves down DNA unwinding a small window of DNA.– Nucleotides are added to the growing RNA chain
• Transcriptional Termination– When the RNA polymerase reaches terminator the RNA and the RNA
polymerase are released from the DNA.
RNA Processing in Eukaryotes5’ 3’
Modification of 5’ and 3’ ends
Pre-mRNA (hnRNA)
Spicing of exons
5’CAP Poly A tailExon1 Intron1 Exon2 Intron2 Exon3 Intron3 Exon4
Genetic Code
Identifying ORF
• Locate start codon (1st ATG from 5’ end)
• Identify Codons (non overlapping units of three codons including and following start codon)
• Stop at stop codon ( remember stop codon doesn’t encode amino acid)
• Nucleotides before start codon – 5’UTR
• Nucleotides after stop codon -3’UTR
• [MetArgAsnAlaSerLeu]
GACGACGGAUGCGCAAUGCGUCUCUAUGAGACGUAGCUCAC5’
Players in Translation
mRNA – Genetic CodeRibosome – synthesizes protientRNA – adaptor moleculeAmino acidsAminoacyl tRNA synthetases
- attach amino acids to tRNAs
Fig. 17-18-4
Amino endof polypeptide
mRNA
5
3E
Psite
Asite
GTP
GDP
E
P A
E
P A
GDPGTP
Ribosome ready fornext aminoacyl tRNA
E
P A
tRNA
Ribosomes
Three parts to Translation• Initiation
– Delivery of Ribosome with first tRNA to start codon.• Elongation Cycle
– Three Parts of Elongation Cycle• Delivery of tRNA to A site• Transpeptidase Activity – Amino acids on tRNA in P site cleaved from
tRNA and attached to amino acid on tRNA in A site.• Translocation – Ribosome ratchets over on codon. The tRNA that was in
the A site is moved to the P site. The uncharged tRNA in the P site exits the ribosome through the E site.
• Termination– When ribosome reaches the stop codon a release factor
binds to the A site and triggers the release of the polypeptide. The ribosome releases the tRNA and the mRNA.
The Functional and Evolutionary Importance of Introns
• Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during RNA splicing
• Such variations are called alternative RNA splicing• Because of alternative splicing, the number of
different proteins an organism can produce is much greater than its number of genes
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Fig. 17-12Gene
DNAExon 1 Exon 2 Exon 3Intron Intron
Transcription
RNA processing
Translation
Domain 2
Domain 3
Domain 1
Polypeptide
Polysomes
• Polypeptide synthesis always begins in the cytosol• Synthesis finishes in the cytosol unless the
polypeptide signals the ribosome to attach to the ER
• Polypeptides destined for the ER or for secretion are marked by a signal peptide
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• A signal-recognition particle (SRP) binds to the signal peptide
• The SRP brings the signal peptide and its ribosome to the ER
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Proteins targeted to ER
Functions of RNA
• mRNA – genetic code• tRNA – adaptor molecules• rRNA- part of ribosome• snRNA – part of splicosome• SRP RNA – part of SRP• siRNA- eukaryotic gene regulation
Silent Mutations
Missense Mutations
Nonsense Mutations
