the blueprint of life, from dna to protein
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The Blueprint of Life, From DNA to Protein. Chapter 7. Preview. How does the genetic information pass on to the next generation? How is the information stored in DNA being used to make protein? How are the protein expression regulated?. The Blueprint of Life. - PowerPoint PPT PresentationTRANSCRIPT
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The Blueprint of Life,From DNA to Protein
Chapter 7
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Preview
• How does the genetic information pass on to the next generation?
• How is the information stored in DNA being used to make protein?
• How are the protein expression regulated?
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The Blueprint of Life
• Characteristics of each cell dictated by information contained on DNA– DNA holds master blueprint
• All cell structures and processes directed by DNA
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Review of DNA basics
5’ end (phosphate)3’ end (hydroxyl)
Two H bondsThree H bonds
•Double-stranded
•Double helix•Sugar-phosphate backbone
•Strands are complementary•Base-pairing rules:
A-TG-C
•Strands are anti-parallel
•Composed of deoxyribonucleotidesCovalently bonded in chains
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N N N N N N N N N N5’ 3’
N N N N N N N N N N5’3’
If there are 400 cytosines in a DNA molecule that has 1000 base-pairs, how many adenines does the molecule have?
C C C C
G G G G
A A A A A A
T T T T T T
question
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Figure 7.1
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DNA Replication
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DNA Replication
•Semi-conservative
Orig.
New
New
Orig.
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DNA Replication
•Synthesis is 5’ 3’ (note: polymerase reads template 3’ 5’)
•Semi-conservative•Bi-directional
•DNA polymerase “reads” template, adds proper nucleotide to the 3’ end of the new chain
•Second round of replication can start before first is complete
•DNA polymerases generally corrects errors during replication (“proofreading”)Error rate = 1/billion nucleotides
•DNA polymerases require a primer (they can only add nucleotides onto an existing chain)
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question
If a primer were available that bound to the center of the template molecule in the diagram below, which way would DNA polymerase move during DNA synthesis?
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A G T C T G C C T A T C G T G A C T A5’ 3’
T C A G A C G G A T A G C A C T G A T5’3’ 5’
5’ 3’
5’
question
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A G T C T G C C T A T C G T G A C T A5’ 3’
T C A G A C G G A T A G C A C T G A T5’3’ 5’
question
5’ 3’
5’
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A G T C T G C C T A T C G T G A C T A5’ 3’
T C A G A C G G A T A G C A C T G A T5’3’ 5’
question
5’ 3’
5’
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A G T C T G C C T A T C G T G A C T A5’ 3’
T C A G A C G G A T A G C A C T G A T5’3’ 5’
question
5’ 3’
5’
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A G T C T G C C T A T C G T G A C T A5’ 3’
T C A G A C G G A T A G C A C T G A T5’3’ 5’
question
5’ 3’
5’
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A G T C T G C C T A T C G T G A C T A5’ 3’
T C A G A C G G A T A G C A C T G A T5’3’ 5’
and so on…
question
5’ 3’
5’
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DNA ReplicationReplication is initiated at a single distinct region (origin of replication = ori)
*Depicts only a small segment of the circular chromosome
5’
3’
3’
5’
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DNA Replication
5’
3’
3’
5’
5’5’
Replication is initiated at a single distinct region (origin of replication = ori)
A short stretch of RNA (complementary to DNA) is synthesized
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DNA Replication
5’
3’
3’
5’
5’
5’
Replication is initiated at a single distinct region (origin of replication = ori)
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DNA Replication
5’
3’
3’
5’
5’
5’
The replication fork (details are shown in Figure 7.6, which is optional)Leading strand - continuous synthesisLagging strand - discontinuous synthesis (Okazaki fragments)
DNA ligase
Replication is initiated at a single distinct region (origin of replication = ori)
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DNA Replication
•Semi-conservative•Bi-directional•Second round of replication can start before first is complete
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DNA Replication
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Gene expression
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DNA to Proteins - General Principles
-- .. -.-. .-. --- -... .. --- .-.. --- --. -.--M I C R O B I O L O G Y
ATGCCCGTAGATGGCCCTGAGCGACCGGACCCTGATGCC
met pro val asp gly pro glu arg pro asp pro asp ala
Morse code: Distinct series of dots and dashes encode the 26 letters of the alphabet
Letters strung together make words sentences stories
DNA: Distinct series (triplets) of the four nucleotides encode the 20 amino acidsAmino acids strung together make proteins (structural and functional) cells organisms
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Gene Expression - Overview
Coded by DNA:
Protein AProtein BProtein CProtein DProtein EProtein FProtein GProtein HProtein I
RNA transcripts:
Protein DProtein D
Protein DProtein D
Protein D
Protein D
Protein D
Protein D
Protein D
Protein D
Protein molecules
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
Transcription Translation
Gene: functional unit of DNA that contains information to produce a specific product
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Gene Expression - Overview
Coded by DNA:
Protein AProtein BProtein CProtein DProtein EProtein FProtein GProtein HProtein I
RNA transcripts:
Transcription
Messenger (mRNA)Ribosomal RNA (rRNA)Transfer RNA (tRNA)
rRNAtRNA
Three functional types of RNA:
Translation
Protein molecules
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Review of RNA basics
•Composed of ribonucleotides (ribose not deoxyribose); uracil replaces thymine
Characteristics of RNA
OH
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Characteristics of RNA
•Composed of ribonucleotides (ribose not deoxyribose); uracil replaces thymine
Characteristics of RNA
•Single-stranded•Sequence is “identical” to a stretch of one strand of DNA; complementary to the other
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•Composed of ribonucleotides (ribose not deoxyribose); uracil replaces thymine
Characteristics of RNA
•Single-stranded•Sequence is “identical” to a stretch of one strand of DNA; complementary to the other
RNA
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•Composed of ribonucleotides (ribose not deoxyribose); uracil replaces thymine
Characteristics of RNA
•Single-stranded•Sequence is “identical” to a stretch of one strand of DNA; complementary to the other
Template strand
RNA
Note: always read (and write) a DNA (or RNA) sequence in the 5’ to 3’ direction, or specify otherwise
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Bacterial Gene Expression - Transcription
Transcription initiates at a promoter (sequence “theme” recognized by RNA polymerase)
Transcription stops at a terminator
5’TTGACA3’
3’AACTGT5’
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Bacterial Gene Expression - Transcription
Terms to note:
MonocistronicPolycistronic (prokaryotes only)
UpstreamDownstream
Initiation - RNA polymerase binds to promoter (guided by sigma factor)
Elongation - RNA polymerase synthesizes RNA in 5’ 3’ (no primer needed)
Termination -
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Bacterial Gene Expression - Transcription
5’ A T G A T C T G A G T A T G C G C T 3’
3’ T A C T A G A C T C A T A C G C G A 5’
3’ T A C T A G A C T C A T A C G C G A 5’
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Bacterial Gene Expression - Transcription
5’ A T G A T C T G A G T A T G C G C T 3’
3’ U A C U A G A C U C A U A C G C G U 5’
5’ A U G A U C U G A G U A U G C G C U 3’
3’ T A C T A G A C T C A T A C G C G A 5’
5’TTGACA3’
3’ -----------5’
5’-----------3’
3’ACAGTT5’
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Prokaryotic Gene Expression - Transcription
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Prokaryotic Gene Expression - Transcription
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Bacterial Gene Expression - Translation
•Ribosomes “read” mRNA; facilitate conversion of the encoded information into proteins•Message is read in triplets (codons)
AGAAUGCCCAAUGCGUUACGAUGCCC
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Bacterial Gene Expression - Translation
•Ribosomes “read” mRNA; facilitate conversion of the encoded information into proteins•Message is read in triplets (codons)
AGAAUGCCCAAUGCGUUACGAUGCCC
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Bacterial Gene Expression - Translation
•Ribosomes “read” mRNA; facilitate conversion of the encoded information into proteins•Message is read in triplets (codons)
But where should the ribosome start “reading”???
•Genetic code is degenerate
AGAAUGCCCAAUGCGUUACGAUGCCC
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Bacterial Gene Expression - Translation
But where should the ribosome start “reading”???
•Prokaryotes (monocistronic and polycistronic messages) - translation begins at first AUG after a ribosome-binding site
•Ribosomes “read” mRNA; facilitate conversion of the encoded information into proteins
•Eukaryotes (moncistronic messages only) - translation begins at first AUG
•Message is read in triplets (codons)•Genetic code is degenerate
AGAAUGCCCAAUGCGUUACGAUGCCC
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Bacterial Gene Expression - Translation
Proper reading frame is critical
AGAAUGCCCAAUGCGUUACGAUGCCC
AUG
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Bacterial Gene Expression - Translation
Proper reading frame is critical
AGAAUGCCCAAUGCGUUACGAUGCCC
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Bacterial Gene Expression - Translation
tRNAs are the “keys” that decipher the code
•Each tRNA carries a specific amino acid•Each tRNA has a specific anticodon, complementary to a codon, that binds mRNA
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Bacterial Gene Expression - Translation
translocation
elongation factors
Initiation
Elongation
5’
E P A
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Bacterial Gene Expression - Translation
Termination
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Bacterial Gene Expression - Translation
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Eukaryotic Gene Expression
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Prokaryotic Gene Expression
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Eukaryotic Gene Expression
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Prokaryotic Gene Expression
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Eukaryotic Gene Expression
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Eukaryotic Gene Expression
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Eukaryotic Gene Expression
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Eukaryotic Gene Expression
AAAAAAAAAA
AAAAAAAAAA
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Regulation of Gene Expression
• Microorganisms regulate its gene expression to adapt environment change– Controls metabolic pathways
• Two general mechanism– Allosteric inhibition of enzymes– Controlling synthesis of enzymes
» Directed at making only what is required
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Prokaryotic Gene Regulation
Coded by DNA:
Protein AProtein BProtein CProtein DProtein EProtein FProtein GProtein HProtein I
RNA transcripts:
Protein DProtein D
Protein DProtein D
Protein D
Protein D
Protein D
Protein D
Protein D
Protein D
Protein molecules
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
Transcription Translation
rRNAtRNA
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Prokaryotic Gene Regulation
Constitutive enzymes
Inducible enzymes
Repressible enzymes
Always produced
Genes turned “on” only when needed
Genes turned “off” when not needed
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• Mechanisms controlling transcription– Often controlled by regulatory region near
promoter• Protein binds to region and acts as “on/off” switch
– Binding protein can act as repressor or activator» Repressor blocks transcription» Activator facilitates transcription
Regulation of Gene Expression
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Regulation of Gene Expression
• Repressors– inhibits gene expression and decreases the
synthesis of enzymes– usually in response to the overabundance of
an end product– Repressors block the ability of RNA polymerase to bind
and initiate protein synthesis– Corepressor– inducer
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Regulation of Gene Expression
• Activators– turns on the transcription of a gene or set of
genes• Inducer• Enzymes synthesized in the presence of inducers
are called inducible enzymes
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Regulation of Gene Expression
• Operon model of gene expression– a set of genes that are controlled by
regulatory proteins – divided into two regions, the control region
and the structural region• The control region include the operator and the
promoter– The operator acts as the “on-off” switch
• The structural region includes the structural genes– This region contains the genes being transcribed
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Operon structure
Promoter – Binding site for RNA polymerase
Operator – binding site for the repressor protein for the regulation of gene expression
Structural Genes – DNA sequence for specific proteins
Operator
Gene 1 Gene 3Gene 2
Promoter
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Prokaryotic Gene Regulation
DNA-binding proteins
repressor binds, blocking transcription
activator binds, facilitating transcription
(negative control)
(positive control)
Activity of activators/repressors can be controlled
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Lac operon -galactosidase
transport
Lactose glucose + galactose
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Lac operon -galactosidase
transport
Turned “on” only when lactose is present AND glucose levels are low
Is lactose present? If no, repress
Is glucose present? If yes, don’t activate
Lactose glucose + galactose
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Lac operonTurned “on” only when lactose is present AND glucose levels are low
Glucose transport into cell lowers cAMP levels
Negative control - repressor is active if lactose is absent; inactive if lactose is present
Positive control - CAP only binds if cAMP is available (glucose levels are low)