Molecular Biology of the Gene DNA Lesson Part 1 Dr. Wilson Muse Schoolcraft College.
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Transcript of Molecular Biology of the Gene DNA Lesson Part 1 Dr. Wilson Muse Schoolcraft College.
Molecular Biology of the Gene
DNA Lesson Part 1
Dr. Wilson MuseSchoolcraft College
10.1 Experiments showed that DNA is the genetic material
– Frederick Griffith discovered that a “transforming factor” could be transferred into a bacterial cell
– Disease-causing bacteria were killed by heat– Harmless bacteria were incubated with heat-killed
bacteria– Some harmless cells were converted to disease-
causing bacteria, a process called transformation – The disease-causing characteristic was inherited
by descendants of the transformed cells
Copyright © 2009 Pearson Education, Inc.
10.1 Experiments showed that DNA is the genetic material
– Alfred Hershey and Martha Chase used bacteriophages to show that DNA is the genetic material
– Bacteriophages are viruses that infect bacterial cells– Phages were labeled with radioactive sulfur to detect
proteins or radioactive phosphorus to detect DNA– Bacteria were infected with either type of labeled
phage to determine which substance was injected into cells and which remained outside
Copyright © 2009 Pearson Education, Inc.
10.1 Experiments showed that DNA is the genetic material
– The sulfur-labeled protein stayed with the phages outside the bacterial cell, while the phosphorus-labeled DNA was detected inside cells
– Cells with phosphorus-labeled DNA produced new bacteriophages with radioactivity in DNA but not in protein
Copyright © 2009 Pearson Education, Inc.
Animation: Hershey-Chase Experiment
Animation: Phage T2 Reproductive Cycle
Head
Tail fiber
DNA
Tail
Head
Tail fiber
DNA
Tail
Batch 1Radioactiveprotein
Bacterium
Radioactiveprotein
DNA
Phage
Pellet
RadioactiveDNA
Batch 2RadioactiveDNA
Emptyprotein shell
PhageDNA
Centrifuge
Radioactivityin liquid
Measure theradioactivity inthe pellet andthe liquid.
4Centrifuge the mixtureso bacteria form apellet at the bottom ofthe test tube.
3Agitate in a blender toseparate phagesoutside the bacteriafrom the cells andtheir contents.
2Mix radioactivelylabeled phages withbacteria. The phagesinfect the bacterial cells.
1
Pellet
CentrifugeRadioactivityin pellet
Batch 1Radioactiveprotein
Bacterium
Radioactiveprotein
DNA
Phage
RadioactiveDNA
Batch 2RadioactiveDNA
Agitate in a blender toseparate phagesoutside the bacteriafrom the cells andtheir contents.
2Mix radioactivelylabeled phages withbacteria. The phagesinfect the bacterial cells.
1
Empty protein shell
Phage DNA
Pellet
Emptyprotein shell
PhageDNA
Centrifuge
Radioactivityin liquid
Measure theradioactivity inthe pellet andthe liquid.
Centrifuge the mixtureso bacteria form apellet at the bottom ofthe test tube.
Pellet
CentrifugeRadioactivityin pellet
43
Phage attachesto bacterial cell.
Phage injects DNA. Phage DNA directs hostcell to make more phageDNA and protein parts.New phages assemble.
Cell lyses andreleases new phages.
DNADNA• DNADNA is often called
the blueprint of life..• In simple terms,
DNA contains the instructions for making proteins within the cell.
NucleotidesNucleotides
C C
C
OPhosphate
O
CC
O -P OO
O
O -P OO
O
O -P OO
O One deoxyribose together with its phosphate and base make a
nucleotide.
Nitrogenous base
Deoxyribose
10.2 DNA and RNA are polymers of nucleotides
– The monomer unit of DNA and RNA is the nucleotide, containing
– Nitrogenous base– 5-carbon sugar– Phosphate group
Copyright © 2009 Pearson Education, Inc.
– DNA and RNA are polymers called polynucleotides
– A sugar-phosphate backbone is formed by covalent bonding between the phosphate of one nucleotide and the sugar of the next nucleotide
– Nitrogenous bases extend from the sugar-phosphate backbone
Copyright © 2009 Pearson Education, Inc.
Animation: DNA and RNA Structure
Sugar-phosphate backbone
DNA nucleotide
Phosphate group
Nitrogenous baseSugar
DNA polynucleotide
DNA nucleotide
Sugar(deoxyribose)
Thymine (T)
Nitrogenous base(A, G, C, or T)
Phosphategroup
Sugar(deoxyribose)
Thymine (T)
Nitrogenous base(A, G, C, or T)
Phosphategroup
Pyrimidines
Guanine (G)Adenine (A)Cytosine (C)Thymine (T)
Purines
Sugar(ribose)
Uracil (U)
Nitrogenous base(A, G, C, or U)
Phosphategroup
Hydrogen Bonds, Hydrogen Bonds, cont.
• When making hydrogen bonds, cytosine always pairs up with guanine,
• And adenine always pairs up with thymine.
• (Adenine and thymine are shown here.)
C
C
CC
N
N
N
N
N
C
C
C
C
C
N
N
OO
OO
C
C
C
C
C
N
N
OO
N
C
C
C
C
N N
OO
NN
N C
Hydrogen BondsHydrogen Bonds
• The bases attract each other because of hydrogen bonds.
• Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.
• (The bonds between cytosine and guanine are shown here.)
Twist
Hydrogen bond
Basepair
Partial chemical structure Computer modelRibbon model
Basepair
Ribbon model
Hydrogen bond
Partial chemical structure
10.4 DNA replication depends on specific base pairing
– DNA replication follows a semiconservative model
– The two DNA strands separate– Each strand is used as a pattern to produce a
complementary strand, using specific base pairing– Each new DNA helix has one old strand with one
new strand
Copyright © 2009 Pearson Education, Inc.
Animation: DNA Replication Overview
Two Stranded DNATwo Stranded DNA• Remember, DNA
has two strands that fit together something like a zipper.
• The teeth are the nitrogenous bases but why do they stick together?
DNA by the numbersDNA by the numbers• Each cell has about 2 m
of DNA.• The average human has
75 trillion cells.• The average human has
enough DNA to go from the earth to the sun more than 400 times.
• DNA has a diameter of only 0.000000002 m.
The earth is 150 billion mor 93 million miles from the sun.
Copyright © 2009 Pearson Education, Inc.
DNA REPLICATION
Makin’ copies ........
10.4 DNA replication depends on specific base pairing
– DNA replication follows a semiconservative model
– The two DNA strands separate– Each strand is used as a pattern to produce a
complementary strand, using specific base pairing– Each new DNA helix has one old strand with one
new strand
Copyright © 2009 Pearson Education, Inc.
Animation: DNA Replication Overview
Parentalmoleculeof DNA
Parentalmoleculeof DNA
Nucleotides
Both parentalstrands serveas templates
Parentalmoleculeof DNA
Nucleotides
Both parentalstrands serveas templates
Two identicaldaughter
molecules of DNA
– DNA replication begins at the origins of replication
– DNA unwinds at the origin to produce a “bubble”
– Replication proceeds in both directions from the origin
– Replication ends when products from the bubbles merge with each other
– DNA replication occurs in the 5’ 3’ direction
– Replication is continuous on the 3’ 5’ template
– Replication is discontinuous on the 5’ 3’ template, forming short segments
10.5 DNA replication proceeds in two directions at many sites simultaneously
Copyright © 2009 Pearson Education, Inc.
Animation: Leading Strand
10.5 DNA replication proceeds in two directions at many sites
simultaneously– Proteins involved in DNA replication– DNA polymerase adds nucleotides to a growing
chain– DNA ligase joins small fragments into a
continuous chain
Copyright © 2009 Pearson Education, Inc.
Animation: Lagging Strand
Animation: DNA Replication Review
Animation: Origins of Replication
Origin of replication Parental strand
Daughter strand
Bubble
Two daughter DNA molecules
3 end 5 end
3 end5 end
3
5
2
4
13
5
2
41
P
P
P
P
P
P
P
P
Parental DNA
35
DNA polymerasemolecule
DNA ligase
35
Overall direction of replication
Daughter strandsynthesizedcontinuously
35
35
Daughter strandsynthesizedin pieces
Copyright © 2009 Pearson Education, Inc.
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
– A gene is a sequence of DNA that directs the synthesis of a specific protein
– DNA is transcribed into RNA– RNA is translated into protein
– The presence and action of proteins determine the phenotype of an organism
Copyright © 2009 Pearson Education, Inc.
10.6 The DNA genotype is expressed as proteins, which
provide the molecular basis for phenotypic traits– Demonstrating the connections between genes
and proteins – The one gene–one enzyme hypothesis was based
on studies of inherited metabolic diseases– The one gene–one protein hypothesis expands the
relationship to proteins other than enzymes– The one gene–one polypeptide hypothesis
recognizes that some proteins are composed of multiple polypeptides
Copyright © 2009 Pearson Education, Inc.
Cytoplasm
Nucleus
DNA
Cytoplasm
Nucleus
DNA
Transcription
RNA
Cytoplasm
Nucleus
DNA
Transcription
RNA
Translation
Protein