Transcript DNA - LiveText

DNA: Structure and Function
The DNA Revolution
• 1940s-1960s
• Griffith & Avery—DNA transformed
pneumococcus bacteria.
• Encouraged the study of prokaryotic
chromosomes.
• Hershey and Chase—Bacteriophage
experiment. DNA from viruses is injected
to host bacteria cells.
Griffith and Avery
Hershey & Chase
Hershey & Chase
Hershey & Chase
The Search for the Structure of
the DNA Molecule
• 1951—Rosalind Franklin—X-ray
crystallography
• Chargaff—Chargaff’s rules. Ratio of
nitrogenous bases in DNA. Complimentary
bases.
• Watson & Crick--1953
Franklin
Chargaff
Watson & Crick Model of DNA
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Nucleotides
Sugar—Deoxyribose
Phosphate Group
Nitrogenous Bases
Adenine & Thymine
are complementary.
• Cytosine and Guanine
are complimentary.
• Purines—Adenine &
Guanine
• Pyrimidines—
Cytosine & Thymine
• 5’ End—Phosphate
side
• 3’ End—Other side
Watson & Crick Model
• DNA is composed of 2
chains of nucleotides that
form a double helix shape.
• The two strands are
antiparallel.
• The backbone of the DNA
molecule is composed of
alternating phosphate
groups and sugars.
• The complimentary
nitrogenous bases
form hydrogen bonds
between the strands.
• A is complimentary to
T and G is
complimentary to C.
DNA Model
DNA
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Functions
1. Storage of genetic information
2. Self-duplication & inheritance.
3. Expression of the genetic message.
DNA’s major function is to code for
proteins.
• Information is encoded in the order of the
nitrogenous bases.
Chromosomes
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Prokaryotic
Circular
Very small
1 chromosome per cell
Some enzymes and
proteins are associated
with the DNA.
• Not housed in a
nucleus.
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Eukaryotic
Linear
Fairly long
Several chromosomes per
cell.
Histone proteins--”spools”. Same in all
eukaryotes
Housed in a nucleus.
Nucleosome—2 loops of
DNA wrapped around 8
histone proteins.
Unity theme.
Central Dogma of Genetics
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DNA
mRNA
Proteins
Traits
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Replication
Unzip
Template
Floating nucleotides
• Template
• Sense strand
• Semiconservative
Replication
• DNA Polymerase
• Proofreading functions
• 5’ to 3’ only
• Replication fork
• Discontinuous assembly
• Okazaki fragments
RNA
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3 types—mRNA, tRNA, rRNA
Ribose
Uracil replaces Thymine
Single stranded helix
Transcription
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RNA polymerase
Messenger RNA
mRNA
Unzipping of DNA helix.
Sense strand or template strand
Codons
Genetic code
Translation
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Ribosomes
rRNA
Large and small subunits
Codons
Initiator or start codon
Methionine (AUG)
Stop codons
tRNA
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Initiation
Chain Elongation
Peptide bonds
Chain termination
Polysome