Download DNA: Structure and Function

DNA: The Genetic Material
1. DNA History,
Structure, and
Function
2. DNA
Replication
DNA (Deoxyribonucleic Acid)
A person’s cellular function and inheritance
depends on DNA.
Famous Experiments from the
1940’s-1960’s that indicated DNA
was the Molecule of Heredity
• Griffith & Avery—DNA transformed nonvirulent bacteria to virulent bacteria
• Hershey & Chase—DNA from viruses is
injected to host bacteria cells, cells become
infected.
Griffith’s Experiment
Somehow the harmless strained
changed and became harmless. HOW?
Transformation
Avery’s Experiments;
The Search for the Substance
Responsible for Transformation
Discovered that DNA
destroying enzymes
stop transformation.
Hershey and Chase Experiment;
More Evidence For DNA
First, a
little
about how
viruses
infect
cells…
Does the protein coat, the DNA, or both direct the
production of new viruses?
Bacteriophage (phage)-a virus that
infects bacteria
A Crocheted
Bacteriophage
Hershey and Chase Experiment;
More Evidence For DNA
Phages were used to
show that DNA, not
protein is the genetic
material of viruses
It’s Confirmed! DNA is the
Mysterious Molecule of Heredity!
1950- the
search to
unravel it’s
structure is
on!
Rosalind Franklin 1951
Chargaff 1950
Discovered that
there were equal
amounts of A &
T, and C & G in
DNA; hinted at
base-pairing
Watson & Crick Propose Model of
DNA 1953
• Made of subunits called
nucleotides
• A nucleotide is made of
three smaller units: a sugar
(deoxyribose), a phospate
group, and a nitrogenous
base
• The 4 nitrogenous bases are:
Adenine (A)
Thymine (T)
Cytocine (C)
Guanine (G)
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 bases
form hydrogen bonds
between the strands
• A is complimentary to T
• G is complimentary to C
DNA Model
Functions of DNA
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.
A protein that gives
you a trait
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-Ribonucleic Acid
Three Kinds of RNA
1.
2.
3.
Messenger RNA (mRNA):
carries genetic code from
nucleus to ribosome in
cytoplasm
Transfer RNA (tRNA):
transfers amino acids to a
ribosome for protein
assembly
Ribosomal RNA (rRNA):
part of the structure of
ribosomes
Three Characteristics
of RNA
1. The sugar in RNA is Ribose
2. Uracil replaces Thymine
U-A, A-U
3. 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