Download DNA - Bishop Shanahan High School

DNA
Roles of DNA
Timeline of DNA Discovery and Structure
DNA Structure
DNA Replication
Roles of DNA
• Store Information
DNA is STABLE!!
Chemically & physically
Stays in nucleus
Roles of DNA
• Copy Information
Two complementary strands
for replication and
crosscheck for error
Roles of DNA
• Transmit Information
Unique base sequences
code for all the proteins
that make up an organism
These codes are
passed from generation
to generation
“Pre-history” of DNA as heredity unit
1866 Mendel - heredity “factors” are segregated, have
dominance and are independently sorted;
used pea plants
1905 Bateson and Punnett – some “factors” are linked;
used pea plants
1910 Morgan – chromosome theory, linkage maps;
used fruit flies
General thought: PROTEINS must be the heredity factor!
DNA is just a structural molecule for the proteins.
WHY was this thought?
Timeline of DNA Discovery
1928 Griffith – “transforming principle” ;
used bacteria and mice
1944 Avery, Macleod, McCarty – proposed DNA is
‘transforming principle’; used bacteria and enzymes
1950 Chargaff – rules of DNA base ratios;
used paper chromatography and spectrophotometry
1952 Hershey and Chase – confirmed DNA as molecule
of heredity; used isotopes and bacteriophage
YAY for DNA!
Griffith’s Experiment
Avery, MacLeod, McCarty
Chargaff’s Results
Hershey-Chase Experiment
Hershey-Chase Experiment
Why it’s called the “Blender Experiment”
Timeline of DNA Structure and Replication
1953 Wilkins and Franklin – image of DNA crystals;
used X-ray crystallography
1953 Watson and Crick – the famous double helix model;
used models
1955 Kornberg – purified DNA polymerase;
used bacterial extracts
1958 Meselson - Stahl – semi-conservative replication;
used isotopes and density gradient centrifugation
Wilkins and Franklin
Watson and Crick
The Double Helix Model
“It has not escaped our notice that the specific pairing we
have postulated immediately suggests a possible copying
mechanism for the genetic material.”
Watson and Crick (1953)
Kornberg
Proposed Models for DNA Replication
• Semi-conservative
- One “old”,
one “new” strand
• Conservative
– “Old” double DNA
directs a “new” DNA
• Dispersive
– “Old” and “new”
get interspersed
Meselson – Stahl Experiment
Meselson – Stahl Results
DNA Structure
• Building Block – Nucleotide
Phosphate-Deoxyribose-Nitrogenous Base
• Sugar-Phosphate Backbone – Anti-Parallel
• Base Pairing: A-T G-C
via Hydrogen Bonds
DNA Structure
Basic Building Block - Nucleotide
Nitrogenous Bases – A T G C
Sugar-Phosphate Backbone
• Covalent bonds
Anti-Parallel Strands
Double Helix
A – T and G – C
• Hydrogen Bonds
DNA Replication
During the S phase of the cell cycle, DNA replicates.
DNA has to unwind to create a replication fork
Enzyme: Helicase
DNA Replication
DNA Replication
DNA Polymerase adds bases 5’  3’ ONLY
This results in two types of replication:
Leading Strand: Add nucleotides 5’  3’ sequentially in
direction of replication fork; continuous
Lagging Strand: Add nucleotides 5’  3’ in sections in
opposite direction which get connected later; discontinuous
DNA Replication
Prokaryote vs Eukaryote
Prokaryote
Eukaryote
Location
Cytoplasm
Nucleus
Chromosome
1 Circular
1
Many –
non-circular
Many
DNA
Polymerases
DNA
Polymerases
AT G C
Complementary
Anti-Parallel
AT G C
Complementary
Anti-Parallel
Origin
Enzymes
DNA
DNA Replication - Prokaryote
DNA Replication - Eukaryote
On to Transcription and Translation ….