DNA and Replication DNA: The Primary Source of Heritable - - PowerPoint PPT Presentation

DNA and Replication

DNA: The Primary Source of Heritable Information

• Genetic information is transmitted from one

generation to the next through DNA or RNA

Chromosomes

• Non-eukaryotic (bacteria) organisms have

circular chromosomes

• Eukaryotic organisms have multiple linear

chromosomes

• Exceptions:

– Some bacterial cells have linear chromosomes – Mitochondria and chloroplasts have been found to have circular and linear chromosomes

Plasmids

• Prokaryotes, viruses and eukaryotes (yeast)

may contain plasmids

• Plasmids are small extra-chromosomal,

double-stranded circular DNA molecules

• Plasmids make excellent cloning vectors

Plasmids as Cloning Vectors

Important Historical Experiments

• The proof that DNA is the carrier of genetic

information involved a number of important historical experiments, including: –Frederick Griffith –Avery-MacLeod-McCarty –Hershey-Chase –Watson, Crick, Wilkins and Franklin

Frederick Griffith

• 1928 - Experiments in bacterial transformation
• Smooth (S) pathogenic bacteria
• Rough (R) nonpathogenic bacteria

Frederick Griffith

• Living bacterial cells were converted to

disease causing bacteria (transformation)

• “Transforming factor”

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Avery-MacLeod-McCarty Experiments

• Experiments demonstrated that DNA is the

“transforming” material, not protein

Avery-MacLeod-McCarty Experiments

• Used different enzymes to destroy protein,

RNA or DNA in separate tubes to determine if transformation occurs

Hershey-Chase Experiment

• 1952 - Concluded that DNA, not protein,

functions as the genetic material of phage T2

Hershey-Chase Experiment

• Tagged protein coat with radioactive sulfur
• Tagged viral genome with radioactive

phosphorus

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Erwin Chargaff

• 1952 - Nitrogenous base

composition

• % of adenine is equal to %
• f thymine
• % of guanine is equal to %

cytosine

• Composition of DNA varies

from species to species

Maurice Wilkins and Rosalind Franklin

• 1951 - Worked with a technique called X-ray

diffraction

• Determined the helical nature of DNA

James Watson and Francis Crick

• 1953 – Determined the structure of DNA

using Chargaff’s and Franklin’s data

• Franklin’s picture showed two strands of

nucleotides

DNA (Deoxyribonucleic acid)

• Nucleic acid
• Consists of monomers called nucleotides
• Stores genetic information, determines an
• rganisms traits by synthesizing proteins
• Each organisms genome is unique

Structure of DNA

• Double helix
• Consists of a double strand of nucleotides
• Two strands are anti-parallel: strands are
• riented in opposite directions

–5’ to 3’ –3’ to 5’

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Nucleotide Composition

• Three parts of a nucleotide

– 5 carbon sugar called deoxyribose –Phosphate group –A single nitrogenous base

Four Nitrogenous Bases

• Purines (double ring)

– Adenine (A) – Guanine (G)

• Pyrimidines (single ring)

– Thymine (T) – Cytosine (C)

Purines pair with Pyrimidines

Chargaff’s Rules

• A-T (2 hydrogen bonds)
• C-G (3 hydrogen bonds)

DNA Replication

Why do cells need to replicate DNA?

Semi-Conservative Replication

• New DNA molecules have one original

template strand and one new strand

• Follows complementary base pair rules and

begins at sites called origins of replication

• “Leading strand” – continuously synthesized
• “Lagging strand” – synthesized in fragments

ANIMATION

Semi-conservative Replication

Origin of Replication - Prokaryotes

Origins of Replication - Eukaryotes

Replication Bubbles

Enzyme Functions

• Helicase
• RNA Primase
• DNA Polymerase III
• DNA Polymerase I
• DNA Ligase
• Topoisomerase
• Single-strand binding proteins (not an

enzyme)

Replication Direction

• Replication proceeds in the 5’ to 3’ direction
• DNA polymerase can only add free

nucleotides to the 3' end of the newly forming strand

DNA Replication Animation Steps of DNA Replication

More animations for your viewing pleasure….

ANIMATION