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

ANIMATION Frederick Griffith • Living bacterial cells were converted to disease causing bacteria (transformation) • “Transforming factor”

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

ANIMATION Hershey-Chase Experiment • Tagged protein coat with radioactive sulfur • Tagged viral genome with radioactive phosphorus

Erwin Chargaff • 1952 - Nitrogenous base composition • % of adenine is equal to % of 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 ( D eoxyribo n ucleic a cid) • Nucleic acid • Consists of monomers called nucleotides • Stores genetic information, determines an organisms traits by synthesizing proteins • Each organisms genome is unique

ANIMATION Structure of DNA • Double helix • Consists of a double strand of nucleotides • Two strands are anti-parallel: strands are oriented in opposite directions – 5’ to 3’ – 3’ to 5’

Nucleotide Composition • Three parts of a nucleotide – 5 carbon sugar called deoxyribose – Phosphate group – A single nitrogenous base

Four Nitrogenous Bases • Purines (double ring) • Pyrimidines (single ring) – Adenine (A) – Thymine (T) – Guanine (G) – 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?

ANIMATION 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

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

ANIMATION More animations for your viewing pleasure…. DNA Replication Animation Steps of DNA Replication