introduction to dna ( d eoxyribo n ucleic a cid)
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Introduction to DNA ( D eoxyribo n ucleic a cid). What do you know?. Scientists. Phoebus Levene. 1920 – Determined the basic structure of nucleotides that make up DNA 5-carbon sugar, phosphate group, and a nitrogenous base. Erwin Chargaff. 1952 - Nitrogenous base composition - PowerPoint PPT PresentationTRANSCRIPT
Introduction to DNA(Deoxyribonucleic acid)
What do you know?
Scientists
Phoebus Levene
• 1920 – Determined the basic structure of nucleotides that make up DNA
• 5-carbon sugar, phosphate group, and a nitrogenous base
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
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What is DNA?
DNA (Deoxyribonucleic acid)
• Nucleic acid• Consists of monomers called nucleotides• Stores genetic information, determines an
organisms traits by synthesizing proteins• Each organisms genome is unique
Structure of DNA
Structure of DNA
• Double helix• Consists of a double strand of nucleotides• Two strands are anti-parallel– 5’ to 3’– 3’ to 5’
Nucleotide• 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)
Chargaff’s Rules
• A-T (2 hydrogen bonds)
• C-G (3 hydrogen bonds)
• Sides of molecule - Alternating sugars and phosphates held together by strong covalent bonds
• Center – two nitrogenous bases held together by weak hydrogen bonds
DNA Structure
• Click on the hyperlink above to watch a short animation about the structure of DNA
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Genes• The sequence of nucleotides in an organisms genome
is unique• Genes consist of sequences of nucleotides
Human Genome
• 3164.7 million nucleotides
• Average gene length is 3000 base pairs
• Largest gene is 2.4 million base pairs
• Approximately 20,000 – 25,000 genes
DNA Replication
Why is DNA replication important?
Why replicate?
• Each new cell created through cell division must receive an exact copy of the original cells DNA
• Occurs in the nucleus of cells
DNA Replication
• Semi-conservative – new DNA molecules have one original template strand and one new strand
• Follows complementary base pair rules
• “Leading strand” – continuously synthesized• “Lagging strand” – synthesized in fragments
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Origins of Replication
Steps of DNA Replication
1. DNA helicase unzips the original DNA molecules by severing hydrogen bonds between nucleotides
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2. New nucleotides are added to the template strands using DNA polymerase enzymes (complementary base pairing)
3. Okazaki fragments are pieced together by DNA ligase
DNA Replication
C C T A A C G G T A C G A A T
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