Do Now Answer the question below in your
Do Now: Answer the question below in your notebook complete sentences. What is DNA?
What is DNA? • DNA is a Nucleic Acid
What is DNA? • DNA is a Nucleic Acid • Polymer of Nucleotides
What is DNA? • DNA is a Nucleic Acid • Polymer of Nucleotides • Each nucleotide consists of – Deoxyribose (5 -carbon sugar) – Phosphate group – A nitrogen-containing base
What is DNA? • DNA is a Nucleic Acid • Polymer of Nucleotides • Each nucleotide consists of – Deoxyribose (5 -carbon sugar) – Phosphate group – A nitrogen-containing base • Four bases – Adenine, Guanine, Thymine, Cytosine
Watson-Crick Model • DNA consists of two nucleotide strands: Double Helix • Strands are held together by hydrogen bonds between bases • A binds with T and C with G • Strands run in opposite directions - Antiparallel • The sides of the ladder are a sugar-phosphate backbone, while the “rungs” of the ladder are the bases
Question: • If there is 30% Adenine, Adenine how much Cytosine is present?
Answer: • There would be 20% Cytosine • Adenine (30%) = Thymine (30%) • Guanine (20%) = Cytosine (20%) • Therefore, 60% A-T and 40% C-G
DNA is antiparallel
DNA Nucleotide Phosphate Group O O=P-O O 5 CH 2 O N C 1 C 4 Nitrogenous base (A, G, C, or T) Sugar (deoxyribose) C 3 C 2 10
DNA replication • Before mitosis and meiosis, all of the DNA in the cell must be copied or replicated • How does this happen?
DNA Replication • The mechanism by which DNA is replicated is considered semi-conservative • Semi-conservative replication: Half of the original parent DNA molecule is conserved in each of the daughter molecules. • This allows for the parent DNA to serve as a template for generating the daughter DNA molecules • Half of the replicated DNA strand is “old” and the other half is “new”
DNA Replication • Semi. Conservative new old new
Base pairing During Replication • Each old strand serves as a template for the new complementary strand
Enzymes Required for Replication • Helicase: “Melts” or opens up the double strand so that the DNA is single stranded • Primase: Adds an RNA primer so that DNA synthesis can begin • DNA polymerase: multiple types, responsible for the actual synthesis of DNA • Ligase: Joins together small newly synthesized pieces of DNA called Okazaki fragments
Original Strand New Strand DNA Polymerase Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Replication Fork Nitrogenous Bases DNA Polymerase
DNA Replication • Since DNA is antiparallel, synthesis occurs in opposite directions • One strand in continuously synthesized - leading strand (5’ 3’) • The other is synthesized in short discontinuous strands - lagging strand (3’ 5’)
DNA Replication
Question: • What would be the complementary DNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’
Answer: DNA 5’-GCGTATG-3’ 3’-CGCATAC-5’
Original Strand Replication Fork Nitrogenous Bases DNA Polymerase New Strand DNA Polymerase Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Replication Fork
DNA Replication: Fast & Accurate! • It takes E. coli <1 hour to copy 5 million base pairs in its single chromosome & divide to form 2 identical daughter cells • Human cell copies its 6 billion bases & divide into daughter cells in only few hours • Remarkably accurate – only ~1 error per 100 million bases – ~30 errors per cell cycle
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