DNA ( Deoxyribonucleic acid ) 1 DNA structure DNA replication DNA repair.
DNA Structure. By the early 1900’s it was known that the chromosomes carry the genetic...
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![Page 1: DNA Structure. By the early 1900’s it was known that the chromosomes carry the genetic (hereditary) information Chromosomes consist of DNA (deoxyribonucleic.](https://reader036.fdocuments.in/reader036/viewer/2022062516/56649d4a5503460f94a27bf7/html5/thumbnails/1.jpg)
DNA Structure
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• By the early 1900’s it was known that the chromosomes carry the genetic (hereditary) information
• Chromosomes consist of DNA (deoxyribonucleic acid)
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I. Chemical Structure of DNA
A. Nucleotide:
1. Thousands of repeating units that make up the DNA (DNA is a polymer)
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a) a phosphate group
b) a deoxyribose molecule (5-carbon sugar)
c) a nitrogenous base
adenine, thymine, guanine, cytosine
(There are four different types of nucleotides, depending on which of the four bases is present- A, T, C, or G)
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II. The Watson-Crick Model of the Structure of DNA
DNA consists of two chains of nucleotides in a ladder-like structure which is twisted
(Double Helix)
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James Watson & Francis Crick:
• Used data of M.H.F. Wilkins and Rosalind Franklin, early 50’s
• Wilkins and Franklin studied the structure of DNA crystals using X-rays.
• The X pattern suggested the structure of DNA was a helix.Distance between the two “backbones” of DNA
is constant along the length of the molecule
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• Used data of Erwin Chargaff, 1940’s and early 50's
• Chargaff’s Rule: His data showed that in each species, the percent of A equals the percent of T, and the percent of G equals the percent of C.
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Watson and Crick (1953)
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Watson and Crick Model:
A. The sides of the ladder are made up of alternating molecules of phosphate and deoxyribose
B. The bases make up the rungs of the ladder
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C. The bases that make up the rungs of the ladder are attracted by a weak chemical bonds called hydrogen bonds
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Base Pairing Rule
Adenine (A) pairs with Thymine (T)
Guanine (G) pairs with Cytosine(C)
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Structure of DNA Animations
• http://207.207.4.198/pub/flash/24/menu.swf
http://www.pbs.org/wgbh/nova/genome/dna.html#
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Watson and Crick’s Double Helix Model explained:
1. How replication of DNA during mitosis produces exact copies for the daughter cells
2. How DNA acts as a code, specifying how proteins are made by the cell
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DNA Replication
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1. The double-stranded DNA molecule separates or “unzips” along the weak hydrogen bonds between the base pairs
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2. Free nucleotides that are present in the nucleus attach themselves by hydrogen bonds to the exposed bases
(A-T, C-G)
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3. Two identical strands form from each strand of DNA
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DNA Replication Animations
http://www.lewport.wnyric.org/JWANAMAKER/animations/DNA%20Replication%20-%20long%20.html
http://www.johnkyrk.com/DNAreplication.html
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• If the order of bases along one strand of DNA is
AGGTTACTGCAC
what is the order of bases on the complementary strand?
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TCCAATGACGTG
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How Does DNA Act As A Code?
• The order of bases on the DNA strand instructs the ribosomes how to synthesize proteins
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• Gene: portion of DNA that codes for the production of a specific polypeptide
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•Polypeptide: building block of a protein
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In terms of decreasing size:
Nucleus → Chromosome → Gene → DNA
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