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DNA Structure
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DNA Structure DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix. A molecule of DNA is made up of millions of tiny subunits called Nucleotides. Each nucleotide consists of: Phosphate group Pentose sugar Nitrogenous base
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Nucleotides Phosphate Nitrogenous Base Pentose Sugar
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Nucleotides The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”. There are four types of nitrogenous bases.
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Nucleotides A Adenine T Thymine C Cytosine G Guanine
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Nucleotides Each base will only bond with one other specific base.
Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Form a base pair. Form a base pair.
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DNA Structure Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.
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A C T G G A T C
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DNA Structure To crack the genetic code found in DNA we need to look at the sequence of bases. The bases are arranged in triplets called codons. A G G - C T C - A A G - T C C - T A G T C C - G A G - T T C - A G G - A T C
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DNA Structure A gene is a section of DNA that codes for a protein.
Each unique gene has a unique sequence of bases. This unique sequence of bases will code for the production of a unique protein. It is these proteins and combination of proteins that give us a unique phenotype.
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Rosalind Franklin Discovered the shape and structure of DNA:
A double helix
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Chargaff’s Rule Discovered that A goes with T
and C goes with G and that if there’s 20 % A, then there’s 20% T… called Chargaff’s Rule.
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Watson & Crick Put first model of DNA together using Franklin and
Chargaff’s work
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DNA, Chromosome, and Chromatin
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Karyotype Humans have 23 pairs of chromosomes: one from
Mom and one from dad, so 46 total chromosomes One pair
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Why are there 2 copies? DNA Replication One pair
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Chromosomal Disorders
Cri-du-Chat (cry of the cat) – deletion of short arm of chromosome 5 Down Syndrome (trisomy 18 or 21) – extra copy of chromosome 18 or 21 Turner Syndrome – missing X chromosome in female Klinefelter syndrome (XXY) - there is at least one extra X chromosome to a standard human male karyotype, for a total of 47 chromosomes rather than the 46 found in genetically typical humans.
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