dna by the numbers - mr. aitken's biology...
TRANSCRIPT
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DNA by the Numbers• Each cell has about 2
m of DNA.• The average human has
75 trillion cells.• The average human has
enough DNA to go from the earth to the sun more than 400 times.
• DNA has a diameter of only 0.000000002 m.
The earth is 150 billion mor 93 million miles from the sun.
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DNA• DNA is often called the blueprint of life.
• In simple terms, DNA contains the instructions for making proteins within the cell.
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Watson & Crick’s ModelIn 1953, James Watson and Francis Crick suggested what is now accepted as the first correct double-helix model of DNA structure
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Why do we study DNA?
We study DNA for many reasons, e.g.,
• its central importance to all life on Earth,
• medical benefits such as cures for diseases,
• better food crops.
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Chromosomes and DNA
• Our genes are on our chromosomes.
• Chromosomes are made up of a chemical called DNA.
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The Shape of the Molecule
• DNA is a very long polymer.
• The basic shape is like a twisted ladder or zipper.
• This is called a double helix.
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One Strand of DNA• The backbone of the molecule is alternating phosphates and deoxyribose sugar
• The teeth are nitrogenousbases.
phosphate
deoxyribose
bases
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Nucleotides
C C
C
OPhosphate
O
O -P OO
O
O -P OO
O
O -P OO
O One deoxyribose together with its phosphate and base
make a nucleotide.
Nitrogenousbase
Deoxyribose
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One Strand of DNA
• One strand of DNA is a polymer of nucleotides.
• One strand of DNA has many millions of nucleotides.
nucleotide
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Four nitrogenous bases
• Cytosine C
• Thymine T
• Adenine A
• Guanine G
DNA has four different bases:
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Two Kinds of Bases in DNA
• Pyrimidines are single ring bases.
• Purines are double ring bases.
C
C
C
C
N
N
O
N
CC
CC
N
N
N
N
N
C
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Thymine and Cytosine are pyrimidines
• Thymine and cytosine each have one ring of carbon and nitrogen atoms.
C
C
C
C
N
N
O
N
cytosine
C
C
C
C
N
N
O
O
thymine
C
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Adenine and Guanine are purines
• Adenine and guanine each have two rings of carbon and nitrogen atoms.
C
C
C
C
N
N
N
Adenine N
N
C
C
C
C
C
N
N
O
N
Guanine N
N
C
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Two Stranded DNA• Remember, DNA has two strands that fit together something like a zipper.
• The teeth are the nitrogenous bases but why do they stick together?
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C
C
C
C
N
N
O
N
C
C
C
C
NN
O
N
N
N C
Hydrogen Bonds
• The bases attract each other because of hydrogen bonds.
• Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.
• The bonds between cytosine and guanine are shown here with dotted lines
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Hydrogen Bonds, cont.• When making hydrogen bonds, cytosine always pairs up with guanine
• Adenine always pairs up with thymine
• Adenine is bonded to thymine here
C
C
C
C
N
N
O
O
C
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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Chargraff’s Rule:
• Adenine and Thymine always join together
A T
• Cytosine and Guanine always join together
C G
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
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.