1 History Before the 1940’s scientists didn’t know what material caused inheritance. They...
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Transcript of 1 History Before the 1940’s scientists didn’t know what material caused inheritance. They...
History
• Before the 1940’s scientists didn’t know what material caused inheritance.
• They suspected it was either DNA or proteins.
History
• A series of experiments proved that DNA was the genetic material responsible for inheritance.
History
• In 1952, Alfred Hershey and Martha Chase did an experiment using a virus that infects E. coli bacteria.
• The experiment proved that DNA and not protein is the factor that influences inheritance.
History
• Erwin Chargaff discovered the base pairing rules and ratios for different species.
• Adenine pairs with Thymine
• Cytosine pairs with Guanine.
History• Rosalind Franklin & Maurice Wilkins had
taken the 1st pictures of DNA using X-ray crystallization
History• The Nobel Prize in Medicine 1962
Francis Harry Compton Crick
James Dewey Watson
Maurice Hugh Frederick Wilkins
Rosalind Franklin(Died of cancer 1958)
Wilkins has become a historical footnote and
Watson & Crick are remembered as the
Fathers of DNA
Watson Crick
13
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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Chromosomes and DNA
• Our genes are on our chromosomes.
• Chromosomes are made up of a chemical called DNA.
15
DNA• Stands for
Deoxyribonucleic acid• Made up of subunits called
nucleotides • Nucleotide made of:
1. Phosphate group2. 5-carbon sugar3. Nitrogenous base
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One Strand of DNA• The backbone of
the molecule is alternating phosphates and deoxyribose sugar
• The teeth are nitrogenous bases.
phosphate
deoxyribose
bases
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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:
Nitrogen Bases
• 2 types of Nitrogen Bases–Purines
• Double ring–G & A
–Pyrimidines• Single ring
–C & U & T
PGA
CUT PY
A or G
T or 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
N N
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
CC
N
N
N
N
N
C
C
C
C
C
N
N
O
O
C
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Chargaff’s Rule:
• Adenine and Thymine always join together
A T• Cytosine and Guanine
always join togetherC G
DNA• DNA is a double-
stranded molecule.• The strands are
connected by complementary nucleotide pairs (A-T & C-G) like rungs on a ladder.
• The ladder twists to form a double helix.
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Answer:• There would be 20% Cytosine
• Adenine (30%) = Thymine (30%)
• Guanine (20%) = Cytosine (20%)
• Therefore, 60% A-T and 40% C-G