dna (deoxyribonucleic acid) mr. coleman biology
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DNADNA
• DNADNA is often called the blueprint of life..
• In simple terms, DNA contains the instructions for making proteins within the cell.
Genetic material of cells…Genetic material of cells…
• GENES – units of genetic material that GENES – units of genetic material that CODES FOR A SPECIFIC TRAITCODES FOR A SPECIFIC TRAIT
• Called Called NUCLEIC ACIDSNUCLEIC ACIDS
• DNA is made up of repeating molecules DNA is made up of repeating molecules called called NUCLEOTIDESNUCLEOTIDES
A HISTORY OF DNAA HISTORY OF DNA
• Discovery of the DNA double helixDNA double helix
A. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)
B. Rosalind Franklin - X-ray photo of DNA.(1952)
C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.(1953)
Why do we study DNADNA?
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.
Chromosomes and DNAChromosomes and DNA
• Our genes are on our chromosomes.
• Chromosomes are made up of a chemical called DNA.
The Shape of the MoleculeThe 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.
The Double Helix MoleculeThe Double Helix Molecule
• The DNA double helix has two strands twisted together.
• (In the rest of this unit we will look at the structure of one strand.)
NucleotidesNucleotides
C C
C
OPhosphate
O
CC
O -P OO
O
One deoxyribose together with its phosphate and base make
a nucleotide.
Nitrogenous base
Deoxyribose
One Strand of DNAOne Strand of DNA
• One strand of DNA is a polymer of nucleotides.
• One strand of DNA has many millions of nucleotides.
nucleotide
One Strand of DNAOne Strand of DNA• The backbone
of the molecule is alternating phosphate and deoxyribose.
• The teeth are nitrogenous bases.
phosphate
deoxyribose
bases
Nitrogenous BasesNitrogenous Bases
• PURINESPURINES
1. Adenine (A)Adenine (A)
2. Guanine (G)Guanine (G)
• PYRIMIDINESPYRIMIDINES
3. Thymine (T)Thymine (T)
4. Cytosine (C)Cytosine (C) T or C
A or G
Two Kinds of Bases in DNA
• Pyrimidines are Pyrimidines are single ring bases.single ring bases.
• Purines are double Purines are double ring bases.ring bases.
C
C
C
C
N
N
OO
N
CC
CC
N
N
N
N
N
C
Thymine and Cytosine are Thymine and Cytosine are pyrimidinespyrimidines
• Thymine and cytosine each have one ring Thymine and cytosine each have one ring of carbon and nitrogen atoms.of carbon and nitrogen atoms.
C
C
C
C
N
N
OO
N
cytosinecytosine
C
C
C
C
N
N
OO
OO
thyminethymine
C
Adenine and Guanine are Adenine and Guanine are purinespurines
• AdenineAdenine and and guanineguanine each have two each have two rings of carbon and nitrogen atoms.rings of carbon and nitrogen atoms.
C
C
C
C
N
N
N
AdenineAdenine N
N
C
C
C
C
C
N
N
OO
N
GuanineGuanine N
N
C
Two Stranded DNATwo 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?
C
C
C
C
N
N
OO
N
C
C
C
C
N N
OO
N
N
N C
Hydrogen BondsHydrogen 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.
Hydrogen Bonds, Hydrogen Bonds, cont.
• When making hydrogen bonds, cytosine always pairs up with guanine,
• And adenine always pairs up with thymine.
C
C
CC
N
N
N
N
N
C
C
C
C
C
N
N
OO
OO
C
ChargaffChargaff’’s Rules Rule
• AdenineAdenine must pair with ThymineThymine
• GuanineGuanine must pair with CytosineCytosine
• Their amounts in a given DNA molecule will be about the sameabout the same.
G CT A
Important:Important:
• Adenine and Thymine always join together
A T
• Cytosine and Guanine always join together
C G
Watson & Crick proposed…Watson & Crick proposed…
•DNA had specific pairing between the DNA had specific pairing between the nitrogen bases:nitrogen bases:
ADENINEADENINE – – THYMINETHYMINE
CYTOSINECYTOSINE - - GUANINEGUANINE
•DNA was made of DNA was made of 22 long stands of long stands of nucleotides arranged in a specific way nucleotides arranged in a specific way
called the called the ““Complementary RuleComplementary Rule””
DNA by the numbersDNA 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.
Genetic Diversity…Genetic Diversity…• Different Different
arrangements of arrangements of NUCLEOTIDESNUCLEOTIDES in a in a nucleic acid (DNA) nucleic acid (DNA) provides the key to provides the key to DIVERSITYDIVERSITY among among living organisms.living organisms.
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