11.2 Notes11.2 Notes
DNA STRUCTUREDNA STRUCTURE
What is DNA?What is DNA?
Deoxyribonucleic acid = DNADeoxyribonucleic acid = DNAHeritable genetic informationHeritable genetic information Information passed down to you from Information passed down to you from
parentsparentsGenomeGenome: the complete set of : the complete set of
genetic material from your parentsgenetic material from your parentsHuman Genome ProjectHuman Genome Project: Scientists : Scientists
tackling the challenge of sequencing tackling the challenge of sequencing the entire human genome (2000)the entire human genome (2000)
NucleotidesNucleotides NucleotidesNucleotides ARE the building ARE the building
blocks (monomers) of blocks (monomers) of nucleic nucleic acidsacids (polymers). (polymers).
DNADNA IS a kind of nucleic acid IS a kind of nucleic acid Each Each nucleotidenucleotide is made up of: is made up of:
1.1. A ring-shaped A ring-shaped sugarsugar called deoxyribose called deoxyribose
2.2. A A phosphate groupphosphate group
3.3. A A nitrogenous basenitrogenous base (a single (a single or double ring of carbon or double ring of carbon and nitrogen atoms) and nitrogen atoms)
There are There are FOUR types of FOUR types of nucleotidesnucleotides found in DNA found in DNA
They only differ by their They only differ by their nitrogenous bases or ring structurenitrogenous bases or ring structure..
1.1. Thymine (T) Thymine (T) single ring=Pyrimadinesingle ring=Pyrimadine
2.2. Cytosine (C) Cytosine (C) single ring=Pyrimadinesingle ring=Pyrimadine
3.3. Adenine (A) Adenine (A) double ring=Purinedouble ring=Purine
4.4. Guanine (G) Guanine (G) double ring=Purinedouble ring=Purine
HINT: CUT PY (cut pie) = HINT: CUT PY (cut pie) =
(Cytosine, Uracil, Thymine = PYrimidine!(Cytosine, Uracil, Thymine = PYrimidine!
How do the nucleotides How do the nucleotides pair?pair?
Cytosine and Cytosine and Guanine pair with Guanine pair with 3 hydrogen bonds3 hydrogen bonds
Thymine and Thymine and Adenine pair with Adenine pair with 2 hydrogen bonds2 hydrogen bonds
A=T and CA=T and C==GG
Quick Quiz…Quick Quiz…
If If GuanineGuanine always pairs with always pairs with CytosineCytosine & & AdenineAdenine always pairs with always pairs with ThymineThymine...then they are always ...then they are always found in set or equal amounts.found in set or equal amounts.
If one strand of DNA has 20% If one strand of DNA has 20% GuaninesGuanines, how many , how many CytosinesCytosines??
And And AdeninesAdenines? And ? And ThyminesThymines??20%G + 20%C = 40% G&C ; 20%G + 20%C = 40% G&C ; that leaves 60%... 30% A and 30% Tthat leaves 60%... 30% A and 30% T
Formation of the DNA Formation of the DNA strandstrand Each nucleotide Each nucleotide
(A,T,G,C) is joined (A,T,G,C) is joined together by together by covalent covalent bondsbonds
The phosphate group on The phosphate group on one nucleotide will join one nucleotide will join with the sugar group of with the sugar group of another nucleotideanother nucleotide
Nucleotides will be Nucleotides will be strung together by strung together by sugar-phosphate-sugar-sugar-phosphate-sugar-phosphate forming what phosphate forming what is known as a is known as a backbonebackbone. .
The nitrogenous The nitrogenous base pairs are lined base pairs are lined up along the up along the backbone.backbone.
They meet in the They meet in the middle of the middle of the Sugar-Phosphate Sugar-Phosphate backbone.backbone.
Are like Are like rungsrungs on a on a ladderladder. .
The Backbone and Base The Backbone and Base PairsPairs
A one ring structure pairs with a two A one ring structure pairs with a two ring structure.ring structure.
Must be a purine+ a pyrimidine Must be a purine+ a pyrimidine Must have three rings TOTAL to Must have three rings TOTAL to
make a make a ““rungrung”” of the DNA of the DNA ““ladderladder””
1952: X-Ray Evidence…1952: X-Ray Evidence…Rosalind Franklin and WilkinsRosalind Franklin and Wilkins
Using X-ray crystallography she was Using X-ray crystallography she was able to take a picture of DNAable to take a picture of DNA
X shaped pattern = DNA twisted X shaped pattern = DNA twisted around itself like a tightly coiled around itself like a tightly coiled springspring
X shape pattern had to be a helix so X shape pattern had to be a helix so DNA was an Alpha Helicase.DNA was an Alpha Helicase.
1953: Watson & Crick1953: Watson & CrickThey were able to take They were able to take
all information from the all information from the work of scientists work of scientists before them…before them…
Proposed a 3-D model Proposed a 3-D model of the DNA molecule of the DNA molecule capable of:capable of:copying itself accuratelycopying itself accuratelybeing translated into a being translated into a
living organismliving organism It was a It was a double helixdouble helix!!
Complimentary Bases Complimentary Bases PairsPairs
Two strands on the double helix. Run in Two strands on the double helix. Run in oppositeopposite directionsdirections of each other. of each other. (you(you’’ll see this in the activity today!!)ll see this in the activity today!!)
The 2 strands are held together by base The 2 strands are held together by base pairs that are complimentary to each pairs that are complimentary to each other. other.
A pairs with TA pairs with T G pairs with C.G pairs with C. These combinations on both strings of These combinations on both strings of
DNA can be passed down from generation DNA can be passed down from generation to generation on chromosomes.to generation on chromosomes.
Each cell of yours, whether blood cell or Each cell of yours, whether blood cell or brain cell has 3 billion nucleotides, or 6 brain cell has 3 billion nucleotides, or 6 feet of DNA.feet of DNA.
DNA DNA supercoilssupercoils around around histoneshistones (proteins) to form (proteins) to form chromosomeschromosomes … … remember where theyremember where they’’re located?? re located?? In the nucleus!In the nucleus!
How does all that DNA fit into one cell?How does all that DNA fit into one cell?
