history of dna ~review discovery of the dna double helix.... a.dates back to the mid 1800s b.dna...
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Question: What is DNA?TRANSCRIPT
History of DNA ~ReviewHistory of DNA ~Review• Discovery of the DNA double
helix....
A. Dates back to the mid 1800’sB. DNA images become clear during 1950’sC. Rosalind Franklin – took X-ray photos of DNA.D. Watson and Crick - described the DNA molecule from Franklin’s X-ray.
Question:Question:•What is DNA?
Deoxyribonucleic Acid (DNA)
• Genetic material made up of nucleotides (DNA molecule) in a DNA double helix.
• Nucleotide:1. Phosphate group2. 5-carbon sugar3. Nitrogenous bases
DNA Nucleotide
OO=P-O O
PhosphatePhosphate GroupGroup
NNitrogenous baseNitrogenous base (A, G, C, or T)(A, G, C, or T)
CH2
O
C1C4
C3 C2
5
SugarSugar(deoxyribose)(deoxyribose)
DNA Double Helix
NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)
““Rungs of ladder”Rungs of ladder”
““Legs of ladder”Legs of ladder”
Phosphate &Phosphate &Sugar BackboneSugar Backbone
DNA Double Helix
P
P
P
O
O
O
1
23
4
5
5
3
3
5
P
P
PO
O
O
1
2 3
4
5
5
3
5
3
G C
T A
Nitrogenous Bases• PURINES
1. Adenine (A)2. Guanine (G)
• PYRIMIDINES3. Thymine (T)4. Cytosine (C) T or C
A or G
Base # of
Purines PyrimidinesPairs H-Bonds
Adenine (A) Thymine (T) A = T 2
Guanine (G) Cytosine (C) C = G 3
BASE-PAIRINGS
CG
H-bonds
T A
Chargaff’s Rule• Adenine must pair with
Thymine• Guanine must pair with
Cytosine• Their amounts in a given DNA
molecule will be about the same.
G CT A
Discovery of DNA Discovery of DNA StructureStructure
• Erwin Chargraff showed the amounts of the four bases on DNA ( A,T,C,G)
• In a body or somatic cell: A = 30.3% T = 30.3% G = 19.5% C = 19.9%
Question:•If there is 30%
Adenine, how much Cytosine is
present?
Answer:•There would be 20%
Cytosine.
Adenine (30%) = Thymine (30%)
Guanine (20%) = Cytosine (20%) (50%) = (50%)
QuestionQuestion
• If 15% of the nucleotides in a DNA molecule
contain Guanine, what percentage of the
nucleotides contain each of the other 3 bases?
Explain your reasoning.
AnswerAnswer• If Guanine has 15% then
Cytosine also has 15% Adenine and Thymine will have 35%.
Question:•When and where does DNA
Replication take place?
Synthesis Phase (S phase)• S phase in interphase of the cell
cycle.• Nucleus of eukaryotes
Mitosis-prophase-metaphase-anaphase-telophase
G1 G2
Sphase
interphase
DNA replication takesDNA replication takesplace in the S phase.place in the S phase.
**DNA Replication** How DNA makes a copy of itself
Before a cell divides, its DNA is replicated. Because the two
strands of a DNA molecule have complementary base pairs, the nucleotide sequence of each
strand automatically supplies the information needed to produce its
partner. If the two strands of a DNA molecule are separated, each
can be used as a pattern or template to produce a
complementary strand. Each template and it’s new complement together form a new DNA double
helix, identical to the original.
The ProcessStep 1 ~The double-helix unwinds
separating the two strands (like the two sides of a zipper). With the help of DNA helicase, the hydrogen bonds are broken. The areas where it breaks is known as the replication fork, b/c of the Y shape.
ReplicationReplicationForkFork
Parental DNA MoleculeParental DNA Molecule
3’
5’
3’
5’
The Process Cont..Step 2 ~ The enzyme DNA
polymerase & ligase move along the exposed DNA strand, adding nucleotides to a new DNA strand that’s complementary to the template. Polymerase also “PROOFREADS” to make sure there are no errors and each copy is identical to the original.
Step 3 ~ Two DNA molecules are formed & are identical to the original. Each one contains a new and original strand of DNA
Question:• What would be the
complementary DNA strand for the following DNA sequence?
DNA 5’-GCGTATG-3’
Answer:DNA 5’-GCGTATG-
3’DNA 3’-CGCATAC-
5’
Animation of DNA Replication
• DNA Replication - long