DNA (deoxyribonucleic acid) is a two stranded molecule called double helix Each strand are made of smaller parts called nucleotides The two strands.
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DNA Structure and Replication
DNA (deoxyribonucleic acid) is a two stranded molecule called double helix
Each strand are made of smaller parts called nucleotides
The two strands are bonded with weak hydrogen bonds
Structure of DNA
Structure of DNA
Nucleotides have 3 parts:
• deoxyribose (sugar)• phosphate group• Nitrogenous base
(A,C,G,T)
Nitrogenous Bases Double Rings called PURINES
• Adenine (A)• Guanine (G)
Single Ring called PYRIMIDINES• Thymine (T)• Cytosine (C)
A or G
T or C
Base-Pairing Rules Adenine bonds with Thymine using
two hydrogen bonds
T A
Base Pairing Rules Guanine bonds with Cytosine using
three hydrogen bonds
CG
3 H-bonds
How did we discover this? Base-Pairing Rules (1950)
• Erwin Chargaff discovered DNA from any species had equal amounts C’s and G’s, and equal amounts A’s and T’s
• In human DNA A = 30% T = ________________ C = 20% G = ________________
How did we discover this? Structure of DNA
(1953)• Rosalind Franklin
takes diffraction x-ray photographs of DNA
• Watson and Crick build the first model of DNA using Franklin’s pictures
DNA Replication When a cell divides (mitosis and
meiosis) chromosomes (DNA) needs to divide to create
DNA division happens during Interphase
Carried by a series of enzymes (proteins)
DNA Replication (in eukaryotic cells)
First, DNA is “unzipped” along the hydrogen bonds by DNA helicase
Each strand is a template to add new nucleotides
DNA Replication DNA polymerase adds new
nucleotides Nucleotides are added using Base
Pairing Rules• A – T• C - G
DNA Replication New DNA consists of one parent
(original) strand and one new strand of DNA
Question What would be the complementary
DNA strand for the following DNA sequence?
Use base pairing rules• A - T• C - G
CGTATG
Answer
Original Strand: CGTATGNew Strand:GCATAC
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