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8.2 Structure of DNA
KEY CONCEPT DNA structure is the same in all organisms.
8.2 Structure of DNA
DNA is the molecule of Life
• Deoxyribonucleic Acid• Contains genetic information for cell
functions, growth, and division
• Shape – Double Helix
• Watson & Crick – Discovered the shape of DNA
8.2 Structure of DNA
• DNA is made up of a long chain of nucleotides.
• Each nucleotide has three parts.– a phosphate group– a deoxyribose sugar– a nitrogen-containing
base
phosphate group
deoxyribose (sugar)
nitrogen-containingbase
8.2 Structure of DNA
-Adenine -Thymine
-Cytosine -Guanine
DNA is composed of four types of nucleotides.
8.2 Structure of DNA
Watson and Crick determined the three-dimensional structure of DNA by building models.
• DNA is a double helix that is made up of a sugar-phosphate backbone on the outside with bases on the inside.
8.2 Structure of DNA
TA
CG
Nucleotides always pair in the same way.
• The base-pairing rules show how nucleotides always pair up in DNA.
– A pairs with T
– C pairs with G
8.2 Structure of DNA
• The backbone is connected by covalent bonds.
hydrogen bond covalent bond
• The bases are connected by hydrogen bonds.
8.2 Structure of DNA
History of Replication
• Watson & Crick – realized that
complementary base pairing
provided a way for DNA to copy itself
- base pairing could allow a new
strand to be built on an old strand
8.2 Structure of DNA
DNA Replication –
• Replication = DNA making copies of itself– DNA must be copied before a cell can divide– Each new cell will have
a complete set of DNA
8.2 Structure of DNA
DNA Replication: Process
• Replication begins when the enzyme DNA helicase opens the DNA forming replication bubbles
8.2 Structure of DNA
DNA Replication- The Big Picture
Each Bubble has 2 Forks – each fork has a leading and lagging strand
8.2 Structure of DNA
DNA Replication – DNA Polymerase
• The enzyme DNA polymerase
brings new nucleotides to the
replication fork
- it pairs them according to base pairing rules A pairs with T
C pairs with G
8.2 Structure of DNA
DNA Replication
• The process continues until 2 complete copies of the DNA are produced
• Each copy of the DNA contains one strand of DNA from
the original DNA molecule and one new strand that was produced by replication
• Known as semi-conservative replication
8.2 Structure of DNA
DNA Replication