KEY CONCEPT DNA structure is the same in all organisms.

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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

• DNA is made up of a long chain of nucleotides.

• Each nucleotide has three parts.– a phosphate group– a deoxyribose sugar– a nitrogen-containing

phosphate group

deoxyribose (sugar)

nitrogen-containingbase

-Adenine -Thymine

-Cytosine -Guanine

DNA is composed of four types of nucleotides.

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.

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

• The backbone is connected by covalent bonds.

hydrogen bond covalent bond

• The bases are connected by hydrogen bonds.

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

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

DNA Replication: Process

• Replication begins when the enzyme DNA helicase opens the DNA forming replication bubbles

DNA Replication- The Big Picture

Each Bubble has 2 Forks – each fork has a leading and lagging strand

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

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

DNA Replication

KEY CONCEPT DNA structure is the same in all organisms.

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