Chapter 6Genes and DNA

Chapter 6.1What Does DNA Look Like?

DNA Model Scientists were unsure of what a DNA

(Deoxyribonucleic acid) looked like. In the 1950’s 2 scientists discovered the

structure.

The Pieces of the Puzzle They knew that the material that made

up genes must do 2 things.1. It must be able to give instructions to

cells 2. It must be replicated every time the cells

divide.

Nucleotides DNA is made up of nucleotides.

Nucleotides are made up of a sugar, phosphate and base.

There are 4 different bases in DNA Adenine - A Thymine - T Guanine - G Cytosine - C

Chargaff’s Rules There is always an equal amount of

adenine and thymine. There is always an equal amount of

guanine and cytosine

Rosalind Franklin

Helped discover more about the structure of DNA. She used a process called x-ray diffraction to create images of the DNA.

Watson and Crick Model After seeing

Franklin’s images they concluded that DNA looked like a long twisted ladder.

DNA’s Structure The twisted ladder shape of DNA is

referred to as a double helix. The 2 sides of the ladder are made of

alternating sugar and phosphate parts. Adenine on one side always pairs with

thymine on the other. Guanine on one side always pairs with

cytosine on the other.

Making Copies of DNA The pairing of A T and G C allows for

DNA replication to occur. Pairs of bases are complementary

CGAC will always pair with GCTG

Replication Step 1: the DNA is unzipped down the

middle where the bases meet. Step 2: each side is now used as a

pattern for the new DNA. Step 3: complementary bases match up

with the original strand. Step 4: two strands have now been

created from the one.