DNA

What is DNA?• A code in the cell that contains the

hereditary material

• The code is a chemical called deoxyribonucleic acid

• Every cell in your body contains DNA

DNA Structure• Rosalind Franklin

discovered that DNA is two chains of molecules in a spiral form by using an X-ray

• Similar to twisted ladder

• James Watson & Francis Crick made a model of DNA molecule

A DNA Model• Each side of the

ladder is made of sugar-phosphate molecule

• Called the “backbone”

• Sugar = deoxyribose

• Rungs of the ladder are made up of nitrogenous bases

• There are four types of bases1. Adenine (A)

2. Guanine (G)

3. Cytosine (C)

4. Thymine (T)

Base Pairing

• Adenine always pairs with Thymine

A-T

• Cytosine always pairs with Guanine

C-G

Copying DNA• The two sides of

DNA unwind and separate

• Each side becomes a pattern for a new DNA strand

Genes• DNA in your cells stores the

instructions for making proteins

• Each chromosome contains hundreds or thousands of genes

Making Proteins• Genes are found in the

nucleus, but proteins are made on ribosomes in the cytoplasm

• The code for making proteins are carried from the nucleus by RNA or Ribonucleic Acid

Ribonucleic Acid

• RNA is different from DNA1. RNA is not a spiral, but one single

strand

2. RNA has the bases A, G, C, and U not T

• U = Uracil3. Sugar is ribose, not deoxyribose

DNA VS. RNADNA RNA

STRUCTURE Double Helix Single Strand

SUGAR Deoxyribose Ribose

BASES A, T, C, G A, U, C, G

Types of RNA1.Messenger RNA (mRNA)

2.Transfer RNA (tRNA)

3.Ribosomal RNA (rRNA)

Controlling Genes• Each cell only uses some of

the thousands of genes to make proteins

• Cells must be able to control genes by turning some genes on and others off

Mutations• Permanent changes

in the DNA sequence of a gene

• These happen when the DNA is not copied correctly

• They cause incorrect proteins to be made

Causes of Mutations

1.X-rays

2.Sunlight

3.Some chemicals

Results of Mutations

• Some mutations are beneficial– They add variety to the species

• Many mutations are harmful and can cause death– Cystic Fibrosis

• Some mutations have no effect on the organism