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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)
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
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
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