CHAPTER 12DNA AND RNA

GENES AND PROTEINSHonors Biology

Genes and Proteins Genes contain instructions for assembling

proteins Proteins are enzymes that catalyze and

regulate chemical reactions Genes code for enzymes that control pigment

(skin or petal color) Proteins regulate the rate & pattern of

growth throughout an organism, controlling size and shape (design of an organism)

Mutations Mistakes in copying DNA are often made

(incorrect base or deleting or inserting bases)

Mutation – changes in genetic material

Gene mutation – changes in single genes Chromosomal mutation – changes in whole

chromosome

Gene Mutations Mutations in genes in 1 or a few nucleotides 2 types of gene mutations

Point Mutations – occur at single point in DNA Substitutions – 1 base changed to another

Frameshift Mutations –shifts every codon that follows. A shift in reading the entire genetic message Insertions or deletions of bases Changes all subsequent amino acids and may change

protein

Point vs Frameshift Mutations

Substitution InsertionDeletion

substitution insertion

deletion

Chromosomal Mutations Chromosomal Mutations – Changes in

number or structure of chromosomes Down syndrome

Significance of Mutations Most mutations are neutral, meaning

they have little or no effect on the genes or the protein they code for

Mutations are the source of genetic variability in species (various environments)

May be harmful or beneficial Genetic disorders Cancer Adaptations

Gene Regulation Not all genes are expressed

simultaneously, some remain “silent” by being turned on or off

All cells contain the same copy of DNA, however they do not all express the same proteins Hemoglobin in red blood cells Keratin in skin cells

Known as cell specialization - only a tiny fraction of available genes are expressed in appropriate cells

Gene Regulation Every cell develops from same fertilized egg cell During cell specialization, cells undergo

differentiation and become specialized in structure and function

Series of genes called Hox Genes control differentiation of cells and tissues in the embryo. Known as the “master control genes”

Mutation of Hox Gene can completely change organs that develop in specific part of body In fruit flies, replacement of antennae on head with

legs

Gene Regulation

Normal fruit fly head.

Fruit fly head showing the effects of the Antennapedia gene. This fly has legs where its antennae should be.