Chapter 3, Section 4The DNA Connection

Monday, November 16, 2009

Pages 107 -- 112

Objectives

• Explain the term “genetic code”.

• Describe the process by which a cell produces proteins.

• Describe the different types of mutations and how they affect organism.

Vocabulary Words

• Messenger RNA

• Transfer RNA

• Mutation

Review…

• The main function of genes is to control the production of proteins in the organism’s cells.

• Proteins help to determine the size, shape, and many other traits of an organism.

• DNA is the major component of chromosomes.

Review--cont’d…

• A DNA molecule is made up of four different nitrogen bases (A, T, G, C).

• Nitrogen bases for the rungs of the DNA ladder.

• A single gene on a chromosome may contain anywhere from several hundred to a million or more bases.

Genetic Code

• The order of the nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced.

• In the genetic code, a group of 3 bases code for the attachment of a specific amino acid.

• The order of these bases determine the type of protein.

Protein Synthesis

• Protein synthesis the process in which protein is produced.

• During protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein.

• Protein synthesis occur on the ribosomes in the cytoplasm of the cell.

The Role of RNA

• RNA is the genetic messenger that carries the genetic code from the DNA inside the nucleus to the cytoplasm.

• Physically, RNA looks like half a ladder.

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RNA vs. DNA

• Looks like half a ladder.

• Contains a different sugar molecule.

• Nitrogen base is different.• RNA contains uracil instead of thymine.

RNA

• There are 2 types of RNA involved in protein synthesis.• Messenger RNA

• Copies the code message from the DNA in the nucleus and carries the message into the cytoplasm.

• Transfer RNA• Carries amino acids and adds them to the

growing protein chain.

Protein Synthesis

DNA

Nucleus

Messenger RNA Messenger RNA

Ribosome

Protein

Amino Acid

Transfer RNA

Protein

Mutations

• A mutation is any change that occurs in a gene or chromosome.

• Mutations can cause a cell to produce an incorrect protein during protein synthesis.

• Result:• The phenotype will be different than

expected.

Types of Mutations

• Mutations occurring protein synthesis.• Substitution of a nitrogen base• DNA replication process

• Incomplete separation during meiosis.

• Mutations in a body cell.

Effects of Mutations

• A source of genetic variety.• Some changes are harmful to the organism.

• It reduces the organism’s chances for survival and reproduction.

• Example: Cancer.

• Some changes are helpful.• Improves an organism’s chances for survival and

reproduction.

• Some changes are neither harmful nor helpful.

Homework

• Workbook 3.4 (due 11/18)

• Vocabulary quiz 3.4 (11/18)