Chapter 3 The Biological Basis of Life The Cell DNA Structure DNA Replication Protein Synthesis What is a Gene?

Chapter 3 The Biological Basis of Life Mutation: When a Gene Changes Chromosomes Cell Division New Frontiers

The Cell The basic units of life in all living organisms. Prokaryotic cells are single celled organisms (bacteria and blue-green algae). Life can be traced back 3.7 billion years in the form of prokaryotic cells. Eukaryotic cells, structurally complex cells, appeared 1.2 billion years ago.

Structure of a Eukaryotic Cell The outer boundary of a cell is the cell membrane. Organelles are functional structures found within the cytoplasm. The nucleus is surrounded by the cytoplasm and contains chromosomes.

Two Types of Cells Somatic - components of body tissues Gametes - sex cells – Ova - egg cells produced in female ovaries. – Sperm - sex cells produced in male testes. – Zygote - union between a sperm and an ovum.

The DNA Replication Process 1. Specific enzymes break the bonds between the DNA molecule. 2. The two nucleotide chains serve as templates for the formation of a new strand of nucleotides.

The DNA Replication Process 3. Unattached nucleotides pair with the appropriate complementary nucleotide 4. The end result is two newly formed strands of DNA. Each new strand is joined to one of the original strands of DNA.

Genes The sequence of DNA bases responsible for the synthesis of a protein. Mutation occurs when the sequence of bases in a gene is altered. Mutations interfere with an organisms ability to produce vital protein.

Universal Genetic Code The DNA code of all life on earth is composed of the same molecules and carries on similar functions. The universality of the genetic code implies a common ancestry for all life on the planet. Organisms differ according to the arrangement of the DNA.

Cell Division: Mitosis and Meiosis Cells are involved with normal cellular and metabolic processes. The cell’s DNA becomes tightly coiled. DNA is visible under a microscope as chromosomes.

Chromosomes and Genetics Each species is characterized by a specific number of chromosomes. Humans have 46 chromosomes. Homologous chromosomes carry genetic information influencing the same traits. Homologous chromosomes are not genetically identical.

Types of Chromosomes Autosomes - carry genetic information for physical characteristics (except sex determination). Sex chromosomes - X and Y chromosome. – Mammal females have two X chromosomes. – Mammal males have one X and one Y chromosome.

Mitosis Mitosis is cell division in somatic cells. Occurs during growth and repair/replacement of tissues. The result of mitosis is two identical daughter cells that are genetically identical to the original cell.

Steps in Mitosis chromosomes line up in the center of the cell. 2. Chromosomes are pulled apart at the centromere. 3. The strands separate and move to opposite ends of the dividing cell. 4. The cell membrane pinches in and two new cells exist.

Meiosis Production of gametes (sex cells). Characterized by two divisions that result in four daughter cells, each of which contains 23 chromosomes (half the original number).

Evolutionary Significance of Meiosis Meiosis increases genetic variation at a faster rate than mutation alone. Offspring in sexually reproducing species represent the combination of genetic information from two parents. Darwin emphasized that natural selection acted on genetic variation in all populations.

Down’s Syndrome Occurs because of three copies of chromosome #21. Congenital problems include mental retardation, heart defects, and susceptibility to respiratory infections.