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Chapter 3. The Biological Basis of Life. Chapter Outline. The Cell DNA Structure DNA Replication Protein Synthesis. Chapter Outline. What is a Gene? Mutation: When a Gene Changes Chromosomes Cell Division: Mitosis and Meiosis New Frontiers. The Cell.
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Chapter 3 The Biological Basis of Life
Chapter Outline • The Cell • DNA Structure • DNA Replication • Protein Synthesis
Chapter Outline • What is a Gene? • Mutation: When a Gene Changes • Chromosomes • Cell Division: Mitosis and Meiosis • New Frontiers
The Cell • Cells are the basic units of life in all living organisms. • Complex life forms, such as plants and animals, are made up of billions of cells. • The cells of all living organisms share many similarities as a result of their common evolutionary past.
Cells • Prokaryotic cells are single celled organisms, such as bacteria and blue-green algae. • Life on earth 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.
Two Types of Cells • Somatic cells are the components of body tissues. • Gametes are sex cells. • Ova are egg cells produced in female ovaries. • Sperm are sex cells produced in male testes. • A zygote is the union between a sperm and an ovum.
The DNA Replication Process • Enzymes break the bonds between the DNA molecule. • Two nucleotide chains serve as templates for the formation of a new strand of nucleotides.
The DNA Replication Process • Unattached nucleotides pair with the appropriate complementary nucleotide • The result is two newly formed strands of DNA. • Each new strand is joined to one of the original strands of DNA.
Proteins • The major structural components of tissue. • Enzymes are proteins that serve as catalysts, initiating chemical reactions in the body. • Amino acids are the building blocks of protein. (There are 20 important amino acids. • Proteins differ according to number of amino acids and the sequence in which they are arranged.
Protein Synthesis • Ribosomes help convert the genetic message from the DNA into proteins. • Messenger RNA (mRNA) carries the genetic message from the cell nucleus to the ribosome. • Transfer RNA (tRNA),found in the cytoplasm, binds to one specific amino acid.
Protein Synthesis: Translation • Decoding and implementing the genetic message on the mRNA. • The mRNA travels through the nuclear membrane to the ribosome. • tRNAs arrive at the ribosome carrying their specific amino acids. • The base triplets on the tRNA match up with the codons on the mRNA. • As each tRNA line up in the sequence of mRNA codons their amino acids link to form a protein.
Genes • A gene is the entire sequence of DNA bases responsible for the synthesis of a protein. • A mutation occurs when the sequence of bases in a gene is altered. • Mutations may interfere with an organisms ability to produce vital protein and may lead to a new variety within the species, hence, evolution.
Gene Structure The gene consists of exons and introns. • Exons are DNA segments transcribed into mRNA that code for specific amino acids. • Introns are DNA sequences not expressed during protein synthesis.
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.
Chromosome Structure • A chromosome is composed of a DNA molecule and associated proteins. • During normal cell functions chromosomes exist as single-stranded structures. • During cell division, chromosomes consist of two strands of DNA joined together at a constricted area called the centromere. • Since the DNA molecules have replicated, one strand of a chromosome is an exact copy of the other.
Chromosomes and Genetics • Each species is characterized by a specific number of chromosomes. • Humans have 46 chromosomes. • Chromosome pairs are called homologus. • Homologous chromosomes carry genetic information influencing the same traits. • Homologous chromosomes are not genetically identical.
Types of Chromosomes • Autosomes - governs all 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. • Mitosis 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.
Evolutionary Significance of Meiosis • Meiosis and sexual reproduction are highly important evolutionary innovations. • Meiosis increases genetic variation at a faster rate than mutation. • Offspring in sexually reproducing species represent the combination of genetic information from two parents.
Problems With Meiosis • Errors in meiosis may lead to spontaneous abortion or miscarriage. • Nondisjunction occurs when chromosomes don’t separate during meiosis. • A gamete containing one less chromosome that fuses with a normal gamete will produce a zygote containing 45 chromosomes. • A game containing one extra chromosome that fuses with a normal gamete will produce a zygote containing 47 chromosomes.
