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Chapter 3

Chapter 3. The Biological Basis of Life. Chapter Outline. The Cell DNA Structure DNA Replication Protein Synthesis What is a Gene? Cell Division: Mitosis and Meiosis. Cells. Basic units of life. Complex life forms have billions of cells. An adult human= as many as 1,000 billion cells.

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Chapter 3

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  1. Chapter 3 The Biological Basis of Life

  2. Chapter Outline • The Cell • DNA Structure • DNA Replication • Protein Synthesis • What is a Gene? • Cell Division: Mitosis and Meiosis

  3. Cells • Basic units of life. • Complex life forms have billions of cells. • An adult human= as many as 1,000 billion cells. • Life on earth can be traced back 3.7 b.y.a. • Prokaryotic cells (i.e. bacteria and blue-green algae). • Eukaryotic cells (1.2 billion years ago).

  4. Types of Cells • Somatic cells are components of body tissue. • Gametes are sex cells. • Ova are produced in female ovaries. • Sperm are produced in male testes. • A zygote is the union between a sperm and an ovum.

  5. DNA Structure • Cellular function and an organism’s inheritance. • DNA is composed of two chains of nucleotides. • A nucleotide consists of a sugar, a phosphate, and one of four nitrogenous bases. • The two chains are held together by bonds formed on their bases with their complement on the other chain. • Adenine (A) is the complement of Thymine(T) • Guanine(G) is the complement of Cytosine(C)

  6. 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. • Proteins differ according to number of amino acids and the sequence in which they are arranged.

  7. 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.

  8. RNA and DNA RNA differs from DNA in three important ways: • It’s usually single-stranded. • It contains a different type of sugar. • It contains the base uracil as a substitute for the DNA base thymine.

  9. Protein Synthesis: Transcription • The process of coding a genetic message for proteins by formation of mRNA. • A portion of the DNA unwinds and serves as a template for the formation of a mRNA strand.

  10. Transcription

  11. Protein Synthesis: Translation • 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.

  12. Assembly of an Amino Acid Chain in Protein Synthesis • As the ribosome binds to the mRNA, tRNA brings a particular amino acid, specified by the mRNA codon, to the ribosome.

  13. Assembly of an Amino Acid Chain in Protein Synthesis • The tRNA binds to the first codon while a second tRNA–amino acid complex arrives at the ribosome.

  14. Assembly of an Amino Acid Chain in Protein Synthesis • The ribosome moves down the mRNA, allowing a third amino acid to be brought into position by another tRNA molecule. Note that the first two amino acids are now joined together.

  15. 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.

  16. Cell Division: Mitosis and Meiosis • Cell division results in production of new cells. • During cell division: • Cells are involved with normal cellular and metabolic processes. • The cell’s DNA becomes tightly coiled. • DNA is visible under a microscope as chromosomes.

  17. 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 at the centromere. • Since the DNA molecules have replicated, one strand of a chromosome is an exact copy of the other.

  18. Chromosomes and Genetics • Each species is characterized by a specific number of chromosomes. • Humans have 46 chromosomes. • Chromosome pairs are called homologus: • These carry genetic information that influences the same traits. • They are not genetically identical.

  19. Types of Chromosomes • Autosomes - govern 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.

  20. 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.

  21. Meiosis • Production of gametes (sex cells). • 2 divisions result in 4 daughter cells. • Each daughter cell contains 23 chromosomes. • Resulting gamete may unite with another gamete to create a zygote. • The zygote inherits the DNA, half from each parent, to develop and function normally.

  22. 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.

  23. Problems With Meiosis • Errors in meiosis may lead to 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 gamete containing one extra chromosome that fuses with a normal gamete will produce a zygote containing 47 chromosomes.

  24. Mitosis and Meiosis Compared

  25. Quick Quiz

  26. 1. The entire sequence of DNA bases on the chromosome that code for a particular polypeptide chain is a(n) • ribosome. • amino acid. • gene. • polypeptide chain.

  27. Answer: c • The entire sequence of DNA bases on the chromosome that code for a particular polypeptide chain is a gene.

  28. 2. Which of the following is NOT true about RNA? • It is single stranded. • Some forms of RNA are involved with protein synthesis. • It has a different type of sugar than DNA has. • It contains the base thymine.

  29. Answer : d • The following is NOT true about RNA. • It contains the base thymine.

  30. 3. Which of the following is true for meiosis? • It has only one division that duplicates the parent cell exactly. • It produces gametes. • When a mutation occurs it affects only the individual. • It has no effect on evolution.

  31. Answer: b • The following is true for meiosis: • It produces gametes.

  32. 4. Chromosomes that carry genes for the same traits are _________________ pairs.

  33. Answer: homologous • Chromosomes that carry genes for the same traits are homologous pairs.

  34. 5. Somatic cell division is termed _________________ .

  35. Answer: mitosis • Somatic cell division is termed mitosis.

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