Biology - Genetic Processes

Biology: Genetic Processes – Chapter 4 Genetics: study of heredity and variation of living organisms and how genetic information is passed from one generation to the next.  Understanding genetics begins with understa ...

Biology: Genetic Processes – Chapter 4 Genetics: study of heredity and variation of living organisms and how genetic information is passed from one generation to the next.  Understanding genetics begins with understanding cellular processes. Cell Theory 1) All living things are composed of one or more cells. 2) Cells are the smallest units of living organisms. 3) New cells come from pre-existing cells by cell division. o Traits are passed on from one cell, the parent cell, to new cells, the daughter cells. o Traits are passed o o o o through genetic material in the form of deoxyribonucleic acid (DNA). The Cell Cycle  Cells produce through controlled growth and division. Somatic Cells: body cells of plants and animals. 3 Functions of Cell Division: growth, repair, and maintenance.  Duration of cell cycle depends on type of cell. 3 Stages of the Cell Cycle: interphase, mitosis, cytokinesis. 1) Interphase: growth and intense cell activity. o Cell grows, copies its DNA, and prepares for cell division. o Three phases of Interphase: i. Growth 1 (G1) is the major period of growth. ii. Synthesis (S) phase is when DNA exists as uncondensed fibers called chromatin; is replicated. iii. Growth 2 (G2) involves further growth and molecule synthesis. 2) Mitosis: cell’s nucleus and genetic material divide. o Key activity is the accurate separation of cell’s repeated DNA. o Enables cell’s DNA to pass into new daughter cells intact. o Four stages of mitosis: prophase, metaphase, anaphase, telophase. Prophase  Chromatin condenses into chromosomes, which contain the DNA.  As a result of DNA replication during interphase, each chromosome exit as two copies on each chromosome.  The two chromosome arms are called sister chromatids.  Sister chromatids are held together by the centromere.  Nuclear membrane breaks down.  Nucleolus disappears.  Spindle fibres form from centrosome, forming spindle apparatus, which move and organize the chromosomes. Metaphase Spindle fibres stretch from the centrosomes (with centriole pairs) on opposite poles of the cell.  Spindle fibres attach to the centromere of each chromosome and guide them to the equator of the cell.  Each pair of sister chromatids is condensed to be a single chromosome as long as they remain joined at the centromere. Anaphase  Each centromere splits apart.  Sister chromatids no longer joined.  Separated sister chromatids now referred to as daughter chromosomes.  Spindle fibres shorten, pulling chromosomes to poles. Telophase  Chromosomes have reached opposite poles.  Chromosomes unwind into less visible chromatin.  Spindle fibres break down.  Nuclear membrane forms around new set of chromosomes.  Nucleolus forms within each nucleus. 3) Cytokinesis in Animal Cells o The process of cytokinesis is different in different cell types. o In animal cells, a cleavage furrow forms in the cell membrane along the equator of the cell. o Furrow deepens as the cytoplasm divides equally, and the cell pinches off into the two cells. o This is accomplished by means of microfilaments constricting. 4) Cytokinesis in Plant Cells o In plant cells, the rigid cell wall does not pinch inward. Instead, a new structure called a cell plate forms between the daughter nuclei. A cell wall forms on each side of the cell plate. Nucleotides Each nucleotide includes: 1. A phosphate group. 2. A pentose sugar. 3. A nitrogenous base (A, T, C, G)  Phosphate and sugar groups form the rails.  Bases protrude inwards forming the rungs. Purine Bases: Adenine and Guanine. Pyrimidine Bases: Thymine and Cytosine. Complimentary Base Pairs: A-T and G-C. Making Exact Copies of DNA  A genetic mutation is a change in the nucleotide sequence of DNA. Genome: complete DNA sequence of an organism. Semi-Conservative Method of Replication: when DNA is replicated during interphase, the double helix unwinds and each strand of DNA serves as a template for a new strand.