The Chromosome Structure - BIO105_1st Lecture PDF

The Chromosome Structure Chin-chin Demayo, PhD Department of Biological Sciences Mindanao State University - Iligan Institute of Technology  Chromosome Is a thread-like self-replicating genetic structure containing organized DNA molecule package found in...

The Chromosome Structure Chin-chin Demayo, PhD Department of Biological Sciences Mindanao State University - Iligan Institute of Technology  Chromosome Is a thread-like self-replicating genetic structure containing organized DNA molecule package found in the nucleus of the cell. In Greek, 'chromosome' is derived from 'chroma' meaning 'color' and 'soma' meaning 'body’. E. Strasburger discovered chromosome in 1875. The term chromosome was coined by Waldeyer in 1888. Human cells have 46 chromosomes or 23 chromosome pairs (Somatic cells) and 23 Chromosomes (Sex cells or gametes).  Features of Chromosomes Each chromosome is made up of DNA tightly coiled proteins called Histones that support its structure. Chromosomes are best visible during metaphase. Chromosomes have property of self duplication and mutation. Chromosomes are composed of DNA, RNA, and Proteins.  Structure of Chromosomes Telomere - It is present at the tips of chromosomes. Centromere - It is the localized region (middle region) of the chromosome to which spindle fibers attach. “P” arm - It is the short arm of the chromosome, located at the top. “Q” arm - It is the long arm of the chromosome, located at the bottom. Chromatid - One of the two distinct longitudinal subunits of a chromosome. Chromatin - Is a complex of DNA and Protein found in the eukaryotic nucleus, which packages chromosomes.  Types of Chromosomes Chromosomes are divided into four types based on the position of centromere: 1. Acrocentric = Very small P arm; centromere is situated close to the end of the chromosome. 2. Telocentric = No P arm; centromere is at the very end of the chromosome. 3. Sub-metacentric = P arm is just a little smaller than Q arm; centromere is located near the center of the chromosome. 4. Metacentric = P and Q arms are exactly the same length; centromere is in exact middle of the chromosome. CELL CYCLE Why do cells divide?  Why Do Cells Divide? GROWTH REPAIR AND REPLACEMENT REPRODUCTIO N  The Cell Cycle  The cell cycle is an ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division. Cell cycle has 2 Parts: I. Interphase  G1 Phase (Gap 1)  S Phase (Synthesis)  G2 Phase (Gap 2) II. M Phase (Mitotic Phase)  Mitosis  Cytokinesis © 2012 Pearson Education, Inc.  The Cell Cycle I. Interphase ↓ 3 Stages:  G1 Phase (Gap 1): Cell growth; organelles and cytosolic components duplicates  S Phase (Synthesis): where DNA replicates  G2 Phase (Gap 2): Cell growth continues and prepares for division ↓ © 2012 Pearson Education, Inc.  The Cell Cycle II. M Phase (Mitotic Phase): The phase where the cell actually divides.  Mitosis (Nuclear division)  Cytokinesis (Cytoplasmic division) © 2012 Pearson Education, Inc. ↓  Cell Division  Cell Division - is the final step of the cell cycle where one cell splits into two or more daughter cells. Two main types: I. Mitosis II. Meiosis  Cell Division  Mitosis: - division of somatic (body) cells -2 identical daughter cells produced 4 Stages: I. Prophase II. Metaphase III. Anaphase IV. Telophase  Mitosis I. Prophase: – Chromosomes pair up! 1. Chromatin condenses into the shape of a chromosome. -2 chromatids are joined by a centromere 2. Centrioles move to the opposite sides of the nucleus 3. Spindle fibers also begin to grow 4. Nuclear membrane disintegrates  Mitosis II. Metaphase: Chromosomes meet in the middle! 1. Chromosomes arrange at the equator of the cell 2. Become attached to spindle fibres by centromeres.  Mitosis III. Anaphase: Chromosomes get pulled apart 1. Spindle fibres contract pulling chromatids to the opposite poles of the cell  Mitosis IV. Telophase: Now there are two! 1. Chromosomes uncoil 2. Spindle fibres disintegrate 3. Nucleur membrane forms 4. The final stage of nuclear division  Mitosis Cytokinesis - formation of contractile ring and cleavage furrow. - takes place when the cytoplasm divides and two daughter cells with identical genetic material are formed.