Transcript Cell Cycle
Introduction to Bi 102 • Pass out Syllabus & Homework. • Go over syllabus and schedule. • Go over Homework 1. The Need for Cell Division • During development – One fertilized egg cell begins to divide – Develops into a mature multicellular organism • In adults – To repair damage – To replace worn out tissue Stages of the Cell Cycle • Before a cell can divide: – Key cellular components must be duplicated • Proteins, membranes, and organelles – Chromosomes must be duplicated • Complete set of genetic information – Ensures that the new cells can survive The Cell Cycle (eukaryotes): Interphase Mitosis cytokinesis Interphase has 3 phases: G1 Phase or Gap 1: • Longest phase • Cell growth, • Proteins/lipids synthesized, • Prepares for replicating DNA G1 Start after cell division Interphase: S Phase DNA Synthesis (Chromosomes/ chromatin Replicated) S G1 Interphase: G2 Phase • Prepares for cell division, proteins made • Mitochondria replicate • Centrioles replicate G2 • Microtubule synthesis S G1 Mitosis: • Nuclear division • Microtubules separate chromosomes G2 S Mitosis G1 Cytokinesis: • Cell division, divides into 2 daughter cells • Cell may renter cell cycle • Or leave cell cycle (G0) G2 S Mitosis G1 Cytokinesis G0 G0 Phase • Most cells are not actively dividing • These cells are in G0 phase – Can leave cell cycle for days to years – Some cells will divide again; e.g. liver cells – Some cells stay in G0; e.g. nerve cells Interphase – G1, S, & G2 Phases Mitosis: Prophase Mitosis: Metaphase 1. Microtubules grow, connect to centromeres, 2. and align the chromosomes Mitosis: Anaphase 1. Sister chromatids separate, move to opposite poles. 2. Microtubules shorten & pull them in. Mitosis: Telophase 1. Chromosomes at poles 2. Nucleus reforms 3. Chromosomes unwind into chromatin 4. Spindle degraded 4 Cytokinesis 1. Cytokinesis follows mitosis. 2. In animal cells, actin filaments (protein) pinch the cell in two. 3. Seen as a cleavage furrow on the cell membrane. 4. Plant cells divide by growing a new cell wall (cell plate) between the 2 nuclei. DNA Synthesis & Replication: DNA Synthesis • DNA “unzips” • Two opposite strands separate • Matching bases are added to each side • Result: Two copies of the original DNA molecule