Cell Cycle and Cell Division

I. Cell Division A. Cell Division Basics 1. Cells are derived from pre-existing cells. (Cell Theory) 2. Cell division is the process by which cells produce new cells 3. Cell division differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants & animals) 4. Some tissues must be repaired often ; such as the lining of gut, white blood cells, skin cells with a short life span 5. Other cells do not divide at all; such as muscle & nerve.

B. Reasons for Cell Division 1. Growth of an organism 2 B. Reasons for Cell Division 1. Growth of an organism 2. Repair & replacement of damaged cells 3. Reproduction of the species C. Copying DNA 1. Since the instructions for making cell parts are encoded in the DNA, each new cell must get a complete set of the DNA 2. This requires that the DNA be copied (replicated, dubplicated) before cell division

D. Chromosomes & Their Structure 1 D. Chromosomes & Their Structure 1. The plans for making cells are coded in DNA 2. DNA, deoxyribonucleic acid, is a long thin molecule that stores genetic information 3. DNA in a human cell is estimated to consist of six billion pair of nucleotides 4. DNA is organized into giant molecules called chromosomes 5. Chromosomes are made of protein & a long, single, tightly-coiled DNA molecule visible only when the cell divides 6. When a cell is not dividing the DNA is less visible & is called chromatin

7. DNA in eukaryotic cells wraps tightly around proteins called histones to help pack the DNA during cell division 8. Centromeres hold duplicated chromosomes (sister chromatids) before they are separated in mitosis. 9. Telomeres are the ends of chromosomes which are important in cell aging 10. When DNA makes copies of itself before cell division, each half of the chromosome is called a sister chromatid 11. DNA of prokaryotes (bacteria) is one, circular chromosome attached of the inside of the cell membrane

(circular chromosome)

E. Chromosome Numbers 1. Human’s somatic or body cells have 23 pairs of chromosomes or 46 chromosomes (diploid or 2n number) 2. The 2 chromatids of a chromosome pair are called homologues (have genes for the same trait at the same location) 3. Human reproductive cells or gametes (sperm & egg) have one set or 23 chromosomes (haploid or n number) 4. Every organism has a specific chromosome number 5. Fertilization, joining of the egg & sperm, restores the diploid chromosome number in the zygote (fertilized egg cell)

II. Cell Cycle A. Description of the Cell Cycle 1. Cells go through phases or a cell cycle during their life before they divide to form new cells 2. The cell cycle includes 2 main parts – interphase , and cell division 3. Cell division includes mitosis (nuclear division) and cytokinesis (division of the cytoplasm) 4. Interphase is the longest part of a cell’s life cycle and is called the “resting stage” because the cell isn’t dividing 5. Cells grow, develop, and carry on all their normal metabolic functions during interphase 6. Interphase consists of 3 parts – G1, S, G2

The Cell Cycle

B. Interphase 1. G1 or 1st Growth Phase occurs after a cell has undergone cell division 2. Cells mature and increase in size by making more cytoplasm & organelles while carrying on normal metabolic activities in G1 3. S or Synthesis Phase follows G1 and the genetic material of the cell (DNA) is copied or replicated. 4. G2 or 2nd Growth Phase occurs after S Phase and the cell makes all the structures needed to divide C. Mitosis – Description 1. Division of the nucleus or mitosis occurs first 2. Mitosis is and asexual method of reproduction 3. Mitosis consists of 4 stages – Prophase, Metaphase, Anaphase, & Telophase

Stages of Mitosis

b. Sister chromatids attach to each other by the centromere D. Stages of Mitosis 1. Prophase a. chromosomes become visible when they condense into sister chromatids b. Sister chromatids attach to each other by the centromere c. centrioles in amimal cells move to opposite ends of the cell d. Spindle forms from centriole (animals) or microtubules (plants) e. Nuclear membrane dissolves f. Nucleolus disintegrates 2. Metaphase – Chromosomes line up in the center or equator of the cell attached to spindle fibers 3. Anaphase (action phase) a. fibers attached to the centromere pull the sister chromatids apart b. Chromosomes move toward opposite ends of the cell

4. Telophase a. Nuclear membranes form at each end of the cell around the chromosomes b. Nucleoli reform c. Chromosomes become less tightly coiled and appear as chromatin again d. Cytokinesis begins E. Cytokinesis 1. Cytoplasm of the cell and its organelles separate into 2 new daughter cells 2. In animals, a groove called the cleavage furrow forms pinching the parent cell in two 3. In plants, a cell plate forms down the middle of the cell where the new cell wall will form.

Mitosis review

F. Cancer 1. Cancer is uncontrolled Mitosis 2 F. Cancer 1. Cancer is uncontrolled Mitosis 2. Mitosis must be controlled, otherwise growth will occur without limit (cancer) 3. Control is by special proteins produced by oncogenes 4. Mutations in control proteins can cause cancer

III. Cell Division in Prokaryotes A. Prokaryotes such as bacteria do not have a nucleus B. Prokaryotes divide into two new cells by the process of binary fission 1. Binary fission is an asexual method of reproduction 2. In binary fission, the chromosome, attached to the cell membrane, makes a copy of itself and the cell grows to about twice its normal size 3. Next, a cell wall forms between the chromosomes and the parent cell splits into 2 new identical daughter cells (clones)

Binary fission

The End