Cell Cycle and Cell Division

I. Cell DivisionA. 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 Division1. Growth of an organism2. Repair & replacement of damaged cells3. Reproduction of the species

C. Copying DNA1. 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. 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 Numbers1. 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 CycleA. 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

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 fibers3. 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. Cytokinesis1. Cytoplasm of the cell and its organelles separate into 2

new daughter cells2. In animals, a groove called the cleavage furrow forms

pinching the parent cell in two3. In plants, a cell plate forms down the middle of the cell

where the new cell wall will form.

Mitosis review

F. Cancer1. Cancer is uncontrolled Mitosis2. Mitosis must be controlled, otherwise growth

will occur without limit (cancer)3. Control is by special proteins produced by

oncogenes4. 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