Chapter 3 cell division

Chapter 3Chapter 3

Cell DivisionCell Division

Two Types of Cells Composing the Two Types of Cells Composing the BodyBody

1. Somatic cells-1. Somatic cells- pertains to the cell pertains to the cell composing the bulk of the body such composing the bulk of the body such as the nerve cell, muscle cells, kidney as the nerve cell, muscle cells, kidney cell, etc.cell, etc.

2. Germ cells2. Germ cells – pertains to the – pertains to the reproductive cells such as the ova of reproductive cells such as the ova of female and the spermatocytes of male.female and the spermatocytes of male.

Types of Cell DivisionTypes of Cell Division

A. MitosisA. Mitosis - division in somatic cells and - division in somatic cells and produces two identical daughter cells during produces two identical daughter cells during prophase, prometaphase, metaphase, prophase, prometaphase, metaphase, anaphase, and telophase.anaphase, and telophase. Consist of two phasesConsist of two phases

• 1. nuclear division (Karyokinesis) plus 1. nuclear division (Karyokinesis) plus • 2. cytoplasm division (cytokinesis), 2. cytoplasm division (cytokinesis),

• InterphaseInterphase is often included in discussions of mitosis, is often included in discussions of mitosis, but interphase is technically not part of mitosis, but but interphase is technically not part of mitosis, but rather encompasses stages G1, S, and G2 of the cell rather encompasses stages G1, S, and G2 of the cell cyclecycle

B. MeiosisB. Meiosis – division in reproductive cells – division in reproductive cells producing four daughter cellsproducing four daughter cells

Meiosis differs from mitosis in that cell division Meiosis differs from mitosis in that cell division begins with a cell that has a full complement of begins with a cell that has a full complement of chromosomes and ends with chromosomes and ends with gamete cellsgamete cells, such , such as as sperm and eggssperm and eggs, that have only half the , that have only half the complement of chromosomes. complement of chromosomes.

When a sperm and egg unite during fertilization, When a sperm and egg unite during fertilization, the cell resulting from the union, called a the cell resulting from the union, called a zygotezygote, , contains the full number of chromosomescontains the full number of chromosomes

46 Chromosomes (23 pairs)46 Chromosomes (23 pairs) 1. Autosome (22 pairs)1. Autosome (22 pairs) 2. Sex Chromosomes (a Pair)2. Sex Chromosomes (a Pair)

X chromosomes – femaleX chromosomes – female XY chromosomes - maleXY chromosomes - male

The human body, for example, consists The human body, for example, consists of an estimated of an estimated 20 to 30 trillion cells20 to 30 trillion cells

Human cells also display a variety of Human cells also display a variety of sizes, from small red blood cells that sizes, from small red blood cells that measure 0.00076 mm (0.00003 in) to measure 0.00076 mm (0.00003 in) to liver cells that may be ten times larger. liver cells that may be ten times larger.

About About 10,00010,000 average-sized average-sized human human cells can fit on the head of a pin.cells can fit on the head of a pin.

Multicellular organisms use mitosis for Multicellular organisms use mitosis for growth, cell repair, and cell replacement. growth, cell repair, and cell replacement.

In the human body, for example, an In the human body, for example, an estimated estimated 25 million mitotic cell 25 million mitotic cell divisions occur every seconddivisions occur every second in order to in order to replace cells that have completed their replace cells that have completed their normal life cycles. normal life cycles.

Cells of the Cells of the liver, intestine, and skin may liver, intestine, and skin may be replaced every few days.be replaced every few days.

Recent research indicates that even Recent research indicates that even brain brain cellscells, once thought to be incapable of , once thought to be incapable of mitosis, mitosis, undergo cell division in the part undergo cell division in the part of the brain associated with memory.of the brain associated with memory.

Regulation of the Regulation of the cell cycle is cell cycle is accomplished in accomplished in several ways. several ways.

Some cells divide Some cells divide rapidly.rapidly.

Beans, for example Beans, for example take 19 hours for take 19 hours for the complete cycle;the complete cycle;

Red blood cells Red blood cells must divide at a must divide at a rate of rate of 2.5 million 2.5 million per second.per second.

Liver cells will divide if Liver cells will divide if part of the liver is part of the liver is removed. The removed. The division division continues until the liver continues until the liver reaches its former sizereaches its former size..

Some cells, such as Some cells, such as liver cells, retain but do liver cells, retain but do not normally utilize not normally utilize their capacity for their capacity for division.division.

Others, such as nerve Others, such as nerve cells, lose their cells, lose their capability to divide capability to divide once they reach once they reach maturity. maturity.

Cells go through two basic phases:  Cells go through two basic phases:  Mitosis, InterphaseMitosis, Interphase

INTERPHASEINTERPHASE G0 phase –G0 phase –

• normal cell functions normal cell functions G1 phase –G1 phase –

• prepares for cell prepares for cell division, division,

• duplicates organelles, duplicates organelles, • centriole replication centriole replication

S phase – S phase –

• DNA replicationDNA replication

• Chromosome Chromosome duplication duplication

G2 phase – G2 phase –

• protein synthesis, protein synthesis,

• centriole replication centriole replication completedcompleted

KaryokinesisKaryokinesis

1. prophase1. prophase 2. metaphase2. metaphase 3. anaphase3. anaphase 4. telophase4. telophase

ProphaseProphase

Prophase Chromosome Chromosome

condense into visible condense into visible structuresstructures

Chromatin - complex of Chromatin - complex of DNA and proteinsDNA and proteins

Sister chromatids - the Sister chromatids - the two copies of the two copies of the chromosome chromosome

Centromere becomes Centromere becomes visible visible

Spindle fibers begin to Spindle fibers begin to extend from centriolesextend from centrioles

MetaphaseMetaphase

AnaphaseAnaphase

Kinetochore AsterKinetochore Aster

TelophaseTelophase

CytokinesisCytokinesis

Cytoplasmic division - Cytoplasmic division - cleavage furrow forms in cleavage furrow forms in anaphase or telophase anaphase or telophase & constricts original cell & constricts original cell into two smaller cells into two smaller cells

Each cell has a copy of Each cell has a copy of hereditary information in hereditary information in its chromosomes its chromosomes

The difference betweenThe difference between

Second Stage Second Stage

Human Life CycleHuman Life Cycle

End of presentationEnd of presentation

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TelophaseTelophase

CytokenesisCytokenesis

InterphaseInterphase

PrometaphasePrometaphase

Metaphase Metaphase

AnaphaseAnaphase

TelophaseTelophase

CytokenesisCytokenesis

Which of the following Which of the following statements is NOT true of statements is NOT true of mitosis? mitosis?

A.A.A single nucleus gives rise to two identical daughter nuclei..B.B.The daughter nuclei are genetically identical to the parent nucleus..C.C.The centromeres divide at the onset of anaphase..D.D.Homologous chromosomes synapse in prophase..

Cytokinesis in a plant Cytokinesis in a plant cell is characterized by: cell is characterized by:

A.A.the equal division of homologous chromosomes..B.B.a pinching off of the cell membrane to divide the cell..C.C.the formation of a cell plate in the cytoplasm..D.D.the movement of the chromosomes from the metaphase plate

The first stage of The first stage of mitosis when mitosis when chromosomes start chromosomes start becoming visible in the becoming visible in the microscope is called: microscope is called:

A.A.anaphaseB.B.prophaseC.C.telophaseD.D.metaphase

Which of the following Which of the following features of cell features of cell division are very division are very different for animal different for animal and plant cells? and plant cells?

A.A.prophaseB.B.metaphaseC.C.anaphaseD.D.cytokinesis

The stage of the cell The stage of the cell cycle where each cycle where each chromosome is chromosome is composed of two composed of two chromatids in chromatids in preparation for preparation for mitosis. mitosis.

A.A.G1G1B.B.SSC.C.MMD.D.G2G2

The stage of the cell The stage of the cell cycle where the cell is cycle where the cell is preparing to begin preparing to begin DNA replication is DNA replication is called: called:

A.A.G1G1B.B.G2G2C.C.SSD.D.MM

Meiosis – Prophase & PrometaMeiosis – Prophase & Prometa

Meta & AnaphaseMeta & Anaphase

Telo & CytokinesisTelo & Cytokinesis

plantplant