CELL REPRODUCTION

THE CELL CYCLE

AND

MITOSIS

Lesson Objectives—Cell Cycle

• Describe the properties of cell division in prokaryotes.

• Describe cell division in eukaryotes. Explain the main

differences between cell division in prokaryotic and

eukaryotic cells.

• Describe the basic properties of chromosomes.

• Describe the key steps in the cell cycle.

• Identify and describe the main processes in mitosis.

• Describe how the cell cycle is controlled and define

cancer.

Vocabulary

• Genes are the basic unit of heredity.

• Chromosomes are composed of deoxyribonucleic acid

(DNA) and protein and are present in the nuclei of all

cells.

• Diploid- All humans have 46 chromosomes in the body

cells, which is the diploid (duplicate) number.

• Haploid-Half of the diploid number of chromosomes is

found in the gametes. 23 chromosomes.

• Homologous-Homo means same. Homologous refers

to the same or similar pairs of chromosomes.

CELL REPRODUCTION

• Cell Division: process by which a cell divides to form

two new cells (daughter cells)

• Three types of cell division, or cell reproduction

– Prokaryotes (bacteria)

• Binary fission divides forming two new identical cells

– Eukaryotes

• Mitosis

– Cell or organism growth

– Replacement or repair of damaged cells

• Meiosis

– formation of sex cells, or gametes

Why do cells divide?

1: DNA Overload

– If cells grow without limit, an “information crisis”

would develop

– DNA cannot serve the needs of the increasing size of

cell

2: Exchange of materials

– Food and oxygen have to cross membrane very

quickly

– Waste must get out

– If cell is too large, this occurs too slowly and cell will

die

PROKARYOTIC CELL DIVISION • Binary fission

– 3 main steps:

1: DNA Replication—DNA is copied, resulting in 2

identical chromosomes

2: Chromosome Segregation—2 chromosomes separate,

move towards ends (poles) of cell

3: Cytokinesis—cytoplasm divides, forming 2 cells

– Each new daughter cell is

genetically identical to parent cell

M phase

G2 phase

S phase

G1 phase

THE CELL CYCLE

CELL CYCLE-INTERPHASE

• Interphase: period of growth and DNA replication between cell divisions

• Three phases:

– G1 Phase

• cell increases in size

– S Phase

• Replication of chromosomes

– Now two strands called sister chromatids joined by a centromere

– G2 Phase

• organelles double

• new cytoplasm forms

• All other structures needed for mitosis form

EUKARYOTIC CELL DIVISION

• DNA found on chromosomes located in nucleus of cell

• Cell cycle continuous process

– Cells grow

– DNA replicated

– Organelles duplicated

– Divide to form daughter cells

– 2 Main steps:

1: Mitosis (4 steps—Prophase, Metaphase, Anaphase, Telophase)

Nucleus divides

2: Cytokinesis—Cytoplasm divide, forming 2 cells

Each new daughter cell is genetically identical to parent cell

• Mitosis = nuclear division

• Mitosis is followed by cytokinesis (cell division) • The steps of mitosis ensure that each new cell

has the exact same number of chromosomes as the original

MITOSIS

• Process that divides cell nucleus to produce two new nuclei each with a complete set of chromosomes. Mitosis is the cell division which occurs in all body cells except in gamete formation.

• Continuous process

• Four phases (PMAT)

– Prophase

– Metaphase

– Anaphase

– Telophase

MITOSIS

• Mitosis results in the formation of two genetically identical cells each containing the same number of chromosomes as the parent cell, the diploid or 2n number.

• Mitosis ensures that the species number of chromosomes is maintained.

• Mitosis ensures that each daughter cell receives an identical combination of genes.

• Mitosis is the method by which all cells of a multicellular organism are formed from the zygote, thus it is essential for growth.

• (1)Prophase • (2)Metaphase • (3)Anaphase • (4)Telophase

•PMAT

Interphase 1 2

3 4

Cytokinesis

1. chromosomes visible (sister chromatids) 2. centrioles migrate to the poles (only in animals) 3. nuclear membrane disappears

4. spindle forms

1. chromosomes line up on the equator of the cell 2. spindles attach to centromeres

Equator

1. sister chromatids separate 2. centromeres divide 3. sister chromatids move to opposite poles

1. chromosomes uncoil • now chromatin

2. nuclear membranes reform

3. spindle disappears

-Occurs at end of Mitosis --division of the cytoplasm to form 2 new daughter

cells

--organelles are divided

-Daughter cells are genetically identical

Cells return to interphase

1.Name the phases starting at the top.

Mitosis

2.Name the phase

3.Identify X

4.Identify Y

5. Name the phase

6. Name the phase

Control of the Cell Cycle

• Regulatory proteins called cyclins control the cell

cycle at checkpoints:

• G1 Checkpoint—decides whether or not cell will

divide

• S Checkpoint—determines if DNA has been

properly replicated

• Mitotic Spindle Checkpoint—ensures

chromosomes are aligned at mitotic plate

Cell Cycle Checkpoints

CANCER CELLS

• Result of uncontrolled cell division of cells that

have lost ability to regulate cell cycle

• Reproduce more rapidly than normal cells

• Masses formed called ‘tumors’

Lesson Summary—Cell Cycle • The cell cycle is a repeating series of events, characterizing the life of a eukaryotic cell.

• Binary fission is a form of cell division in prokaryotic organisms that produces identical

offspring.

• As a eukaryotic cell prepares to divide, the DNA and associated proteins coil into a

structure, known as a chromosome.

• The DNA copies during the S phase of the cell cycle, resulting in a chromosome that

consists of two identical chromatids, known as sister chromatids, attached at a region

called the centromere.

• Any cell containing two sets of chromosomes is said to be diploid; the zygote forms

from the fusion of two haploid gametes.

• The cell cycle has five phases: the first growth (G1) phase, the synthesis (S) phase,

the second growth (G2) phase, mitosis, and cytokinesis.

• Mitosis is the division of the nucleus; four distinct phases of mitosis have been

recognized: prophase, metaphase, anaphase, and telophase.

• Cytokinesis is the division of the cytoplasm.

• The cell cycle is controlled through feedback mechanisms.

• Cancer results from uncontrolled cell division, due to the loss of regulation of the cell

cycle.