CELL DIVISION

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What is cell division?All species pass on their genetic information by producing offspring. Both prokaryotes and eukaryotes

use a process known as cell division to make new cells. Cell division is when a parent cell divides into

two daughter cells. Prokaryotes use cell division to reproduce. Eukaryotes use cell division for growth

and maintenance of cells, as well as for reproduction.

What are the types of cell division?There are three main types of cell division:

1. Binary Fission – prokaryotes use this type of cell division to reproduce

2. The Cell Cycle/Mitosis – eukaryotes use this type of cell division to make new cells

3. Meiosis – this is a special type of cell division used by organisms that sexually reproduce

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CELL DIVISION IN PROKARYOTES

• Binary fission involves the replication

of the prokaryotic chromosome to

produce new cells.

• In bacteria, this chromosome is a

circular double-stranded DNA

molecule.

• This circular DNA molecule constitutes

the entire genome of the bacteria.

• The reproduction of bacteria is clonal,

meaning each cell produced is an

identical copy of the parent cell.

Chromosomes

Centrioles

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Centromere

Spindle fibers

Bacterial cell Origin of replication

Double-stranded DNA (bacterial chromosome)

Terminus of replication

5. When the septum is complete, the cell pinches in two. Two daughter cells are formed, each containing a bacterial DNA molecule.

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BINARY FISSIONBinary fission is the cellular reproduction mechanism used by single-celled prokaryotes, like

bacteria. It occurs in five main steps:

3. The cell elongates as the DNA is replicated.

4. A new membrane and cell wall begin to grow and form a septum at the midpoint of the cell.

1. Replication of the circular bacterial DNA begins at the origin of replication.

2. Starting at the origin of replication, the replication enzymes make copies of each strand of DNA. The enzymes continue until they meet at the terminus of replication.

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THE CELL CYCLECell division in eukaryotes occurs in a cycle that consists of five phases. This cycle is called the cell

cycle.Phases of the Cell Cycle:

G1 (gap phase 1): this is the primary growth phase in which

the cell prepares for DNA replicationf

S (synthesis): during this phase, the cell synthesizes a replica

of its DNAf

G2 (gap phase 2): this is the second growth phase in which

microtubules begin to form a spindle in order to

prepare for separation of the replicated DNAf

Mitosis: during this phase, the replicated DNA separatesf

Cytokinesis: during this phase, the cytoplasm separates, and

two daughter cells are formed

G1SG2MitosisCytokinesis

EUKARYOTIC REPLICATION STRUCTURES

• Nucleus: a structure located in the center of all eukaryotic cells that contains genetic information in the form of chromosomes

• Chromosomes: structures located in the nucleus of a cell; they contain the genetic information of the organism (DNA) and protein

• Sister chromatids: two identical copies of a chromosome that are attached to each other by a centromere

• Centromere: a structure that connects two sister chromatids and serves as a point of attachment for spindle fibers

• Spindle fibers: filaments that pull sister chromatids apart during cell division

• Centrioles: structures that assist in the formation of spindle fibers

Chromosomes

Centrioles

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Centromere

Sister chromatids

Spindle fibers

Nucleus

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MITOSIS

TelophaseMetaphaseInterphase Prophase Anaphase

Mitosis is the cell division process used by eukaryotes in which a single cell divides into two identical daughter cells. Mitosis allows organisms to grow and replace old cells. Mitosis is divided into five phases: interphase, prophase, metaphase, anaphase, and telophase.

The cell’s DNA replicates.

Microtubules begin to extend

from the centrioles.

The chromosomes condense and the mitotic spindles form. The nuclear envelope also begins to

disintegrate.

The chromosomes align in the

center of the cell.

The chromosomes

are pulled to the opposite sides

of the cell.

The cell elongates and

begins to divide into two identical

daughter cells.

SEXUAL REPLICATION VIA MEIOSIS

• Meiosis is separated into two parts –

Meiosis I and Meiosis II.

• Each part consists of prophase, metaphase,

anaphase, and telophase.

• A key feature of Meiosis is the crossing

over that occurs in Prophase I.

• Crossing over is what gives us genetic

variation.

• Homologues are separated during

Meiosis I and sister chromatids are

separated during Meiosis II.

• The steps of Meiosis are listed to the

right.

Chromosomes

Centrioles

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Centromere

Spindle fibers

PROPHASE IThe chromosomes begin to condense and crossing over occurs.

The spindle begins to form.

1

METAPHASE IThe pairs of homologous chromosomes align at the equator of the cell.

2

ANAPHASE IThe homologous pairs of chromosomes are pulled apart.

3

TELOPHASE I & CYTOKINESISThe separated homologues cluster at each end of the cell.

The cell is split, forming two new cells, each with half the number of chromosomes as the original cell.

4

PROPHASE IIA new spindle forms in each cell and the nuclear envelope breaks down.

5

METAPHASE IIChromosomes are joined at the centromere and align at the equator of the cell.

6

ANAPHASE IIThe sister chromatids are pulled apart.

7

TELOPHASE II & CYTOKINESISThe separated sister chromatids cluster at each end of the cell.The cells are both split, forming four genetically diverse cells.

8

MEI

OSI

S I

MEI

OSI

S II

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MEIOSISInterphase Metaphase IProphase I Anaphase I Telophase I

& Cytokinesis Prophase II Metaphase II Anaphase II Telophase II& Cytokinesis

REFERENCESMason, K. Understanding Biology. McGraw-Hill Education; 1st

edition, 2014.

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