Chapter 5c

Cell Division and Mitosis

Division Mechanisms

Eukaryotic organisms

– Mitosis

– Meiosis

Prokaryotic organisms

– Prokaryotic fission`

Roles of Mitosis

• 1) Multicelled organisms

– a) Growth

– b) Cell replacement

• 2) Some protistans, fungi, plants, animals

– a) Asexual reproduction`

Chromosome

• 1) A DNA molecule & attached proteins

• 2) Duplicated in preparation for mitosis`

one chromosome (unduplicated)

one chromosome (duplicated)

Chromosome Number

• 1) Sum total of chromosomes in a cell

• 2) Somatic cells– a) Chromosome number is diploid (2n)

– b) Two of each type of chromosome

• 3) Gametes– a) Chromosome number is haploid (n)

– b) One of each chromosome type`

Human Chromosome Number

• 1) Diploid chromosome number (n) = 46

• 2) Two sets of 23 chromosomes each– a) One set from father– b) One set from mother

• 3) Mitosis produces cells with 46 chromosomes--two of each type`

Cell Cycle

• 1) Cycle starts when a new cell forms

• 2) During cycle, cell increases in mass and duplicates its chromosomes

• 3) Cycle ends when the new cell divides`

Interphase

• 1) Usually longest part of the cycle

• 2) Cell increases in mass

• 3) Number of cytoplasmic components

doubles

• 4) DNA is duplicated`

Stages of Interphase

• 1) G1 – a) Interval or gap after cell division

• 2) S– a) Time of DNA synthesis (replication)

• 3) G2– a) Interval or gap after DNA replication`

Mitosis

• 1) Period of nuclear division

• 2) Ending with telophase and cytoplasmic division

• 3) Four stages:– a) Prophase

– b) Metaphase

– c) Anaphase

– d) Telophase`

The Spindle Apparatus

• 1) Consists of two distinct sets of

microtubules

– a) Each set extends from one of the cell

poles

– b) Two sets overlap at spindle equator

• 2) Moves chromosomes during mitosis`

Spindle Apparatus

one spindle pole

one of the condensed chromosomes

spindle equator

microtubules organized as a spindle apparatus

one spindle pole

Early Prophase - Mitosis Begins

1) Duplicated chromosomes begin to condense``

Late Prophase

• 1) New microtubules are assembled

• 2) One centriole pair is moved toward opposite pole of spindle

• 3) Nuclear envelope starts to break up`

Prometaphase

• 1) Spindle forms

• 2) Spindle microtubules become attached to the two sister chromatids of each chromosome`

Metaphase

• 1) All chromosomes are lined up at the spindle equator

• 2) Chromosomes are maximally condensed`

Anaphase

• 1) Sister chromatids of each chromosome are pulled apart

• 2) Once separated, each chromatid is a chromosome `

Telophase

• 1) Chromosomes decondense

• 2) Two nuclear membranes form, one around each set of unduplicated chromosomes`

Results of Mitosis

• 1) Two daughter nuclei

• 2) Each with same chromosome number as parent cell

• 3) Chromosomes in unduplicated form`

nucleusplasmamembrane

pair of centrioles

chromosomesnuclear envelope

CELL AT INTERPHASE EARLY PROPHASE LATE PROPHASE

TRANSITION TO METAPASE

The cell duplicates its

DNA, prepares for

nuclear division

Mitosis begins. The DNA and its

associated proteins have started to

condense. The two chromosomes

color-coded purple were inherited

from the female parent. The other

two (blue) are their counterparts.,

inherited from the male parent.

Chromosomes continue to

condense. New

microtubules become

assembled. They move one

of the two pairs of centrioles

to the opposite end of the

cell. The nuclear envelope

starts to break up.

Now microtubules penentrate

the nuclear region. Collectively,

they form a bipolar spindle

apparatus. Many of the spindle

microtubules become attatched

to the two sister chromatids of

each chromosome.

MITOSIS

METAPHASE ANAPHASE TELOPHASE INTERPHASE

All chromosomes have become

lined up at the spindle equator.

At this stage of mitosis (and of

the cell cycle), they are most

tightly condensed

Attachments between the

two sister chromatids of each

chromosome break. The two

are separate chromosomes,

which microtubules move to

opposite spindle pores.

There are two clusters

of chromosomes, which

decondense. Patches of

new membrane fuse to form

a new nuclear envelope.

Mitosis is completed.

Now there are two

daughter cells. Each

is diploid; its nucleus

has two of each type

of chromosome, just

like the parent cell.

Cytoplasmic Division

• 1) Usually occurs between late

anaphase and end of telophase

• 2) Two mechanisms

– a) Cell plate formation (plants)

– b) Cleavage (animals)`