Cell Reproduction
8.1 – Chromosomes
8.2 – Cell Division
8.3 - Meiosis
What factors limit cell size?

Diffusion

DNA Content

Surface area-to-volume ratio
DIFFUSION

Certain materials needed for the survival of
the cell can only enter through diffusion.
Ex. waste, carbon dioxide, oxygen


Diffusion is only efficient over a short
distance.
A 20 cm cell would have to wait several
months to receive the above listed
molecules
DNA CONTENT

Most cells have only 1 nucleus

The DNA in the nucleus makes RNA and releases
it to the cytoplasm where it directs the production
of enzymes

Lack of enzymes = Lack of cellular metabolism

Some large cells have compensated by having
multiple nuclei.
Surface area-to-volume ratio

If you double the size of a cell…
-It has 8x as much volume
-Gives rise to 8x as much waste and need for
nutrients
-It becomes impossible for diffusion to keep up
with the cellular demands
Chromosomes

Rod-shaped structures
made of DNA and protein


Coiled chromatin
=chromosomes
Histones = proteins that help
maintain the shape of the
chromosome
Types of Chromosomes

Sex Chromosomes



X or Y chromosomes
Determine sex of individual
Autosomes


Non-sex chromosomes
Determine all other characteristics or
traits

Ex. Hair color, eye color, hemophilia
Chromosome Number

Diploid



Having 2 sets of chromosomes (2n)
Creates genetic diversity
Hapliod


Contain one set of chromosomes (n)
Sex cells
Two major stages of the cell
cycle

Interphase – the growth period of time
where cell activities are carried out
-most of the cells life

Mitosis – process of nuclear division,
followed by the division of the cytoplasm
INTERPHASE

What is going on during this time?
 G1 Phase



S Phase






Metabolism – making ATP
Cell growth, maintenance, repair
Chromosomes are replicated (ready for mitosis)
Make new proteins
Synthesizing new organelles
Conducting photosynthesis (autotrophs)
Storing excess glucose (starch, glycogen)
G2 Phase

Final preparation before cell division (mitosis)
Stages of Mitosis




Prophase
Metaphase
Anaphase
Telophase
PROPHASE

First stage of mitosis





Longest phase of mitosis
Chromatin the nucleus becomes visible
chromosomes
Nucleus disappears
The chromatin, which was copied during
interphase forms 2 complete sets of chromosomes
called sister chromatids
Spindle fibers form between pairs of centrioles
METAPHASE

Second stage of mitosis


Chromosomes move to the equator of the cell
Spindle fibers attach to each chromatid by its
centromere
ANAPHASE

Third stage of mitosis


Chromosomes separate at the centromere
Each sister chromatid begins to move to opposite
ends of the cell
TELOPHASE

Fourth stage of mitosis






Two daughter cells are formed
Each new cell has a complete set of chromosomes
The cytoplasm then divides (cytokinesis)
Nucleus reappears
Chromosomes uncoil to form chromatin
Interphase begins
Control of the Cell Cycle

Cellular enzymes and genes play a key role in
checking and balancing cell division

Tells cells when to divide/stop

Proto-oncogene – regulates cell growth, division and
the ability for cells to adhere to one another


Mutation of the proto-oncogene causes an oncogene
ONCOGENE = UNCONTROLLED CELL DIVISION
Control of the Cell Cycle (2)

Contact inhibition – cell to cell
communication between neighboring
cells…stops the cellular division

Eliminates an over-production of certain types of
cells within the body.
CANCER – a loss of control

Cancer – an uncontrolled dividing of cells


Caused by a change in one or more of the
genes synthesizing enzymes to control the cell
cycle (genetic factor)
The cancer genes are often expressed when
environmental conditions change
(environmental factor)
How can cells regain control


Some genes act as brakes to suppress
cancer expression
Tumor-suppressor genes – code for
proteins that prevent cell division from
occurring too often

To get cancer, these tumor suppressor genes
(all 3 of them) must be damaged
Carcinogen

Any substance that can induce or promote
cancer

Most carcinogens are mutagens


Cause mutation within the cell
Known carcinogens include:




Chemicals in tobacco smoke
Radiation
UV light
Certain viruses
MEIOSIS
INTERPHASE
INTERPHASE MAIN EVENTS

Chromatin replicates
Just like in mitosis
 Forms 2 identical chromatids


Centriole pairs replicate (animal cells
only)
PROPHASE I
PROPHASE I MAIN EVENTS





Chromatin condenses into
chromosomes
Tetrad forms by synapsis
Crossing over occurs between
homologous chromosomes
Centriole pairs move apart
Nuclear envelope and nucleoli
disappear
METAPHASE I
METAPHASE I MAIN EVENTS

Tetrads align along the metaphase
plate


Centromeres of homologous
chromosomes point toward opposite poles
Attach to spindle fibers
ANAPHASE I
ANAPHASE I MAIN EVENTS

Homologous chromosomes separate

Sister chromatids move as a unit

remain attached at the centromere
TELOPHASE I AND
CYTOKINESIS
TELOPHASE I MAIN EVENTS

Chromosomes reach poles




Still as sister chromatids
Cytokinesis occurs simultaneously
Interkinesis
No DNA replication before meiosis II
MEIOSIS II MAIN EVENTS

Very similar to mitosis
PII – spindles form
 MII – chromosomes align
 AII – centromeres split
 TII – nuclei reform
 Cytokinesis – 4 haploid cells

PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II AND
CYTOKINESIS
KEY DIFFERENCES BETWEEN
MEIOSIS AND MITOSIS…

Meiosis is reduction division




2n to n
Meiosis creates genetic variation
Meiosis is 2 successive nuclear
divisions
Meiosis I separates pairs of
chromosomes; centromeres do not
divide
GAMETE PRODUCTION
THROUGH MIEOSIS

Spermatogenesis


Creates 4 sperm cells
Oogenesis
Creates 1 ootid (egg cell)
 3 polar bodies (nonfunctional)

ASEXUAL REPRODUCTION

Production of offspring from one parent
without the union of gametes

Occurs only by mitosis
SEXUAL REPRODUCTION


Production of offspring through meiosis
and the union of gametes
Offspring genetically different due to
genetic recombination
Parts of chromatids can be exchanged
(crossing over)
 Homologous pairs separate
