1.3 Cell Division

Where do cells come from?All cells come from other cells in order for this to happen, cells must divide

Why is cell division important?1. Growth

cells must divide in order to maintain a high surface area

allows for many access points for nutrients to enter & wastes (CO2) to leave the cell

the distance from the nucleus to all parts of the cell must be kept small so messages can be relayed quickly

2. Repair dead cells need to be replaced

3. Reproduction unicellular organisms can create 2 organisms multicellular organisms can repair & grow

The Cell Cycle

Cells alternate between stages of growth and division growth = interphase division = mitosis

Most of a cell’s life is spent in interphase

Only a small portion of its cycle is cell division, aka mitosis (& cytokinesis)

Mitosis The process where

(the nucleus of) new cells form from other cells

Two exact copies (of the nucleus) are made by doubling one cell’s genetic material (DNA)

pronounced my-TOE-sis

Cell Division process where one

(parent) cell divides to make two (daughter) cells

in multicellular organisms like humans, this is:how a fertilized egg

becomes an adult with trillions of cells

how we replace damaged cells

Let’s review…

(just a little)

Limiting Cell Size a cell can’t get too big or it will not have enough

surface area for the passage of: nutrients it needs in the cell (O2, H2O, Na1+, Ca2+, …)

wastes it produces out of the cell (CO2, H2O, K1+, …)

this is why when cells get to be a certain size, they must divide to survive!

The greater the surface area, the easier it is for a cell to function

The bottom line:

Cells must divide in order to remain small so:messages can be

transmitted quicklydiffusion (of nutrients)

can get happen quicklywastes can be sent out

of the cell quickly

mitosis = the division of a cell’s nucleus into two equal parts

cytokinesis = the division of the cytoplasm & the rest of the cell’s organelles to form 2 daughter cells

happens after mitosis

So, what do mitosis & cytokinesis really mean?

The Cell Cycle

What happens during interphase?

1. Cell grows

2. DNA doubles parent cell must make a copy of its genetic info

before it divides so that each daughter cell will get a complete set of chromosomes

chromosomes, which are normally thin thread-like structures, thicken

each chromosome is duplicated, making sister chromatids

chromatid = thickened, duplicated chromosomes

chromatin = term used to describe thin, thread-like chromosomes

DNA replication

The 4 phases of mitosis: PMAT

Remember, mitosis actually involves just the nucleus contents of the

nucleus double the nucleus divides

into two equal parts

4 phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Sister chromosomes coil & condense Chromosomes become visible (now officially called chromatids)

Membrane around the nucleus dissolves Nucleolus disappears Organelles called centrosomes head to opposite

ends of the cell & begin to form structures called spindle fibres (which help with cell division)

Phase 1: Prophase

Chromosomes line up in the middle of the cell Spindle fibres are completely formed and stretch

from one side of the cell to the other Chromosomes attach to spindle fibres, special

structures that help chromosomes move

Phase 2: Metaphase

Sister chromosomes split (at the middle, called the centromere)

Chromosome pairs (sisters) separate and move to opposite ends of the cell spindle fibres help this process

Phase 3: Anaphase

Chromosomes reach opposite ends of the cell Membranes begin to form around each set of

daughter cells’ nuclear material Nucleolus begins to appear in each cell Chromosomes become less coiled and harder to

see (return to chromatin form) Spindle fibres disappear Cytokinesis begins

Phase 4: Telophase

Cytoplasm & cell organelles divide into two equal parts

Two daughter cells are formed

Cytokinesis

Sooo… let’s recap

Mnemonic to remember the stages of cell division:

IPMATC (ip-MAT-see)

Sexual vs. Asexual Reproduction:

What’s the diff, anyway? Asexual reproduction involves one organism

the parent cell makes 2 daughter cells that are identical to the parent

aka cloning body cells & single-celled organisms reproduce this

way Sexual reproduction involves two organisms

two parent cells (sperm & egg) create 1 daughter cell the offspring receives half of its genes from each

parent daughter cell is 50% mom, 50% dad

Asexual Reproduction

Cell division is an example of asexual reproduction

Sexual Reproduction

haploid = 23 chromosomes

diploid = 2 x 23 chromosomes

meiosis = cell division of sex cells

Mitosis & cytokinesis are only a fraction of the cell

cycle!

Quiz time!i. Identify which number

represents the following stages of cell division:

a) interphaseb) prophasec) metaphased) anaphasee) telophasef) cytokinesis

ii. Identify the following structures:• parent cell• daughter cells• nucleus (3x)• sister chromatids (3x)• spindle fibres (4x)• centrosomes (at least 3x)

Can’t get enough???

Check out http://www.biologycorner.com/bio1/cellcycle.html for more cool visuals on mitosis!