Cell Growth & Division

Do now: Who has bigger cells?

Do Now:Which has larger cells, a mouse or an elephant?

CELLS ARE SMALL!

Why do we need to make more cells?

From One Cell to Many

Sea Urchin Cell Division

Why do we need to make more cells?

Why are we one hundred trillion SMALL cells and not one hundred LARGE cells?

100,000,000,000,000 cells because....

They need to be small!

I. Why do Cells Divide?

A. Cells need to stay small because:

– The larger a cell becomes, the more demands on its DNA

– Better organization

– Needs to move nutrients and wastes across the cell membrane quickly

– If too big, cannot get nutrients fast enough

DNA “Overload”• DNA is the cell’s “library” of information.• Imagine a very large city using one local

library for all materials

A big bag is weaker, harder to find things

Large cell, difficult to maneuver organelles

More volume = bigger need

The larger the volume of the balloon, the weaker it is. The balloon skin stays the same.

B. What is Surface area? The total area of the

surface of a 3D object

*Large surface area SPEEDS UP the movement of materials*

What is the surface area of this cube?24 cm2

2 cm

2 cm

C. What is Volume?

The amount of 3-D space that an object occupies, “capacity”

*Large volume SLOWS down movement of materials*

What is the VOLUME of the shape here?

200 cm3

cm

D. Ratio of Surface Area to Volume  

• As the length of cell increases, volume increases faster surface area

(cm3 compared to cm2)

• HIGH ratio desired: quick movement of materials

• Ex: 6000/1 is better than 2/1

It’s better to have lots of small cells

instead of fewer large cells!

II. Chromosomes

A. All genes located in DNA in nucleus of

eukaryotic cell

B. Chromosomes are condensed forms of DNA

Chromosomes C. Chromosome number is unique to every species

• Humans: 46 chr.• Chimpanzees: 48 chr.• Yeast: 32 chr.• Adders-Tongue Fern: 1440 chr.!

How is DNA Packaged? • Chromosome- when chromatin coils for

Mitosis

Copied duringInterphase

D. After duplication phase, each

chromosome consists of two identical “sister” chromatids

Anatomy of a Chromosome

Chromatids attached at the centromere

III. Cell Division

B. Chromosome # stays the same

(Cells growths, doubles chromosomes, then splits, forming two daughter cells with original # of chromosomes)

46chromosomes

46 chr

46 chr

A.

C. Common Locations for Cell Division

• Intestinal lining- every 24 hours

• Skin• Blood cells/bone marrow- 120

days• Liver- sometimes

D. Cells that Rarely Divide(in G0 phase)

• Muscle Cells• Cardiac cells• Kidney• Nerve cells

IV. Cell Cycle

A. Interphase: “I-ball” 90% of the time! Gap0 “resting phase”, cell is not growing Gap1 cell grows, doubles organelles Synthesis duplication of the DNA in

the cell's chromosomesGap2 cell grows, microtubules assembled

C. Checkpoints

i. G1 Checkpoint: DNA to be replicated is healthy; cell size

ii. G2 Checkpoint: Checks that DNA that was replicated is healthy; rest of cell ready for division

iii. M checkpoint:Chromosomes are properly attached to the spindle fibers.

What happens if the cell cannot pass through

the checkpoint?

A) Repair the damage

OR

B) Self-destruct: APOPTOSIS

(Programmed Cell Death)

There are proteins in the cell that regulate these processes and determine which way the cell will go.

C. Steps of MitosisProphase- “pasta”• Chromatin fibers condense• Nuclear membrane breaks down• Spindle of microtubules forms from centrioles [animals only]• Attach to chromatids on centromere

Metaphase- “middle”• Chromosomes line up in the middle• Spindle fibers attach centrioles to

centromeres• Every sister chromatid has fiber attached to

it

Centriole

Spindle

Anaphase: “away phase”, form “A’s”• Spindle fibers contract• Pull sister chromatids apart• The chromosomes continue to move until they

are in two groups• Each side has own copy of DNA

Individualchromosomes

Telophase- “end phase”• Nuclear membranes reform at each pole• Chromosomes unwind• Spindle disappears

D. CYTOKINESISDuring cytokinesis, the cytoplasm cuts in half

1. Cytokinesis in Plants

A structure known as the CELL PLATE forms midway between the divided nuclei.

2. Cytokinesis in Animals

Animal cells contract across middle of cell and “pinch” making a “cleavage furrow”.

http://iknow.net/cell_div_education.html

Twilight STUDIES IT TOO!

MITOSIS VideoParent

CellDaughter Cells

V. TermsA. Spindle: network of microtubules that

move chromosomes during mitosis and meiosis

B. Equator: center line of cell where chromosomes line up during metaphase

C. Poles: the opposite ends of cell

D. Centrioles: animal cells only, move the spindle and chromosomes during division

E. Centromere: region where two sister chromatids are joined tightly together

VII. Results of Mitosis

A. Production of 2 new daughter cells

B. Daughter cells are exactly the same as original parent cell

C. Cell --> Tissue --> Organ --> Organ System --> Organism

D. This is how organisms grow & repair!