Cell Cycle and Cell Division

Objectives

1. What problems does growth cause for cells? What factors control cell growth?

2. Why do cells divide? What factors control cell division?

3. What are the phases of the cell cycle? What is each for?

4. Describe the processes that occur in each stage of cell division (mitosis).

5. Compare and contrast plant and animal cell division.

6. How does cell division in prokaryotes differ from eukaryotes?

7. Why do chromosomes form?

8. How many chromosomes are in each cell before and after cell division?

9. What is cancer?

What problems does growth cause for

cells?

Objective #1

Cell Size Limits (Part A)

Cells grow until they reach their maximum size limit. Then they must divide or die.

Unfortunately, everything the cell needs to take in or get rid of must leave through the cell membrane, which is proportional to the cell’s surface area.

Cell Size Limits (Part B)Cell Size Limits (Part B)As a cell grows, surface area does not

grow as fast as volume. At some point, the cell’s needs are too

great to be met by diffusion through its cell membrane. That is the cell’s maximum size limit.Cell Size (Length of a Side)

Cell Volume (Needs)

Cell Surface Area (Ability to Meet Needs)

1 1 6

2 8 24

3 27 54

4 64 96

5 125 150

6 216 216

7 343 296

Cell

DIES!!

Cell Size Limits (Part C)

Cellular communications also limit the maximum size of a cell.

In a cell’s normal activities, signaling proteins, raw materials, and enzymes must diffuse through the cell’s cytoplasm to get to areas where they are needed.

If the cell gets too big, then these materials move too slowly to be used in the reactions needed to keep the cell alive.

Summary #1

When a cell grows, a much greater demand is placed on the limited amount of DNA. The instructions for making proteins can’t be used fast enough. This is called DNA overload.

Summary #2

Volume increases much faster than surface area. Surface area to volume ratio decreases, which means eventually there is not enough cell membrane to do the job.

Summary #3

The space inside the membrane is too great; thus the cell cannot efficiently move materials within the cell.

Why do cells divide?

Objective #2

Cell Division

The process a cell undergoes

in order to replace aging or dying cells.

1. Reduce the volume to increase the import/export of materials

2. Reduce the volume to more easily move materials within the cell

3. Minimize DNA “overload”

Cell division helps to…

What are the phases of the cell cycle?

Objective #3

The Cell Cycle

Stages or phases:

Interphase Mitosis Cytokinesis

Interphase (G1 phase)

“Growth 1”

= making proteins and organelles

(“inter” = between)

Interphase (S phase)

“Synthesis”

= replication

(sister chromatids form)

Interphase (G2 phase)

“Growth 2”

= making more organelles and fulfilling cell’s function

(until maximum SA:V)

Length of Cell Cycle

Varies depending on type of cell.If cell cycle took 12 hours:

G1:5 hrs

S: 4.5 hrs

G2: 2 hrs

M: 0.5 hrs

*Which stage does the cell spend most of it’s time?

Objective #4

Describe the processes that occur in each

stage of cell division (or mitosis).

Mitosis begins…Prophase

“pro” = before chromosomes form nucleus breaks up centrioles appear spindle fibers form

Which of these is in prophase?

A

C

D

E

B

Mitosis: Metaphase

“meta” = after or next in line

Spindles attach to chromatids

Centromeres align at middle

Which of these is metaphase?

A

C

D

E

B

Mitosis: Anaphase

“ana” = leading up to…

chromatids separate

chromatids pull to opposite ends of the cell

Which of these is in anaphase?

A

C

D

E

B

Mitosis: Telophase

“telo” = end 2 new nuclei form Coiled

chromosomes change back to relaxed chromatin

Mitosis ends

Which of these is in telophase?

A

C

D

E

B

Cytokinesis

Cytoplasm and cell contents divide as cell membrane moves inward to create 2 daughter cells – each with its own nucleus & identical DNA

Other pictures of mitosis

Other pictures of mitosis

Other pictures of mitosis

Other pictures of mitosis

Other pictures of mitosis

Other pictures of mitosis

Objective #5

Compare & contrast cell division in plant

and animal cells.

Animal cell mitosis

Plant cell mitosis

Cytokinesis differs…

CELL PLATE

TOTDA scientist is observing an animal cell with a microscope. She notices that the chromosomes are becoming visible. Which phase of the cell cycle is the cell MOST likely entering into?

a) Prophase

b) Interphase

c) Metaphase

d) Anaphase

Compare cell division in prokaryotes (bacteria)

and eukaryotes.

Objective #6

Prokaryotic Cell Division

1. Replication: copy the DNA* 2. Cell splits in half, called binary

fission3. This is a form of asexual

reproduction*Each cell has identical DNA copy

Eukaryotic Cell Division

1. Replication

2. Mitosis: chromosomes are assembled, sorted, and divided up through a series of phases

3. Cytokinesis: cytoplasm divides

* Each cell has an identical DNA copy

Why do chromosomes form?

Objective #7

Chromosome Structure…DNA is usually in the form of

chromatin. (very loose strands)

Chromatin is made of DNA that is coiled around proteins called Histones and organized into groups called Nucleosomes

Chromatin continues to condense as the cell prepares for replication

Chromosome structure…

Before the cell divides, the super-condensed chromatin is duplicated as sister chromatids.

Sister chromatids are like matched socks and are held together by a Centromere

This forms homologous chromosomes

Cells organize the DNA into chromosomes – condensed colored bodies that can be sorted during cell division.

To handle the amount of DNA

How many chromosomes are in each cell before and after cell division?

Objective #7

46

Mitosis = diploid to diploid

46

S phase46

46

92 Mitosis

Diploid means: The somatic (body) cell contains two copies of each chromosome. In humans we have 46 chromosomes. There are 23 chromosomes you get from Mom and 23 chromosomes you get from Dad.

When a somatic cell divides each new daughter cell must have the same amount of DNA. That’s the purpose of Replication and Mitosis.

What factors control cell division?

Control of the Cell Cycle

Cells require growth factors to divide (cyclins or hormones)

Cells need room to grow - if it’s cramped, no division

Cells normally stop dividing if they lose their anchorage

Objective #9

What is cancer?

Apoptosis

Programmed cell deathApoptotic cells shrink in size, break into

smaller pieces that other body cells recognize and eatFor tissue developmentTo remove damaged cellsTo destroy viral infected cellsTo balance mitosis rate

What is Cancer? Disease of defective apoptosis Cyclins and CDK (cyclin dependent kinases)

control transition from G1 to S and G2 to M. If these don’t work properly it leads to…

tumor growth

“Mitosis gone mad”

Cancer causes

Mutated genes (called oncogenes) can over-stimulate cell division

Mutated tumor supressor genes fail to prevent tumor growth

*Mutagenic factors (mutation producing) include radiation, some foods, drugs & chemicals, viruses & microbial agents, smoke, dust like asbestos, inhalants, gasoline, lead…

Healthful Decisions to reduce Cancer Risk

Avoid carcinogens! (smoking) Eat whole foods (fresh fruit and grains) Exercise regularly to boost immune system Don’t drink alcohol in excess Don’t get sunburned or overexpose your skin

to UV (watch out tanning bed victims) Undergo regular screening and self-

examination