Mitosis

The process of cell division occurs in a series of stages or phases!!!

Limited cell size (reason they must divide)

DNA “overload” Instructions found in the nucleus are

sufficient to meet all the cells’ needs Exchanging Materials & Messages

All requirements must pass into the cell through the membrane and all wastes must pass out of the cell through the membrane

Surface Area-to-Volume Ratio Want greater surface area compared to

volume Volume increases faster than does the surface

area as a cell gets larger

Cell division accounts for three essential life processes:

Growth-happens because cells grow to a maximum size, then divide

Repair-repairing tissues only happens because of cell division Repairing a tiny cut to regeneration of an arm

on a sea star Reproduction- asexual and sexual

reproduction are dependent on cell division Asexual, a whole new organism grows (mitosis) Sexual, specialized cell division leads to

production of egg and sperm cells allowing this to occur (meiosis)

Cell Cycle

G1 = cell growth S = (synthesis) DNA replication G2 =some growth, preparation for

mitosis M = mitosis (not a part of

interphase) Cytokinesis

These three make up Interphase which is the longest part of the cell cycle

Interphase (G1, S, G2)

DNA starts as chromatin (long threads), but then winds up into chromosomes (coils) AFTER the copy is made. Each chromosome and its copy (sister) are attached and called sister chromatids at the end of this phase.

-Area where the sister chromatids are joined.

nucleolus

MitosisCell Division

ProphaseMetaphaseAnaphaseTelophase

Prophase

Centrioles appear and begin to move to opposite ends of the cell.

Spindle fibers form between the centrioles.

Nuclear membrane starts to disappear.

Chromosomes condensed/nucleolus not visible.

Centrioles

Spindle fibers

Metaphase

Chromatids (or pairs of chromosomes) attach to the spindle fibers.

Centrioles are at poles. Line up in middle

Anaphase

Chromatids separate and begin to be pulled to opposite ends of the cell.

Telophase Two new nuclei form Chromosomes just begin to unwind Cytoplasm pinches inward

Cytokinesis

• In plant cells, a structure known as the cell plate forms midway between the divided nuclei

In animal cells, the cell membrane pinches inward to create two daughter cells – each

with its own nucleus with identical chromosomes.

12

Mitosis in Actual cells

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Animal cell(Early prophase, Prophase, Metaphase, Anaphase, Telophase): © Ed Reschke; Animal cell(Prometaphase): © Michael Abbey/Photo Researchers, Inc.;

Plant cell(Early prophase, Prometaphse): © Ed Reschke; Plant cell(Prophase, Metaphase, Anaphase): © R. Calentine/Visuals Unlimited; Plant cell(Telophase): © Jack M. Bostrack/Visuals Unlimited;

Plant Cellat Interphase

centromere

aster

kinetochore

polar spindle fiber

chromosomescell wall25µm

centrosome

lacks centrioles

MIT

OS

IS

centrosomehas centrioles

Animal Cellat Interphase

nuclearenvelopefragments

chromatincondenses

nucleolusdisappears

Early ProphaseCentrosomes have duplicated.Chromatin is condensing into

chromosomes, and the nuclearenvelope is fragmenting.

ProphaseNucleolus has disappeared, and

duplicated chromosomes are visible.Centrosomes begin moving apart,

and spindle is in process of forming.

ProphaseNucleolus has disappeared, and

duplicated chromosomes are visible.Centrosomes begin moving apart,

and spindle is in process of forming.

20 µm duplicatedchromosome

20 µm

spindlefibers forming

spindlepole

9 µm

kinetochorespindle fiber

cleavage furrow

spindle fibers

20µm 16µm

kinetochorespindle fiber

AnaphaseSister chromatids part and become daughterchromosomes that move toward the spindle

poles. In this way, each pole receives the samenumber and kinds of chromosomes as the parent cell.

MetaphaseCentromeres of duplicated chromosomes

are aligned at the metaphase plate (centerof fully formed spindle). Kinetochore spindle

fibers attached to the sister chromatidscome from opposite spindle poles.

chromosomes atmetaphase plate

6.2µm6.2µm20µm6.2µmspindle pole lackscentrioles and aster

TelophaseDaughter cells are formingas nuclear envelopes and

nucleoli reappear. Chromosomes willbecome indistinct chromatin.

daughter chromosome 20µm

nucleolus

cell plate 6.6µm

Cell Cycle Control Cells have very careful control over

the cell cycle: To maintain quality of cells Uncontrolled growth is Cancer

Three environmental factors that cause cancer are:

1. cigarette smoke2. air and water pollution3. exposure to ultraviolet radiation from

the sun AND TANNING BEDS!!!

14

The Cell Cycle

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

G1

(growth)G0

G2 checkpointMitosis checkpoint.Mitosis will occurif DNA hasreplicated properly.Apoptosis willoccur if the DNA isdamaged andcannot be repaired.

S(growth and DNA

replication)

M

Cytoki

nesis

Telo

phase

An

ap

hase

Meta

ph

ase

Late

pro

phas

e

Prophase

Interphase

G1 checkpointCell cycle main checkpoint.If DNA is damaged, apoptosiswill occur. Otherwise, the cellis committed to divide whengrowth signals are presentand nutrients are available.

M checkpointSpindle assemblycheckpoint. Mitosiswill not continue ifchromosomes arenot properly aligned.

M

G2

G1 G2

(growth and finalpreparations for

division)

Apoptosis

Programmed cell death Like the cell is committing suicide

16

Characteristics of Cancer Cells Lack differentiation

Are nonspecialized Are immortal (can enter cell cycle repeatedly)

Have abnormal nuclei May be enlarged May have abnormal number of chromosomes Extra copies of genes

Form tumors Mitosis controlled by contact with neighboring

cells – contact inhibition Cancer cells have lost contact inhibition

17

Characteristics of Cancer Cells

Undergo metastasis Original tumor easily fragments New tumors appear in other organs

Undergo angiogenesis Formation of new blood vessels

Brings nutrient and oxygen to tumor

18

Progression of CancerCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

primary tumor

New mutations arise, and one cell (brown) has the ability to start a tumor.

Cancer in situ. The tumor is at its place of origin. One cell (purple)mutates further.

Cancer cells now have the ability to invade lymphatic and blood vesselsand travel throughout the body.

New metastatic tumors are found some distance from the primary tumor.

lymphaticvessel

bloodvessel

lymphaticvessel

bloodvessel

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Origins of Cancer: Oncogenes

Mutations in DNA repair mechanisms

Oncogenes Proto-oncogenes (when they are healthy) promote

the cell cycle in various ways

Tumor suppressor genes inhibit the cell cycle in various ways

Both normally regulated in coordination with organism’s growth plan

If either mutates, may lose control and become oncogene (either one).

20

Origins of Cancer: Telomerase Chromosomes normally have special material

at each end called telomeres (end parts) These get shorter each cell division When they get very short

The cell will no longer divide Almost like running out of division tickets

Telomerase is an enzyme that adds telomeres Mutations in telomerase gene:

Keeps adding new telomeres Allow cancer cells to continually divide Like counterfeit tickets

21

Causes of CancerCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

d: © Biophoto Associates/Photo Researchers, Inc.

activatedsignalingprotein

growthfactor

receptorprotein

signalingprotein

phosphate

b. Effect of growth factor

P

P

P

proto-oncogeneCodes for a growth factor,a receptor protein, or asignaling protein in astimulatory pathway.If a proto-oncogenebecomes an oncogene,the end result can beactive cell division.

tumor suppressor geneCodes for a signalingprotein in an inhibitorypathway. If a tumorsuppressor gene mutates,the end result can beactive cell division.

c. Stimulatory pathway andinhibitory pathway

1,100Xd. Cancerous skin cell

gene productpromotescell cycle

Stimulatorypathway

Inhibitorypathway

gene productinhibitscell cycle

growth factorActivates signalingproteins in a stimulatorypathway that extendsto the nucleus.

a. Influences that cause mutated proto-oncogenes(called oncogenes) and mutated tumorsuppressor genes

Heredity Radiationsources

Pesticides and

herbicides

Viruses

oncogene

Animation

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Cyclin- any gene involved in regulating the cell cycle.

Normal cells obey strict rules.Divide only when told. Die rather than misbehave.

~Dr. Andrew Murray Harvard University

If only students were like “normal cells”.

~Dr. Tracey Schneeman Streetsboro High School

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Stem Cells ADULT STEM CELLS Many mammalian organs contain

stem cells Retain the ability to divide Aren’t totally differentiated

(specialized) bone marrow stem cells divide to

produce various types of blood cells EMBRYONIC STEM CELLS

Have the ability to become ANY type of cell

Currently controversial

Therapeutic cloning to produce human tissues can begin with either adult stem cells or embryonic stem cells

Embryonic stem cells can be used for reproductive cloning, the production of a new individual

28

Prokaryotic Cell Division Prokaryotic chromosome is a ring of DNA

1,000 X length of cell Replicated into two rings prior to division Replicate rings attach to plasma membrane

Binary fission Splitting in two between the two replicate

chromosomes Produces two daughter cells identical to

original cell – Asexual Reproduction

29

Binary Fission of Prokaryotes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5. New cell wall and plasmamembrane has divided thedaughter cells.

1. Attachment of chromosome toa special plasma membranesite indicates that thisbacterium is about to divide.

2. The cell is preparing for binaryfission by enlarging its cell wall,plasma membrane, and overallvolume.

3. DNA replication has producedtwo identical chromosomes.Cell wall and plasma mem-brane begin to grow inward.

4. As the cell elongates, thechromosomes are pulled apart.Cytoplasm is being distributedevenly..

(All): © Stanley C. Holt/Biological Photo Service.

200 nm

200 nm

200 nm

chromosome

cell wall

plasmamembrane

cytoplasm

January 30, 2008

Do you think all cells continue to cycle through mitosis throughout the entire life of a person? Are there any cells that you think do? Name them. Are there any cells that you think do not? Name them. (4 points)