How do you get to be 6 ft tall if you started out as a single cell?

How do you heal a wound?

How do you replace worn out cells?

Cell cycle and Cell Division

Ability to reproduce is one characteristic that distinguishes living things from

nonliving matter.

The continuity of life from one cell to another is based on cell division

This division process occurs as part of the cell cycle

cell division

Cells come from cells

Cell division is needed for growth, replacement and repair

Body cells are called somatic cellsSex cells are called gametes

What is Mitosis?Mitosis

Takes one cell and produce two cells that are the genetic equivalent of the parent.

Mitosis is nuclear division. It is the process by which a new cell receives the identical DNA

as its parent cellThe new cell is called the daughter cell. Mitosis

produces two identical daughter cells

Why is mitosis important?This is how multicellular organisms grow,

repair or heal injuries and maintain function.

It is also how asexual reproduction takes place

Mitosis accompanied by Cytokinesis

Functions in reproduction, growth, and repair– reproduces an entire unicellular

organism, increasing the population.

– on a larger scale can produce progeny for some multicellular organisms.

• organisms that can grow by cuttings or by fission.

• Is central to the development of a multicellular organism that begins as a fertilized egg or zygote.

• For repair and renew cells that die from normal wear and tear or accidents.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Prokaryotes( bacteria) reproduce by binary fission– Prokaryotic cells

• Reproduce asexually by cell division

Col

oriz

ed T

EM

32,

500

Prokaryotic chromosomes

Figure 8.3B

What is a genome?An organism’s complete collection

of all its genes

DNA is the molecule that makes up your genes

DNA is packaged into units called chromosomes in the nucleus of cells

What is DNA?

DNA or deoxyribonucleic acid is a large molecule made of chains of repeating units called nucleotides.

It contains the information for specifying the proteins that allow life

What kind of information is encoded in DNA?

Instructions on how to make proteins.

Organisms function as a result of its proteins. Proteins make up structural parts and function as defenses, hormones, enzymes, transport among

many others

What is a gene?

A segment of DNA on a chromosome containing instruction on how to

make a protein

What are chromosomes? A DNA molecule with its associated proteins called

histones

The number of chromosomes is the same for all the members of a

species.

Humans have 46 chromosomes

What is the HAPLOID number of chromosomes? What is DIPLOID?

• What cells have the haploid number? Why?

• What cells have the diploid number of chromosomes? Why?

– Before a cell starts dividing, the chromosomes replicate– Producing sister

chromatids joined together at the centromere

TE

M 3

6,00

0

Centromere

Sister chromatids

Figure 8.4B

Where are the chromosomes found?

Chromosomes are found in the nucleus of eukaryotic cells

one chromosome (unduplicated)

one chromosome (duplicated)

Chromosome

Chromosome Number • Sum total of chromosomes in a cell

• Somatic cells (body cells)

– Chromosome number is diploid (2n)

– Two of each type of chromosome

• Gametes ( sex cells)

– Chromosome number is haploid (n)

– One of each chromosome type

Chromosome Number

•Sum total of chromosomes in a cell

•Somatic cells

–Chromosome number is diploid (2n)

–Two of each type of chromosome

•Gametes

–Chromosome number is haploid (n)

–One of each chromosome type

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00

-Chromosomes contain a very long DNA molecule associated with proteins• And are visible only when the cell is dividing

– If a cell is not undergoing division• Chromosomes

occur in the form of thin, loosely packed chromatin fibers

Figure 8.4A

– Before a cell starts dividing, the chromosomes replicate– Producing sister

chromatids joined together at the centromere

TE

M 3

6,00

0

Centromere

Sister chromatids

Figure 8.4B

What must happen before mitosis?

The cell must make exact copies of its chromosomes in the nucleus so each

new daughter cell gets the same number and type of chromosomes as

its parent cell

Cell division requires the distribution of genetic material - DNA - to two

daughter cells.

A dividing cell duplicates its DNA, moves the two copies to opposite ends of the cell, and then splits

into two daughter cells.

Slide 4

Fig. 8.6, p. 131

chromosome (unduplicated) in a cell at interphase

same chromosome (duplicated) in interphase prior to mitosis

mitosis, cytoplasmic division

chromosome (unduplicated) in a daughter cell at interphase

chromosome (unduplicated) in a daughter cell at interphase

– Cell division involves the separation of sister chromatids

• results in two daughter cells, each containing a complete and identical set of chromosomes Centromere

Chromosomeduplication

Sisterchromatids

Chromosomedistribution

todaughter

cells

Figure 8.4C

What is the cell cycle?

The cell cycle is an ordered set of events, resulting in cell growth

and division into two daughter cells

The stages of the cell cycle are :

G1(stands for Gap1), S (stands for synthesis, this is when DNA is replicated) and

G2 (stands for Gap 2)

Cell Cycle

• Cycle starts when a new cell forms

• During cycle, cell increases in mass and duplicates its chromosomes

• Cycle ends when the new cell divides

The Cell Cycle

What are the phases of the cell cycle?

Interphase: This takes up most of the cell cycle G1This is a time when a cell doubles organelles in its cytoplasm and grows

S is when DNA in the nucleus is doubled

G2 each chromosome now consists of two identical sister chromatids and the cell is preparing to divide

Mitosis: the nucleus and its duplicated chromosomes divide

Cytokynesis: the cytoplasm is divided in two

• The mitotic (M) phase of the cell cycle alternates with the much longer interphase.– The M phase includes mitosis and

cytokinesis.

– Interphase accounts for 90% of the cell cycle.

The mitotic phase alternates with interphase in the cell cycle

Slide 3

Fig. 8.4, p. 130

Interphase

•Usually longest part of the cycle

•Cell increases in mass

•Number of cytoplasmic

components doubles

•DNA is duplicated

Stages of Interphase

•G1

–Interval or gap after cell division

•S

–Time of DNA synthesis (replication)

•G2

–Interval or gap after DNA replication

•Period of nuclear division

•Usually followed by cytoplasmic division - Cytokynesis

Mitosis

The four stages of mitosis

Prophase

Metaphase

Anaphase

telophase

Fig. 12.9

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 12.5 left

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 12.5 right

• On the cytoplasmic side of the cleavage furrow a contractile ring of actin microfilaments and the motor protein myosin form.

• Contraction of the ring pinches the cell in two.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 12.8a

• Cytokinesis, division of the cytoplasm, typically follows mitosis.

• In animals, the first sign of cytokinesis (cleavage)

is the appearance of a cleavage furrow in the cell surface near the old metaphase plate.

Cytokinesis divides the cytoplasm: a closer look

Fig. 12.8a

– In plants• A membranous cell

plate splits the cell in two

Figure 8.7B

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M 7

,500

Cell plateforming

Wall ofparent cell

Daughternucleus

Cell wall New cell wall

Vesicles containingcell wall material

Cell plateDaughter cells

Check these web sites:• http://www.cellsalive.com

• http://www.biology.arizona.edu/cell_bio/cell_bio.html

• http://www.loci.wisc.edu/outreach/bioclips/CDBio.html

• http://gslc.genetics.utah.edu/units/stemcells/whatissc

Play this game:• http://science.nhmccd.edu/biol/bio1int.htm

• The distinct events of the cell cycle are directed by a distinct cell cycle control system.

– These molecules trigger and coordinate key events in the cell cycle.

– The control cycle has a built-in clock, but it is also regulated by external adjustments and internal controls.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Control System of the Cell Cycle

Cell cycle control system• There are three major checkpoints in the cell

cycle. These are “stop and go” signals.(G1, M, and G2)

• It checks whether or not the cellular processes have been completed up to that point so it can proceed.

• The G1 check point is very important. Nerve cells and muscle cells switch into a non dividing stage called G0. They do not get a “go ahead” signal and stop dividing.

Regulation of the cell cycle

How cell division is regulated is very complex and when there are errors it

results in cancer

Cancer is a disease where control of cell division is lost. The cells don’t

grow or behave normally

An example of a cell cycle control is p53

P53 is a protein that functions to block the cell cycle if the DNA is

damaged

A p53 mutation ( non functioning or reduced levels)is the most frequent

mutation leading to cancer

• A variety of chemical and physical factors can influence cell division.

Important for mammalian cells are growth factors, proteins released by one group of cells that stimulate other cells to divide.

• Each cell type responds specifically to a certain growth factor or combination of factors.

– For example, platelet-derived growth factors (PDGF), produced by platelet blood cells, bind to tyrosine-kinase receptors of fibroblasts, a type of connective tissue cell.

– This triggers a signal-transduction pathway that leads to cell division.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• The role of PDGF is easily seen in cell culture.– Fibroblasts in culture will only divide in the presence of

medium that also contains PDGF.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 12.15

• Growth factors appear to be a key in density-dependent inhibition of cell division.– Cultured cells normally

divide until they form a single layer on the inner surface of the culture container.

– If a gap is created, the cells will grow to fill the gap.

– At high densities, the amount of growth factors and nutrients is insuffi-cient to allow cell growth and division stops.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 12.16a

• Most animal cells also exhibit anchorage dependence for cell division.– To divide they must be anchored to a substratum,

typically the extracellular matrix of a tissue.– Control appears to be mediated by connections

between the extracellular matrix and plasma membrane proteins and cytoskeletal elements.

• Cancer cells are free of both density-dependent inhibition and anchorage dependence.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 12.16b

tumors

Growing out of control, cancer cells produces malignant tumors– Cancer cells

• divide excessively to form masses called tumors

Tumors can be benign and malignant (cancerous neoplasm)

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 12.17

What is a metastasis?

1.Cancer cells break away from tumor

2. Cancer cells migrate to blood vessels. These cells are able to secrete enzymes that open vessel wall and enter the blood stream or lymph.

3. Cells move with the blood, exit vessel and invade a new site.

4. This new growth on a new site is a metastasis

– Radiation and chemotherapy• Are effective as cancer treatments because they

interfere with cell division

Web sites about cancer:http://outreach.mcb.harvard.edu/animations_S03.htm

• About mitosis:http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter11/animations.html

Check these web sites:• http://www.cellsalive.com

• http:/www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells2.html

• http://www.loci.wisc.edu/outreach/bioclips/CDBio.html• http://gslc.genetics.utah.edu/units/stemcells/whatissc

Play this game:• http://science.nhmccd.edu/biol/bio1int.htm

Comparison of mitosis and meiosis

• MITOSIS MEIOSIS-OCCURS IN ALL SOMATIC CELLS -OCCURS ONLY IN SEX CELLS:

• GAMETES (ova or eggs and sperm) -PRODUCES IDENTICAL COPIES - PRODUCES VARIATION IN OF PARENT CELL. Daughter cell has TRAITS

• same number of chromosomes as parent. -RESULTS IN 2 DIPLOID (2n) cells - Results in 4 haploid (n) cells complete number of chromosomes reduced number of chromosomes

• -ONE REPLICATION OF CHROMOSOMES - ONE REPLICATION OF FOLLOWED BY 1 CELL DIVISION CHROMOSOMES FOLLOWED BY 2 CELL

-           DIVISIONS

FACTORS THAT CONTRIBUTE TO GENETIC VARIATION

MUTATIONSCROSSING OVER DURING PROPHASE I

OF MEIOSISINDEPENDENT ASSORTMENT OF

CHROMOSOMES during meiosisRANDOM FERTILIZATION OF THE

EGG BY SPERM    

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