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Chapter 9

Chapter 9

The cell cycle has 4 main stages.

The cell cycle is a regular pattern of growth, DNA replication, and cell division.

KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

• Interphase is the longest phase in the cell cycle. • During interphase, the cell carries out all its usual

functions like respiration, enzyme production and growing

Interphase

There are three (3 ) stages of interphase:

•Gap 1 (G1 )•DNA Synthesis (S)•Gap 2 (G2 )

The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis.

– Gap 1 (G1): cell growth , normal functions, replicate organelles

• Mitosis occurs only if the cell is large enough and the DNA is undamaged.

– DNA synthesis (S): copies DNA

– Gap 2 (G2): additional growth

– Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis)

INTERPHASE

G1

G2

S(DNA synthesis)

G1 stage/phase Cell GrowthS stage/phase DNA Replication: the genetic material (chromosomes) are replicated or copied.

G2 stage/phase Preparation for Mitosis

The rate of cell division varies with the need for those types of cells.

• Some cells are unlikely to divide (G0).

The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock

The cell cycle control system is regulated by both internal and external controls

The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received

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G1 checkpoint

G1

G2

G2 checkpoint

M checkpoint

M

SControlsystem

For many cells, the G1 checkpoint seems to be the most important

If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide

If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0

phase

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G1 checkpoint

G1 G1

G0

(a) Cell receives a go-aheadsignal.

(b) Cell does not receive ago-ahead signal.

Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin-dependent kinases (Cdks)

Cdks activity fluctuates during the cell cycle because it is controlled by cyclins, so named because their concentrations vary with the cell cycle

MPF (maturation-promoting factor) is a cyclin-Cdkcomplex that triggers a cell’s passage past the G2

checkpoint into the M phase

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Chromosomes condense at the start of mitosis.

DNA wraps around proteins (histones) that condense it.

DNA doublehelix

DNA andhistones

Chromatin SupercoiledDNA

KEY CONCEPT Cells divide during mitosis and cytokinesis.

Review of Chromatin

• DNA plus proteins is called chromatin.

• One half of a duplicated chromosome is a chromatid.

• Sister chromatids are held together at the centromere.

• Telomeres protect DNA and do not include genes.

Condensed, duplicated chromosome

chromatid

telomere

centromere

telomere

Parent cell

centrioles

spindle fibers

centrosome

nucleus withDNA

Mitosis and cytokinesisproduce two genetically identical daughter cells.

Interphase prepares the cell to divide.

During interphase, the DNA is duplicated.

Mitosis divides the cell’s nucleus in four phases.

Centrioles (centrosomes) are microtubules that move cell structures during cell division

The SPINDLE FIBERS attach to the centromere and move the chromosomes and then pull the chromosomes apart

PROPHASE– During prophase, chromosomes condense and spindle

fibers form.

– The nuclear membrane disintegrates

METAPHASE– During metaphase, chromosomes line up in the middle

of the cell.

ANAPHASE– During anaphase, sister chromatids separate to

opposite sides of the cell.

TELOPHASE– During telophase, the new nuclei form and chromosomes

begin to uncoil.

Cytokinesis

– Cytokinesis differs in animal and plant cells.

– In animal cells, the membrane pinches closed : cleavage furrow.

– In plant cells, a cell plate forms.

PREFIX MEANING

Pro “Before”

Meta “Middle”

Ana “Away”

Telo “End”

Simple way to remember the order of mitosis: PMATProphase, Metaphase, Anaphase, Telophase

One cell with two of each chromosomes chromosomes divides to create two cells with two of each chromosome : the number of chromosomes per cell is conserved !

2 cells with identical genetic information and Cytoplasm, organelles etc.

Chapter 9

Internal and external factors regulate cell division. External factors include physical and chemical signals. Growth factors are proteins that stimulate cell division.

Most mammal cells form a single layer in a culture dish and stop dividing once they touch other cells.

KEY CONCEPTCell cycle regulation is necessary for healthy growth.

Apoptosis is programmed cell death.

a normal feature of healthy organisms

caused by a cell’s production of self-destructive enzymes

occurs in development of infants

webbed fingers

Apoptosis

Cell division is uncontrolled in cancer.

Cancer cells form disorganized clumps called tumors.

cancer cellbloodstream

normal cell

– Benign tumors remain clustered and can be removed.

– Malignant tumors metastasize, or break away, and can form more tumors.

A TUMOR is a an abnormal mass of tissue. An abnormal mass of essentially normal cells

is called a benign tumor.

Malignant tumors are masses

of cells that result from the reproduction of cancer cells.

These malignant tumors can metastasis•The most dangerous characteristic of cancer cells is their ability to spread.•A malignant tumor displaces normal tissue as it grows,.•If a malignant tumor is not killed or removed, it can spread into surrounding tissues.•Cells may split off from the tumor and travel to other parts of the body, where they can form new tumors. The spread of cancer cells beyond their original site (metastasis).

Cancer cells do not carry out necessary functions. Cancer cells come from normal cells with damage to

genes involved in cell-cycle regulation.

Carcinogens are substances known to promote cancer. Examples of carcinogens are tobacco smoke, Hepatitis B, and

human papilloma viruses (HPV)

• Standard cancer treatments typically kill both cancerous and healthy cells.

• 4 major types of treatment for cancer are surgery, radiation, chemotherapy, and biologic therapies

Multicellular organisms depend on interactions among different cell types.

Tissues are groups of cells that perform a similar function.

Organs are groups of tissues that perform a specific or related function.

Organ systems are groups of organs that carry out similar functions.

CELL TISSUE ORGAN

vascular tissue

leaf

stem

lateralroots primary

root

SYSTEMS

roo

t sy

ste

msh

oo

t sy

ste

m

KEY CONCEPT Cells work together to carry out complex functions.

Specialized cells perform specific functions.

Cells develop into their mature forms through the process of cell differentiation.

Cells differ because different combinations of genes are expressed.

A cell’s location in an embryo helps determine how it will differentiate.

Outer: skin cells Middle: bone cells Inner: intestines

Stem cells are unique body cells.

Stem cells have the ability to divide and renew themselves

remain undifferentiated in form

develop into a variety of specialized cell types

Stem cells are classified into three types.

– totipotent, or growing into any other cell type

– pluripotent, or growing into any cell type but a totipotent cell

– multipotent, or growing into cells of a closely related cell family

First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules.

Stem cells come from adults and embryos.– Adult stem cells can be hard to isolate and grow.

– The use of adult stem cells may prevent transplant rejection.

– The use of embryonicstem cells raisesethical issues

– Embryonic stem cellsare pluripotent andcan be grown indefinitelyin culture.

The use of stem cells offers many currently realized and potential benefits.

– Stem cells are used to treat leukemia and lymphoma.

– Stem cells may cure disease or replace damaged organs.

– Stem cells may revolutionize the drug development process.