AP BiologyAP Biology

Ch. 12Ch. 12

The Cell The Cell CycleCycle

Limits to Cell Growth: Why do Limits to Cell Growth: Why do cells need to divide?cells need to divide?

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

The cell has “DNA overload”, and The cell has “DNA overload”, and the needs of the growing cell can the needs of the growing cell can no longer be met.no longer be met.

The more trouble a cell has The more trouble a cell has moving enough nutrients and moving enough nutrients and wastes across the cell membrane.wastes across the cell membrane.

Surface area to Volume Surface area to Volume RatioRatio

As a cell grows, the volume of the cell As a cell grows, the volume of the cell increases faster than the surface increases faster than the surface area.area.

The resulting decrease in the cell’s The resulting decrease in the cell’s ratio of surface area to volume ratio of surface area to volume makes it difficult for the cell to move makes it difficult for the cell to move needed materials in and waste needed materials in and waste products out.products out.

Cell Size

Surface Area (length x width x 6)

Ratio of Surface Area Ratio of Surface Area to Volume in Cellsto Volume in Cells

Cell Size

Surface Area(l x w x 6)Volume(l x w x h)

Surface area toVolume ratio

Cell DivisionCell Division

Before it becomes too large, a growing Before it becomes too large, a growing cell must divide into two “daughter” cell must divide into two “daughter” cells. This is cells. This is cell divisioncell division..

Before cell division occurs, the cell Before cell division occurs, the cell copies its DNA. This ensures that each copies its DNA. This ensures that each daughter cell gets a complete set of daughter cell gets a complete set of genetic information.genetic information.

Division increases the cell’s surface Division increases the cell’s surface area to volume ratio.area to volume ratio.

Overview: Key Roles of Overview: Key Roles of Cell DivisionCell Division Cell Division plays several important Cell Division plays several important

roles in the life of an organism:roles in the life of an organism:1.1. Reproduction (unicellular Reproduction (unicellular

organisms)organisms)2.2. Allows multicellular Allows multicellular

organisms to reproduceorganisms to reproduce3.3. Cell and tissue renewal Cell and tissue renewal

and repairand repair4. Passing identical genetic material 4. Passing identical genetic material

from existing cells to new cellsfrom existing cells to new cells

Reproduction: An amoeba is dividing into two cells. Each new cell will be an individual organism.

Growth and Development: A sand dollar embryo shortly after the fertilized egg divided, forming two cells.

Tissue renewal: These dividing bone marrow cells will

give rise to new blood cells.

Cellular Organization of the Cellular Organization of the Genetic MaterialGenetic Material

Cell division involves the distribution of Cell division involves the distribution of identical genetic material—DNA—to identical genetic material—DNA—to two daughter cells.two daughter cells.

A cell’s genetic information is called its A cell’s genetic information is called its genomegenome..

When cells divide, the DNA is When cells divide, the DNA is packaged into packaged into chromosomeschromosomes..

Chromosomes are made of DNA, which Chromosomes are made of DNA, which carries the cell’s coded genetic carries the cell’s coded genetic information, and proteins.information, and proteins.

ChromosomesChromosomes Cells of each organisms have a specific Cells of each organisms have a specific

number of chromosomes. number of chromosomes. Human somatic cells (body cells) have Human somatic cells (body cells) have

46 (23 pairs)46 (23 pairs) Reproductive cells, or gametes, have Reproductive cells, or gametes, have

23 chromosomes.23 chromosomes. Chromosomes are not visible except Chromosomes are not visible except

during cell division.during cell division. Each chromosome consists of two Each chromosome consists of two

identical “sister” identical “sister” chromatidschromatids that are that are attached at the attached at the centromerecentromere..

Eukaryotic chromosomes: Chromosomes are visible within the nucleus asthe cell prepares to divide.

Cell DivisionCell Division

A.A. The Cell CycleThe Cell CycleB.B. Events of the Cell CycleEvents of the Cell CycleC.C. MitosisMitosis

1.1. Prophase/PrometaphaseProphase/Prometaphase2.2. MetaphaseMetaphase3.3. AnaphaseAnaphase4.4. TelophaseTelophase

D.D. CytokinesisCytokinesis

The Cell CycleThe Cell Cycle

During the cell cycle, a cell grows, During the cell cycle, a cell grows, prepares for division, and divides to prepares for division, and divides to form two new daughter cells.form two new daughter cells.

InterphaseInterphase is the period between is the period between divisions, and includes G1, S, and divisions, and includes G1, S, and G2 phases.G2 phases.

The M phase follows interphase, and The M phase follows interphase, and includes mitosis and cytokinesis.includes mitosis and cytokinesis.

includes

is divided into is divided into

Concept MapConcept MapSection 10-2

Cell Cycle

M phase (Mitosis)

Interphase

G1 phase S phase ProphaseG2 phase Metaphase TelophaseAnaphase

InterphaseInterphase

InterphaseInterphase takes much longer than takes much longer than actual cell division.actual cell division.

G1G1: Cells do most of their growing. : Cells do most of their growing. Cells increase in size and synthesize Cells increase in size and synthesize new proteins and organelles.new proteins and organelles.

SS: DNA is copied: DNA is copied G2G2: Cell prepares for mitosis, makes : Cell prepares for mitosis, makes

organelles and structures needed for organelles and structures needed for cell divisioncell division

M phase

G2 phase

S phase

G1 phase

Figure 10–4 The Cell CycleFigure 10–4 The Cell CycleSection 10-2

Go to Section:

INTERPHASE

MitosisMitosis

Following the events of Following the events of Interphase, the cell will begin to Interphase, the cell will begin to divide. This is divide. This is mitosismitosis..

Biologists divide mitosis into four Biologists divide mitosis into four phases: prophase/prometaphase, phases: prophase/prometaphase, metaphase, anaphase, and metaphase, anaphase, and telophasetelophase

ProphaseProphase

The first and longest phase of The first and longest phase of mitosis is prophase.mitosis is prophase.

During prophase, the chromatin During prophase, the chromatin condenses to form chromosomes.condenses to form chromosomes.

The centrioles separate, and a The centrioles separate, and a spindle begins to form.spindle begins to form.

The nuclear membrane begins to The nuclear membrane begins to break down.break down.

PROPHASE

PrometaphasePrometaphase

Nuclear envelope fragmentsNuclear envelope fragments Microtubules extend from each Microtubules extend from each

centrosome toward the middle of centrosome toward the middle of the cell.the cell.

Microtubules attach to the Microtubules attach to the kinetochores, moving the kinetochores, moving the chromosomeschromosomes

PROMETAPHASE

MetaphaseMetaphase

The stage following prophase is The stage following prophase is metaphase.metaphase.

During metaphase, the During metaphase, the chromosomes line up across the chromosomes line up across the center of the cell.center of the cell.

Each chromosome is connected Each chromosome is connected to a spindle fiber at its to a spindle fiber at its centromere.centromere.

METAPHASE

AnaphaseAnaphase

Following metaphase is anaphase.Following metaphase is anaphase. During anaphase, the sister During anaphase, the sister

chromatids separate into individual chromatids separate into individual chromosomes and are moved chromosomes and are moved apart.apart.

The chromosomes form groups The chromosomes form groups near the poles of the spindle.near the poles of the spindle.

Anaphase ends when the Anaphase ends when the chromosomes stop moving.chromosomes stop moving.

ANAPHASE

TelophaseTelophase

The fourth and final stage of The fourth and final stage of mitosis is telophase.mitosis is telophase.

The chromosomes gather at The chromosomes gather at opposite ends of the cell, and lose opposite ends of the cell, and lose their distinct shapes.their distinct shapes.

Two nuclear membranes begin to Two nuclear membranes begin to form.form.

TELOPHASE

CytokinesisCytokinesis

Cell division is not complete until Cell division is not complete until cytokinesis occurs. Cytokinesis is division cytokinesis occurs. Cytokinesis is division of the cytoplasm.of the cytoplasm.

In animal cells, the cell membrane is In animal cells, the cell membrane is drawn inward until the cytoplasm is drawn inward until the cytoplasm is pinched into two equal parts. A cleavage pinched into two equal parts. A cleavage furrow forms.furrow forms.

In plants, a cell plate forms midway In plants, a cell plate forms midway between the divided nuclei. The cell between the divided nuclei. The cell plate gradually develops into a separating plate gradually develops into a separating membrane.membrane.

Cleavage furrow in Cleavage furrow in animal cellsanimal cells

Cell plate forming in Cell plate forming in plant cellplant cell

Binary FissionBinary Fission

Prokaryotes such as bacteria Prokaryotes such as bacteria reproduce by binary fission.reproduce by binary fission.

Most genes are carried on a Most genes are carried on a single bacterial chromosome.single bacterial chromosome.

During binary fission, a bacterial During binary fission, a bacterial chromosome replicates and the chromosome replicates and the two daughter chromosomes move two daughter chromosomes move apart.apart.

BINARY FISSION

Evolution of MitosisEvolution of Mitosis

Since prokaryotes came before Since prokaryotes came before eukaryotes, it is likely that mitosis eukaryotes, it is likely that mitosis evolved from prokaryotic cell evolved from prokaryotic cell division.division.

Certain protists exhibit cell division Certain protists exhibit cell division processes that seem somewhere processes that seem somewhere between bacterial binary fission between bacterial binary fission and mitosis in eukaryotic cells.and mitosis in eukaryotic cells.

Evolution of Mitosis?

Regulating the Cell CycleRegulating the Cell Cycle

A.A. Controls on Cell DivisionControls on Cell Division

B.B. Cell Cycle RegulatorsCell Cycle Regulators

1.1. Internal RegulatorsInternal Regulators

2.2. External RegulatorsExternal Regulators

C.C. Uncontrolled Cell GrowthUncontrolled Cell Growth

Cell Cycle RegulatorsCell Cycle Regulators

Cyclins regulate the timing of the Cyclins regulate the timing of the cell cycle in eukaryotic cells.cell cycle in eukaryotic cells.

Proteins that respond to events Proteins that respond to events inside the cell are called inside the cell are called internal internal regulators.regulators.

Proteins that respond to events Proteins that respond to events outside the cell are called outside the cell are called external external regulators.regulators.

Cyclins and CDKCyclins and CDK

Most of the kinases that activate the cell cycle Most of the kinases that activate the cell cycle are present at a constant concentration in the are present at a constant concentration in the cell, but most are in the inactive form.cell, but most are in the inactive form.

Kinases (CDK) must be attached to a cyclin to Kinases (CDK) must be attached to a cyclin to become active.become active.

Cyclin levels rise during the S and G2 phases, Cyclin levels rise during the S and G2 phases, and falls during the M phase.and falls during the M phase.

MPF (maturation promoting factor) level rises MPF (maturation promoting factor) level rises with the rise in cyclin concentration, causing with the rise in cyclin concentration, causing the cell to go past the G2 checkpoint into M the cell to go past the G2 checkpoint into M phase.phase.

Does PDGF stimulate the division of humanfibroblasts in culture?

HUMAN FIBROBLASTS

Density-dependent Density-dependent inhibitioninhibition

Cultured cells normally divide Cultured cells normally divide until they form a single layer until they form a single layer of cells on the inner surface of of cells on the inner surface of the culture container, at which the culture container, at which point they stop dividing.point they stop dividing.

This is known as contact This is known as contact inhibition, or density-inhibition, or density-dependent inhibitiondependent inhibition..

Uncontrolled cell Uncontrolled cell growthgrowth Cancer cells do not respond to the Cancer cells do not respond to the

signals that regulate the growth of most signals that regulate the growth of most cells. They have been cells. They have been transformed transformed from a normal cell to a cancer cell.from a normal cell to a cancer cell.

A defect in a gene called p53 has been A defect in a gene called p53 has been found in many types of cancer cells. found in many types of cancer cells.

They continue to grow out of control, They continue to grow out of control, and can form masses of cells called and can form masses of cells called tumorstumors..

Benign vs. Malignant tumorsBenign vs. Malignant tumors

Tumors can damage surrounding Tumors can damage surrounding tissues.tissues.

If the abnormal cells remain at the If the abnormal cells remain at the original site, the tumor is BENIGN original site, the tumor is BENIGN and can usually be surgically and can usually be surgically removed.removed.

If the tumor invades other organs If the tumor invades other organs and impairs their function, the and impairs their function, the tumor is MALIGNANT.tumor is MALIGNANT.

The spreading of cancer cells is The spreading of cancer cells is METASTASIS.METASTASIS.

BREAST CANCER

BREAST CANCER CELL

NORMAL MAMMOGRAM

CANCEROUSMASS