chapter 12 the cell cycle lab 3 mitosis and meiosis

Chapter 12Chapter 12The Cell CycleThe Cell Cycle

Lab 3

Mitosis and Meiosis

MitosisMitosis

Division of the cell nucleus.

Division of the cell nucleus.

CytokinesisCytokinesis

Division of the cell cytoplasm.

Division of the cell cytoplasm.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Cell Cycle

The continuity of life

Is based upon the reproduction of cells, or cell division


The Cell Cycle – Making an “EXACT copy” Unicellular organisms

Reproduce by cell division


The Cell Cycle Multicellular organisms depend on cell division for

Development from a fertilized cell

Growth

Repair

Growth and development Tissue renewal

Cell DivisionCell Division Cell division results in genetically

identical daughter cells Cells duplicate their total genetic material

(genome) Before they divide, ensuring that each

daughter cell receives an exact copy of the genetic material, DNA

Cell division results in genetically identical daughter cells

Cells duplicate their total genetic material (genome) Before they divide, ensuring that each

daughter cell receives an exact copy of the genetic material, DNA


Genetic Material

The DNA molecules in a cell

Are packaged into chromosomes

50 µm

Genetic MaterialGenetic Material

Eukaryotic chromosomes Consist of chromatin, a complex of DNA &

protein that condenses during cell division In animals

Somatic cells have two sets of chromosomes46 in humans

Gametes (egg & sperm) have one set of chromosomes23 in humans

Eukaryotic chromosomes Consist of chromatin, a complex of DNA &

protein that condenses during cell division In animals

Somatic cells have two sets of chromosomes46 in humans

Gametes (egg & sperm) have one set of chromosomes23 in humans


DNA Replication Each duplicated

chromosome

Has two sister chromatids, which separate during cell division

They are attached by a central area called the centromere

0.5 µm

Chromosomeduplication(including DNA synthesis)

Separation of sister

chromatids

chromatids

centromere


Phases of the Cell Cycle

The cell cycle consists of

Interphase

Mitotic phase

INTERPHASE

G1

S(DNA synthesis)

G2Cyto

kines

is

Mito

sis

MITOTIC(M) PHASE


Mitotic Phase

Mitosis consists of five distinct phases

1.) Prophase

2.) Prometaphase

G2 OF INTERPHASE

PROPHASE PROMETAPHASE

Centrosomes(with centriole pairs) Chromatin

(duplicated)

Early mitoticspindle

Aster

CentromereFragmentsof nuclearenvelope

Kinetochore

Nucleolus Nuclearenvelope

Plasmamembrane

Chromosome, consistingof two sister chromatids

Kinetochore microtubule

Nonkinetochoremicrotubules


Mitotic Phase

3.) Metaphase

4.) Anaphase

5.) Telophase (usually followed by cytokinesis)

Centrosome at one spindle pole

Daughter chromosomes

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS

Spindle

Metaphaseplate Nucleolus

forming

Cleavagefurrow

Nuclear envelopeforming

Types of MicrotubulesTypes of MicrotubulesKinetochore microtubules

Attach to the kinetochores of chromosomes and move the chromosomes to the metaphase plate

Nonkinetechore microtubules from opposite poles Overlap and push against each other,

elongating the cell

Kinetochore microtubules Attach to the kinetochores of

chromosomes and move the chromosomes to the metaphase plate

Nonkinetechore microtubules from opposite poles Overlap and push against each other,

elongating the cell

Assembly of the spindle microtubules starts in the centrosome. The centrosome (microtubule-organizing

center) of animals has a pair of centrioles at the center, but the function of the centrioles is somewhat undefined.

Assembly of the spindle microtubules starts in the centrosome. The centrosome (microtubule-organizing

center) of animals has a pair of centrioles at the center, but the function of the centrioles is somewhat undefined.

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

As mitosis starts, the two centrosomes are located near the nucleus.

As the spindle fibers grow from them, the centrioles are pushed apart.

By the end of prometaphase they develop as the spindle poles at opposite ends of the cell.

As mitosis starts, the two centrosomes are located near the nucleus.

As the spindle fibers grow from them, the centrioles are pushed apart.

By the end of prometaphase they develop as the spindle poles at opposite ends of the cell.


Each sister chromatid has a kinetochore of proteins and chromosomal DNA at the centromere.

The kinetochores of the joined sister chromatids face in opposite directions.

During prometaphase, some spindle microtubules attach to thekinetochores.

Each sister chromatid has a kinetochore of proteins and chromosomal DNA at the centromere.

The kinetochores of the joined sister chromatids face in opposite directions.

During prometaphase, some spindle microtubules attach to thekinetochores.


When a chromosome’s kinetochore is “captured” by microtubules, the chromosome moves toward the pole from which those microtubules come.

When microtubules attach to the other pole, this movement stops and a tug-of-war ensues.

Eventually, the chromosome settles midway between the two poles of the cell, the metaphase plate.

Other microtubules from opposite poles interact as well, elongating the cell.

When a chromosome’s kinetochore is “captured” by microtubules, the chromosome moves toward the pole from which those microtubules come.

When microtubules attach to the other pole, this movement stops and a tug-of-war ensues.

Eventually, the chromosome settles midway between the two poles of the cell, the metaphase plate.

Other microtubules from opposite poles interact as well, elongating the cell.


One hypothesis for the movement of chromosomes in anaphase is that motor proteins at the kinetochore “walk” the attached chromosome along the microtubule toward the opposite pole. The excess microtubule sections

depolymerize.

One hypothesis for the movement of chromosomes in anaphase is that motor proteins at the kinetochore “walk” the attached chromosome along the microtubule toward the opposite pole. The excess microtubule sections

depolymerize.


Fig. 12.7a

Experiments support the hypothesis that spindle fibers shorten during anaphase from the end attached to the chromosome, not the centrosome.

Experiments support the hypothesis that spindle fibers shorten during anaphase from the end attached to the chromosome, not the centrosome.


Fig. 12.7b

Nonkinetichore microtubules are responsible for lengthening the cell along the axis defined by the poles. These microtubules interdigitate across the

metaphase plate. During anaphase motor proteins push

microtubules from opposite sides away from each other.

At the same time, the addition of new tubulin monomers extends their length.

Nonkinetichore microtubules are responsible for lengthening the cell along the axis defined by the poles. These microtubules interdigitate across the

metaphase plate. During anaphase motor proteins push

microtubules from opposite sides away from each other.

At the same time, the addition of new tubulin monomers extends their length.



Cytokinesis

In animal cells

Cytokinesis occurs by a process known as cleavage, forming a cleavage furrow

Cleavage furrow

Contractile ring of microfilaments

Daughter cells

100 µm


Cytokinesis

In plant cells, during cytokinesis

A cell plate forms

Daughter cells

1 µmVesiclesforming cell plate

Wall of patent cell Cell plateNew cell wall


Cell Cycle Control System

The sequential events of the cell cycle

Are directed by a distinct cell cycle control system, which is similar to a clock

Control system

G2 checkpoint

M checkpoint

G1 checkpoint

G1

S

G2M


Cell Cycle Control System

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

received

G1 checkpoint

G1G1

G0

(a) If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.

(b) If a cell does not receive a go-ahead signal at the G1checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.


Normal Cell Behavior

In density-dependent inhibition

Crowded cells stop dividing

Most animal cells exhibit anchorage dependence

In which they must be attached to a substratum to divide

Cells anchor to dish surface anddivide (anchorage dependence)

When cells have formed a complete single layer, they stop dividing (density-dependent inhibition)

If some cells are scraped away, the remaining cells divide to fill the gap and then stop

25 µm


Abnormal Cell Behavior

Cancer cells

Transformation is the process of a normal cell becoming cancerous

Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence

Why cells transform is often a mystery but most likely genes controlling the cell control system are involved

25 µm

Cancer cells. Cancer cells usually continue to divide well beyond a single layer, forming a clump of overlapping cells.


Cancerous Cells

Malignant tumors invade surrounding tissues and can metastasize

Exporting cancer cells to other parts of the body where they may form secondary tumors

Cancer cells invade neighboring tissue.

2 A small percentage of cancer cells may survive and establish a new tumor in another part of the body.

4Cancer cells spread through lymph and blood vessels to other parts of the body.

3A tumor grows from a single cancer cell.

1

Tumor

Glandulartissue

Cancer cell

Bloodvessel

Lymphvessel

MetastaticTumor

Thinking QuestionThinking Question

Many cancer drugs (chemotherapy) work by interfering with the production or proper function of microtubules. What specific effect would this have on cell division and why is this beneficial in the treatment of cancer? Common side effects of chemotherapy are hair loss and nausea. Why do you think this is the case?

Many cancer drugs (chemotherapy) work by interfering with the production or proper function of microtubules. What specific effect would this have on cell division and why is this beneficial in the treatment of cancer? Common side effects of chemotherapy are hair loss and nausea. Why do you think this is the case?

Key Points of Chapter 12Key Points of Chapter 12

Cell division results in two genetically identical daughter cells

The mitotic phase alternates with interphase in the cell cycle

The cell cycle is regulated by a molecular control system

Cell division results in two genetically identical daughter cells

The mitotic phase alternates with interphase in the cell cycle

The cell cycle is regulated by a molecular control system

chapter 12 the cell cycle lab 3 mitosis and meiosis

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