CHAPTER 9

MITOSIS (CELL DIVISION) AND CELL CYCLE

ACTIVATOR—KWL CHART MITOSISWhat do you know about mitosis?

What do you want to know about mitosis?

What did I learn today about mitosis?

ACTIVATORName the stages of mitosis in order.

IMPACTS, ISSUES: HENRIETTA’S IMMORTAL CELLS Cancer cells isolated from Henrietta Lacks

established a self-perpetuating lineage of cancer cells

The cell lineage, name HeLa cells, is used in research laboratories across the world

Henrietta Lacks’ contribution is used to research cancer, viral growth, protein synthesis, effects of radiation, and more

Fig. 9-2, p.141

Henrietta’s Immortal Cells

UNDERSTANDING CELL DIVISION “Omnis cellula e cellula”---ALL cells from cells

What instructions are necessary for inheritance?

How are those instructions duplicated for distribution into daughter cells?

By what mechanisms are instructions parceled out to daughter cells?

REPRODUCTION Parents produce a new generation of cells or

multicelled individuals like themselves Parents must provide daughter cells with

hereditary instructions, encoded in DNA, and enough metabolic machinery to start up their own operation

DIVISION MECHANISMS

Eukaryotic organisms Mitosis(nuclear division) & cytokinesis

(cytoplasm division) Meiosis—ch 10

Prokaryotic organisms Prokaryotic fission—replicates only a small,

single, circular chromosome

HUMAN LIFE CYCLE

BOZEMAN VIDEO--MITOSIShttp://www.youtube.com/watch?v=1cVZBV9tD-A

ROLES OF MITOSIS Multicelled organisms

Growth Cell replacement

Some protistans, fungi, plants, animals Asexual reproduction

CELL DIVISION Individual cells of a human embryo divide,

developing from a paddlelike structure into a hand

Fig. 9-10, p.149

Cell Division

CHROMOSOME A DNA molecule & attached proteins Duplicated in preparation for mitosis

one chromosome (unduplicated)

one chromosome (duplicated)

a One chromosome (unduplicated)

b One chromosome (duplicated)

one chromatid two sister chromatidsone chromatid

Fig. 9-3a, p.142

Stepped Art

Chromosome

STRUCTURE OF CHROMOSOME PAIR

Sister chromatids Centromere locus

ORGANIZATION OF CHROMOSOMES

DNA and proteinsarranged as cylindrical fiber

DNA

histoneone nucleosome

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

THE CELL CYCLE—ALTERNATES BETWEEN M (MITOSIS) PHASE AND INTERPHASE

G1S

G2Mitosistelophaseanaphasemetaphaseprophase

interphase

Figure 9.5Page 144

INTERPHASE Usually longest part of the cycle Nondividing phase Cell increases in mass (grows & PREPARES

for division) Number of cytoplasmic components doubles DNA is duplicated

G1—1st growth phase S– synthesis (DNA replicates) G2– 2nd growth phase; considered by some to

be the first phase of mitosis

MITOSIS Period of nuclear division Usually followed by cytoplasmic

division(cytokinesis) Four stages:

ProphaseMetaphaseAnaphaseTelophase

CONTROL OF THE CYCLE Once S begins, the cycle automatically runs

through G2 and mitosis The cycle has a built-in molecular brake in G1 Cancer involves a loss of control over the

cycle, malfunction of the “brakes”

STOPPING THE CYCLE Some cells normally stop in interphase

Neurons in human brainArrested cells do not divide

Adverse conditions can stop cycleNutrient-deprived amoebas get stuck in

interphase

THE SPINDLE APPARATUS Consists of two distinct sets of microtubules

Each set extends from one of the cell poles Two sets overlap at spindle equator

Moves chromosomes during mitosis

SPINDLE APPARATUS

one spindle pole

one of the condensed chromosomes

spindle equatormicrotubules organized as a spindle apparatus

one spindle pole

MAINTAINING CHROMOSOME NUMBER

mitosis, cytoplasmic divisionchromosome (unduplicated) in daughter cell at interphase

chromosome (unduplicated) in daughter cell at interphase

chromosome (unduplicated) in cell at interphase

same chromosome (duplicated) in interphase prior to mitosis

Fig. 9-6a, p.145

1 2 3 4 5

6 7 8 9 10 11 12

13 14 15 16 17 18

19 20 21 22 XX (or XY)

MAINTAINING CHROMOSOM

E NUMBER

a Two of the chromosomes(unduplicated) in a parent cell at interphase

b The same two hromosomes, nowduplicated, in thatcell at interphase, prior to mitosisc

c Two chromosomes(unduplicated) in the parent cell’s daughtercells, which both startlife in interphase

Fig. 9-6b, p.145

Maintaining Chromosome Number

microtubule ofbipolar spindle

p.145

pole

pole

Maintaining Chromosom

e Number

STAGES OF MITOSIS

Prophase

Metaphase

Anaphase

Telophase

EARLY PROPHASE - MITOSIS BEGINSDuplicated chromosomes begin to condense and

become observable under a microscope; mitotic spindle

forms

Figure 9.7 Page 146

LATE PROPHASE—AKA PROMETAPHASE New microtubules are

assembled One centriole pair is

moved toward opposite pole of spindle

Nuclear envelope starts to break up

Figure 9.7 Page 146

TRANSITION TO METAPHASE

Spindle formsSpindle

microtubules become attached to the two sister chromatids of each chromosome

Figure 9.7 Page 146

METAPHASE All chromosomes are

lined up at the spindle equator

Chromosomes are maximally condensed

Figure 9.7 Page 147

ANAPHASE Characterized by

MOVEMENT! Sister chromatids of

each chromosome are pulled apart thus elongating the cell

Once separated, each chromatid is a chromosome

Kinetechore vs. nonkinetechore microtubles

Figure 9.7 Page 147

TELOPHASE Chromosomes loosen and

become less distinct Two nuclear membranes form,

one around each set of unduplicated chromosomes

Cytokinesis starts to produce 2 identical daughter cells

Plasmodia—when some slime molds have NO cytokinesis resulting in mulitnucleated masses

Figure 9.7 Page 147

RESULTS OF MITOSIS Two daughter nuclei Each with same

chromosome number as parent cell

Chromosomes in unduplicated form

Figure 9.7 Page 147

Mitosispair of

centrioles

nuclearenvelop

chromosomes

b EARLY PROPHASE c LATE PROPHASE d TRANSITION TO METAPASE

Mitosis begins. The DNA and its associated proteins have started to condense. The two chromosomes color-coded purple were inherited from the female parent. The other two (blue) are their counterparts., inherited from the male parent.

Chromosomes continue to condense. New microtubules become assembled. They move one of the two pairs of centrioles to the opposite end of the cell. The nuclear envelope starts to break up.

Now microtubules penentrate the nuclear region. Collectively, they form a bipolar spindle apparatus. Many of the spindle microtubules become attatched to the two sister chromatids of each chromosome.

a Cell at InterphaseThe cell

duplicates its DNA, prepares

for nuclear division

Fig. 9-7a, p.146

e METAPHASE f ANAPHASE g TELOPHASE h INTERPHASEAll chromosomes have become lined up at the spindle equator. At this stage of mitosis (and of the cell cycle), they are most tightly condensed

Attachments between the two sister chromatids of each chromosome break. The two are separate chromosomes, which microtubules move to opposite spindle pores.

There are two clusters of chromosomes, which decondense. Patches of new membrane fuse to form a new nuclear envelope. Mitosis is completed.

Now there are two daughter cells. Each is diploid; its nucleus has two of each type of chromosome, just like the parent cell.

microtubule

Fig. 9-7b, p.146

ANIMAL CELL DIVISION—CLEAVAGE FURROW FORMS AT OLD METAPHASE PLATE BY WAY OF AN ACTIN CONTRACTILE RING

1 Mitosis is over, and the spindle is now disassembling.

2 At the former spindle equator, a ring of micro-filaments attached to the plasma membrane contracts.

3 As its diameter shrinks, it pulls the cell surface inward.

4 Contractions continue; the cell is pinched in two.

Fig. 9-8a, p.148

Animal Cell Division—

cell plane forming

1 As mitosis ends, vesicles cluster at the spindle equator. They contain materials for anew primary cell wall.

2 Vesicle membranes fuse. The wall material is sandwiched between two new membranes that lengthen along the plane of a newly forming cell plate.

3 Cellulose is deposited inside the sandwich. In time, these deposits will form two cell walls. Others will form the middle lamella between the walls and cement them together.

4 A cell plate grows at its margins until it fuses with the parent cell plasma membrane. The primary wall of growing plant cells is still thin. New material—cellulose- is deposited on it.

Fig. 9-8b, p.148

Cell Plate Formation

MITOTIC CONTROL

Growth factors—such as needed nutrients

Density-dependent inhibition—overcrowding=less growth

Checkpoint(restriction point)—Ex: cells have a checkpoint in G1 where cell can either go on with cycle or go into G 0 (this is where mature muscle and nerve cells are)

CONTINUED MITOTIC CONTROL CYCLIN-DEPENDENT KINASES-AKA Cdks enzymes(proteins) which are affected by the

cell cycle regulatory protein cyclin; when these enzymes are active & attached to cyclin, then mitosis can happen)

Ex: MPF (maturation promoting factor)

CELL CYCLE & RELATIVE CYCLIN CONCENTRATION

TUMORS Sometimes a checkpoint gene mutates and

control over cell division is lost.

Cells uncontrollable division forms an abnormal mass called a tumor.

Neoplasms

Fig. 9-12, p.150

Cancer

MALIGNANT VS. BENIGN (SEE P. 151)

Fig. 9-15, p.153

cell at interphase

nucleuscytoplasm

telophase

prophase

anaphase

metaphase