the cell cycle chapter 12 ap bio - cflsap.files.wordpress.com

Fig. 12-1

The Cell Cycle

Chapter 12 AP Bio

You should now be able to:

1. Describe the structural organization of the prokaryotic genome and

the eukaryotic genome

2. List the phases of the cell cycle; describe the sequence of events

during each phase

3. List the phases of mitosis and describe the events characteristic of

each phase

4. Draw or describe the mitotic spindle, including centrosomes,

kinetochore microtubules, nonkinetochore microtubules, and asters

5. Compare cytokinesis in animals and plants

6. Describe the process of binary fission in bacteria and explain how

eukaryotic mitosis may have evolved from binary fission

7. Explain how the abnormal cell division of cancerous cells escapes

normal cell cycle controls

8. Distinguish between benign, malignant, and metastatic tumorsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Overview: The Key Roles of Cell Division

• The ability of organisms to REPRODUCE best

distinguishes living things from nonliving

matter

• The continuity of life is based on the

reproduction of cells, or cell division

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Why do cells divide?

• In unicellular organisms, division of one cell

reproduces the entire organism

• Multicellular organisms depend on cell

division for:

– Development from a fertilized cell

– Growth

– Repair

• Cell division is an integral part of the cell

cycle, the life of a cell from formation to its

own division

▪As the cell grows, its volume increases much more

rapidly than the surface area.

▪ The cell might have difficulty supplying nutrients

and expelling enough waste products.

▪Diffusion over large distances is slow and

inefficient.

▪Substances move by diffusion or by motor

proteins.

▪Small cells maintain more efficient transport

systems.

Cellular Growth

Transport of Substances

Cellular Growth

Cellular Communications

▪ The need for signaling proteins to move

throughout the cell also limits cell size.

▪Cell size affects the ability of the cell to

communicate instructions for cellular functions.

▪Cell division prevents the cell from becoming too

large.

▪ It also is the way the cell reproduces so that you

grow and heal certain injuries.

▪Cells reproduce by a cycle of growing and dividing

called the cell cycle.

The Cell Cycle

Cellular Organization of the Genetic Material

• All the DNA in a cell constitutes the cell’s genome

• A genome can consist of a single DNA molecule

(common in prokaryotic cells) or a number of

DNA molecules (common in eukaryotic cells)

• DNA molecules in a cell are packaged into

chromosomes

Fig. 12-3

20 µm

• Eukaryotic

chromosomes

consist of

chromatin, a

complex of

DNA and

protein that

condenses

during cell

division

• Every eukaryotic species has a

characteristic number of chromosomes in

each cell nucleus – not related to the

complexity of the organism

• Somatic cells (nonreproductive cells) have

two sets of chromosomes - diploid (2N).

The members of the pair are called

homologous chromosomes.

• Gametes (reproductive cells: sperm and

eggs) have half - haploid (1N) as many

chromosomes as somatic cells. They only

have one member of each pair.

23 pairs of homologous chromosomes in humans

karyotype

in somatic cells

• In preparation for cell division, DNA is

replicated and the chromosomes

condense

• Each duplicated chromosome has two

sister chromatids (identical DNA), which

separate during cell division

• The centromere is the narrow “waist” of

the duplicated chromosome, where the

two chromatids are most closely attached

Fig. 12-40.5 µm Chromosomes

Chromosomeduplication(including DNAsynthesis)

Chromo-some arm

Centromere

Sisterchromatids

DNA molecules

Separation ofsister chromatids

Centromere

Sister chromatids

• Most cell division (mitosis) results in

daughter cells with identical genetic

information, DNA, and used for

growth, development, and repair

• A special type of division (meiosis)

produces nonidentical daughter cells

(gametes, or sperm and egg cells)

with half the number of chromosomes


• Eukaryotic cell division consists of:

– Mitosis, the division of the nucleus

– Cytokinesis, the division of the cytoplasm

▪ Interphase is the stage during which the cell

grows, carries out cellular functions, and

replicates.

▪ Mitosis is the stage of the cell cycle during which

the cell’s nucleus and nuclear material divide.

▪ Cytokinesis is the method by which a cell’s

cytoplasm divides, creating a new cell.


The Stages of Interphase

▪The first stage of interphase, G1

▪The cell is growing, carrying out

normal cell functions, and preparing to

replicate DNA.

Cellular Growth

The Second Stage of Interphase, S

▪The cell copies its DNA in

preparation for cell division.

The Third Stage of Interphase, G2

▪The cell prepares for the division of its nucleus.

• Interphase (about 90%

of the cell cycle) can be

divided into subphases:

– G1 phase (“first

gap”)

– S phase (“synthesis

of DNA”)

– G2 phase (“second

gap”)

• The cell grows during all

three phases, but

chromosomes are

duplicated only during

the S phase.

What is the Go stage?

• Cells that do not normally divide or for various

reasons, are not preparing to divide, enter a state

of arrest.

Ex: - nerve cells, muscle cells, rbc’s

- cells that are starved of nutrients, density-

inhibited, or treated with growth inhibitors

The Stages of Mitosis

• Mitosis is conventionally divided into five

phases:

– Prophase

– Prometaphase

– Metaphase

– Anaphase

– Telophase

• Cytokinesis (division of the cytoplasm) is

well underway by late telophase.

Fig. 12-UN1

Telophase andCytokinesis

Anaphase

Metaphase

Prometaphase

Prophase

MITOTIC (M) PHASE

Cytokinesis

Mitosis

SG1

G2

Prophase 1st step in Mitosis

• Mitosis begins (cell begins to divide)

• Centrioles (or poles) appear and begin to move to opposite end of the cell.

• Spindle fibers form between the poles.

•Centrioles•Sister

chromatids

•Spindle fibers

The mitotic spindle is an apparatus of microtubules that controls chromosome movement during mitosis

During prophase, assembly of spindle microtubules begins in the centrosome, the microtubule organizing center

The centrosome replicates, forming two centrosomes that migrate to opposite ends of the cell, as spindle microtubules grow out from them

An aster (a radial array of short microtubules) extends from each centrosome

• The spindle includes the centrosomes, the spindle microtubules, and the asters

Prophase•Animal Cell •Plant Cell

•Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

•Spindle fibers

•Centrioles

PROMETAPHASE AND METAPHASE

• During prometaphase, some

spindle microtubules attach to the

kinetochores of chromosomes and

begin to move the chromosomes

• At metaphase, the chromosomes

are all lined up at the metaphase

plate, the midway point between

the spindle’s two polesCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 12-7

Microtubules Chromosomes

Sisterchromatids

Aster

Metaphaseplate

Centrosome

Kineto-chores

Kinetochoremicrotubules

Overlappingnonkinetochoremicrotubules

Centrosome 1 µm

0.5 µm

Metaphase•Animal Cell •Plant Cell


ANAPHASE

• Sister chromatids separate and

move along the kinetochore

microtubules toward opposite

ends of the cell

• The microtubules shorten by

depolymerizing at their

kinetochore ends


Fig. 12-8a

Kinetochore

Spindlepole

Mark

EXPERIMENT

RESULTS

Notice

the shortening of

the spindle fibers

Anaphase•Animal Cell •Plant Cell


TELOPHASE

• In telophase, genetically identical daughter

nuclei form at opposite ends of the cell


http://www.molecularexpressions.com/cells/fluorescencemitosis/telophasesmall.html

Telophase

•Animal Cell •Plant Cell


Mitosis

CytokinesisCell plate:

In plant cells, a new cell wall made of cellulose forms between the 2 new nuclei

Cleavage furrow: In animals, a indentation begins from the outside, pinching inwards.

Cleavage furrow

Fig. 12-9a

100 µm

Daughter cells

(a) Cleavage of an animal cell (SEM)

Contractile ring ofmicrofilaments

Fig. 12-9b

Daughter cells

(b) Cell plate formation in a plant cell (TEM)

Vesiclesformingcell plate

Wall ofparent cell

New cell wallCell plate

1 µm

Fig. 12-UN2

•1 2 34 5 6 7

8

9

10

1112

1314

15

16

Fig. 12-UN5

Interphase

The mitotic phase alternates with interphase in the cell cycle

• In 1882, the German anatomist Walther

Flemming developed dyes to observe

chromosomes during mitosis and cytokinesis


What is the purpose of mitosis?

• To produce two genetically

identical cells – ie, have the same

number of chromosomes as the

original cell.

• Occurs in eukaryotic multicellular

somatic cells for growth,

development, and repair.

• In unicellular organisms, it is a

method of asexual reproduction.

Binary Fission

• Prokaryotes (bacteria and archaea)

reproduce by a type of cell division

called binary fission

• In binary fission, the chromosome

replicates (beginning at the origin of

replication), and the two daughter

chromosomes actively move apart

• No mitosis is involved


Fig. 12-11-4

Origin ofreplication

Two copiesof origin

E. coli cellBacterialchromosome

Plasmamembrane

Cell wall

Origin Origin

The Evolution of Mitosis

• Since prokaryotes evolved

before eukaryotes, mitosis

probably evolved from binary

fission

• Certain protists exhibit types of

cell division that seem

intermediate between binary

fission and mitosisCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The eukaryotic cell cycle is regulated by a molecular control system

• The frequency of cell division varies with the

type of cell

• These cell cycle differences result from

regulation at the molecular level

• The cell cycle appears to be driven by specific

chemical signals present in the cytoplasm

• Some evidence for this hypothesis comes from

experiments in which cultured mammalian

cells at different phases of the cell cycle were

fused to form a single cell with two nuclei

The 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

• 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

• For many cells, the G1 checkpoint seems

to be the most important one

• 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

The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases

• Two types of regulatory proteins are

involved in cell cycle control: cyclins and

cyclin-dependent kinases (Cdks)

• Cyclin + Cdk = MPF

• The activity of cyclins and Cdks fluctuates

during the cell cycle

• MPF (maturation-promoting factor) pushes

the cell past the G2 checkpoint into the M

phaseCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Stop and Go Signs: Internal and External Signals at the Checkpoints

• An example of an internal signal is that

kinetochores not attached to spindle microtubules

send a molecular signal that delays anaphase until

they all have attached; making sure that the cell

doesn’t divide until it has all its parts

• Some external signals are growth factors,

proteins released by certain cells that stimulate

other cells to divide

• For example, platelet-derived growth factor

(PDGF) stimulates the division of human fibroblast

cells in cultureCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Internal Signals

• An example of an internal signal is that

kinetochores not attached to spindle

microtubules send a molecular signal that

delays anaphase


External Signals:

• Growth Factors – example platelet

derived

growth factor PDGF

• Density-dependent inhibition, in which

crowded cells stop dividing

• Most animal cells also exhibit anchorage

dependence, in which they must be

attached to a substratum in order to

divideCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Loss of Cell Cycle Controls in Cancer Cells

Cancer cells exhibit neither

density-dependent inhibition nor

anchorage dependence

Cancer cells do not respond

normally to the body’s control

mechanisms

Cancer cells may not need

growth factors to grow and

divide:

They may make their own

growth factor

They may convey a growth

factor’s signal without the

presence of the growth

factor

They may have an abnormal

cell cycle control system


• A normal cell is converted to a cancerous

cell by a process called transformation

• Cancer cells form tumors, masses of

abnormal cells within otherwise normal

tissue

• If abnormal cells remain at the original site,

the lump is called a benign tumor

• Malignant tumors invade surrounding

tissues and can metastasize, exporting

cancer cells to other parts of the body,

where they may form secondary tumorsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

p53 genes and p27 genes in cancer

• p53 is a protein that functions to block the cell cycle if the DNA is damaged. If the damage is severe this protein can cause apoptosis (cell death).

• p53 levels are increased in damaged cells. This allows time to repair DNA by blocking the cell cycle.

• A p53 mutation is the most frequent mutation leading to cancer.

• p27 is a protein that binds to cyclin and cdkblocking entry into S phase. Recent research suggests that breast cancer prognosis is determined by p27 levels. Reduced levels of p27predict a poor outcome for breast cancer patients.

Fig. 12-20

Tumor

A tumor grows

from a single

cancer cell.

Glandulartissue

Lymphvessel

Bloodvessel

Metastatictumor

Cancercell

Cancer cells

invade neigh-

boring tissue.

Cancer cells spreadto other parts ofthe body.

Cancer cells maysurvive and

establish a new

tumor in another

part of the body.

1 2 3 4

Unfortunately, the majority of drugs currently

on the market are not specific, which leads to

the many common side effects associated with

cancer chemotherapy.

Since the drugs are not specific to recognize

normal cells from cancerous cells, the side

effects are seen in bodily systems that

naturally have a rapid turnover of cells

including skin, hair, gastrointestinal, and bone

marrow. These healthy, normal cells, also end

up damaged by the chemotherapy program.

Case Study: The Immortal Cells of Henrietta Lacks

•http://www.cbsnews.com/8301-

3445_162-6300824/the-immortal-

henrietta-lacks/

http://www.foxnews.com/opinion/2013/08/26/scientific-breakthroughs-vs-your-privacy-lessons-from-henrietta-lacks-saga/

http://www.cbsnews.com/8301-3445_162-6300824/the-immortal-henrietta-lacks/

• Part I: The HeLa Cells

• Part II: The Family

• Part III: Henrietta’s Cancer Cells

• Part IV: The Continuing Story:

Henrietta’s Genome

•http://www.cbsnews.com/8301-3445_162-

6300824/the-immortal-henrietta-lacks/

•http://www.foxnews.com/opinion/2013/08/26/scientific-

breakthroughs-vs-your-privacy-lessons-from-henrietta-

lacks-saga/

http://www.cbsnews.com/8301-3445_162-6300824/the-immortal-henrietta-lacks/

http://www.foxnews.com/opinion/2013/08/26/scientific-breakthroughs-vs-your-privacy-lessons-from-henrietta-lacks-saga/

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