Chapter 10Cellular Growth and Division

CP BIO Ch. 10 Cell Division

Why are new cells needed?• For growth and repair

– Replace damaged or old cells– Regeneration – replace lost body part– Growth

• For asexual reproduction– Offspring are genetic copies of parent

Regeneration – replace lost body part

starfish can replace an arm flatworms can regrow a body

Lizards can replace a tail

Some organisms reproduce asexually• Offspring are genetic copies of the parent and of

each other

Prokaryotic cells divide by binary fission

One-celled protists also do fission, but

must do mitosis first to divide chromosomes

evenly

Col

oriz

ed T

EM

32

,500

Prokaryotic chromosomes

LM

34

0

– Sexual Reproduction – two parents• Genetic mix in offspring, each is different

p. 274

Some cells divide oftenBone marrow stem cells

Plants and simple organisms

Skin cells Digestive lining cells

embryo

Some divide rarely or not at all

Muscle cells Cartilage or tendon cells

Nerve cells

Eukaryotic nuclei contain many chromosomes

Each chromosome contains thousands of genes - must be organized before cell can dividing Both new cells need EACH gene/chromosome

• DNA is ALREADY COPIED (“replicated”) -coils, condenses

• forms tightly packed, dense “CHROMOSOMES”

• keeps copies organized and intact until cell splits

Chromatin (loose form of chromosome) packs and condenses before a cell can divide

DNA wraps around

histones

DNA

One chromosome (copied and packed

for cell division)

Groups of histones form nucleosomes

This coils and wraps until it all fitsinto the nucleus.

These group to form chromatin

Sister chromatidsidentical copies

Centromereholds chromatids

together

Double-stranded (replicated)

chromosome

SEM of human chromosomes

Prokaryotes have a single, circular chromosome, no histones; no nucleus

Mitotic Phase - cell divides - 2 new cells form

Figure 10.7

Interphase - normal cells - most of cell life - non-dividing cell

Cell Cycle - has two phases

INTERPHASE

S(DNA synthesis)

G1

G2

Cytokin

esis

Mito

sis

MITOTICPHASE (M)

G1 growth, normal life functions

S “synthesis” – DNA replicates

G2 final growth; prepares to divide

INTERPHASE

A) Mitosis – chromosomes condense, organize and divide

- each new cell gets one copy of every chromosome

B) Cytokinesis – cytoplasm divides

INTERPHASE

S(DNA synthesis)

G1

G2

Cytokin

esi

s

Mito

sis

MITOTICPHASE (M)

Mitotic Phase

DNA replicates during S of interphase

1. Molecule “unzips”

2. Free nucleotides match up

with open partner

3. A-T and C-G

4. Two identical molecules

PHASES OF MITOSIS

PROPHASE – cell organizes & prepares• Chromatin • nuclear membrane, nucleolus disappear• spindle and asters form• Centrioles move to poles of cell

METAPHASE – chromosomes in middle• Centromeres attached to spindle fibers

ANAPHASE -chromosomes copies separate• spindle fibers pull chromatids to

opposite poles of cell

TELOPHASE – return to normal• chromosomes relax/uncoil into chromatin

• nuclear membranes form; nucleoli appear• spindle fibers disappear

Animal cytokinesis

• Cell membranes pulls in

• Cytoplasm pinches in two

Cleavagefurrow

SE

M 1

40

Daughter cells

Cleavage furrow Contracting ring ofmicrofilaments

CYTOKINESIS – cytoplasm divides 2 identical daughter cells

TE

M 7

,500

Cell plateforming

Wall ofparent cell

Daughternucleus

Cell wall New cell wall

Vesicles containingcell wall material

Cell plateDaughter cells

Plant cell cytokinesis

- cell wall is rigid

- cell plate forms

- new cell wall grows

NO centrioles or asters

Plant cell mitosis

Same stages

NO CENTRIOLES OR ASTERS

Control of Cell Division

Chemical signals tell a cell when to divide

Normal rate: growth, repair

- asexual reproduction in some organisms

Slow rate: some cell types divide rarely (liver)

- aging slow healing, lose some cells

Rarely or not at all: nerve, muscle, cartilage

Fast rate: some cell types (skin, digestive lining)

- embryo, growth zones (bones, root tips)

Uncontrolled cancer

Growth factors & cyclins• Chemicals secreted by cells • Can start or stop cell

division

After forming asingle layer,cells havestopped dividing.

Providing anadditional supply ofgrowth factorsstimulatesfurther cell division.

Cell Growth and Healing

• Injury – damaged cells secrete growth factors

• Cells at edge of injury start dividing rapidly

• New cells that form heal the break

• As injury heals, cell division slows

Programmed Cell Deathapoptosis

Self-destruct if damaged too much to repair a) DNA damageb) Embryonic development – unneeded cells

DNA damageCells begin to divide abnormally

Continue dividing, invade healthy tissue (malignant)

Spread through blood or lymph stream, can start new tumors

(metastatic)

Cancer is uncontrolled cell division

Tumor

Glandulartissue

A tumor grows from asingle cancer cell.

Cancer cells invadeneighboring tissue.

Cancer cells spread throughlymph and blood vessels toother parts of the body.

Lymphvessels

Bloodvessel

Cancer cells do not respond to signals that regulate the cell cycle• If not treated early, cancer will spread• kills by destroying organ function

What causes cancer?

• Defects in Genes– Cells do not make or do not respond to

control signals• Age and Environmental Injury

– Age, smoking, pollution, asbestos, radiation• Genetic Tendency

– Some cancers run in families (colon, breast)

BE CAREFUL when sunning• Wear sunscreen, sunglasses• Avoid brightest part of the day• Don’t use tanning beds

The most common cancer - skin

Basal cell

Squamous Cell

Melanoma

Cancer treatmentRadiation – high-energy, carefully aimed at tumor

Chemotherapy – drugs specific for tumor types

• interfere with cell division

• some normal cells destroyed, too

– Skin (lose hair); digestive lining (nausea)

Surgery – remove tumor and nearby cells

Boost immune system – healthy diet, reduce stress

Stem cells and differentiation

Differentiate – cells specialize as embryo develops

Stem cell – unspecialized cell

- can differentiate to form many kinds of cells

- depends on chemical signals from nearby cells

Kinds of Stem CellsTotipotent

- can form an entire organism from one cell- fertilized egg embryo full organism

Pluripotent - specialize to form different kinds of cells- embryo cells all cells in an organism

Multipotent – can develop into most, but not all, cell types- adult stem cells many kinds of cells

Multipotent stem cells can form tissues

Ch. 11.4 Meiosis Cell Division for Sexual Reproduction

Sexual Reproduction - two parents

a. Offspring have NEW combination of genes

b. genetic mix of both parents

Advantage – genetic variation

a. Some may have traits that favor survival

b. Variation in individuals allows a species to evolve 

a. CONJUGATION

b. Recipient cell gets new genes

Sexual Reproduction in bacteria and protists

Complex organisms – make special cells

a. gametes – sperm and egg

b. Gametes combine in fertilization

- make a zygote new organism

Chromosome Number: Diploid and Haploid

Homologous chromosomes

a. matched chromosome pairs

b. one member of pair from each parent

c. carry genes for the same traitsd. 22 pairs autosomes; one pair sex chromosomes X, Y

Gene for one trait

Cells with paired chromosomes are diploid

a. Somatic (body) cells are diploid

b. 2n (n = number) Humans: 2n = 46

Fruit fly 2n = 8

2 sets of chromosomes

- 2 of every gene

Locus – location of gene on a

chromosome

one chromosome pair

Humans: 2n = 46

23 pairs of chromosomes

One set of 23 came from each parent

Chromosomes photographed during mitosis

Haploid cells have ONE set of chromosomes

(n) = ONE MEMBER from EACH homologous PAIR

human: n = 23 gametes - sperm or egg

Meiosis is “Reduction Division”

Reduces chromosome number

• from diploid to haploid

• Cell DIVIDES TWICE

Meiosis - two cell divisions

2n parent cell

DNA replicates in interphase

First division – pairs separate

Second division – sister chromatids separate

4 haploid daughter cells

Homologous pairs separate in MEIOSIS

TWO cell divisions

- Daughter cells have ½ parent

chromosome number

Diploid cell - Has pairs

(2n=2)

Haploid cells - (n = 1)

Meiosis I - Pairs separate

(n = 1)

Meiosis II - copies separate

(n = 1)

Crossing over – only in meiosis

a. during Prophase I

b. Homologous chromatids trade pieces

c. Increases genetic variation

Meiosis I

Anaphase I

Metaphase IInterphase

Prophase I

Telophase I

Cytokinesis

Meiosis II

Prophase II

Metaphase II

Anaphase II

Telophase II

Haploid (n) cellsDoubled chromosomes

Haploid cellsSingle chromosomes

Compare mitosis and meiosis

Making sperm and egg

Sperm:2n parent cell 4 haploid sperm

Ovum:2n parent cell 1 haploid egg+ haploid polar bodies

Ovum needs all the cytoplasm

Ovum and polar body Sperm needs only nucleus(DNA)

- flagellum

- mitochondria for energy

Causes of genetic variation

1. Homologous pairs have different genes

• same traits, but may be different forms

2. Crossing over – homologs trade pieces before

separating new gene combinations

3. Pairs position in Metaphase I - independent

• n pairs 2n possible combinations

4. Random fertilization of eggs by sperm

• Any egg or sperm is equally likely to be used

5. Gene or chromosome mutation

- Error in replication or cell division

Many different gene combinations in haploid gametes

Combination 1 Combination 2 Combination 3 Combination 4

Gametes

Metaphase II

Two equally probablearrangements of chromosomes at

metaphase I

Possibility 1 Possibility 2

Figure 8.16

Chromosomes line up randomly in meiosis

When meiosis goes wrong

Nondisjunction

- do not separate correctly

In mitosis defective nucleus, cell usually dies

In meiosis defective gamete

wrong number of chromosomes in zygote

Accidents during meiosis wrong chromosome number

Nondisjunction in meiosis I

Normal meiosis II

Gametes

n + 1 n + 1 n 1 n 1

Number of chromosomes

Nondisjunction in meiosis II

Normal meiosis I

Gametes

n + 1 n -1 n n

Number of chromosomes

Nondisjunction in meiosis I Nondisjunction in meiosis II All gametes abnormal Some gametes normal

If cell is fertilized after nondisjunction trisomy in zygote

Sperm cell

Egg cell

n (normal)

n + 1

Zygote2n + 1

Trisomy = 3

Wrong chromosome number in zygote wrong number in every cell in organism

KARYOTYPE picture of a person’s chromosomes

Photographed during mitosis

- sorted into homologous pairs

- largest-to-smallest

- sex chromosomes last

Abnormalities visible:

- missing or extra

- pieces broken or moved

- pieces added or lostautosomes sex chrom.

Trisomy 21

Normal male karyotype

Normal female karyotype

Down SyndromeTrisomy chromosome # 21

Turner Syndrome XO

Figure 8.22B

Characteristic facialfeatures

Web of skin

Constrictionof aorta

Poor breastdevelopment

Under developedovaries

Klinefelter Syndrome XXY

Other chromosomes mutations