chapter 10 cellular growth and division. cp bio ch. 10 cell division why are new cells needed? for...
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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