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Ch. 2.2 and 3.2. Cell Division and Death. Cell Division & Death. Normal growth and development require an intricate interplay between the rates of two processes Mitosis – Cell division - Produces two somatic cells from one Apoptosis – Cell death

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ch 2 2 and 3 2

Ch. 2.2 and 3.2

Cell Division and Death

cell division death
Cell Division & Death
  • Normal growth and development require an intricate interplay between the rates of two processes
  • Mitosis – Cell division

- Produces two somatic cells from one

  • Apoptosis – Cell death

- Precise genetically-programmed sequence. EX: Webbing between fingers and toes. Frog Tails.

cell division
Cell Division
  • SOMATIC CELLS (body cells) are made by the process of mitosis.
  • SEX CELLS (gametes) are made by the process of meiosis.
the cell cycle
The Cell Cycle
  • Broken into two basic time frames: INTERPHASE (not dividing) and MITOSIS (dividing).

Figure 2.14

overview stages of the cell cycle
Overview: Stages of the Cell Cycle
  • Interphase

- Prepares for cell division

- Replicates DNA and subcellularstructures

- Composed of G1, S, and G2

- Cells may exit the cell cycle at G1 or enter G0, a quiescent phase

  • Mitosis – Division of the nucleus
  • Cytokinesis– Division of the cytoplasm
interphase
INTERPHASE
  • GAP PHASE I:
    • Cells normal functioning occurs during G1. The cell resumes synthesis (production) of proteins, lipids, and carbohydrates.
    • This phase varies drastically among different cell types. EX: Slowly dividing cells (liver cells) may remain in G1 for years. Quickly dividing cells like the bone marrow spend as little as 16 to 24 hours in G1.
synthesis phase
SYNTHESIS PHASE:
  • -This phase includes the REPLICATION of the entire GENOME (DNA) and assembly of proteins, lipids, etc. needed for replication.
  • This phase takes 8-10 hours in most human cells.
  • Proteins that will from the spindle structure are made.
replication of chromosomes
Replication of Chromosomes
  • Process of duplicating a chromosome
  • Occurs prior to division, during S of interphase
  • Produces sister chromatids
  • Held together at centromere

Figure 2.14

gap phase ii
GAP PHASE II:
  • -The final preparation for the CELL DIVISION.
  • - Membranes that were formed in G1 are assembled and stored as empty vesicles beneath the cell membrane. These will be used to enclose both daughter cells.
  • Some specialized cells go from G1 to G0. They never go through the synthesis or G2 phases. These cells cannot divide, but they can maintain cellular functions.
slide15
MITOSIS, the process of CELL DIVISION that produces 2 identical DAUGHTER CELLS from one, occurs in most cells of the body, or SOMATIC CELLS.
  • -Each DAUGHTER CELL receives the full set of 23 CHROMOSOME PAIRS, just like the PARENT.
  • MITOSIS begins with the replicated DNA condensed into CHROMOSOME form, with two identical CHROMATIDS attached at a CENTROMERE.
prophase
Prophase
  • In PROPHASE (1st phase)
  • Replicated chromosomes condense
  • Microtubules organize into a spindle (centrioles)
  • Nuclear membrane breaks down
metaphase
Metaphase
  • In METAPHASE the SPINDLE FIBERS attach to the CHROMOSOMES at the CENTROMERES and pull them to the cell equator (middle = metaphase plate).
anaphase
Anaphase

In ANAPHASE

  • Centromeres divide
  • Chromosomes (chromatids) move to opposite ends of the cell
telophase cytokinesis
Telophase & Cytokinesis
  • In TELOPHASE, the SPINDLES fall apart, the NUCLEOLUS and NUCLEAR MEMBRANES re-form, and
  • CYTOKINESIS distributes macromolecules and ORGANELLES between the two DAUGHTER CELLS.
slide23

If mitosis happens to little, then an injury will go unrepaired, if it happens to often, then an abnormal growth will form.

  • There are many CHECKPOINTS that control the CELL CYCLE.
  • Mammalian cells will only divide about 40 – 60 times. A sort of internal “clock” controls the number of divisions.
cell cycle control
Cell Cycle Control

Proteins called “checkpoint proteins” monitor

progression through the cell cycle.

Figure 2.16

telomeres
TELOMERES
  • Located at the ends of the

chromosomes

  • Contain hundreds to

thousands of six nucleotide

repeats

  • Most cells lose 50-200

repeats after each cell division

  • After about 50 divisions,

shortened telomeres signal

the cell to stop dividing

  • Sperm, eggs, bone marrow, and cancer cells produce an enzyme that prevents shortening of telomere
  • CROWDING limits mitosis.
slide26
HORMONES and GROWTH FACTORS can also influence MITOTIC RATES.
  • CELL DEATH (APOPTOSIS) is as important to body growth and DEVELOPMENT as is MITOSIS.
  • -When “DEATH RECEPTORS” receive signals to die, enzymes are activated to snip apart cell components in a stepwise cycle.
  • -PHAGOCYTES gobble up the remains when called in.
  • -If APOPTOSIS is too infrequent, a CANCER may grow out-of-control.
sexual reproduction
Sexual Reproduction
  • Why sexual reproduction?
    • shuffles alleles; new combinations
    • provides genetic variation in species
gametes
Gametes
  • Form from cell division of germline cells
  • Meiosis is cell division to produce gametes
  • Meiosis has two divisions of the nucleus (Meiosis I and Meiosis II) and produces cells with half the number of chromosomes (haploid)
  • Whereas SOMATIC CELLS are DIPLOID (containing a double-set of genetic information), the GAMETES are HAPLOID (containing only one copy)
meiosis

from mother

from father

child

too

much!

Meiosis
  • Reduces the genetic material by half
  • Why is this necessary?

meiosis reduces genetic content

homologous chromosomes
Homologous Chromosomes
  • Matched Pair of Chromosomes = Carry the same genes
  • Pair during Meiosis I
  • Separate in the formation of gametes
  • One copy of each pair is from the mother and one is from the father.

Figure 1.2

homologous chromosomes1

eye color

locus

eye color

locus

hair color

locus

hair color

locus

Paternal(fromDad)

Maternal(from Mom)

Homologous Chromosomes
sexual reproduction1
Sexual Reproduction
  • Meiosis and sexual

reproduction increases

genetic diversity in a

population

  • Variation is important

in a changing environment

  • Evolution is the genetic change in a population over time
meiosis cell division in two parts

Meiosis I

(reduction

division)

Meiosis II

(equational

division)

Diploid

Haploid

Haploid

Meiosis: Cell Division in Two Parts

Result: one copy of each chromosome in a gamete.

meiosis1
Meiosis

Interphase precedes meiosis I

Meiosis I

Prophase I

Metaphase I

Anaphase I

Telophase I

Meiosis II

Prophase II

Metaphase II

Anaphase II

Telophase II

meiosis i the reduction division

Spindle

fibers

Nucleus

Nuclear

envelope

Prophase I

(early)

(diploid)

Prophase I

(late)

(diploid)

Metaphase I

(diploid)

Anaphase I

(diploid)

Telophase I

(diploid)

Meiosis I : the reduction division
slide38
In PROPHASE I, HOMOLOGOUS CHROMOSOME PAIRS line up gene-by-gene in SYNAPSIS (Pairing of homologous chromosomes) and sometimes CROSSING-OVER occurs.
  • -Each HOMOLOGOUS CHROMOSOME PAIR contains four CHROMATIDS
recombination crossing over

A

A

a

a

B

B

b

b

C

C

c

c

D

D

d

d

E

E

e

e

F

F

f

f

Recombination (crossing over)
  • Occurs in prophase of meiosis I
  • Homologous chromosomes exchange genes
  • Generates diversity

Figure 3.5

recombination crossing over1
Recombination (crossing over)

A

a

a

  • Exchange between homologs
  • Occurs in prophase I

A

B

b

b

B

c

C

C

c

D

D

d

d

E

E

e

e

F

F

f

f

Figure 3.5

Letters denote genes and case denotes alleles

recombination crossing over2
Recombination (crossing over)

a

A

a

A

B

b

B

b

c

c

C

C

  • Creates chromosomes with new combinations of alleles for genes A to F

D

D

d

d

E

E

e

e

F

F

f

f

Figure 3.5

prophase i synapsis

sister chromatids

sister chromatids

Tetrad

Prophase I - Synapsis

Nonsister chromatids

crossing over provides variation

Tetrad

nonsister chromatids

Chiasma: site of crossing over

Crossing Over - Provides Variation

variation

slide44
In METAPHASE I, the HOMOLOGUES line up in one of 8,388,608 ways and undergo INDEPENDENT ASSORTMENT as HOMOLOGUES are separated in ANAPHASE I.
independent assortment
Independent Assortment

The homolog of one chromosome can be inherited

with either homolog of a second chromosome.

Figure 3.6

meiosis ii the equational division

Prophase II

(haploid)

Metaphase II

(haploid)

Anaphase II

(haploid)

Telophase II

(haploid)

Four

nonidentical

haploid

daughter cells

Meiosis II : the Equational division

Figure 3.4

slide48

In METAPHASE II, the CHROMOSOMES line up once again, and in ANAPHASE II, the SISTER CHROMATIDS separate.

slide49

TELOPHASE II brings the new NUCLEAR ENVELOPES in, resulting in four HAPLOID CELLS, each carrying a new combination of the GENOME.

results of meiosis
Results of Meiosis
  • Gametes
  • Four haploid cells
  • Contain one copy of each chromosome and one allele of each gene
  • Each cell is unique

Figure 3.4

consequences of meiotic mistakes
Consequences of Meiotic Mistakes
  • Nondisjunctions occur when homologous chromosomes fail to separate at meiosis I or when chromatids fail to separate at meiosis II. 
  • Fertilization can result in embryos that are 2n + 1 (a "trisomy") or 2n – 1. 
  • Abnormal copy numbers of one or more chromosomes is usually, but not always, fatal (Example: Down syndrome)
  • Lethal most of the time
slide53

Downs Syndrome

  • Trisomy 21
  • 47, XY, +21
  • The only trisomysurvivable toadulthood
slide61

Sperm

surrounding an egg

slide62

This shows how only one single sperm gets to penetrate the egg, releasing its nucleus of 23 chromosomes to merge with the nucleus of the egg and its 23 chromosomes.

gamete formation in animals
Gamete Formation in Animals
  • Diff. bet. male and female gametes.

Male: spermatogenesis

    • all 4 develop into sperm cells.

Female: oogenesis

    • cytokinesis is uneven.
    • most cytoplasm goes to 1 of the 4 “eggs”(forms 1 large egg cell)
    • 3 other cells are small “polar bodies” which die
  • A discontinuous process
    • At birth, oocytes are arrested in prophase I
    • At ovulation, an oocyte continues to metaphase II
maturation and aging
Maturation and Aging
  • Genes may impact health throughout life
  • Single gene disorders are expressed early in life and tend to be recessive
  • Adult onset single gene traits are often dominant
  • Interaction between genes and environmental factors
    • Example: malnutrition before birth
    • coronary artery disease , stroke, hypertension , type 2 diabetes
aging
Aging
  • Segmental progeroid syndromes-accelerated aging
  • Increases the rate of aging associated changes
  • Inheritance of longevity –chromosome 4
homologous chromosomes2
Homologous Chromosomes
  • Pair of chrom. similar in shape , size, and types of genes.
    • Each locus (location of the gene) in same position on chrom.
  • Humans have 23 pairs of homologues
    • Housefly – 6 prs
    • Chicken – 39 prs
    • Apple – 17 prs
    • Dog – 39 prs
    • Cat – 19 prs

This is a karyotype

(an image of an organism’s

chromosomes)

This is a karyotype of a

normal human male

slide74

Some sex chromosome trisomies are as follows: XXY, XXX, XYY – but there cannot be a YYY because there MUST be at least one X chromosome present!!

  • The only sex chromosome monosomy that could produce a viable offspring is just “X” (there can never be just a “Y”)
slide77
XXX
  • Triple X Syndrome
  • Basically the same as a normal “XX”
  • Usually inherited from the mother
  • Not diagnosed until later in life
x turner syndrome
X – Turner Syndrome
  • Short stature
  • Lymphoedema (swelling) of the hands and feet
  • Broad chest (shield chest) and widely-spaced nipples
  • Low hairline
  • Low-set ears
  • Reproductive sterility
  • Amenorrhea, or the absence of a menstrual period
  • Increased weight, obesity
  • Other symptoms may include a small lower jaw (micrognathia), cubitus valgus (turned-out elbows), a webbed neck, soft upturned nails, Simian crease and drooping eyelids. Less common are pigmented moles, hearing loss, and a high-arch palate (narrow maxilla).
chromosome numbers
Chromosome numbers:
  • However many “types” of chrom. an organism has, that number is the “n” number of chrom. it has.
mitosis vs meiosis
Mitosis vs Meiosis
  • Mitosis
    • Body (somatic cells)
    • 2 daughter cells made(identical)
    • Each w/ same # & kind of chrom. as parent cell
    • 1 division process
    • 1 cytokinesis
    • No synapsis or crossing over
    • Are diploid (2n)
  • Meiosis
    • Germ cells of gonads
    • 4 gamete cells made(all different)
    • Each w/ ½ chrom. # as parent cell
    • 2 divisions
    • 2 cytokineses events
    • Synapsis & crossing over occurs in Prophase 1
    • Are haploid (n)
2 4 stem cells
2.4) STEM CELLS
  • When SPERM meets OVUM in FERTILIZATION, one of 70 trillion combinations can be created in a TOTIPOTENT STEM CELL called a ZYGOTE.
  • -It can become an entire baby if implanted in a mother.
  • -The idea of using these TOTIPOTENT CELLS upsets many.
slide86

Rapid CELL DIVISION (called CLEAVAGE) forms a “MULBERRY” which eventually grows into a BLASTOCYST, with an INNER CELL MASS

  • The INNER CELL MASS alone cannot survive if implanted
slide87

-The CELL MASS is only PLURIPOTENT: It can only form the “many parts” of the human body.

  • -The INNER CELL MASS will DIFFERENTIATE (genes turn on and off) into one of three PRIMARY CELL LINES
slide88

The future of these STEM CELL LINES will become even more limited as cells DIFFERENTIATE further.

  • -BLOOD STEM CELLS can only become red blood cells, WBCs, or platelets.
  • -SKIN STEM CELLS can become the various parts of skin.
slide89

These and other MULTIPOTENT STEM CELLS still have multiple possible futures. These are the “Sixty-Four STEM CELL LINES” that were approved by George W. Bush for research.

  • Some tissues contain ADULT STEM CELLS that can be used for various purposes.