Download In Plant Cells

Limits of Cell Growth:
The larger the cell, the
more difficult it is
for materials to enter
and leave it.
Rates of Cell Growth:
E. coli can double its volume in = 30 minutes.
In one day, a single cell would grow into a 14 kg mass of
bacteria. In 3 days = mass of the earth
Controls on Cell Growth: cells of the heart and
nervous system rarely grow. Cells of the skin and
digestive tract grow and divide rapidly throughout
Life; old, worn out, and damaged cells. Cells will
grow until they come into contact with each other.
Uncontrolled Cell Growth:
Cancer cells grow out of control
until they have used up all of their nutrients
Chromosomes: Made up of chromatin
(DNA and protein)
Total length of DNA is = 10,000 x length of
the chromosome.
In 1973, Don and Ada Olins and Christopher
Woodcock discovered the chromosome’s
DNA was coiled around special proteins
called histones.
DNA and histone molecules form beadlike
structures called nucleosomes.
Nucleosomes form a thick fiber, shortened
by a system of loops and coils.

Composed of 2 sister chromatids and a
centromere.
A form of asexual reproduction and cell
division
 Used by all prokaryotes and some
protozoa
 The cell divides into two parts that each
have the potential to grow to the size of
the original cell.

Skin cancer - the abnormal growth of
skin cells - most often develops on skin
exposed to the sun.
Cell that reproduce by asexual
reproduction reproduce constantly.

The cell cycle is a series of events that
occur in a cell to allow it to replicate,
divide, and reproduce.
Animated Mitosis Cycle
http://www.cellsalive.com/mitosis.htm
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase & Cytokinesis
Chromosomes are copied (# doubles)
• Chromosomes appear as threadlike coils
(chromatin) at the start, but each chromosome
and its copy(sister chromosome) change to sister
chromatids at end of this phase
•
Nucleus
CELL
MEMBRANE
Cytoplasm
•
•
•
•
•
Consists of G1, S, and G2
Cells do not move through the cycle at the
same rate
G1 (Gap 1) – cell grows and develops;
increase in supply of proteins, and synthesis of
some organelles
S (Synthesis) – DNA replication occurs
G2 (Gap 2) – Synthesis of more organelles and
the cell prepares for mitosis
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Division of the
nucleus
 Occurs in somatic
or body cells
 Can last from a
few minutes to
several days

•
•
•
•
•
Mitosis begins (cell begins to divide)
Chromosomes become visible as they shorten and
thicken
Centrioles (or poles) appear and begin to move to
opposite end of the cell.
Nucleolus and Nuclear envelope disintegrate.
Spindle fibers form between the poles.
Centrioles
Sister chromatids
Spindle fibers
Animal Cell
Plant Cell
Spindle fibers
Centrioles
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Chromatids (or pairs of chromosomes) attach to the
spindle fibers and line up along the equator or middle of
the cell.
• Centrioles have reached the opposite poles.
• Centromere of each chromosome is attached to a
spindle fiber.
•
Centrioles
Spindle fibers
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
•
Centromeres split.
Chromatids (or pairs of chromosomes)
separate and begin to move to opposite
ends of the cell and are now individual
chromosomes.
Centrioles
Spindle fibers
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
•
•
•
•
Two new nuclei form.
Chromosomes reach opposite poles and appear as
chromatin (less distinct).
Nuclear membrane begins to reform around
chromosomes.
Nucleolus reappears.
Mitosis ends.
Nuclei
Chromatin
Nuclei
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
Cell membrane moves inward to create two
daughtercells – each with its own nucleus with
identical chromosomes.



In Animal Cells:
Microfilaments
constrict (or pinch)
the cytoplasm
allowing cytokinesis
to occur
A cleavage furrow
forms allowing the
cell to become two
new cells


In Plant Cells:
A cell plate forms
between two
daughter nuclei and
then cell walls form
on either side of the
cell plate.
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
28
http://www.cellsalive.com/mitosis.htm
Meiosis
Organisms that reproduce Sexually are made
up of two different types of cells.
1. Somatic Cells are “body” cells and contain the normal
number of chromosomes ….called the “Diploid”
number (the symbol is 2n). Examples would be … skin
cells, brain cells, etc.
2. Gametes are the “sex” cells and contain only ½ the
normal number of chromosomes…. called the
“Haploid” number (the symbol is n)….. Sperm cells and
ova are gametes.
n = number of chromosomes in the set… so….2n means 2
chromosomes in the set…. Polyploid cells have more than two
chromosomes per set… example: 3n (3 chromosomes per set)
Gametes
• The Male Gamete is the Sperm and is produced
in the male gonad the Testes.
• The Female Gamete is the Ovum (ova = pl.) and is
produced in the female gonad the Ovaries.
During Ovulation the ovum is released
from the ovary and transported to an area
where fertilization, the joining of the
sperm and ovum, can occur……
fertilization, in Humans, occurs in the
Fallopian tube. Fertilization results in the
formation of the Zygote. (fertilized egg)
Sperm + Ovum (egg)
fertilization
Zygote
Fertilization
• The fusion of a sperm and egg to form a zygote.
• A zygote is a fertilized egg
n=23
egg
sperm
n=23
2n=46
zygote
Chromosomes
• If an organism has the Diploid number (2n) it has two
matching homologues per set. One of the homologues
comes from the mother (and has the mother’s DNA).…
the other homologue comes from the father (and has the
father’s DNA).
• Most organisms are diploid. Humans have 23 sets of
chromosomes… therefore humans have 46 total
chromosomes….. The diploid number for humans is 46
(46 chromosomes per cell).
Homologous Chromosomes
• Pair of chromosomes (maternal and paternal) that are similar
in shape and size.
• Homologous pairs (tetrads) carry genes controlling the same
inherited traits.
• Each locus (position of a gene) is in the same position on
homologues.
• Humans have 23 pairs of homologous chromosomes.
22 pairs of autosomes
1 pair of sex chromosomes
Homologous Chromosomes
(because a homologous pair consists of 4 chromatids it is called a “Tetrad”)
eye color
locus
eye color
locus
hair color
locus
hair color
locus
Paternal
Maternal
Humans have 23 Sets of Homologous Chromosomes
Each Homologous set is made up of 2 Homologues.
Homologue
Homologue
Sex Chromosomes
The Sex Chromosomes code for the sex of the offspring.
** If the offspring has two “X” chromosomes it will be a female.
** If the offspring has one “X” chromosome and one “Y” chromosome it will be a
male.
In Humans the “Sex
Chromosomes” are
the 23rd set
XX chromosome - female
XY chromosome - male
Sex Chromosomes
“Sex Chromosomes”
…….the 23rd set
This person has 2
“X” chromosomes…
and is a female.
23
Meiosis
is the process by which ”gametes” (sex cells) , with half the number of
chromosomes, are produced.
During Meiosis diploid cells are reduced to haploid cells
Diploid (2n)
 Haploid (n)
If Meiosis did not occur the chromosome number in
each new generation would double…. The
offspring would die.
Meiosis
Meiosis is Two cell divisions
(called meiosis I and meiosis II)
with only one duplication of chromosomes.
Meiosis in males is called spermatogenesis
and produces sperm.
Meiosis in females is called oogenesis and
produces ova.
Spermatogenesis
Secondary Spermatocyte
n=23
human
sex cell
2n=46
sperm
n=23
Primary Spermatocyte
n=23
Secondary Spermatocyte
haploid (n)
n=23
diploid (2n)
n=23
4 sperm cells are
produced from each
primary spermatocyte.
meiosis I
n=23
meiosis II
Oogenesis
*** The polar bodies die… only one ovum
(egg) is produced from each primary oocyte.
Interphase I
• Similar to mitosis interphase.
• Chromosomes replicate (S phase).
• Each duplicated chromosome consist of two identical
sister chromatids attached at their centromeres.
• Centriole pairs also replicate.
Interphase I
• Nucleus and nucleolus visible.
chromatin
nuclear
membrane
cell membrane
nucleolus
Meiosis I (four phases)
• Cell division that reduces the chromosome number
by one-half.
• four phases:
a. prophase I
b. metaphase I
c. anaphase I
d. telophase I
Prophase I
• Longest and most complex phase.
• 90% of the meiotic process is spent in Prophase I
• Chromosomes condense.
• Synapsis occurs: homologous chromosomes come together
to form a tetrad.
• Tetrad is two chromosomes or four chromatids (sister and
nonsister chromatids).
Prophase I - Synapsis
Homologous chromosomes
sister chromatids
Tetrad
sister chromatids
During Prophase I
“Crossing Over” occurs.
Crossing Over is one of the Two major occurrences of Meiosis
(The other is Non-disjunction)
• During Crossing over segments of nonsister
chromatids break and reattach to the other
chromatid. The Chiasmata (chiasma) are the
sites of crossing over.
Crossing Over
creates variation (diversity) in the offspring’s traits.
nonsister chromatids
chiasmata: site
of crossing over
Tetrad
variation
Question:
• A cell containing 20 chromosomes (diploid) at the
beginning of meiosis would, at its completion,
produce cells containing how many
chromosomes?
Answer:
• 10 chromosomes (haploid)
Question:
• A cell containing 40 chromatids at the beginning of
meiosis would, at its completion, produce cells
containing how many chromosomes?
Answer:
• 10 chromosomes
Prophase I
spindle fiber
aster
fibers
centrioles
Metaphase I
• Shortest phase
• Tetrads align on the metaphase plate.
• INDEPENDENT ASSORTMENT OCCURS:
1. Orientation of homologous pair to poles is random.
2. Variation
3. Formula: 2n
Example:
2n = 4
then n = 2
thus
22 = 4 combinations
Metaphase I
OR
metaphase plate
metaphase plate
Anaphase I
• Homologous chromosomes separate and move
towards the poles.
• Sister chromatids remain attached at their
centromeres.
Anaphase I
Telophase I
• Each pole now has haploid set of chromosomes.
• Cytokinesis occurs and two haploid daughter cells
are formed.
Telophase I
Meiosis II
• No interphase II
(or very short - no more DNA replication)
• Remember: Meiosis II is similar to mitosis
Prophase II
• same as prophase in mitosis
Metaphase II
• same as metaphase in mitosis
metaphase plate
metaphase plate
Anaphase II
• same as anaphase in mitosis
• sister chromatids separate
Telophase II
• Same as telophase in mitosis.
• Nuclei form.
• Cytokinesis occurs.
• Remember:
four haploid daughter cells
produced.
gametes = sperm or egg
Telophase II
Non-disjunction
Non-disjunction is one of the Two major occurrences of Meiosis
(The other is Crossing Over)
• Non-disjunction is the failure of homologous
chromosomes, or sister chromatids, to separate
during meiosis.
• Non-disjunction results with the production of
zygotes with abnormal chromosome numbers……
remember…. An abnormal chromosome number
(abnormal amount of DNA) is damaging to the
offspring.
Non-disjunctions usually occur in one
of two fashions.
• The first is called Monosomy, the second is
called Trisomy. If an organism has Trisomy 18
it has three chromosomes in the 18th set,
Trisomy 21…. Three chromosomes in the 21st
set. If an organism has Monosomy 23 it has
only one chromosome in the 23rd set.
Common Non-disjunction Disorders
•
•
•
•
Down’s Syndrome – Trisomy 21
Turner’s Syndrome – Monosomy 23 (X)
Kleinfelter’s Syndrome – Trisomy 23 (XXY)
Edward’s Syndrome – Trisomy 18
Amniocentesis
• An Amniocentesis is a procedure a pregnant
woman can have in order to detect some
genetics disorders…..such as non-disjunction.
Amniocentesis
Amniotic fluid withdrawn
Karyotype
(picture of an individual’s chromosomes)
One of the ways to
analyze the
amniocentesis is to
make a Karyotype
What genetic disorder
does this karyotype
show?
Trisomy 21….Down’s
Syndrome
MITOSIS
1 cell division:
2 daughter cells
2n
MEIOSIS
2 cell divisions:
4 product of meiosis
2n
Somatic cells
2n
Cells in sexual cycle
n
n
n
n
2n
n=chromosome number
Mitosis :
two genetically identical diploid cells
from one diploid parent cell
Diploid
organism: two sets of chromosomes (one
from each parent); 2n
Mitosis
Conservative process:
Daughter cells genotypes identical
to parental genotypes
Final Result of Meiosis :

Four genetically different haploid cells;
from one diploid parent cell
Haploid
organism: one set of chromosomes; n
Meiosis
Promotes variation among the product
of meiosis (crossing over)
Alike







Both have the stages
PMAT
Both go through
Cytokinesis
Both divide and make
daughter cells
Both are a form of
reproduction
Both take place inside
the cell
Chromosomes duplicate
and DNA replication
occurs in each process







Different
Mitosis produces two
identical daughter cell,
meiosis produces four
genetically different
cells
Crossing over and
tetrad formation
(synapsis) occur in
prophase I of Meiosis
The centromeres split in
Anaphase II
Mitosis has one division,
Meiosis has two
Mitosis occurs in
somatic or body cells
Meiosis occurs in
reproductive organs;
producing gametes
Mitosis is asexual
reproduction
Meiosis ensures sexual
reproduction