Transcript mitosis notes - Elmwood Park Memorial High School

Limits to cell growth
• Surface area to volume ratio
Cell Division
• About 2 trillion cells are produced
every day by an adult human body.
• This is about to about 25 million per
second!!
• Cells undergo growth, development
repair and reproduction.
• The division of somatic cells in
eukaryotes is Mitosis (asexual
reproduction).. Ex. skin cells, heart
cells, blood cells.
• A second type of reproduction
takes place in prokaryotes.
Bacterial cells called binary fission.
• There are two stages in binary
fission: first DNA is copied, second
the cell divides, resulting in two
identical cells also known as
clones.
• The third type is sexual
reproduction of gametes (sperm
and egg), this is known as Meiosis.
Chromosomes
• Chromosomes are located in
the _____ of the cell.
• Each chromosome is made up
of segments called genes.
• Genes produce proteins that
determine characteristics and
functions of the cell.
Structure of a chromosome
Homologous Chromosomes
• Humans have 46 chromosomes
• 23 from each parent
• These are called homologous chromosomes
because:
– They are the same length
– Have the centromere in the same location
– Carry genes for the same trait
• Same trait different characteristics
Sex cells
• Every cell contains a full set of
chromosomes
• Only half of these chromosomes are
passed on to the offspring
• Special cells called gametes (sex cells)
are produced containing ½ of the
original number of chromosomes.
– Example: a human has 46
chromosomes in a normal cell. A
gamete or sex cell only has 23
chromosomes
Haploid and diploid cells
• Every species has a different
number of chromosomes see
table 1 p.121
• The letter n is used to represent
the number of chromosomes in
general terms
• A gamete with half the number of
chromosomes is called haploid
and is represented by n
• When two haploid cells come
together during fertilization a
diploid cell is formed and is
represented by 2n page 120
fig.3
• A zygote is a fertilized egg the
first cell of a new individual
Questions
• Where in the cell are chromosomes
located?
• Each chromosome has segments
called?
• What product do genes code for?
• What are homologous chromosomes?
• What is the name given to sex cells?
How many chromosomes do
(humans) sex cells have?
Chromosomes Continued….
• You have 23 pairs of homologous
chromosomes.
• 22 of the pairs are autosomes not
involved with determining sex of an
individual.
• the 23rd pair does determine the sex
of an individual.
• In humans XX is female and XY is
male
Karyotype
• A human has 46 chromosomes and each
chromosome has thousands of genes.
• Each gene plays an important role in growth
and function.
• A karyotype is a picture (see p. 122) of the
chromosomes in a dividing cell arranged by
size.
• An extra chromosome 21 means the person
has trisomy 21 also known as Down
Syndrome.
Karyotype
Mutations
• Are changes in chromosome structure.
• There are four types of mutations:
1. Deletion - a piece breaks off and is lost.
2. Duplication - A piece is repeated.
3. Inversion - A piece breaks off and reattaches in
the wrong order.
4. Translocation - Apiece attaches to a different
chromosome.
Check Point Analysis
• Describe how a cell might
be affected by each
mutation if the cell were to
receive a chromosome with
that mutation?
Cell Cycle
• Regulates cell size and
reproduction
• Each time a cell completes one
cycle a new cell is formed
• three main stages of the cycle
–interphase
–Mitosis
–Cytokinesis
Cell Cycle
Interphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Interphase – substage 1
• G1 (first stage) – cell growth and
daily functions.
– Nerve and muscle cells may not
ever divide again. So they are
suspended in G1 and if they die
they are not replaced.
–Major portion of cells life is G1
Interphase – substage 2
• S (second stage) – Synthesis stage - DNA is
replicated.
– Chromosomes contain genetic material.
Chromosomes are tightly coiled and are
located in the nucleus.
– Chromatin is the uncoiled form of a
chromosome. The chromosome must
uncoil and become chromatin before it is
replicated.
Interphase – substage 3
• G2 (third stage) – cell prepares for
mitosis
–Microtubules (hollow protein
fibers) are formed
–The nucleus prepares to divide
–Cell makes sure it is ready for
division
After interphase
• Mitosis and cytokinesis
–Mitosis – cells nuclear
material divides and
seperates
–Cytokinesis – the rest of the
cell divides to form two
separate daughter cells
Mitosis
• During mitosis the cell is replicated
• The DNA that was copied in the S
phase of interphase is now separated
equally during mitosis
• The two new cells are called daughter
cells and are identical
• There are four stages
– Prophase
– Metaphase
– Anaphase
– Telophase
The cell between
Interphase & Mitosis
• At the end of the G2 phase of
interphase the cell has two copies
of its DNA inside one nucleus
• Mitosis will separate those two
copies so that the two new
daughter cells have one set of
DNA each
Prokaryotic vs. Eukaryotic
cells
• Because eukaryotic cells have
membrane bound organelles
and a nucleus they must go
through the cell cycle
• Prokaryotic cells are less
complex and go through binary
fission
Cell Division Check Point
• What is the purpose of cell division?
• How many cells are reproduced from
each cell?
• Do cells reproduce throughout your
entire life?
• What are the five stages of the cell
cycle?
• What are the three phases of
interphase?
Thursday, January 7, 2010
• Do Now: The nerve cells in a human
nervous system seldom undergo
mitosis. Predict how well you think the
body is able to repair damage to parts
of the nervous system.
• Objective:
Examine the events that take place in
mitosis.
• Homework: Page 134 #1-7.
Prophase
see p. 130-131.
• First the chromatin recoils to form
chromosomes what look like X’s
– Each ½ of the X is a sister chromatid
(identical copies of the DNA)
– The X is held together by a
centromere
• The nuclear membrane & nucleolus
dissolves
• Spindles begin to form between the two
nuclei
Prophase
Animal Cell
Plant Cell
Spindle fibers
Centrioles
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Metaphase
• Chromosomes line up (in
center) along the equator.
• Spindle fibers connect to sister
chromatids.
• Ensures that each daughter
cell have accurate copies of
the chromosome
Metaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Anaphase
• The chromatids are pulled apart as the
microtubules begin to shorten.
• The microtubule is pulling on the centromere
of each sister chromatid.
• Separation of the sister chromatids happens
all at the same time. Now are chromosomes.
• At the end of the anaphase the sister
chromatids are separated equally and are
moving toward opposite sides or poles of
the cell
Anaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Telophase
• A new nuclear membrane begins to forms
around each set of chromatids and the
nucleolus reappears in the nucleus on
each side.
• The spindles disassemble and the
microtubules are recycled to be used as
part of the cells cytoskeleton.
• At the end of the Telophase the sister
chromatids are separated equally and are
on opposite sides or poles of the cell with
a new nucleus and nucleolus.
Telophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Cytokinesis
• Cytokinesis is the separation
of the cytoplasm and the
pinching in of the cell
membrane.
• Ex. similar to the way draw
sting pants tighten when you
pull the string.
Cytokinesis
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Cells
• The plant cell has a cell wall.
• Plant cells do not undergo
cytokinesis.
• The cell wall does not pinch in,
instead a
cell plate is formed between the
two new cells. The plate will
develop into a cell wall and
separate the two cells.
Plants cell plate
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Cell Cycle
44
- Cell Division
The Cell Cycle
45
45
Cell cycle controls
• The normal cell cycle is controlled
by cyclic proteins.
• As the cell cycle progresses the
cell pauses to check and make
sure there are no abnormalities
before moving on.
• When this check point system fail
cancer may ensue.
How abnormalities get through
• Because the cell cycle is so very
complex there are many things that
can go wrong
• When the cell misses an abnormality
or does not respond to the cyclic
proteins a condition called cancer can
form
• Cancer is an uncontrolled cell cycle
when cell begins to divide and doesn’t
stop
Cancer cell karyotype
What causes cancer
• Weak organisms as well as healthy ones
can get cancer
• Cancer is caused by mutations in sections
of the DNA
• The mutations are often repaired but when
they are not they can cause cancer
• The mutations in the DNA can be caused by
environmental factors such as carcinogens
– things that are known to cause cancer
The genetics of cancer
• Cancer is not the result of one
DNA mutation
• Over a lifetime several changes in
the DNA may occur possibly
resulting in cancer – multi - hit.
• The possibility of cancer increases
with age
• Offspring can inherit these
changes leading to an increased
risk of cancer
The death of a cell
• Apoptosis is when cells are
programmed to die
– Examples
• the cells between the fingers and
toes of a developing child
• Leaves falling off trees in autumn
• Apoptosis can also protect an organism
from defective or mutated cells
Stem cells
• Stem cells are cells that do not yet have a
specialization
• Embryonic stem cells
– The first 100 or so cells of an organism are
stem cells
– The stem cells, after forming the basis of the
organism begin to specialize into tissues and
organs
• Adult stem cells
– Found sporadically throughout an organism
and are used for repairs in that adult