Download Cell Cycle & Division

Cell Cycle & Division
Biology I
Cell Division
Cell Division:
• All cells are derived from
preexisting cells (Cell Theory)
• Cell division is the process by
which cells produce new cells
• Cell division differs in
prokaryotes (bacteria) and
eukaryotes (protists, fungi, plants,
& animals)
• Cells grow in number, not in
size.
Reasons for Cell
Division:
• Cell growth
• Repair & replacement of
damaged cell parts
• Reproduction of the species
How often do cells divide?
• Some cells must be repaired
often such as cells lining the
intestines, white blood cells,
skin cells with a short lifespan.
• Other cells DO NOT divide at
all after birth such as muscle,
nerve cells, brain cells, female
egg cells.
Chromosomes & Their
Structure
• The plans for making cells are coded in
their DNA.
• DNA, deoxyribose nucleic acid, is a long
thin molecule that stores genetic
information.
• DNA is organized into molecules called
chromosomes.
Chromosomes & Their
Structure
• Chromosomes are made of protein & a
long, single, tightly- coiled DNA molecule
visible only when the cell divides.
• When a cell is NOT dividing the
chromosome (DNA) is less visible & is
called chromatin.
Chromosomes & Their
Structure
• Centromeres hold duplicated chromosomes
together until they are separated in cell
division.
• When DNA makes copies of itself before
cell division, each half of the chromosomes
is called a sister chromatid.
– Each sister chromatid contains identical genetic
information.
Chromosomes & Their
Structure
Chromosome Numbers
• Humans somatic or body cells • Human reproductive cells or
gametes (sperms & eggs) have
have 23 pairs of chromosomes
one set or 23 chromosomes
or 46 chromosomes (diploid or
(haploid or n number)
2n number)
• Every organism has a specific
• The 2 chromatids of a
chromosome number
chromosome pair are called
homologues (have genes for the
Organism
Chromosome
same trait at the same location)
Number (2n)
Human
46
Fruit fly
8
Lettuce
14
Goldfish
94
Types of Reproduction
• Asexual Reproduction
– Reproduction of cells involving only ONE
parent.
– The organism will make a copy of itself.
Produces identical offspring.
– Types:
• Binary Fission (bacteria)
• Mitosis (most
eukaryotic cells)
• Vegetative propagation
• Budding
Binary Fission
• Bacteria, cyanobacteria, and most single celled
organisms reproduce by
Vegetative Propagation
• Form of asexual reproduction in plants.
• Part of the plant detaches from the parent
plant to form their own organism.
• Genetically identical to parent.
Budding
• A form of asexual reproduction in the plant
in which a new organism develops from an
outgrowth of the parent.
• Genetically identical to the parent plant.
Types of Reproduction
• Sexual Reproduction
– Reproduction that involves TWO parents
– Produces offspring that are genetically diverse.
– Happens in the sex cells (sperm and egg) which
are called gametes.
Cell Cycle
S
phase
G1
interphase
Mitosis
-prophase
-metaphase
-anaphase
-telophase
G2
Cell Cycle
• The cell cycle includes 3 main parts:
interphase, mitosis, and cytokinesis.
– Mitosis = nuclear division
– Cytokinesis = division of the cytoplasm
Interphase
• The longest stage of the cell cycle.
• Called the resting stage because the cell
isn’t dividing.
• Consists of 3 stages:
– G1: cell growth
– S (synthesis): DNA synthesis
– G2: prepare for cell division
Interphase
1. G1 (gap) phase:
 Main growth stage
 Cell increases in size
 Cell makes organelles
2. S phase:
 Copying of all of DNA’s instructions (DNA Replication)
 DNA in the form of chromatin (not visible)
3. G2 (gap) phase:
 Preparation time for mitosis/meiosis (cell division)
 Cell continues growing
 Needed proteins produced
Mitosis
• Division of the nucleus occurs first
(mitosis)
• Mitosis is asexual reproduction.
– Only ONE parent cell
– Daughter cells are genetically identical
• Mitosis consists of four stages –
Prophase
• Longest phase of mitosis
• Nucleolus disappears
• Chromatin condenses into chromosomes, consisting
of two sister chromatids.
• Centrioles move apart (not found in plants).
• Spindle fibers form and attach from
centrioles to centromeres.
• Nuclear membrane disappears.
Prophase
early prophase
late prophase
centrioles
spindle fibers
aster
fibers
nuclear envelope
disappearing
centromere
Prophase
• Animal Cell
• Plant Cell
Metaphase
• Shortest phase of mitosis
• Chromosomes line up across the middle of cell
(center of cell – equator of cell).
• The centromere of each chromosome attaches to
spindle fibers.
Metaphase
centrioles
aster
fibers
spindle fibers
metaphase plate
Metaphase
• Animal Cell
• Plant Cell
Anaphase
• Sister chromatids separate and move apart.
• After separation, chromatids are now considered
chromosomes.
• During this phase, the cell contains twice the
normal number of chromosomes.
• Cell begins to elongate.
• At the end, there are equal numbers
of chromosomes at the poles.
Anaphase
No longer sister chromatids, now chromosomes
aster
fibers
spindle fibers
centrioles
Anaphase
• Animal Cell
• Plant Cell
Telophase
• Nuclear membrane reappears.
• Nucleolus reforms.
• Chromosomes uncoil and appear as chromatin
again.
• In the end, two genetically identical nuclei are
present.
• Cytokinesis begins.
Telophase
cleavage furrow (cytokinesis)
nuclear membrane reforming
nucleolus reappears
Telophase
• Animal Cell
• Plant Cell
Cytokinesis
• Division of the cytoplasm of
the cell and its organelles
into two new daughter cells.
• Cytokinesis differs between
plants and animals:
– Animals: a cleavage furrow
forms to make the circular
shape.
– Plants: a cell plate forms
where new cell wall will be to
make the rectangular shape.
cell plate
cell plate
Cytokinesis
• Animal Cell: cleavage
furrow
• Plant Cell: cell plate
Parent cell
Chromosomes are
copied and double
in number
Chromosomes
now split
2 daughter cells
identical to original
Question:
• A cell containing 20 chromosomes at the
beginning of mitosis would, at its completion,
produce cells containing how many chromosomes
each?
Answer:
• 20 chromosomes
Question:
• A cell containing 40 chromatids at the beginning of
mitosis would, at its completion, produce cells
containing how many chromosomes each?
Answer:
• 20 chromosomes
CANCER
• Cancer is Uncontrolled
Mitosis:
• Mitosis must be
controlled, otherwise
growth will occur
without limit (cancer)
• Control is by special
proteins produced by
oncogenes