Download the cell cycle

THE CELL CYCLE
THE CYCLE OF LIFE
Unicellular
Offspring
Unicellular You
Mitosis
Multicellular
You
Meiosis
WHY MUST CELLS DIVIDE?
Cells must be small
As cells grow bigger, problems develop
DNA Overload
 Same amount of DNA must serve larger and larger
areas
Surface Area/Volume Ratio
 Cytoplasm increases faster than cell membrane
 Cell can’t exchange enough material
 Material can’t reach center fast enough
SURFACE AREA/ VOLUME RATIOS
Surface Area (cube) = 6 x width 2
Volume (cube) = width 3
Surface Area/ Volume
COMPARING ORGANISMS
Unicellular
 Single cell will go through
cycle
 When cell gets too large, it
will divide
 Produces two new cell,
each one is its own
organism
 Form of asexual
reproduction called binary
fission
 Each “offspring” is
identical to the parent cell
 Multicellular
 Beginning Cell- Zygote
 Cell(s) go through cell cycle
to form parts of organism
 Cell division continues
through development,
growth, repair, and wear and
tear
 Each division creates 2 new
cells identical to the parent
cell
 In some species, can be
used for asexual
reproduction such as
budding and fragmentation
DNA REVIEW
 Chromatin Form of DNA during interphase
 Chromosome
 Form of DNA during cell division
 Centromere
 center point holding two sister
chromatids together
 Sister chromatids
 two copies of a chromosome
held together by a centromere
DIPLOID
Diploid (2n)
 Cells have 2 sets of chromosomes
 one inherited from mom and one from
dad
 Found in somatic cells (all cells
except sex cells)
 Different number in different
organisms
 Humans diploid # is 46
 Homologous chromosomes- name
of the 2 alike chromosomes from
each set
HAPLOID
Haploid (n)
 Cells have 1 set of
chromosomes
 Found in gametes (sex
cells)
 Diploid # / 2
 Human # is 23 (46 / 2)
 When fertilization occurs,
the organisms will have
the diploid number again
SOMATIC CELLS
 All cells in a multicellular organism except sex cells
 Beginning cell- zygote (fertilized egg)
 Totipotent- able to divide and create all the cell types needed in the
body
 Starts dividing to form early embryo (at 5 days is called a
blastocyst)
 Pluripotent- able to divide and create many of the cell types needed
in the body
 Continues to divide to form the all the structures
 Adult stem cells- found in various parts of the body
 Multipotent- able to divide and create some of the cell types needed
in the body
CELL SPECIALIZATION
Also called cell
differentiation
Many different cell
types
 Each has identical copies
of DNA
 Each type has a unique
shape and function
THE CELL CYCLE
INTERPHASE
INTERPHASE
G1
 Gap phase
 Cell grows and carries out normal functions
S PHASE
G2
 Gap phase
 Cell grows and carries out normal functions
 Other organelles replicate
G0
 Some cells will never leave interphase or will stay in
interphase for a very long time
 Phase looks like G1
 These cells will not divide
CELL DIVISION
MITOSIS




Division of the nucleus of somatic cells
One division with 4 phases
Cell divides into two identical daughter cells
Cells start diploid and end diploid
PROPHASE
PROMETAPHASE
METAPHASE
ANAPHASE
TELOPHASE
CY TOKINESIS
ANIMAL VS PLANT CY TOKINESIS
Animal
 Cell membrane pinches together to form two cells
Plant
 Cell plate forms
 Will become cell wall to form two new cells
CONTROLLING CELL DIVISION
External Controls
 Growth Factors and Hormones- stimulate cell division
 Crowding- inhibits cell division
Internal Controls
 Cyclins- proteins whose levels rise and fall during the
cell cycle; must reach a certain amount and interact
with kinases to create cell division
 Checkpoints- check that cell cycle is proceeding
correctly
 S phase- checks if all DNA has been copied correctly
 Metaphase- checks if all chromosomes are on spindle fiber
CANCER
Uncontrolled cell division
 Usually results from mutations to
 Oncogenes- accelerate the cell cycle
 Genes that stop the cell cycle
 p53 gene- normally stops cell division from occurring until all
chromosomes are replicated
Cells are undifferentiated and don’t do their
job
Benign tumors- stay clustered together
Malignant spread into other area creating
problems (metastisize)
ASEXUAL REPRODUCTION
 Occurs in
 Unicellular prokaryotes
 Unicellular eukaryotes
 Some multicellular eukaryotes
 Done by mitosis or processes similar to mitosis
 Examples
 Binary fission
 Budding
 Fragmentation
SEXUAL REPRODUCTION
 Combines genetic information from two parents
 Creates a unique of fspring
 Parents create gametes (sex cells) using meiosis
 In humans, egg and sperm
MEIOSIS
CHARACTERISTICS
 Meiosis
 Occurs in games (sex cells)
 2 divisions with 4 phases each (8 phases total) creating 4 unique
cells
 Cells start out diploid and end haploid
PROPHASE I
PROMETAPHASE I
METAPHASE I
ANAPHASE I
TELOPHASE I
CY TOKINESIS I
MEIOSIS II
 Similar to mitosis
 Two haploid cells created by Meiosis I both divide
 Creates four haploid cells
SPERMATOGENESIS




Formation of sperm
Starts at puberty
Forms 4 sperm during each meiosis
Men will make 5 to 200 million sperm/day
OOGENESIS
 Formation of the egg
 Meiosis starts inside the womb,
continues is some during every
cycle after puberty
 1 egg and 3 polar bodies created
after every meiosis
 Egg must contain lots of
cytoplasm to support the
developing embryo after
fertilization