Transcript Chapter 12 – The Cell Cycle

Chapter 12 – The Cell Cycle
AP Biology
In 1855 Rudolf Virchow stated
“where a cell exists, there must have been a
preexisting cell, just as animal arises from
animal and plant arises from plant.”
“Omnis cellula e cellula” means
every cell from a cell.
How does an organism such as
Amoeba produce offspring compared
to a human?
• Amoeba - one cell divides to create an
entire organism.
• Human - cells divide to repair, maintain,
or become part of a multicellular
organism ; gametes (half the
chromosomes) are made for reproduction
What might be a disadvantage to the progeny of an Amoeba
compared to the offspring of humans?
• Offspring of humans have more variation
• because gametes are continuously mixing
chromosomes from different organisms while in
Amoebas the organisms itself is copied and
divided to make more which leads to less
variation which is bad if the environment
changes and the population is not suited for the
change.
Vocab
1) genome – all genetic
information in a cell (organism)
2) chromosomes - packages of
DNA molecules (46 in humans)
3) somatic cells - all body cells
except reproductive cells
4) gametes - reproductive cells
with half the # of chromosomes
5) chromatin - DNA-protein
complex
6) sister chromatids - identical
copies of chromosomes
7) centromere - the “waist” where
sisters are connected
8) Mitosis - division of the nucleus
(P,PM,M,A,T) which produces
genetically equivalent cells
9) cytokinesis - division of the
cytoplasm
10) Meiosis - division that produces
gametes
Stages of the Cell Cycle
Interphase
• G1 - phase
– Cell is performing
normal cell functions
while growing
• S - phase
– DNA replicates
(copies)
• G2 - phase
– Organelles double in
number to prepare for
division
Prophase
• Spindle fibers (ropes) form
• Centrioles (make spindles)
move to opposite poles
• Chromosomes become
visible
• Nuclear membrane and
nucleolus breaks apart
Metaphase
• Chromosomes
line up along the
equator (middle
of the cell)
Anaphase
• Chromatids (copies
of chromosomes)
separate and move to
opposite poles
Telophase
• Nuclear membrane
forms around each
group of chromosomes
and the nucleolus
reappears
• Chromosomes unwind
and seem to disappear
• Spindle fibers degrade
• Cytokinesis begins
(pinches in)
Cytokinesis
• The process by which the
cytoplasm divides and one
cell becomes two
individual cells.
Purpose of Mitosis - Cell Division
• Growth
• Repair
During cell divison, parent cells must be able to:
• Make a copy of all
information (DNA)
• Transfer one copy of
this information (DNA)
to each daughter cell so
they get the same
instructions
• Provide each daughter
cell with enough cellular
machinery (organelles)
in order to function
Things to think about:
1) Why is it important that DNA copies are
distributed equally to the daughter cells?
2) Why is it important that each daughter cell
receive all of the cellular organelles? (These
include mitochondria, chloroplasts, Golgi
apparatus, and endoplasmic reticulum.)
Describe which processes might be affected if
a daughter cell did not receive one of these
organelles.
3) Cells need nutrients as building blocks for
new biomolecules. Other than nutrients, what
product(s) of metabolism is provided for the
cell? At what points during the stages of cell
division are these products required?
4) What difficulties might arise for an organism
if muscle cells or nerve cells are damaged?
Mitosis
Mitosis
Cytokinesis
• Division of the cytoplasm
Mitosis Animation
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/chap
ter2/animation__mitosis_and_cytokinesis.html
More Vocab
1) mitotic spindle - fibers made of microtubules;
attach to chromosomes
2) centrosome - non-membranous organelle; assembly
of spindle microtubules starts
3) kinetochore - structure of protein and chromosomal
DNA at the centromere; “walks” the chromosome
down the microtubule
4) metaphase plate - the plane midway between the
two poles where the chromomomes line-up during
metaphase
What is the function of kinetochore
and non-kinetochore microtubules?
• kinetechore - “walk” the chromosomes to one
pole
• non-kinetechore - elongating the whole cell
during anaphase
Animal vs. Plant
• Animal
– cleavage;
– cleavage furrow appears, deepens until cell is spit
in two
• Plant
– cell plate;
– vesicles from Golgi apparatus move to middle of
cell
Binary Fission – “division in half”
What brings about the separation
of the two daughter cells?
Still a mystery …
Evolution of Mitosis
Regulation of the Cell Cycle
The cell cycle is
driven by
specific
chemical signals
in the
cytoplasm.
1970’s – Experimentation:
• Two cells in different phases of the cell cycle are
fused together. If one is in S while another in G1,
the G1 immediately enters S.
• Likewise, if one is undergoing Mitosis the second
nucleus also enters Mitosis.
More Vocab
• Cell Cycle Control System:
– A cyclically operating set of
molecules in the cell that
both triggers and
coordinates key events in
the cell cycle.
• Checkpoint:
– Point where stop and goahead signals regulate the
cycle.
• 2 main regulatory
molecules:
– Protein kinases
– Cyclins
• Cdks:
• proteins that drive the cell
cycle and rise and fall
depending on the
concentration of cyclin.
• MPF:
• “maturation or M-phase
promoting factor”
• cyclin-Cdk complex
• Triggers cells passage past
the G2 checkpoint and into
M-phase
Figure 12.14 – Campbell 6th Edition
Role of Cdk, cyclin, and MPF:
• Cdk:
– Binds to cyclin to form MPF
• Cyclin:
– Binds to Cdk to form MPF
• MPF: Cdk + cyclin
– Promotes mitosis by phosphorylating proteins
– Breakdown of its own cyclin
• Which is conserved? Why?
Cdk: It’s an enzyme so it’s reusable!
Kinetechore Involvement:
• Kinetechores not yet attached to microtubules trigger
a signal that delays the onset of anaphase by keeping
the Anaphase Promoting Complex (APC) in an
inactive state.
• After all kinetochores are attached the “wait” signal
ceases and APC becomes active.
• Cyclin is broken down and proteins holding sister
chromatids together are inactivated.
More Vocab:
• Growth Factor:
– Protein released by
certain body cells that
stimulate other cells to
divide.
• PDGF:
– Stimulates the division
of fibroblast cells; helps
heal wounds.
• Density dependent
inhibition:
– Crowded cells stop
dividing.
• Anchorage dependence:
– Cells must be attached to
substratum in order to
divide.
Cancer
• Failure to exhibit density dependent
inhibition
• Failure to exhibit anchorage dependent
inhibition
• Cell cycle control system is abnormal
• Manufactures its own growth factors or
abnormal signal pathway
Last of the Vocab:
• Transformation:
– Process that converts
normal cells to cancer
cells
• Tumor:
– Mass of abnormal cells
within otherwise normal
tissue
• Benign Tumor:
– Remain at original site
– Can be removed
• Malignant Tumor:
– Abnormal cells move to
different regions, impair
function of one or more
organs; CANCER
• Metastasis:
– Spread of cancer cells to
locations distant from the
original site
Breast Cancer