Chapter 12 Flashcards
The ability of organisms to produce more of their own kind best distinguishes living things from
nonliving matter
The continuity of life is based on the reproduction of cells, or
cell division
In unicellular organisms,
division of one cell reproduces the entire organism
asexual reproduction
Multicellular organisms depend on cell division for
growth and development, and repair
3 key roles of Mitosis
- asexual reproduction
- growth and development
- repair
Cell division is an integral part of the cell cycle,
the life of a cell from formation to its own division
Mitosis-
dividing of DNA in the nucleus
Most cell division results in
daughter cells with identical genetic information, DNA
The exception is meiosis,
a special type of division that can produce sperm and egg cells
Cytokinesis
dividing the cytoplasm
All the DNA in a cell constitutes the cell’s
genome
A genome can consist of
a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells)
DNA molecules in a cell are packaged into
chromosomes
Eukaryotic chromosomes consist of a chromatin,
a complex of DNA and protein that condenses during cell division
Every eukaryotic species has a characteristic number of
chromosomes in each cell nucleus.
Humans have 46
Somatic cells (nonreproductive cells)
have two sets of chromosomes
called diploid cells; 2n
Gametes (reproductive cells: sperm and eggs)
have half as many chromosomes as somatic cells
called haploid cells; n
Somatic Cells
body cell 2 sets of chromosomes diploid 2n 2n=46
Gametic Cells
egg/sperm (germ)
1 set of chromosomes
haploid
n
In preparation for cell division,
DNA is replicated and the chromosomes condense
Each duplicated chromosome has
two sister chromatids (joined copies of the original chromosome), which separate during cell division
The centromere is the
narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached
During cell division,
the two sister chromatids of each duplicated chromosome separate and move into two nuclei
Sister chromatids ONLY exist as
sisters
Once separate, the (sister?) chromatids are called
chromosomes
Eukaryotic cell division consists of
Mitosis
and
Cytokinesis
Mitosis
the division of the genetic material (DNA) in the nucleus
Cytokinesis
the division of the cytoplasm
Gametes are produced by a
variation of cell division called meiosis
Meiosis yields nonidentical daughter cells that have only
one set of chromosomes, half as many as the parent cell
Humans 2n=46 to n=23
The mitotic phase alternates with
interphase in the cell cycle
Interphase (about 90% of the cell cycle) can be divided into subphases
G1 phase ("first gap")
S phase ("synthesis")
G2 phase ("second gap")The cell grows during all three phases, but
chromosomes are duplicated only during the S phase
Mitosis is conventionally divided into five phases
P- Prophase P- Prometaphase M- Metaphase A- Anaphase T- Telophase
Prophase
chromosomes become visible
Prometaphase
nuclear envelope disappears/ spindle fibers attach to kintochore (DNA)
Metaphase
line up
Anaphase
pull apart
Telophase
nuclear envelope reforms, goes back to chromatin
Cytokinesis overlaps the
latter stages of mitosis
The mitotic spindle is a structure made of
microtubules that controls chromosome movement during mitosis
In animal cells, assembly of spindle microtubules begins in the
centrosome, the microtubule organizing center
The centrosome replicates during interphase (G2 phase), forming
two centrosomes that migrate to opposite ends of the cell during prophase and prometaphase
An aster (a radial array of short microtubules)
extends from each centrosome
The spindle includes the
centrosomes, the spindle microtubules, and the asters
During prometaphase,
some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes
Kinetochores are
protein complexes associated with centromeres
At metaphase,
the chromosomes are lined up at the metaphase plate, an imaginary structure at the midway point between the spindle’s two poles
In anaphase,
sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell.
Proteins holding together sister chromatids are suddenly inactivated
The microtubules shorten by
depolymerizing at their kinetochore ends.
Motor proteins on a kinetochore “walk” a chromosome along a microtubule toward the nearest pole
Nonkinetochore microtubules from opposite poles overlap and
push against each other, elongating the cell. (stretches the cell).
(They don’t grab onto the DNA, but they are really important)
In telophase,
genetically identical daughter nuclei form at opposite ends of the cell
Cytokinesis beings during
anaphase or telophase and the spindle eventually disassembles.
Cytokinesis is NOT part of
Mitosis.
They just overlap a bit sometimes.
In animal cells, cytokinesis occurs by a process known as
cleavage, forming a cleavage furrow.
Cleavage furrow is
a contractile ring of actin and microfilaments myosin protein.
Like a drawstring pulling it tight, until it pops apart.
Cytokinesis in animal cells
cleavage- process
cleavage furrow- structure formed
In plant cells, cytokinesis occurs by a process known as
cell plate formation, which forms a cell plate
A cell plate is
specialized vesicles grown and then fuse
Cytokinesis in plant cells
cell plate formation- process
cell plate- structure formed
Prokaryotes (bacteria and archaea) reproduce by a type of cell division called
binary fission
In binary fission,
the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes actively move apart.
Prokaryotes do NOT have any
mitotic spindles or microtubules that direct this traffic (replication, binary fission)
In binary fission, the plasma membrane
pinches inward, dividing the cell into two
The Eukaryotic cell cycle is regulated by a
molecular control system
The frequency of cell division varies with the
type of cell.
These differences result from regulation at the molecular level.
Cancer cells manage to
escape the usual controls on the cell cycle
The cell cycle appears to be driven by
specific chemical signals present in the cytoplasm.
a specific chemical signal is the reason a cell divides
The sequential events of the cell cycle are directed by a distinct
cell cycle control system, which is similar to a clock
The cell cycle control system is regulated by
both internal and external controls
The clock (cell cycle) has specific checkpoints where
the cell cycle stops until a go-ahead signal is received
For many cells, the G1 checkpoint seems to be
the most important
If a cell receives a go-ahead signal at the G1 checkpoint, it will usually
complete the S, G2, and M phases and divide
If the cell cycle does not receive the go-ahead signal at the G1 checkpoint, it
will exit the cycle, switching into a non-dividing state called the G0 phase.
In the G0 phase,
cells will never divide again.
Two types of regulatory proteins are involved in cell cycle control:
Cyclins
and
Cyclin-dependent kinases (Cdks)
Cyclin-dependent kinases (Cdks) activity fluctuates during the cell cycle because it is
controlled by cycles, so named because their concentrations vary with the cell cycle
MPF (maturation-promoting factor) is a
cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase
Cyclin is what is
cycling and is around sometimes but not always
??
Cyclin is really high during the
G2 and M phase, so cyclin-dependent kinases works best at the G2 and M phase too.
An example of an internal signal is that
kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase
Some external signals are
growth factors (paracrine signaling), proteins released by certain cells that stimulate other cells to divide
For example, platelet-derived growth factor (PDGF) stimulates the division of
human fibroblast cells in culture.
(have to have PDGF if want a cell to divide??)
(external signal?)
A clear example of external signals is
density-dependent inhibition, in which crowded cells stop dividing.
(As soon as things become dense, packed, crowded, and full, the cells stop dividing.
Most animal cells also exhibit
anchorage dependence, in which they must be attached to a substratum in order to divide
(has to be stuck to something in order to divide)
Cancer cells exhibit neither
density-dependent inhibition nor anchorage dependence.
cancer cells just divide and don’t obey those two things. They don’t need any signals or growth factors.
Cancer cells do not respond normally to the
body’s control mechanisms
HeLa cells
“immortal cell line”
Cancer cells may not need growth factors to grow and divide.
- They may make their own growth factor.
- They may convey a growth factor’s signal without the presence of the growth factor.
- They may have an abnormal cell cycle control system.
A normal cell is converted to a cancerous cell by a process called
transformation
Cancer cells that are not eliminated by the immune system form
tumors, masses of abnormal cells within otherwise normal tissue
If abnormal cells remain only at the original site, the lump is called a
benign tumor
Malignant tumors invade
surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form additional tumors.
(Malignant tumors grow bigger and bigger. They are really bad)
Recent advantages in understanding the cell cycle and cell cycle signaling have led to
advances in cancer treatment
Cancer results from
genetic changes that affect cell cycle control
