Chapter 9- cell cycles Flashcards
T/F - Some plant species may be polyploid.
True.
Plant species may have three, four, or even more complete sets of chromosomes in each cell
Growth followed by nuclear division and cytokinesis
Cell cycle
Division of the cytoplasm
Cytokinesis
The equal distribution of daughter chromosomes to each of two daughter cells
Segregation
T/F - In a multicellular organism, cells of different tissues contain different genetic information
All of the cells that make up a multicellular organism arose by mitosis from a single cell, the zygote, so they all have the same genetic material.
State of cellular arrest
g0 phase
Sister chromatids are apparent for the first time; spindle begins to develop
prophase
Part of cytokinesis in plants; involves formation of a new cell wall from vesicles at the former spindle midpoint
cell plate
Stage during which DNA is replicated
S phase
Stage preceding mitosis
g2 phase
Spindle midpoint in metaphase
metaphase plate
After nuclear division, cytoplasm divides and two daughter cells result
cytokinesis
Stage during which spindles enter the former nuclear area
prometaphase
Phase of cell growth and DNA replication
interphase
Sister chromatids move to opposite poles
anaphase
Spindle disassembles, nuclear envelope reappears, chromosomes become less condensed
telophase
Sister chromatids are aligned at the midpoint of the spindle
metaphase
Phase of cell growth after cytokinesis
g1 phase
Nuclear division; consists of 4–5 phases
mitosis
T/F - During G1, cells are synthesizing RNA, proteins, and DNA.
F – DNA is synthesized during the S phase;
T/F- In multicellular organisms, if cells or certain tissues are mature and do not need to increase in numbers or turn over, they enter G0
True
T/F - During G2, cells are metabolically inactive.
F – they are synthesizing RNA and proteins in preparation for mitosis
What are the three interrelated systems that contribute to the eukaryotic cell cycle?
- Master program of molecular checks and balances to ensure orderly & timely progression through the cell cycle
- within overall regulation of cell cycle, process of DNA synthesis replicates each DNA chromosome into 2 copies w/ near perfection
- Structural & mechanical web of interwoven “cables” and “motors” of mitotic cytoskeleton
that separate DNA copies into daughter cells
What is a chromosome composed of?
Each chromosome composed of one linear DNA molecules along w/ assoc’d proteins (which stabilize DNA, assist in packaging DNA during cell division and influence expression of individual genes)
How does cytokinesis differ in plant and animal cells?
Animals, protists, and many fungi: a groove (furrow) girdles cell and gradually deepens until it cuts cytoplasm into 2 parts
Plants: new cell wall (cell plate) forms between daughter nuclei and grows laterally until it divides cytoplasm
In both cases: the plane of cytoplasmic division is determined by the layer of microtubules that persist at former spindle midpoint
´Time when cells need to be diff from parent cells
meiosis
if eukaryotes require their daughter cells to be exact genetic copies of the parental cell - which process is used?
mitosis
number of chromosome sets in a cell is called a ___
ploidy of the cell or species
equal distribution of daughter chromosomes to each of the two cells the result from cell division is called___
chromosome segregation
The precision of chromosome replication and segregation in the mitotic cell cycle creates a group of cells called a__
clone
true or false: all cells of a clone are genetically identical
yes except in the case of genetic mutation
which phase of the cell cycle varies in length between species?
G1 phase
thus, whether cells divide rapidly or slowly depends on length of g1
furrowing
- the layer of microtubules that remains at the former spindle midpoint expands laterally until it stretches entirely across the dividing cell
- as layer develops, band of microfilaments forms just inside plasma membrane, forming a belt that follows the inside boundary of the cell plane in the microtubule layer
- powered by motor proteins, microfilaments slide together, tightening the band and constricting the cell - forming a groove or furrow in plasma membrane that gradually deepens until daughter cells are separated
- cytoplasmic division isolates the daughter nuclei in the 2 cells at distributes organelles/ other structures approximately equally
mitotic spindle is made of
microtubules and their proteins
primary function of centrioles
to generate the microtubules needed for flagella or cilia, the whiplike extensions that provide cell motility
-when DNA replicates during the S phase of the cell cycle, the centrioles within the centrosomes also duplicate, producing 2 pairs of centrioles
asters
the centrosomes at the spindle tips, which form the poles of the spindle
which organisms do not contain centrosomes or centrioles
angiosperms (flowering plants), gymnosperms (conifers)
- instead, the spindle forms from microtubules that assemble in all directions from multiple MTOCs surrounding the entire nucleus
- when the nuclear envelope breaks down at the end of prophase, spindle moves into the former nuclear region, as in animals
two groups of microtubules (eukaryotes)
kintechore microtubules: connective chromosomes to the spindle poles
nonkintechore microtubules: extend between the spindle poles without connecting to chromosomes; at the spindle midpoint, these microtubules from one pole overlap with the microtubules from the opposite pole
Cyclin- dependent kinases (CDK)
(discovered by Timothy hunt) -directly affect progression (and control) through the cell cycle
- CDKS are protein kinases, enzymes that add phosphate groups to target proteins
- CDK enzymes are called ‘‘cyclin dependant’’ because they are switched on only when combined with another protein called a cyclin
- enzyme activity of CDKs rises and falls with the concentration of the cyclins
- name cyclin reflects cyclic fluctuations in its concentration
- several different cyclin:CDK combinations regulate cell cycle transitions at different ‘‘checkpoints’’
what’s the mechanism that makes chromosomes move?
uncertain. thought at one point that the microtubules pulled chromosomes toward the poles of dividing cells, but recent data suggests they ‘‘walk’’ themselves to the poles along stationary microtubules, using motor proteins in their kintechores
- tubulin subunits of kintechore microtubules disassemble as the kintechores pass along them, thus microtubules become shorter as the movement progresses, like pulling yourself hand over hand up a rope as it falls apart behind you
- in nonkintechore microtubule based movement: entire spindle is lengthened, pushing the poles further apart
- pushing movement produces by microtubules siding over one another in the zone of overlap, powered by proteins acting as microtubule motors
contact inhibition
cell surface receptors in animal cells recognize contact with other cells or molecules of the extracellular matrix, triggering internal reaction pathways that inhibit division by arresting the cell cycle (usually in the g1 phase)
- in response, contract inhibition stabilizes cell growth in fully developed organs and tissues
- As long as cells of most tissues are in contact with one another or with the EC matrix, they are shunted into G0 phase and prevented from dividing
- If contacts are broken, freed cells often enter rounds of division
why is cellular senescence important?
import anti tumour mechanism
- some researchers have stimulated the telomerase of cultured cells, they become immoral and divide out of control
- seems that by the time cells are short on telomeres, many of them are also a long way toward cancerous growth
what is cellular senescence?
- Cellular senescence = loss of proliferative ability over time
- 2 possible “Hayflick factors” responsible: DNA damage and telomere shortening
metastis
when cancer cells divide uncontrollably and lose their adhesions to other cells and become actively mobile, breaking loose from the original tumour and spreading throughout the body
-metastasis promoted by changes that defeat contact inhibition and alter the cell-surface molecules that link cells together or to the extracellular matrix
oncogenes
mutated genes
apoptosis
'’programmed cell death’’
- ancient mechanism common to all mutlicellular eukaryotes studied so far
- initiation of cell death can result from either internal or external signals
reasons for apoptosis
-removing cells that are surplus for development, but also,
beneficial for an organism to provoke apoptosis in cells suffering severe DNA damage, viral infection, or mutations leading to unctontrolled division
-sometimes perfectly normal/healthy cells die by apoktoises: ex cells that make up xylem elements in the vascular tissue of woody plants actually function as ‘‘skeletons’’ and must die to fulfill their function as hollow water conducting pipes
binary fission
mechanism of prokaryotic cell division, splitting or dividing into 2 parts
3 main parts:
(cytoplasmic growth, DNA replication, cell division, producing 2 daughter cells from exact parent cell = binary fission)
where does replication of a bacterial chromosome take place
specific region called the origin of replication (ori)
- middle of the cell where the enzymes for DNA are located
- once the ori has duplicated, two origins migrate toward the two ends (poles) of the cell as replication continues for the rest of the chromosome
describe how the genetic material of eukaryotes is organized (i.e., in chromosomes)
Human DNA is organized into chromosomes which are diploid (is when there are 2 copies which is shown as n). Human chromosomes contain 23 diploid chromosome pairs, since human chromosomes are 2n humans have 2*23 = 46 chromosomes. Sometimes it is organized into haploids (1n which would mostly be microorganisms). Also, they can be organized as ploidy (mostly plants and have multiple chromosomes). When DNA is separated (chromosome segregation) it would be split into 2 sister chromatids
describe the function of mitosis as equal distribution of chromosomes and DNA from the dividing parent cell to two daughter cells.
Chromosomes consist of 2 genetically identical pairs of chromatids which are bound together at the centromere. When they are pulled to each spindle pole the identical pairs are separated and each spindle pole contains 23 chromatids from the 46 that were aligned in metaphase. Replication of the DNA of each individual chromosome creates two identical molecules called sister chromatids. Newly formed sister chromatids are held together until mitosis separates them, placing one in each of the two daughter nuclei. As a result of this precise division, each daughter nucleus receives exactly the same number and types of chromosomes, and contains the same genetic information, as the parent cell entering the division. The equal distribution of daughter chromosomes to each of the two cells that result from cell division is called chromosome segregation.
contrast how binary fission (the cell division in prokaryotes) differs from that in eukaryotes.
Most prokaryotes have a single circular DNA (bacterial Chromosome) vs the multiple chromatids in eukaryotes. DNA is not separated by microtubuli but rather from the origin of replication (ori) in a zipper like fashion where DNA is separated actively on opposite ends of the cell. When replication is complete the cell division begins as the plasma membrane grows inward, and a new cell wall is synthesized. Prokaryotic cells only have one circular DNA and if each daughter cell gets one copy the genetic information was separated evenly where eukaryotic cells have much more DNA to split and more chance of error.
