| What is the cell cycle? | Series of biological processes that are repeated.
Divided into two major parts: M phase and interphase.
Interphase (19hours- 3 stages) lasts longer than mitosis (1 hour-5/4 stages) |
| Do all cells undergo cell division? | Certain cell types are highly differentiated such as muscle fibers, red blood cells and neurons.
They usually leave the cell cycle and enter a phase called G0 which is a quiescent state, where some cells are blocked in that state and others regenerate. |
| Talk about rapid interphase phase. | For fertilized eggs, interphase is very short and zygote divides many times without increasing its size. However M and interphase are intimate (no one can occur without the other) |
| Talk about interphase. | Divided into 3 stages: G1 (gap) S (synthesis) G2 (gap)
Each is characterized by specific processes.
During interphase the cell doubles the amount of content so that the daughter cells are supplied with the necessary cellular structures organelles and components (macromolecules)
Lipids, proteins and carbohydrates are synthesized throughout the whole interphase, however DNA is only synthesized during S producing two cohesion and centromere linked sister chromatids |
| Talk about the centrioles during cell cycle. | They duplicate as the cell makes the G1-S transition but they do not separate from each other until late prophase.
Centriole duplication is the assembly of new centriole at the right angles with respect to older ones. |
| How is cell cycle controlled? | Since any disturbance of cell cycle will lead to cell death or cancer, it is controlled and may not be disturbed (mutation, chemicals, signalling pathways)
The most important check point is the G1-S transition, the other is G2-M transition, where there is replication there is cell division.
The cycle is controlled by CNC (cyclin dependent proteins) with the aid of G1 cyclin and M cyclin by catalyzing interaction between subunits
These cnc phosphorylate some proteins to initiate cell division (condensation...) |
| What is mitosis? | Mitos means thread,
Mitosis is the process of nuclear division whereby replicated DNA is partitioned into two daughter cells nuclei.
It is the mode of asexual reproduction for many bacteria, plants... and are the growth factors.
It is characterized by production of two daughter cells identical to mother cell
Divided into four stages without a sharp limit between them |
| Talk about prophase. | First stage.
Characterized by complex events, condensation of long chromatin fibers into chromosomes to make their seggregation possible. Which is triggered by phosphorylation of Histones and non-histones. Condensins are proteins that attach to chromosomes while condensing, scaffold shape.
Cohesins join chromatids as well as centromere.
Kinetochore proteins assemble to form button like structures bound on centromeres of each chromatid. These mediate the attachment to microtubules and motor proteins.
Nucleoli disappear because no NOR. |
| Talk about mitotic spindle | Duplicated centrioles is initially happening.
Disassembly of cytoskeleton components (MT AND IF) then pair of centrosomes increase formation of MT so that asters appear. centrosomes repel to opposite sides because of MT synthesis extending the spindle, some cells have no centrioles so minus ends of MT join by activity of motor proteins.
Spindle is of three kinds:
Astral MT (outward of centrosome, help positioning and division plane)
Chromosomal or Kinetochore MT (Attach to chromosomes)
Polar or interpolar MT (overlap with counterpart from opposite pole, responsible for cell stretching during cytokinesis. |
| Talk about cell organelles during prophase. | Lamina is disassembled by Cdk so that envelope is fragmented that either merge with ER or remain vesicles. NPC are dismantled
Endomembrane system disassemble and fragment equally between cells whereas mitochondria, chloroplast and peroxisomes remain intact |
| Talk about Late prophase. | Growth and shrinking of MT, allowing them to meet kinetochores chromosomes move due to motor proteins, and are anchored to more than one MT plus end, in end they oscillate around equator plate by polymerization and depolymerization of MT, |
| Talk about metaphase | Alignment of centromeres of all chromosomes across spindle on equator plate/ metaphase plate.
Congression is force generated by motor proteins moving chromosomes.
Movement is associated with lengthening of kinetochore MT and shortening of long ones.
All three MT types are present with loss compensated by polymerization at plus end |
| Talk about Anaphase. | There is a checkpoint before it called spindle checkpoint where cells are arrested (blockage) until all chromosomes align perfectly controlled by MAD2 protein which is removed when alignment is perfect
Chromosomes split in synchrony and chromatids migrate lead by centromeres. Pulled by dyneins and kinesins low velocity
they move farther apart by polar tubules elongation. |
| Talk about telophase. | Uncondensation of chromosomes starts, nuclei turning to interphase making nuclear lamina and reassembly of nuclear envelope and endomembrane system.
Lamins assemble chromosomes to vesicles which makes the nucleus again. |
| Talk about cytokinesis. | Cytoplasm division to give two daughter cells independent of nuclear division but occurs simultaneously some cell types no cytokinesis occurs forming syncituim multi-nucleated cell like drysophila.
It begins in end of telophase where clear indentation occurs at cell circumference forming equatorial. Which deepens to form cleavage furrow making contractile ring for separation.
Plant cells have no rigidity (cell wall formation after cell plate(phragmoplast) formation MT driving golgi to form cell wall components whereas cellulose occurs in situ) |
