Cell Division Flashcards
Define Mitosis
Mitosis is division of the nucleus into two genetically identical daughter nuclei each with an identical set of chromosomes
Define Cytokinesis, when it occurs? Is the occurrence the same in plants and animal cells
the division of the cytoplasm to form two cells. It occurs after mitosis and is
diferent in plant and animal cells.
State the two main phases of the cell cycle
1) Interphase — Culmination of G1, S phase & G2
2) M phase (Cell Division) —- Culmination of Mitosis & Cytokinesis
List the stages of the cell cycle in order
1) G1
2) S
3) G2
4) Mitosis
(Cell cycle is cyclical, thus, stages repeat)
Which phase of the cell cycle is the longest?
Interphase
Describe what happens in interphase (with refer to G1, S & G2)
Interphase consists of three phases, the G1 phase, S phase
and G2 phase.
1) During the first phase of growth (G1), the cell grows and the synthesis of new organelles takes place in the cytoplasm. also a time of intense biochemical activity in the cytoplasm and organelles and there is an accumulation of energy store as the prepares for DNA replication.
2) Followed by S phase — a period of synthesis of DNA (S), when each chromosome makes a copy of itself. It is said to replicate. The two identical structures formed are called chromatids. The chromatids remain attached until they divide during mitosis
3) Finally in (G2) — There is a continuation of the earlier time of intense biochemical activity as the cell finishes growing and prepares for cell division
What regulates the cell cycle?
a molecular control system
Describe how the molecular control system functions (Mechanism of Cyclin Action – Cyclins and cell cycle control)
Each of the phases of the cell cycle involves many important tasks. A group of proteins called cyclins is used to ensure that tasks are performed at the correct time and that the cell only moves on to the next stage of the cycle when it is appropriate.
The molecular control signal substances in the cytoplasm of cells are proteins known as kinases and cyclins. Kinases are enzymes that either activate or inactivate other proteins. Kinases are activated by specific cyclins and attach phosphate groups to other proteins in the cell. The attachment of phosphate triggers the other proteins to become active and carry out tasks specific to one of the phases of the cell cycle, so they are referred to as cyclin-dependent kinases (CDKs). As the concentrations of cyclins increase, they combine with CDK molecules to form a complex that functions as a mitosis promoting factor (MPF). As MPF accumulates, it triggers chromosome condensation, fragmentation of the nuclear membrane, and, finally, spindle formation – that is, mitosis is switched on. By anaphase of mitosis, destruction of cyclins commences (but CDKs persist in the cytoplasm).
State the function of a centromere
structure that attaches replicated strands of DNA
Distinguish between a Chromatin & a Chromosome in the cell cycle
1) DNA is organized as chromosomes during the process of mitosis (condense in prophase via supercoiling, and decondense in telophase)
2) Whilst DNA is organised as chromatin in all non-dividing cells and throughout the process of interphase
Distinguish between Chromatids and Chromosomes
As the DNA is replicated during the S phase of interphase, the chromosome will initially contain two identical DNA strands
These genetically identical strands are called sister chromatids and are held together by a central region called the centromere
When these chromatids separate during mitosis, they become independent chromosomes, each made of a single DNA strand
Describe the process of mitosis
Process of mitosis:
1) During Prophase
DNA supercoils and chromosomes condense (becoming visible under microscope). Chromosomes are comprised of genetically identical sister chromatid held together by a centromere. Spindle microtubules form and extended from each pole to the equator. Also the nuclear membrane breaks down and the nucleus dissolves.
2) In Metaphase:
Microtubule spindle fibres from both poles are attached to each centromere, on opposite sides.. Microtubule depolymerization causes spindle fibers to shorten in length and contract. This causes chromosomes to align along the center of the cell (equatorial plane or metaphase plate).
3) In Anaphase:
Continued contraction of the spindle fibres causes genetically identical sister chromatids to separate. Once the chromatids separate, they are each considered an individual chromosome in their own right. The genetically identical chromosomes move to the opposite poles of the cell
4) In Telophase:
Once the two chromosome sets arrive at the poles, spindle fibres dissolve. The Chromosomes uncoilsand decondense (no longer individuallyvisible). Nuclear membranes reform around each chromosome set.
The cell divides (cytokinesis) to form two cells with genetically identical nuclei
Define the mitotic index & its function
The mitotic index is a measure of the proliferation status of a cell population. It is the ratio between the number of cells in mitosis in a tissue and the
total number of observed cells
The mitotic index is used by doctors to predict how rapidly a tumor will grow and therefore what treatment is needed. A high index indicate a fast-growing tumour
Define Cyclins
Cyclins are a family of regulatory proteins that control the progression of the cell cycle. Cyclins activate cyclin-dependent kinases (CDKs), which control cell cycle processes through phosphorylation
Define tumors
tumors are abnormal cell growths resulting from uncontrolled cell division and can occur in any tissue or organ. Diseases caused by the growth of tumors are collectively known as cancers
