Cell biology

Topics: Cell cycle, Mitosis, Chromosome Pages: 8 (1863 words) Published: February 9, 2014


Important Questions of this chapter:

**Definition
Cell cycle
2. Homologous Chromosome
3. Sister Chromatid
4. Synapsis
**Short Questions
1.Describe the chief events of mitosis and show how these differ from meiosis. (V.V.I.) 2. What ‘checkpoints’ occur in cell cycle? What is the role of each? **Long Questions
1.Describe the phases of the cell cycle and the events that characterize each phase.

Answer of short Definition is given below

1. Cell Cycle:
The cell cycle is an orderly sequence of events that occurs from the time when a cell is first formed until it divides into two new cells. Or the period from the end of the first mitosis division of a cell to the end of the second mitosis division. 2.Homologous chromosomes:

Homologous chromosomes line up and then separate. In Meiosis 1, chromosomes in a diploid cell resegregate, producing four haploid daughter cells. It is this step in Meiosis that generates genetic diversity. 3.Sister Chromatid: Sister chromatids are generated when a single chromosome is replicated into two copies of itself, these copies being called sister chromatids. Compare sister chromatids to homologous chromosomes, which are the two different copies of a chromosome that diploid organisms (like humans) inherit, one from each parent. (collected from internet.see more from book & slide  :P) 4. Synapsis: (also called syndesis) is the pairing of two homologous chromosomes that occurs during meiosis. This is not to be confused with mitosis. Mitosis also has prophase, but does not ordinarily do pairing of two homologous chromosomes. (collected from internet.see more from book & slide  :P)

Answer of short Question

Mitosis

Meiosis

Cell type

Somatic cell

Germ cell

DNA replication

One

One

Cell division

One

Two

Daughter cell

Two

Four

Chromosome number
in daughter cell

Same

Half

Biological significance

Ensure the consistency of the DNA

Ensure the consistency of the chromosome number
Embodies the diversity of biological species

1. Describe the chief events of mitosis and show how these differ from meiosis. ***Answer is given below    (very important question, so 3 star)

2. What “checkpoints” occur in the cell cycle? What is the role of each? *Answer is given below :
There are three major checkpoints exist within the cell cycle, where the cell is monitored or “checked” before it can proceed to the next stage of the cycle to ensure that incomplete or damaged chromosomes are not replicated and passed on to daughter cells. The three checkpoints are:

1.G1/S Checkpoint
Role: it monitors the cell size achieved following the previous mitosis, and whether the DNA has been damaged. 2. G2/M Checkpoint
Role: where physiological conditions in the cell are monitored prior to entering mitosis.it prevents the initiation of mitosis until DNA replication is completed. 3. M checkpoint: The final Checkpoint occurs during mitosis and is called the M checkpoint. Role: It maintains the integrity of the genomes occurs toward the end of mitosis.as a result of this checkpoint, the chromosomes do not separate until a complete complement of chromosomes has been organized for distribution to each daughter cell.

Answer of long Question
**Describe the phases of the cell cycle & the events that characterize each phase. What are the stages of the cell cycle? How does the cell cycle? How does the cell cycle vary among different types of cells?    (Too long) Answer of this Question:

*Stages of the Cell Cycle: there are two stages of cell cycle, they are given below. 1. Interphase
2. Mitotic phase
* Interphase: Interphase is the "holding" stage or the stage between two successive cell divisions. Interphase, which appears to the eye to be a resting stage between cell divisions, is actually a period of diverse activities. Most of the cell cycle is spent in interphase. Cell spends about 90% of the time in interphase. Mice...
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