HUMAN CELL CYCLE:
This our third topic and today we are going to discuss about cell cycle. As we have discussed in our earlier topics about cell, organelles of cell . In this topic we are going discuss how the cells divide ,process of division etc. By using these slides I'm doing an brief explanation video in Tamil and English. My YouTube channel is "Nursing Abstract". You can share your doubts and suggestions in the comment section below . This is my YouTube channel link
https://www.youtube.com/channel/UCZrabu-CtMa5AEexu1j2GNw
English video link: https://youtu.be/-NNLv7cU3X0
Tamil video link: https://youtu.be/4omiJmAZxfw
INTRODUCTION:
Many damaged , dead and worn out cells can be replaced by the growth and division of other similar cells .this allows the effective maintenance of the body tissues.
Cells with nuclei have 46 chromosomes and divide by MITOSIS, the process that result in two new genetically identical daughter cells.
The only exception to this is the formation of gametes (sex cells) i.e. ova and spermatozoa which takes place by meiosis.
The period between 2 cell division is known as CELL CYCLE , which has 2 phases that can be seen on light microscopy: MITOSIS (M phase) and INTERPHASE.
INTERPHASE:
This is the longer phase and 3 different stages are recognized
The FIRST GAP PHASE (G1)-
the cell grow in size and volume . this is usually the longest phase and most variable in length. Sometimes cell do not continue round the cell cycle but enter the resting phase (G0).During this time cell carry their specific functions e.g. secretion , absorption.
S PHASE ( SYNTHESIS OF DNA):
The chromosome replicate forming two identical copies of DNA. Therefore following the S phase ,the cell now has 92 chromosomes i.e. enough DNA for 2 cells and is nearly ready to divide by mitosis.
SECOND GAP PHASE (G2):
There is further growth and preparation for cell division.
MITOSIS:
This is continuous process involving 4 distinct stages visible by light microscopy.
PROPHASE:
Each of the original 46 chromosomes (called chromatid at this stage)is paired with its copy in a double chromosome unit.
The 2 chromatids joined to each other at the centromere.
The mitotic apparatus appears .this consists of 2 centrioles.
Separated by mitotic spindle, which is formed from micro tubules .
The centriole migrate , one to each end of the cell and the nuclear envelope develops.
METAPHASE:
The chromatids align on the center of the spindle, attached to the centromeres.
ANAPHASE:
In this process the centromeres separate ,and one of each pair of sister chromatids (now called chromosomes again) migrates to each end of the spindle as the microtubules that form the mitotic spindle contract.
TELOPHASE:
The mitotic spindle disappears, the chromosomes uncoil and the nuclear envelope reforms.
CYTOKINESIS:
Following telophase ,cytokinesis occurs: the cytosol ,intra cellular organelles and plasma membrane split forming two identical daughter cells.
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Thank you for supporting me . ;I'll try my level best to give the accurate and updated knowledge in all the topics . please visit my YouTube channel named Nursing Abstract ; for viewing a brief explanation in both Tamil and English . see you again in my next post.