Lecture 15 Flashcards
The key roles of cell division
the ability of organisms to reproduce best distinguishes living things from non-living matter
the continuity of life is based on the reproduction of cells or cell division
Why do cells divide?
to pass on genetically identical information to offspring
The cell cycle
the life of a cell from the time it is formed form a parent cell until its own division into two cells
cell division is only a small part of the cell cycle
Cell division importance in multicellular organisms
development from a fertilised cell
growth
repair
cell division
most cell division results in daughter cells with identical genetic information
All the DNA in a cell constitutes the cells genome
a genome can consist of a single DNA molecule or a number of DNA molecules
DNA molecules in a cell are packaged into chromosomes
Somatic cells
non-reproductive cells
two sets of chromosomes
Gametes
reproductive cells
have half as many chromosomes as somatic cells
Distribution of chromosomes during cell division
in preparation for cell division, DNA is replicated and the chromosomes condense
each duplicated chromosomes have two sister chromatids, which separate during cell division
the centromere is the narrowest waist of the duplicated chromosome, where the two chromatids are most closely attached
Eukaryotic cell division consists of:
mitosis (division of nucleus)
cytokinesis (division of cytoplasm)
Meiosis
yields non-identical daughter cells that have only one set of chromosomes, half as many as the parent cell
Phases of the cell cycle
mitotic (M) phase (mitosis and cytokinesis)
interphase (cell growth and copying of chromosomes in preparation for cell division)
Mitosis- 5 phases
prophase
prometaphase
metaphase
anaphase
telophase
The mitotic spindle
is an apparatus of microtubules that controls chromosomes movement during mitosis
during prophase assembly of spindle microtubules begins int he centrosome, the microtubule organising centre
the centrosome replicated forming two centrosomes that migrate to opposite ends of the cell, as spindle microtubules grow out of them
An aster
a radial array of short microtubules
extends from each centrosome
Spindle in pro metaphase
some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes
The mitotic spindle at metaphase
- condensed chromatin
- mitotic spindle is made of tubule
- chromosomes bind to spindle via kinetochores
- the kinetochore is bound to centromeric DNA
Mitotic spindle at anaphase
sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell
microtubules shorten by depolymerising at their kinetochore ends
How do we know which end microtubule shorten
microtubules were labelled fluorescently
photobleaching was used to recolour a section of the microtubule
as the chromosomes moved towards the poles, the pole-side Mts stayed the same length but the kinetochore side Mts shortened
Non-kinetochore microtubules
from opposite poles overlap and push against each other elongating the cell
Cytokinesis
in animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow
in plant cells, a cell plate forms during cytokinesis
