Mitosis Flashcards
T/F. Mitotic cell division occurs in all embryonic tissues and continues at a lower rate in most adult tissues other than end cells, e.g. neurones. Thus, mitosis is vital for both tissue formation and maintenance.
True.
In cultured mammalian cells, the duration of the cell cycle varies but is usually about 24h. Mitosis itself occupies only ____ of the total, whereas DNA synthesis for replication takes ____.
20min to 1 h; 6–8 h
Each chromosome has its own pattern of DNS synthesis. What are examples of genes that are replicated late and early.
Early - housekeeping genes and expressed tissue- specific genes
Late - centromeric heterochromatin and non-expressed tissue-specific genes
Five arbitrary stages are apparent in mitosis: _____. A cell that is not actively dividing is in _____. This phase includes ____, periods of the cell cycle and during this phase the nuclear material appears relatively homogeneous.
interphase, prophase, metaphase, anaphase and telophase; interphase; G1 (gap 1), S (DNA synthesis) and G2 (gap 2)
Replication of DNA occurs during the ____, so that the nucleus in G2 contains ____ the diploid amount of DNA present in G1.
S phase; twice
The last chromosome to complete replication.
The inactive X
As the cell prepares to divide, the chromosomes condense and become visible. At this stage, it can be seen that each chromosome consists of a pair of long thin parallel strands, or ____, which are held together at the centromere.
sister chromatids
Cross-overs, with exchange of material between sister chromatids, may occur at this stage.
Pachytene stage of prophase
What staining may be used to demonstrate these sister chromatid exchanges.
BrDU
In this stage, the nuclear membrane disappears and the nucleolus becomes undetectable as its component particles disperse. The centriole divides and its two products migrate towards opposite poles of the cell.
Prophase
The acrocentrics are often clustered at this stage (satellite association).
Metaphase
____ begins when the chromosomes have reached their maximal contraction. They move to the equatorial plate of the cell and the spindle forms.
Metaphase
____ begins when the centromeres divide and the paired chromatids separate, each to become a daughter chromosome. The spindle fibres contract and draw the daughter chromosomes, centromere first, to the poles of the cell.
Anaphase
Anaphase is triggered when a large protease named ____ becomes activated following the destruction of its inhibitory regulator, _____.
separase; securin
A surveillance mechanism known as the _____ operates in which centromeres that are not properly attached to spindle microtubules (i.e. in chromosomes that are not yet fully aligned on the spindle) prevent securin degradation and thus prevent the onset of anaphase
‘spindle assembly check- point’
