Samenvatting van het onderwerp genetica uit Campbell Biology a Global Approach, 11e druk. Deze samenvatting is inclusief aantekeningen van hoorcollege's en eventuele werkcollege's.
Summary of the topic of genetics from Campbell Biology a Global Approach, 11th edition. This summary includes notes o...
Genetics 1&2 (BOOK)
CH12. Mitosis
12.0
Cell division is an integral part of the cell cycle, the life of the cell from them moment it was formed
out of a parent cell, to the moment it splits in two daughter cells.
12.1
The genome is the genetic information of a cell. DNA molecules are packaged into chromosomes.
Each eukaryotic chromosome consists of one very long linear DNA molecule. The entire complex of
DNA and proteins (building material of chromosomes) is called the chromatin. Somatic cells (all
human body cells except reproductive cells = gametes, they have half that much) each contain 46
chromosomes.
In the picture below, chromosome duplication and distribution during cell division is shown = mitosis.
After mitosis which is also the division of the genetic material in the nucleus, usually cytokinesis
follows, which is the division of the cytoplasm.
G2/interphase, prophase, prometaphase, metaphase, anaphase and telophase
Mendelian Genetics
, The mitotic spindle is very important during mitosis. It consists of fibers made of microtubules and
associated proteins.
In animal cells the spindle starts at the centrosome, which organizes the cell’s microtubules. During
the interphase in animal cells, the single centrosome duplicates and these two move apart to other
sides of the cell during the prophase and prometaphase. From each centrosome radial array of short
microtubules extend called aster. The spindle also includes aster, spindle microtubules and
centrosomes.
Both sister chromatids have kinetochore which are the bonding spots at the centromere. The
kinetochore of both chromatids are faced in different directions. When a microtubule binds to the
kinetochore they pull the chromosome toward that pole. When both kinetochore are connected to
microtubule from different poles, a tug-of-war starts. During the metaphase the centromeres are
midway between the spindle’s two poles, this is called the metaphase plate.
Anaphase begins when the cohesin bondings that holds both daughter chromosomes together are
separated by the enzyme separase.
The microtubules that are not bonded to a kinetochore called nonkinetochore microtubules are
responsible for elongating the cell during anaphase. The nonkinetochore microtubules from opposite
poles overlap but during metaphase motor proteins ‘walk them away’ from eachother.
Cytokinesis
In animal cells, cytokinesis occurs by cleavage. The first sign of cleavage is the cleavage furrow, a
shallow grove in the cell. On the inside of this furrow actin microfilaments and myosin molecules
interact causing the ring/furrow to extract pulling of a drawstring.
Cytokinesis in plant cells is different because of the cell walls. In plant cells a cell plate is produced by
coalescing vesicles from the golgi apparatus with microtubules. This cell plate slowly fuses with the
membrane and new cell walls are built for both daughter cells.
Binary fission is another way to divide what happens in prokaryotes (bacteria and archaea). During
this process the cell grow to roughly twice its size and then splits.
In some bacteria cell division start when DNA replicates at a specific place called the origin of
replication. When replicating, the other chromosome quickly moves to the other side of the cells
before the cell got twice as big and splices by pinching the membrane inwards.
12.3
The eukaryotic cell cycle is regulated by a molecular control system. This makes that some type of
cells divide often (skin cells) an others don’t (nerve cells).
The events of the cell cycle are directed by a distinct cell cycle control system, a set of molecules in
the cell that triggers and coordinates. In the cell cycle there are multiple checkpoints, which function
as control points where ‘stop’ and ‘go-ahead’ signals can regulate the cycle.
The regulating molecules are mainly proteins of two types protein kinases ((in)activating other
proteins) and cyclins. Many kinases are inactive, but become active when they attach to a cyclin.
These kinases are called cyclin-dependent kinases Cdks. The activity rises and falls because the
concentration cyclin fluctuates. These level rises during S and G2 phase and falls abruptly during M
phase. MPF is a cyclin-Cdk complex and it triggers the cell’s passage into the M phase. During
anaphase, MPF helps switching itself off by initiating a process that leads to the destruction of its
own cyclin.
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