The Nucleus & Cell Cycle
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Summary
The nuclear envelope
- consists of 2 parallel membranes.
- The nucleoplasm is a fluid consists of water, proteins, dissolved ions
The nuclear pore complex (NPC)
- regulates the traffic between the cytoplasm and the nucleus.
- contains 8 protein subunits arranged in a framework surrounding the pore.
- The nuclear ring is attached to the nuclear “basket.”
The nuclear chromatin
- consists of DNA bound to histones arranged as nucleosomes.
- The DNA is a double-stranded poly-nucleotide chain forming a double helix.
- Each two opposite bases form a “base pair”.
- Genes are located at specific regions on the DNA molecule.
- DNA specifies the synthesis of proteins because it contains a triplet code: every 3 bases stand for one amino acid.
The RNA
- Three types of RNA are involved in gene expression: mRNA, rRNA, and tRNA.
- The nucleolus synthesizes rRNA forming new ribosomes.
The cell cycle
- Consists of 4 phases, termed G1 "gap1", S "synthesis", G2 "gap2", and M "mitosis" phases.
- Interphase is the phase between 2 successive divisions.
- Cyclins and checkpoint proteins control the cell cycle.
Mitosis occurs in 4 successive phases: “prophase, metaphase, anaphase, and telophase”.
Apoptosis
- Active, physiological, non-accidental form of cell death.
- It occurs in response to physiological stimuli as in the developing tissues.
- involved in many physiological and pathological processes.
- Requires 2 sets of enzymes called caspases: initiators and executioners.
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