Cell cycle Flashcards
What is the cell cycle?
Is the life of a cell from the time it is first formed from dividing parent cell until its own division into two cells.
What does genome mean?
A cell’s endowment of DNA its genetic information
Before the cell divides what does the genome need to do?
It must be copied
How many chromosomes has a human somatic cell?
46 chromosomes - diploid number.
What is mitosis?
The process by which somatic cells divide, forming daughter cells that contain the same chromosome number as the parent cell
Human gametes
sperm and egg cells - are haploid and have half the number of chromosomes as a diploid cell.
They have 23 chromosomes
Meiosis is a special type of cell division that ends in gametes.
Sister chromatids
When the chromosomes are replicated, each duplicated chromosome consists of two sister chromatids attached by a centromere
the two sister c. have identical DNA sequences.
Mitosis
Division of the cell’s nucleus.
It may be followed by cytokinesis which is the division of the cytoplasm.
The phases of mitosis
Interphase Prophase Metaphase Anaphase Telophase
INTERPHASE - mitosis
G1 phase - the cell grows while carrying out cell functions unique to its type.
S phase - the cell continues to carry out its unique functions and it duplicates its chromosomes
G2 phase - is the period after the chromosomes have been duplicated and just before mitosis.
PROPHASE - mitosis
- The chromatin becomes more tightly coiled into discrete chromosomes
- The nucleoli disappear
- The mitotic spindle begins to form in the cytoplasm
PROMETHAPHASE - mitosis
- The nuclear envelope begins to fragment, allowing the microtubules to attach to the chromosomes.
- The two chromatids of each chromosome are held together by the centromere. The centromere contains protein kinetochores on each chromatid, which is where the microtubules will attach.
METAPHASE - mitosis
- The microtubules move the chromosomes to the metaphase plate at the equator of the cell. The microtubule complex is referred to as the spindle.
- The centrioles have migrated to opposite poles in the cel, riding along on the developing spindle.
ANAPHASE - mitosis
- Sister chromatids begin to separate, pulled apart by motor molecules interacting with kinetochore microtubules.
- The cell elongates, as the nonkinetochore microtubules ratchet apart, again with the help of motor molecules.
- By the end of anaphase, the opposite ends of the cell both contain complete and equal sets of chromosomes.
TELOPHASE - mitosis
- The nuclear envelopes reform around the sets of chromosomes located at the opposite end of the cell.
- The chromatin fiber of the chromosomes becomes less condensed.
- Cytokinesis begins, during which the cytoplasm of the cell is divided. In animal cells, a cleavage furrow forms that eventually divides the cytoplasm; in plant cells, a cell plate forms that divides the cytoplasm.
- Prokaryotes replicate their genome by binary fission rather than mitosis.
What controls the steps of the cycle?
Cell cycle control system - moves the cell through its stages by a series of checkpoints, during which molecular signals tell the cell either to continue dividing or to stop.
The major cell cycle includes what?
G1 phase checkpoint
G2 phase checkpoint
M phase checkpoint.
G1 phase checkpoint
If the cell gets the go-ahead signal at this checkpoint, it usually completes the whole cell cycle and divides. If it does not receive the go-ahead signal, it enters a nondividing phase called G0 phase.
G0 phase
Most mature human cells remain in G0 and never receive the molecular signal to divide.
Muscle and nerve cells never divide, but liver cells can respond to signals, moving from G0, back to the cell cycle at G1
Kinases
Are the protein enzymes that control the cell cycle.
They exist in the cells at all times but are active only when they are connected to cyclin proteins.
Thus they are called cyclin-dependent kinases (cdks)
Specific kinases give the go-ahead signals at the G1 and G2 checkpoints
Normal cell division has two key characteristics:
density-dependent inhibition - the phenomenon in which crowded cells stop dividing
Anchorage dependency - Normal cells must be attached to a substratum, like the extracellular matrix of tissues to divide.
Transformation
The process that converts a normal cell to a cancer cell
A tumor
a mass of abnormal cell within otherwise normal tissue. If the abnormal cells remain at the original site, the lump is called a benign tumor. A malignant tumor becomes invasive enough to impair the functions of one or more organs.
Metastasis
Occurs when cells separate from a malignant tumor and enter blood or lymph vessels and travel to other parts of the body.
