Chapter 12: The Cell Cycle Flashcards
Chromosomes
Structures of DNA molecules and associated proteins that consist of a single long strand of DNA
Chromatin
Complex of DNA and proteins that compose the chromosome
Somatic cells
All cells except reporductive cells
Gametes
Sperm and egg cells; have half as many chromosomes as somatic cells
Sister chromatids
Identical copies of chromosomes which are joined together along their lengths by protein complexes called cohesions
A chromatid is one of the two identical halves of a chromosome
Sister chromosomes are duplicaed during the S phase of mitosis and condense during prophase and prometaphase of mitosis
Centromere
Narrow central region where sister chromatids are attached most closely that gives them a narrow “waist”
Cytokinesis
The division of the cytoplasm that follows mitosis and completes the mitotic phase
Usually is well under way by late telophase
Phases of the cell cycle
Interphase- accounts for 90% of the cell cycle; cell grows by producing proteins and cytoplasmic organelles
- G1 (first gap) phase
- S (synthesis) phase- duplication of the chromosomes occurs
- G2 (second gap) phase
Mitotic Phase- shortest part of the cell cycle
- Mitosis
- Cytokinesis
Mitotic spindle
Forms in the cytoplasm during prophase; consists of fibers composed of microtubules and associated proteins, the centrosomes, and the asters
Spindle microtubules elongate (polymerize) by incorporating more subunits of the protein tubulin and shorten (depolymerize) by losing subunits
Aster
A radial array of short microtubules that extend from each centrosome
Kinetochore
Structure made up of proteins that have assembled on specific section fo DNA at each centromere
During prometaphase some spindle microtubules attach to the kinetochores and are called kinetochore microtubules
Cleavage
Process by which cytokinesis occurs in animal cells
First sign of cleavage is the appearance of a cleavage furrow- a shallow groove in the cell surface near the old metaphase plate
A contractile ring of actin microfilaments on the cutoplasmic side of the furrow contracts to complete cytokenisis
Cell plate
Process by which cytokenisis occurs in plant cells
Vesicles derived from the Golgi apparatus move along microtubules to the middle of the cell where they coalesce
Cell plate enlarges until its surrounding membrane fuses with the plasma membrane along the perimeter of the cell
Prokaryotic reporduction
Prokaryotes (bacteria annd archea) and single-celled eukaryotes (amoeba) undergo binary fission in which cells grows to roughly double in size and then divides to form two identical cells
The plasma membrane pinches inward, dividing the cell into two
Checkpoints
A control point in the cell cycle where “stop” and “proceed” signals can regulate the cycle
Three checkpoints:
1. G1 checkpoint
2. G2 checkpoint
3. M checkpoint
If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide
If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase
Cell cycle clock
Rhythmic fluctuations in the abundance and activity of cell cycle control molecules pace the sequential events of the cell cycle
Regulator molecules are two types of proteins:
1. Protein kinases- enzymes that activate or inactivate other proteins by phosphorylating them; cyclin dependent kinases (Cdks)
2. Cyclins- a protein that gets its name from its cyclically fluctuating concentrations
Together, Cdks and cyclin form a complex called maturation promoting factors (MPF)
Maturation promoting factors (MPF)
Complexes formed by Cdk and their cyclin partners
Act as M-phase promoting factors that trigger a cell’s passage into M phase past the G2 checkpoint
MPF activity peaks in conjunction with cyclin concentration; cyclin levels rise during the S and G2 phases and then fall abruptly during the M phase
G2 of interphase
Prophase
Prometaphase
Metaphase
Duplicated chromosomes line up along the metaphase plate
In humans all 46 chromosomes line up along the metaphase plate
Anaphase
Cohesins are cleaved by an enzyme called separase
Sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell
Nonkinetochore microtubules from opposite poles overlap and push against each other, elongating the cell
Telophase and cytokenesis
Genetically identical daughter nuclei form at opposite ends of the cell
Cytokinesis begins during anaphase or telophase and the spindle eventually disassembles
Density-dependent inhibition
An external physical factor that limits cell division; a phenomenon in which a cell in a crowded environment stops growing
The binding of cell-surface proteins to their counterparts on adjoining cells sends a division-inhibiting signal which limits further growth even in the presence of growth factors
Anchorage dependence
A cell must be attached to a substratum such as the extracellular matrix of a tissue in order to divide
Anchorage is signaled to the cell cycle control system via pathways involving plasma membrane proteins and elements of the cytoskeleton
Transformation
Regarding normal vs. cancerous cells
A process that imparts the ability of cells to be able to divide indefinitely and behave like cancer cells
