Chapter 12: The Cell Cycle Flashcards
Cell division is essential for
The perpetuation of life. It provides for the development, growth, and repair of multicellular organisms; and the reproduction of unicellular organisms
A cell’s complement of DNA is called its
Genome
A genome is organized into
Chromosomes
Each eukaryotic chromosome is
A very long, linear DNA molecule with associated proteins that help structure the chromosome and control the activity of genes
The entire complex of DNA and protein is called
Chromatin
Duplicated chromosomes consist of
Two identical sister chromatids are attached along their length by proteins known as cohesion (attachment known as sister chromatid cohesion)
Each sister chromatid has a
Centromere: a region where proteins bind to specific centromeric DNA sequences and hold the chromatids closely together
When sister chromatids separate each is considered a
Chromosome
Meiosis produces
Daughter cells that have half the number of chromosomes as the parent cell; when a sperm fertilizes an egg (both of which are formed by meiosis in animals), the chromosome number is restored, and the somatic cells of the new offspring again have two sets of chromosomes
How many chromosomes are in your somatic cells?
46
How many chromosomes are in your gametes?
23
How many chromatids are in one of your somatic cells that has duplicated its chromosomes prior to mitosis?
92 (each duplicated chromosome consists of two sister chromatids)
What event is common to all three subphases of interphase
Cell growth (produces proteins and cytoplasmic organelles)
What key event happens during the S phase?
Duplication of the chromosomes, which is crucial for eventual division of the cell (DNA synthesis)
Describe one chromosome as it proceeds through an entire cell cycle, starting with G1 of interphase and ending with telophase of mitosis
G1 phase - chromosome consists of a long, thin chromatin fiber made of DNA and associated proteins; growth and metabolic activities occur
S phase - (still chromatin fiber) chromosomes are duplicated and DNA is synthesized
G2 phase - growth and metabolism continue
Mitotic phase- cell division consisting of mitosis and cytokinesis
Prophase - sister chromatids become condensed into discrete chromosomes and the mitotic spindle begins to form
Prometaphase - kinetochore fibers from opposite ends of the mitotic spindle attach to the kinetochores of sister chromatids
Metaphase - chromosomes are all aligned at the metaphase plate
Anaphase - the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell
Telophase - The chromatin fiber uncoils and is surrounded by a reforming nuclear membrane; daughter nuclei are forming and cytokinesis has typically begun
What is MPF?
Known as a “maturation-promoting factor” or “M-phase-promoting factor” it is a complex that is only activated when bound to a cyclin-dependent kinase and triggers the passage past the G2 checkpoint into M phase
Describe the concentrations of MPF throughout the cell cycle
It has a high concentration as it triggers mitosis but is reduced at the end of mitosis because it depends on the concentration of cyclin in the cell
Describe the concentrations of Cdk throughout the cell cycle
Constant throughout the cycle but rises and falls with changes in the concentration of its cyclin partner
Describe the concentrations of cyclin throughout the cell cycle
Has a cyclically fluctuating concentration in the cell (increases during G1, S, and G2, and breaks down at the end of mitosis)
In addition to phosphorylating proteins and other kinases that initiate mitotic events, MPF can
Activate a protein breakdown process that destroys its cyclin component and thus MPF activity during anaphase
The Cdk portion of the complex remains to
Associate with new cyclin synthesized during the S and G2 phases of the next cycle
If a mammalian cell does not receive a go-ahead signal at the G1 checkpoint, the cell will usually exit the cell cycle to a nondividing state called
The G0 (Gzero) phase
An internal signal is required to move past the M phase checkpoint into
Anaphase
Density-dependent inhibition of cell division appears to involve
The binding of cell-surface proteins of adjacent cells, which sends a cell-division-inhibiting signal to both cells
Only after all chromosomes are attached at their _________ to __________ is the enzyme separate activated and the cohesions holding sister chromatids together are cleaved
Kinetochores; spindle microtubules
Certain nutrients and regulatory proteins called ________ _________ have been found to be essential for cells to divide in culture.
Growth factors
Most animal cells also show ________ _________ and must be attached to a substratum in order to divide
Anchorage dependence
When grown in cell culture, cancer cells do not exhibit
Density-dependent inhibition or anchorage dependence, do not depend on growth factors to divide, do not undergo apoptosis when appropriate, and may continue to divide indefinitely instead of stopping after the typical 20 to 50 divisions of normal mammalian cells in culture
Cells in culture that can divide indefinitely are said to have undergone
Transformation
When a normal undergoes changes that begin its conversion to a cancer cell, the body’s immune system may destroy it. If it proliferates, a mass of abnormal cells develops within a tissue. A _________ __________ remains at its original site and can be removed by surgery
Benign tumor
The cells of a __________ ___________ are considered to be transformed cells. They have significant genetic changes that enable them to invade and disrupt the functions of one or more organs
Malignant tumor, an individual with a malignant tumor is said to have cancer
Malignant tumor cells lose their attachment to other cells and may enter the blood and lymph systems and spread to other sites, a process called
Metastasis
Radiation treatment preferentially affects cancer cells because
They are unable to repair the resulting DNA damage
Chemotherapy involves drugs that
Affect stages in the cell cycle and therefore target actively dividing cells
Most cells that will no longer divide are in this phase
G zero
Sister chromatids separate and chromosomes move apart in this phase
Anaphase
Mitotic spindle begins to form in this phase
Prophase
Cell plate forms or cleavage furrow pinch cells apart in this phase
Telophase
Replication of DNA occurs in this phase
S phase
Chromosomes line up at central plane during this phase
Metaphase
Nuclear membranes form around separated chromosomes during this phase
Telophase
Chromosomes become visible during this phase
Prophase
Kinetochore-microtubule interactions move chromosomes to the midline during this phase
Metaphase
Restriction point occurs in this phase
G1 phase
One of the differences between prokaryotic binary fission and eukaryotic mitosis is that
The duplicated signle chromosome does not separate along a mitotic spindle in prokaryotic cells (prokaryotes do not do mitosis because they do not have a nucleus)
A plant cell has 12 chromosomes at the end of mitosis. How many chromosomes would it have in the G2 phase of its next cell cycle
12
How many chromatids would this plant cell have in the G2 phase of its cell cycle
24
The longest part of the cell cycle is
Interphase
In animal cells, movement of the chromosomes is accomplished using ___________, but division of the cytoplasm requires the action of __________
Microtubules; actin filaments
In eukaryotic organisms, chromosomes are duplicated
Before mitosis (in S phase)
When do chromatids become chromosomes
When cohesins are degraded by separase (in anaphase)
A cell in this phase has the least amount of DNA
G zero
What is not true of a cell plate
It results from the fusion of microtubules in a dividing plant cell (actually is golgi vesicles)
A cell that passes the restriction point in G1 will most likely
Undergo chromosome duplication
During cell division, cyclin combines with Cdk to form a complex called MPF; this complex
Moves the cell past the G2 checkpoint into mitosis and promotes the degradation of cyclin, but leaves Cdk intact
What initiates the separation of sister chromatids
Activation of a regulatory protein complex and the enzyme separase after all kinetochores are attached to microtubules
Knowledge of the cell cycle control system will be most beneficial to understanding
Cancer
Vinblastine is a chemotherapeutic drug used to treat certain cancers. It acts by interfering with microtubule assembly. The effectiveness of vinblastine must be related to
Disruption of mitotic spindle formation (prevents cell division during metaphase)
Checkpoints in cell division
G1 checkpoint - (the most important)
G2 checkpoint - a cyclin-Cdk complex in animal cells called MPF acts at the checkpoint as a go-ahead signal, triggering the events of mitosis
M checkpoint - (internal signal) anaphase does not begin until all the chromosomes are properly attached to the spindle at the metaphase plate.
S phase checkpoint - stops cells with DNA damage from proceeding in the cell cycle
