Chapter 5 Flashcards
stages of the cell cycle
Interphase and Mitotic stage
Interphase
Three stages
G1—stage before DNA synthesis.
> cell doubles its organelles and accumulates material for DNA synthesis.
> G0 occurs in some cells: pause and carry out normal functions but don’t prepare to divide.
S—DNA synthesis.
> DNA replication occurs.
> After DNA replication, each chromosome has gone from one DNA molecule, called a chromatid, to two DNA molecules, called sister chromatids.
G2—stage after DNA synthesis.
> the cell synthesizes proteins for cell division
Mitotic stage
Mitosis—division of the nucleus, follows interphase
> The sister chromatids separate into daughter chromosomes.
> Distributed to two daughter nuclei.
Cytokinesis—division of the cytoplasm, follows mitosis
> Two daughter cells that are identical to the mother cell are the result.
What is the purpose of checkpoints during the cell cycle?
Three checkpoints control the cell cycle.
> G1—Are the building blocks available? Is DNA damaged?
> G2—Is DNA replication complete? Is the DNA damaged?
> S—Are chromosomes going to be properly distributed?
Checkpoints are critical for preventing cancer development.
A damaged cell should not complete mitosis.
stages in mitosis
prophase
prometaphase
metaphase
anaphase
telophase
prophase
Starts the process of nuclear division
Centrosomes have duplicated; they begin moving to opposite poles (end of the nucleus).
Spindle begins to form.
Nuclear membrane fragments; nucleolus begins to disappear.
Chromatin condenses and chromosomes become visible.
> Each composed of two sister chromatids held together at centromere.
prometaphase
Kinetochores appear on each side of the centromere.
Kinetochore of each chromatid is attached to a kinetochore spindle fiber.
Spindle fibers extend from the poles to the chromosomes.
Kinetochore fibers pull chromosomes back and forth toward alternate poles to begin aligning chromosomes.
metaphase
Spindle is fully formed and consists of poles, asters, and fibers.
> Polar fibers overlap.
Centromeres of chromosomes are aligned at the metaphase plate.
anaphase
Centromeres divide, and sister chromatids are moved to opposite poles by fibers.
> Kinetochore spindle fibers shorten, pulling daughter chromosomes.
> Polar spindle fibers push the poles apart.
telophase
Spindle disappears.
Nuclear membrane components reassemble around daughter chromosomes.
Chromosomes become more diffuse again.
Nucleolus appears in each daughter nucleus.
Cytokinesis begins.
compare Meiosis and Mitosis
DNA replication occurs only once prior to either meiosis or mitosis.
Meiosis requires two nuclear divisions, mitosis requires one.
Meiosis produces four daughter cells, mitosis produces two.
Four daughter cells from meiosis are haploid; two from mitosis are diploid.
Daughter cells from meiosis are genetically variable, while those from mitosis are genetically identical.
Occurrence
> Meiosis occurs only at certain times of the life cycle of sexually reproducing organisms.
> After the reproductive organs mature to produce gametes.
> Mitosis takes place almost continuously in all tissues as part of growth and repair.
apoptosis
is programmed cell death - decreases number of cells
somatic cells
are the body cells that continue to undergo cell division even as an adult.
proto-oncogenes
Encode proteins that promote the cell cycle and prevent apoptosis.
Mutate to become oncogenes (cancer-causing genes).
tumor suppression genes
Encode proteins that stop the cell cycle and promote apoptosis.
Mutation causes the uncontrolled cell growth.
