Mitosis/Meiosis

What is the centromere? How is it related to the chromatids and chromosome?

A DNA-protein complex that binds together each pair of sister chromatids.

What roles does cell division play? In what kinds of situations does mitosis occur?

Cell division enables growth and the replacement of worn-out or damaged cells. Cells may divide to repair injury.

What's the difference between autosomes and sex chromosomes? What's the difference between diploid and haploid cells? Is a zygote diploid or haploid?

Chromosomes other than the sex chromosomes are called autosomes, and sex chromosomes determine the sex of a person. In human fertilization, two 1n haploid cells—an ovum (female gamete) and a sperm cell (male gamete)—combine to form a single 2n diploid cell called the zygote.

What happens during cytokinesis? How is cytokinesis different in plant and animal cells? Why?

Cleavage is the process that separates the two daughter cells in animals. A cleavage furrow on the cell surface forms, as a ring of actin microfilaments, interacting with myosin proteins, begins to contract on the cytoplasmic side of the membrane. Cleavage furrow depends until the dividing cell is pinched in two. In plant cells, a cell plate forms from the fusion of membrane vesicles derived from the Golgi apparatus. The 2 sides of the membrane thus formed join with the plasma membrane, separating the 2 daughter cells. A new cell wall develops between the cells.

Technically speaking, if a cell completed mitosis but failed to complete cytokinesis, what would that cell look like?

Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells. So if cytokinesis was not completed the cell would look like a double cell.

Why is cell cycle control so important? Imagine what happens in a cell in which cell cycle control fails?

Errors in cell cycle can lead to uncontrolled cell growth. Cell division is used to repair injuries

Why is genetic variation so important to a population?

Genetic variations in a population results in adaptation as the individuals best suited to an environment produce the most offspring.

What is G0 (G zero) phase?

If a mammalian cell does not receive a go-ahead signal at the G1 checkpoint, called the "restriction point," the cell will usually exit the cell cycle to a nondividng state called the G0 phase.

Explain the basic concept of the cell cycle checkpoint system.

Important internal and external signals are monitored to determine whether the cell cycle will proceed past the three main checkpoints in the G1, G2, and M phases.

Compare and contrast asexual and sexual reproduction. In what situations would one be favored over the other? Think about pros and cons of each type of reproduction.

In asexual reproduction, a single parent passes all its genes onto its offspring. Occasional genetic differences may result from rare DNA changes known as mutations. A clone is a group of genetically idential offspring of an asexually reproducing individual. In sexual reproduction, an individual receives a unique combination of genes inherited from 2 parents.

3. What's the difference between somatic cells and gametes?

In somatic cells, there are 2 chromosomes of each type (homologous chromosomes); gametes only contain a single set of chromosomes.

Be prepared to understand and explain an example of cell cycle control like the MPF example.

MPF triggers passage past teh G2 checkpoint into M phase. In addition to phosphorylating proteins and other kinases that initiate mitotic events, MPF activates certain proteolytic enzymes that may move the cell past the M phase checkpoint but also that destroy cyclin and thus MPF activity.

How does meiosis differ from mitosis (in process and in results)?

Mitosis produces daughter cells that are genetically identical to teh parent cell. Meiosis prodcues haploid cells that differ genetically from their parent cell and from each other. The 3 unique events that produce this result occur during meiosis I: in prhophase I, when homologous chromosomes synapse to form a tetread, genetic material is rearranged by crossing over between non-sister chrmoatids, which is visible during this stage by the appearance of X-shaped regions called chiasmata. In metaphase I, chromosomes line up in pairs, not as individuals, on the metaphase plate. During anapahse I, the homologous pairs separate and one homolog goes to each pole.

How does bacterial cell division compare to mitosis?

Prokaryotes reproduce by a process known as binary fission. The single circular DNA molecule attached to the plasma membrane replicates; growth of the membrane separates the duplicate chromosomes; the membrane pinches in between the chromosome; and a cell wall develops- creating 2 identical daughter cells.

What is the difference between a chromosome and a chromatid?

The chromatin is copied, so you now have 92 strands, that are each spiraled up to form the chromatids. The 2 copies of each chromatid are joined together by a centromere to form a chromosome. You have 23 pairs of these, for 46 total. Chromatin is the protein-layer coating the chromosomes.

Understand the concept of the mitotic spindle, but don't worry about the details. What is it and what is it made of (physically)? What is the main role it plays during cell division?

The mitotic spindle consists of fibers made of microtubules and associated proteins. The mitotic spindle distributes chromosomes to daughter cells.

Generally speaking, what is the main difference between mitosis and meiosis (cell division that produces eggs and sperm)?

The two cells produced in mitosis contain all the same parts and largely identical genomes. Meiosis produces daughter cells that contain half the number of chromosomes of the parent cell; thus, the duaghter cells are not exact copies. Meiosis leads to the formation of gametes, which then fuse with another gamete during sexual reproduction.

What are the 4 parts of the cell cycle? You should know them in order and be prepared to describe the basic events that happen during each phase. Think about what a cell would look like if we paused the cell cycle at various points in the cell cycle.

mitotic (M) phase, which includes mitosis and cytokinesis, where cytoplasm of daughter cell divides, chromosomes decondense, and plasma membrane closes up and interphase, during which the cell grows and replicates its chromosomes. Interphase usually lasts 90% of the cell cycle, includes the G1 phase, where chromosomes are decondensed, allowing gene expressionthe S phase, where chromosomes replicate, each forming 2 identical sister chromatids, and the G2 phase, where centrioles, mitochondria and other oragnelles replicate for deivision. Spindle formation begins.

Rather than memorize the stages of mitosis, be prepared to describe mitosis in a step-by-step fashion and in your own words. What happens first? Then what? How does mitosis end?

prophase: chromosomes condense premetaphase: chromosomes condense further. Sister chromatids bind kinetochores (the protein structure on chromatids where the spindle fibers attach during cell division to pull sister chromatids apart) which attach to spindle fibers metaphase: chromosomes line up along cell equator anaphase: sister chromatids pulled to opposite poles telophase: nuclear membranes reform. Chromosome segregation is complete. Mitosis ends with cytokinesis.

What are the three sources of genetic variation? Be prepared to explain each source.

random fertilization, crossing over, and independent assortment.

How many chromosomes does a human somatic cell contain? What about a gamete?

somatic cell has 46 chromosomes and gamete has 23 chromosomes