Biology - Chapter 5: Cell Division

Gamete

haploid sex cell, e.g. sperm or egg

Cleavage furrow

indentation in the plasma membrane of animal cells during cell division; formation marks the start of cytokinesis

Homologous chromosome

member of a pair of chromosomes that are alike and come together in synapsis during prophase of the first meiotic division

What are the differences of mitosis and meoisis?

-DNA replication takes place only once prior to either meiosis or mitosis. However, meiosis requires two nuclear divisions, whereas mitosis requires only one nuclear division. -Meiosis followed by cytokinesis produces four daughter cells. Mitosis followed by cytokinesis results in two daughter cells. -The four daughter cells following meiosis are haploid and have half the chromosome number as the parental cell. The daughter cells following mitosis have the same chromosome number as the parent cell. -The daughter cells resulting from meiosis are not genetically identical to each other or to the parental cell. The daughter cells resulting from mitosis are genetically identical to each other and to the parent cell.

Describe the stages of the cell cycle.

1. Interphase: duplication of cell contacts(longest phase) G1- growth, increase cytoplasm S-duplication of chromosomes G2- growth, preparation for division 2. Mitotic phase: division of the nucleus (includes prophase, metaphase, anaphase, and telophase) Cytokinesis- division of cytoplasm and organelles Result: 2 genetically identical cell

Checkpoint

A control point in the cell cycle where stop and go-ahead signals can regulate the cycle.

Describe the human life cycle in terms of haploid and diploid cells.

A haploid sperm (n) and a haploid egg (n) join together at fertilization, resulting in a zygote with diploid number of chromosomes (2n)

Chromosome

A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.

Egg

Also called an ovum; haploid cell that is usually fertilized by a sperm to form a diploid zygote.

Cell cycle

An ordered sequence of events in eukaryotes that involves cell growth and nuclear division; consists of the stages G1, S, G2, and M.

Somatic cell

Body Cell; Excludes cells that undergo meiosis and become sperm or egg

What happens at the G1 checkpoint?

Cell cycle main checkpoint. If DNA is damaged, apoptosis may occur. Otherwise, the cell is committed to divide when growth signals are present and nutrients are available.

Explain what is happening during the mitosis phase: metaphase.

Centromeres of duplicated chromosomes are aligned along at the metaphase plate (center of fully formed spindle). Kinetochore spindle fibers attached to the sister chromatids come from opposite spindle poles.

Spindle

Collection of microtubules that assist in the orderly distribution of chromosomes during cell division.

Explain what is happening during the mitosis phase: telophase.

Daughter cells are forming as nuclear envelopes and nucleoli reappear. Chromosomes will become indistinct chromatin.

Describe the process of human gamete production.

Gametes are formed through a process of cell division called meiosis. This two-step division process produces four haploid daughter cells. Haploid cells contain only one set of chromosomes. When the haploid male and female gametes unite in a process called fertilization, they form what is called a zygote.

Explain how mutations in tumor suppressor genes and protooncogenes (RAS, p53, BRCA can lead to cancer)

If tumor suppressor genes are not functioning properly, they can't act as gatekeepers, and instead will allow cells to divide continuously. Unrestricted cell growth is a characteristic of cancer.

Sperm

Male sex cell

What is the purpose of meiosis?

Meiosis is a modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication. It results in cells with half the number of chromosome sets as the original cell, producing gametes, and introducing genetic variability.

What happens at the G2 checkpoint?

Mitosis checkpoint. Mitosis will occur if DNA has replicated properly. Apoptosis may occur if the DNA is damaged and cannot be repaired.

Explain the difference between the nuclear division of mitosis and cytoplasmic division of cytokinesis.

Mitosis is the nuclear division in which the chromosome number stays constant. Cytokinesis usually accompanies mitosis, but they are separate processes. Division of the cytoplasm begins in anaphase and continues to telophase but does not reach completion until just before the next interphase. By that time, the newly forming cells have received a share of the cytoplasmic organelles that have duplicated.

Polar body

Nonfunctional product of oogenesis produced by the unequal division of cytoplasm in females during meiosis. In humans, three of the four cells produced by meiosis are polar bodies.

Explain what is happening during the mitosis phase: prophase.

Nucleus has disappeared, and duplicated chromosomes are visible. Centrosomes begin moving apart, and spindle is in the process of forming.

spermatogenesis

Production of sperm in males by the process of meiosis and maturation.

Apoptosis

Programmed cell death; involves a cascade of specific cellular events leading to death and destruction of the cell.

What are the steps of meiosis and what is happening at each step

Prophase 1, Metaphase 1, Anaphase 1, Telophase 1, Interkinesis, Prophase 2, Metaphase 2, Anaphase 2, Telophase 2, Daughter cells.

Explain what is happening during the mitosis phase: anaphase.

Sister chromatids part and become daughter chromosomes that move toward the spindle poles. In this way, each pole receives the same number and kinds of chromosomes as the parent cell.

What happens at the M checkpoint?

Spindle assembly checkpoint. Mitosis will not continue if chromosomes are not properly aligned.

Interphase

Stages of the cell cycle (G1, S, G2) during which growth and DNA synthesis occur when the nucleus is not actively dividing.

Explain what is happening during the mitosis phase: prometaphase.

The kinetochore of each chromatid is attached to a kinetochore spindle fiber. Polar spindle fibers stretch from each spindle pole and overlap.

Mitosis

The stage of cellular reproduction in which nuclear division occurs; process in which a parent nucleus produces two daughter nuclei, each having the same number and kinds of chromosomes as the parent nucleus.

What is the purpose of mitosis?

To divide the nucleus. A parent nucleus will produce two daughter nuclei, each having the same number of chromosomes as the parent nucleus.

Haploid

cell condition in which only one of each type of chromosome is present

Diploid

cell condition in which two of each type of chromosome are present

Centromere

constriction where sister chromatids of a chromosome are held together

zygote

diploid cell formed by the union of two gametes; the product of fertilization

Cytokinesis

division of the cytoplasm following mitosis or meosis

Crossing-over

exchange of segments between nonsister chromatids of a bivalent during meiosis

Proto-oncogenes

gene that promotes the cell cycle and prevents apoptosis; may become an oncogene through mutation

Oncogenes

genes that cause cancer

Oogenesis

production of eggs in females by the process of meiosis and maturation

What are the phases of mitosis?

prophase, prometaphase, metaphase, anaphase, telophase

What is the purpose of the cell cycle?

regulate cell division