GEN BIO - Lesson 5

39問 • 2年前

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involves the distribution of identical genetic material or DNA to two daughter cells. What is most remarkable is the fidelity with which the DNA is passed along, without dilution or error, from one generation to the next

Cell Division

functions in reproduction, growth, and repair.

Cell Division

a critical control point in the Cell Cycle where ‘stop’ and ‘go-ahead’ signals can regulate the cell cycle

The Checkpoint

Three major checkpoints are found in the

G1, G2 and M Phase of the cell cycle

the Restriction Point

The G1 Checkpoint

ensures that the cell is large enough to divide and that enough nutrients are available to support the resulting cell

the G1 checkpoint

Non dibisyong state

most cells in the human body are in

ensures that DNA replication in S phase has been successfully completed.

the G2 checkpoint

ensures that all of the chromosomes are attached to the mitotic spindle by a kinetochore

The Metaphase

protein which activates or deactivates another protein by phosphorylating them.

Kinase

the ‘go-ahead’ signals at the G1 and G2 checkpoints. The ____ that drive these checkpoints must themselves be activated.

Kinase

Activating molecule

Cyclin

(apparent division)—is nuclear division; the process by which the nucleus divides to produce two new nuclei. Mitosis results in two daughter cells that are genetically identical to each other and to the parental cell from which they came.

Mitosis

the division of the cytoplasm. Both mitosis and cytokinesis last for around one to two hours.

Cytokines

the preparatory stage, during this, centrioles move toward opposite sides of the nucleus.

Prophase

first become visible during early prophase as long, thin, and intertwined filaments but by late prophase, chromosomes are more compacted and can be clearly discerned as much shorter and rod-like structures.

Chromosomes

is when chromosomes become arranged so that their centromeres become aligned in one place, halfway between the two spindle poles. The long axes of the chromosomes are 90 degrees to the spindle axis. The plane of alignment is called the metaphase plate.

Metaphase

is initiated by the separation of sister chromatids at their junction point at the centromere. The daughter chromosomes then move toward the poles.

Anaphase

is when daughter chromosomes complete their migration to the poles. The two sets of progeny chromosomes are assembled into two-groups at opposite ends of the cell. The chromosomes uncoil and assume their extended form during interphase. A nuclear membrane then forms around each chromosome group and the spindle microtubules disappear. Soon, the nucleolus reforms.

Telophase

Parts of Mitosis

1. Cytokinesis 2. Prophase 3. Metaphase 4. Anaphase 5. Telophase

reduces the amount of genetic information

Meiosis

results in reducing the number of chromosomes (reduction division). In most cases, the division is accompanied by cytokinesis.

First Meiotic Division

has been subdivided into five substages:

Prophase I

5 Stages of Prophase 1

1. Leptonema 2. Zygonema 3. Pachynema 4. Diplonema 5. Dyakinesis

Replicated chromosomes have coiled and are already visible. The number of chromosomes present is the same as the number in the diploid cell

Leptonema

Homologue chromosomes begin to pair and twist around each other in a highly specific manner. The pairing is called synapsis. And because the pair consists of four chromatids it is referred to as bivalent tetrad.

Zygonema

Chromosomes become much shorter and thicker. A form of physical exchange between homologues takes place at specific regions.

Pachynema.

The process of physical exchange of a chromosome region is called

Crossing over

The two pairs of sister chromatids begin to separate from each other. It is at this point where crossing-over is shown to have taken place. The area of contact between two non- sister chromatids, called chiasma, become evident.

Diplonema

The four chromatids of each tetrad are even more condensed and the chiasma often terminalize or move down the chromatids to the ends. This delays the separation of homologous chromosomes.

Dyakinesis

The spindle apparatus is completely formed and the microtubules are attached to the centromere regions of the homologues. The synapsed tetrads are found aligned at the metaphase plate (the equatorial plane of the cell) instead of only replicated chromosomes.

Metaphase 1

Chromosomes in each tetrad separate and migrate toward the opposite poles. The sister chromatids (dyads) remain attached at their respective centromere regions.

Anaphase I

The dyads complete their migration to the poles. New nuclear membranes may form. In most species, cytokinesis follows, producing two daughter cells. Each has a nucleus containing only one set of chromosomes (haploid level) in a replicated form.

Telophase I

the number is reduced to half in meiosis.

Second Meiotic Division

—The dyads contract

Prophase II

The centromeres are directed to the equatorial plate and then divide

Anaphase II

The monads are at the poles, forming two groups of chromosomes. A nuclear membrane forms around each set of chromosomes and cytokinesis follows. The chromosomes uncoil and extend.

Telophase II

The telophase stage of mitosis is accompanied by cytokinesis. The two nuclei are compartmentalized into separate daughter cells and complete the mitotic cell division process. In animal cells, cytokinesis occurs by the formation of a constriction in the middle of the cell until two daughter cells are formed. The constriction is often called cleavage, or cell furrow. However, in most plant cells this constriction is not evident. Instead, a new cell membrane and cell wall are assembled between the two nuclei to form a cell plate. Each side of the cell plate is coated with a cell wall that eventually forms the two progeny cells.

Cytokinesis

GEN BIO

Precious Mendez · 71問 · 2年前

GEN BIO