Cell and Cell Structure

I. Overview

II. Plasma Membrane (Cell Membrane) Diagram

III. Cytoplasm

IV. Membrane Transport Processes

V. Cell Division (Cell Life Cycle)

Multicellular organisms develop from a zygote, which is formed by the fusion of a sperm and an egg (gametes). Each gamete has half a half compliment of chromosomes (haploid number) and when combined gives rise to a zygote with a complete set (diploid number) of chromosomes. In order for the zygote to develop into a multicellular organism, it must repeatedly undergo cellular divisions. The series of events a cell (or zygote) undergoes that ultimately produces a new cell is called the cell cycle.

The cell cycle is divided into two major stages: Mitosis and Interphase. Interphase is subdivided into three phases: S, G1, and G2 phases. During the S phase, DNA is duplicated in order to provide a full compliment for the new cell, called a daughter cell. The G phases are periods of growth and differentiation of a cell. The cell spends 90% of its time in interphase. Diagram

Mitosis, in comparison to interphase, is subdivided into four phases: Prophase, Metaphase, Anaphase, and Telophase. During prophase, chromosomes (consisting of DNA and proteins) become distinguishable in the nucleus. In early prophase, the nuclear membrane breaks down, and the chromosomes condense and become distributed throughout the cytoplasm. At high magnifications, sister chromatids may be detected. Chromatids, which are joined to each other in a region called the centromere, are identical copies made during DNA replication. The chromosomes may be sorted or arranged with the aid of contractile fibers called mitotic spindle fibers. By late prophase the chromosomes are drawn toward the middle of the cell.

In metaphase, sister chromatids become arranged toward the center of the cell (equatorial plate) in a plane at right angles to the long axis of the spindle. Once all chromatids are aligned at the equatorial plate, anaphase begins. The pair of chromosomes that comprise the chromatid are separated and transported to the polar (opposite) ends of the cell. Telophase will begin. During this stage in plant cells a cell plate will form and divide the original cell into two daughter cells. In animal cells, the cytoplasm pinches inward forming the cleavage furrow. Towards the end of telophase, in both plant and animal cells, the nuclei begin to reorganize, chromosomes uncoil, and the nuclear membrane reforms. Diagram and uncontrolled mitosis? Diagram

VI. Protein Synthesis Diagram Diagram