A&P Lecture 1.2: Cytoplasm

This is an in depth  explanation of the Cytoplasm as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE NOTE 1.2

CYTOPLASM, CYTOSOL, CYTOSKELETON, 

AND CYTOPLASMIC INCLUSION

CYTOPLASM

Cytoplasm, the cellular material outside the nucleus but inside the plasma membrane, is about half cytosol and half organelles.

CYTOSOL

Cytosol consists of a fluid portion, a cytoskeleton, and cytoplasmic inclusions. The fluid portion of cytosol is a solution with dissolved ions and molecules and a colloid with suspended molecules, especially proteins. Many of these proteins are enzymes that catalyze the breakdown of molecules for energy or the synthesis of sugars, fatty acids, nucleotides, amino acids, and other molecules.

CYTOSKELETON

The cytoskeleton supports the cell and holds the nucleus andother organelles in place. It is also responsible for cell movements,such as changes in cell shape and the movement of cell organelles. The cytoskeleton consists of three groups of proteins: microtubules, actin filaments, and intermediate filaments ( figure 3.27 ).

Microtubules are hollow tubules composed primarily of protein units called tubulin. The microtubules are about 25 nanometers (nm) in diameter, with walls about 5 nm thick. 

Microtubules vary in length but are normally several micrometers (μm) long. Microtubules play a variety of roles within cells. They help provide  support and structure to the cytoplasm of the cell, much like an internal scaffolding. They are involved in the process of cell division and in the transport of intracellular materials, and they form essential components of certain cell organelles, such as centrioles, spindle fibers, cilia, and flagella.

Actin filaments, or microfilaments, are small fibrils about 8 nm in diameter that form bundles, sheets, or networks in the cytoplasm of cells. These filaments have a spiderweb-like appearance within the cell. Actin filaments provide structure to the cytoplasm and mechanical support for microvilli. Actin filaments support the plasma membrane and define the shape of the cell. Changes in cell shape involve the breakdown and reconstruction of actin filaments. These changes in shape allow some cells to move about. Muscle cells contain a large number of highly organized actin filaments, which are responsible for the muscle’s contractile capabilities.

Intermediate filaments are protein fibers about 10 nm in diameter. They provide mechanical strength to cells. For example, intermediate filaments support the extensions of nerve cells, which have a very small diameter but can be a meter in length. 

CYTOPLASMIC INCLUSION

The cytosol also contains cytoplasmic inclusions, which are aggregates of chemicals either produced by the cell or taken in by the cell.For example, lipid droplets or glycogen granules store energy-rich molecules; hemoglobin in red blood cells transports oxygen; melanin is a pigment that colors the skin, hair, and eyes; and lipochromes are pigments that increase in amount with age. Dust, minerals, and dyes can also accumulate in the cytoplasm.