Cell Biology: Cytoplasm Overview

Cytoplasm Definition

• Cytoplasm is the semi-viscous ground substance of a cell.
• It comprises all the volume of substance outside the nucleus and inside the plasma membrane.
• It can also be described as the non-nuclear content of protoplasm.
• In prokaryotes, all cellular components are within the cytoplasm.
• In eukaryotes, the nucleus is separated from the cytoplasm.

Cytoplasm Composition

• It's the substance of life, acting as a molecular soup.
• Cellular organelles are suspended in the cytoplasm.
• Organelles are held together by a lipid bilayer membrane.
• Cytoplasm was discovered in 1835 by Robert Brown and other scientists.

Components of Cytoplasm

• Cytosol: A gel-like substance that is not occupied by organelles.
• Organelles: Internal sub-structures within cells with specific functions; examples include mitochondria, endoplasmic reticulum, Golgi apparatus, vacuoles, lysosomes, and chloroplasts (in plant cells).
• Cytoplasmic inclusions: Insoluble particles or molecules that stay suspended in the cytosol; they do not have a membrane and include starch, glycogen, crystals, lipid droplets, etc.

Properties of Cytoplasm

• Primarily composed of 70-80% water, usually colorless.
• Contains proteins, carbohydrates, salts, sugars, amino acids, and nucleotides.
• Contains dissolved nutrients and waste products.
• Ectoplasm: The outer, clear, glassy layer of cytoplasm (cell cortex)
• Endoplasm: The inner granular mass of cytoplasm.
• Plasmogel: The thick, jelly-like peripheral zone of cytoplasm.
• Plasmosol: The thin, liquefied surrounding area of the nuclear zone.
• Cytoplasm's physical nature varies, sometimes resembling a colloidal solution, a gel-like, or glass-like substance.
• It is viscous and elastic, capable of deformation and regaining its original shape.
• Cytoskeleton gives the cell shape.
• Cytoplasm facilitates movement of cellular materials via cytoplasmic streaming (cyclosis).
• Being rich in salts, it is a good conductor of electricity.
• The cytoplasm shows differential staining, with areas stained basophilic termed as ergatoplasm.

Functions of Cytoplasm

• Site of most enzymatic reactions and metabolic activity.
• Location for cell expansion and growth.
• Provides a medium for organelles to remain suspended.
• Acts as a buffer, protecting genetic material and organelles from damage.
• Begins cellular respiration with glycolysis (providing intermediates used by mitochondria for ATP generation).
• Location for mRNA translation into proteins on ribosomes.
• Contains monomers for cytoskeleton generation.
• Plays a role in creating order within the cell, with specific locations for organelles.

Cytoplasmic Streaming and Inheritance

• Cytoplasmic streaming is critical for positioning chloroplasts close to the plasma membrane (increasing photosynthesis efficiency) and for distributing nutrients.
• Cytoplasmic Inheritance: Some organelles (chloroplasts and mitochondria) have their own genomes and are inherited from the mother (via the oocyte). These organelles replicate independently of the nucleus and respond to cell needs.