The Cell - Structure and Function

Cell Structure and Organelles

• The cell is the basic unit of the body's structure, consisting of the nucleus, cytoplasm, and cell membrane.

Nucleus

• The nucleus is a specialized spherical mass of protoplasm, usually located at the center of the cell.
• The nuclear membrane is composed of 2 layers with a small space between them.
• Ribosomes are sometimes attached to the outer membrane, while the innermost membrane is smooth.
• The two membranes fuse to form a thin single layer, forming a pore, which serves as an avenue for material exchange between the nucleoplasm and cytoplasm.

Nucleolus

• The nucleolus is the site where ribosomal RNA is synthesized and ribosome subunits are assembled.
• It plays a central role in regulating protein synthesis, earning it the title "pacemaker of the cell".

Chromatin Granules

• Chromatin granules are composed primarily of protein and RNA.
• They are smaller than nucleoli, have an irregular shape and size, and are only seen in non-dividing (interphase) cells.
• Chromatin granules are areas where chromosome filaments or threads are condensed by being wound into a tight coil.
• These chromosomal threads contain genes, which determine heredity.

Organelles in the Cytoplasm

• The endoplasmic reticulum (ER) is a network of channels or tubules pervading the entire cytoplasm.
• The ER is also composed of a lipid bilayer, similar to the cell membrane and nuclear membrane.
• There are two kinds of ER: smooth ER and rough ER.
• Smooth ER produces lipids or carbohydrates and glycogen, and has no ribosomes.
• Rough ER produces and synthesizes proteins and is scattered with regular ribosomes.

Cell Membrane

• The cell membrane, also known as the plasmalemma, is a lipid membranous bilayer.
• It is composed predominantly of phospholipids with a hydrophilic polar head (outside) and a hydrophobic nonpolar tail (inner part).
• The cell membrane is fluid, limiting, and separates the cell's contents from its external environment.