Cell Organelle Structure and Function Essentials
Structure and Function of Cell Organelles
Membrane Components
Plasma Membrane
The plasma membrane is a thin envelope surrounding all known cells. It is a lipid-protein structure. The plasma membrane is fluid; molecules move within it to some degree. The fluidity depends on the type of lipid composing it. In animal cells, the membrane's fluidity is controlled by cholesterol molecules. Tissue cells bind through the extracellular matrix.
Cell Wall
The cell wall is found in plant cells. It is an extracellular matrix formed by cellulose fibers, providing rigidity and maintaining cell shape. Walls accumulate substances like lignin, causing them to stiffen.
Internal Cellular Environment
Cytoplasm
The cytoplasm is the space between the cell nucleus and the plasma membrane. It consists of organelles suspended in a watery medium called cytosol. The cytoplasm contains the cytoskeleton, which is composed of microfilaments, microtubules, and intermediate filaments.
Key Organelles
Centrosome
The centrosome is the microtubule organizing center, found only in animal cells. Inside it is the diplosoma, formed by centrioles. Centrioles are formed by three groups of nine microtubules each.
Ribosomes
Ribosomes are organelles located in the cytosol, composed of protein subunits and RNA. Their function is to synthesize proteins.
Endoplasmic Reticulum (ER)
The ER is a membrane system similar to the plasma membrane, forming interconnected tubules and saccules linked to the Golgi apparatus and the cell membrane. Some areas have a granular appearance and are called the rough endoplasmic reticulum (due to ribosomes); others are not granular and are called the smooth endoplasmic reticulum.
Golgi Apparatus
The Golgi apparatus is a pile of membranous sacs located near the nucleus, associated with smaller vesicles.
Lysosomes
Lysosomes are Golgi vesicles that contain acidic digestive enzymes.
Peroxisomes
Peroxisomes are sacs where oxidation reactions occur to remove toxic substances.
Vacuoles
Vacuoles are membranous organelles present in almost all cell types; in plant cells, they are large.
Mitochondria
Mitochondria are organelles located in the cytoplasm of all eukaryotic cells. The inner membrane has folds called mitochondrial cristae; the interior space is the mitochondrial matrix.
Chloroplasts
Chloroplasts are found in plant cells where photosynthesis occurs. They are limited by an external and internal membrane. Inside, they have the stroma. In most of the stroma, stacks of sacs called thylakoids form the grana. The thylakoids contain various photosynthetic pigments.