Eukaryotic cells consist of three components: an outer membrane called the plasma membrane, a fluid filling called the cytoplasm, and the intracellular “organs” called the organelles. These organelles are membrane bound and include the nucleus of the cell.
Nucleus (largest membrane bound organelle)
- Location: Surrounded by the cytoplasm and generally is located in the center of the cell.
- Nucleolus is a small dense structure composed of RNA, cellular DNA, DNA binding proteins, and histones (bind DNA together)
- Outer Membrane is a membrane compromised of endoplasmic reticulum
- Primary Function: Cell division and control genetic information
UNDERSTANDING CYTOPLASMIC ORGANELLE FUNCTIONS
Cytoplasm is an aqueous solution (cytosol) that fills the cytoplasmic matrix (space between nuclear envelope and the plasma membrane). The cytoplasm is the bed of the cell.
- Cytosol represents half the volume of a eukaryotic cell. There cytosol is crowded with ribosomes (protein makers).
- Organelles are suspended in the cytoplasm and are enclosed in biologic membranes.
- Function: storage unit for fat, carbohydrate, and secretory vesicles.
Cytosol is the gelatinous, semiliquid portion of the cytoplasm accounting for about 55% of the total cell volume.
- Intermediary metabolism involving enzymatic biochemical reactions
- Intracellular chemical reactions that include synthesis, degradation, and transformation of small organic molecules (simple sugar, fatty acids, and amino acids)
- Ribosomal protein synthesis
- Takes place in free ribosomes and synthesizes identical proteins into factories known as polyribosomes
- Storage of carbohydrates, fats, and secretory vesicles
- Converts excess nutrients not used for ATP production such as excess glucose is store as glycogen
Ribosomes are RNA-protein complexes that are synthesized in the nucleolus and secreted into the cytoplasm through pores in the nuclear envelope called nuclear pore complexes.
- Location: Inside the nucleolus prior to secretion, free floating inside the cytoplasm, and attached to the endoplasmic reticulum.
- Primary Function: Provide sites for cellular protein synthesis.
Endoplasmic Reticulum is a membrane factory that specializes in the synthesis and transport of the protein and liquid components of most of the cell’s organelles.
- Consist of a network of tubular or saclike channel called cisternaethat extend throughout the cytoplasm and are continuous with the outer nuclear membrane.
- The Endoplasmic Reticulum is responsible for much of the cell’s protein synthesis and folding and sensing cellular stress (defensive process by unfolding abnormal or immature proteins).
- Two categories of endoplasmic reticulum
- Rough (granular) endoplasmic reticulum is rough because ribosomes and ribonucleoprotein particles are attached to it.
- Smooth (agranular) endoplasmic reticulum does not carry ribosomes or ribonucleoprotein particles. Surface contains enzymes involved in the synthesis of steroid hormones and reaction required to remove toxic substances from the cell.
Golgi complex is a network of flattened, smooth membranes and vesicles frequently located near the nucleus of the cell. It’s like the ticket and transportation center at Walt Disney World.
- Proteins from the endoplasmic reticulum are processed and packed into small membrane-bound sacs called secretory vesicles. These vesicles collect at the end of the membranous folds of the Golgi bodies called cisternae. Secretory vesicles break off from the Golgi complex and migrate to a variety of intracellular and extracellular dimensions including the plasma membrane. The vesicle fuse with the plasma membrane and their content are released from the cell.
- The Golgi complex is a refining plant for lipids, proteins, glycoproteins, and enzymes of lysosomes. It also directs traffic within the cell.
Lysosomes are saclike structures that originate from the Golgi complex. Think of Lysol and its function to destroy bad things
- Lysosomes contain more than 40 digestive enzymes called hydrolases that catalyze bonds in proteins, lipids, nucleic acids, and carbohydrates. Can digest most cellular constituents back into their basic components (amino acids, fatty acids, and carbohydrates).
- Primary functions
- Digestion of cellular nutrients, intracellular debris, and potentially harmful substances
- Can cause Cellular Self-Digestion. The lysosomal membrane acts as a protective shield between the digestive enzymes and the cytoplasm. Disruption of the membrane by various treatments or cellular injury leads to a release of lysosomal enzymes.
- Residual bodies store indigestible material into vesicles and expel the contents from the cell
- Primary functions
Peroxisomes are membrane-bound organelles that contain several oxidative enzymes such as catalase and urate oxidase. This organelle is similar to lysosomes but are larger, oval, and irregular in shape.
- Like mitochondria, peroxisomes are major sites of oxygen utilization.
- Peroxisomes gets its name from the oxidative reaction it produces. Peroxisomes use oxygen to remove hydrogen atoms from specific substrates in an oxidative reaction that produces hydrogen peroxide (H202).
- Hydrogen peroxide is a power oxidant and can be destructive if it accumulates and escapes from peroxisomes.
- Peroxisomes have another important role in the synthesis of specialized phospholipids necessary for nerve cell myelination.
- Reaction detoxifies various wastes within the cell or foreign components that enter the cell such as ethanol (ethyl alcohol = drinking alcohol). Impairment of peroxisomes can lead to disease.
Mitochondria are organelles found in large numbers of most cells and are responsible for cellular respiration and energy production. This organelle is can appear as sphere, rod, or filamentous bodies and are bound by a double membrane.
- Outer membrane is smooth and surrounds the mitochondrion itself.
- The inner membrane is convoluted in the mitochondrial matrix to form cristae (partial ridge infoldings of the inner membrane).
- Function for mitochondria
- The inner membrane contains enzymes of the respiratory chain. The enzymes are essential to the process of oxidative phosphorylation that generates the cells ATP (energy).
- The outer membrane is permeable (passable) to many substances; however, the inner membrane is highly selective and contains many transmembranous transport systems.
Vaults are cytoplasmic organelles that are much larger than ribosomes and shaped like octagonal barrels. Think of shape as vaulted or cathedral ceilings and their function as trucks.
- Function of vaults
- Function for vaults are not fully understood and there is a lot of speculation regarding their function
- Vaults would dock at the nuclear pores, pick up molecules synthesized by the nucleus and deliver their “load” elsewhere within the cell