Lipids, Cell Biology, and Immunology Overview
Lipids
Properties and Classification
Lipids are organic molecules composed of carbon, hydrogen, and oxygen. Some complex lipids also contain nitrogen, phosphorus, or sulfur. Key properties include insolubility in water, solubility in organic solvents, and low density.
Lipids are classified into:
- Fatty acids
- Saponifiable lipids:
- Simple: Triacylglycerols and waxes
- Complex: Phosphoglycerides and sphingolipids
- Non-saponifiable lipids:
- Steroids
- Terpenes
- Icosanoids
Cholesterol
Cholesterol, a sterol, is present in all animal cells, blood, and bile. It plays a crucial structural role in cell membranes, influencing their fluidity. Cholesterol is also a precursor for bile acids and sex hormones.
Cellular Processes
Glycolysis
Glycolysis is the metabolic pathway that oxidizes or ferments glucose to produce energy. This 10-step enzymatic process occurs in the cytosol, converting glucose into two pyruvate molecules. Pyruvate can then enter other metabolic pathways for further energy production.
Fermentation
Fermentation is an anaerobic, incomplete oxidation process. Microorganisms and animal cells use fermentation to produce organic end products and generate energy, albeit less efficiently than respiration.
Fermentation has various industrial applications, including producing wine, beer, bread, and preserving food. Biotechnology utilizes fermentation in food processing for products like yogurt and cheese.
Osmosis in Cells
In a hypotonic environment, animal cells swell due to water influx. Lacking a cell wall, they can burst (cytolysis). Plant cells, with their rigid cell walls, experience turgor pressure as the vacuole swells, preventing bursting.
In a hypertonic environment, animal cells shrink (plasmolysis) as water exits. In plant cells, the vacuole and cytoplasm shrink, and the cell membrane separates from the cell wall (plasmolysis).
Endocytosis: Pinocytosis and Phagocytosis
Pinocytosis and phagocytosis are endocytic processes. Pinocytosis involves the intake of fluids and solutes through small vesicles at coated pits on the cell membrane. Clathrin proteins facilitate this process.
Phagocytosis involves ingesting large particles. Specific receptors on the phagocyte’s surface bind to the particle, triggering pseudopodia formation that engulf the particle into a phagosome.
Peroxisomes
Peroxisomes are spherical organelles found in plant and animal cells. They contain oxidative enzymes (oxidases and peroxidases) that do not produce energy but generate heat.
Peroxisomes perform functions such as fatty acid and amino acid degradation, and detoxification. In plants, specialized peroxisomes called glyoxysomes convert stored fats in seeds into sugars for embryo development.
Immunology
Immunity and Immunodeficiency
Innate immunity is a non-specific, inherent defense mechanism present from birth. It lacks memory but can distinguish self from non-self.
Immunodeficiency is a condition where the immune system fails to protect the body, increasing susceptibility to infections.
Allergy and Inflammation
Allergy is a harmful hypersensitivity reaction. Inflammation is a non-specific response to injury, occurring in vascularized connective tissue. It aims to isolate, destroy harmful agents, and repair damaged tissue.
Antibodies
Antibodies, also known as immunoglobulins or gamma globulins, are proteins produced by plasma cells derived from B lymphocytes. They neutralize pathogens, mark them for destruction, and stimulate phagocytosis. Antibody types include IgD, IgE, IgG, IgA, and IgM.