Cellular Nutrition and Metabolism: A Comprehensive Guide
Nutrition
Introduction
Nutrition is the process by which organisms obtain energy and matter from their environment to maintain life functions. It involves three main phases: intake of materials, processing of matter and energy, and excretion of waste products.
Intracellular Digestion
In intracellular digestion, a food particle is enclosed within a vesicle called a phagosome. The phagosome fuses with a lysosome containing digestive enzymes, forming a digestive vacuole. Nutrients are absorbed into the cytoplasm, and undigested residues are expelled.
Extracellular Digestion
In extracellular digestion, lysosomes release enzymes outside the cell to break down large food molecules into smaller, absorbable nutrients.
Autotrophs
Autotrophs synthesize organic matter from inorganic nutrients like water, minerals, and CO2, using energy from light or chemical reactions. Algae are an example of autotrophs.
Heterotrophs
Heterotrophs obtain organic matter by consuming other organisms or organic substances from the environment. Animals are heterotrophs.
Molecular Transport
Passive Transport
Passive transport moves substances across the cell membrane without energy expenditure, along the concentration gradient. This includes simple and facilitated diffusion.
Active Transport
Active transport moves substances against the concentration gradient, requiring energy from ATP. This is often carried out by protein pumps, such as the sodium-potassium pump.
Transport of Large Molecules
Exocytosis
Exocytosis is the expulsion of waste products or secretions from the cell.
Endocytosis
Endocytosis is the process of incorporating large particles into the cell.
Metabolism
Metabolism encompasses all enzyme-catalyzed chemical reactions within cells. It involves the exchange of matter and energy with the environment, maintaining cellular structures and providing energy. Metabolic processes are characterized by:
- Enzyme catalysis
- Linked metabolic pathways
- Oxidation-reduction reactions
Oxidation-Reduction Processes
Oxidation involves the loss of electrons (electron donor), while reduction involves the gain of electrons (electron acceptor).
Energy Intermediary: ATP
ATP (adenosine triphosphate) is a nucleotide that transfers energy from catabolic reactions to anabolic reactions.
Electron Transport
Coenzymes like NAD+, NADP+, and FAD facilitate electron transfer in redox reactions.
Catabolism
Catabolism involves the breakdown of complex molecules into simpler ones, releasing energy, electrons, and H+. This can occur through:
Fermentation
Fermentation is an anaerobic process where cells obtain energy by partially oxidizing glucose. Examples include alcoholic fermentation (beer, wine) and lactic acid fermentation (yogurt, cheese).
Cellular Respiration
Cellular respiration is the complete oxidation of glucose in the presence of O2, producing ATP. It involves:
- Glycolysis: Glucose is converted into pyruvic acid.
- Krebs cycle: Acetyl-CoA is oxidized to CO2.
Anabolism
Anabolism involves the synthesis of complex molecules from simpler ones, requiring energy input. There are two main types:
Photoautotrophs
Photoautotrophs use light energy to build organic molecules (photosynthesis).
Chemoautotrophs
Chemoautotrophs use energy from exergonic chemical reactions (chemosynthesis).
Photosynthesis
Photosynthesis is the process by which photoautotrophs synthesize organic matter from inorganic substances using light energy. It involves a light-dependent phase (thylakoid membrane) and a light-independent phase (stroma).
Chemosynthesis
Chemosynthesis is the synthesis of organic matter from inorganic matter using energy from chemical reactions.
Cellular Responses
Cellular responses allow organisms to react to environmental changes. These responses can be:
- Static: No cell movement
- Dynamic: Involve movement (taxis)
Types of Movement
- Ciliary and flagellar movement: Used for locomotion in unicellular organisms and movement of substances in multicellular organisms.
- Amoeboid movement: Cell movement through pseudopods.
- Contractile movement: Shortening of the cell through actin and myosin interaction.