Osmosis, Carbohydrates, Lipids, and Proteins in Cells
Osmosis: Diffusion of Water
Osmosis is the movement of water from a hypotonic (diluted, more water) medium to a hypertonic (concentrated, less water) medium across a semi-permeable membrane. Water moves until the concentrations are equal (isotonic), and osmosis stops.
Osmotic Processes in Cells:
Cells are surrounded by isotonic media to prevent harmful osmotic processes. Animal cells are more sensitive due to their thin plasma membrane.
Processes Affecting Cells:
1. Plasmolysis: Occurs when a cell is in a hypertonic medium, losing water and potentially dying. Cells can recover if water loss is minimal.
2. Turgor: Occurs when a cell is in a hypotonic medium, gaining water and increasing in volume. Excessive water intake can lead to cell lysis (rupture).
Water: Essential for Life
Each water molecule (H2O) has two hydrogen atoms and one oxygen atom joined by covalent bonds. Water molecules form hydrogen bonds due to the attraction between opposite charges.
Properties:
Water is an excellent solvent, separating ionic substances like NaCl into ions and surrounding them. Water has a high specific heat due to hydrogen bonds, slowing temperature changes.
Carbohydrates
Carbohydrates are biomolecules made of carbon (C), oxygen (O), and hydrogen (H). They are classified into:
1. Monosaccharides: Simple sugars with 3-7 carbon atoms. Aldoses have an aldehyde group, and ketoses have a ketone group. They are sweet, white, and soluble in water, providing energy. Glucose (fruit and honey), fructose (fruit), and galactose are common monosaccharides.
2. Disaccharides: Formed by the union of two monosaccharides, releasing a water molecule. The bond is called a glycosidic bond. They are sweet, crystallizable, and soluble.
Polysaccharides
Polysaccharides are large carbohydrates made of many monosaccharides linked by glycosidic bonds. Glucose is a common repeating unit. They are not sweet or crystallizable.
Starch: Energy storage in plants, abundant in seeds and tubers.
Glycogen: Energy storage in animals, found in the liver and muscles.
Cellulose: Structural component of plant cell walls.
Chitin: Structural component of insect exoskeletons and fungal cell walls.
Lipids
Lipids are organic biomolecules made of C, O, and H, insoluble in water but soluble in alcohol and acetone.
Complex Lipids:
- Triacylglycerols: Glycerol with three fatty acids, used for energy storage.
- Glycerophospholipids: Glycerol with two fatty acids and a phosphate group.
- Sphingolipids
- Waxes: Esters of long-chain fatty acids and alcohols.
Simple Lipids:
Do not contain fatty acids. Include vitamins A, D, E, K, and hormones like androgens and estrogens. Cholesterol is a simple lipid found in cell membranes.
Proteins
Proteins are abundant organic biomolecules made of amino acids linked by peptide bonds. Water is released during this process.
Simple Proteins: Chains of polypeptides.
Conjugated Proteins: Polypeptide chains with a prosthetic group (e.g., glycoproteins with carbohydrates, lipoproteins with lipids).