The Chemistry of Life
The Chemistry of Life
Proteins
Biological macromolecules composed of amino acids.
Lipids
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Fatty acids, triglycerides, phospholipids, steroids.
Carbohydrates
Includes sugars and polymers of sugars (e.g. starch, cellulose).
Nucleic Acids
Polymers made of nucleotides, such as DNA and RNA.
Lipids
1. Fats
Functions:
Storage of energy
Insulation and protection
2. Membrane Lipids
Major component of cell membranes.
3. Steroids
Characterized by a carbon skeleton with four fused rings.
Fats
Composed of two molecule types:
Fatty Acids
Structure: Long hydrocarbon chains with a carboxyl group (e.g., Palmitic acid, oleic acid).
Glycerol
Structure: A three-carbon alcohol.
Fatty Acids
Types:
Saturated
Unsaturated
Unsaturated Fatty Acids:
Have kinks due to double bonds, preventing them from stacking.
Tend to remain liquid at room temperature.
Saturated Fatty Acids:
No double bonds; solid at room temperature.
Examples:
Saturated: Palmitic acid
Monounsaturated: Oleic acid
Polyunsaturated: Linoleic acid
“Trans” Fat and Health
Cis and Trans Configurations:
Cis configuration introduces a kink, allowing for fluidity.
Trans configuration prevents kinks, making the fatty acid straighter.
In biological systems, most fatty acids are in the cis form.
Esterification:
Fatty acids attach covalently to other molecules via this dehydration reaction.
Health Implications:
Trans fats increase LDL (“bad” cholesterol) and decrease HDL (“good” cholesterol).
Triglycerides (fats)
Formed from three fatty acids covalently bonded to glycerol through dehydration synthesis, resulting in the release of water molecules (
3H_2O).Structure:
Glycerol + 3 Fatty Acids → Triglyceride.
Hydrolysis
Process Description:
The addition of water to break down molecules (opposite of dehydration synthesis).
Example Reaction:
ext{Fatty acid} + ext{Glycerol} + H_2O o ext{Hydrolyzed Product}
Phospholipids
Components:
Fatty Acids.
Glycerol.
Polar Head Group:
Example: Phosphocholine.
Phospholipids undergo dehydration synthesis similar to triglycerides, forming a bilayer structure in cell membranes.
Amphiphilic Nature
Description:
Phospholipids possess both hydrophilic (polar head) and hydrophobic (nonpolar tails) regions, critical for the formation of the phospholipid bilayer.
Cholesterol
Role and Function:
Most common steroid in humans.
Provides structure to cell membranes.
Precursor to steroid hormones (like testosterone and estradiol).
Characteristic: Mostly insoluble in water.
Emulsification Role:
Cholesterol acts as an emulsifier in bile, aiding in fat digestion alongside other components like taurocholic acid and phospholipids.
Carbohydrates
General formula: C:H:O in the ratio of 1:2:1.
Monosaccharides: Simple sugars with two variations of the carbonyl group: Aldoses (e.g., glucose) and Ketoses (e.g., fructose).
Cyclic Monosaccharides
Rarely Exist in Linear Form:
Fisher Projection: Linear form representation.
Haworth Projection: Cyclic representation where hydroxyl groups are either above or below the plane of the ring.
Example of Equilibrium: In aqueous solution, alpha and beta glucose exist in a 36:64 ratio.
Various Common Monosaccharides
Examples of Common Hexoses:
Glucose, Fructose, Galactose, Mannose (epimers).
Disaccharides
Formed via dehydration synthesis of two monosaccharides connected by glycosidic bonds.
Example: Two alpha-glucose molecules form maltose via an alpha 1-4 glycosidic bond.
Polysaccharides
Starch: A polysaccharide formed by repeating eta -1,4 linkages of glucose produced exclusively by plants for energy storage; branched form called amylopectin also contains eta -1,6 bonds.
Glycogen: Similar to amylopectin, but with more frequent eta -1,6 branches; stored in liver and muscle cells.
Cellulose: Polymeric molecule with eta -1,4 bonds. Provides rigidity to plant cell walls; resistant to digestion as only certain microorganisms can break these bonds.
Chitin: Modified glucose (N-acetyl-glucosamine) structure; common in exoskeletons of arthropods.
Peptidoglycan: Component of bacterial cell walls; made of alternating N-acetyl-muramic acid subunits, crosslinked for strength.
Nucleic Acids
Composed of polymers of nucleotides which consist of:
Nitrogenous Base.
5-Carbon Sugar (ribose or deoxyribose).
Phosphate Group (mono, di, or tri).
Nucleotide Hydrolysis
Hydrolysis of ATP (adenosine triphosphate) involves breaking phosphoanhydride bonds, releasing energy crucial for cellular processes.
Nitrogenous Bases
Five types included:
Adenine (A) and Guanine (G): Purines.
Thymine (T), Cytosine (C), and Uracil (U): Pyrimidines.
Differences Between RNA and DNA
RNA contains Uracil (U), while DNA contains Thymine (T).
RNA includes ribose; DNA has deoxyribose.
DNA is typically double-stranded; RNA is usually single-stranded.
Directionality of Polynucleotides
Nucleic acids exhibit directionality with 5’ phosphate end and the 3’ hydroxyl end, causing them to hybridize in an antiparallel fashion.
DNA Structural Features
Double Helix: Formed by complementary base pairing, involving hydrogen bonds.
Base Pairing Rules:
Adenine pairs with Thymine (for DNA).
Cytosine pairs with Guanine.
Cell Theory
Basic Principles:
All living things are composed of cells.
Cells arise from pre-existing cells.
Cells are the fundamental units of life, demonstrating all vital functions.
Eukaryotic Cells vs. Prokaryotic Cells
Eukaryotic Cells: Contain a nucleus and membrane-bound organelles.
Prokaryotic Cells: Lack a nucleus; contain a nucleoid with genetic material but no membrane-bound structures.
The Plasma Membrane
Comprised primarily of phospholipids arranged in a bilayer, creating a barrier to polar substances.
The arrangement of hydrophobic tails and hydrophilic heads provides selective permeability essential for cellular function.