Cell Structure and Non-Covalent Interactions

• Living organisms can self-replicate and self-assemble.
• Biological macromolecules have a basic simplicity in their structure.
• Living cells function as chemical engines at a constant temperature.
• Living cells are self-regulating chemical engines, adjusted for maximum economy.
• All living organisms rely on each other for energy and matter exchanges.
• The cell wall provides mechanical support, maintains shape, and prevents bursting, serving as a structural barrier.
• The cell membrane acts as a selective barrier, regulating substance movement and facilitating cell signaling and communication.

Non-Covalent Interactions

• Ionic interaction occurs between a negatively charged carbonyl group (-C=O) and a positively charged ammonium group (NH3+).
• Hydrogen bonding occurs between partially negative oxygen (O=) and partially positive hydrogen (NH-); also between (-C=O) and (HO-).
• Hydrophobic interactions occur between nonpolar molecules, such as hydrocarbons (H3C and C-H3C).

Hydrogen Bonding Strength

• Hydrogen bonding in HO-H is stronger than in HN-H.
• Oxygen is more electronegative than nitrogen, creating a larger dipole moment and stronger hydrogen bonding.
• Water's bent structure and high polarity enable stronger hydrogen bonds than in ammonia.

Carbohydrates

• Includes sugars, starches, and cellulose.
• Makes up most of the organic matter on Earth.
• Hydrates of carbon contain hydrogen and oxygen in a 2:1 ratio, like water.
• Defined as polyhydroxyaldehydes, polyhydroxyketones or substances that yield these compounds on hydrolysis.

Carbohydrate Functions

• Act as storehouses of chemical energy, e.g., glucose, starch, glycogen.
• Serve as components of supportive structures such as cellulose in plants and chitin in shells.
• Act as essential components of nucleic acids (DNA and RNA).

Carbohydrate Origin and Classification

• Carbohydrates are produced through photosynthesis: Sunlight+ CO2 + H20 -> C6H12O6 + O2
• Carbohydrates are classified into: Monosaccharides Disaccharides Polysaccharides

Monosaccharides

• They are simple sugars and categorized by the number of carbon atoms
• General formula: CnH2nOn
• "ose" ending indicates a carbohydrate
• Aldehyde group are aldoses, ketone group are ketoses.
• Common monosaccharides contain 3 to 8 carbon atoms.

Physical Properties of Monosaccharides

• They are colorless and crystalline solids.
• Very soluble in water, fairly soluble in ethyl alcohol, insoluble in nonpolar solvents, and sweet to the taste.

Trioses

• A 3-carbon simple sugar formed from the metabolic breakdown of hexoses in muscle metabolism.
• Two trioses exist: glyceraldehyde and dihydroxyacetone.

Tetroses

• Four-carbon sugars.
• Examples include tetrose and erythrose.

Pentoses

• Five-carbon sugar molecules
• Ribose and deoxyribose are the most important
• Ribose forms part of ribonucleic acid (RNA), and deoxyribose forms part of deoxyribonucleic acid (DNA).
• Both DNA and RNA are components of every cell nucleus and cytoplasm.

Hexoses

• Six-carbon sugars, the most common carbohydrates.
• Important for the human body like glucose, galactose, and fructose
• All have the same molecular formula (C6H12O6) but different structural formulas; are isomers.

Glucose

• Also known as dextrose: is the most important monosaccharide and a white crystalline solid.
• Soluble in water, insoluble in most organic liquids.
• Found with fructose in many fruit juices and prepared by the hydrolysis of sucrose or starch.
• Normally found in the bloodstream and tissue fluids.
• Does not require digestion and can be given intravenously.
• Primary fuel for living cells and the preferred energy source for brain cells.

Galactose

• Isomer of glucose and an aldohexose, does not occur freely in nature but is a constituent of lactose.
• Present in glycoproteins and glycolipids, and also necessary to synthesize biomolecules.

Fructose

• Ketohexose with molecular formula C6H12O6
• Can be represented as a straight-chain or ring structure; the ring structure is predominant.
• Often called levulose or fruit sugar, and found in fruit juices and honey.
• Prepared by the hydrolysis of sucrose or inulin.

Disaccharides

• Carbohydrates contain more than one monosaccharide unit.
• Oligosaccharides contain three to ten monosaccharide units.
• Yield two simple sugars upon hydrolysis and are joined by a glycosidic bond.

Sucrose

• Used as sugar, also known as cane sugar and produced commercially from sugar cane and sugar beets.
• Composed of glucose and fructose with the general formula C12H22O1

Maltose

• Known as malt sugar and is present in germinating grain and consists of two glucose molecules.
• A white crystalline solid, sweet-tasting, and fairly soluble in water with the general formula C12H22O11.
• It is a reducing sugar.

Lactose

• Commonly known as milk sugar present in milk and of animal origin
• A white crystalline solid, sweet to the taste, slightly soluble in water.
• A reducing sugar with the general formula C12H22O11.

Polysaccharides

• Are complex sugars that yield simple sugars after hydrolysis.
• Polymers of monosaccharides which produce numerous monosaccharide molecules upon complete hydrolysis.
• Formed from pentoses are called pentosans, and those formed from hexoses are called hexosans.
• Hexosans are most important in physiology with the general formula (C6H10O5)x.

Starch

• Plants store energy primarily in the form of starch granules.
• A mixture of amylopectin and amylose: Amylopectin is a highly branched polysaccharide present to a small extent.
• Present in the covering of starch granules and contains both α(1,4) and α(1,6) glycosidic linkages.
• Insoluble in cold water; when placed in boiling water, the granules rupture, forming a paste that gels on cooling.
• Is a straight-chain polysaccharide present in starch and its monosaccharide units are joined together by the α-glycosidic bond.

Cellulose

• Composed of monosaccharides joined by B-glycosidic bonding
• Wood, cotton, and paper are composed primarily of cellulose.
• Supporting and structural substance of plants, not affected by enzymes in the human digestive system so it cannot be digested.
• Does not dissolve in water or most ordinary solvents.
• Gives no color test with iodine and gives negative test with Cu2+ complexions.

Glycogen

• Present in the body stored in the liver and muscles, it serves as a reserve supply of glucose, having an animal origin.
• Its structure is similar to amylopectin except that it has more branch points, possibly at every fourth glucose residue in the core of the molecule.

Acidic Polysaccharides

• A group of polysaccharides that contain carboxyl groups and/or sulfuric ester groups.
• Play important roles in the structure and function of connective tissues, providing mechanical strength and filtering molecular information flow between cells.

Dextrin

• Produced during starch hydrolysis, as an intermediate between starch and maltose.
• Forms sticky colloidal suspensions with water, used for adhesives such as the glue on postage stamps.
• Also used for people with the inability to digest starch easily, such as infants and elderly persons.

Hayluronic Acid

• Simplest and present in connective tissue, most abundant in embryonic tissues and in specialized connective tissues.
• Is composed of D-glucoronic acid linked by α-1,3-glycosidic bond to N-acetyl-D-glucosamine.

Dextran

• A polysaccharide produced by certain bacteria grown on sucrose
• Various types exist, differing in chain length and degree of branching.
• Used as a blood extender to hold water in the bloodstream and help prevent drops in blood volume and blood pressure.

Lipids

• Diverse group of biomolecules that differ in both structure and function.
• Substances from living organisms dissolve in nonpolar solvents such as ether and CHCI3 but not appreciably in water.
• Serve as food for the body as a secondary source of energy (9 kcal/gram).
• They are a primary structural component of biological membranes, act as hormones, antioxidants, or vital growth factors.

Simple Lipids

• Also called triacylglycerols or triglycerides which are also examples of the fats and oils.
• They are ester of fatty acids and when hydrolyzed gives glycerol and fatty acids.

Fatty Acids

• They are the monocarboxylic acids in the fats and oils that contains hydrocarbon chains of variable length and are primarily important components of several types of lipid molecules.
• They occurs primarily in triacylglycerols and several types of membrane- bound lipid molecules.
• Can be saturated and unsaturated, with an even number of carbon atoms that form an unbranched chain

Unsaturated Fatty Acids

• The unsaturated fatty acid can be in the cis, or trans isomer, although the cis isomers predominate.
• The cis configuration causes an inflexible "kink' in the fatty acid chains so that the fatty acids interruptions the regular packing of the chains resulting to low melting point.

Esstenial Fatty Acids

• Th fatty acids that cannot be synthesized by mammals but are needed by the body are called essential fatty acids (examples are the linoleic and linolenic acids).

Fats and Oils

• Are known as triacylglycerols or triglycerides but can also be monoacylglycerol and diacylglycerol
• On hydrolysis yield fatty acids and glycerol and have no charge thus referred to as neutral fats.
• At room temperature, fats are solid because they contain large portion of saturated fatty acids while oils are liquid, and they are practically unbranched carboxylic acids

Lipid Functions

• Major storage and transport form of fatty acids, are hydrophobic and so they coalesce into compact, anhydrous droplets within cells, and store in adipose tissues.
• Less oxidize than carbohydrates and used to serve as protectors for vital organs, provide insulation in low temperature.

Wax

• Complex mixtures of nonpolar lipids and are protective coatings on leaves, stems, fruits of plants and skin and fur of animals.
• Composed of long chain fatty acids and long chain alcohols, examples are carnauba wax and also contain hydrocarbons, alcohols, fatty acids, aldehydes and sterols.

Complex lipids

• Constitute the main components of membranes.
• Are classified into two groups: phospholipids and glycolipids

Phospholipids

• Structural components of membranes.
• Contain an alcohol, two fatty acids and a phosphate group, and are several emulsifying agents and surface active agents.
• Are consisted of the hydrophobic end and the hydrophilic end, with the fatty acid is hydrophobic while the nitrogen compound and the phosphoric side are hydrophilic and called amphipathic.

Sphingolipids

• Are important components of animal and plant membranes
• Contain long chain amino alcohol in animal -Sphingomyelin is found in greatest abundance in the myelin sheath of nerve cells facilitiate the rapid transmission of nerve impulses.

Steroids

• Each type of steroid is composed of four fused ring.
• The most common is cholesterol, most abundant in the human body and most important; serve as membrane component mostly in the plasma membrane of red blood cells
• Serve as raw materials for other steroids that serve as precursor in the biosynthesis of all steroid hormones, and exists both in the free and esterified with fatty acid

Peroxisomes and Mitochondria

• Theyare both important organelles in eukaryotic cells, but they differ in function and structure; mitochondria are the powerhouse of the cell, producing ATP through cellular respiration
• Peroxisomes are involved in various metabolic processes, including fatty acid breakdown and detoxification.