BIO SEM 1 UNIT 4

What elements are organic molecules built from, and name the major classes of biomolecules.

Carbon plus a few other atoms (commonly H, O, N, P, S); major biomolecule classes are nucleic acids, proteins, carbohydrates, and lipids

What two features of carbon give organic molecules great versatility, and what effect do alternating double bonds have?

Carbon can self-associate into chains/rings and can form double bonds; alternating ("conjugated") double bonds make a molecule coloured, with more double bonds shifting colour towards red (e.g. beta carotene, haem, chlorophyll)

Name five biologically important chemical groups and their structures.

Hydroxyl (-OH), carbonyl (-C=O), carboxyl (-COOH ↔ -COO-), amino (-NH2 ↔ -NH3+), sulfhydryl (-SH), and phosphoryl (-PO3)

List three biologically important properties of organic molecules linked to their chemical groups.

1) Solubility in water; 2) ability to form weak, non-covalent bonds; 3) ability to bind metal ions

Why are some organic molecules soluble in water, and what happens with very large molecules instead?

Polar groups (e.g. -OH) form hydrogen bonds with water, letting small molecules join the water network and dissolve; very large molecules may instead form a gel (e.g. cytoplasm, cartilage, vitreous humour)

How do weak, non-covalent bonds help molecules, and how do organic molecules bind metal ions?

Ionic/hydrogen bonds can cross-link distant parts of a chain (giving a more resilient shape) or allow temporary binding between molecules; nitrogen atoms in ring structures form dative covalent bonds with metal ions (e.g. haem binds Fe2+, chlorophyll binds Mg2+)

What is the general hierarchy of biopolymer assembly, and what are condensation and hydrolysis reactions?

Monomer → dimer → oligomer → polymer; condensation reactions join monomers and release water; hydrolysis reactions break polymer bonds by adding water, releasing free monomers

Match each type of monomer to its resulting polymer.

Monosaccharides → polysaccharides; amino acids → polypeptides (proteins); mononucleotides → polynucleotides (DNA/RNA); fatty acids & glycerol → triglycerides (fats & oils)

What is the general chemical formula of a carbohydrate, and what is another name for carbohydrates?

CH2O (a "carbon hydrate"); also called glycans (hence "glycobiology")

How are monosaccharides classified by size and by chemical family, and what suffix do most sugar names share?

By size: triose, pentose, hexose; by chemical family: aldose (aldehyde group) or ketose (ketone group); most simple sugar names end in "-ose" (e.g. glucose, sucrose, lactose)

What is glucose, chemically, and what is the difference between alpha and beta glucose?

An aldose hexose with molecular formula C6H12O6; alpha and beta glucose are structural isomers differing in the orientation of the -OH group at carbon 1

What is a disaccharide, and describe Benedict's test for reducing sugars.

Two monosaccharides joined by a glycosidic bond (alpha or beta linkage), e.g. glucose+fructose or glucose+galactose; Benedict's test: mix sample with Benedict's solution and boil — sugars with an aldehyde group turn the solution from blue to a colour change (orange/red) as copper sulfate is reduced (disaccharides may need acid hydrolysis first)

What is a polysaccharide, and how can the chains be arranged?

Many monosaccharides/disaccharides joined together, forming linear chains (e.g. amylose, cellulose) or branched chains (e.g. amylopectin, glycogen)

List the three main functions of carbohydrates.

1) Energy source/storage (sugars, starch, glycogen); 2) structural support (cellulose, chitin, peptidoglycan); 3) molecular tags (oligosaccharide trees, e.g. blood group antigens)

Compare starch and glycogen as energy storage polysaccharides.

Both are glucose polymers with identical chemical composition; starch (plants) is a mix of linear (amylose) and branched (amylopectin) forms, while glycogen (animals) is only the branched form

Describe the glycosidic linkages in branched glucose polymers like glycogen/amylopectin, and describe the iodine test for starch.

Main chain = α(1→4) linkages, branches = α(1→6) linkages; iodine test: add iodine solution — starch/glycogen turns blue-black as iodine concentrates within the helical structure

List the structural polysaccharides in plant cell walls, fungal cell walls/arthropod exoskeletons, and bacterial cell walls.

Plant cell walls: cellulose; fungal cell walls/arthropod exoskeletons: chitin; bacterial cell walls: peptidoglycan

How does cellulose differ chemically from starch, and what is chitin made of?

Cellulose = glucose polymer with β(1→4) linkages (vs starch's α(1→4) linkages), making it structurally rigid; chitin = polymer of N-acetylglucosamine (NAG) with β(1→4) linkages

What is a lipid (Greek origin and definition), and what is the difference between a fat and an oil?

From Greek "lipos" (fat); a broad category of hydrophobic molecules (fats, oils, waxes, cholesterol); fat = solid at room temperature, oil = liquid at room temperature

List the main functions of lipids in the body.

Main energy store (triglycerides), structural support/cushioning, thermal/electrical insulation, forming membranes (phospholipids/cholesterol), waterproofing (waxes), and forming steroid hormones

Describe the structure of a triglyceride and why it is an efficient energy store.

Three fatty acid chains attached to a glycerol backbone via condensation; very hydrophobic, making it compact and energy-dense

Compare the energy storage of triglycerides versus glycogen.

Triglycerides store ~38 kJ (9 kcal)/g and remain ~100% lipid; glycogen stores ~17 kJ (4 kcal)/g and also carries ~2g of water per gram stored, making it far less energy-dense

Describe the grease spot test and the emulsion test for lipids.

Grease spot test: spot sample on filter paper and dry — lipids leave a translucent mark; emulsion test: mix sample with ethanol, then add to water — lipids form a cloudy emulsion

How does a phospholipid differ from a triglyceride, and why does this make it form a membrane bilayer?

A phospholipid has only two fatty acids, with a phosphate (or more complex) group in the third position instead of a fatty acid; this gives it a hydrophobic tail and hydrophilic head, so it spontaneously forms a bilayer in water

What is a fatty acid structurally, and what are the three saturation categories?

A long-chain (12-24C) hydrocarbon carboxylic acid; saturated (no double bonds), monounsaturated (one double bond), polyunsaturated (more than one double bond)

How does the number of double bonds affect a fatty acid's melting point, and what are essential fatty acids?

More (cis) double bonds cause kinking, increasing molecular motion and lowering melting point (more oil-like); essential fatty acids (omega-3 e.g. α-linolenic acid, omega-6 e.g. linoleic acid) cannot be made by the body and must come from the diet

What roles do fatty acids play in membrane phospholipids?

Chain length affects bilayer thickness; degree of unsaturation affects membrane fluidity; composition is tissue-specific (e.g. brain is rich in omega-3/6); some fatty acids are precursors to signalling molecules

What is a wax, structurally, and give a biological example of its use.

A fatty acid joined to a fatty alcohol, forming long hydrophobic, solid chains; used for waterproofing leaves/honeycombs and for buoyancy/sonar in sperm whales

Describe the structure and membrane function of cholesterol.

Four fused rings, a hydrophobic tail, and a hydroxyl group; it fits between phospholipids and stiffens the membrane, protecting its integrity at both high and low temperatures

List four steroid hormones derived from cholesterol.

Cortisol (stress hormone), aldosterone (kidney function), progesterone/oestrogen/testosterone (sex hormones), and vitamin D