Biological Macromolecules - Revision Sheet 02

A complete set of 64 flashcards reviewing biological macromolecules, including carbohydrates, lipids, proteins, and nucleic acids, covering structures, functions, bonds, and key exam concepts.

What are the main biological roles and building blocks of carbohydrates?

• Roles: Cellular fuel and structural building materials. • Building blocks: Monosaccharides (sugar monomers).

What are lipids, what are their main types, and what is their key structural distinction?

• Types: Fats (triacylglycerols), phospholipids, and steroids. • Properties: Hydrophobic molecules. • Distinction: They are NOT true polymers (not composed of repeating chains of monomer units).

What are the main biological functions and building blocks of proteins?

• Functions: Catalyse biochemical reactions (enzymes), provide structural support, transport substances, and enable cell communication. • Building blocks: Amino acids.

What is the primary role and building block of nucleic acids?

• Role: Store, transmit, and help express hereditary information (DNA and RNA). • Building blocks: Nucleotides.

What is a biological macromolecule, and which of the 4 classes is NOT considered a true polymer?

A large chain-like molecule composed of many covalently linked atoms. Carbohydrates, proteins, and nucleic acids are true macromolecules and polymers. Lipids are NOT true polymers.

Define a monomer and a polymer.

• Monomer: A small repeating molecular unit that serves as a building block for a polymer. • Polymer: A long chain-like molecule consisting of many similar or identical building blocks linked by covalent bonds.

What is dehydration (condensation) synthesis, and what happens to water?

A reaction that covalently joins monomers into polymers, releasing one $H_2O$ molecule per bond formed. • Mechanism: One monomer contributes a hydroxyl group (–OH) and the other contributes a hydrogen (–H). Associated with anabolism and biosynthesis.

What is hydrolysis, and what happens to water?

A reaction that breaks covalent bonds in polymers, consuming one $H_2O$ molecule per bond broken. • Mechanism: Water splits: –H attaches to one monomer and –OH attaches to the adjacent monomer. Associated with catabolism and digestion.

Complete the chemical reaction diagrams for dehydration synthesis and hydrolysis.

• Dehydration: Monomer–OH + H–Monomer → Monomer–Monomer + $H_2O$ • Hydrolysis: Monomer–Monomer + $H_2O$ → Monomer–OH + H–Monomer

Explain the "n − 1 rule" with an example: How many water molecules are released to synthesize a 45-amino-acid polypeptide?

To synthesize a linear polymer of n monomers, (n − 1) covalent bonds are formed and (n − 1) water molecules are released. • For 45 amino acids: 44 peptide bonds are formed, so 44 $H_2O$ molecules are released.

Define anabolism and catabolism in relation to polymer reactions.

• Anabolism: Metabolic pathways that consume energy to synthesize complex molecules from simpler ones (uses dehydration reactions). • Catabolism: Metabolic pathways that release energy by breaking down complex molecules into simpler ones (uses hydrolysis reactions).

What is a glycosidic linkage, and which functional groups participate?

A covalent bond that connects two monosaccharides to form disaccharides or polysaccharides. • Formed between two hydroxyl (–OH) groups via dehydration synthesis.

What is an ester linkage, and which functional groups participate?

A covalent bond in lipids (fats/triacylglycerols) that connects glycerol to a fatty acid. • Formed between a glycerol hydroxyl (–OH) and a fatty acid carboxyl (–COOH).

What is a peptide bond, and which functional groups participate?

A covalent bond linking amino acids in polypeptides. • Formed between the carboxyl group (–COOH) of one amino acid and the amino group ($-NH_2$) of another.

Quick recall: Match each class of macromolecule to its specific covalent bond.

• Sugars / Carbohydrates → Glycosidic linkage • Fats / Lipids → Ester bond • Proteins / Polypeptides → Peptide bond

What is the general chemical formula of a monosaccharide, and what is the formula of glucose?

• General formula: Often multiples of $CH_2O$ (1:2:1 ratio of C:H:O). • Glucose formula: $C_6H_{12}O_6$.

What functional groups are found in all monosaccharides?

Exactly one carbonyl group (C=O) and multiple hydroxyl groups (–OH).

Distinguish between an aldose and a ketose, with specific examples of each.

• Aldose: Carbonyl group (C=O) is located at the end of the carbon skeleton (forming an aldehyde). Examples: Glucose, Galactose, Glyceraldehyde. • Ketose: Carbonyl group (C=O) is located within the carbon chain (forming a ketone). Examples: Fructose, Dihydroxyacetone.

What happens to the structure of pentose and hexose sugars in aqueous solution?

In water, 5-carbon pentoses (e.g., ribose) and 6-carbon hexoses (e.g., glucose) spontaneously form stable ring structures.

What is maltose composed of, what is its linkage, and what is its common use?

• Composition: Glucose + Glucose • Linkage: 1→4 glycosidic linkage • Use: Brewing.

What is sucrose composed of, what is its linkage, and what is its biological role?

• Composition: Glucose + Fructose • Linkage: 1→2 glycosidic linkage • Role: Table sugar and the primary transport form of carbohydrates in plants.

What is lactose composed of, and what is its biological role?

• Composition: Glucose + Galactose • Role: Milk sugar (major energy source in mammalian milk).

What is starch? Describe its two molecular forms (amylose vs. amylopectin) and where it is stored.

A plant α-glucose storage polysaccharide stored in plastids (including chloroplasts). • Amylose: Unbranched chain with α(1→4) glycosidic linkages. • Amylopectin: Branched form with α(1→4) linkages and α(1→6) branch points.

What is glycogen? Where is it stored, and why is its high degree of branching beneficial?

A highly branched α-glucose storage polysaccharide stored in vertebrate liver and muscle tissue. • Benefit: Extensive branching provides many open ends, allowing rapid enzymatic breakdown to release free glucose when energy is urgently required.

What is cellulose, and what is its primary biological role?

A structural, unbranched β-glucose polysaccharide that forms straight microfibrils, serving as the major structural component of tough plant cell walls.

What is chitin, where is it found, and what makes its chemical composition distinct?

A structural carbohydrate found in arthropod exoskeletons (insects, crustaceans) and fungal cell walls. • Distinction: It contains a nitrogen-containing attachment on its glucose monomers.

Explain the difference between α-glucose and β-glucose ring configurations.

• α-glucose: The hydroxyl group (–OH) on carbon 1 points below the plane of the glucose ring. • β-glucose: The hydroxyl group (–OH) on carbon 1 points above the plane of the ring.

How do the glycosidic linkages and 3D shapes of starch and cellulose compare?

• Starch: α(1→4) linkages; all monomers have the same orientation → coils into a helical, flexible shape suited for compact energy storage. • Cellulose: β(1→4) linkages; every second glucose monomer is upside down relative to its neighbour → forms straight, rigid, unbranched cables.

How do parallel cellulose chains interact, and what structure do they form?

Hydroxyl groups on parallel cellulose chains hydrogen-bond with each other, bundling together into tough structural cables called microfibrils.

Why can humans digest starch but cannot digest cellulose?

Human digestive enzymes (amylase) can hydrolyse the α(1→4) linkages in starch, but humans lack enzymes to hydrolyse the β(1→4) linkages of cellulose. Cellulose passes through the human digestive tract as insoluble dietary fibre.

How do cows and termites obtain nutrition from cellulose?

They host symbiotic microorganisms (prokaryotes and protists) in their digestive tracts that produce cellulase enzymes capable of hydrolysing β(1→4) glycosidic linkages.

Why are all lipids hydrophobic, and why do vegetable oils separate from water?

Lipids consist predominantly of nonpolar C–H hydrocarbon bonds. Water molecules preferentially hydrogen-bond with each other and exclude the nonpolar lipid molecules, forcing them to separate into distinct layers.

What is a triacylglycerol (triglyceride/fat)? Describe its structural components.

A fat molecule consisting of one 3-carbon glycerol backbone linked to three fatty acid chains via ester linkages.

What are the biological functions of fats in adipose tissue?

1. Long-term energy storage (fats store about twice as much energy per gram as starch or glycogen)
2. Thermal insulation
3. Cushioning and mechanical protection of vital organs

Describe the structure of a phospholipid and identify its hydrophilic and hydrophobic parts.

• Composition: One glycerol attached to two hydrophobic fatty acid tails and one hydrophilic phosphate group (often linked to a polar molecule like choline). • Hydrophilic head: Phosphate group + polar group (faces water). • Hydrophobic tails: Two hydrocarbon fatty acid chains (avoid water).

What does amphipathic mean, and how does this property explain cell membrane structure?

Amphipathic means having both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region. • In water, phospholipids spontaneously self-assemble into a bilayer: hydrophilic heads face outward toward aqueous fluid, while hydrophobic tails face inward, creating the core boundary of biological membranes.

What is the basic chemical structure of steroids? Give two key biological examples.

A carbon skeleton composed of four fused carbon rings with attached functional groups (no fatty acids or glycerol). • Cholesterol: Animal cell membrane fluidity buffer and precursor for steroid hormones. • Estrogen and Testosterone: Vertebrate sex hormones.

What is a saturated fatty acid? Describe its bonds, hydrogen content, shape, and room-temperature state.

• Bonds: Only C–C single bonds (no C=C double bonds). • Hydrogen: Saturated with the maximum possible number of hydrogen atoms. • Shape: Straight, flexible hydrocarbon tail. • State at room temp: Solid (packs tightly together, e.g., butter, lard, animal fat).

What is an unsaturated fatty acid? Describe its bonds, shape, packing, and room-temperature state.

• Bonds: Contains one or more C=C double bonds (usually in cis configuration). • Shape: Cis double bonds create kinks/bends in the hydrocarbon tail. • Packing: Kinks prevent tight packing. • State at room temp: Liquid oils (e.g., olive oil, cod liver oil).

What health risk is associated with saturated fats, and what is trans fat produced by hydrogenation?

• Diets high in saturated fats are associated with increased risk of cardiovascular disease. • Industrial hydrogenation artificially adds $H_2$ to unsaturated oils to make them solid (e.g., margarine), often producing trans double bonds (trans fats), which are unhealthy.

Describe the universal structure of an amino acid (the 4 partners of the central α-carbon).

The central α-carbon is covalently bonded to:

1. A hydrogen atom (–H)
2. An amino group ($-NH_2$)
3. A carboxyl group (–COOH)
4. A variable R group (side chain)

What forms do the amino group and carboxyl group take at physiological pH (~7.2)?

• Amino group acts as a base and is protonated: –NH₃ • Carboxyl group acts as an acid and is ionized/deprotonated: –COO

What role does the R group (side chain) play in an amino acid?

The R group varies among the 20 universal amino acids; its unique chemical structure determines the specific chemical properties and reactivity of each amino acid.

Describe nonpolar (hydrophobic) R groups. How do they behave inside a folded protein?

They contain hydrocarbon chains, aromatic rings, or C–H bonds (e.g., Gly, Ala, Val, Leu, Ile, Met, Phe, Trp, Pro). • Behaviour: Cluster in the interior of folded globular proteins, shielded away from surrounding water.

Describe polar (hydrophilic) R groups. How do they behave inside a folded protein?

They contain polar groups such as –OH, –SH, or amides (e.g., Ser, Thr, Cys, Tyr, Asn, Gln). • Behaviour: Form hydrogen bonds with water, typically orienting toward the outer surface of the protein.

Describe acidic (charged) R groups and their charge at pH 7.

They contain side-chain carboxyl groups (–COO) that donate H. • Charge: Negatively charged at pH 7. • Examples: Aspartate (Asp), Glutamate (Glu).

Describe basic (charged) R groups and their charge at pH 7.

They contain side-chain amino/nitrogenous groups (+NH₃) that accept H. • Charge: Positively charged at pH 7. • Examples: Lysine (Lys), Arginine (Arg), Histidine (His).

What is primary protein structure? What bond stabilizes it, and what determines it?

The unique linear sequence of amino acids linked by covalent peptide bonds. • Determined by inherited DNA genetic information.

Give a clinical example of how a single amino acid substitution in primary structure alters protein function.

Sickle-cell disease: A single mutation substituting valine for glutamic acid at position 6 in the β-chain of haemoglobin causes abnormal haemoglobin aggregation, deforming red blood cells.

What is secondary protein structure? What specific bond stabilizes it?

Repetitive coiling or folding of the polypeptide chain stabilized by hydrogen bonds between the atoms of the polypeptide BACKBONE (between carbonyl C=O and amino N–H groups), NOT by R-group interactions.

Compare the two main secondary structure motifs: α-helix and β-pleated sheet.

• α-helix: A delicate coil held by hydrogen bonds between every 4th amino acid (e.g., α-keratin in hair). • β-pleated sheet: Two or more parallel or antiparallel polypeptide segments held together by lateral hydrogen bonds (e.g., spider silk).

What is tertiary protein structure, and what causes it?

The overall 3D shape of a single polypeptide chain, resulting from interactions among the variable R groups (side chains) of the amino acids.

List the four types of interactions that stabilize tertiary protein structure.

1. Hydrophobic interactions & Van der Waals forces (nonpolar R groups cluster inside)
2. Hydrogen bonds (between polar R groups)
3. Ionic bonds (between positively and negatively charged R groups)
4. Disulfide bridges (covalent –S–S– bonds)

What is a disulfide bridge, which amino acid forms it, and why is it unique in tertiary structure?

A covalent bond (–S–S–) formed between the sulfhydryl groups (–SH) of two cysteine monomers. • Uniqueness: It is a strong covalent bond, unlike all other tertiary interactions which are weak, noncovalent bonds.

CRITICAL EXAM DISTINCTION: Secondary structure vs. Tertiary structure stabilizing interactions.

• Secondary structure: Hydrogen bonds between atoms of the polypeptide BACKBONE. • Tertiary structure: Chemical interactions and bonds between variable R GROUPS (side chains).

What is quaternary protein structure? Give two major biological examples.

The overall protein structure that results when two or more individual polypeptide chains (subunits) aggregate into a single functional macromolecule. • Collagen: 3 intertwined helical polypeptides (fibrous strength in skin/tendons). • Haemoglobin: 4 subunits (two α and two β chains), each with an iron-containing heme group.

What is protein folding, and what are molecular chaperones?

The spontaneous process by which a polypeptide chain collapses into its specific functional 3D conformation. • Chaperones (chaperonins): Specialized cellular protein complexes that assist and protect newly synthesized proteins during folding, preventing improper aggregation.

What is protein denaturation, and why does a denatured protein lose its biological activity?

The process where environmental stress disrupts the native 3D conformation of a protein. • Loss of function: Biological activity relies strictly on exact shape (e.g., an enzyme's active site fitting a substrate); when the 3D shape unfolds, function is completely lost.

EXAM TRAP: Does protein denaturation break peptide bonds?

NO. Denaturation disrupts higher-level secondary, tertiary, and quaternary weak interactions (and sometimes disulfide bridges), but leaves the primary structure (covalent peptide bonds) completely intact.

What are the four primary environmental causes of protein denaturation, and what does each disrupt?

1. Excessive temperature: Thermal agitation breaks hydrogen and ionic bonds (e.g., cooking egg white).
2. Extreme pH: Alters charges on acidic/basic R groups, disrupting ionic bonds.
3. High salt concentration: Shielding by ions disrupts ionic and hydrogen interactions.
4. Nonpolar organic solvents (e.g., ether): Causes nonpolar hydrophobic R groups to flip outward.

What is protein renaturation, and what fundamental biological fact does it prove?

The process where a denatured protein refolds into its functional native shape when the denaturing agent is removed. • Proof: Proves that all information required to specify a protein's 3D tertiary structure is intrinsically contained in its primary amino acid sequence.

Exam Trap: Are lipids biological polymers? Explain.

FALSE. Fats, phospholipids, and steroids are not built from continuous chains of repeating identical or similar monomer units; therefore, they are not true polymers.

Exam Trap: Are starch and cellulose made from different monosaccharides? Explain.

FALSE. Both starch and cellulose are made entirely of glucose monomers. Their structural differences stem strictly from α-glucose vs. β-glucose ring isomers and the resulting glycosidic bond angles.

Exam Trap: Do unsaturated fats pack more tightly than saturated fats? Explain.

FALSE. Cis double bonds in unsaturated fatty acids introduce rigid kinks in the hydrocarbon chain, preventing tight packing and making them liquid oils at room temperature.