Topic 1: Biological Molecules

A comprehensive set of Q&A flashcards covering monomers and polymers, carbohydrates, biochemical tests, lipids, proteins, enzymes, nucleic acids, ATP, water properties and key inorganic ions.

What is a monomer in biological chemistry?

A small, basic molecular unit that can join with others to form polymers; examples include monosaccharides, amino acids and nucleotides.

Define a polymer.

A large molecule composed of many repeating monomer units joined together.

During which type of reaction are monomers joined and what by-product is released?

Condensation reaction; a molecule of water is released.

What reaction breaks a polymer into monomers and what does it require?

Hydrolysis reaction; it requires the addition of water.

Which three elements are found in all carbohydrates?

Carbon, hydrogen and oxygen.

What is the general formula for monosaccharides?

(CH₂O)n where n is 3–7.

Name the two isomers of glucose.

α-glucose and β-glucose.

What bond forms between two monosaccharides in a disaccharide?

A glycosidic bond.

Which monosaccharides form maltose?

Two α-glucose molecules.

Which monosaccharides condense to form sucrose?

Glucose and fructose.

Which monosaccharides condense to form lactose?

Glucose and galactose.

What polysaccharide is the main energy store in animals?

Glycogen.

Why can glycogen be broken down rapidly?

It has many side branches so enzymes can act simultaneously on the molecule.

Name the two components of starch.

Amylose and amylopectin.

Why is amylose described as ‘compact’?

Its unbranched 1,4-linked chain coils into a helix, packing many glucose units into a small space.

Which glucose isomer makes up cellulose?

β-glucose.

What structural feature gives cellulose high tensile strength?

Parallel β-glucose chains form microfibrils cross-linked by hydrogen bonds.

Which reagent tests for reducing sugars and what colour indicates a positive result?

Benedict’s reagent; an orange-brick-red precipitate.

How is the Benedict’s test modified to detect non-reducing sugars?

Hydrolyse the sample with dilute HCl, neutralise with NaHCO₃, then repeat the Benedict’s test.

What colour change indicates starch in the iodine test?

Orange-brown to blue-black.

What are the two main types of lipid?

Triglycerides and phospholipids.

Describe the basic structure of a triglyceride.

One glycerol molecule bonded to three fatty acids via ester bonds.

What distinguishes saturated from unsaturated fatty acids?

Saturated fats have no C=C double bonds; unsaturated fats contain one or more C=C double bonds.

Why are unsaturated fats usually liquid at room temperature?

C=C double bonds create kinks, preventing tight packing of molecules.

Name two biological advantages of triglycerides as energy stores.

High energy density (many C–H bonds) and being insoluble so they don’t affect water potential.

Which part of a phospholipid is hydrophilic and which is hydrophobic?

The phosphate ‘head’ is hydrophilic; the fatty-acid ‘tails’ are hydrophobic.

Why do phospholipids form bilayers in water?

Their polar nature causes hydrophilic heads to face water while hydrophobic tails avoid it.

What positive result indicates lipids in the emulsion test?

A cloudy-white emulsion after adding ethanol then water.

Name the three common functional groups in an amino acid.

Amino group (-NH₂), carboxyl group (-COOH) and variable R group.

What bond links amino acids in a polypeptide?

A peptide bond.

Define the primary structure of a protein.

The specific sequence of amino acids in a polypeptide chain.

Which two shapes form the secondary structure of proteins?

α-helix and β-pleated sheet.

Name three bonds that stabilise the tertiary structure of a protein.

Disulfide bridges, ionic bonds and hydrogen bonds.

What colour change indicates a positive Biuret test for protein?

Blue to purple.

What is meant by the induced-fit model of enzyme action?

The enzyme’s active site changes shape slightly to fit the substrate when forming the enzyme–substrate complex.

How does increasing substrate concentration affect reaction rate once all active sites are occupied?

It has no further effect; enzyme concentration becomes the limiting factor.

Why do non-competitive inhibitors reduce enzyme activity regardless of substrate concentration?

They bind to sites other than the active site, altering enzyme shape and activity.

Which sugar is found in DNA and which in RNA?

DNA contains deoxyribose; RNA contains ribose.

State the complementary base pairs in DNA.

Adenine–Thymine and Guanine–Cytosine.

What enzyme unzips the DNA double helix during replication?

DNA helicase.

How does DNA polymerase contribute to semi-conservative replication?

It joins free nucleotides to the template strand by forming phosphodiester bonds.

Name the three components of an ATP molecule.

Ribose sugar, adenine base and three phosphate groups.

What enzyme hydrolyses ATP and what products are formed?

ATP hydrolase; ADP and inorganic phosphate (Pi).

Why is water’s high specific heat capacity biologically important?

It buffers organisms against rapid temperature changes, maintaining stable internal conditions.

Which property of water allows insects to walk on its surface?

High surface tension due to strong cohesion between water molecules.

What role do sodium ions play in nutrient absorption?

They drive co-transport of glucose and amino acids across cell membranes.

Why are phosphate ions essential in cells?

They form part of DNA backbones and ATP molecules.