Biomolecules & Macromolecules – Lecture Review

A comprehensive set of Q&A flashcards covering key definitions, structures, functions, and examples of carbohydrates, lipids, proteins, and nucleic acids as outlined in the lecture notes.

What defines a macromolecule?

A very large molecule composed of thousands of covalently connected atoms.

Which three classes of life’s organic molecules are true polymers?

Carbohydrates, proteins, and nucleic acids.

What is a polymer?

A long molecule consisting of many similar or identical building blocks called monomers.

Name the reaction that links monomers together in polymers.

Dehydration (condensation) reaction.

What reaction breaks polymers into monomers?

Hydrolysis.

Why are lipids not considered polymers?

Because they are not built from repeating monomeric sub-units in a long chain.

What two factors determine the structure and function of a polysaccharide?

Its sugar monomers and the positions of glycosidic linkages.

Give the general molecular formula for a monosaccharide.

A multiple of CH₂O (e.g., glucose = C₆H₁₂O₆).

Which monosaccharide is most common in biology?

Glucose.

How are monosaccharides classified?

By the position of the carbonyl group (aldose vs ketose) and the number of carbons in the skeleton.

List the common triose, pentose, and hexose examples given in class.

Triose: glyceraldehyde; Pentose: ribose; Hexoses: glucose, galactose, fructose.

In solution, monosaccharides form what structural shape?

Ring structures.

What covalent bond joins two monosaccharides?

A glycosidic bond.

Match each disaccharide to its monosaccharide components: lactose, maltose, sucrose.

Lactose = glucose + galactose; Maltose = glucose + glucose; Sucrose = glucose + fructose.

What is the storage polysaccharide in plants?

Starch.

Name the two structural forms of starch.

Amylose (unbranched) and amylopectin (branched).

Where do plants store starch?

As granules inside chloroplasts and other plastids.

What is the storage polysaccharide in animals?

Glycogen.

In which tissues is glycogen primarily stored?

Liver and muscle cells.

What structural polysaccharide forms plant cell walls?

Cellulose.

What type of glucose linkage distinguishes cellulose from starch?

β-1,4 glycosidic linkages (cellulose) versus α-1,4 linkages (starch).

Why can most animals digest starch but not cellulose?

Their enzymes hydrolyze α linkages in starch but cannot break β linkages in cellulose.

What passes through the human gut as insoluble fiber?

Cellulose.

Name the structural polysaccharide in arthropod exoskeletons and fungal cell walls.

Chitin.

What unique functional group does chitin contain?

A nitrogen-containing amide group (N-acetylglucosamine).

What two smaller molecules construct fats?

Glycerol and fatty acids.

Define triacylglycerol (triglyceride).

A fat molecule consisting of glycerol linked to three fatty acids via ester linkages.

Why are lipids hydrophobic?

They consist mostly of non-polar hydrocarbon chains that do not mix with water.

Differentiate saturated and unsaturated fatty acids.

Saturated: no double bonds, straight chains, solid at room temperature; Unsaturated: one or more C=C double bonds, bent chains, liquid oils.

What health risk is associated with a diet high in saturated fat?

Increased risk of cardiovascular disease due to plaque formation.

Describe a phospholipid’s basic structure.

Two fatty acid tails and a phosphate-containing hydrophilic head attached to glycerol.

What happens when phospholipids are placed in water?

They self-assemble into a bilayer with hydrophobic tails inward, forming the basis of cell membranes.

What defines a steroid?

A lipid with a carbon skeleton of four fused rings.

Why is cholesterol biologically important?

It stabilizes animal cell membranes and serves as a precursor for steroid hormones.

List at least three major functions of proteins.

Enzymatic catalysis, structural support, storage, transport, cellular communication, movement, and defense.

What monomers make up proteins?

Amino acids.

How many different amino acids are used in proteins?

Twenty.

Which part of an amino acid differs among the 20 varieties?

The R group (side chain).

Identify the three categories of amino acid side chains.

Non-polar (hydrophobic), polar uncharged (hydrophilic), and electrically charged (acidic or basic).

What type of bond links amino acids in a polypeptide?

Peptide bond.

What are the N-terminus and C-terminus of a polypeptide?

The free amino (N) end and the free carboxyl (C) end, respectively.

Name and briefly describe the four levels of protein structure.

Primary: amino acid sequence; Secondary: α-helix or β-sheet H-bonding patterns; Tertiary: 3-D folding via side-chain interactions; Quaternary: association of multiple polypeptides.

Give one example each of proteins with quaternary structure.

Collagen (three polypeptides) and hemoglobin (two α + two β chains).

How does a single amino acid substitution cause sickle-cell disease?

It alters hemoglobin’s primary structure, leading to abnormal aggregation and sickled red blood cells.

Define protein denaturation.

The loss of a protein’s native conformation (and function) due to environmental changes such as pH, salt, or temperature.

What are chaperonins?

Protein complexes that assist the proper folding of other proteins.

Name two techniques used to determine protein 3-D structure.

X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy.

What is a gene?

A unit of inheritance that encodes the amino acid sequence of a polypeptide, composed of DNA.

List the three main types of RNA involved in protein synthesis.

Messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

What are the monomers of nucleic acids called?

Nucleotides.

Name the three components of a nucleotide.

Nitrogenous base, pentose sugar, and phosphate group.

What is a nucleoside?

A nitrogenous base plus a sugar, without the phosphate.

Differentiate purines and pyrimidines.

Purines (adenine, guanine) have a double ring; pyrimidines (cytosine, thymine, uracil) have a single six-membered ring.

Which sugar is found in DNA and which in RNA?

DNA contains deoxyribose; RNA contains ribose.

What covalent bond links nucleotides in a polynucleotide chain?

A phosphodiester bond between the 3′ hydroxyl of one nucleotide and the 5′ phosphate of the next.

Describe the orientation of the two strands in the DNA double helix.

Antiparallel: one strand runs 5′→3′, the other 3′→5′.

State the complementary base-pairing rules in DNA.

A pairs with T, and G pairs with C via hydrogen bonds.

Why is complementary base pairing essential for DNA function?

It enables accurate replication and transcription, preserving genetic information.

List three key differences between DNA and RNA.

DNA: deoxyribose sugar, thymine, double-stranded; RNA: ribose sugar, uracil, usually single-stranded.

Explain the main implication of antiparallel strands for DNA replication.

DNA polymerases can only add nucleotides to the 3′ end, leading to leading and lagging strand synthesis.

How can molecular biology be used to assess evolutionary relationships?

By comparing DNA or protein sequences; closer similarity indicates closer evolutionary kinship.

What is the major biological role of fats?

Long-term energy storage.

Which type of molecule forms microfibrils that strengthen plant cell walls?

Parallel β-glucose cellulose chains bound by hydrogen bonds.

Why do phospholipid bilayers form spontaneously in aqueous environments?

Hydrophobic tails avoid water while hydrophilic heads interact with it, minimizing free energy.

Which enzymes can hydrolyze α linkages but not β linkages?

Human digestive enzymes such as amylase for starch; they cannot digest cellulose.

What structural feature of unsaturated fatty acids keeps plant oils liquid at room temperature?

Cis double bonds introduce kinks that prevent tight packing of molecules.

Why does cholesterol at high blood levels pose a health risk?

It can contribute to plaque buildup in arteries, increasing cardiovascular disease risk.

What is the role of hydrogen bonds in secondary protein structure?

They stabilize the α-helix and β-pleated sheet by linking backbone N–H and C=O groups.

Give the one-letter code for the amino acid lysine.

K.

Which amino acid contains a sulfhydryl (–SH) group capable of forming disulfide bridges?

Cysteine.

During peptide bond formation, what molecule is released?

Water (H₂O).

Explain why cellulose serves as dietary fiber for humans.

Humans lack enzymes to break β-1,4 linkages, so cellulose passes undigested, aiding bowel movement.

What happens to a denatured protein if favourable conditions return?

Some proteins can renature and regain function; others cannot.

Describe the basic flow of genetic information in cells (central dogma).

DNA → RNA → Protein.

What is the major component of biological membranes?

A phospholipid bilayer.

How do enzymes accelerate chemical reactions?

By lowering the activation energy barrier.

Why are proteins said to be the most diverse macromolecules?

Because 20 amino acids in different sequences and conformations create an enormous range of structures and functions.

What causes the sickle shape in red blood cells of affected individuals?

Aggregated mutant hemoglobin forms fibers that distort the cell.

Name the bond that links glycerol to a fatty acid in fats.

Ester linkage.

What is the defining chemical feature of a saturated fatty acid?

No carbon–carbon double bonds, fully saturated with hydrogen.

Which macromolecule class includes hormones like insulin and glucagon?

Proteins (specifically, hormonal proteins).