Most Important Biological Molecules MCQs with Answers

Water's high specific heat capacity helps living organisms resist drastic temperature changes, thus maintaining a stable internal environment (homeostasis).

As water freezes, hydrogen bonds stabilize, forming an open, crystalline lattice that spaces the molecules further apart, making ice less dense than liquid water, allowing it to float.

A large amount of energy is required to break the hydrogen bonds and convert liquid water to water vapor. This property allows for effective cooling as heat is removed from the body during evaporation (e.g., sweating).

In hydrolysis, water actively participates in the chemical reaction by splitting into H+ and OH- and adding across a bond, thus acting as a reactant or reagent.

Water molecules have the ability to spontaneously dissociate or ionize into a hydrogen ion (H+) and a hydroxide ion (OH-).

Cohesion, the strong attraction between water molecules due to hydrogen bonding, creates surface tension at the air-water interface.

Hydrophobic exclusion describes the tendency of nonpolar substances (like oil) to aggregate and separate from water, as water molecules prefer to hydrogen bond with each other rather than with the nonpolar molecules.

The lower density of ice means it floats on the surface, insulating the water below and preventing it from freezing completely, allowing aquatic organisms to survive.

The extensive network of hydrogen bonds between water molecules requires a significant amount of energy to break, leading to its unusually high boiling point.

The ionization of water into H+ and OH- ions is fundamental to the pH scale and the concept of neutrality (where [H+] = [OH-]).

Adhesion is the attraction between water molecules and molecules of other substances, such as the cellulose in plant cell walls or glass in a narrow tube.

Water, acting as a solvent, fills the plant cells, and its cohesive properties help maintain turgor pressure within the cells, which prevents wilting.

Water's high specific heat capacity allows it to absorb excess heat when metabolic activity is high and release it when the environment is cold, thus buffering temperature fluctuations.

Pure water at 25°C is neutral, meaning the concentration of H+ and OH- ions are equal, resulting in a pH of 7.

In ice, hydrogen bonds form a stable, crystalline lattice where molecules are more spread out compared to the constantly breaking and reforming bonds in liquid water, leading to its lower density.

Monosaccharides are true carbohydrates represented by the general molecular formula (CH2O)n, where 'n' is the number of carbon atoms, ranging from 3 to 7.

Monosaccharides are the simplest sugars, defined as polyhydroxy aldehydes (aldoses) or polyhydroxy ketones (ketoses).

Glucose is a simple sugar, specifically a hexose monosaccharide, as it cannot be hydrolyzed into simpler sugar units.

Glucose is an aldose because it contains an aldehyde functional group (-CHO).

The number of carbon atoms in monosaccharides ranges from 3 to 7.

Oligosaccharides are carbohydrates that yield 2 to 10 monosaccharide units upon hydrolysis. Sucrose (cane sugar), maltose, and lactose are common disaccharides, a type of oligosaccharide.

Monosaccharide units are joined together by a covalent bond known as a glycosidic bond, formed by a condensation reaction.

Sucrose is commonly known as cane sugar or table sugar and is formed by the condensation of one molecule of glucose and one molecule of fructose.

Lactose is formed by the condensation of one molecule of glucose and one molecule of galactose.

Starch is the principal carbohydrate stored in plant cells as an energy reserve.

Cellulose is a fibrous polysaccharide that forms the major structural component of plant cell walls.

Glycogen is the primary storage form of glucose in animals, especially abundant in the liver and muscle cells.

Alpha-glucose and beta-glucose are anomers, differing in the orientation of the hydroxyl group (-OH) on the anomeric carbon (carbon 1) when in ring form.

Chitin is a structural polysaccharide found in the cell walls of fungi and the exoskeletons of arthropods (insects, crustaceans).

In aqueous solutions, monosaccharides with five or more carbon atoms predominantly exist in cyclic (ring) forms, which are more stable than their open-chain counterparts.

Maltose is a disaccharide commonly known as malt sugar, composed of two glucose units joined by an alpha-1,4 glycosidic bond.

Disaccharides are formed from two monosaccharides by a condensation reaction, where a molecule of water is removed.

D-glucose and L-glucose are stereoisomers, specifically enantiomers, meaning they are non-superimposable mirror images of each other.

Biological systems, including human enzymes, are highly stereospecific. Most naturally occurring sugars are D-isomers, and the enzymes that process them are structured to recognize and act upon these 'right-handed' forms, making L-isomers non-metabolizable.

Starch is the primary storage polysaccharide in plants, allowing them to store excess glucose as a readily available energy reserve.

Glycogen is the animal equivalent of starch and is often referred to as 'animal starch' due to its role as the primary glucose storage form in animals.

Polysaccharides are complex carbohydrates (macromolecules) formed by the polymerization of hundreds to thousands of monosaccharide units linked by glycosidic bonds. They are generally not sweet and are less soluble or insoluble in water.

Hydrolysis is the reverse of condensation; it involves the addition of a water molecule to break the glycosidic bond, yielding two monosaccharide units from a disaccharide.

Monosaccharides are simple sugars, generally sweet in taste, readily soluble in water, and can be oxidized.

In the open-chain form of a monosaccharide, all carbon atoms except one (which is part of an aldehyde or ketone group) have a hydroxyl (-OH) group attached.

Proteins are polymers made up of repeating monomer units called amino acids, linked together by peptide bonds.

Every amino acid contains at least one amino group (-NH2) and one carboxyl group (-COOH), both attached to the central carbon atom (alpha-carbon).

The R-group, or side chain, differs among the 20 amino acids and gives each its unique properties.

Amino acids are linked by peptide bonds, formed during a condensation reaction between the carboxyl and amino groups.

Peptide bond formation is a dehydration synthesis reaction where a water molecule is removed.

The primary structure is the unique linear sequence of amino acids in a protein.

A single amino acid change in hemoglobin leads to sickle cell disease, showing the importance of amino acid sequence.

Secondary structure includes localized folding like alpha-helices and beta-sheets, stabilized by hydrogen bonds.

Tertiary structure is the full 3D structure formed by the folding and interactions of the polypeptide chain.

Quaternary structure describes the interaction and arrangement of multiple polypeptide subunits in a protein.

Most enzymes are proteins that catalyze biological reactions.

Fibrous proteins have elongated shapes and provide structural support (e.g., collagen, keratin).

Globular proteins are spherical, soluble, and perform functional roles in the body.

Hydrolysis is the reaction that breaks peptide bonds by adding water, releasing amino acids.

Hydrophobic interactions drive protein folding by keeping nonpolar side chains away from the aqueous environment.

Lipids are a diverse group of organic compounds characterized by their insolubility in water and solubility in nonpolar organic solvents due to their nonpolar hydrocarbon nature.

Triglycerides are formed when glycerol reacts with three fatty acids via ester bonds in a condensation reaction.

Triglycerides serve as the main form of long-term energy storage in many organisms.

Phospholipids are amphipathic, having both a hydrophilic head and hydrophobic tails, enabling them to form cell membranes.

Cholesterol is a steroid composed of a four-ring structure and is a precursor for many hormones.

Waxes are hydrophobic lipids that serve as waterproof coatings on plant leaves, fruits, and animal surfaces.

Terpenes include biologically important molecules like vitamins A, D, E, K and pigments like carotenoids.

The phosphate group is polar and hydrophilic, making it the water-attracting portion of a phospholipid.

Unsaturated fatty acids contain double bonds, unlike saturated fatty acids which have only single bonds.

Prostaglandins are eicosanoids that function as local hormones, playing roles in inflammation and other processes.

RNA differs from DNA by having ribose instead of deoxyribose and uracil instead of thymine. RNA is usually single-stranded; both contain phosphate groups.

Messenger RNA (mRNA) carries genetic code from the DNA to ribosomes, where it is translated into proteins.

Ribosomal RNA (rRNA) is part of ribosomes and catalyzes the formation of peptide bonds during protein synthesis.

Conjugated molecules consist of two or more different biological components, such as protein and carbohydrate.

Glycoproteins help in cell communication and recognition by acting as molecular identifiers on cell surfaces.

Lipoproteins transport hydrophobic lipids in blood. LDL and HDL are examples of lipoproteins.

Glycolipids are involved in cell recognition and communication, especially in neural tissue.

Nucleoproteins are DNA/RNA-protein complexes found in chromosomes and ribosomes, essential for gene expression and protein production.