Question 1

Describe the classification of carbohydrates.

Accepted Answer

Carbohydrates are classified based on the number of sugar units they contain. They are broadly divided into three groups: monosaccharides, disaccharides, and polysaccharides. Monosaccharides are single sugar units like glucose and fructose. Disaccharides consist of two monosaccharides linked by a glycosidic bond, such as sucrose and lactose. Polysaccharides are long chains of monosaccharide units and serve as energy storage (e.g., starch, glycogen) or structural components (e.g., cellulose). — The classification is based on the complexity and number of sugar units. Monosaccharides are simplest sugars, disaccharides are formed by two monosaccharides, and polysaccharides are polymers of many monosaccharides. This classification helps understand their biological roles and properties.

Question 2

Differentiate between D- and L-forms of glucose.

Accepted Answer

D- and L-forms of glucose are stereoisomers that differ in the spatial arrangement of atoms around the asymmetric carbon farthest from the aldehyde or ketone group. In D-glucose, the hydroxyl group (-OH) on the asymmetric carbon farthest from the aldehyde group is on the right side in the Fischer projection, whereas in L-glucose, it is on the left side. — The D- and L- notation is based on the configuration relative to D- and L-glyceraldehyde. Most naturally occurring sugars are in the D-form. This difference affects the way enzymes interact with the sugar.

Question 3

Draw the structure of a disaccharide made up of two monosaccharides glucose and fructose.

Accepted Answer

The disaccharide formed by glucose and fructose is sucrose. It consists of glucose and fructose units linked by an α-1,2-glycosidic bond between the anomeric carbon of glucose (C1) and the anomeric carbon of fructose (C2). The structure shows glucose in α-D-glucopyranose form and fructose in β-D-fructofuranose form connected via the glycosidic bond. — Sucrose is a common disaccharide where glucose and fructose are linked through their anomeric carbons, making it a non-reducing sugar. Drawing the structure involves showing the ring forms of glucose and fructose and the glycosidic bond connecting them.

Question 4

Draw the partial structure of starch and glycogen.

Accepted Answer

Starch is composed of two types of molecules: amylose (linear chains of α-D-glucose units linked by α-1,4-glycosidic bonds) and amylopectin (branched chains with α-1,4-glycosidic bonds and α-1,6-glycosidic bonds at branch points). Glycogen is similar to amylopectin but more highly branched, with α-1,4-glycosidic bonds in linear chains and α-1,6-glycosidic bonds at branch points occurring more frequently. — Both starch and glycogen are polysaccharides made of glucose units. Starch serves as energy storage in plants, glycogen in animals. Drawing partial structures involves showing the glucose units linked by α-1,4 bonds and branches via α-1,6 bonds.

Question 5

Write the major functions of carbohydrates.

Accepted Answer

Major functions of carbohydrates include: (1) Serving as a primary source of energy (e.g., glucose), (2) Acting as energy storage molecules (e.g., starch in plants, glycogen in animals), (3) Providing structural support (e.g., cellulose in plant cell walls), (4) Participating in cell recognition and signaling (e.g., glycoproteins and glycolipids), and (5) Forming components of nucleic acids (e.g., ribose and deoxyribose sugars). — Carbohydrates play diverse roles in organisms, from energy provision to structural integrity and cellular communication.

Question 6

Describe isomerisation in monosaccharides.

Accepted Answer

Isomerisation in monosaccharides refers to the process where a sugar molecule changes into another isomeric form without altering its molecular formula. For example, glucose and fructose are isomers; glucose is an aldose sugar (contains an aldehyde group), while fructose is a ketose sugar (contains a ketone group). Isomerisation can involve changes between aldoses and ketoses or between different stereoisomers (e.g., D- and L-forms). — Isomerisation is important in carbohydrate metabolism and biosynthesis, allowing sugars to interconvert and participate in various biochemical pathways.

Question 7

Differentiate between sphingolipids and glycerolipids.

Accepted Answer

Sphingolipids have a sphingoid base backbone, whereas glycerolipids have a glycerol backbone. Sphingolipids are a class of compound lipids that include ceramides and sphingomyelins, important in membrane structure and signaling. Glycerolipids include simple lipids like triacylglycerols and phospholipids, where fatty acids are esterified to glycerol. — The backbone difference affects the structure and function of these lipids in biological membranes and storage.

Question 8

Why are membrane lipids called amphipathic?

Accepted Answer

Membrane lipids are called amphipathic because they contain both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. Typically, they have hydrophilic phosphate head groups and hydrophobic fatty acid tails. This dual nature allows them to form bilayers in aqueous environments, essential for membrane structure and function. — The amphipathic property is critical for the formation of biological membranes, enabling selective permeability and compartmentalization.

Question 9

Differentiate between saturated and unsaturated fatty acids.

Accepted Answer

Saturated fatty acids have no double bonds between carbon atoms in their hydrocarbon chain, meaning all carbons are saturated with hydrogen atoms. Unsaturated fatty acids contain one or more double bonds, which introduce kinks in the chain. Saturated fats are typically solid at room temperature, while unsaturated fats are liquid. — The presence or absence of double bonds affects the physical properties and biological roles of fatty acids.

Question 10

Describe the various categories of amino acids.

Accepted Answer

Amino acids are categorized based on the properties of their side chains (R groups). Categories include: (1) Nonpolar (hydrophobic) amino acids like alanine and valine, (2) Polar uncharged amino acids like serine and threonine, (3) Positively charged (basic) amino acids like lysine and arginine, (4) Negatively charged (acidic) amino acids like aspartic acid and glutamic acid, and (5) Special amino acids like proline and glycine. Additionally, there are standard amino acids (20 common ones), non-standard amino acids (e.g., 4-hydroxy proline), and non-protein amino acids (e.g., ornithine). — This classification helps understand protein structure and function, as side chain properties influence folding and interactions.

Question 11

What is zwitterion? Draw the structure of zwitterion.

Accepted Answer

A zwitterion is a molecule that contains both positive and negative charges but is overall electrically neutral. In amino acids, at physiological pH, the amino group (-NH3+) is positively charged and the carboxyl group (-COO-) is negatively charged, forming a zwitterion. The structure shows the amino acid with NH3+ on the amino end and COO- on the carboxyl end. — Zwitterions are important for amino acid solubility and behavior in biological systems. The dual charge allows amino acids to act as buffers.

Question 12

What are non-standard and non-protein amino acids?

Accepted Answer

Non-standard amino acids are amino acids that are not among the 20 standard amino acids encoded by the genetic code but may be found in proteins due to post-translational modifications (e.g., 4-hydroxy proline, 5-hydroxy lysine). Non-protein amino acids are amino acids that are not incorporated into proteins but have biological roles (e.g., L-ornithine, L-citrulline). — Understanding these amino acids is important for studying protein modifications and metabolic pathways.

Question 13

How the peptide bonds are formed?

Accepted Answer

Peptide bonds are formed by a condensation reaction between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of another amino acid. This reaction releases a molecule of water (H2O) and forms a covalent bond called a peptide bond (-CO-NH-), linking the amino acids in a polypeptide chain. — Peptide bond formation is fundamental to protein synthesis. The bond is planar and has partial double bond character, restricting rotation and influencing protein structure.

Question 14

Draw the structure of Lys-Glu-Lys.

Accepted Answer

Lys-Glu-Lys is a tripeptide composed of lysine, glutamic acid, and lysine linked by peptide bonds. The structure shows the amino group of the first lysine, the peptide bond to glutamic acid, then another peptide bond to the second lysine, with side chains of lysine (positively charged) and glutamic acid (negatively charged) depicted appropriately. — Drawing the tripeptide involves showing the sequence of amino acids connected by peptide bonds and the side chains, which influence the peptide's properties.

Question 15

Describe the various secondary structures of protein.

Accepted Answer

The secondary structure of proteins refers to the local three-dimensional arrangement of the polypeptide backbone. The two major types are: (1) α-helix, a right-handed coil stabilized by hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen four residues ahead, and (2) β-pleated sheets, formed by hydrogen bonding between adjacent polypeptide chains or segments, arranged in parallel or antiparallel fashion. These structures contribute to the protein's overall shape and stability. — Secondary structures are stabilized by hydrogen bonds and are critical for protein folding and function.

Biomolecules

Biomolecules — Study Notes

Introduction to Biomolecules

Carbohydrates

Monosaccharides: Structure and Isomerism

Practice Questions — Biomolecules

All 12 Chapters in Biotechnology