BIO NMDCAT

While the sugar-phosphate backbone provides structural integrity, genetic information is encoded in the specific linear sequence of the four nitrogenous bases (A, T, G, C). This sequence is the code that dictates protein synthesis and is heritable.

Both glycogen and cellulose are glucose polymers, but glycogen has α-1,4 and α-1,6 glycosidic bonds, allowing it to be a branched, digestible energy source. Cellulose has β-1,4 glycosidic bonds, which create straight chains that form strong structural fibers and are indigestible by most animals.

Condensation (or dehydration synthesis) is the anabolic process where monomers are covalently bonded together with the simultaneous removal of a water molecule. This is the fundamental mechanism for polymer formation. Hydrolysis is the reverse, catabolic process.

Quaternary structure exists only in proteins composed of more than one polypeptide chain (subunit). It describes the specific 3D arrangement and interactions between these individual, folded subunits, as seen in hemoglobin (α2β2).

A non-competitive inhibitor binds to a site different from the active site (an allosteric site). This binding alters the three-dimensional shape of the enzyme, including the active site, so the substrate can no longer bind effectively, regardless of substrate concentration.

The specific base pairing (A-T with 2 H-bonds, G-C with 3 H-bonds) between a purine and a pyrimidine ensures the two DNA strands are equidistant apart, creating a uniform diameter. This complementarity is also the molecular logic for semi-conservative replication.

Terpenoids (or terpenes), including steroids, carotenoids, and natural rubber, are a large class of lipids built from multiple isoprene units (C5H8). This distinguishes their biosynthetic origin from acylglycerols, which are fatty acid esters.

Sucrose is dextrorotatory, but upon hydrolysis, the resulting mixture of glucose (dextrorotatory) and fructose (strongly levorotatory) makes the overall solution levorotatory. This change in optical rotation is called inversion, and the product is called invert sugar.

The lock-and-key model proposes a rigid active site that is perfectly complementary only to a specific substrate, ensuring high specificity. The induced fit model expands on this, adding flexibility, but the lock-and-key concept directly explains absolute specificity.

Pepsin is a gastric enzyme that has adapted to function in the highly acidic environment of the stomach, where HCl is present. Therefore, its optimum pH is strongly acidic (around 1.5-2.0), unlike enzymes like trypsin which function in the alkaline small intestine (pH ~8.0).

The covalent bond linking the nitrogenous base (purine or pyrimidine) to the 1' carbon of the pentose sugar (ribose or deoxyribose) is an N-glycosidic bond. The phosphate group is linked to the 5' carbon.

A reducing sugar has a free aldehyde or ketone group that can reduce (donate electrons to) another compound, such as Cu²⁺ to Cu⁺ in Benedict's test. Glycosidic bond formation masks this group. Polymerization is a separate property, and glucose is lipid-insoluble.

The covalent linkage in the sugar-phosphate backbone of nucleic acids is a phosphodiester bond. It is formed between the 3' carbon of one sugar and the 5' phosphate group of the adjacent sugar. Glycosidic bonds link sugar to base, and peptide bonds link amino acids.

A triglyceride has glycerol esterified to three fatty acids. A phospholipid is a modified triglyceride where one fatty acid chain is replaced by a highly polar phosphate group, which is often further linked to a nitrogenous compound, creating an amphipathic molecule.

The bulk of a lipid molecule, like a fatty acid or triglyceride, consists of long hydrocarbon chains (C-H bonds). These bonds are non-polar and hydrophobic, repelling interaction with polar water molecules and leading to insolubility.

Non-essential amino acids are those the human body can synthesize de novo. Alanine can be produced from pyruvate. Lysine, phenylalanine, and valine are essential amino acids that cannot be synthesized and must be obtained from the diet.

Both α-helices and β-pleated sheets are secondary structures stabilized by regular hydrogen bonding between the backbone atoms (the C=O of one amino acid and the N-H of another). R-group interactions define the tertiary structure. Disulfide bridges are covalent, not hydrogen, bonds.

Tertiary structure is the overall 3D conformation of a single polypeptide chain, driven by interactions between the R-groups. This includes hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges. The backbone H-bonding defines secondary structure.

Changing one amino acid (primary structure) can disrupt the local folding (secondary), which in turn alters the overall 3D shape (tertiary) and its ability to bind with other subunits (quaternary). Thus, all higher levels of structure are ultimately dependent on the primary sequence.