Biological Catalysts and Related Topics

This set of flashcards covers key concepts related to enzymes, carbohydrates, proteins, nucleotides, and cellular signaling important for understanding biological catalysis and molecular biology.

What are enzymes?

Enzymes are biological catalysts that act to accelerate chemical reactions.

How do enzymes differ from inorganic catalysts?

Enzymes are largely organic in nature, while inorganic catalysts can be inorganic compounds.

What advantages do enzymes have over inorganic catalysts?

Milder reaction conditions, higher reaction rates, and capacity for regulation.

What is an apoenzyme?

The protein part of an enzyme that requires a cofactor to be active.

Define coenzyme.

An organic molecule often derived from vitamins that is necessary for the functioning of an enzyme.

What is a holoenzyme?

An active enzyme consisting of an apoenzyme and its cofactors.

What factors can affect enzyme activity?

Enzyme concentration, substrate concentration, temperature, pH, ionic strength, and the presence of cofactors.

What happens to enzymes at high temperatures?

Enzymes will denature at high temperatures.

What is the enzyme's active site?

The region of an enzyme where substrate molecules bind and undergo a chemical reaction.

What is transition state in catalysis?

The state corresponding to the highest potential energy along a reaction coordinate.

What is the Michaelis-Menten equation?

V = V{max}[S]/(Km + [S]) describes the rate of enzyme-catalyzed reactions.

What do Km and K{cat} represent in enzyme kinetics?

Km is the Michaelis constant, and K{cat} is the turnover number, indicating how many substrate molecules one enzyme can convert per second.

What distinguishes competitive inhibitors from non-competitive inhibitors?

Competitive inhibitors mimic the substrate and compete for the active site, while non-competitive inhibitors alter the enzyme's conformation.

What is meant by allosteric regulation?

Regulation of enzyme activity via binding of modulator to a site other than the active center.

What characters define monosaccharides?

Monosaccharides are characterized by their empirical formula (CH2O)n and can be aldoses or ketoses.

What are the two main types of fatty acids?

Saturated fatty acids (no double bonds) and unsaturated fatty acids (one or more double bonds).

What is a glycosidic bond?

A bond formed between the anomeric carbon of one monosaccharide and a hydroxyl group of another monosaccharide.

Define phosphodiester bond.

The bond linking successive nucleotides in the linear polymers of nucleic acids.

What are the primary functions of biological membranes?

To define cell boundaries, allow import/export, retain metabolites, sense signals, provide compartmentalization, and support ATP synthesis.

What are the three main types of membrane proteins?

Peripheral, integral, and anchored proteins.

What is G-protein coupled signaling?

A mechanism by which GPCRs interact with G proteins to mediate signal transduction activities.

What is the "lock and key" model?

A theory suggesting that the active site of an enzyme is precisely complementary in shape to its substrate.

What is the "induced fit" model?

A theory proposing that an enzyme's active site changes shape slightly upon substrate binding to achieve a tighter fit.

Name common carbohydrates composed of two monosaccharide units.

Examples include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).

Describe the typical structure of a DNA molecule.

It consists of two antiparallel polynucleotide strands coiled around a central axis, forming a double helix.

How do enzymes lower activation energy?

By providing an alternative reaction pathway with a lower activation energy.

What is enzyme specificity?

The ability of an enzyme to catalyze only one reaction or a specific type of reaction with specific substrates.

What is a cofactor?

A non-protein chemical compound that is required for the enzyme's biological activity. It can be a metal ion or an organic molecule (coenzyme).

What types of interactions are involved in substrate binding at the active site?

Mainly non-covalent interactions such as hydrogen bonds, ionic bonds, and van der Waals forces.

What does V_{max} represent in enzyme kinetics?

The maximum rate of reaction when the enzyme is saturated with substrate.

What does a low K_m indicate about an enzyme's affinity for its substrate?

A low K_m indicates a high affinity of the enzyme for its substrate.

How does competitive inhibition affect V{max} and Km?

V{max} remains unchanged, while Km increases.

How does non-competitive inhibition affect V{max} and Km?

V{max} decreases, while Km remains unchanged.

What is feedback inhibition?

Regulation where the end product of a metabolic pathway inhibits an enzyme early in the pathway, controlling the pathway's activity.

What is the general chemical formula for most carbohydrates?

(CH2O)n

Name a common example of an aldose and a ketose monosaccharide.

Glucose (aldose) and Fructose (ketose).

What are the main storage polysaccharides in plants and animals?

Starch in plants and glycogen in animals.

What is the primary function of triglycerides?

Energy storage.

Define phospholipid.

A lipid containing a phosphate group, forming the basic structure of cell membranes.

What are the three components that make up a nucleotide?

A nitrogenous base, a five-carbon sugar (pentose), and one or more phosphate groups.

What type of bond is responsible for holding the two strands of a DNA double helix together?

Hydrogen bonds between complementary nitrogenous bases.

What are two key structural differences between DNA and RNA?

DNA contains deoxyribose sugar and thymine, is double-stranded; RNA contains ribose sugar and uracil, is typically single-stranded.

Describe the "fluid mosaic model" of biological membranes.

A model describing the cell membrane as a fluid structure with a mosaic of various proteins embedded in or attached to a double layer of lipids.

What is the role of cholesterol in animal cell membranes?

It modulates membrane fluidity, making it less fluid at high temperatures and preventing it from becoming too rigid at low temperatures.

What is passive transport across a membrane?

The movement of substances across a cell membrane without the input of metabolic energy, typically down a concentration gradient.

Name two common second messengers involved in cell signaling.

Cyclic AMP (cAMP) and calcium ions (Ca^{2+}).

What is a Receptor Tyrosine Kinase (RTK)?

A high-affinity cell surface receptor for many polypeptide growth factors, hormones, and cytokines. Upon binding a ligand, RTKs activate by autophosphorylation of tyrosine residues.