Q: What are the four major classes of biological macromolecules?
A: Carbohydrates, Proteins, Nucleic acids, and Lipids.
Q: How are macromolecules synthesized in cells?
A: By linking monomers into polymers via condensation/dehydration reactions.
Q: What are the 20 amino acids used for?
A: They are the monomers that form polypeptides and proteins.
Q: Distinguish peptide, polypeptide, and protein.
A: Peptide = short chain (2–50 aa); polypeptide = longer chain (≈51+ aa); protein = functional folded polypeptide(s).
Q: What are the four levels of protein structure?
A: Primary (sequence), Secondary (α-helices/β-sheets), Tertiary (3D fold), Quaternary (multi-subunit assembly).
Q: Why is protein conformation important?
A: Shape determines function — active sites, binding, catalysis depend on conformation.
Q: What stabilizes secondary and tertiary protein structures?
A: Hydrogen bonds, ionic interactions, hydrophobic interactions, and disulfide bonds.
Q: What are nucleic acids and their basic function?
A: DNA and RNA; they store, transmit, and express genetic information.
Q: What is a nucleotide?
A: A monomer of nucleic acids composed of a sugar, phosphate group, and nitrogenous base (A, T/U, C, G).
Q: Briefly describe gene expression.
A: DNA → transcription to mRNA → translation at ribosomes → polypeptide → folded protein.
Q: What are lipids and why are they critical for cells?
A: Hydrophobic molecules (fats, phospholipids, steroids) used for energy storage and membrane structure.
Q: What is the amphipathic phospholipid and what structure does it form?
A: Molecule with hydrophilic head and hydrophobic tails; forms the phospholipid bilayer of membranes.
Q: Define selective permeability of the plasma membrane.
A: The membrane permits certain substances to pass (e.g., gases, small nonpolar molecules) while restricting others.
Q: What is diffusion and give a biological example.
A: Passive movement down a concentration gradient; e.g., O₂ entering a cell.
Q: What is facilitated diffusion?
A: Passive transport of polar/charged molecules through specific transmembrane proteins (channels/carriers).
Q: What is active transport and a key example?
A: Energy-dependent movement against gradients; e.g., Na⁺/K⁺ ATPase pump.
Q: How does the Na⁺/K⁺ pump operate and why is it important?
A: Pumps 3 Na⁺ out and 2 K⁺ in per ATP; maintains ionic gradients and contributes to membrane potential.
Q: Name three types of transmembrane transport proteins.
A: Channels (including leak), gated channels (voltage/ligand/mechanosensitive), and pumps.
Q: What are leak channels?
A: Channels that remain open allowing steady passive ion flow (e.g., K⁺ leak channels).
Q: What is a ligand in the context of membrane proteins?
A: A molecule (e.g., neurotransmitter) that binds to a specific site on a receptor or channel.
Q: What is the endomembrane system?
A: ER, Golgi apparatus, vesicles, and lysosomes — organelles that synthesize, modify, and traffic proteins and lipids.
Q: What are the roles of rough ER vs smooth ER?
A: Rough ER: protein synthesis (has ribosomes). Smooth ER: lipid synthesis, detoxification, Ca²⁺ storage.
Q: What does the Golgi apparatus do?
A: Modifies, sorts, tags, and packages proteins into vesicles for secretion or delivery to organelles.
Q: What are lysosomes and their function?
A: Vesicles with digestive enzymes that degrade macromolecules and recycle cellular debris.
