Cellular and Molecular Biology and Biochemistry — True/False: 20-Bio-A3 Biomechanics, December 2018, Q6

Question 6: Cellular and Molecular Biology and Biochemistry — True/False (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Approach. Each statement is evaluated against the precise underlying molecular/cell biology definition it tests; several items are deliberately constructed as a plausible-sounding but swapped, inverted, or mis-attributed version of a true fact and must be checked term-by-term rather than pattern-matched.

Question 6 — True/False verdicts and rationale (20 items, 1 mark each)
#	Statement (paraphrased)	Verdict	Rationale
1	Hydrogen bonds are weak/broken by thermal energy, yet contribute significantly to the specificity of macromolecular interactions.	True	Individually weak and reversible, but numerous and highly directional (base pairing, protein folding) — their collective geometry, not individual strength, gives specificity.
2	The active site of an enzyme usually occupies only a small fraction of the enzyme surface.	True	Standard biochemistry — the catalytic pocket is a small, precisely shaped region of an otherwise much larger protein.
3	Non-covalent bonds are too weak to influence the 3D structure of macromolecules.	False	Non-covalent interactions (H-bonds, ionic, hydrophobic, van der Waals) collectively determine secondary, tertiary and quaternary structure.
4	Affinity chromatography separates molecules according to their intrinsic charge.	False	That describes ion-exchange chromatography; affinity chromatography separates based on a specific binding interaction (e.g. antibody–antigen, enzyme–ligand).
5	Proteins can carry overall negative, positive, or no charge depending on solution pH.	True	Amphoteric behaviour; net charge depends on pH relative to the protein's isoelectric point (pI).
6	Ultracentrifugation allows greater separation of small molecules than centrifugation at lower g-force.	True	Higher gravitational force is needed to resolve/sediment smaller particles with higher resolving power.
7	If 14% of a bacterial DNA's nucleotides are adenine, must 36% be guanine?	True	Chargaff's rules (dsDNA): %A=%T so %T=14%, leaving %G+%C=72%, and %G=%C so each is 36%.
8	A G–C base pair is stabilized by at most two hydrogen bonds.	False	G–C pairs form THREE hydrogen bonds; A–T pairs form two — the statement has the count backwards.
9	During interphase, DNA is in the nucleus and each chromosome can be easily identified without staining.	False	Interphase chromatin is decondensed/diffuse; individual chromosomes are not distinguishable without staining (or condensation, as in mitosis).
10	Two closely related species should have the same number of chromosomes.	False	Chromosome number varies widely even between closely related species due to chromosomal fusions/rearrangements; relatedness does not fix karyotype.
11	Chromosomes, chromatin and chromatids all refer to DNA in association with proteins.	True	All three terms describe DNA–histone/protein complexes at different packaging states (general complex, condensed structure, one replicated copy).
12	Chromatids are always present in the cell.	False	Sister chromatids exist only after DNA replication (S phase through mitosis); a G1 chromosome has a single chromatid.
13	DNA was shown to be the hereditary material by an experiment where live VIRUS took up DNA from lysed cells.	False	The classic transformation experiment (Avery, MacLeod & McCarty) used live BACTERIA taking up DNA released from lysed/heat-killed bacteria, not a virus.
14	Chemical modification of histones (e.g. methylation) can regulate DNA packing in eukaryotic chromosomes.	True	Epigenetic histone modifications (methylation, acetylation) directly regulate chromatin condensation state.
15	Ion-exchange chromatography separates molecules based on charge.	True	Correct definition of ion-exchange chromatography.
16	SDS-PAGE separates proteins based on charge.	False	SDS coats proteins with a uniform negative charge-to-mass ratio and denatures them, so separation is by molecular SIZE, not native charge.
17	Only the sulfur in cysteine residues can form disulfide bridges in proteins.	True	Disulfide bonds form between cysteine thiol (–SH) side chains specifically; methionine's thioether sulfur does not participate.
18	In gel-filtration chromatography, large molecules are recovered quicker because they cannot enter the porous material as easily as smaller molecules.	True	Correct description of size-exclusion chromatography — large molecules are excluded from pores and elute first.
19	A protein can have multiple functional domains.	True	Multidomain proteins (each domain often independently folded/functional) are common.
20	Antibodies and antibiotics are similar molecules that function in similar ways.	False	Antibodies are large immune-system glycoproteins that bind antigens specifically; antibiotics are structurally diverse small molecules acting through distinct microbial-target mechanisms (see Question 3).

Topic: Core molecular biology and biochemistry facts across macromolecular interactions, chromatography, DNA chemistry, and chromosome biology.

Key relations: Chargaff's rules (%A=%T, %G=%C); G–C (3 H-bonds) vs. A–T (2 H-bonds); affinity vs. ion-exchange vs. size-exclusion (gel-filtration) chromatography principles; DNA-as-hereditary-material transformation experiment (bacteria, not virus).

Why this works: A large fraction of these statements are constructed as near-miss inversions of a genuinely true fact (swap which chromatography technique separates by charge, swap the H-bond count between base pairs, swap bacteria for virus in the classic transformation experiment) — recognizing that a plausible-sounding statement is testing one precise, named term or number is the key exam skill, since several items are specifically engineered to catch pattern-matching rather than definitional recall.

Common pitfall: answering by "vibe" (the statement sounds textbook-like, so mark True) instead of checking the precise definition of each named technique/term; items 4, 8, 13, and 16 are specifically designed to catch this.

Source: Alberts et al., Molecular Biology of the Cell, chs. 1–7; Nelson & Cox, Lehninger Principles of Biochemistry, chs. 3, 8–10.

Question 6 of 6: Cellular and Molecular Biology and Biochemistry — True/False

Question 6: Cellular and Molecular Biology and Biochemistry — True/False (20 marks)