Water & Chemistry
Identify the intermolecular attraction that occurs between water molecules and explain why it can form.
Hydrogen bonding. Water is polar because oxygen is partially negative and the hydrogens are partially positive, allowing the H of one molecule to be attracted to the O of another.
Identify the monomer and the covalent linkage associated with proteins.
Amino acids; peptide bonds
What level of protein structure is determined directly by the sequence of amino acids?
Primary structure
Why can O₂ pass directly through the phospholipid bilayer while Na⁺ cannot?
O₂ is small and non-polar and can pass through the hydrophobic interior of the membrane. Na⁺ is charged and therefore cannot readily cross the hydrophobic region.
DNA and RNA are both nucleic acids. Identify two structural differences between them.
Any two: DNA contains deoxyribose while RNA contains ribose; DNA contains thymine while RNA contains uracil; DNA is generally double-stranded while RNA is generally single-stranded.
A molecule contains several hydroxyl groups. Predict whether it will generally be hydrophilic or hydrophobic and explain why.
Hydrophilic. Hydroxyl groups are polar and can form hydrogen bonds with water.
Explain the difference between hydrolysis and condensation reactions in terms of both water and biological polymers.
Condensation joins smaller molecules while removing/forming water as a product, whereas hydrolysis uses water to break covalent linkages and separate larger molecules.
Explain why changing the pH around an enzyme can change its activity even though the enzyme's amino acid sequence remains unchanged.
Changes in pH can affect the charges of R-groups and disrupt interactions that maintain the enzyme's three-dimensional structure, potentially changing the shape/properties of its active site.
A molecule crosses a membrane through a carrier protein without the cell directly using energy. What additional information would you need to determine whether this is facilitated diffusion?
Its concentration gradient. If it moves from higher to lower concentration through the carrier, it is facilitated diffusion.
A researcher finds a biological polymer composed of repeating monomers containing a sugar, phosphate group, and nitrogenous base. Identify the class of macromolecule and its monomer.
Nucleic acid; nucleotide.
Sweating cools the human body even though the sweat initially has approximately the same temperature as the skin. Explain why.
Water has a high heat of vaporization. Considerable energy is required to overcome hydrogen bonding and convert liquid water to vapour. That energy is absorbed from the body, producing a cooling effect.
A fatty acid contains 18 carbon atoms and one carbon-carbon double bond. Classify it and predict how its structure would influence its physical properties compared with an 18-carbon fatty acid containing no double bonds.
It is unsaturated. The double bond changes the shape of the hydrocarbon chain, reducing how tightly the molecules can pack. It would be liquid at room temperature, whereas the saturated hydrocarbon would be solid.
An enzyme functions at 25% of its maximum rate at 10°C and 100% at 37°C. Explain this difference.
At 10°C, molecules have less kinetic energy, resulting in fewer successful collisions between enzyme and substrate and therefore fewer enzyme-substrate complexes forming per unit time.
A cell containing 0.40 mol/L non-permeable solute is placed in a 0.65 mol/L solution. Predict what happens to the cell and explain why.
The external solution is hypertonic. Water undergoes net movement out of the cell by osmosis, so the cell decreases in volume.
An enzyme has the following reaction rates:
Temperature: 15°C, 25°C, 35°C, 45°C, 60°C
Rate: 18, 46, 91, 63, 7
Based on these data, estimate the enzyme's optimum temperature and explain why you cannot conclude the exact optimum from this experiment.
Approximately 35°C, because that temperature produced the highest measured rate. However, temperatures between the tested values were not investigated, so the true optimum could be somewhat above or below 35°C.
A pond begins to freeze during the winter. Explain why the ice forms at the surface rather than sinking and how this property benefits aquatic organisms.
Hydrogen bonding creates an open lattice in ice that spaces water molecules farther apart, making solid water less dense than liquid water. Ice therefore floats and forms an insulating surface layer, allowing liquid water to remain underneath.
A scientist hydrolyzes a biological molecule and obtains glycerol and three fatty acids. Identify the original molecule and the type of linkage that was broken.
A triglyceride; ester linkages were broken.
Two inhibitors decrease the activity of the same enzyme. Inhibitor A resembles the substrate, while Inhibitor B binds to a location far from the active site. Compare how each inhibitor affects the enzyme.
A is a competitive inhibitor that competes with the substrate for the active site. B is a non-competitive/allosteric inhibitor that binds elsewhere and changes the enzyme's conformation, altering its active site/function.
A toxin prevents cells from producing ATP. Predict the effect on each process and justify your choices:
O₂: can continue through simple diffusion.
Na⁺: would be impaired because movement against the gradient requires active transport/energy.
A red blood cell is placed into an unknown solution and decreases in volume. What can you conclude about the solution and the direction of water movement? Explain.
The solution is hypertonic relative to the cell. It contains a greater concentration of non-permeable solute, resulting in net movement of water out of the cell by osmosis.
Name a functional group that can act as a base and one that can act as an acid. Explain how each functional group can do this.
Acid: carboxyl group (-COOH) can donate H+
Base: amino group (-NH2) can accept H+
A student forms a triglyceride. How many water molecules are produced, how many ester linkages are formed, and which functional groups participate in forming each linkage?
3 H₂O molecules and 3 ester linkages. Each linkage forms between a hydroxyl group of glycerol and the carboxyl group of a fatty acid.
A mutation replaces a hydrophobic amino acid located inside a folded protein with a charged amino acid. The protein loses its function even though it is still produced. Explain the sequence of events connecting the mutation to the loss of function.
The substitution changes the primary structure. Because the new R-group has different chemical properties, its interactions with other R-groups change. This can alter tertiary structure/folding, changing the protein's three-dimensional shape. If a functional region such as an active or binding site changes shape, the protein may no longer perform its function.
An intestinal cell needs to accumulate glucose until its intracellular concentration is much greater than its extracellular concentration. Glucose is large and polar. Explain how the cell can accomplish this.
Glucose must be transported through a symporter alongside Na+. Na+ is pumped against its concentration gradient using a K+/Na+ antiporter using ATP energy. The Na+ then follows its concentration gradient back into the cell, bringing a glucose molecule with it.
A biological molecule:
Identify the class of macromolecule, its monomer, the bond joining its monomers, and the structural feature responsible for its information content.
Nucleic acid
Monomer = nucleotide
Linkage = phosphodiester bond
Information comes from the sequence of nitrogenous bases/nucleotides.