Amino Acids Β· Protein Structure Β· Enzymes Β· Applications
π About this quiz
12 questions covering Units 1.3.1β1.3.4
Mix of multiple choice, true/false, and fill-in-the-blank
Instant feedback after each question
Unlimited attempts for practice
Estimated time: 20β25 minutes
QUESTION 1
What four groups are attached to the central carbon of every amino acid?
β Correct! Every amino acid has a central carbon bonded to an amino group (-NHβ), a carboxyl group (-COOH), a hydrogen atom, and a variable R group (side chain) that determines its properties.
QUESTION 2
Which level of protein structure refers to the local folding patterns like Ξ±-helices and Ξ²-sheets?
β Correct! Secondary structure refers to local folding patterns (Ξ±-helices, Ξ²-sheets) stabilized by hydrogen bonds between backbone atoms. Primary = sequence; Tertiary = overall 3D shape; Quaternary = multiple subunits.
QUESTION 3
How do enzymes speed up chemical reactions?
β Correct! Enzymes lower the activation energy (the energy barrier that must be overcome for a reaction to proceed). They do not change the equilibrium or provide energy; they make it easier for the reaction to occur.
QUESTION 4
Which model of enzyme action proposes that the active site changes shape slightly when the substrate binds?
β Correct! The induced fit model proposes that the active site is somewhat flexible and changes conformation upon substrate binding, becoming complementary only after binding. This stresses bonds and aids catalysis.
QUESTION 5
Why does enzyme activity decrease sharply at very high temperatures?
β Correct! High temperatures disrupt the hydrogen bonds and hydrophobic interactions that maintain the enzyme's 3D structure. The enzyme denatures (unfolds), losing the shape of its active site and thus its catalytic ability.
QUESTION 6
In competitive inhibition, the inhibitor binds to:
β Correct! Competitive inhibitors resemble the substrate and bind to the active site, blocking the real substrate from binding. This inhibition can be overcome by increasing substrate concentration.
QUESTION 7
What enzyme is primarily responsible for the browning of cut apples and potatoes?
β Correct! Polyphenol oxidase (PPO) catalyzes the oxidation of phenolic compounds to quinones, which then polymerize into brown melanins. This requires oxygen and occurs when cells are damaged.
QUESTION 8
The process by which an enzyme loses its three-dimensional structure and becomes inactive is called ________.
β Correct! Denaturation is the loss of a protein's three-dimensional structure (unfolding) due to heat, pH extremes, or other factors. The primary structure (sequence) remains intact, but function is lost.
QUESTION 9
Which enzyme breaks down pectin in cell walls during fruit ripening, leading to softening?
β Correct! Polygalacturonase breaks down pectin in the middle lamella and cell walls, causing fruit softening. This is a key enzyme in the ripening of climacteric fruits like tomatoes, bananas, and apples.
QUESTION 10
True or False: All enzymes require cofactors to function.
β Correct! It's False. Many enzymes function without cofactors. However, some enzymes require cofactors (inorganic ions like MgΒ²βΊ, ZnΒ²βΊ) or coenzymes (organic molecules like NADβΊ) for activity. These are called conjugated enzymes or holoenzymes.
QUESTION 11
Why are vegetables blanched (briefly heated) before freezing?
β Correct! Blanching denatures enzymes (like lipoxygenase, polyphenol oxidase, peroxidase) that would otherwise continue to cause off-flavors, color changes, and texture loss during frozen storage. Freezing slows but doesn't stop enzyme activity.
QUESTION 12
Which Ethiopian staple grain is valued for its very low prolamin content, making it suitable for people with celiac disease?
β Correct! Teff (Eragrostis tef) is an Ethiopian staple grain with very low prolamin content, making it safe for people with celiac disease. Its protein content (8-11%) is higher than many other cereals.
π Section 1.3 Complete!
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π Section 1.3 Complete!
You have completed all units in Section 1.3: Proteins and Enzymes. You should now be able to:
Describe amino acid structure and protein organization (primary to quaternary)