Unit notes and practice questions
Everything here is for unit 3 of the Grade 11 Biology textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.
The cards filed under this chapter on the Grade 11 Biology page. Open one at a time.
When you use it
Use when relating the rate of an enzyme-catalyzed reaction to substrate concentration.
Watch out
KM represents the substrate concentration at half Vmax, not half the substrate concentration.
Drafted from Grade 11 Biology, pages 79-112, then checked twice before it went up
| Level | Description |
|---|---|
| Primary | Linear sequence of amino acids linked together by peptide bonds. |
| Secondary | Folding into alpha-helix or beta-pleated sheets via hydrogen bonds. |
| Tertiary | Overall three-dimensional shape formed by side-chain interactions. |
| Quaternary | Spatial arrangement of multiple folded polypeptide subunits. |
When you use it
Use when distinguishing between the four structural levels of enzyme proteins.
Watch out
Primary structure is held exclusively by covalent peptide bonds, while secondary and higher structures rely on hydrogen and side-chain bonds.
Drafted from Grade 11 Biology, pages 79-112, then checked twice before it went up
| Class | Catalytic Function |
|---|---|
| Oxidoreductases | Catalyze oxidation-reduction reactions and electron transfer. |
| Transferases | Transfer functional groups from a donor to an acceptor. |
| Hydrolases | Catalyze the cleavage of chemical bonds by hydrolysis. |
| Lyases | Cleave bonds by means other than hydrolysis or oxidation. |
| Isomerases | Convert molecules from one structural isomer to another. |
| Ligases | Join two molecules coupled with di-phosphate bond cleavage in ATP. |
When you use it
Use when classifying enzymes by the chemical reaction type they catalyze.
Watch out
Lyases break chemical bonds without water or oxidation, whereas hydrolases require water.
Drafted from Grade 11 Biology, pages 79-112, then checked twice before it went up
10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.
Question 1
Which enzyme found in human saliva helps to break down starches into sugars?
Answer: B Amylase
Why
According to the textbook, amylase is present in saliva and converts starches into simpler sugars.
Question 2
What is the inactive protein part of a conjugated enzyme called before it joins with a cofactor?
Answer: A Apoenzyme
Why
A conjugated enzyme (holoenzyme) is made of a protein part called the apoenzyme, which is inactive on its own, and a non-protein part called a cofactor.
Question 3
What is the first step in the traditional Ethiopian malting process used to prepare grains for beverages like tella?
Answer: B Steeping
Why
The three main steps of malting are steeping (soaking the grains in water), germinating (sprouting), and kilning (heating/drying).
Question 4
Which class of enzymes catalyzes the transfer of functional groups, such as a methyl group, from one molecule to another?
Answer: C Transferases
Why
Transferases are enzymes that transfer functional groups (like methyl groups) from a donor molecule to an acceptor molecule.
Question 5
Why do enzymes exhibit a colloidal nature that allows little or no dialysis across a semipermeable membrane?
Answer: A Because they have a high molecular weight and large size
Why
The textbook states that the colloidal property of enzymes is their tendency to show little or no movement across semipermeable membranes because of their large size or high molecular weight.
Question 6
In the secondary structure of proteins, how is the right-handed coiled strand of an α-helix held stable?
Answer: B By hydrogen bonds between N-H and C=O groups
Why
The α-helix is stabilized by hydrogen bonding between the hydrogen of the N-H group and the oxygen of the C=O group of amino acid residues.
Question 7
Which type of inhibitor binds only to the enzyme-substrate complex and not to the free enzyme?
Answer: B Uncompetitive inhibitor
Why
An uncompetitive inhibitor binds only to the enzyme-substrate complex (ES) rather than the free enzyme, slowing down the reaction.
Question 8
In the food industry, which enzyme is commonly used to tenderize meat for cooking?
Answer: A Papain
Why
Papain has culinary uses specifically for tenderizing meat before cooking.
Question 9
During modern and traditional malting, why must the green malt undergo kilning (heating)?
Answer: A To stop germination so the growing plant does not consume all the starch reserves
Why
Kilning dries the green malt and halts further growth. If germination continued, the growing seedling would use up all the starch reserves needed for brewing.
Question 10
How does a prosthetic group differ from a coenzyme in the structural classification of enzymes?
Answer: A A prosthetic group is firmly attached (often a metal ion), while a coenzyme is loosely attached (often a vitamin B complex).
Why
The non-protein cofactor part is classified into firmly attached prosthetic groups (usually metal ions) and loosely attached coenzymes (usually vitamin B complex molecules).
The app holds 12 questions on this unit, marked as you go. These are the first 10.
Unit 3 runs from page 79 to page 112 of the Ministry of Education edition.
Ministry of Education edition, English, 294 pages
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