SBI4U · Unit 1 test review

Biochemistry: Test Review

Everything for the Unit 1 test on one page: the key facts from all 5 lessons, the mistakes that cost the most marks, and a practice test that points you back to the lessons you need.

Key facts

The Chemistry of Life: Bonds, Water and Functional Groups

$Δ EN$ < about 0.5: nonpolar covalent; about 0.5–1.7: polar covalent; > about 1.7: ionic.
A hydrogen bond is an attraction between a $δ^{+}$ H (on O or N) and a $δ^{-}$ O or N elsewhere; it is weak alone but powerful in large numbers.
$pH = - lo g [H^{+}]$ ; each pH unit is a tenfold change in $[H^{+}]$ . Blood is buffered at 7.35–7.45 by $H_{2} CO_{3} / HCO_{3}^{-}$ .
Functional groups: hydroxyl –OH, carbonyl C=O, carboxyl –COOH (acid), amino –NH₂ (base), phosphate –OPO₃²⁻, sulfhydryl –SH (disulfide bridges).
Condensation releases $H_{2} O$ to join monomers; hydrolysis uses $H_{2} O$ to split them. Joining $n$ monomers releases $n - 1$ water molecules.
Redox: OIL RIG. The molecule that loses electrons is oxidized; the one that gains them is reduced.

Carbohydrates, Lipids, Proteins and Nucleic Acids

Glycosidic bond (sugars), ester bond (fats), peptide bond (proteins), phosphodiester bond (nucleic acids): all made by condensation, all broken by hydrolysis.
Alpha glucose builds coiled storage polymers (starch, glycogen); beta glucose builds straight structural fibres (cellulose). Chitin is a beta-linked structural polysaccharide.
Saturated fats: no C=C, straight tails, solid. Unsaturated: cis C=C kinks, liquid. Trans fats: straight despite C=C, raise LDL.
Protein structure: primary (sequence, peptide bonds), secondary (α-helix, β-sheet, backbone H bonds), tertiary (R group interactions, disulfide bridges), quaternary (multiple chains). Denaturation destroys levels 2–4, not 1.
DNA: deoxyribose, A-T and G-C, double-stranded. RNA: ribose, uracil replaces thymine, single-stranded. ATP = adenine + ribose + 3 phosphates.
Food tests: Benedict's (reducing sugar, brick-red when heated), iodine (starch, blue-black), biuret (protein, violet), Sudan IV or grease spot (lipid).

Enzymes: Structure, Mechanism and Regulation

Enzymes lower activation energy ( $E_{a}$ ); they do not change $Δ G$ and are not used up.
$E + S \to ES \to E + P$ . Induced fit: binding changes the active site's shape, straining the substrate's bonds.
Rate rises with temperature up to an optimum, then falls as the enzyme denatures; each enzyme has an optimum pH.
Increasing [S] raises the rate until the enzyme is saturated at $V_{ma x}$ ; increasing [E] raises $V_{ma x}$ when substrate is in excess.
Competitive inhibitors block the active site (overcome by more substrate). Non-competitive inhibitors bind elsewhere and lower $V_{ma x}$ .
Feedback inhibition: a pathway's end product allosterically inhibits its first enzyme.

Organelles, the Fluid Mosaic Model and Membrane Transport

Endomembrane pathway for secreted proteins: rough ER ribosome $\to$ ER lumen $\to$ transport vesicle $\to$ Golgi $\to$ secretory vesicle $\to$ exocytosis.
Fluid mosaic model: phospholipid bilayer + cholesterol + integral and peripheral proteins + glycoproteins; small nonpolar molecules cross freely, ions and large polar molecules need proteins.
Passive transport (diffusion, osmosis, facilitated diffusion) goes down the concentration gradient with no ATP; active transport goes against it and uses ATP.
Water moves toward the hypertonic side. Hypotonic solution: animal cells lyse, plant cells turgid. Hypertonic: animal cells crenate, plant cells plasmolyze.
Sodium-potassium pump: 3 Na⁺ out and 2 K⁺ in per ATP.
$% change in mass = \frac{final - initial}{initial} \times 100%$

Viruses, Cancer and Cell-Targeted Medicine

Viruses are obligate intracellular parasites: attach to a specific receptor, enter, copy the genome with host machinery, assemble, leave.
HIV: gp120 binds CD4, then the CCR5 (or CXCR4) co-receptor; gp41 drives fusion; reverse transcriptase makes DNA; integrase inserts it; protease matures new virions.
Antiretroviral classes match life-cycle steps: entry (CCR5 antagonists, fusion inhibitors), NRTIs and NNRTIs, integrase inhibitors, protease inhibitors. ART combines about three drugs to prevent resistance.
HIV cannot yet be cured because integrated proviruses hide in resting cells; HCV never integrates, so 8–12 weeks of direct-acting antivirals cure more than 95% of patients.
Monoclonal antibodies come from hybridomas (B cell fused with a myeloma cell); they neutralize, block, flag cells for destruction, release immune brakes or deliver drugs.
Log reduction in viral load: $lo g_{10} (\frac{initial}{final})$ ; each 1-log drop is a tenfold decrease.

Where marks get lost

Calling the O–H bond inside a water molecule a hydrogen bond. That bond is polar covalent; a hydrogen bond is the weaker attraction between separate molecules (or distant parts of one large molecule). (The Chemistry of Life: Bonds, Water and Functional Groups)
Mixing up hydrolysis and dehydration synthesis. Hydro-lysis means water-splitting: water is used to break a bond. Dehydration synthesis removes water to make a bond. (The Chemistry of Life: Bonds, Water and Functional Groups)
Thinking pH 4 is twice as acidic as pH 8. The scale is logarithmic, so a 4-unit difference is $1 0^{4} = 10000$ times more $H^{+}$ . (The Chemistry of Life: Bonds, Water and Functional Groups)
Confusing carbonyl (C=O) with carboxyl (–COOH). A carboxyl contains a carbonyl plus an –OH on the same carbon, and that combination makes it acidic. (The Chemistry of Life: Bonds, Water and Functional Groups)
Thinking oxidation always means adding oxygen. In biology it means losing electrons, often by losing hydrogen atoms, as when glucose is oxidized and $NAD^{+}$ is reduced to NADH. (The Chemistry of Life: Bonds, Water and Functional Groups)
Calling triglycerides polymers. Lipids are macromolecules but are not built from repeating monomers; a triglyceride is one glycerol plus three fatty acids. (Carbohydrates, Lipids, Proteins and Nucleic Acids)
Thinking denaturation breaks peptide bonds. Denaturing disrupts the weaker bonds of secondary, tertiary and quaternary structure; the amino acid sequence (primary structure) stays intact. (Carbohydrates, Lipids, Proteins and Nucleic Acids)
Assuming every sugar gives a positive Benedict's test. Sucrose is a non-reducing sugar and leaves Benedict's blue until it is hydrolyzed. (Carbohydrates, Lipids, Proteins and Nucleic Acids)
Saying unsaturated fats are liquid because they have fewer carbons. It is the cis double bonds that kink the tails and stop them packing closely. (Carbohydrates, Lipids, Proteins and Nucleic Acids)
Mixing up the bonds of secondary and tertiary structure. Secondary structure is hydrogen bonds along the backbone; tertiary structure comes from interactions between R groups. (Carbohydrates, Lipids, Proteins and Nucleic Acids)
Saying enzymes "die" at high temperatures. Enzymes are molecules, not living things; they denature, meaning they lose their 3D shape. (Enzymes: Structure, Mechanism and Regulation)
Saying an enzyme provides the activation energy. It lowers the activation energy by giving the reaction a different pathway; it does not supply energy or change $Δ G$ . (Enzymes: Structure, Mechanism and Regulation)
Thinking cold temperatures denature enzymes. Cold slows collisions, but the shape survives, so activity returns on warming; heat denaturation is usually permanent. (Enzymes: Structure, Mechanism and Regulation)
Mixing up the two inhibitors. Competitive inhibitors compete for the active site and can be outcompeted by more substrate; non-competitive inhibitors bind elsewhere and lower $V_{ma x}$ whatever the [S]. (Enzymes: Structure, Mechanism and Regulation)
Explaining the plateau at high [S] as the enzyme being used up. The enzyme is saturated: every active site is busy, so the rate is limited by how fast each enzyme can turn substrate over. (Enzymes: Structure, Mechanism and Regulation)
Saying water moves toward the hypotonic solution. Water moves toward the solution with more solute (the hypertonic side), where there is less free water. (Organelles, the Fluid Mosaic Model and Membrane Transport)
Calling facilitated diffusion active transport because it uses a protein. Using a protein does not mean using energy: facilitated diffusion goes down the gradient and needs no ATP. (Organelles, the Fluid Mosaic Model and Membrane Transport)
Using hypertonic or hypotonic without saying compared with what. These terms are relative; state whether the solution is hypertonic to the cell or the cell to the solution. (Organelles, the Fluid Mosaic Model and Membrane Transport)
Getting the pump ratio backwards. The sodium-potassium pump sends 3 Na⁺ out and brings 2 K⁺ in per ATP. (Organelles, the Fluid Mosaic Model and Membrane Transport)
Reporting the raw change in mass in the potato lab instead of percent change. Cores start at different masses, so only percent change allows a fair comparison. (Organelles, the Fluid Mosaic Model and Membrane Transport)
Saying antibiotics treat viral infections. Antibiotics target bacterial structures such as cell walls and 70S ribosomes, which viruses do not have. (Viruses, Cancer and Cell-Targeted Medicine)
Mixing up reverse transcriptase and integrase. Reverse transcriptase copies RNA into DNA; integrase inserts that DNA into the host chromosome. (Viruses, Cancer and Cell-Targeted Medicine)
Thinking protease inhibitors stop HIV from entering cells. Protease acts last, cutting polyproteins inside new virions; blocking it leaves immature, non-infectious particles. (Viruses, Cancer and Cell-Targeted Medicine)
Claiming ART cures HIV. It suppresses replication to undetectable levels, but integrated proviruses in resting cells survive, so the virus returns if treatment stops. (Viruses, Cancer and Cell-Targeted Medicine)
Thinking a monoclonal antibody can be taken as a pill. It is a protein, so stomach and intestinal proteases would digest it; it is injected or given by IV. (Viruses, Cancer and Cell-Targeted Medicine)

Practice test

25 questions from across the unit. Each one shows the lesson it comes from.

The Chemistry of Life: Bonds, Water and Functional Groups
1
Nitrogen has an electronegativity of 3.04 and hydrogen 2.20. Calculate $Δ EN$ for an N–H bond in an amino group. Give two decimal places.
The Chemistry of Life: Bonds, Water and Functional Groups
2
How many kilojoules are needed to warm 250 g of water by 10.0 °C? Use $c = 4.18\ \text{J/{(g}\cdot{}^\circ\text{C)}}$ and give three significant figures.
kJ
The Chemistry of Life: Bonds, Water and Functional Groups
3
Which reaction is an example of hydrolysis?
The Chemistry of Life: Bonds, Water and Functional Groups
4
What is the name of the weak attraction between a slightly positive hydrogen on one water molecule and the slightly negative oxygen of a neighbouring water molecule?
The Chemistry of Life: Bonds, Water and Functional Groups
5
In cellular respiration, glucose loses electrons and oxygen gains them. What is the process called when a molecule gains electrons?
Carbohydrates, Lipids, Proteins and Nucleic Acids
6
Match each macromolecule to the bond that links its building blocks.
Starch
Triglyceride
Protein
DNA
Carbohydrates, Lipids, Proteins and Nucleic Acids
7
How many peptide bonds are in a single straight polypeptide made of 51 amino acids?
bonds
Carbohydrates, Lipids, Proteins and Nucleic Acids
8
Which change would make a fatty acid more likely to be solid at room temperature?
Carbohydrates, Lipids, Proteins and Nucleic Acids
9
A protein is heated to 70 °C and loses its function. Which statement is correct?
Carbohydrates, Lipids, Proteins and Nucleic Acids
10
Which nitrogenous base is found in RNA but not in DNA?
Enzymes: Structure, Mechanism and Regulation
11
Which statement about an enzyme-catalyzed reaction is correct?
Enzymes: Structure, Mechanism and Regulation
12
A catalase reaction produces 18.0 mL of oxygen in 45.0 s. What is the average rate of oxygen production in mL/s? Give three significant figures.
mL/s
Enzymes: Structure, Mechanism and Regulation
13
Match each technological application to the enzyme it uses.
Curdling milk to make cheese
Helping yeast make bread rise
Letting lactose-intolerant people digest dairy
Removing grease stains in cold-water laundry
Enzymes: Structure, Mechanism and Regulation
14
Pepsin works in the stomach at pH 2. What happens to its activity when it moves into the small intestine at pH 8?
Enzymes: Structure, Mechanism and Regulation
15
A student tests catalase at five temperatures but uses a different-sized piece of potato each time. What is the main problem with this design?
Organelles, the Fluid Mosaic Model and Membrane Transport
16
A potato core's mass rises from 2.400 g to 2.620 g after 24 h in distilled water. Calculate the percent change in mass to three significant figures.
%
Organelles, the Fluid Mosaic Model and Membrane Transport
17
A red blood cell is placed in a solution and swells until it bursts. What was the solution?
Organelles, the Fluid Mosaic Model and Membrane Transport
18
Glucose enters a red blood cell through a GLUT protein, moving from higher to lower concentration without using ATP. What kind of transport is this?
Organelles, the Fluid Mosaic Model and Membrane Transport
19
Which membrane component acts as an identity tag that lets immune cells recognize the body's own cells?
Organelles, the Fluid Mosaic Model and Membrane Transport
20
Why can oxygen cross the plasma membrane by simple diffusion while sodium ions cannot?
Viruses, Cancer and Cell-Targeted Medicine
21
Put the steps of the HIV life cycle in order.
1. 1Host enzymes and ribosomes make viral RNA and polyproteins
2. 2Integrase inserts the viral DNA into a host chromosome
3. 3New particles bud from the cell and protease matures them
4. 4gp120 binds CD4 and the CCR5 co-receptor
5. 5gp41 fuses the viral envelope with the plasma membrane
6. 6Reverse transcriptase copies the RNA genome into DNA
Viruses, Cancer and Cell-Targeted Medicine
22
Why can hepatitis C be cured with direct-acting antivirals while HIV cannot yet be cured with ART?
Viruses, Cancer and Cell-Targeted Medicine
23
In a trial, 1250 people with chronic hepatitis C took a 12-week DAA combination and 1203 had no detectable virus 12 weeks after finishing. What is the cure rate as a percentage? (1 decimal place)
%
Viruses, Cancer and Cell-Targeted Medicine
24
What is the name for the immortal cell, made by fusing a B cell with a myeloma cell, that produces a monoclonal antibody?
Viruses, Cancer and Cell-Targeted Medicine
25
Pembrolizumab binds PD-1 on T cells. How does this help treat melanoma?

Endless drill

Fresh numbers every time, for the calculation questions in this unit.

Endless drillnew numbers every time

Generating a problem…