ETEA Medical Test Biology Syllabus

Classify carbohydrates into their three main groups with one example of each.

Monosaccharides (single sugars, e.g., glucose, fructose, galactose), disaccharides (two monosaccharides, e.g., sucrose, maltose, lactose), and polysaccharides (many monosaccharides, e.g., starch, glycogen, cellulose).

What monosaccharides make up sucrose, maltose, and lactose?

Sucrose = glucose + fructose; maltose = glucose + glucose; lactose = glucose + galactose. Each is formed by a condensation (dehydration) reaction with the loss of a water molecule.

What type of bond links monosaccharides together, and how is it formed and broken?

A glycosidic bond links monosaccharides. It is formed by condensation (dehydration synthesis) with the removal of a water molecule, and broken by hydrolysis with the addition of a water molecule.

Compare starch, glycogen, and cellulose.

All are glucose polymers. Starch is the storage carbohydrate in plants (amylose + amylopectin). Glycogen is the storage carbohydrate in animals and is highly branched. Cellulose is a structural carbohydrate in plant cell walls with straight, unbranched chains and beta-glycosidic bonds.

What is the general structure of an amino acid?

An amino acid has a central (alpha) carbon bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable R group (side chain) that determines the amino acid's identity and properties.

How many amino acids are commonly found in proteins, and what distinguishes essential from non-essential amino acids?

There are 20 standard amino acids. Essential amino acids cannot be synthesized by the body and must be obtained from the diet; non-essential amino acids can be synthesized by the body itself.

What bond joins amino acids in a protein, and how is it formed?

A peptide bond joins amino acids. It forms by a condensation reaction between the carboxyl group of one amino acid and the amino group of another, with the loss of a water molecule.

Describe the four levels of protein structure.

Primary - the linear sequence of amino acids. Secondary - local folding into alpha-helices and beta-pleated sheets stabilized by hydrogen bonds. Tertiary - the overall 3D folding of a polypeptide. Quaternary - the assembly of two or more polypeptide chains into a functional protein (e.g., haemoglobin).

What is protein denaturation and what causes it?

Denaturation is the loss of a protein's native three-dimensional structure (secondary, tertiary, quaternary) without breaking peptide bonds, resulting in loss of function. It is caused by heat, extreme pH, heavy metals, and organic solvents.

What elements are found in proteins that distinguish them from carbohydrates and lipids?

Proteins always contain carbon, hydrogen, oxygen, and nitrogen; many also contain sulfur. The presence of nitrogen (and sometimes sulfur) distinguishes them from carbohydrates and lipids, which lack nitrogen.

What is the general composition of a triglyceride (neutral fat)?

A triglyceride consists of one molecule of glycerol bonded to three fatty acid chains through ester bonds, formed by condensation reactions (loss of three water molecules).

What is the difference between saturated and unsaturated fatty acids?

Saturated fatty acids have no carbon-carbon double bonds (single bonds only), are usually solid at room temperature (animal fats). Unsaturated fatty acids have one or more double bonds, are usually liquid at room temperature (plant oils).

What type of bond links fatty acids to glycerol in a lipid?

An ester bond links each fatty acid to glycerol, formed by a condensation (esterification) reaction with the removal of a water molecule.

What is the structure of a phospholipid and why is it important?

A phospholipid has a glycerol backbone, two fatty acid tails (hydrophobic), and a phosphate-containing head (hydrophilic), making it amphipathic. This dual nature allows phospholipids to form the bilayer of cell membranes.

Give three biological functions of lipids.

Lipids serve as long-term energy storage (yielding ~9 kcal/g, more than carbohydrates), structural components of membranes (phospholipids), thermal insulation and cushioning, and precursors of steroid hormones and vitamins (e.g., cholesterol, vitamin D).

What is cholesterol and what are its functions?

Cholesterol is a steroid lipid with a four-ring structure. It is a component of animal cell membranes (regulating fluidity), and a precursor for steroid hormones, bile salts, and vitamin D.

What are the three components of a nucleotide?

A nucleotide consists of a pentose (5-carbon) sugar, a nitrogenous base, and a phosphate group.

Compare the structure of DNA and RNA.

DNA is double-stranded, contains deoxyribose sugar, and uses the base thymine. RNA is single-stranded, contains ribose sugar, and uses uracil instead of thymine. Both contain adenine, guanine, and cytosine.

What are the purine and pyrimidine bases in DNA?

Purines (double-ring): adenine (A) and guanine (G). Pyrimidines (single-ring): cytosine (C) and thymine (T). In RNA, thymine is replaced by uracil (U), also a pyrimidine.

State the base-pairing rules in DNA and the type of bond involved.

Adenine pairs with thymine (A-T) via two hydrogen bonds, and guanine pairs with cytosine (G-C) via three hydrogen bonds. This is complementary base pairing (Chargaff's rule: A=T, G=C).

What bond joins nucleotides together in a nucleic acid strand?

A phosphodiester bond joins nucleotides, linking the phosphate group of one nucleotide to the sugar (3' carbon) of the next, forming the sugar-phosphate backbone.

What is ATP and why is it important?

ATP (adenosine triphosphate) is a nucleotide consisting of adenine, ribose, and three phosphate groups. It is the universal energy currency of the cell; energy is released when the terminal high-energy phosphate bond is hydrolyzed to form ADP + inorganic phosphate.

Why is water described as a polar molecule, and what property does this give it?

In water, oxygen is more electronegative than hydrogen, creating a partial negative charge on oxygen and partial positive on hydrogen. This polarity allows hydrogen bonding between molecules and makes water an excellent solvent (the 'universal solvent').

What is the difference between cohesion and adhesion in water?

Cohesion is the attraction between water molecules themselves (due to hydrogen bonding), important for surface tension and water transport in plants. Adhesion is the attraction between water molecules and other surfaces, contributing to capillary action.

Why does water's high specific heat capacity matter biologically?

Water requires a large amount of heat to change temperature because hydrogen bonds absorb energy. This high specific heat capacity allows water to act as a temperature buffer, stabilizing the temperature of cells, organisms, and aquatic environments.

Define an enzyme and explain the 'lock and key' model of enzyme action.

An enzyme is a biological catalyst (usually a protein) that speeds up reactions by lowering activation energy. In the lock and key model, the substrate (key) has a shape exactly complementary to the rigid active site (lock) of the enzyme, so only the specific substrate fits.

What is the 'induced fit' model of enzyme action and how does it differ from the lock and key model?

In the induced fit model (Koshland), the active site is not rigid but flexible; binding of the substrate causes the active site to change shape slightly to fit snugly around the substrate. Unlike the lock and key model, the enzyme is moulded around the substrate.

How does an enzyme speed up a reaction in terms of activation energy?

An enzyme lowers the activation energy (the minimum energy needed for a reaction to proceed) by stabilizing the transition state. This allows the reaction to occur faster and at lower temperatures, without the enzyme being consumed.

How do temperature and pH affect enzyme activity?

Each enzyme has an optimum temperature and pH at which activity is maximal. Below the optimum, activity is slow; above the optimum (or at extreme pH), the enzyme denatures and loses function. Most human enzymes have an optimum around 37 degrees Celsius and pH near 7.

How does substrate concentration affect the rate of an enzyme-catalyzed reaction?

As substrate concentration increases, the reaction rate increases proportionally until all active sites are occupied (saturation point). Beyond this, the rate plateaus at Vmax (maximum velocity) because the enzyme is the limiting factor.

Compare competitive and non-competitive enzyme inhibition.

Competitive inhibitors resemble the substrate and bind to the active site, blocking substrate binding; their effect can be overcome by increasing substrate concentration. Non-competitive inhibitors bind to an allosteric site (other than the active site), changing the enzyme's shape; their effect is not reversed by adding more substrate.

What is the overall balanced equation for photosynthesis?

6CO2 + 6H2O + light energy --> C6H12O6 + 6O2 (carbon dioxide plus water, using light energy and chlorophyll, produces glucose and oxygen).

What are the two main stages of photosynthesis and where do they occur?

The light-dependent reactions occur in the thylakoid membranes of the chloroplast and produce ATP, NADPH, and oxygen. The light-independent reactions (Calvin cycle) occur in the stroma and use ATP and NADPH to fix carbon dioxide into glucose.

What is produced during the light-dependent reactions of photosynthesis?

The light-dependent reactions produce ATP (via photophosphorylation), NADPH (reduced electron carrier), and oxygen (from the photolysis/splitting of water).

What is the role of chlorophyll in photosynthesis?

Chlorophyll is the green pigment in chloroplasts that absorbs light energy (mainly red and blue wavelengths, reflecting green) and converts it into chemical energy, exciting electrons to drive the light-dependent reactions.

What happens in the Calvin cycle (light-independent reactions)?

In the stroma, carbon dioxide is fixed by combining with RuBP (catalyzed by the enzyme RuBisCO) and, using ATP and NADPH from the light reactions, is reduced to form glucose. This is the carbon fixation stage and does not directly require light.