FSc Pre-Medical Biology Syllabus

What does the high specific heat of water mean for living organisms?

Water absorbs or releases large amounts of heat with only a small change in its own temperature, helping organisms maintain a stable internal temperature and protecting them from sudden temperature fluctuations.

Explain how the high heat of vaporization of water benefits organisms.

A large amount of heat is needed to evaporate water, so evaporation (e.g. sweating, transpiration) removes a lot of heat and provides an effective cooling mechanism.

What is the general formula of carbohydrates, and into what three classes are they divided?

General formula (CH2O)n. They are classified into monosaccharides, oligosaccharides, and polysaccharides.

Define monosaccharides and give the classification of trioses, pentoses, and hexoses by carbon number.

Monosaccharides are simple single-unit sugars. Trioses have 3 carbons, pentoses have 5 carbons, and hexoses have 6 carbons.

Give the molecular formula of glucose and name two other hexose sugars that share it.

Glucose is C6H12O6. Fructose and galactose are other hexoses with the same molecular formula.

What is the most important pentose sugar in cells and why?

Ribose (and deoxyribose); they are important as components of nucleic acids (RNA and DNA) and of nucleotides such as ATP. 

Define oligosaccharides and name the monosaccharide units of maltose, sucrose, and lactose.

Oligosaccharides yield 2–10 monosaccharides on hydrolysis. Maltose = glucose + glucose; Sucrose = glucose + fructose; Lactose = glucose + galactose.

What type of bond joins monosaccharide units, and what byproduct is released during its formation?

A glycosidic bond joins them; a molecule of water is released during the condensation (dehydration synthesis) reaction.

Name the three most important polysaccharides and give the storage role of each.

Starch (storage carbohydrate in plants), glycogen (storage carbohydrate in animals/fungi), and cellulose (structural carbohydrate forming plant cell walls).

What is the building-block (monomer) of proteins, and how many kinds commonly occur?

Amino acids are the monomers of proteins; there are 20 common kinds of amino acids. 

Draw/describe the general structure of an amino acid.

A central (alpha) carbon bonded to an amino group (–NH2), a carboxyl group (–COOH), a hydrogen atom (–H), and a variable R group (side chain). 

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

A peptide bond, formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of the next, releasing a molecule of water.

Name the four levels of protein structure.

Primary, secondary, tertiary, and quaternary structure.

Define the primary and secondary structures of a protein.

Primary structure is the linear sequence of amino acids in a polypeptide chain. Secondary structure is the regular folding/coiling of the chain into alpha-helices or beta-pleated sheets, stabilized by hydrogen bonds.

Define the tertiary and quaternary structures of a protein.

Tertiary structure is the overall three-dimensional folding of a single polypeptide. Quaternary structure is the arrangement of two or more polypeptide chains into a functional protein (e.g. hemoglobin).

What is meant by an essential amino acid?

An essential amino acid is one that the body cannot synthesize and must obtain ready-made from the diet.

Define lipids and state their key solubility property.

Lipids are organic compounds made mainly of C, H and O (with proportionally less oxygen than carbohydrates); they are insoluble in water but soluble in organic (non-polar) solvents.

What are the building blocks of a fat (triglyceride)?

One molecule of glycerol and three molecules of fatty acids.

What bond is formed between glycerol and fatty acids, and what is released?

An ester bond (ester linkage) is formed by condensation, releasing a molecule of water for each fatty acid joined.

Differentiate between saturated and unsaturated fatty acids.

Saturated fatty acids have no double bonds between carbon atoms (single bonds only) and are usually solid at room temperature; unsaturated fatty acids have one or more C=C double bonds and are usually liquid (oils).

Describe the structure of a phospholipid and why it is important in membranes.

A phospholipid has a glycerol backbone with two fatty acid chains and a phosphate-containing group, giving a hydrophilic (water-loving) head and hydrophobic (water-hating) tails. This amphipathic nature lets it form the bilayer of cell membranes.

Why are lipids a better long-term energy store than carbohydrates?

Lipids yield about twice as much energy per gram as carbohydrates (because they are more reduced) and, being insoluble, can be stored compactly without affecting cell osmotic balance. 

What are the two types of nucleic acids and what are their monomers?

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid); their monomers are nucleotides.

Name the three components of a nucleotide.

A pentose sugar, a nitrogenous base, and a phosphate group.

Distinguish purines from pyrimidines and give examples of each.

Purines have a double-ring structure (adenine and guanine); pyrimidines have a single-ring structure (cytosine, thymine, and uracil).

State the main differences between DNA and RNA.

DNA has deoxyribose sugar, the base thymine, and is usually double-stranded; RNA has ribose sugar, the base uracil instead of thymine, and is usually single-stranded.

What is a conjugated molecule? Give two examples.

A conjugated molecule is formed when two different kinds of compounds combine. Examples: glycoproteins (carbohydrate + protein), lipoproteins (lipid + protein); also glycolipids and nucleoproteins. 

List the main characteristics (properties) of enzymes.

Enzymes are biological catalysts that are protein in nature; they speed up reactions without being consumed, are highly specific, are needed in minute amounts, are sensitive to temperature and pH, and their action can be reversible.

Why are enzymes described as specific, and what part of the enzyme is responsible?

Each enzyme acts on a particular substrate (or reaction) because the substrate fits into the enzyme's specifically shaped active site, like a lock and key. 

Explain the lock-and-key model and the induced-fit model of enzyme action.

In the lock-and-key model, the substrate fits exactly into the rigid active site like a key in a lock. In the induced-fit model, the active site is flexible and changes shape slightly to mould around the substrate when it binds. 

How do enzymes speed up reactions in terms of activation energy, and what is the enzyme–substrate complex?

Enzymes lower the activation energy needed for a reaction. They do so by binding the substrate at the active site to form a temporary enzyme–substrate complex, which then breaks down into product(s) plus the unchanged enzyme.

How do temperature and pH affect enzyme activity?

Each enzyme has an optimum temperature and optimum pH at which activity is maximum. Below the optimum activity is low; above it the enzyme denatures (loses its shape) and activity falls. Extreme pH values also denature the enzyme. 

How do substrate concentration and enzyme concentration affect the rate of an enzyme-catalysed reaction?

Increasing substrate concentration raises the rate until all active sites are saturated, after which the rate levels off. Increasing enzyme concentration increases the rate as long as excess substrate is available. 

Distinguish between competitive and non-competitive enzyme inhibitors.

A competitive inhibitor resembles the substrate and competes for the active site, blocking it. A non-competitive inhibitor binds at a site other than the active site, changing the enzyme's shape so the substrate can no longer bind properly. 

What is a cofactor, and how do coenzymes and prosthetic groups differ?

A cofactor is a non-protein substance required for an enzyme to work. A coenzyme is a loosely bound organic cofactor (often a vitamin derivative); a prosthetic group is a cofactor tightly/permanently bound to the enzyme.