National MDCAT Biology Syllabus

Why is water described as a polar molecule, and what type of bonding results between water molecules?

Water is polar because oxygen is more electronegative than hydrogen, giving oxygen a partial negative charge and hydrogen a partial positive charge. This polarity allows hydrogen bonding between water molecules.

Why is water called the 'universal solvent' and a good biological medium?

Because its polarity allows it to dissolve a wide range of polar and ionic substances, making it an ideal medium for transport, metabolic reactions, and biochemical processes in cells.

Explain the biological importance of water's high specific heat capacity.

Water's high specific heat means it absorbs or releases large amounts of heat with little temperature change, helping organisms maintain a stable internal temperature (thermal buffering).

What property of water makes it act as an effective coolant in organisms, and how?

Its high heat of vaporization; evaporation of water (e.g., sweating or transpiration) absorbs large amounts of heat, cooling the organism.

Define carbohydrates and give their general empirical formula.

Carbohydrates are polyhydroxy aldehydes or ketones (or compounds that yield them on hydrolysis). General formula: (CH2O)n, i.e., Cn(H2O)n.

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

Monosaccharides (glucose), disaccharides (sucrose), and polysaccharides (starch).

Name the three common disaccharides and the monosaccharides that make up each.

Sucrose (glucose + fructose), maltose (glucose + glucose), and lactose (glucose + galactose).

Compare starch, glycogen, and cellulose by their function/role.

Starch is the storage polysaccharide in plants, glycogen is the storage polysaccharide in animals, and cellulose is the structural polysaccharide of plant cell walls.

What type of bond joins monosaccharides in carbohydrates, and what reaction forms it?

A glycosidic bond, formed by a condensation (dehydration) reaction in which a water molecule is removed.

What are the building blocks (monomers) of proteins, and what bond joins them?

The monomers are amino acids, joined by peptide bonds (formed by condensation between the carboxyl group of one amino acid and the amino group of another).

Describe the general structure of an amino acid.

An amino acid has a central carbon (alpha carbon) bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable R group (side chain).

Name the four levels of protein structure.

Primary (amino acid sequence), secondary (alpha-helix and beta-pleated sheet via hydrogen bonds), tertiary (overall 3D folding), and quaternary (assembly of multiple polypeptide subunits).

What is denaturation of a protein, and name two factors that cause it?

Denaturation is the loss of a protein's native three-dimensional structure (and function) without breaking peptide bonds. It is caused by heat, extreme pH, heavy metals, or certain chemicals.

Define lipids and state their key solubility property.

Lipids are a diverse group of organic compounds made of C, H, and O that are insoluble in water but soluble in organic (non-polar) solvents like ether and chloroform.

What are the building blocks of a triglyceride (neutral fat), and what bond links them?

One glycerol molecule and three fatty acids, linked by ester bonds formed through condensation reactions.

Differentiate between saturated and unsaturated fatty acids.

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

Why are phospholipids ideal components of cell membranes?

Because they are amphipathic: they have a hydrophilic (polar) phosphate head and two hydrophobic (non-polar) fatty acid tails, allowing them to form a bilayer in water.

What are the building blocks (monomers) of nucleic acids, and what three components make up each?

The monomers are nucleotides. Each nucleotide consists of a pentose sugar, a phosphate group, and a nitrogenous base.

Name the nitrogenous bases found in DNA and classify them as purines or pyrimidines.

DNA bases are adenine and guanine (purines, double-ring), and cytosine and thymine (pyrimidines, single-ring).

State the base-pairing rule in DNA and the number of hydrogen bonds in each pair.

Adenine pairs with thymine via 2 hydrogen bonds; guanine pairs with cytosine via 3 hydrogen bonds (complementary base pairing).

According to the Watson-Crick model, describe the overall structure of DNA.

DNA is a double helix of two antiparallel polynucleotide strands held together by hydrogen bonds between complementary bases, with a sugar-phosphate backbone on the outside and bases on the inside.

State three key differences between DNA and RNA.

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

What is a conjugated molecule in biochemistry? Give an example.

A conjugated molecule is a compound made of a basic biomolecule covalently joined with a different group (prosthetic group). Examples: glycoproteins (protein + carbohydrate), lipoproteins (lipid + protein), and nucleoproteins (nucleic acid + protein).

What two components make up a glycoprotein, and where are they important?

A glycoprotein is a protein joined to a carbohydrate; they are important in cell membranes for cell recognition and as receptors and antibodies.

Name two examples of conjugated molecules that combine lipids with another group and state their roles.

Lipoproteins (lipid + protein) transport fats/cholesterol in the blood, and glycolipids (lipid + carbohydrate) are found in cell membranes for cell recognition.

State the three main postulates of the cell theory.

All living organisms are composed of one or more cells; the cell is the basic structural and functional unit of life; all cells arise from pre-existing cells.

State three key differences between prokaryotic and eukaryotic cells.

Prokaryotic cells lack a true (membrane-bound) nucleus, lack membrane-bound organelles, and have 70S ribosomes; eukaryotic cells have a true nucleus, possess membrane-bound organelles, and have 80S ribosomes.

List three structural differences between a plant cell and an animal cell.

Plant cells have a cellulose cell wall, chloroplasts, and a large central vacuole; animal cells lack a cell wall and chloroplasts, have small/temporary vacuoles, and contain centrioles.

What is the function of mitochondria, and why are they called the 'powerhouse of the cell'?

Mitochondria are the sites of aerobic respiration where ATP is produced; they are called the powerhouse of the cell because they generate most of the cell's energy (ATP).

Differentiate between rough and smooth endoplasmic reticulum by function.

Rough ER bears ribosomes and is involved in protein synthesis and transport; smooth ER lacks ribosomes and functions in lipid/steroid synthesis and detoxification.

What is the function of the Golgi apparatus?

The Golgi apparatus modifies, sorts, packages, and secretes proteins and lipids, and forms lysosomes and secretory vesicles.

Why are lysosomes called 'suicidal bags' of the cell?

Because they contain hydrolytic (digestive) enzymes that can digest worn-out cell components and, on rupture, can digest the entire cell (autolysis).

What is the structure and function of a chromosome?

A chromosome is a thread-like structure of DNA tightly coiled around histone proteins (forming chromatin); it carries genes and transmits hereditary information from one generation to the next.

What is a centromere, and how does it relate to chromosome classification?

The centromere is the constricted region of a chromosome where the two sister chromatids are joined and to which spindle fibres attach. Its position (metacentric, submetacentric, acrocentric, or telocentric) classifies the chromosome shape.

How many chromosomes are present in a normal human somatic (body) cell, and how are they arranged?

46 chromosomes arranged as 23 pairs: 22 pairs of autosomes and 1 pair of sex chromosomes (XX in females, XY in males).

What are receptors in a biological context?

Receptors are specialized protein molecules or sensory structures that detect specific stimuli (chemical or physical signals) and initiate a response, such as cell-membrane receptors that bind hormones/neurotransmitters or sensory receptors that detect environmental changes.

Classify sensory receptors according to the type of stimulus they detect.

Photoreceptors (light), chemoreceptors (chemicals/taste/smell), mechanoreceptors (touch/pressure/sound), thermoreceptors (temperature), and nociceptors (pain).

What is a neuron, and what are its three basic structural parts?

A neuron is the structural and functional unit of the nervous system that transmits nerve impulses. Its three parts are the cell body (soma), dendrites (receive impulses), and the axon (carries impulses away).

Classify neurons by their function.

Sensory (afferent) neurons carry impulses from receptors to the CNS; motor (efferent) neurons carry impulses from the CNS to effectors; interneurons (association neurons) connect neurons within the CNS.

What is a synapse, and how is a nerve impulse transmitted across it?

A synapse is the junction between two neurons (or a neuron and an effector). The impulse is transmitted chemically when neurotransmitters are released from the presynaptic neuron, cross the synaptic cleft, and bind receptors on the postsynaptic membrane.

What is the myelin sheath, and what is its function?

The myelin sheath is a fatty insulating layer (formed by Schwann cells) around the axon; it speeds up nerve impulse conduction via saltatory conduction (jumping between Nodes of Ranvier) and insulates the axon.

Name the three main parts of the human brain.

The forebrain (cerebrum, thalamus, hypothalamus), the midbrain, and the hindbrain (cerebellum, pons, medulla oblongata).

What are the main functions of the cerebrum?

The cerebrum controls higher functions: thinking, memory, intelligence, reasoning, voluntary movements, and interpretation of sensory information.

What is the function of the cerebellum?

The cerebellum coordinates voluntary muscle movements, and maintains balance, posture, and body equilibrium.

State the functions of the medulla oblongata.

The medulla oblongata controls vital involuntary functions such as heartbeat, breathing (respiration), blood pressure, and reflexes like coughing, sneezing, and swallowing.

What is the function of the hypothalamus?

The hypothalamus regulates body temperature, hunger, thirst, sleep, and emotions, and links the nervous system to the endocrine system by controlling the pituitary gland.

What is an enzyme, and what is its chemical nature?

An enzyme is a biological catalyst that speeds up biochemical reactions without being consumed. Chemically, most enzymes are globular proteins (some are RNA, called ribozymes).

List four key characteristics of enzymes.

They are highly specific for their substrate, speed up reactions by lowering activation energy, are required in very small amounts, and remain unchanged at the end of the reaction (reusable).

Explain the 'lock and key' model of enzyme action.

The model proposes that the enzyme's active site has a specific shape that fits only a particular substrate, like a key fitting a lock, ensuring enzyme specificity.

How do temperature and pH affect enzyme activity?

Each enzyme has an optimum temperature and pH at which activity is maximum. Beyond these, activity declines and very high temperature or extreme pH denatures the enzyme, destroying its function.

Differentiate between a cofactor and a coenzyme.

A cofactor is a non-protein helper required for enzyme activity; if it is an inorganic ion (e.g., Mg2+, Zn2+) it is simply a cofactor, while if it is an organic molecule (e.g., vitamins like NAD, FAD) it is called a coenzyme.

What is meant by enzyme specificity, and what determines it?

Enzyme specificity means each enzyme acts only on a particular substrate or type of reaction; it is determined by the unique three-dimensional shape of the enzyme's active site.

What is activation energy, and how do enzymes affect it?

Activation energy is the minimum energy required to start a chemical reaction. Enzymes lower the activation energy, allowing the reaction to proceed faster and at lower temperatures.

What is the fluid mosaic model of the cell membrane?

It describes the plasma membrane as a fluid phospholipid bilayer in which proteins (integral and peripheral) are embedded like a mosaic, with the whole structure being dynamic and able to move laterally.

What are ribosomes made of, and what is their function?

Ribosomes are made of ribosomal RNA (rRNA) and proteins; they are the sites of protein synthesis (translation) in the cell.