Allied Health Sciences Entry Test Biology Syllabus

What type of bond links monosaccharide units in disaccharides and polysaccharides?

A glycosidic bond.

Compare the storage polysaccharides of plants and animals.

Plants store glucose as starch; animals store glucose as glycogen (in liver and muscle).

Which structural polysaccharide forms plant cell walls, and which forms the exoskeleton of insects?

Cellulose forms plant cell walls; chitin forms the insect exoskeleton (and fungal cell walls).

What is the general structure (functional groups) of an amino acid?

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

How many standard amino acids make up proteins, and what bond joins them?

20 standard amino acids, joined by peptide bonds (formed by condensation between the carboxyl of one and the amino group of the next).

Name and describe the four levels of protein structure.

Primary = sequence of amino acids; Secondary = local folding into alpha-helix or beta-pleated sheet (H-bonds); Tertiary = overall 3D folding of one chain; Quaternary = assembly of two or more polypeptide chains.

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

Loss of a protein's native three-dimensional shape (and function) without breaking peptide bonds; caused by heat, extreme pH, heavy metals, or certain chemicals.

What are the three main classes of lipids based on composition?

Simple lipids (e.g., fats/oils and waxes), compound lipids (e.g., phospholipids, glycolipids), and derived lipids (e.g., steroids, terpenes).

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

One molecule of glycerol and three fatty acid molecules, joined by ester bonds.

What is the difference between saturated and unsaturated fatty acids?

Saturated fatty acids have no carbon-carbon double bonds (solid at room temp, e.g., animal fats); unsaturated have one or more double bonds (liquid oils, e.g., plant oils).

Why are phospholipids ideal components of cell membranes?

They are amphipathic, with a hydrophilic (phosphate) head and hydrophobic (fatty acid) tails, so they spontaneously form a bilayer in water.

Give two biological functions of steroids, naming an example steroid.

Cholesterol stabilizes membranes and is a precursor for steroid hormones (e.g., testosterone, estrogen, and bile salts).

What are the three components of a nucleotide?

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

State the key differences between DNA and RNA in sugar, bases, and number of strands.

DNA: deoxyribose sugar, bases A-T-G-C, double-stranded. RNA: ribose sugar, bases A-U-G-C (uracil replaces thymine), usually single-stranded.

What are the complementary base-pairing rules in DNA?

Adenine pairs with Thymine (A-T) by 2 hydrogen bonds; Guanine pairs with Cytosine (G-C) by 3 hydrogen bonds.

Classify the nitrogenous bases into purines and pyrimidines.

Purines (double ring): Adenine and Guanine. Pyrimidines (single ring): Cytosine, Thymine, and Uracil.

Name the three types of RNA and their main roles.

mRNA carries the genetic code to ribosomes; tRNA brings amino acids during translation; rRNA forms part of the ribosome structure.

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

A molecule formed when two different classes of biomolecules combine; e.g., glycoproteins (carbohydrate + protein), lipoproteins (lipid + protein), nucleoproteins (nucleic acid + protein).

What type of conjugated molecule is hemoglobin, and what is its non-protein part called?

Hemoglobin is a conjugated protein; its non-protein prosthetic group is the iron-containing heme group.

Chemically, what are enzymes, and what is their general role?

Enzymes are biological catalysts, mostly globular proteins, that speed up biochemical reactions by lowering the activation energy without being consumed.

List four key characteristics (properties) of enzymes.

They are specific in action, highly efficient, reusable (not consumed), sensitive to temperature and pH, and lower activation energy.

What is the difference between the lock-and-key model and the induced-fit model of enzyme action?

Lock-and-key: the active site has a fixed shape exactly complementary to the substrate. Induced-fit: the active site is flexible and changes shape slightly to fit the substrate after binding.

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

Activation energy is the minimum energy needed to start a reaction; enzymes lower it, allowing the reaction to proceed faster.

What is the active site of an enzyme?

The specific region of an enzyme where the substrate binds and the catalytic reaction takes place, forming the enzyme-substrate complex.

How does temperature affect enzyme activity, including the optimum?

Activity increases with temperature up to an optimum (often ~37 C in humans); beyond it the enzyme denatures and activity falls sharply.

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

Rate increases with substrate concentration until all active sites are saturated, after which the rate levels off (maximum/plateau).

Why does pH affect enzyme activity, and what is meant by optimum pH?

Extreme pH alters the charges/bonds in the active site and can denature the enzyme; optimum pH is the pH at which the enzyme works fastest (e.g., pepsin ~2, trypsin ~8).

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

A cofactor is a non-protein helper needed for enzyme activity; a coenzyme is a loosely bound organic cofactor (often a vitamin derivative), while a prosthetic group is tightly/permanently bound.

Distinguish between competitive and non-competitive enzyme inhibition.

Competitive inhibitors resemble the substrate and bind the active site (effect reduced by more substrate); non-competitive inhibitors bind a different site, change the enzyme's shape, and are not overcome by more substrate.

What is feedback (end-product) inhibition?

A regulatory mechanism where the final product of a metabolic pathway inhibits an enzyme earlier in the pathway, preventing overproduction.

State the three principles of the cell theory.

1) All living organisms are composed of one or more cells; 2) the cell is the basic structural and functional unit of life; 3) all cells arise from pre-existing cells.

What are the functions of the mitochondrion, and why is it called the 'powerhouse of the cell'?

It carries out aerobic respiration to produce ATP (energy); it is the powerhouse because it generates most of the cell's usable energy.

Compare rough and smooth endoplasmic reticulum.

Rough ER has ribosomes and synthesizes/processes proteins; smooth ER lacks ribosomes and synthesizes lipids, stores calcium, and detoxifies substances.

What is the main function of the Golgi apparatus?

To modify, sort, package, and dispatch proteins and lipids into vesicles for secretion or delivery within the cell.

What do lysosomes contain and do?

They contain hydrolytic (digestive) enzymes that break down worn-out organelles, food particles, and foreign material (intracellular digestion).

What is the function of ribosomes and what are they made of?

Ribosomes are the sites of protein synthesis; they are composed of rRNA and proteins, with large and small subunits.

Describe the fluid mosaic model of the cell membrane.

The membrane is a fluid phospholipid bilayer with proteins (and cholesterol and carbohydrates) embedded in or attached to it, able to move laterally like a mosaic.

Distinguish between passive and active transport across the cell membrane.

Passive transport moves substances down a concentration gradient without energy (diffusion, osmosis, facilitated diffusion); active transport moves substances against the gradient using ATP.

Define osmosis.

The net movement of water molecules from a region of higher water potential (lower solute) to lower water potential (higher solute) across a selectively permeable membrane.

What is the difference between endocytosis and exocytosis?

Endocytosis brings large materials into the cell by engulfing them in a vesicle (phagocytosis/pinocytosis); exocytosis expels materials out of the cell by fusing a vesicle with the membrane.

List at least four differences between prokaryotic and eukaryotic cells.

Prokaryotes: no true nucleus (nucleoid), no membrane-bound organelles, 70S ribosomes, circular DNA, usually small (1-10 um). Eukaryotes: true membrane-bound nucleus, membrane-bound organelles, 80S ribosomes, linear DNA with histones, larger (10-100 um).

Which organisms are prokaryotic, and which kingdoms are eukaryotic?

Bacteria (kingdom Monera) are prokaryotic; kingdoms Protista, Fungi, Plantae, and Animalia are eukaryotic.

What is binomial nomenclature, who introduced it, and how is a name written?

A two-name system introduced by Carolus Linnaeus: Genus (capitalized) + species (lowercase), italicized or underlined, e.g., Homo sapiens.

List the taxonomic hierarchy from the broadest to the most specific rank.

Kingdom -> Phylum (Division in plants) -> Class -> Order -> Family -> Genus -> Species.

Name the five kingdoms of Whittaker's classification system and a defining feature of each.

Monera (prokaryotic), Protista (mostly unicellular eukaryotes), Fungi (heterotrophic by absorption, chitin walls), Plantae (multicellular autotrophs, photosynthesis), Animalia (multicellular heterotrophs).

Who proposed the five-kingdom classification system and in what year?

Robert H. Whittaker, in 1969.

To which kingdom do bacteria and cyanobacteria belong, and what cell type are they?

Kingdom Monera; they are prokaryotic cells.

What mode of nutrition characterizes kingdom Fungi?

Heterotrophic nutrition by absorption (saprophytic or parasitic), digesting food externally and absorbing the nutrients.