biological molecules

monomer

Smaller, single units from which larger molecules (polymers) are made.

polymer

Molecules made from a large number of monomers joined together.

three major examples of biological monomers

Monosaccharides, amino acids, and nucleotides.

condensation reaction

A reaction that joins two molecules together with the formation of a chemical bond, involving the elimination of a molecule of water.

hydrolysis reaction

A reaction that breaks a chemical bond between two molecules and involves the use of a water molecule.

What are the monomers of larger carbohydrates, and what are three common examples?

Monosaccharides. Examples: Glucose, galactose, and fructose.

What type of bond is formed during the condensation of carbohydrates?

A glycosidic bond.

How is maltose formed?

Condensation of two glucose molecules.

How is sucrose formed?

Condensation of a glucose molecule and a fructose molecule.

How is lactose formed?

Condensation of a glucose molecule and a galactose molecule.

difference between alpha-glucose and beta-glucose?

On Carbon-1, the hydroxyl (OH-) group points down in alpha-glucose and points up in beta-glucose.

Which monomers form glycogen and starch?

Condensation of alpha-glucose units.

Which monomer forms cellulose?

Condensation of beta-glucose units.

How do the structures of starch and glycogen relate to their functions as storage molecules?

• Insoluble: Does not affect the water potential of cells (no osmotic water uptake).

• Coiled/Compact: Lots of glucose can be stored in a small space.

• Branched: Allows enzymes easy access to the ends to hydrolyze and release glucose rapidly.

• (Note: Glycogen is more highly branched than starch because animals have higher metabolic rates).

How does the structure of cellulose relate to its structural function in plant cell walls?

Long, straight, unbranched chains run parallel to one another. Hydrogen bonds form cross-linkages between adjacent chains, grouping them together to form microfibrils. This provides high tensile strength to resist osmotic turgor pressure.

How do you test for reducing sugars?

Add Benedict's reagent and heat in a water bath. A positive result changes color from blue to brick-red precipitate.

How do you test for non-reducing sugars (e.g., sucrose)?

1. Heat a fresh sample with dilute hydrochloric acid (hydrolyzes it into monosaccharides).

2. Neutralize with sodium hydrogencarbonate.

3. Heat with Benedict’s reagent. (Color changes to brick-red).

How do you test for starch?

Add iodine dissolved in potassium iodide solution. A positive result changes color from orange-brown to blue-black.

How can you determine an unknown concentration of glucose?

Produce a dilution series of known glucose concentrations, use colorimetric techniques to measure light absorbance, plot a calibration curve, and match the unknown sample's absorbance value to find its concentration.

What are the two main groups of biological lipids?

Triglycerides and phospholipids.

How is a triglyceride formed?

By the condensation of one molecule of glycerol and three molecules of fatty acids.

What type of bond is formed in lipids, and between what components?

An ester bond, formed between the glycerol -OH and the fatty acid carboxyl group (-COOH).

What is the difference between saturated and unsaturated fatty acids?

Saturated fatty acids have hydrocarbon chains with no double bonds between carbon atoms (C=C). Unsaturated fatty acids contain at least one double bond (C=C), causing the chain to kink.

How does the structure of a phospholipid differ from a triglyceride?

One of the three fatty acids is substituted by a phosphate-containing group.

Explain the different properties/functions of triglycerides and phospholipids.

• Triglycerides: Excellent energy storage molecules because they have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms. They are large and hydrophobic (insoluble in water), meaning they don't affect cell water potential.

• Phospholipids: Polar/Amphipathic. They have a hydrophilic (water-loving) phosphate head and hydrophobic (water-repelling) fatty acid tails. This causes them to naturally form a bilayer in cell membranes.

Describe the emulsion test for lipids.

Add ethanol to the sample and shake thoroughly, then pour the mixture into water and shake gently. A positive result is a milky-white emulsion.

What are the monomers of proteins, and what is their general structure?

Amino acids. Structure consists of a central Carbon atom attached to an amine group (-NH2), a carboxyl group (-COOH), a Hydrogen atom (-H), and a variable side chain (-R group).

How many common amino acids exist, and how do they differ?

There are 20 common amino acids, and they differ only in their side group (R-group).

What bond joins amino acids, and how are dipeptides/polypeptides formed?

A peptide bond formed by a condensation reaction. Dipeptides are formed by 2 amino acids; polypeptides are formed by many amino acids.

the 4 structural levels of a protein.

• Primary: The unique sequence of amino acids in a polypeptide chain.

• Secondary: The curling or folding of the chain into alpha-helices or beta-pleated sheets, held by local hydrogen bonds.

• Tertiary: The specific 3D folding of the entire polypeptide chain, stabilized by hydrogen bonds, ionic bonds, and disulfide bridges between R-groups.

• Quaternary: A functional protein made of more than one polypeptide chain working together (e.g., hemoglobin).

Describe the biochemical test for proteins.

Add Biuret reagent (sodium hydroxide and dilute copper sulfate). A positive result changes color from blue to purple.

How do enzymes act as biological catalysts?

They lower the activation energy of the chemical reaction they catalyze.

Describe the induced-fit model of enzyme action.

The enzyme's active site is not perfectly complementary initially. As the substrate binds, the active site changes shape slightly to mold around the substrate. This strains the substrate's bonds, lowering the activation energy needed to break them.

Why are enzymes highly specific?

Enzyme specificity is determined by its tertiary structure, which dictates the exact shape of its active site. Only a substrate with a complementary shape can bind to form an enzyme-substrate complex.

6 factors that affect the rate of enzyme-controlled reactions.

Enzyme concentration, substrate concentration, concentration of competitive inhibitors, concentration of non-competitive inhibitors, pH, and temperature.

Contrast competitive and non-competitive inhibitors.

• Competitive: Have a similar shape to the substrate and bind directly to the active site, blocking the substrate. Can be overcome by increasing substrate concentration.

• Non-competitive: Bind to an allosteric site (away from the active site). This alters the tertiary structure and deforms the active site, so the substrate can no longer fit. Cannot be overcome by adding more substrate.

What is the formula to calculate pH from hydrogen ion concentration?

pH = -log10[H+]

How do you find the initial rate of an enzyme reaction from a graph?

Draw a tangent line touching the steepest part of the curve at time = 0 (t = 0). Calculate the gradient of this tangent.

What are the functions of DNA and RNA?

DNA holds genetic information. RNA transfers genetic information from DNA to the ribosomes.

What three components make up a nucleotide?

A pentose sugar, a nitrogen-containing organic base, and a phosphate group.

Compare the components of a DNA nucleotide vs. an RNA nucleotide.

• DNA: Pentose sugar is deoxyribose; bases are Adenine, Cytosine, Guanine, or Thymine.

• RNA: Pentose sugar is ribose; bases are Adenine, Cytosine, Guanine, or Uracil.

What bond joins nucleotides together, and how is it formed?

A phosphodiester bond formed via a condensation reaction between the sugar of one nucleotide and the phosphate group of another.

the structural differences between a DNA molecule and an RNA molecule.

• DNA: A double helix composed of two long polynucleotide chains held together by hydrogen bonds between complementary base pairs.

• RNA: A relatively short, single polynucleotide chain.

Why is DNA replication called "semi-conservative"?

Because each new DNA molecule contains one original (template) strand and one newly synthesized strand, ensuring genetic continuity between generations.

Describe the step-by-step process of semi-conservative DNA replication.

1. DNA helicase unwinds the double helix by breaking the hydrogen bonds between complementary bases.

2. Both separated strands act as templates.

3. Free DNA nucleotides are attracted to exposed bases via complementary base pairing (A-T and G-C)

4. DNA polymerase catalyzes condensation reactions to join adjacent nucleotides together with phosphodiester bonds, forming the new sugar-phosphate backbone.

The molecular structure of an ATP molecule.

It is a nucleotide derivative formed from a molecule of ribose, a molecule of adenine, and three phosphate groups.

the equation for the hydrolysis of ATP and name the enzyme.

ATP + H2O —> (ATP hydrolase) ADP + Pi (inorganic phosphate) + energy

How is ATP hydrolysis used within cells?

• It can be coupled to energy-requiring reactions (like active transport or muscle contraction) so they can occur.

• The inorganic phosphate (Pi) released can be used to phosphorylate other compounds, making them more reactive.

the equation for the resynthesis of ATP and name the enzyme.

ADP + Pi —> (ATP synthase) ATP + H2O
(This condensation reaction happens during photosynthesis or respiration).

5 major properties of water that make it vital to living organisms.

1. Metabolite: Directly involved in chemical reactions like hydrolysis and condensation.

2. Solvent: Readily dissolves metabolic substances (polar/ionic molecules), allowing reactions to take place.

3. High Specific Heat Capacity: Buffers changes in temperature, providing a stable aquatic environment and stable internal body temperatures.

4. Large Latent Heat of Vaporization: Provides a cooling effect through evaporation (sweating/transpiration) with minimal water loss.

5. Strong Cohesion: Hydrogen bonds keep water molecules stuck together. This supports columns of water moving up xylem tissue and produces surface tension where water meets air.

Where do inorganic ions occur, and what determines their roles?

They occur in solution in the cytoplasm and body fluids of organisms. Their specific role depends entirely on their chemical properties.

the physiological roles of Hydrogen, Iron, Sodium, and Phosphate ions.

Hydrogen ions (H+): Determine the pH of solutions and thus affect enzyme structure/function.

Iron ions (Fe2+): Found at the center of the prosthetic group in haemoglobin, binding directly to oxygen for transport.

Sodium ions (Na+): Involved in the co-transport of glucose and amino acids across cell-surface membranes.

Phosphate ions (PO4 3-): Structural components of DNA, RNA, and ATP molecules.