Biological molecules

Question 1

What are monomers and polymers?

Answer 1

Monomer: A small, single molecule that can join with others to form a polymer.
Polymer: A large molecule made of many similar or identical monomers linked together.

Question 2

What occurs during condensation and hydrolysis reactions?

Answer 2

Condensation Reaction:
Joins two molecules together.
Eliminates a water molecule.
Forms a chemical bond, e.g., glycosidic bond.
Hydrolysis Reaction:
Separates two molecules.
Requires the addition of a water molecule.
Breaks a chemical bond.

Question 3

What are monosaccharides and disaccharides?

Answer 3

Monosaccharides: Simple sugars that are the monomers of carbohydrates, e.g., glucose, fructose, galactose.
Disaccharides: Formed by the condensation of two monosaccharides, e.g., glucose + glucose = maltose, glucose + fructose = sucrose, glucose + galactose = lactose.

Question 4

What are the isomers of glucose and how do they differ?

Answer 4

Isomers: Molecules with the same molecular formula but different arrangements of atoms.
α-Glucose: OH group is below carbon 1.
β-Glucose: OH group is above carbon 1.

Question 5

What are the functions and structures of glycogen, starch, and cellulose?

Answer 5

Glycogen:
Function: Energy storage in animal cells.
Structure: Branched polysaccharide of α-glucose with C1-C4 and C1-C6 glycosidic bonds.
Starch:
Function: Energy storage in plant cells.
Structure: Polysaccharide of α-glucose, composed of amylose (unbranched) and amylopectin (branched).
Cellulose:
Function: Provides strength and structural support to plant cell walls.
Structure: Unbranched chain of β-glucose with every other glucose molecule inverted, forming strong hydrogen bonds.

Question 6

Describe the structure and function of glycogen, starch, and cellulose.

Answer 6

Glycogen: Energy storage in animal cells. Polysaccharide of α-glucose with C1-C4 and C1-C6 glycosidic bonds, making it branched.
Starch: Energy storage in plant cells. Polysaccharide of α-glucose; a mixture of amylose (unbranched with C1-C4 bonds) and amylopectin (branched with C1-C4 and C1-C6 bonds).
Cellulose: Provides strength and structural support to plant cell walls. Made of β-glucose with every other glucose molecule inverted, forming long, straight chains.

Question 7

How is the structure of glycogen, starch, and cellulose related to their function?

Answer 7

Glycogen: Branched for rapid hydrolysis, large, and insoluble, preventing osmotic effects in cells.
Starch (Amylose): Helical and compact for storage, large and insoluble, preventing osmotic effects.
Cellulose: Inverted β-glucose molecules form long, straight chains with hydrogen bonds between strands, creating strong fibers for structural support.

Question 8

What are the steps for Benedict’s test for reducing and non-reducing sugars?

Answer 8

Reducing Sugars Test:
Add Benedict’s reagent (blue) to the sample.
Heat in a boiling water bath.
Positive result: green/yellow/orange/red precipitate.
Non-Reducing Sugars Test:
Add dilute HCl and heat in a boiling water bath.
Neutralize with sodium bicarbonate.
Add Benedict’s reagent and heat again.
Positive result: green/yellow/orange/red precipitate.

Question 9

How do you determine glucose concentration using a Benedict’s test and a colorimeter?

Answer 9

1.Produce a dilution series of glucose solutions.
2.Perform a Benedict’s test on each sample.
3.Filter and measure absorbance using a colorimeter.
4.Plot a calibration curve of absorbance against glucose concentration.
5.Use the curve to determine the glucose concentration of unknown samples.

Question 10

What is the iodine test for starch?

Answer 10

Add iodine dissolved in potassium iodide to the sample.
Positive result: Blue-black color indicates the presence of starch.

Question 11

What are triglycerides and phospholipids, and how are their structures related to their functions?

Answer 11

Triglycerides:
Formed by condensation of 1 molecule of glycerol and 3 fatty acids.
High ratio of C-H bonds to C atoms in the hydrocarbon tail, releasing more energy than carbohydrates.
Insoluble in water, forming droplets to avoid affecting water potential.
Phospholipids:
Similar to triglycerides but with one fatty acid replaced by a phosphate group.
Form bilayers in cell membranes, with hydrophilic phosphate heads facing outward and hydrophobic tails facing inward.

Question 12

What are phospholipids and their properties related to structure?

Answer 12

Phospholipids: One fatty acid in a triglyceride is substituted by a phosphate group.
Properties:
Form a bilayer in cell membranes, allowing diffusion of non-polar/small molecules.
Polar phosphate heads are hydrophilic and orient to aqueous environments, while non-polar fatty acid tails are hydrophobic and orient to the membrane interior.

Question 13

What is the difference between saturated and unsaturated fatty acids?

Answer 13

Saturated Fatty Acids: No C=C double bonds in the hydrocarbon chain; all carbons are fully saturated with hydrogen.
Unsaturated Fatty Acids: One or more C=C double bonds in the hydrocarbon chain.

Question 14

What is the emulsion test for lipids?

Answer 14

Add ethanol and shake (dissolves lipids).
Add water.
Positive result: A milky/cloudy white emulsion indicates the presence of lipids.

Question 15

What are amino acids, dipeptides, and polypeptides?

Answer 15

Amino Acids: The monomers from which proteins are made.
Dipeptides: Formed by the condensation of two amino acids.
Polypeptides: Formed by the condensation of many amino acids.

Question 16

What are the structural levels of proteins and the role of bonds in each level?

Answer 16

Primary Structure: Sequence of amino acids in a polypeptide chain.
Secondary Structure: Folding into alpha helices or beta-pleated sheets stabilized by hydrogen bonds.
Tertiary Structure: 3D structure of a polypeptide stabilized by interactions between R-groups (ionic bonds, disulfide bridges, hydrogen bonds).
Quaternary Structure: Multiple polypeptides linked together.

Question 17

What is the Biuret test for protein?

Answer 17

Add Biuret solution (sodium hydroxide + copper (II) sulfate) to the sample.
Positive result: Purple colour indicates the presence of protein (detects peptide bonds).

Question 18

What are enzymes and what are the models of enzyme action?

Answer 18

Enzymes: Biological catalysts that lower activation energy, speeding up reactions.
Lock and Key Model: Active site is a fixed shape, complementary to a specific substrate.
Induced Fit Model: Active site changes shape to fit the substrate, forming an enzyme-substrate complex.

Question 19

what determines the specificity of enzymes?

Answer 19

Enzymes have a specific tertiary structure and active site.
The primary structure (sequence of amino acids) determines the tertiary structure.
The active site is complementary to a specific substrate, which can induce fit and form an enzyme-substrate complex.

Question 20

How do enzyme and substrate concentration affect enzyme-controlled reactions?

Answer 20

Enzyme Concentration:
Increasing concentration increases the rate of reaction (substrate in excess).
Rate plateaus when substrate becomes the limiting factor.
Substrate Concentration:
Increasing concentration increases the rate of reaction (enzyme molecules are limiting).
Rate plateaus when all enzyme active sites are saturated.

Question 21

How do temperature and pH affect enzyme-controlled reactions?

Answer 21

Temperature:
Increasing temperature up to the optimum increases the rate due to higher kinetic energy.
Above the optimum, the rate decreases as enzymes denature, changing the active site’s shape.
pH:
Deviations from the optimum pH decrease the rate as enzymes denature, altering the active site.

Question 22

How do competitive and non-competitive inhibitors affect enzyme activity?

Answer 22

Competitive Inhibitors:
Resemble the substrate and compete for the active site, reducing enzyme activity.
Increasing substrate concentration can reduce the effect.
Non-Competitive Inhibitors:
Bind to an allosteric site, causing a permanent change in the active site.
Increasing substrate concentration has no effect on the level of inhibition.

Question 23

What is the structure of DNA and RNA?

Answer 23

DNA:
Double-stranded helix with a sugar-phosphate backbone.
Nucleotides contain deoxyribose, and bases are adenine, guanine, cytosine, and thymine.
RNA:
Single-stranded polynucleotide.
Nucleotides contain ribose, and bases are adenine, guanine, cytosine, and uracil.

Question 24

What are the functions of DNA and RNA?

Answer 24

DNA: Stores genetic information.
RNA: Transfers genetic information from DNA to ribosomes, which are formed from RNA and proteins.

Question 25

What are the steps involved in DNA replication?

Answer 25

DNA Helicase unwinds the double helix by breaking hydrogen bonds.
Each strand acts as a template.
Free DNA nucleotides pair with exposed bases via complementary base pairing.
DNA polymerase joins adjacent nucleotides, forming phosphodiester bonds.
The result is two DNA molecules, each containing one original and one new strand (semi-conservative replication).

Question 26

What was the Meselson and Stahl experiment and what did it demonstrate?

Answer 26

Bacteria were grown in heavy nitrogen (15N), then in light nitrogen (14N), and their DNA was analyzed after replication.
Findings:
After one replication: DNA contained one heavy and one light strand.
After two replications: 50% of DNA molecules had one heavy and one light strand, and 50% had both light strands.
Demonstrated that DNA replication is semi-conservative.

Question 27

What is ATP, and what are its properties related to its structure?

Answer 27

ATP (Adenosine Triphosphate):
Composed of ribose, adenine, and three phosphate groups.
Releases energy in small, manageable amounts when hydrolyzed.
Properties:
Cannot be stored.
Immediate energy source for cellular processes.

Question 28

How does ATP hydrolysis and condensation occur?

Answer 28

ATP Hydrolysis (ATP → ADP + Pi):
Catalyzed by ATP hydrolase.
Energy is released when bonds between phosphate groups are broken.
The inorganic phosphate can phosphorylate other compounds, making them more reactive.
ATP Condensation (ADP + Pi → ATP):
Catalyzed by ATP synthase during respiration or photosynthesis.

Question 29

What are the important properties of water in biology?

Answer 29

High Specific Heat Capacity: Water can absorb a large amount of heat energy before changing temperature, stabilizing environments and organisms’ internal temperature.
High Latent Heat of Evaporation: A lot of energy is needed to evaporate water, making it an effective cooling mechanism (e.g., sweating).
Cohesion: Water molecules stick together, allowing transport in plants and surface tension for small organisms to walk on.
Solvent: Water dissolves ionic compounds, enabling metabolic reactions and transportation in biological systems.
Metabolite: Water participates in hydrolysis and condensation reactions.

Question 30

What are the roles of key inorganic ions in biological processes?

Answer 30

Phosphate (PO4³⁻):
In DNA nucleotides, forming phosphodiester bonds.
In ATP, storing/releasing energy.
Hydrogen (H⁺):
Maintains pH levels; too much H⁺ = acidic, too little = alkaline.
Affects enzyme-controlled reaction rates.
Iron (Fe²⁺):
Component of hemoglobin, transporting oxygen in the body.
Sodium (Na⁺):
Involved in co-transport of glucose and amino acids.
Generates nerve impulses and muscle contraction.