Topic 2: Molecular Biology

Question 1

State one role in living organisms for each of the following: sulfur, calcium, phosphorus and iron. [4]

Answer 1

Sulfur - Amino acids
Calcium - Bone/Teeth
Phosphorus - DNA/RNA
Iron - hemoglobin (blood transport)

Question 2

Outline the role of condensation and hydrolysis in the relationship between fatty acids, glycerol and triglycerides. [6]

Answer 2

• Hydrolysis: when large molecules are broken down into smaller ones
• Addition of water
• Fatty acids produced by hydrolysis of fats
• Breaking of ester bonds
• Condensation: when small molecules are joined to form a larger molecule
• Fatty acids linked to glycerol
• Up to three fatty acids
• Formation of ester bonds

Question 3

Explain the relationship between the properties of water and its uses in living organisms as a coolant, a medium for metabolic reactions and a transport medium. [8]

Answer 3

• polar molecule
• oxygen partial negative charge, hydrogen partial positive charge
• hydrogen bonds form between adjacent water molecules
• water remains liquid over wide range of temp
• moderate temp fluctuation
• high latent heat of vaporization
• allows sweating to cool organisms
• polarity makes it a good universal solvent
• blood transport solutes in water
• cohesive properties allow transpiration stream

Question 4

State the role of four named minerals needed by living organisms. [4]

Answer 4

• sulfur: amino acids
• calcium: bone/teeth
• iron: hemoglobin
• phosphorus: DNA/RNA
• potassium: sodium-potassium pumps
• magnesium: part of chlorophyll molecule

Question 5

Outline the role of condensation and hydrolysis in metabolic reactions involving carbohydrates. [4]

Answer 5

• hydrolysis: breaking down of large molecules into smaller ones with the addition of water
• disaccharides break down to form monosaccharides
• condensation: building up of large molecules from small ones with the release of water
• two monosaccharides join to form one disaccharide

Question 6

Metabolic reactions are catalysed by enzymes. Explain how enzymes catalyse reactions and how a change in pH could affect this. [8]

Answer 6

• enzymes speed up rate of reaction
• active site specific to substrate
• forms enzyme-substrate complex
• lock and key model
• works best at optimal pH
• increase/decrease from optimal pH decreases activity
• changes structure/active site
• changes 3d structure of protein
• substrate cannot fit into active site
• enzymes becomes denatured
• loss of biological properties

Question 7

Outline the thermal, cohesive and solvent properties of water. [5]

Answer 7

• high specific heat capacity
• large amount of heat causes small change in temp
• high latent heat of vaporization
• large amount of heat energy required to vaporize water
• hydrogen bonds make water cohesive
• high surface tension
• polar molecule
• good solvent

Question 8

State one disaccharide and the two monomers from which it can be synthesized. [2]

Answer 8

• Sucrose (Fructose, glucose)
• Galactose (Glucose, lactose)
• Maltose (Glucose, glucose)

Question 9

Define metabolism. [1]

Answer 9

all the enzyme-catalyzed reactions in a cell

Question 9

Discuss the roles of the enzymes secreted by the pancreas during digestion. [3]

Answer 9

• amylase breaks down starch to maltose
• lipase breaks down lipids into glycerol and fatty acids
• proteases break down proteins into amino acids

Question 9

Compare and contrast cis-fatty acids and trans-fatty acids. [2]

Answer 9

• both unsaturated fatty acids (C=C double bond)

cis-fatty

• two H atoms on the same side
• healthier
• lower melting point

trans-fatty

• two H atoms on different sides
• less healthy
• higher melting point

Question 10

Distinguish between the thermal properties of water and methane. [2]

Answer 10

water

• higher boiling point
• higher melting point
• higher specific heat capacity
• higher latent heat of vaporization

Question 11

Explain the reasons for the unique thermal properties of water. [2]

Answer 11

• polar molecule
• partial negative charges on oxygen, partial positive charges on hydrogen
• strong hydrogen bonds form between molecules
• require high amount of energy to break

Question 12

Outline what type of sugar lactose is and its function. [2]

Answer 12

• disaccharide
• made from monosaccharides glucose and galactose
• provide energy for young mammals

Question 13

Explain the production of lactose-free milk. [3]

Answer 13

• run milk with lactose through immobilized beads of lactase
• lactase breaks down lactose into glucose and galactose
• lactose-free milk is sweeter
• suitable for people who are lactose-intolerant

Question 14

List the general functions of non-membrane proteins. [4]

Answer 14

• contraction/movement
• acts as catalysts
• structural support
• transport
• immunity
• hormones
• DNA packing

Question 15

Define anabolism and catabolism. [2]

Answer 15

Anabolism

• synthesis of complex molecules from simpler molecules (condensation reaction produces water)

Catabolism

• breakdown of complex molecules into simpler molecules (hydrolysis reaction splits water)

Question 16

Outline the types of lipids. [3]

Answer 16

Triglycerides

• three fatty acids and one glycerol linked by ester bonds (condensation)

Phospholipids

• two fatty acids linked to glycerol linked by ester bonds (condensation)

Steroids

• four fused rings e.g. progesterone, estrogen, testosterone

Question 17

BMI Equation

Answer 17

BMI = Mass in kg / (height in meters)^2

Question 18

Outline six examples of proteins and their functions. [6]

Answer 18

• Rubisco - an enzyme that catalyzes photosynthesis reaction that fixes CO2 from the atmosphere
• Insulin - hormone that lowers blood glucose conc
• Immunoglobulins - antibodies that bind to antigens on pathogens
• Rhodopsin - pigment that makes rod cells
• Collagen - structural protein to prevent skin tearing/give tensile strength
• Spider silk - structural protein used to make webs for catching prey

Question 19

Outline how three properties of water enhance its use by living organisms. [6]

Answer 19

• cohesive properties help in transpiration pull
• high surface tensions allow organisms to stride across the surface
• high latent heat of vaporization, good coolant
• high specific heat capacity, maintain environmental temperatures
• low density, ice forms insulation of lakes allowing life below
• transparency for vision in animals
• solvent properties, medium for metabolic reactions
• solvent properties allow the transport of soluble molecules

Question 20

Respiration and other processes in cells involve enzymes. Explain the factors that can affect enzymes. [8]

Answer 20

• collisions between enzyme active site and substrate
• temperature rise, enzyme activity increases
• more frequent collisions
• fastest rate at optimum temperature
• high temperatures above optimum denatures enzyme
• optimum pH
• increase/decrease from optimum pH decreases activity
• extreme pH alters 3D protein structure
• increasing substrate concentration increases rate
• increases chance of collision
• until plateau
• when all active sites occupied

Question 21

Explain the solvent properties of water using an example. [3]

Answer 21

• water is a polar molecule
• substances that dissolve in water are hydrophilic
• water forms hydrogen bonds with polar substances
• H side of water attracted to negative ions/vice versa
• e.g. glucose dissolves because it is polar

Question 22

Describe the structure of proteins, including features common to all proteins and features that vary. [7]

Answer 22

• one of more polypeptides
• polypeptide is a chain of amino acids
• amino acids linked by peptide bonds
• twenty different amino acids
• primary structure is the sequence and order of amino acids
• any sequence can be linked together → many possible polypeptides
• secondary structure is the formation of alpha helices and beta pleated sheets
• stabilized by hydrogen bonding
• tertiary structure is the further folding of the polypeptide
• stabilized by interactions between R groups
• two main classes: fibrous or globular
• 3D structure determined by amino acid sequence
• quarternary structure if two or more polypeptides are linked to form a protein

Question 23

Explain the role of proteins in the movement of substances across membranes. [5]

Answer 23

• protein pumps for active transport
• movement of particles against conc. gradient
• requires ATP
• protein channels for facilitated diffusion
• particles diffuse along conc. graident
• allows hydrophilic/polar particles to diffuse across
• aquaporins for movement of water by osmosis
• more aquaporins, more membrane permeability to water
• proteins are integral/embeddeded in phospholipid bilayer