2.1 - 2.5, 8.1 Molecular Biology Extended Response Q. Flashcards
Distinguish between fibrous and globular proteins with reference to one example of each protein type. ( 6 Marks )
- fibrous proteins are strands whereas globular proteins are rounded
- fibrous insoluble whereas globular soluble
- globular more sensitive to change in pH/temperature/salt
- fibrous proteins have structural roles
- globular for catalysis and transport
- name fibrous- keratin, fibrin, collagen, actin, myosin
- name globular- insulin, hemoglobin, immunoglobin
Role of condensation and hydrolysis in relationship of amino acids and dipeptides. ( 4 Marks )
Condensation - dehydration synthesis, water produced (amino acid + amino acid) - Amino Acid -> dipeptide
Hydrolysis - water needed to break bond - Dipeptide -> amino acid
Example of proteins with different numbers of polypeptide chains.
1 - Lysozyme - enzyme in secretion i.e nasal mucus - kills bacteria by digesting peptidoglycan in their cell walls
2 - Integrin - membrane protein - makes connections between structures
3- collagen - structural protein - high tensile strength found in skin and blood vessels
4 - Hemoglobin - transport protein in red blood cells; it binds oxygen in the lungs and releases it in the tissue
Describe the structure of protein. ( 9 Marks )
PRIMARY STRUCTURE - 1. chains of amino acids, 2. each position occupied by one of 20 different amino acids. 3. linked by peptide bonds
SECONDARY STRUCTURE - 1. interaction of amine and carboxyl group, 2. hydrogen bonds form, 3. a helix forms and polypeptide coils up or ß pleated sheet forms
TERTIARY STRUCTURE - 1. folding up of the polypeptide, 2. stabilised by disulfide bridges/hydrogen/ionic/hydrophobic bond
QUATERNARY STRUCTURE - 1. several polypeptides subunits join 2. conjugated proteins combine with non - proteins molecules i.e metals, nucleic acid,carbohydrates, lipids
List four functions of protein - named example ( 4 Marks )
transport - hemoglobin hormones - insulin, TSH receptors - neurotransmitter receptor defense - immunoglobin structure - collagen active transport - sodium potassium pump facilitated diffusion - sodium channels
List three functions of Lipids ( 3 marks )
- protection of internal organs
- structural component of cell membranes
- glycolipids act as receptors
- heat insulation
- energy storage
Describe the significance of water to living organisms ( 6 Marks )
surface tension - allows organisms i.e insects to move on water
polarity/ adhesion - helps plants transport water
transparency - allows plants to photosynthesize in water
excellent solvent - capable of dissolving substances for transport in organism
high heat of vaporization - coolant
structure - hydrostatic pressure in plant cells
Describe the use of carbohydrates and lipids for energy storage in animals ( 5 marks )
carbohydrates
- stored as glycogen in liver
- short term energy storage
- easily digested so energy quickly available
- more soluble in water so easier transport
Lipids
- stored as fat in animals
- long term energy storage
- more energy per gram
- lipids insoluble in water so less osmotic effect
Describe the significance of polar and non-polar amino acids ( 5 Marks )
Polar amino acids
- hydrophilic
- can make hydrogen bonds
- found in hydrophilic channels
- found in surface of water-soluble protein
Non-polar amino acids
- hydrophobic
- found in protein in interior of membranes
- found in interior of water-soluble proteins
Outline the thermal, cohesive and solvent properties of water. ( 5 Marks )
- high specific heat capacity - large amount of heat causes small increase in temp
- high latent heat of vaporization - large amount of heat energy needed to evaporate water
- hydrogen bonds between water make them cohesive ; stick together - gives water high surface tension, explains how water rises up the xylem
- water molecules are are polar - making water a good solvent
Explain the reason for converting lactose to glucose and galactose during food processing. ( 3 Marks )
- allows people with lactose intolerance consume milk
- galactose and glucose tase sweeter than lactose
- galactose and glucose more soluble than lactose ( smoother texture )
- bacteria ferment glucose and galactose more rapidly shortening production time
Simple laboratory experiments show that when enzyme lactase is mixed with lactose the initial rate is highest at 48 degrees. In food processing, lactose is used at 5 degrees. Why lower temp in food processing? ( 2 Marks )
- less denaturation/ enzymes last longer at low temperatures
- lower energy cost
- reduces bacterial growth
- control rate of reaction
Outline one industrial use of lactase. ( 5 Marks )
- lactose intolerance high in some human pop. - asian, African , native American
- lactase used to produce lactose free milk
- lactase breaks down lactose to glucose and galactose
- source of lactase usually yeast
- milk passed over immobilized lactase
- increases sweetness no need for extra sugar
- can add bacteria L.acidophilus which same effect on lactose as in yoghurt
Outline how enzymes catalyse reactions. ( 7 Marks )
- they increase rate of reaction
- remain unchanged at end of reaction
- lower activation energy - activation energy is energy needed to overcome energy barrier that prevents reaction
- substrate joins with enzyme at active site
- forms enzyme-substrate complex
- active site - enzyme specific for particular substrate
- enzyme binding with substrate brings reactants closer together to facilitate chemical reactions (such as electron transfer)
- induced fit model / change in enzyme conformation (when enzyme-substrate/ES complex forms);
making the substrate more reactive;
Effects of pH on enzyme activity. ( 3 Marks )
- enzymes have an optimal pH
- lower activity above and below optimum pH / graph showing this
- too acidic / base pH can denature enzyme
- change shape of active site / tertiary structure altered
- substrate cannot bind to active site / enzyme-substrate complex cannot form
hydrogen / ionic bonds in the enzyme / active site are broken / altered
