Topic Biomolecule (Lipid) Essay - Main Points!

Q) Lipids is a better energy storage molecule than carbohydrates. Despite this, explain why, unlike animal cells, plant cells tend to store carbohydrates.

Main points
Key idea:	Varied functions of lipids in animals
Triglycerides ·Energy store ·Buoyancy (for aquatic animals e.g. whales) ·Thermal insulation (for animals living in cold climate) ·Source of metabolic water (for animals living in the desert) ·Protects internal organs
Key idea:	Advantage of lipids over carbohydrates in terms of energy storage capacity
·Lipid stores more energy per unit mass compared to carbohydrate ·Hence, greater mobility for animals
Key idea:	Possible reason why plants can afford to store their energy as carbohydrates
·Plants are not mobile
Comments: (i) Visualize the answer with the aid of a labelled diagram (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Lipids store more energy per unit mass than carbohydrates because it has a higher proportion of H to O atoms per unit mass. Hence, they are easily oxidized and produce more ATP compared to an equivalent mass of carbohydrate (eg. glycogen)

Topic Biomolecule & cell signalling

Q) Describe the differences between glycogen and glucagon

Main points
Key idea:	Type of molecule + building blocks + bonds
Glycogen ·  Polysaccharide, made up of many α glucose ·Joined by α-1,4 glycosidic bonds ·Highly branched struc ·Ref to α-1,6 glycosidic bonds at branch pts Glucagon ·Protein, made up of aa ·Joined by peptide bonds ·Globular struc due to infolding of polypep chain upon itself ·Ref to interactions (e.g. H, ionic, disulphide & hydrophobic) b/w R gps of faraway aa residues
Key idea:	Role + location
Glycogen ·Energy storage mol · Stored in muscle & liver Glucagon ·Hormone; regulates bl glucose level ·Stored in the α cells, islets of Langerhans, pancreas
Key idea:	Solubility in water
Glycogen ·Soluble in H2O; can be transported via blood to targe cells/tissue ·Infolding of polypep affect distribution of aa ·Ref to polar aa residues on ext surf of mol; non-polar aa residues in the interior Glucagon ·Insoluble in H2O ·Ref to polar OH gps project into mol ·Ref to large size as a contributing factor too
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Biomolecule (Enzyme) Essay - Main Points!

Q) Explain the effect of temperature on the rate of an enzyme-catalyzed reaction

Main points
Key idea:	Enzyme is inactive at low temperature
·Increasing temp increase kinetic energy of both substrate & enz mol ·Result: higher freq of successful collision b/w enz & substrate mol, form enzyme-substrate (ES) complexes ·Ref to rate of increase doubles /10oC rise in temp (i.e. temp coefficient, Q10 = 2) ·Rate of rx increases until optimum temp of enz reached
Key idea:	Enzyme denatures beyond optimum temperature
·Ref to drastic decrease in rate of rx ·Reason: increase in kinetic energy of enz mol disrupts H & ionic bonds that maintain specific conformation of its active site (AS) ·Result: AS no longer complementary to its substrate; substrate cannot fit into AS to form ES complex
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Explain how the other variables (e.g. pH, enzyme and substrate concentrations) affect the rate of enzyme-catalyzed reaction

Topic Biomolecule (Enzyme) Essay - Main Points!

Q) Explain the effect of pH on the rate of an enzyme-catalyzed reaction

Main points
Key idea:	Every enzyme has an optimal pH
·Ref to enz functioning most efficiently + ref to max rate of rx
Key idea:	Deviation from the optimal pH denatures the enzyme
·Ref to decreases in biological activity of enz ·Reason: ionic & H bonds maintaining specific shape of protein mol including its active site (AS) disrupted ·AS of enz no longer complementary to substrate ·ES complex cannot form
Key idea:	Changes in pH affects electrostatic bonds between substrate and active site of enzyme molecule during formation of ES complex
·Ref to changes in pH can also affect R gps of key aa at AS ·Hence, may affect ionisation of key aa at AS, affect electrostatic binding b/w them, ES complex cannot form
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Biomolecule (Enzyme) Essay - Main Points!

Q) Describe the mechanism of action of all enzymes

Main points
Key idea:	What are enzymes
·Biological catalysts - speed up rate of chemical rx ·by lowering activation energy of rx
Key idea:	Formation of the enzyme-substrate (ES) complex
·Effective collision b/w substrate & enz mol ·Substrate binds to active site (AS) of enz by ionic or/& H bonds for transient period
Key idea:	Lowering of activation energy through formation of the ES complex
·Due to stress to bonds in substrate mol – become easily broken ·Or diff substrate mol bound at AS in close proximity & correct orientation - faciliates formation of bonds b/w mol
Key idea:	Specificity of enzyme action
·Ref to induced fit hypothesis to explain specificity of enz action Details: ·Shape of AS not complementary to substrate initially ·Upon binding to AS, substrate induces conformation change ·Result - AS now fits substrate ·Ref to complementary binding of substrate to AS of enz
Key idea:	Enzyme is recycled
·When product is formed, it no longer fits AS & will leave ·Enz is re-used for other rx
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Biomolecule (Lipid) Essay - Main Points!

Q) Describe the main differences in the molecular structure of triglycerides and phospholipids

Main points
Key idea:	Components and bonds
Triglyceride · Formed fr 1 glycerol + 3 fatty acids (FA) via condensation rx · Via formation of 3 ester linkages · Ref to each ester linkage due to · Ref to hydroxyl (OH) gp of glycerol reacts w carboxyl (COOH) gp of FA Phospholipid · Formed fr 1 glycerol + 2 FA + 1 phosphoric acid via condensation rx · Via formation of 2 ester linkages + 1 phosphoester linkage, respectively
Key idea:	Type of lipid
Triglyceride · Simple lipid Phospholipid · Complex lipid
Key idea:	Amphiphathic property of phospholipid
Phospholipid · Phosphate often bonded to a nitrogen-containing organic gp (e.g. choline) · Hydrophilic polar head comprises of glycerol residue, phosphate & organic base; can ionize in water · 2 hydrophobic non-polar hydrocarbon chains of FA residues · Ref to both hydrophilic + hydrophobic regions of mol gives rise to amphipathic property (absent in triglyceride)
Comments: (i) Visualize the answer with the aid of a labelled diagram (showing the formation of triglyceride and phospholipid) (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Biomolecule (Carbohydrate) Essay - Main Points!

Q) Describe the structural features of cellulose

Main points
Key idea:	What is cellulose + bonds + building blocks
· A polysaccharide made up of a chain of β glucose mol · joined by β-1,4 glycosidic bonds · Each cellulose chain consists of 1000 or more β glucose · Ref to alternate glucose rotated 180o to form a straight chain
Key idea:	Organization of cellulose
· Hydroxyl (OH) gp project outward fr each cellulose chain in all direction · Form H bonds w neighbouring chains, form microfibrils · Ref to microfibrils bundled to form macrofibrils
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) You should be able to explain the structural adaptation of cellulose to its function and compare between collagen and cellulose

Topic Biomolecule (Protein) Essay - Main Points!

Q) Describe the structural features of collagen

Main points
Key idea:	What is collagen  + bonds + building blocks
· A fibrous protein made up of aa · joined by peptide bonds · Each polypeptide chain made up of mainly glycine, proline & hydroxyproline · Ref to polypep having a kinked helical shape (as glycines are small compared to larger sized proline & hydroxyproline)
Key idea:	Organization of collagen
· 3 of such polypep coil around each other (by H bonds), to form the triple helical struc of repeating unit - tropocollagen · Ref to covalent cross-linkages b/w adjacent tropocollagens, to form collagen fibril · Ref to staggered arrangement of tropocollagens - no weak point a/x collagen fibril · Collagen fibrils bundle to form collagen fibres
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) You should be able to explain the structural adaptation of collagen to its function and compare between collagen and cellulose

Topic Biomolecule (Lipid) Essay - Main Points!

Q) Describe the usefulness of phospholipids in living organisms

Main points
Key idea:	Main component of cell membranes
· Amphipathic property of phospholipid · Ref to a polar head + 2 non-polar hydrocarbon tails · Result: mol arrange to form a bilayer struc · Ref to polar heads pointing towards aq medium; hydrocarbon tails form hydrophobic core · Ref to bilayer struc forming cell surface membr + compartmentalize cell throu formation of membrane-bound organelles (where specialized rx can take place w/n)
Key idea:	Regulates passage of substances in and out of cell
· Ref to hydrophobic core of bilayer excludes large polar substances + charged particles/ions fr passing throu by simple diffusion
Key idea:	Good thermal insulator + provides buoyancy
· Prevents excessive heat loss + less dense than water · Ref to its usefulness to animals (e.g. whale) that live in cold environment + aquatic mammals (e.g. whales and seals)
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)