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Topics 1-4: Biological molecules
Lipids





Made
of

Bonds

Prope
rties

S&F

Insoluble in water
High solubility in non-polar solvents
Simple lipids, compound lipids, and lipid derivatives
Non-polymer
Simple Lipid
(triglycerides)
 Glycerol
 3 fatty acids

Compound Lipid
(phospholipids)
 Esters of 2 fatty acids
 An alcohol
 Additional small charged
group (eg choline, serine)
Ester linkage btw OH
Ester linkage; phosphoester
group of Glycerol and
linkage btw 3rd OH group of
COOH group of a fatty
glycerol and phosphate
acid by condensation
group
 Melting point
 Amphipathic
increases with
 Aggregate in aqueous
hydrocarbon chain
environment to shield
length and degree of
hydrophobic tails from
saturation
water
 Saturated fats (no
 Micelle: small, spherical
double bonds)
droplet; monolayer
 Unsaturated fats
 Bilayer: 2D sheet
(contains double
 Liposome/vesicle: hollow
bonds)
sphere formed when
bilayer folds back on itself
Structure
Function
Structure
Function
Hydrophobic Allow motile Amphipathic  Forms a

organisms hydrophobic selectively
fatty acid;
to keep
permeable cell
their mass hydrophilic
membrane;
phosphate
to a
boundary btw
head
minimum
cell & external
environment
 Does not
 Liposome/
affect cells’
water
vesicle:
potential
storage and
transport of
 Good
cellular
thermal
products
insulator
 Micelles:
transport fats
Weak
Adipose
Hydrophobic  Maintain
hydrophobic tissue
interaction
integrity of
interaction cushions & btw fatty
membrane
protects
acid tails
bilayer

Compound Lipid (glycolipids)




Glycerol
2 hydrocarbon tails
A polar, short
carbohydrate chain
Glycosidic bond btw OH
group of glycerol and C atom
on carbohydrate chain


Amphipathic due to
soluble carbohydrate
chain and insoluble
hydrocarbon tails

Structure
Carbohydra
te chain
attached to
lipid

Hydrocarbo
n tails

Function
 Found on cell
surface
membrane
facing
external
environment
 Serves as a
marker in
cell-cell
recognition
 Involves in
cell-cell
adhesion as
a result of
binding
Hydrophobic
interaction
btw fatty acid
tails serve to

Topics 1-4: Biological molecules
vital organs
anchor the
 Permit lateral
against
glycolipids at
movement:
physical
cell surface
membrane
impact
membrane
fluidity
Lower
Aid
Contain
Important for
density than buoyancy of choline
synthesis of
water
aquatic
acetycholine
animals
Higher
Efficient
proportion energy
of C and H to store:
O atoms
releases
38kJ/g upon
oxidation
Large
Release
number of C- metabolic
H bonds
water
Kink: a bend in the hydrocarbon chain caused by a C=C double bond; prevents the molecules from
packing closely enough, thus weakening hydrophobic interactions and lowering the melting point
Lipid derivative: eg
...
Intercalated in
phospholipid membrane; interferes in hydrophobic interactions
...
Starch
and glycogen)
 Serve as structural
materials (eg
...
Proline: bulky aa residue; does not fit readily into secondary
structure, producing kinks Cysteine: forms strong covalent disulphide bridge with another
cysteine aa residue
...
collagen,
haemoglobin
• Ionic, Hydrogen,
disulfide bonds and
hydrophobic
interactions

Topics 1-4: Biological molecules
α-helix
Extended spiral spring (3
...


Topics 1-4: Biological molecules
Enzymes lower activation energy by:
1
...
Straining critical bonds in the substrate molecule(s), allowing the substrates to attain
their unstable transition state configuration
3
...
Name limiting factor
2
...
Frequency of effective collision between
E and S
4
...
Rate of formation of products

Temperature:
1
...

3
...


Change in kinetic energy of E and S
Frequency of effective collisions btw E and S
Rate of formation of E-S complex
Likeliness of over activation energy barrier

1
...
Less/more H+ ions to neutralise negative
charges present in enzyme
3
...
Denaturation
5
...
Rate of formation of products
6
...
At high [S], S can out-compete I
Effect on Km increase

Non-competitive Inhibition
Structurally not similar to substrate
Any other part, alters 3D conformation of E
Decrease in [E]
Decrease
Same

Allosteric regulation:





Usually occurs in multi-subunit enzymes
Regulation of an enzyme by the binding of molecules at an allosteric site
Activators stabilise the active form of the enzyme, increasing the affinity of E for S
Inhibitors binds to the same region, stabilizing the inactive form of the enzyme, and
decreasing the affinity of E for S

Control and Regulation of Metabolic Pathways




Controlled by multi-enzyme complex
o Biological reactions may proceed with no accumulation of products in cells, as
products become substrates of subsequent reactions
o Reactants are modified in series of small steps enabling controlled release of energy
and minor adjustments to be made to molecules
o Each step is catalysed by a specific enzyme, so each enzyme act represents a point
of control of the overall pathway
o Spatially arranged so that product of one reaction is ideally located to become the
substrate of the next enzyme, permitting the build up of high local [S] and
biochemical reactions can proceed rapidly
o Sequencing of reactions greatly increase the efficiency of the enzyme pathway
End-product inhibition is when accumulation of end-products act as inhibitors on the
enzyme(s) controlling the preceding step(s) of the pathway



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