Assignment 1: Lipid
Teaching plan
• Week 4
: Lipid
• Week 5-6
: Water
• Week 7-8 :pH, buffer, solutions,
stoichiometry and material balance
• Mid term test (6 April 2016)
• Week 9
: Semester break
• Week 10-11: Phytochemical
2
1. List a major function of each of the following classes of lipid:
i.
ii.
iii.
iv.
v.
vi.
Phospholipids
Sphingolipids
Oils
Waxes
Steroids
Carotenoids
i.
ii.
iii.
iv.
v.
vi.
Phospholipids perform major roles as structural components of
membranes, emulsifiers, and surface active agents.
Perform major roles as membranes components in plant and
animal.
Oils serve as an important energy reserve of fruits and seeds.
Waxes serve as protective coatings on the surface of leaves and
stems, on the fur of animals, and on the shells of insects.
Steroids play an important structural role in animal membranes.
Certain steroids act as hormones.
By acting as light-trapping pigments, carotenoids play an important
role in photosynthesis.
2. Sphingomyelins are amphipathic molecules. Draw the structure of a
typical sphingomyelin. Identify which regions are hydrophilic and which
are hydrophobic.
• The polar head region containing the ester and amide linkages would
be hydrophilic; the hydrocarbon tail region would be hydrophobic.
CH
CH CH2 12 CH3
CH OH
O
CH NH C R1
O
+
CH2O P O CH2CH2N (CH3)3
O
3. Stearic acid, oleic acid, linoleic acid and α-linolenic acid are common
examples of fatty acids. Each fatty acid contains same number of
carbon (18) but the melting points between them are different.
Draw the structure of each fatty acid and explain why their melting
points are different.
• Stearic acid – saturated fatty acids – the chain contain only carbon-carbon single bond –
long straight structure.
• The saturated hydrocarbon tail of stearic acid is flexible since rotation can occur around
every carbon-carbon bond.
• In a crystal of stearic acid, the hydrocarbon chains are extended and pack together
closely.
•
• Oleic acid – unsaturated fatty acid – also refers as monosaturated – a cis bond will cause
a bend in the structure, making it less likely to pack a crystal than will a saturated
molecule of the same length
• Linoleic acid – unsaturated fatty acid – also refers as polysaturated – two cis bond
• α-linolenic acid – unsaturated fatty acid - also refers as polysaturated – all cis (three cis
bond)
•
• The presence of cis double bond in oleic acid, linoleic acid and α-linolenic acid produces
pronounced bends in the hydrocarbon chains since rotation around double bonds is
hindered.
• These bends prevent close packing and extensive van der waals interactions among the
hydrocarbon chains.
• Consequently, cis unsaturated fatty acids have lower melting points than saturated fatty
acids. As the degree of unsaturation increase, fatty acids become more fluid.
4. What are the differences between neutral lipids and waxes
Waxes
Neutral lipids
1.Digestibility:
Indigestible (not hydrolyzed by lipase).
Digestible (hydrolyzed by lipase).
2-Type of alcohol:
Long-chain monohydric alcohol + one fatty
acid.
Glycerol (trihydric) + 3 fatty acids
3-Type of fatty acids:
Fatty acid mainly palmitic or stearic acid.
Long and short chain fatty acids.
4-Acrolein test:
Negative.
Positive.
5-Rancidability:
Never get rancid.
Rancidible.
6-Nature at room
temperature.
Hard solid.
Soft solid or liquid.
7-Saponification
Nonsaponifiable.
Saponifiable.
8-Nutritive value:
No nutritive value.
Nutritive.
9-Example:
Bee & carnuba waxes.
Butter and vegetable oils.
5. Describe saponification process
- Saponification (soap making)
- basic hydrolysis of fats
6. Describes several factors that influence membrane fluidity.
Unsaturated fatty acids content increases fluidity, whereas
cholesterol decreases fluidity.
7. Explain how potassium moves across a membrane. How are the
channels opened?
7. Explain how potassium moves across a membrane. How are the
channels opened?
- facilitated diffusion transport
- acetylcholine binds to the acetylcholine receptor complex.
- Na+ rushes into the cell and the membrane potential falls
(membrane depolarization)
- Depolarization caused by acetylcholine leads to the opening of
nearby Na+ channels ( refer as voltage-gated Na+ channels)
- Repolarization begin with the diffusion of K+ out of the channel
through voltage-gated K+ channel.
- Further reading: Biochemistry, McKee, McGraw Hill
8. Compare and contrast the following process: active transport,
passive transport, diffusion and facilitated diffusion.
8. Compare and contrast the following process: active transport, passive transport,
diffusion and facilitated diffusion.
•
•
•
•
•
•
•
•
•
In passive transport,
substances diffuse down a gradient.
No energy is directly used to effect the transport.
The simplest membrane transporters – whether active or passive – carry out
uniport: they carry only a single type of solute across the membrane. Many
transporters carry out the simultaneous transport of two different solute molecules.
If both solutes are transported in the same direction this process is called symport.
If they are transported in opposite directions the process is antiport.
Passive transport also called facilitated diffusion since it does not required an
energy source.
e.g.
diffusion of oxygen and carbon dioxide.
osmosis of water.
facilitated diffusion
• In active transport,
• energy is required to move solutes across a membrane against the
concentration gradient. Most commonly ATP. Divided into 2:
•
• Primary active transport
• Energy is usually provided directly by ATP hydrolysis. The Na+-K+
pump is a prominent example of a primary transporter.
•
• Secondary active transport
• Solutes are moved across a membrane by energy stored in a
concentration gradient of a second substance that has been created
by ATP hydrolysis or other energy-generating mechanisms. e.g. the
Na+ gradient created by the Na+-K+ ATPase pump is used in kidney
tubule cells and intestinal cell to transport D-glucose.
• In simple diffusion, solutes move down a concentration gradient i.e.,
from an area of high concentration to an area of low concentration.
Spontaneous process, there is a net movement of solute until an
equilibrium is reach. Because there is no input of energy, transport
occurs with a negative charge in free energy. In general, the higher
the concentration gradient, the faster the rate of solute diffusion.
Example:
• diffusion of oxygen and carbon dioxide and osmosis of water.
• Diffusion of organic molecules also depends on molecular weight and lipid
solubility.
• Facilitated diffusion
• Is the movement of a solute/ subtances down its concentration
gradient across a membrane that occurs through protein channels or
carriers.
• Channel are tunnel-like transmembrane protein. Each type is designed
for the transport of specific solute.
• Many channels are chemically or voltage-regulated.
• Chemically regulated channels open or close in response to a specific
chemical signal.
• e.g: A chemically gated Na+ channel in the nicotinic acetylcholine
receptor complex opens when acetylcholine binds.
9. Describe how glucose is transported across membranes in the
kidney. What type of transport is involved?
• Secondary active transport
• Solutes are moved across a membrane by energy stored in a
concentration gradient of a second substance that has been created
by ATP hydrolysis or other energy-generating mechanisms. e.g. the
Na+ gradient created by the Na+-K+ ATPase pump is used in kidney
tubule cells and intestinal cell to transport D-glucose.
10. Suggest the mechanism(s) by which each of the following substance
is (are) transported across cell membranes:
• i. CO2
• ii. Glucose
• iii. H2O
• iv. Na+
• v. Cl• vi. K+
• vii. Fat molecules
• viii. α-tocopherol
10. Suggest the mechanism(s) by which each of the following substance
is (are) transported across cell membranes:
• i. CO2 - simple diffusion
• ii. Glucose - facilitated diffusion (glucose in red blood cell);
secondary active in kidney
• iii. H2O – diffusion (osmosis)
• iv. Na+ - facilitated diffusion
• v. Cl- - facilitated diffusion
• vi. K+ - facilitated diffusion
• vii. Fat molecules – diffusion
• viii. α-tocopherol - facilitated diffusion which involves carrier
Assignment 3: Group discussion and
presentation
• Divide yourself into 10 groups
• Choose from the following topic (2 groups for one topic)
•
•
•
•
•
pH
buffer
solutions,
stoichiometry
material balance
• Present on week 7 and 8