MEMBRANES
1. Triglycerides
2. Saturated fatty acids
3. Phospholipids
4. Phospholipid bilayer
5. Other lipids
6. Membrane permeability
7. Membrane proteins
8. 6 types of membrane protein
9. Passive transport
10. Concentration gradient
11. osmosis
12. Active transport
13. Na –K pump
14. Coupled transport
15. Bulk transport
Review from NYA.
1. Triglycerides
Hydrocarbons
This can be made into a fatty acid by putting a carboxyl at
one end:
*normally fatty acids have 14-20 carbons
2. Saturated fatty acids
Fatty acids can be SATURATED or UNSATURATED
Unsaturated fatty acids can be cis or trans
We do not have
enzymes to make ω 3
fatty acids, which is
why they are GOOD
Unsaturated ω3 cis
Unsaturated ω3 trans
ώ (omega)
ends of molecule
We do not have
enzymes to break down
Trans fatty acids, which
is why they are BAD.
(Usually manufactured
by hydrogenation)
Triglycerides are made by attaching 3 fatty acids to
glycerol:
The name of the bond is an ESTER
Esterification reaction (joins an alcohol to an acid):
NOTE: water is produced, so this is a DEHYDRATION reaction
Fig. 3.27
Figure 6.13 The Shape of a Fatty Acid Depends on Its Chemical Bonds.
6-7
3. Replace a fatty acid with a phosphate to make a
PHOSPHOLIPID
Fig. 3.29
4. Phospholipid bilayer
A micelle
Easily forms a phospholipid bilayer membrane
https://www.youtube.com/watch?v=dySwrhMQdX4
Minute 6, 8, 9.3 – about Protocells
A liposome
Figure 6.5 Liposomes Are Artificial Membrane-Bound Vesicles.
6-10
• The membrane is a fluid
structure – the molecules can
move around.
• However they rarely flip from
one side to another.
• Fluidity is affected by packing.
Saturated fats pack more
tightly, making a less fluid
membrane.
• Cholesterol stabilises
membrane fluidity in differing
conditions.
• Patches of membrane can be
Figure 6.12 Phospholipids Move within Membranes.
less fluid. These are
lipid rafts.
6-11
Fig. 5.6
mRNA lipid
nanoparticle
Covid-19 vaccines
(Pfizer, Moderna)
Ionizable cationic
lipid binds to RNA
(pioneered by
Canadian, Pieter
Cullis) – converts to
neutral charge in body
to reduce toxicity.
PEGylated lipid
attached to another
molecule, for stability
Fig. 3.28
5. Other Lipids
5. Other lipids
Prostaglandins:
•Cause inflammation, smooth muscle contractions
•Found in semen
Cause of period pain (take ibuprofin e.g. Motrin)
TRIGLYCERIDES example: body fat
PHOSPHOLIPIDS example: membrane
STEROIDS example: testosterone
TERPENES example: cannabis fragrance, chlorophyll, vitamin A
PROSTAGLANDINS example: PGF2α (uterine contractions)
•Are all LIPIDS
•They are all HYDROPHOBIC
•They all pass easily through membranes
•They all associate with membranes
6. Membrane permeability
Figure 6.7 Lipid Bilayers Show Selective Permeability.
6-17
7. Membrane proteins
Fig. 5.3
Fig. 5.5
REVIEW – Membrane structure
•Phospholipid
– degree of saturation affects fluidity of membrane
•Cholesterol
– changes membrane fluidity and permeability, forms lipid rafts
•Transmembrane proteins
– can be fixed or floating, or on lipid rafts
•Interior Protein network
– give cell its shape, hold membrane proteins in place
•Cell surface markers
- glycoproteins or glycolipids
Peripheral proteins are tethered to phospholipids
Integral proteins are stuck into the membrane
8. 6 types of membrane protein
RHODOPSIN – light energy is absorbed by the chromophore, causing a
change in the shape of the protein
Aquaporin: 6 alpha helices surround hydrophilic pore that allows
passage of water molecules
Porin – allows passive diffusion of material across membrane
9. PASSIVE TRANSPORT
• Diffusion
• Facilitated diffusion
• Osmosis
Fig. 5.9
10. Concentration gradient
DIFFUSION: Material moves DOWN the concentration gradient
ANALOGY: height gradient on a hill:
The ball moves DOWN the gradient
HIGH  LOW
FACILITATED DIFFUSION:
Material moves DOWN the concentration gradient
Fig. 5.10
DIFFUSION:
Rate depends on relative concentrations on either side of the
membrane, until EQUILIBRIUM is reached
FACILITATED DIFFUSION:
• Rate depends on relative concentrations on either side of
the membrane
• Can be saturated (as can be enzyme catalysed reactions)
• Specific (as can be enzyme catalysed reactions)
11. Osmosis = facilitated diffusion of water
(through AQUAPORINS)
Where there is a lot of
water
HIGH [water]
(low [solute])
Water moves
DOWN its
concentration
gradient
Where there is not much
water
LOW [water]
(high [solute])
Osmotic Pressure
= pressure that must be applied to prevent osmosis
Fig. 5.11
Fig. 5.12
Figure 6.17 Osmosis C an Shrink or Burst Membrane-Bound Vesicles.
6-33
MEMBRANE STRUCTURE AND FUNCTION
THINK-PAIR-SHARE
• What is the solution outside cell?
• What will be net movement of water
relative to the cell?
• What will happen to cell?
© 2014 Pearson Education Ltd.
7-34
12. ACTIVE TRANSPORT
Material moves UP its concentration gradient
HIGH
ATP is used
LOW
EXAMPLES:
1. CFTR protein channel, which uses ATP to transport Cl- out of cells.
In cholera, this protein is permanently activated by a toxin produced by
cholera bacteria.
2. Na/K pump
Uses HUGE amounts of ATP. Needed to make nerve cells function.
13. Sodium – Potassium pump
Fig. 5.13
14. Coupled Transport
Uses concentration gradient of one substance to carry another
substance up its concentration gradient.
Example:
Dopamine reuptake with dopamine active transporter protein
requires 2 sodium ions and 1 chloride ion to be cotransported
with the dopamine.
https://www.youtube.com/watch?v=Tqwo9dmIXAQ
• SGL2 is a SYMPORT. Facilitated diffusion.
• GLUT2 is also an example of facilitated diffusion. Iit is a uniport.
• Na K pump is not considered to be an antiport, because ATP is
involved. It is ACTIVE TRANSPORT
Figure 6.30 Summary of the Passive and Active Mechanisms of Membrane Transport.
6-40
15. Bulk transport
Transport of large volumes across membranes OUT of cells
= EXOCYTOSIS
http://kenpitts.net/bio/images/exocytosis.gif
Example:
Production of milk in mammary gland
http://yallaah.files.wordpress.com/2013/08/yaallahin-mammary-gland.jpg?w=314&h=461
Transport of large volumes across membranes INTO cells
= ENDOCYTOSIS
Types of Endocytosis:
• PINOCYTOSIS (cell drinking): uptake of fluids
• Example: blastocyst absorbs nutrients from uterine
secretions before it implants in the endometrium.
• PHAGOCYTOSIS (cell eating): uptake of large particles
Example: when an amoeba engulfs a paramecium
• RECEPTOR-MEDIATED ENDOCYTOSIS:
uptake of a specific substance
Figure 7.15 Two Ways to Deliver Materials to Lysosomes.
7-43
Figure 7.16 Receptor-Mediated Endocytosis May Lead to Lysosome Formation.
7-44
Coronavirus
tricks the cell
into taking it in
by Receptor
mediated
endocytosis.
Its spike
protein binds
to the ACE2
(Angiotensin
Converting
enzyme2)
receptor of the
cell
REVIEW - Transport
Diffusion
Substance moves DOWN
concentration gardient.
Equilibrium is reached
when concentration is
equal on both sides of
membrane.
Not specific
Not saturatable
Does not use ATP
Facilitated diffusion
Substance moves DOWN
concentration gradient.
Equilibrium is reached
when concentration is
equal on both sides of
membrane.
specific
Can be saturated: rate
limited by number of
carriers.
Does not use ATP
Osmosis
Water moves DOWN
concentration gradient.
Equilibrium is reached
when concentration is
equal on both sides of
membrane.
specific
Active Transport
Material moves UP
concentration gradient.
Equilibrium is reached
when concentration is
equal on both sides of
membrane.
specific
Can be saturated: rate
limited by number of
aquaporins.
Does not use ATP
Can be saturated: rate
limited by number of
transporters.
Uses ATP
You need to know from this PowerPoint:
• Structure of a triglyceride
• Structure of a phospholipid
• Phospholipid bilayer composition and fluidity
• Types of membrane proteins
• Table of different types of transport
Almost all of the examples will become relevant later in the course, so
remember them!