Theme 1: The Composi-on and Structure
of Membranes(2:15-17; 5:1-15; 26:22)
Lipids are Hydrophobic Molecules
• Lipids aren't defined by a chemical structure, but by their tendency to
be hydrophobic
• Triacylglycerol: A lipid that is used for energy storage
◦ A major component of animal fat and vegetable oil
◦ Such a molecule is made up of 3 faBy acids joined to glycerol
• Fa4y Acid- A long chain of carbons aBached to a carboxyl
group (COOH)
• FaBy acids differ in length of their hydrocarbon chain
◦ Most cells contain an even number of carbons
because they are synthesized by a stepwise
addiOon of 2-carbon units
• Saturated- FaBy acids that don't contain double
bonds
◦ Maximum number of hydrogen atoms is
aBached to each carbon atom
◦ Generally, animal fats (solid) are made of
saturated faBy acids
• Unsaturated- FaBy acids that contain carbon-carbon
double bonds
◦ Generally, plant fats and fish oils (liquid) are
made of unsaturated faBy acids
• Hydrocarbon chains of faBy acids don't contain polar
covalent bonds and so, the electrons are distributed
uniformly and these molecules are uncharged
◦ BUT, constant moOon of electrons leads to
regions of slight posiOve or negaOve charges
• Due to van der Waals forces, melOng points of faBy
acids depend on their length and level of saturaOon
, ◦ Longer hydrocarbon chain= More van der Waals
forces= Higher melOng point
◦ Kinks (due to double bonds) reduces the
Oghtness of the molecular packing and leads to
fewer IMFs and lower melOng point
• Glycerol- A 3-carbon molecule with OH groups aBached to
each carbon
◦ Can contain different types of faBy acids aBached to the glycerol
backbone
◦ Efficient for energy storage because of absence of water which
means many triacylglycerols can be packed into a small volume
• Van der Waals Forces: Transient asymmetry in the distribuOon of
electrons alone faBy acid chains leads to asymmetry in neighbouring
molecules, resulOng in weak electrostaOc aBracOons
◦ Many of them acOng together help to stabilize molecules
• Steroids: Like other steroids, cholesterol has a core composed of 20
carbon atoms bonded to 4 fused hydrocarbon rings; Cholesterol is a
component of animal cell membranes and is a precursor for the
synthesis of steroid hormones (like estrogen and testosterone)
• Phospholipids: Most are made up of glycerol aBached to 2 faBy acids
and a 3rd molecule containing a phosphate group
◦ The phosphate "head" is hydrophilic and the faBy acid "tails" are
hydrophobic
◦ When placed in water, they form many structures the minimize
exposure of hydrophobic tails to water
• Example: Bilayer- A 2 layered structure with the hydrophilic
heads poinOng outward toward the aqueous environment
and the hydrophobic tails oriented inward
Organizing Principles: Lipids, Membranes, and Cell
Compartments
• Cells first seen and named in 1665 by Robert Hooke who observed thin
secOons of dried cork Ossue from plants
of Membranes(2:15-17; 5:1-15; 26:22)
Lipids are Hydrophobic Molecules
• Lipids aren't defined by a chemical structure, but by their tendency to
be hydrophobic
• Triacylglycerol: A lipid that is used for energy storage
◦ A major component of animal fat and vegetable oil
◦ Such a molecule is made up of 3 faBy acids joined to glycerol
• Fa4y Acid- A long chain of carbons aBached to a carboxyl
group (COOH)
• FaBy acids differ in length of their hydrocarbon chain
◦ Most cells contain an even number of carbons
because they are synthesized by a stepwise
addiOon of 2-carbon units
• Saturated- FaBy acids that don't contain double
bonds
◦ Maximum number of hydrogen atoms is
aBached to each carbon atom
◦ Generally, animal fats (solid) are made of
saturated faBy acids
• Unsaturated- FaBy acids that contain carbon-carbon
double bonds
◦ Generally, plant fats and fish oils (liquid) are
made of unsaturated faBy acids
• Hydrocarbon chains of faBy acids don't contain polar
covalent bonds and so, the electrons are distributed
uniformly and these molecules are uncharged
◦ BUT, constant moOon of electrons leads to
regions of slight posiOve or negaOve charges
• Due to van der Waals forces, melOng points of faBy
acids depend on their length and level of saturaOon
, ◦ Longer hydrocarbon chain= More van der Waals
forces= Higher melOng point
◦ Kinks (due to double bonds) reduces the
Oghtness of the molecular packing and leads to
fewer IMFs and lower melOng point
• Glycerol- A 3-carbon molecule with OH groups aBached to
each carbon
◦ Can contain different types of faBy acids aBached to the glycerol
backbone
◦ Efficient for energy storage because of absence of water which
means many triacylglycerols can be packed into a small volume
• Van der Waals Forces: Transient asymmetry in the distribuOon of
electrons alone faBy acid chains leads to asymmetry in neighbouring
molecules, resulOng in weak electrostaOc aBracOons
◦ Many of them acOng together help to stabilize molecules
• Steroids: Like other steroids, cholesterol has a core composed of 20
carbon atoms bonded to 4 fused hydrocarbon rings; Cholesterol is a
component of animal cell membranes and is a precursor for the
synthesis of steroid hormones (like estrogen and testosterone)
• Phospholipids: Most are made up of glycerol aBached to 2 faBy acids
and a 3rd molecule containing a phosphate group
◦ The phosphate "head" is hydrophilic and the faBy acid "tails" are
hydrophobic
◦ When placed in water, they form many structures the minimize
exposure of hydrophobic tails to water
• Example: Bilayer- A 2 layered structure with the hydrophilic
heads poinOng outward toward the aqueous environment
and the hydrophobic tails oriented inward
Organizing Principles: Lipids, Membranes, and Cell
Compartments
• Cells first seen and named in 1665 by Robert Hooke who observed thin
secOons of dried cork Ossue from plants
