Chapter 3 - Lipids Flashcards
What are the 2 major functions of lipids?
- Energy storage
- Membrane formation
What are 2 other functions of lipids?
- Form micelles
- Serve as signal molecules
What is the most prominent class of polar lipids?
Phospholipids
What are the building blocks of lipids?
Fatty Acids
What are the components of triglyceride (triacylglycerol)
3 fatty acids bonded to a glycerol
What are the 2 components in the structure of fatty acids
tail - hydrocarbon chain with a variable number of double bonds
head- typically a carboxyl group
In a fatty acid, which carbon is considered carbon number 1?
Carbon of the carboxyl group
What does the delta sign (little triangle) symbolize in a chemical formula for a fatty acid?
There is a double bond at that position
fatty acids containing double bonds are considered _____
unsaturated
What does the term polyunsaturated mean?
When more than one double bond exists in a fatty acid
Double bonds in fatty acids can either be ___ or ____. Which one produces a kink in the chain?
cis, trans.
cis
Cis fatty acids have a ______melting point than trans.
lower
Can carbon-carbon single or double bonds rotate freely around their bond axis??
single
Are cis fatty acids liquid or solid?
liquid
Are conjugated or isolated double bonds more reactive
isolated. conjugated are stabilized by resonance (electrons are delocalized)
Polyunsaturated fatty acids always have ______ double bonds
isolated
Why is the head of a fatty acid so soluble in water?
COOH is a weak acid, so it is almost always in its anionic form (COO-)
What is the term to describe that fatty acids have both a hydrophilic/phobic part?
amphipathic
Which fatty acid is the most common in mammals and is an energy storage form
Triglyceride (triacylglycerol)
An ester bond describes the bond between…..?
Fatty acid and glycerol
Triglycerides are formed by..
dehydration synthesis
Are triacylglycerols hydrophilic or hydrophobic? why?
Hydrophobic - the ester bond is not able to form H bonds with water
-O-
Why is it a benefit for triglycerides to be hydrophobic?
Excluding water reduces the weight of the fat cells
Animals use _____
Plants use _____
Animals use lipids
Plants use carbohydrates
Molecularly - why do carbohydrates weigh more than lipids?
Many more oxygen molecules in carbohydrates
What is visceral fat?
Triglycerides with saturated side chains. Solid fat that is deposited near organs
Less saturated side chains are a fat called _________. Where are they found?
subcutaneous fat. Just under the skin
Even more unsaturated triglycerides are known as _______. They are found in seeds
oils
What are the molecular components of phospholipids?
2 fatty acids and a phosphate group bonded to glycerol
Phopshate is a polyprotic acid meaning what?? This makes it a good _____
Phosphate can donate more than one proton. It has multiple equilibria.This makes it a good buffer
Phosphates are derivatives of….?
Phosphatidic acid
Inorganic Phosphate is a ____acid
weak
Phosphate reacts with _____s to form _______s
phosphate reacts with alcohol to form esters
Phosphates have a lot of variability. They can form _____ and attach to all different kinds of alcohols and fatty acids.
diesters
Cholesterol is a ______
steroid
Steroids are _____
lipids
Cholesterol consists of…
4 fused, flat rings and a hydroxyl group
Is cholesterol hydrophobic or hydrophilic?
mostly hydrophobic
Give 3 examples of amphipathic molecules
fatty acids
cholesterol
phospholipids
Amphipathic molecules will form either _____ or _____
micelles or liposomes
What is a micelle?
Polar portions face the aqueous exterior. Nonpolar portion forms an interior core excluded from water.
Fatty acids form ______ in water
micelles
Name 3 steroid derivatives of cholesterol
Testosterone, estradiol, aldosterone
Amphipathic molecules have 2 conflicting natures. What are they?
Water solubility and lipid solubility
What does CMC stand for and explain what it means
CMC = critical micelle concentration. This value is the concentration at which fatty acids form micelles
The higher the CMC of a substance, the ____ soluble it is in water
more
When fatty acids are added beyond the CMC, new micelles are formed but the concentration of free fatty acids in the water solution remains ______
constant
CMC depends strongly on ________ such as ______
CMC depends strongly on experimental conditions such as salt concentration
Liposomes consist of 3 layers. What are they?
- Exterior water phase
- Interior water phase
- Non polar phase between
Essentially, liposomes form a _______
biological membrane - a bilayer
How can you determine if a micelle or liposome will form?
If the volumes of the hydrophilic and hydrophobic portions are unequal, a micelle will form. If the volumes are equal, a liposome will form
Phophatidylcholine is a major component of the _______
cell membrane
Phosphatidylcholine forms a ______ in water
liposome
Can water readily cross the cell membrane?? Why??
Yes - because of the extremely large concentration of water
In general, can hydrophilic substances cross the cell membrane?
NO
What are aquaporins?
Protein channels that can accelerate or regulate the flow of water through the cell membrane
Because of the composition of a membrane, what can exist on either side?
2 solutions with distinct composition
What is diffusion?
The movement of substances due to differences in concentration
What is osmosis?
Movement of water across a semipermeable membrane from a region of low concentration to a region of high concentration
Do double bonds in fatty acid chains decrease or increase membrane fluidity?
increase
At low temperatures, cholesterol ______ the fluidity of the cell membrane
increases
At high temperatures, cholesterol ________ the fluidity of the cell membrane
decreases
Give another example of a lipid aside from triacylglycerol, phospholipids, and sterols
lipopolysaccharide - lipid + sugar
In naturally occurring fatty acids, the double bonds are in the ______ conformation
cis
Unsaturated fatty acid tails are more hydrophobic or hydrophilic?
hydrophilic
Long fatty acid tails are more/less soluble in water than short tails
less
What are the 3 major types of lipids
- Phospholipids
- Triglycerides
- sterols
Why do single bonds not possess cis/trans stereochemistry?
They can rotate
Whose melting temperature is higher at the same molecular weight? (saturated or unsaturated fatty acids)
saturated fatty acids (double bonds change shape. single bonds are more well packed)
