Lipids Flashcards
What is a triglyceride?
A fat made up of ONE glycerol molecule and THREE fatty acids.
What is glycerol?
Glycerol is a simple polyol compound (member of the alcohol family)
What are fatty acids?
A carboxylic acid with a long aliphatic chain , either saturated or unsaturated.
(typical) Difference between fats and oils.
Fats are SATURATED lipids that are SOLID at RTP.
Oils are UNSATURATED lipids that are LIQUID at RTP.
Why are lipids not soluble in water?
Lipids are non polar - the electrons are distributed evenly in the outer orbital - and so there are no positive or negative areas around the molecule.
What type of molecule are lipids?
Lipids are large complex molecules known as MACROMOLECULES.
What are the bonds between glycerol and fatty acids called?
Ester bond
How does the bond between glycerol and fatty acids arise?
Both types of molecules contain hydroxyl groups and these interact to produce three water molecules and three ester bonds.
HYDROGEN from GLYCEROL
HYDROXIDE from FATTY ACIDS
What is esterification an example of?
Condensation reaction
Formula for fatty acids (extra) ?
C=O(CH2)nCOOH
Formula for Glycerol?
C3H8O3
Why are oils liquid at room temp?
They are unsaturated compounds, and the double carbon=carbon bond causes the chain to bend, so they cannot be packed as close together.
What is a phospholipid?
A modified triglyceride, containing ONE glycerol molecule, TWO fatty acids, and ONE phosphorous atom
_________ phosphate ions are found in the cytoplasm.
What is the formula for this ion?
Inorganic, PO4,3-
Why are phosphate ions soluble in water?
Contain 3 extra electrons, so are charged.
What does hydrophobic mean?
Repels water
What does hydrophilic mean?
Attracts water
How would you identify whether a molecule is hydrophobic or hydrophilic?
Hydrophilic— polar/charged
Hydrophobic— non polar/not charged
Describe the structure of phospholipids according to ‘heads’ and ‘tails’
Phospholipids have hydrophilic heads- the phosphate atom- and hydrophilic tails- the fatty acids.
How area phospholipids arranged in the bilayer? Why is this useful?
They are arranged with the hydrophilic heads facing out of the membrane and the hydrophobic tails pointing towards the cytoplasm. Like this, the cell’s aqueous cytosol is kept separate from the aqueous environment outside.
What are sterols?
Steroid alcohols, a type of lipid found in cells.
What is the structure of sterols?
4 carbon ring ring structure and a hydroxyl group which is polar and so is hydrophilic, the rest of the molecule is hydrophobic.
What is cholesterol?
Cholesterol is a sterol. The body mainly produces cholesterol in the liver and intestines.
Structure of cholesterol?
Hydrophilic hydroxyl group
Hydrophobic rest of molecule
How is cholesterol involved in the cell membrane?
It is positioned between the phospholipids, as the hydrophilic tail (hydroxyl group) of cholesterol is attracted to the hydrophilic head of the phospholipids, and vice versa.
The hydroxyl group is at the PERIPHERY of the membrane.
Why is the positioning of cholesterol in the bilayer useful?
It adds stability to cell membranes as it regulates their fluidity, making sure it’s fluid at low temps and not too fluid at high temps.
What are manufactured from cholesterol in the body?
Vitamin D, steroid hormones and bile.
What roles do lipids play due to their non polar nature? (4)
- membrane formation and the creation of hydrophobic barriers
- hormone production
- waterproofing e.g. in birds feathers
- electrical insulation necessary for impulse transmission
Lipids (triglycerides) play an important role in long-term energy storage. Where are they stored and why?
Under the skin and around vital organs
—thermal insulation
—cushioning to protect vital organs
—buoyancy for aquatic organisms
What is the test to identify lipids?
Emulsion test
Outline the steps in the emulsion test for lipids
- Sample mixed with ethanol
- Solution mixed with water and shaken
- White layer forms, lipid is present.
Why is ethanol added to lipids (during the emulsion test) ? Explain why this happens.
To dissolve the lipids in the ethanol.
Because lipids are insoluble in water, as they are non polar organic compounds, so will be soluble in organic solvents
Why is water added in the emulsion test?
Ethanol (previously added) is soluble in water, while lipids are not, so they fall out and form a cloudy white, insoluble layer
What lipids are in plants?
UNSATURATED triglycerides, occur mainly as oils
What lipids are in our diet?
Animals (that we eat)(but generally not fish) contain saturated triglycerides.
What are better, unsaturated or saturated triglycerides for our diets?
Unsaturated.
Saturated fats were thought to cause coronary heart disease, it recent evidence contradicted this.
What are cis fats?
Where the hydrogens are on the same side as the double bond.
H H
| |
C=C
What are trans fats?
When the hydrogens are on opposite sides of the double bond.
H
|
C=C
|
HWhy is it good to have a low overall saturated fat intake?
Saturated fats are more closely packed together and so have a higher energy intake but this can lead to obesity
What is the problem with trans fats?
Add
Why are phospholipids known as surfactants?
They arrange themselves in a way that the hydrophilic heads face the water and the hydrophobic tails against.
where are lipids to provide electrical insulation?
in nerve cells
where are lipids to provide thermal insulation?
blubber, adipose tissue
phospholipids are amphipathic, what does this mean?
have both hydrophobic and hydrophilic properties
