Lipids Flashcards
Main facts about lipids (compostition, polarity, solubility)
- Composed mainly of H and C
- Nonpolar
- Insoluble in water - hydrophobic
4 types of lipids
- Steroids, Phospholipids, triglycerides, waxes
Triglycerides function
- Long term energy storage (carbs are short term)
Roles of lipids
- Energy source
- Stored in adipose tissue (body fat) which helps with heat insulation and protection for organs
- Make up cell membranes
- Plant scents are derivatives of lipids and attract insects for pollination
- Waxy cuticle contains lipids which reduce water loss for plants
What is the structure of a triglyceride?
H O H H
│ ║ │ │
H - C - O - C - C - C - H
│ │ │
│ H H
│
│ O H H
│ ║ │ │
H - C - O - C - C - C - H
│ │ │
│ H H
│
│ O H H
│ ║ │ │
H - C - O - C - C - C - H
│ │ │
H H H
Describe how a tiglyceride forms?
3 Condensation reactions between a glycerol and 3 fatty acids
These bonds are called ester bonds
3 molecules of water are formed as a biproduct
Why might lipids be a more suitable long-term energy store than carbohydrates?
- Carbs are soluble and can easily be transported, and they are more easily and quickly digested so they are good as a short term energy source. Also carbs can be used in both anaerobic and aerobic respiration, lipids can only be used in aerobic.
- Lipids are insoluble, so they do not affect osmosis and cause problems within cells when stored. They also have 2x more energy per gram than carbs, so they are a lighter store than carbs. Fats can also not be mobilised and broken down quickly.
Define saturated, unsaturated and polyunsatured
Saturated - no double bonds in fatty acid tail, no more H atoms can be added
Unsaturated - At least one C=C double bond in hydrocarbon chain
Polyunsaturated - More than one C=C bond in Fatty acid tail
What is formed when a fatty acid is unsaturated
Kinks in the chain
Short, medium and long fatty acid chain legths
short - 2-6 carbons
medium - 8-12 carbons
long - 14-24 carbons
Why does melting point of fatty acids increase as chain length increases?
- More energy required to break attractions between fatty acid tails on different trigylerides
- The longer the chain, the more attractions which need to be broken, so more energy required
Why does melting point of fatty acid chains decrease as number of double bonds increases?
- Kinks in the fatty acid tails means they can’t be packed as tightly
- So, attractions between unsaturated fatty acids are less strong and frequent and less energy is required to break them.
What are the two types of unsaturated fatty acids?
Cis-unsaturated and Trans-unsaturated
Cis vs Tran unsaturated fatty acids
Cis - hydrogens at the double bond are on the same side of the chain (CIS-ters)
Trans - hydrogens at double bond are on different sides of the chain
How do cis and trans unsaturated fatty acids vary in shape?
Cis - causes larger kinks in fatty acid chain
Trans - causes a straighter fatty acid chain
