2.2.4
Triglycerides & Phospholipids
Triglycerides
Triglycerides
Triglycerides are a type of lipid that are mainly used as energy storage molecules.


Formation of triglycerides
Formation of triglycerides
- Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid.
- Ester bonds form between the glycerol and the fatty acid chains.
- One water molecule is released per ester bond.
- So, three molecules of water are released per triglyceride formed.


Structure of fatty acids
Structure of fatty acids
- Fatty acids have long 'tails' made of a chain of hydrocarbons with 4-36 carbon atoms.
- The hydrocarbon tail is variable but most fatty acids contain 12-18 carbons.
- Glycerol links to the central carbon atom on fatty acids.


Types of fatty acids
Types of fatty acids
- The three fatty acids in the triglyceride may be similar or dissimilar.
- Fatty acids may be saturated or unsaturated.
- Some fatty acids have names that come from their origin.
- E.g. Palmitic acid is a saturated fatty acid that comes from the palm tree.
Functions of Triglycerides
Functions of Triglycerides
The structures of triglycerides are related to their functions as molecules responsible for storing energy.


Triglycerides in energy release
Triglycerides in energy release
- Chemical energy is stored in the fatty acid hydrocarbon tails.
- So, lots of energy is released when triglycerides are broken down.


Lipids contain lots of energy
Lipids contain lots of energy
- Carbohydrates contain half the amount of energy per gram as lipids do.


Triglycerides repel water
Triglycerides repel water
- Triglycerides are insoluble in water because the fatty acid tails are hydrophobic.
- This means that the cell's water potential is NOT affected by triglycerides.
- This is important because if triglycerides didn't repel water, the water would enter the cell through the process of osmosis. This would make the cells swell up.


Lipid droplets
Lipid droplets
- In cells, the insoluble triglycerides crowd together as droplets because the hydrophobic fatty acid tails face inwards.
Phospholipids
Phospholipids
Phospholipids are a type of lipid that forms a bilayer. They are the main component of cell membranes and are responsible for controlling what goes into and out of cells.


Structure of phospholipids
Structure of phospholipids
- Phospholipids and triglycerides are quite similar. They are both composed of fatty acid chains attached to glycerol.
- The main difference is that one of the three hydrophobic fatty acid tails is replaced by a hydrophilic phosphate group in phospholipids.
- This means that a phospholipid molecule has a hydrophobic and hydrophilic part.
- This kind of molecule is called an amphipathic molecule.


Hydrophobic tail
Hydrophobic tail
- Phospholipids have two fatty acid chains.
- The two fatty acid chains in phospholipids are hydrophobic and cannot interact with water.
- In membranes, the hydrophobic fatty acid tails face inside the cell.
- This means that water-soluble substances can't easily pass through the membrane.


Hydrophilic head
Hydrophilic head
- The modified phosphate group in phospholipids is hydrophilic and can interact with water.
- In membranes, the hydrophilic phosphate group faces the outside.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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