Lipids - Triglycerides, Phospholipids & Cholesterol

What is a triglyceride?

a type of lipid that are mainly used as energy storage molecules

How are triglycerides formed?

Formed by the condensation of one molecule of glycerol and three molecules of fatty acid.

What bonds are formed between glycerol and fatty acids in a triglyceride?

• 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.

What is the common structure of a triglyceride?

• a glycerol backbone

• fatty acid chains

Functions of Triglycerides - How are triglycerides able to release energy?

• Chemical energy is stored in the fatty acid hydrocarbon tails.

• So, lots of energy is released when triglycerides are broken down.

Functions of Triglycerides - How are triglycerides able to repel water?

• Triglycerides are insoluble in water because the fatty acid tails are hydrophobic (water-hating)

• 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 and burst

Between lipids and carbohydrates, which one contains more energy than the other?

Lipids contain lots of energy.

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

What is this structure known as? (it relates to triglycerides repelling water)

Structure is called Lipid micelle

In cells, how do triglycerides crowd together?

In cells, the insoluble triglycerides crowd together as droplets because the hydrophobic fatty acid tails face inwards.

What are Phospholipids?

They 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.

What is the common structure of a Phospholipid?

• Quite similar to triglycerides as they are both composed of fatty acid chains attached to glycerol

• Main difference: one of the three hydrophobic fatty acid tails is replaced by a hydrophilic phosphate group in phospholipids.

How do phospholipids have a hydrophobic and hydrophillic part?

it contains both a hydrophilic (water-loving) polar head - the phosphate group - and a hydrophobic (water-fearing) nonpolar tail - fatty acids - within the same molecule

What is the hydrophobic tail in a phospholipid and what’s its purpose?

• Phospholipids have two fatty acid chains.

• The two fatty acid chains in phospholipids are the hydrophobic tails 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.

What is the hydrophilic head in a phospholipid and what’s its purpose?

• The modified phosphate group in phospholipids is the hydrophilic head and can interact with water.

• In membranes, the hydrophilic phosphate group faces the outside.

What is the fluidity of the membrane controlled by?

The proportion of saturated and unsaturated fatty acids

What is a bilayer?

It is 2 layers of phospholipids back to back. This forms when phospholipids are placed in water

How is a phospholipid amphipathic?

Because the whole molecule is both hydrophobic and hydrophilic. It has a hydrophilic head - phosphate group- and a hydrophobic tail - 2 fatty acids

What does being amphipathic make phospholipids ideal for?

It makes them ideal for making cell membranes

How does the membrane get stability?

Because the tails repel water and attract each other

What does the layer of hydrophobic tails form?

It forms a barrier to any charged or polar molecules

What is Cholesterol ?

It’s a type of lipid known as a sterol and is used by animal cells to increase stability of the cell membrane. Cholesterol is also used to make vitamin D, steroid hormones, and bile.

Is cholesterol a polar or non-polar molecule?

Cholesterol is a polar molecule. Similar to Phospholipids, cholesterol has both hydrophobic and hydrophilic molecules. The OH group is hydrophilic whereas the rest of the molecule is hydrophobic

What is the role of Cholesterol in the cell surface membrane ?

Cholesterol binds to phospholipid fatty acid tails, causing the phospholipids to pack more closely together. This reduces the fluidity of the cell membrane

What is the structure of the phosholipid bilayer?

The hydrophilic heads are facing out (towards the water) and the hydrophobic tails are facing in (away from the water)