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Fats and Lipids 40,107 views

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Fats and lipids are large organic molecules which are used for energy storage and which make up the which make up the lipid bi-layer of the plasma membrane of cells. Lipids have hydrophobic tails which are composed of chains of hydrocarbons and hydrophilic heads which are composed of a carboxyl group. A lipid monomer is either glycerol and fatty acids or a steroid core. Types of lipids include triglycerides (fats) and phospholipids (e.g. soap).

Fats and lipids are one of the four basic kinds of organic molecules. Unlike the other three however, rather than sharing a common Chemistry and structure, fats and lipids are often grouped together simply because that they don't interact well with the other kinds of molecules they're what are known as hydrophobic, so what are their basic functions? Well it's kind of diverse based on their diversity of fats and lipid that you find.

Many of them are used to store energy those are the very familiar fats that some of us have a little bit too much in our bodies. Well they also are used to help form membranes like the fats or lipids and then they are the steroid hormones that you're familiar with like testosterone and estrogen that uses chemical signals between cells.

Now what are the monomers, they include glycerol and fatty acids for some of the fats and lipids the others use something called the steroid core which I'll discuss in just a moment. But let's take a closer look first at what is glycerol and fatty acids and how do they together to form lipids? Well this three carbon chain here if it was by itself you'd have a hydrogen attached to the group of three oxygens over there that's a molecule called glycerol. These long dangly genes here are fatty acids long chains of carbons with hydrogens attached to them. Because they're three of them here this is called a triglyceride and this is what you guys mean when you say what's a fat? This is a fat alright all these carbon and hydrogen bonds here have a lot of energy and that's why fat is so useful for storing tons of energy.

Now over here we have a special kind of molecule called a phospholipid where if you rip off one of those fatty acids you can you can stick on this phosphate head. Now phosphate has a very strong negative charge and because it has a strong negative charge, it can hydrogen bond with water which means it will be hydro wait a second that is hydrophobic actually instead of hydrophobic they should be labeled hydrophilic my graphic artist made the same mistake that a lot of students do they don't keep track of what does it mean to be hydrophobic or hydrophilic so I'll explain it to you. Hydrophilic molecules are parts or molecules that can through charges interact strongly with water. Hydrophobic and the two fatty acid tails here those are hydrophobic because they don't hydrogen bond, they dont interact well with water and so they will be repel by water and this is why phospholipids are so useful in making the cell membrane because the phosphate heads can interact with water on the exterior and interior of the cell while the fatty acid tails stay together and form the hydrophobic region of the membrane that blocks so many chemicals from being able to move in and out of the cell unless the cell chooses to allow it through.

Steroid molecules and if you ever see a name of a molecule and it has the syllable ster in it like cholesterol estrogen, testosterone, aldosterone you'll you got a good chance of guessing that is a steroid because this group of four interlocking rings of carbon is called the steroid core. Now what makes one steroid different from the other, the side groups that are attached to this, but there you go that's the fats and lipids where there is the triglycerides or phospholipids or the steroids.