My AP Biology Thoughts  

Unit 1 Episode #43

Welcome to My AP Biology Thoughts podcast, my name is Helena and I am your host for episode #43 called Unit 1 Lipids Structure, Function & Example. Today we will be discussing what lipids are and look at some examples. Then we will take a look at their significance. 

Segment 1: Introduction to Lipids, Structure & Examples 

• First of all, what are Lipids? Well, Lipids are molecules that contain hydrocarbons and yield high energy. They are formed by the chemical linking of small constituent molecules. They consist of a glycerol molecule (which is a small organic molecule with three hydroxyl groups) that is bonded to long hydrocarbon chains and depending on the lipid, they can be bonded to other molecules as well. Lipids are hydrophobic meaning they are nonpolar and insoluble in water. Some are amphipathic. This means that part of the lipid is hydrophobic and another part in hydrophilic. These lipids form molecular aggregates with their hydrophilic ends touching the water and the hydrophobic parts on the inside. This is what oil looks like when mixed with water. So now that we understand what Lipids are, let's take a look at some examples.

Segment 2: Example of Lipids

• There are many varieties of lipids, and each of these varieties have different structures and functions. The main groups of lipids are Triglycerides, Phospholipids, Steroids, and Waxes. Triglycerides are your fats and oils. They consist of a glycerol backbone and three fatty acid tails. A fatty acid is a long hydrocarbon chain attached to a carboxyl group. The fatty acid tail is bound to the glycerol backbone via ester linkages, which are linkages containing an oxygen atom next to a carbonyl. Triglycerides can be unsaturated or saturated. In order to be saturated the bonds between neighboring carbons in the hydrocarbon chain have to be single bonds. In order to be unsaturated there has to be at least one double bond between neighboring carbons in the hydrocarbon chain. Saturated triglycerides are called fats and they are solid at room temperature because of their tightly packed. They are mainly found in animals. Unsaturated triglycerides are called oils and they are liquid at room temperature because of their cis structure that causes them to bend so they cant be tightly backed like saturated fats. They are mainly found in fish and plants. Phospholipids consist of a glycerol backbone, two fatty acid tails, and the modified phosphate group occupies the third carbon in the glycerol backbone. These are amphipathic molecules. The fatty acid tail chains are hydrophobic, and the phosphate group head is hydrophilic. Phospholipids are found in biological membranes because of their amphipathic property. Their hydrophobic tails stand as a barrier between the inside of the cell and its surroundings while the hydrophilic ends touch the outside and inside of the cell and allow for only certain components to travel between the membrane. This structure is called a bilayer, and it creates a low-energy, stable arrangement. Steroids are another lipid molecule. Their structure consists of four fused carbon rings. The hydrocarbon tail is connected to the steroid at one end, and the hydroxyl group is connected to the other end. Many steroids have an -OH functional group (called sterols), and some have short tails. Cholesterol is the most common steroid, is mainly created in the liver, and is the precursor to many steroid hormones. For example, sex hormones, testosterone and estradiol. In the bloodstream there is good and bad cholesterol. HDL is good and lowers your risk for some health conditions, while LDL is bad and does the opposite. Finally, waxes are the last main group of lipids I am going to discuss. They contain long fatty acid chains connected to alcohols by ester linkages. Many produced by plants also have plain hydrocarbons mixed in as well. Waxes cover feathers of some aquatic birds and the lead surfaces of some plants. This is why water beads up on the leaves of many plants and why water runs off birds wings. 

Segment 3: Digging Deeper Lipids Structure Function & Examples

• As you can see lipids have many different roles in organisms. Phospholipids are essential to membrane structure . Wax forms water-repellent layers on leaves so they aren't soaked and they protect birds from getting wet and freezing. Cholesterol provides building blocks for hormones, is the starting hormone for other important molecules in the body such as Vitamin D and bile acids, and is important to altering the fluidity and dynamics of cell membranes. Triglycerides are essential for vitamin absorption as a lot of vitamins are fat soluble. They are also an efficient way to store energy over long periods of time (which prevents you from starving), and they provide insulation for the body. Fat has more than double the amount of energy than carbohydrates and protein, meaning they are a great source of energy. Lipids are essential to the brain structure and also signaling. Without lipids organisms would not be able to function or survive.