Biochem Quiz 2 Study: Lipids

Lipids are mainly nonpolar and hydrophobic. What does this mean?

A typical lipid consists of a long chain of carbon atoms flanked by hydrogen atoms. Sometimes the end of the chain contains atoms other than carbon and hydrogen. The oil on a loon's feathers is hydrophobic, or water avoiding. The oil's molecular structure gives it that property—the long tail of the molecule is not electrically charged; it is neither positive nor negative. In other words, this portion of the lipid is nonpolar. These electrically neutral tails are not attracted to polar molecules like water, which have a slightly negative side and a slightly positive side. But, as you might suspect, the polar head of the lipid, which you can see in the diagram, is attracted to polar water molecules. The properties of polarity and nonpolarity play an important role in how lipids function in the body, especially in their formation of cell membranes.

How do waxes repel water?

How do certain desert plants retain water and keep it from evaporating? They cover their leaves in a water-repelling substance that keeps water from getting to the surface where it might evaporate. One feature common to these plants and others is a waterproof coating called wax. Wax is a type of lipid made of extremely long chains of fatty acids linked to an alcohol molecule. The fatty acids in waxes are saturated, meaning they form long chains that pack well together. Fatty acid chains are nonpolar, so they do not attract water, which makes waxes hydrophobic or water-repellent.

How do phospholipid bilayers behave in a watery environment?

In a watery environment, phospholipids arrange themselves so that the fatty acid chains (hydrophobic tails) point inward toward each other, while the phosphate groups (hydrophilic heads) point out, interfacing with the water. This interaction creates two layers of phospholipids-a bilayer. The phospholipid bilayer makes up the outer membrane of all the cells in your body. Because of its unique structure and chemical properties, the phospholipid bilayer can contain a separate internal aqueous environment, relative to the outside.

What are lipids?

Lipids are organic molecules that do not mix with water to form solutions. After a loon dives underwater to hunt fish, it pops up to the surface, and beads of water run down its neck and back. Why doesn't the loon sink under the weight of the water? Why does water roll right off its body? Loons produce an organic molecule called oil in a special gland near the base of their tail. They use their beak to extract oil from this gland and work it through their feathers, giving them an effective waterproof coating. The oil that waterproofs a loon's feathers is one example of a lipid, a type of organic molecule that generally repels water. Lipids are hydrocarbons, a class of organic molecules that are made almost entirely of hydrogen and carbon.

What are saturated fats?

Many of those fats are found in animals and the animal food you eat. A carbon atom has space to form four chemical bonds with other atoms. A saturated fat is made up of fatty acid chains with single bonds between each carbon atom. In the chain, two bond spaces are taken up by other carbon atoms. The other two bond spaces are filled with hydrogen atoms. Because all remaining spaces are filled with hydrogen atoms, the fat is said to be saturated. That arrangement makes long, straight fatty acid chains, which can easily pack together. Scientists suggest that the ability to pack together may cause saturated fats to build up in the arteries, possibly leading to heart disease.

What are phospholipids?

Phospholipids form cellular membranes. All organisms are composed of structures called cells. A cell maintains a constant internal environment, relative to the external environment. In other words, the cell is key to maintaining homeostasis. But how do cells maintain a specific internal environment? The outer membrane of a cell comprises a dual layer of lipids called phospholipids. The structure of this layer helps the cell maintain a constant internal environment—one of the key requirements for homeostasis.

What role do (s/us) fats play in health?

Saturated fats have single bonds between carbon atoms. Saturated and unsaturated fats have been getting a lot of attention in the news for their roles in health and nutrition. You may have heard that unsaturated fats are healthier for you than saturated fats are. The structure of each of those categories of fat explains why and tells you some important things about lipid structure.

What are steroids?

Steroids are lipids that include carbon rings. Testosterone is one type of steroid. Steroids are a class of lipids that contain ring structures made of carbon. One steroid you may have heard of is the molecule cholesterol. While it receives attention because of its association with conditions such as heart disease, cholesterol is an important component of many cellular structures. Your body also uses cholesterol to make testosterone and other steroids like estrogen.

Fats and oils are energy-storage lipids. What are some examples of this?

The blackpoll warbler is a tiny bird that undergoes an incredible transformation every fall. It eats enough food to double its body weight in just a few weeks, with all that additional weight stored as fat. It relies on those fat reserves as fuel for its annual migration, a trek that takes it from New England to the Caribbean—a distance of nearly 4,000 km, which the bird travels in one continuous 90-hour flight. Why would the blackpoll warbler store all that energy as fat, instead of a carbohydrate like glycogen? Per unit volume, fat is lighter in weight than carbohydrates. And, a given volume of fat contains twice as much chemical energy (the energy of chemical bonds) as the same volume of carbohydrates—another bonus for a tiny bird trying to maximize its energy-storage potential. All this fat is converted to glucose as part of the bird's metabolism, but fat is excellent for storing chemical energy.

What does a phospholipid bilayer contain?

The cell membrane is a phospholipid bilayer. A phospholipid is similar to a fat: It contains fatty acid chains and glycerol. However, a phospholipid contains only two fatty acid chains, while a fat contains three. It also includes a chemical structure called a phosphate group. A phosphate group gives one end of a phospholipid a negative electrical charge—that is, this end of the chain is hydrophilic because it attracts water molecules. The fatty acid chain is nonpolar and repels water.

Fats and oils store energy in carbon-hydrogen bonds. Fats and oils (like butter, lard, and olive oil) are types of lipids called triglycerides. What are they?

Triglycerides comprise two types of chemical building blocks: a small glycerol molecule and three small fatty acid molecules. A fatty acid is a long chain of carbon and hydrogen atoms that has a cluster of carbon, oxygen, and hydrogen at one end. Fats are triglycerides that are solid at room temperature, while oils are triglycerides that are liquid at room temperature. How do fats and oils store more chemical energy than equivalent volumes of carbohydrates? For a given volume, fats and oils contain more energy-rich carbon-hydrogen bonds than carbohydrates. The breakdown of fats and oils produces more energy in the form of adenosine triphosphate (ATP) than the breakdown of glucose. However, the first thing that happens is that the body converts these fats to glucose.

What are unsaturated fats?

Unsaturated fats have double bonds between carbon atoms. Unsaturated fats, many of which are found in plant products, have a double bond between some carbon atoms in the fatty acid chain. That double bond takes up two available bond spaces, leaving space for only one hydrogen atom on a double-bonded carbon. Because hydrogen atoms do not fill all the available bond spaces, those fats are unsaturated. Double bonds produce bends or kinks in the fatty acid chain. Those kinks keep unsaturated fats from stacking together as smoothly as saturated fats. Scientists suggest that the lack of ability to pack together may cause unsaturated fats to build up less slowly in blood vessels than saturated fats.

How are steroids chemical messengers?

Your body produces a steroid hormone called cortisol in response to stress. One of its effects is to inhibit your immune system, making you more likely to get sick when you're stressed out. Like other hormones, cortisol is a chemical messenger. It carries information from one part of the body to another. Testosterone and estrogen, which direct your body's development into adulthood, are also steroid hormones. They are produced in the reproductive organs and travel throughout the body.