2.6.T - Lesson: Biological Molecules: Part II Biology

Since oligosaccharides and polysaccharides contain monosaccharides that have been strung together in chains, they digest slowly and are considered complex carbohydrates. While still being broken down into glucose, they provide longer-lasting energy for your body since the bonds of the long chains of sugar units take more time to break apart. Foods that contain starches, such as sweet potatoes, oatmeal, whole grains, and brown rice, are examples of complex carbs. Fibrous foods such as spinach, mushrooms, onions, broccoli, and peppers are also excellent examples of complex carbs. In fact, the fiber found in such foods does not break down into glucose as a nutrient to the body, but rather, it can contribute to slowing down the rate of absorption of sugar from other foods to maintain control of blood sugar levels.

Complex Carbohydrates

Carbohydrates are molecules that contain carbon, hydrogen and oxygen. They are known as saccharides, another term for sugar. There are four types of carbohydrates. The name for each of these subgroups has a prefix for how many saccharides (sugars) are present: Monosaccharides: mono- indicates 1 Disaccharides: di- indicates 2 Oligosaccharides: oligo- indicates 3-9 Polysaccharides: poly- indicates "many"

Composition of Carbohydrates

Lipids are unique from the other biological molecules since they do not have true monomers. Instead, they are considered hydrocarbons, since they are made of hydrogen and carbon. The breaking of those bonds allows for the release of energy. Lipids can be classified into four categories: triglycerides (basic fat), phospholipids, steroids, and waxes.

Composition of Lipids

Glucose

Form of sugar that is used by the body for energy

The fourth and final group of biological molecules that we will discuss is that of lipids, or fats. Fats can often have a bad reputation in fields of health science if discussing high cholesterol, inflammation, heart disease, diabetes, etc. However, there is a certain amount of fat that our bodies need to function properly, and we are unable to make those lipids on our own! They contribute to storing energy, protecting our vital organs, serving as the structures for the membranes of our cells, and starting reactions needed for metabolism, growth, immunity, and reproduction.

Lipids

Carbohydrates

Most of the energy that you obtain comes from the carbohydrates that you consume. Many of the foods that you eat have carbohydrates in various amounts that can be found in the forms of sugar, starch and fiber: fruits, vegetables, beans, legumes, grains, milk and the byproducts of milk. Other sources of carbohydrates are not as good for you, but contain carbohydrates none-the-less (and all-the-more!): juices, sodas, cookies, cupcakes, candy... anything with added sugar can make it on this list!

Each point on the fatty acid tail represents a carbon molecule. Without getting into the depths of organic chemistry, it is implied that two hydrogens are attached to each carbon to fulfill the Octet Rule.

Notice the difference between the first fatty acid and the bottom two fatty acids. The first fatty acid is a straight chain with all single bonds between the carbons of the tail. This fat is considered saturated. This chemical structure determines the properties of the fat itself: it is solid at room temperature. A common example of a saturated fat in the American diet is margarine. The second and third fatty acids, however, have the presence of one or more double bonds between carbons that create a bend in the carbon chain. These fats are unsaturated. The double bonds change the quality of the fats: they are liquids at room temperature. One common example is olive oil.

Triglycerides are basic fats. They are named and characterized by their structure, having a glycerol "head" and three (tri-) fatty acid tails. During the process of digestion, your body breaks down fats into fatty acids that are then absorbed into your blood.

Triglycerides

Molecules Essential to Life

Two other biological molecules that are present in living organisms are carbohydrates and lipids.

Waxes are commonly used as forms of protection. Use the tabs below to discover some interesting ways that wax is useful!

Waxes

Every membrane of every cell in your body (and in all living organisms) is made from phospholipids! Phospholipids have a structure that is similar, but not identical, to that of triglycerides. Phospholipids have a negatively charged phosphate group that is attached to the glycerol head. Attached to the phosphate group are two fatty acid tails that do not have charges. When phospholipids group together, they arrange themselves into two parallel layers. This is called the phospholipid bilayer, which makes up your cell membranes. The negative charges of the phosphate heads give them hydrophilic (attraction to water) tendencies. Because of this, the heads stick to one another and face the aqueous (watery) areas that are inside and outside of the cell. The tail sections of the molecules, however, are hydrophobic (repulsion to water) and make up the interior of the membrane.

Phospholipids

Monosaccharides and disaccharides are both considered simple carbohydrates because they can be quickly broken down and digested. Most foods or drinks that identify as simple carbs contain refined sugar, such as table sugar/brown sugar, milk, honey, syrup, molasses, fruit juice, ice cream, soda etc. Once the carbohydrates are ingested, they are broken down into simple sugar molecules, specifically glucose. Glucose then quickly rushes into your bloodstream, usually causing you to feel a rush of energy. This sudden spike in your blood sugar causes your body to react, signaling your pancreas to produce insulin at a higher rate to remove the excess sugar from your bloodstream to your cells. This can lead to a cycle of sugar cravings as your blood sugar peaks and then suddenly drops, resulting in a desire for more energy.

Simple Carbohydrates

Carbohydrates

Simple and complex sugars made up of carbon, hydrogen and oxygen

Monosaccharides

Simple sugars, the most common of which is glucose

Your body produces natural steroids every day. The most common steroid, cholesterol, is involved in the function of nerve cells, in the production of male and female hormones, and in the composition of cell membranes to provide flexibility. It also plays an important role in our body's digestion as its levels determine the ability of the body to metabolize energy. There are several versions of steroids, but they all have one thing in common: a four-ring structure. Remember that the rings here are also considered hydrocarbons; each point is understood to represent a carbon molecule and has one or more hydrogen molecules to which it is bonded.

Steroids

Disaccharides

Sugars formed when two simple sugars (monosaccharides) bind together

Simple Carbohydrates

Sugars that are made up of just one or two sugar molecules (monosaccharides and disaccharides); digested quickly into the bloodstream

Complex Carbohydrates

Sugars that consist of three or more simple sugars; digest slowly and are rich in fiber and nutrients

Hydrophilic

Tending to be attracted to water molecules

Hydrophobic

Tending to be repelled by water molecules

Phospholipid Bilayer

The arrangement of phospholipids into two parallel layers that make up cellular membranes

Triglyceride

A common lipid that is composed of three (tri-) fatty acids bound to a glyceride molecule

Lipids

A group of biological compounds that includes cholesterol, fats, phospholipids, and steroids

Polysaccharides

A long chain of simple sugars, such as starch