Describe the effect on a protein if one or more amino acids are changed.
Cite a specific example.
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Introduction
We tend to think of protein as a mass noun: a homogeneous substance, something that your diet should contain in a certain proportion. But if you ever work in a molecular biology lab (say, for a summer internship), protein may start to look very different to you.
How so? Well, you may see firsthand that protein isn’t just a single substance. Instead, there are lots and lots of different proteins in an organism, or even in a single cell. They come in every size, shape, and type you can imagine, and each one has a unique and specific job. Some are structural parts, giving cells shape or helping them move. Others act as signals, drifting between cells like messages in a bottle. Still others are metabolic enzymes, putting together or snapping apart biomolecules needed by the cell. And, odds are, one of these unique molecular players will become yours for the duration of your research!
Proteins are among the most abundant organic molecules in living systems and are way more diverse in structure and function than other classes of macromolecules. A single cell can contain thousands of proteins, each with a unique function. Although their structures, like their functions, vary greatly, all proteins are made up of one or more chains of amino acids. In this article, we will look in more detail at the building blocks, structures, and roles of proteins.
Types and functions of proteins
Proteins can play a wide array of roles in a cell or organism. Here, we’ll touch on a few examples of common protein types that may be familiar to you, and that are important in the biology of many organisms (including us).
Enzymes
Enzymes act as catalysts in biochemical reactions, meaning that they speed the reactions up. Each enzyme recognizes one or more substrates, the molecules that serve as starting material for the reaction it catalyzes. Different enzymes participate in different types of reactions and may break down, link up, or rearrange their substrates.
One example of an enzyme found in your body is salivary amylase, which breaks amylose (a kind of starch) down into smaller sugars. The amylose doesn’t taste very sweet, but the smaller sugars do. This is why starchy foods often taste sweeter if you chew them for longer: you’re giving salivary amylase time to get to work.
Hormones
Hormones are long-distance chemical signals released by endocrine cells (like the cells of your pituitary gland). They control specific physiological processes, such as growth, development, metabolism, and reproduction. While some hormones are steroid-based (see the article on lipids), others are proteins. These protein-based hormones are commonly called peptide hormones.
For example, insulin is an important peptide hormone that helps regulate blood glucose levels. When blood glucose rises (for instance, after you eat a meal), specialized cells in the pancreas release insulin. The insulin binds to cells in the liver and other parts of the body, causing them to take up the glucose. This process helps return blood sugar to its normal, resting level.
Proteins come in many different shapes and sizes. Some are globular (roughly spherical) in shape, whereas others form long, thin fibers. For example, the hemoglobin protein that carries oxygen in the blood is a globular protein, while collagen, found in our skin, is a fibrous protein.
A protein’s shape is critical to its function, and, as we’ll see in the next article, many different types of chemical bonds may be important in maintaining this shape. Changes in temperature and pH, as well as the presence of certain chemicals, may disrupt a protein’s shape and cause it to lose functionality, a process known as denaturation.
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