For example, some people can be allergic to the protein found in fish, seafood, dairy, peanuts or soy. In people with celiac disease, an autoimmune reaction can occur from exposure to the protein called gluten, found in wheat, rye and barley.
Aglaee Jacob is a registered dietitian. She has experience working with people who have diabetes, cardiovascular disease, hypertension and obesity issues. Jacob obtained a bachelor of science and a master of science, both in nutrition, from Laval University in Quebec City, Canada. Healthy Eating Nutrition Protein. By Aglaee Jacob. Related Articles. Amino Acids Proteins are made of amino acids. Proteins are built from a set of only twenty amino acids, each of which has a unique side chain.
The side chains of amino acids have different chemistries. The largest group of amino acids have nonpolar side chains. Several other amino acids have side chains with positive or negative charges, while others have polar but uncharged side chains.
The chemistry of amino acid side chains is critical to protein structure because these side chains can bond with one another to hold a length of protein in a certain shape or conformation. Charged amino acid side chains can form ionic bonds, and polar amino acids are capable of forming hydrogen bonds.
Hydrophobic side chains interact with each other via weak van der Waals interactions. The vast majority of bonds formed by these side chains are noncovalent.
In fact, cysteines are the only amino acids capable of forming covalent bonds, which they do with their particular side chains. Because of side chain interactions, the sequence and location of amino acids in a particular protein guides where the bends and folds occur in that protein Figure 1.
Figure 1: The relationship between amino acid side chains and protein conformation The defining feature of an amino acid is its side chain at top, blue circle; below, all colored circles.
When connected together by a series of peptide bonds, amino acids form a polypeptide, another word for protein. The polypeptide will then fold into a specific conformation depending on the interactions dashed lines between its amino acid side chains.
Figure Detail. Figure 2: The structure of the protein bacteriorhodopsin Bacteriorhodopsin is a membrane protein in bacteria that acts as a proton pump. Its conformation is essential to its function. The overall structure of the protein includes both alpha helices green and beta sheets red. The primary structure of a protein — its amino acid sequence — drives the folding and intramolecular bonding of the linear amino acid chain, which ultimately determines the protein's unique three-dimensional shape.
Hydrogen bonding between amino groups and carboxyl groups in neighboring regions of the protein chain sometimes causes certain patterns of folding to occur. Known as alpha helices and beta sheets , these stable folding patterns make up the secondary structure of a protein. Most proteins contain multiple helices and sheets, in addition to other less common patterns Figure 2.
The ensemble of formations and folds in a single linear chain of amino acids — sometimes called a polypeptide — constitutes the tertiary structure of a protein. Finally, the quaternary structure of a protein refers to those macromolecules with multiple polypeptide chains or subunits.
The final shape adopted by a newly synthesized protein is typically the most energetically favorable one. As proteins fold, they test a variety of conformations before reaching their final form, which is unique and compact. Folded proteins are stabilized by thousands of noncovalent bonds between amino acids. In addition, chemical forces between a protein and its immediate environment contribute to protein shape and stability.
For example, the proteins that are dissolved in the cell cytoplasm have hydrophilic water-loving chemical groups on their surfaces, whereas their hydrophobic water-averse elements tend to be tucked inside. In contrast, the proteins that are inserted into the cell membranes display some hydrophobic chemical groups on their surface, specifically in those regions where the protein surface is exposed to membrane lipids.
It is important to note, however, that fully folded proteins are not frozen into shape. Rather, the atoms within these proteins remain capable of making small movements. Even though proteins are considered macromolecules, they are too small to visualize, even with a microscope. So, scientists must use indirect methods to figure out what they look like and how they are folded.
The most common method used to study protein structures is X-ray crystallography. With this method, solid crystals of purified protein are placed in an X-ray beam, and the pattern of deflected X rays is used to predict the positions of the thousands of atoms within the protein crystal. In theory, once their constituent amino acids are strung together, proteins attain their final shapes without any energy input.
The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. What are proteins and what do they do? From Genetics Home Reference. Proteins can be described according to their large range of functions in the body, listed in alphabetical order: Examples of protein functions Function Description Example Antibody Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body.
Immunoglobulin G IgG Enzyme Enzymes carry out almost all of the thousands of chemical reactions that take place in cells. Phenylalanine hydroxylase Messenger Messenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.
Growth hormone Structural component These proteins provide structure and support for cells. Topics in the How Genes Work chapter What are proteins and what do they do?
How do genes direct the production of proteins? Can genes be turned on and off in cells?
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