Protein Structure - Biology

Proteins can be inhibited in numerous ways by different types of inhibitors. Competitive inhibitors will compete with substrate for the active site to block the protein from performing its function. If there is enough substrate and very little competitive inhibitor, proteins will perform their functions almost as if there were no competitive inhibitors.

In contrast, allosteric inhibitors bind to regions of the protein away from the active site, but change the shape of the active site such that substrate cannot bind. Since there is no direct competition, increasing substrate concentration cannot overcome allosteric inhibition. Non-competitive inhibition is a type of allosteric inhibition. Uncompetitive inhibition occurs when the inhibitor will only bind to the enzyme-substrate complex, locking the substrate in place and preventing other substrates from binding.

The active site on a protein is the area where a substrate can attach. This relationship is most often described using a metaphor of a lock and a key because each protein has an active site specific to one substrate much like a lock can only be opened by one key.

The key here is to know that if something binds the enzyme at a location other than the active site, the type of modification is defined as allosteric. The other words more generally describe things that can bind to receptors, enzymes, etc., but the best and most specific answer is "allosteric."

It is important to know that when exposed to high temperatures, all proteins become denatured, and lose their native shape/conformation.

This has nothing to do with the activation energy of the reaction (eliminating that answer). While some substrates may be degraded at high temperatures, the word "all" renders this answer incorrect, nor does this describe what happens to the enzyme. Covalent modificatinos can change enzymatic function, but do not have anything to do with higher temperature.

The correct answer is that the enzyme itself is denatured, thus changing the shape and the way the active site is shaped, resulting in an inability to efficiently bind its substrate. The structure of the enzyme is dictated by intermolecular forces, which are susceptible to interference from temperature changes (unlike covalent bonds).

Competitive inhibition is the only type of inhibition in which the inhibitor molecule directly binds the active site of the enzyme, thereby 'competing' with the actual substrate for location on the enzyme. The other choices involve binding elsewhere on the enzyme (non-competitive) or binding the enzyme-substrate complex but not an isolated enzyme (mixed), but none of them describe binding the active site except for competitive.

A peptide bond is formed between the carboxyl group and amino group of adjoining amino acids. The energy in proteins is released when peptide bonds are broken. Peptide bonds also determine the primary structure of proteins.

An ionic bond is formed when one element loses an electron and another element gains an electron. Ionic bonds most frequently form between metals and non-metals, and are not commonly seen in proteins.

A glycosidic bond is formed between a carbohydrate and another molecule. Glycosidic bonds can help form carbohydrate polymers, like glycogen, or link sugars to other groups, like in the DNA backbone.

An ester bond can be found in fatty acids, and contains a carbonyl group next to an ether linkage.

Collagen is the most abundant protein in the human body. It adds great strength and flexibility to skin, tendons, and ligaments. These qualities are characteristic of structural proteins.

Globular proteins are generally rounded, protecting a nonpolar center from the aqueous environment around the protein. Most cytoplasmic proteins and enzymes are globular proteins. In contrast, fibrous proteins are generally elongated and designed for structural support; collagen is a fibrous protein, in addition to a structural protein. Integral proteins span the plasma membrane, often creating channels.

Proteins are classified into several categories based on where they perform their function. Peripheral membrane proteins span only one side of the lipid bilayer and thus have mobility. Unlike integral membrane proteins, which span the entire lipid bilayer, peripheral membrane proteins have the liberty of traveling from layer to layer as well as flip flop between the two bilayers.

Isomers are molecules that have the same molecular formula, but have different chemical structures. Isomerases are enzymes that are able to rearrange the structure of a molecule while keeping its chemical formula the same.

A protein consists of amino acids. Essential amino acids cannot be synthesized by the body, and must be included in the diet. A protein containing all of the essential amino acids is called a complete protein. An incomplete protein lacks one or more of the essential amino acids.

Neurotransmitters are chemicals that relay messages from one cell to the next. Enzymes are protein catalysts that speed up biological reactions. Minerals are inorganic compounds and are not present in the body in large amounts, with the exception of hydroxyapatite crystal found in bones. Electrolytes are ionic salts in the blood, tissue fluids, and cells, such as sodium, potassium, and chlorine.

Protein quaternary structure involves interactions between different subunits. Each subunit will be created by folding an independent polypeptide chain into a 3-dimensional tertiary structure. The joining of these independent subunits results in quaternary structure. In order for a protein to have quaterary structure, it must have multiple subunits; this means it must consists of at least two polypeptide chains.

Receptor proteins in a signal transduction pathways can be found both within the plasma membrane or cytosol; as a result, protein Y could potentially function as a receptor. The electron transport chain occurs in the mitochondria, and relies on the movement of electrons; the proteins that “move” these electrons, and subsequently pump protons (creating a gradient), are located in the inner membrane. An antiporter functions in a membrane as well due to its importance in creating and maintaining a concentration gradient. In a similar fashion, nuclear trafficking refers to the regulation or movement of molecules in and out of the nuclear membrane. Last, DNA replication occurs in the nucleus and does not involve a membrane of any sort; therefore, the membrane dwelling protein Y cannot function in this process.

Ribosomes are responsible for translating mRNA into protein. tRNA molecules transport amino acids to the ribosome, where they are joined by peptide bonds to form a chain. This chain of amino acids is known as the protein primary structure.

Secondary structure, tertiary structure, and quaternary structure form in the cytoplasm or endoplasmic reticulum after the ribosome has released the polypeptide.

Proteins have four levels of structure. Secondary structure involves the formation of alpha-helices and beta-sheets via hydrogen bonding between the amino acid backbone in the protein chain.

Primary protein structure simply refers to the linear sequence of amino acid residues in the polypeptide chain. After initial folding of the backbone in secondary structure, functional groups of the amino acids interact to generate tertiary structure. Tertiary structure contains hydrogen bonding, hydrophobic interactions, and disulfide bridges. Some proteins then develop quaternary structure, when multiple polypeptide chains are joined as subunits to build a large protein complex.

Formation of a protein involves four distinct levels of structure. The tertiary structure is the third level of protein formation, and occurs when the side chains of the individual amino acids interact. These side chains can attract one another to form hydrogen bonds or disulfide bonds, or they can repel each other and contribute ot hydrophobic interactions. The result is a three-dimensional shape. This is the final level of structure to create a function protein subunit.

The primary structure of the protein is derived from the chain of amino acids synthesized during translation; this amino acid sequence is the primary structure. Secondary structure is generated from the interactions between amino and carboxyl groups in the polypeptide backbone. These groups can form hydrogen bonds to generate alpha-helices and beat-pleated sheets. Tertiary structure, as described above, results in a functional protein subunit. For some protiens, tertiary structure is the final step in folding. For other proetins, multiple subunits can be bound together to generate a quaternary structure.

There are four essential levels of protein structure. The fourth and final level is called quaternary structure. This level of structure is only present in proteins with multiple subunits. Since hemoglobin has four subunits, we know that the question is talking about the quaternary structure of the protein.

Primary structure is simply the amino acid sequence generated during translation. Soon after translation, the carboxyl and amino groups present in the polypeptide backbone begin to form hydrogen bonds. The result is the protein's secondary structure, frequently made of alpha-helices and beta-pleated sheets. Tertiary structure is the three-dimensional shape of the final polypeptide, and is derived from hydrophobic interactions, hydrogen bonds, and disulfide bonds related to the amino acid side chains (R groups). When multiple polypeptides (subunits) join together, they generate a quaternary structure.

The protein does possess primary, secondary, and tertiary structure but since the protein has three distinct subunits, the entire molecule is exhibiting a higher order quaternary structure.

The primary structure of a protein is the sequence of amino acids, which determines the unique shape of the protein. The secondary structure consists of the coiled and folded patterns that contribute to the protein’s overall shape (alpha helix or beta pleated sheet respectively). The tertiary structure is the overall shape of the polypeptide that results from interactions and hydrogen bonding between the side chains, or R groups, of the various amino acids present. It is during this stage of protein formation that disulfide bridges and hydrophobic interactions are first seen. Last,the quaternary structure is the overall protein structure resulting from the aggregation of at least two polypeptide units.

Water is known as the “universal solvent.” Life could not exist on earth without water. Our bodies are mostly water; therefore, the environment of our cells is aqueous as well. Hydrophobic (“water fearing") amino acids would condense to "hide" from an aqueous environment. Polar and/or hydrophilic (“water loving”) amino acids would be found on the exterior of globular proteins near the aqueous environment. Hydrophobicity and hydrophilicity are major forces that drive the formation of the tertiary or three-dimensional shape of a protein post translation.

Primary structure refers to a linear sequence of amino acids in the polypeptide chain, such as the example in the question stem. Secondary structure has two main types, the alpha helix and the beta strand (or beta sheets). The alpha helix or beta sheets are folded into a compact globular structure to form the tertiary structure. Quaternary structure is a three-dimensional structure of a multi-subunit protein and how the subunits fit together. There is no such thing as auxiliary protein structure.