In fact, each gene in cellular DNA contains the code for a unique protein structure. Not only are these proteins assembled with different amino acid sequences, but they also are held together by different bonds and folded into a variety of three-dimensional structures. The folded shape, or conformation, depends directly on the linear amino acid sequence of the protein.
The building blocks of proteins are amino acids, which are small organic molecules that consist of an alpha central carbon atom linked to an amino group, a carboxyl group, a hydrogen atom, and a variable component called a side chain see below.
Within a protein, multiple amino acids are linked together by peptide bonds , thereby forming a long chain. Peptide bonds are formed by a biochemical reaction that extracts a water molecule as it joins the amino group of one amino acid to the carboxyl group of a neighboring amino acid.
The linear sequence of amino acids within a protein is considered the primary structure of the protein. 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. The amino acids in a protein are determined by the nucleotide sequence of the gene coding for them. The amino acid sequence often determines how the protein folds into a particular 3D configuration. This, in turn, determines the activity and function of the protein.
In biological systems, proteins have varying functions. Some of them are structural materials e. Other functions include transport e. In biology and biochemistry, a protein is a biomolecule or a macromolecule characterized by being made up of chain s of amino acids joined together by peptide bonds.
A peptide is a compound consisting of amino acids connected by a peptide bond, particularly between the carboxyl group of one amino acid the amine group of another amino acid. A polypeptide is a peptide comprised of several amino acid residues as many as 4, forming an unbranched linear chain. A protein is a complex of polypeptides or a polypeptide with a 3D structure and carries out a particular function.
Proteins are composed of polymers of amino acid residues. The amino acids are joined together by peptide bonds. Each protein is a linear polymer built from different amino acids. The type and the sequence of amino acids in a protein are specified by the DNA in the cell that produces them.
The genetic code typically specifies for 20 standard amino acids. However, some organisms, such as archaea, have a genetic code that specifies for more. This sequence of amino acids is essential since it determines the overall structure and function of a protein.
Some proteins can form a complex together with another protein. Others form a complex with other biomolecules other than the peptide. Some of these non-peptide groups in a protein are referred to as cofactors or prosthetic groups. There are four distinct types of a protein structure: 1 primary structure, 2 secondary structure, 3 tertiary structure, and 4 quaternary structure.
The secondary structure of a protein refers to the regularly repeating local structures that are stabilized by hydrogen bonds. The tertiary structure sometimes called fold pertains to the spatial relationship of the secondary structures from one to another.
It is often stabilized by nonlocal interactions, e. This structure of the protein is what determines the fundamental function of the protein. The quaternary structure refers to the protein complex, i. The tertiary and quaternary structures are often called conformations.
The protein may transition from one structure to another and the transition between tertiary and quaternary by a conformational change. Conformational changes may be induced for example when a substrate binds to a protein particularly, an enzyme at its active site. A protein may be classified based on its form and main functions: it can be a globular protein like most enzymes , a fibrous protein with a structural role, such as collagen, keratin, etc.
Protein synthesis is the creation of proteins. In biological systems, it is carried out inside the cell. In prokaryotes , it occurs in the cytoplasm. The transcript leaves the nucleus and reaches the ribosomes for translation into a protein molecule with a specific sequence of amino acids.
Protein synthesis also called protein biosynthesis when performed by a living organism is a process of creating protein molecules. In biological systems, it involves amino acid synthesis , transcription , and translation. Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains.
There are 20 different types of amino acids that can be combined to make a protein. Amino acids are coded by combinations of three DNA building blocks nucleotides , determined by the sequence of genes. Proteins can be described according to their large range of functions in the body, listed in alphabetical order:. Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body. Immunoglobulin G IgG.
Enzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA. Phenylalanine hydroxylase. Messenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.
Growth hormone.
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