4.12
What are Proteins?
Proteins are polymers of amino acids linked together by peptide bonds. Proteins and polypeptides are interchangeably used to refer to long chains of a…
A protein is a chain of amino acids, compounds that contain amine and carboxyl groups, along with different side chains denoted as R, attached to a core carbon.
Amino acids are linked through covalent peptide bonds, and the repeating series of atoms along the core is called the polypeptide backbone.
The sequence begins at the N-terminus, with a free amino group, NH3+, and ends with the C terminus, a free carboxyl group, COO-.
Each protein is unique, depending on the number of amino acids and their side chains.
There are 20 different side chains, which fall into one of four groups. Acidic amino acids, like aspartic and glutamic acids, have side chains with a carboxyl group. Because of this, they act like acids at physiological pH.
Basic amino acids have an amino group in their side chain and act like bases.
Several amino acids are polar but uncharged. They tend to be hydrophilic and make up the outer portion of a folded protein, where they are free to interact with the aqueous environment.
Lastly, a large group of amino acids contains nonpolar side chains. They can be simple, as in glycine, or complex, like proline and tryptophan.
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Q1: What are the basic building blocks that make up proteins?
Proteins are polymers composed of amino acids linked together by peptide bonds. These amino acids contain a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a distinctive side chain. The sequence and arrangement of these amino acids determine each protein's unique structure and function.
Q2: How do proteins differ from other biological macromolecules?
Proteins are distinct macromolecules composed of amino acids, while other compounds essential to human function include carbohydrates, lipids, and nucleic acids. Each macromolecule type has different elemental composition and structural organization. Proteins specifically contain nitrogen in their amino groups, making them unique among major biological polymers.
Q3: What are the two main categories of protein structure?
Proteins are classified into fibrous proteins and globular proteins based on their three-dimensional shape. Fibrous proteins are elongated and typically provide structural support, while globular proteins are compact and spherical, often serving dynamic roles like catalysis and transport. Both types are essential for different physiological functions.
Q4: Why is protein structure important for biological function?
A protein's three-dimensional structure determines its ability to perform specific functions in cells and tissues. The folding of amino acid chains creates active sites, binding regions, and structural features necessary for the role of proteins in the human body. Disruptions to this structure can impair or eliminate protein function.
Q5: What factors can cause proteins to lose their functional structure?
Proteins can undergo protein denaturation when exposed to extreme conditions such as high temperature, extreme pH, or certain chemical solvents. Denaturation disrupts the bonds maintaining protein structure, causing the molecule to unfold and lose its three-dimensional shape. This structural change typically results in loss of biological activity.
Q6: How do amino acid side chains influence protein properties?
Amino acid side chains vary in chemical composition, ranging from nonpolar hydrophobic groups to polar and charged groups. These differences determine how amino acids interact with each other and their environment, influencing protein solubility, charge, and overall three-dimensional folding. Side chain properties are fundamental to protein diversity and function.
Q7: What role do peptide bonds play in protein formation?
Peptide bonds are covalent linkages that connect amino acids together in a linear chain, forming the protein backbone. These bonds form between the carboxyl group of one amino acid and the amino group of the next through a dehydration reaction. The sequence of amino acids linked by peptide bonds determines the primary structure of every protein.