Biochemistry: Amino Acids and Proteins

Proteins are large molecules composed of long chains of amino acids. They play crucial roles in nearly every aspect of life, from building tissues to regulating chemical reactions.

The most abundant and functionally diverse group of macromolecules within living organisms.

A type of protein that acts as a catalyst, speeding up the rate of a chemical reaction without being consumed in the process.

Chemical messengers that are produced in one part of the body and travel to another part to exert a specific effect.

Substances that bind to and transport other molecules within the body.

Proteins that help stop bleeding by forming clots.

Proteins that bind to specific molecules, triggering a response within the cell.

A type of protein that serves as a component of the immune system, recognizing and neutralizing foreign invaders.

Amino acids like serine, threonine, and tyrosine have a hydroxyl group (OH) in their side chain. Serine and threonine contain an alcoholic OH group while tyrosine contains a phenolic OH group.

Asparagine and glutamine have amide groups in their side chains. These groups can participate in hydrogen bond formation within proteins, contributing to their structure and stability.

Cysteine amino acid contains a thiol (sulfhydryl) group (-SH) in its side chain. This group is important for the active site of many enzymes, which are biological catalysts.

When two cysteine amino acids are near each other, their thiol groups can oxidize and form a disulfide bond (-S-S-). This bond creates a strong link between different parts of the protein, contributing to its structure and stability.

Amino acids with charged polar side chains are classified into acidic and basic. Acidic amino acids have an extra carboxyl group making them negatively charged (COO-) at physiological pH. These are aspartate and glutamate. Basic amino acids have an extra amino group making them positively charged at physiological pH. These are lysine and arginine. Histidine is also basic but its charge is weaker.

All amino acids, except glycine, have at least one asymmetric carbon atom, making them optically active. This means they can exist in two non-superimposable mirror image forms, called enantiomers.

The L-configuration of amino acids is the only form found in proteins.

Proteins absorb ultraviolet light at a specific wavelength (280nm) due to the presence of the amino acid tryptophan.

A zwitterion is a molecule with both positive and negative charges, but with a net neutral charge.

The isoelectric point (pI) is the pH at which an amino acid has a net charge of zero. At this point, the amino acid is electrically neutral.

Transamination reactions are reversible processes where an amino group is transferred from an amino acid to a keto acid, forming a new amino acid and a new keto acid. Most amino acids participate in these reactions, except for lysine, threonine, proline, and hydroxyproline.

Deamination reactions remove an amino group from an amino acid. Oxidative deamination involves the removal of both a hydrogen and the amino group as ammonia (NH3). Non-oxidative deamination removes the amino group from glutamine and asparagine.

Oxidative deamination is a type of deamination that involves the removal of both a hydrogen and the amino group as ammonia. There are three main ways this reaction occurs, each catalyzed by a specific enzyme.

A tripeptide (a molecule made of three amino acids) found in cell membranes. It's essential for a range of cell functions, including detoxification and amino acid transport.

The functional group of glutathione is the thiol group (–SH) found on the cysteine amino acid. This group plays a key role in glutathione's functions by acting as a reducing agent, donating electrons.

Glutathione exists in two forms. The 'reduced form' (G-SH) is the active, functional form. The 'oxidized form' (G-S-S-G) is less active and needs to be converted back to G-SH to work.

The specific sequence of amino acids in a protein chain. This sequence determines the protein's overall structure and function.

The spatial arrangement of adjacent amino acids in a protein chain, often forming alpha helices or beta sheets. Hydrogen bonds help stabilize this structure.

The three-dimensional structure of a protein, determined by interactions between different parts of the polypeptide chain. This structure is essential for the protein's function.

The arrangement of multiple polypeptide chains, each with its own tertiary structure, to form a functional protein. Not all proteins have a quaternary structure.

A type of protein that is soluble in acidic conditions and found in many plants, like wheat. They have a key role in plant structure and function.

Proteins that are rich in proline, but lack lysine. They are soluble in alcohol. Examples include gliadin in wheat and zein in maize.

A complex group of proteins that are highly basic in nature due to their high content of arginine and lysine residues. They are especially important in packaging and regulating DNA.

Proteins that form structural components of connective tissues. They are known for their strength and flexibility. Examples include collagen, keratin, and elastin.

A major type of scleroprotein that forms the basis of connective tissues like skin, tendons, and bones. It has a unique triple helix structure.

The basic building block of collagen, consisting of three polypeptide chains arranged in a triple helix. Think of it as the strand of a rope.

Proteins that contain a non-protein component called a prosthetic group. Examples include nucleoproteins (with nucleic acids), lipoproteins (with lipids), and glycoproteins (with carbohydrates).

Proteins that are formed by breaking down other proteins. Examples include proteoses and peptones, which are formed by partial hydrolysis of simple and conjugated proteins.

Elastin is a fibrous protein found in connective tissues. It's known for its high elasticity and ability to stretch and recoil to its original shape.

Elastin is primarily composed of glycine, proline, and a small amount of hydroxyproline. It lacks hydroxylysine, a key component of collagen.

Elastin forms cross-links called desmosines, which are unique for its structure. These cross-links involve four lysine residues, forming a strong, branched network.

Collagen and elastin are both fibrous proteins found in connective tissues. Collagen provides strength and structure, while elastin allows for stretching and recoil.

Phosphoproteins are a type of conjugated protein with a phosphate group attached to the hydroxyl (OH) group of serine or threonine amino acids.

Lipoproteins are proteins associated with lipid molecules, found in blood and cell membranes. They are crucial for transporting fats throughout the body.

Glycoproteins consist mainly of proteins with small amounts of carbohydrates, while proteoglycans are mostly carbohydrates with a smaller protein component.

Nucleoproteins are conjugated proteins associated with nucleic acids like DNA or RNA. They are essential components of chromosomes and ribosomes.