A protein is a 'polymeric macromolecule formed by peptide bonding of monomeric amino acids'. They are the most abundant macromulecules, there can be hundreds of different types in a single cell. They aid in providing structure, transporting oxygen, directing biological reactions, controlling against infection and can even be a source of energy. Proteins have the following functions: transport and storage (ferritin), catalysis (enzymes), support (collagen), immunity (antiboies), nerve impulses (ion channels/receptors), hormones (insulin) and gene expression (DNA folding/transcription factors).
Amino acids are the building blocks of proteins. All body proteins are constructed from a basic set of only 20 amino acids. Proteins and peptides are formed from a string of amino acids linked together. Amino acids contain an amine and acid group while the central carbon is the alpha carbon which has bonds to an amino grop, a carboxylic acid, a hydrogen and a variable side chain (R group) which defines the compound (simplest R group being Hydrogen).
Amino acid classification is based on polarity and charge on R groups, structure of side chains, catabolic fate of the amino acid, Body's ability to synthesize amino acid. Amino acids with a non-polar R group have residues which are buried in hydrophobic interior of the protein biomeoluecle and are out of contact wih water, alanine is the most abundant amino acid (with no R group) in most proteins. Proline from this group is different from other amino acids in that its side chain includes both the alpha carbon and the alpha amino group. Some amino acids can bond towater as they have an uncharged polar R group and thus are hydrophilic. Five amino acids have a charged polar R group which are either acidic or basic and can assume negative or positive charge at physiologic pH values. Basic amino acids have a positive charge on their R group and ionise beweteen pH 6-7 and are hydrophilic, lysine and arginine are fully charged at physiologic pH. Acidic amino acids have a negative charge at physiologic pH and are hydrophillic, often having carboxylic acids on their side chains, they carry a negative charge at pH 7.
Amino acids based on structure of side chain can be classified in the following groups; aromatic, imino acid, heterocyclic, dicarboxylic and dibasic amino acids. Amino acids based on catabolic fate can be classified in the following groups; glucogenic, ketogenic and gluco-ketogenic. Amino acids can also be classified as essential (cannot be synthesized by the body) or non-essential (can be synthesized by the body).
Some amino acids and amino acid derivatives have roles as neurotransmitters. Glycine (inhibitory) and glutamic acid (excitatory) both have roles as neurotransmitters. Dopamine, noradrenaline and adrenaline are all neurotransmitters derived from tyrosine, Serotonin is derived from tryptophan and GABA is derived from glutamate.
peptides and proteins are polymers of amino acids. Polypeptides range in size from small to very large consist of two or three to thousands of linked amino acid residues. Two amino acid molecules can be covalently joined through a substituted amide linkage (a peptide bond)- this linkage is formed by removal of the elements of water from the carboxyl group of one amino acid and the amino group of another. Further additions at the carboxyl end produces a peptide chain. Protein diversity can be further generated by post-syntehsis modifications.
conjugated proteins are ones containing permanently associated chemical components in addition to amino acids. The non-amino acid part of a conjugated protein is usually called its prosthetic group. Protein structure is also important as it confers structure.
Keratins are the major proteins of hair and fingernails and compose a major fraction of animal skin. Alpha keratins are intermediate filament proteins and the secondary structure is composed predominantly of alpha-helices. The secondary structure of a beta-pleated sheet consists of polypeptide chains arranged side by side with hydrogen bonds in-between and R groups above and below the sheet. It is very strong and slightly extensible and is typical of fibrous proteins, such as silk. The secondary structure of a triple helix is 3 polypeptide chains woven together and is typical of collagen, connective tissue, skin, tendons and cartilage. The tertiary structure is an overall 3D shape and is determined by cross-links and held together by four different bonds and interactions; disulphide bonds, ionic bonds, hydrogen bonds and hydrophobic and hydrophillic interactions. The quarternary structure is the combination of two or more protein units, and the joining of polypeptide chains in such proteins is requried for their function, it is stabilised by same interacts found in tertiary structures.
Globular proteins have compact, spherical shapes. They have hydrophobic parts toward the centre and hydrophobic towards the edges so are water soluble they carry out synthesis, transport and cell metabolism. Fibrous proteins consist of long fibre-like shaps and are insoluble in water. Such as alpha keratins in hair, wool and skin.
protein denaturation involves the disruption of bonds in the secondary, tertiary and quarternary protein structures.
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rediscovering biology: Proteins and Proteomics
Protein Structure and Function
Kristina Gremski: Protein Structure and Function
Study.com: Protein Structure and Function
Questions
Amino acids are the building blocks of proteins. All body proteins are constructed from a basic set of only 20 amino acids. Proteins and peptides are formed from a string of amino acids linked together. Amino acids contain an amine and acid group while the central carbon is the alpha carbon which has bonds to an amino grop, a carboxylic acid, a hydrogen and a variable side chain (R group) which defines the compound (simplest R group being Hydrogen).
Amino acid classification is based on polarity and charge on R groups, structure of side chains, catabolic fate of the amino acid, Body's ability to synthesize amino acid. Amino acids with a non-polar R group have residues which are buried in hydrophobic interior of the protein biomeoluecle and are out of contact wih water, alanine is the most abundant amino acid (with no R group) in most proteins. Proline from this group is different from other amino acids in that its side chain includes both the alpha carbon and the alpha amino group. Some amino acids can bond towater as they have an uncharged polar R group and thus are hydrophilic. Five amino acids have a charged polar R group which are either acidic or basic and can assume negative or positive charge at physiologic pH values. Basic amino acids have a positive charge on their R group and ionise beweteen pH 6-7 and are hydrophilic, lysine and arginine are fully charged at physiologic pH. Acidic amino acids have a negative charge at physiologic pH and are hydrophillic, often having carboxylic acids on their side chains, they carry a negative charge at pH 7.
Amino acids based on structure of side chain can be classified in the following groups; aromatic, imino acid, heterocyclic, dicarboxylic and dibasic amino acids. Amino acids based on catabolic fate can be classified in the following groups; glucogenic, ketogenic and gluco-ketogenic. Amino acids can also be classified as essential (cannot be synthesized by the body) or non-essential (can be synthesized by the body).
Some amino acids and amino acid derivatives have roles as neurotransmitters. Glycine (inhibitory) and glutamic acid (excitatory) both have roles as neurotransmitters. Dopamine, noradrenaline and adrenaline are all neurotransmitters derived from tyrosine, Serotonin is derived from tryptophan and GABA is derived from glutamate.
peptides and proteins are polymers of amino acids. Polypeptides range in size from small to very large consist of two or three to thousands of linked amino acid residues. Two amino acid molecules can be covalently joined through a substituted amide linkage (a peptide bond)- this linkage is formed by removal of the elements of water from the carboxyl group of one amino acid and the amino group of another. Further additions at the carboxyl end produces a peptide chain. Protein diversity can be further generated by post-syntehsis modifications.
conjugated proteins are ones containing permanently associated chemical components in addition to amino acids. The non-amino acid part of a conjugated protein is usually called its prosthetic group. Protein structure is also important as it confers structure.
Keratins are the major proteins of hair and fingernails and compose a major fraction of animal skin. Alpha keratins are intermediate filament proteins and the secondary structure is composed predominantly of alpha-helices. The secondary structure of a beta-pleated sheet consists of polypeptide chains arranged side by side with hydrogen bonds in-between and R groups above and below the sheet. It is very strong and slightly extensible and is typical of fibrous proteins, such as silk. The secondary structure of a triple helix is 3 polypeptide chains woven together and is typical of collagen, connective tissue, skin, tendons and cartilage. The tertiary structure is an overall 3D shape and is determined by cross-links and held together by four different bonds and interactions; disulphide bonds, ionic bonds, hydrogen bonds and hydrophobic and hydrophillic interactions. The quarternary structure is the combination of two or more protein units, and the joining of polypeptide chains in such proteins is requried for their function, it is stabilised by same interacts found in tertiary structures.
Globular proteins have compact, spherical shapes. They have hydrophobic parts toward the centre and hydrophobic towards the edges so are water soluble they carry out synthesis, transport and cell metabolism. Fibrous proteins consist of long fibre-like shaps and are insoluble in water. Such as alpha keratins in hair, wool and skin.
protein denaturation involves the disruption of bonds in the secondary, tertiary and quarternary protein structures.
Learn More
rediscovering biology: Proteins and Proteomics
Protein Structure and Function
Kristina Gremski: Protein Structure and Function
Study.com: Protein Structure and Function
Questions
- list any 4 protein functions with an example for each.
- write the structure for Glycine and label the parts.
- what features of an amino acid mean it can be acidic or basic?
- what is the importance of the R group?
- why is the peptide bond considered rigid?
- list and describe the 4 levels of protein structure