Proteins & Enzymes Overview

Study Notes

Proteins are the workhorses of biological systems.
They play a crucial role in building and maintaining living cells.
Proteins are polymers of amino acids.
Amino acids are the basic building blocks.
Peptides are short polymers of amino acids (up to 40).
Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.
Primary structure is the sequence of amino acids in a polypeptide chain.
Secondary structure includes alpha-helices and beta-pleated sheets, formed by hydrogen bonds.
Tertiary structure is the three-dimensional arrangement of the polypeptide chain.
Quaternary structure describes the arrangement of multiple polypeptide chains.
Proteins perform various roles, including enzymes, hormones, storage, transport, structural, protective, contractile, and toxic proteins.
Enzymes are biological catalysts, speeding up reactions.
They decrease the activation energy needed for reactions.
Enzymes are highly specific to the type of reaction they catalyze and the substrates they act on.
The active site is the region on the enzyme where the substrate binds and reaction occurs.

Around 500 amino acids are known.
Only 20 are used to form proteins in eukaryotes (22 in total)
Selenocysteine and pyrrolysine are incorporated into proteins via special mechanisms.
11 amino acids can be produced in the body, the other 9 are essential amino acids.
Amino acids have an amino group, a carboxyl group, a hydrogen atom, and a variable side chain.
Amino acids can be classified based on their side chain properties: polar, nonpolar, acidic, or basic.

Proteins are polymers of 2-amino-carboxylic acids.
The α-carbon atom in amino acids is a chiral center.
All amino acids in biological systems are L-enantiomers.
Amino acids have an amino end (N-terminus) and a carboxyl end (C-terminus).
The primary structure is determined by the sequence of amino acids linked by peptide bonds.
The sequence dictates the protein’s properties and function.
Alterations in the amino acid sequence can lead to a loss of protein function.

Determining the amino acid sequence is done via Edman degradation (often on smaller proteins).
Automated machines exist for this; often starting by determining N-terminal amino acid.
Mass spectrometry can also be used to determine protein sequence.

Classifying proteins based on structure, roles, and other properties.
Globular (spherical) versus fibrous (linear) proteins based on shape.
Solubility is a key factor, depending on amino acid makeup and secondary/tertiary structure.

Denaturation is the loss of a protein's native, functional three-dimensional structure.
This happens due to various factors like temperature (heat), solvents, pH, and chemicals.
These factors disrupt the bonds and interactions holding the protein in its native conformation.
Denatured proteins often become insoluble and lose their biological activity.

Proteins influence structure, taste, texture, aroma, and viscosity in foods.
The ability to bind water is crucial for various food processes.
Proteins affect dough formation, and various other food properties.
Several aspects influence functional protein properties like shape/structure, hydrophobicity, type of amino acid, flexibility, etc.

Proteins interaction with components such as water, ions and other macromolecules.
The capacity to bind water
These interactions affect various food properties, including wettability, swelling, water sorption, water retention, viscosity, emulsion formation, foaming, and gelation.

Enzymes are biological catalysts.
They speed up reactions by lowering the activation energy.
Enzymes are highly specific for their substrates and the reactions they catalyze.
Different classifications of enzymes exist, based on the reaction type.