Proteins (2)
Chapter 20: Proteins
20.1 Characteristics of Proteins
Definition:
A protein is a naturally-occurring, unbranched polymer made up of amino acids.
Consists of one or more polypeptide chains (chain of amino acids).
Abundance:
Proteins are the most abundant molecules in cells after water, accounting for about 15% of a cell’s overall mass.
Elemental Composition:
Composed of Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), and Sulfur (S).
Average nitrogen content is approximately 15.4% by mass.
Types of Proteins by Composition:
Simple Proteins: Only amino acids; examples include albumins and globulins.
Conjugated Proteins: Contain additional groups (prosthetic groups) like carbohydrates or lipids.
Protein Based on Shape Fibrous:
20.1 Characteristics of Proteins
Definition:
A protein is a naturally-occurring, unbranched polymer made up of amino acids.
Consists of one or more polypeptide chains (chain of amino acids).
Abundance:
Proteins are the most abundant molecules in cells after water, accounting for about 15% of a cell’s overall mass.
Elemental Composition:
Composed of Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), and Sulfur (S).
Average nitrogen content is approximately 15.4% by mass.
Types of Proteins by Composition:
Simple Proteins: Only amino acids; examples include albumins and globulins.
Conjugated Proteins: Contain additional groups (prosthetic groups) like carbohydrates or lipids.
Classification by Size:
Monomeric Proteins: Single polypeptide chain.
Multimeric Proteins: Multiple polypeptide chains.
20.2 Amino Acids: The Building Blocks for Proteins
Structure of Amino Acids:
Contain an amino (-NH2) and carboxyl (-COOH) group attached to the alpha (α) carbon.
There are 20 standard amino acids based on the variety of side chains (R groups).
Classification of Amino Acids:
Non-Polar (Hydrophobic): These amino acids are insoluble in water.
Polar (Hydrophilic): Can be broken down into neutral, acidic, and basic types.
Essential Amino Acids:
Cannot be synthesized by the body and must be obtained from the diet.
Examples include Arginine, Methionine, Histidine, and others.
20.3 Chirality and Amino Acids
Chirality:
19 out of 20 standard amino acids (except glycine) are chiral, meaning they exist in two enantiomeric forms (L and D).
Natural proteins are composed primarily of the L-isomers.
20.5 Acid–Base Properties of Amino Acids
Zwitterions:
Forms of amino acids that have both positive and negative charges, existing in physiological conditions.
Isoelectric Point (pI):
pH at which the Zwitterion concentration is maximized and the net charge is zero.
20.7 Peptides
Peptide Bond Formation:
The reaction between the amino group of one amino acid and carboxyl group of another leads to peptide bonds connecting the amino acids.
Peptide Nomenclature:
The C-terminal residue retains its full name, while others end with -yl (e.g., Ala-leu-gly).
20.10 Primary Structure of Proteins
Definition:
Sequence of amino acids linked in a protein chain via peptide bonds. Each sequence is unique and determines protein function.
Sequencing Methods:
Methods include acid hydrolysis, alkaline hydrolysis, and enzymatic hydrolysis using proteases.
20.11 Secondary Structure of Proteins
Characteristics:
Arrangements of the peptide backbone influenced by hydrogen bonds; notable structures include the alpha-helix and beta-pleated sheets.
20.12 Tertiary Structure of Proteins
Overall Shape:
The 3D conformation of proteins results from interactions between R groups. Interactions include disulfide bonding, electrostatic interactions, and hydrophobic interactions.
20.13 Quaternary Structure of Proteins
Definition:
Refers to the arrangement of multiple polypeptide chains into a single protein complex, often consisting of two or more subunits (oligomeric proteins).
20.15 Protein Denaturation
Definition:
Process that disrupts protein structure, affecting its function. Can occur due to heat, pH changes, and other chemicals.
Effects of Cooking:
Denatures proteins, making them easier to digest and killing harmful microorganisms.
20.18 Glycoproteins and Lipoproteins
Glycoproteins:
Proteins with carbohydrate moieties; important for blood group markers and immune responses.
Lipoproteins:
Conjugated proteins that facilitate lipid transport in the bloodstream, critical in managing cholesterol levels in the body.
Classification by Size:
Monomeric Proteins: Single polypeptide chain.
Multimeric Proteins: Multiple polypeptide chains.
20.2 Amino Acids: The Building Blocks for Proteins
Structure of Amino Acids:
Contain an amino (-NH2) and carboxyl (-COOH) group attached to the alpha (α) carbon.
There are 20 standard amino acids based on the variety of side chains (R groups).
Classification of Amino Acids:
Non-Polar (Hydrophobic): These amino acids are insoluble in water.
Polar (Hydrophilic): Can be broken down into neutral, acidic, and basic types.
Essential Amino Acids:
Cannot be synthesized by the body and must be obtained from the diet.
Examples include Arginine, Methionine, Histidine, and others.
20.3 Chirality and Amino Acids
Chirality:
19 out of 20 standard amino acids (except glycine) are chiral, meaning they exist in two enantiomeric forms (L and D).
Natural proteins are composed primarily of the L-isomers.
20.5 Acid–Base Properties of Amino Acids
Zwitterions:
Forms of amino acids that have both positive and negative charges, existing in physiological conditions.
Isoelectric Point (pI):
pH at which the Zwitterion concentration is maximized and the net charge is zero.
20.7 Peptides
Peptide Bond Formation:
The reaction between the amino group of one amino acid and carboxyl group of another leads to peptide bonds connecting the amino acids.
Peptide Nomenclature:
The C-terminal residue retains its full name, while others end with -yl (e.g., Ala-leu-gly).
20.10 Primary Structure of Proteins
Definition:
Sequence of amino acids linked in a protein chain via peptide bonds. Each sequence is unique and determines protein function.
Sequencing Methods:
Methods include acid hydrolysis, alkaline hydrolysis, and enzymatic hydrolysis using proteases.
20.11 Secondary Structure of Proteins
Characteristics:
Arrangements of the peptide backbone influenced by hydrogen bonds; notable structures include the alpha-helix and beta-pleated sheets.
20.12 Tertiary Structure of Proteins
Overall Shape:
The 3D conformation of proteins results from interactions between R groups. Interactions include disulfide bonding, electrostatic interactions, and hydrophobic interactions.
20.13 Quaternary Structure of Proteins
Definition:
Refers to the arrangement of multiple polypeptide chains into a single protein complex, often consisting of two or more subunits (oligomeric proteins).
20.15 Protein Denaturation
Definition:
Process that disrupts protein structure, affecting its function. Can occur due to heat, pH changes, and other chemicals.
Effects of Cooking:
Denatures proteins, making them easier to digest and killing harmful microorganisms.
20.18 Glycoproteins and Lipoproteins
Glycoproteins:
Proteins with carbohydrate moieties; important for blood group markers and immune responses.
Lipoproteins:
Conjugated proteins that facilitate lipid transport in the bloodstream, critical in managing cholesterol levels in the body.