Introduction to Amino Acids and Proteins

Amino Acids Introduction

• Proteins are biopolymers assembled in ribosomes, controlled by nucleic acids, using L-α-amino acids.
• Proteins have diverse roles in cell structure and function, including: holding the body together, protecting it (e.g., muscle, skin, hair), acting as enzymes, hormones, and antibodies to regulate body chemistry, forming nerve and blood components (e.g., hemoglobin, myoglobin), and transporting oxygen.
• Proteins are vital for life.

Amino Acids and Proteins- Types and Functions

• Enzymes increase reaction rates by a billion-fold.
• Carriers include hemoglobin and transferrin.
• Receptors bind hormones and cytokines.
• Transport proteins include membrane channels.
• Structural proteins include collagen and elastin.
• Protective proteins are immunoglobulins.
• Contractile proteins are in muscle and cytoskeleton.
• Regulatory proteins (hormones) govern metabolic pathways.

Amino Acids, Peptides and Proteins Introduction

• Amino acids (α-amino acids) link via amide (peptide) bonds to create macromolecules (polypeptides).
• Amino acid side chains have diversified functionalities.
• Amino acids polymerize, conceptually, by losing a water molecule to form an amide bond (peptide bond).
• The building blocks of proteins are investigated to understand their overall structure and function.

Amino Acids Definition

• Protein and peptide properties are determined by constituent α-amino acids.
• Understanding individual amino acids helps understand how they influence peptide and protein characteristics.
• Amino acids are carboxylic acids with an amino functional group.

Amino Acids Classification

• Amino acids are classified (α, β, γ, δ...) based on the amino group's position relative to the carboxylic acid group on the parent chain.
• The discussion often focuses on α-amino acids.

α-Amino Acids Definition

• Over 700 different amino acids exist, but 20 are classified as standard, vital for nearly all natural proteins.
• These 20 amino acids are used in protein biosynthesis according to the genetic code.
• The amino group structure governs the nature of these acids.

α-Amino Acids Structure: Things to Note

• All α-amino acids (except proline) share a common structure with a primary amino group and a carboxyl group attached to the same carbon atom.
• Proline has a secondary amino group forming a cyclic ring structure with the amino nitrogen.
• Glycine (aminoacetic acid) is the simplest α-amino acid.
• Most α-amino acids are chiral, exhibiting differing properties in their side chains.

α-Amino Acid Structures (Standard Amino Acids)

• The side chain (R group) gives different structures and categories.
  • R is hydrogen or an alkyl group
  • R has an alcohol function.
  • R has sulfur
  • The amino group is secondary or part of a ring.
  • One hydrogen is replaced with aromatic/heteroaromatic ring.
  • One amino group and two carbonyl groups
  • One carbonyl group and two amino groups.

Structures of α-Amino Acids

• Amino acids are given three-letter abbreviations.
• Isoelectric points, structures, and abbreviations are detailed for amino acids Glycine, Alanine. Valine, Leucine, and Isoleucine.

Structures of α-Amino Acids (cont'd)

• Tables of amino acids specifying abbreviations, structures, and isoelectric points are given for various types:
  • R groups with alcohol functions (Serine, Threonine, etc.).
  • R groups containing sulfur (Cysteine, Methionine).
  • R groups secondary or ring based (Proline).
  • R groups with aromatic or indole rings (Phenylalanine, Tyrosine , Tryptophan).
• Detailed tables include information of amino acids with one carbonyl group and two carbonyl groups

Hydrophilic (polar) R Group

• Uncharged side chains; they have zero net charge at neutral pH (e.g., Serine, Threonine, etc).
• Explains the role of these amino acids in various reactions.

Polar, Uncharged R Groups

• These amino acids (e.g., Serine, Threonine, Cysteine, Asparagine, and Glutamine) have neutral side chains without charge and play important roles in various biochemical processes.
• Their side chains act as sites for molecular attachment and reactions, like phosphorylation, with special emphasis on serine and threonine.
• Details of the important roles played by tyrosine.

Aromatic R Groups

• Explores the roles of aromatic groups (e.g., Phenylalanine, Tyrosine, Tryptophan).
• Explains the hydroxyl group in various biochemical processes.

Acidic and Basic Amino Acids

• Acidic amino acids contain a carboxyl group (−COOH) as part of their R group, donating H+ and carrying negative charges (e.g., Aspartate, Glutamate).
• Basic amino acids contain an amino group (−NH2) in their R group, accepting H+ and carrying positive charges (e.g., Lysine, Arginine, Histidine) and describes them as positively charged.
• Histidine is unique due to its ionization at pH 6.0.

Amino Acids as Acids and Bases

• Amino acids can ionize because of the –NH2 and –COOH groups, resulting in a zwitterion: a molecule with both positive and negative charges.
• Neutral overall due to equal positive and negative charges.
• Illustrated via ionization states at different pH levels.

Structures of α-Amino Acids – Essential Amino Acids

• Humans can synthesize some amino acids but they need to consume others (essential amino acids) from their diet.
• The 10 essential amino acids: Arginine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.
• The essential amino acids are vital for human growth and health.

Structures of α-Amino Acids – Sources of Amino Acids

• Proteins are the natural source of amino acids.
• Proteases hydrolyze peptide bonds to break proteins to individual amino acids in the body.
• Complete proteins offer sufficient amounts of all essential amino acids (e.g., meat, fish).

Structures of α-Amino Acids – Complete vs Incomplete Proteins

• Animal proteins are generally complete.
• Plant proteins, such as those found in rice, maize, wheat, and legumes, are often incomplete, lacking or insufficient in one or more essential amino acids.
• The importance of combining different plant protein sources to achieve complete protein intake.

Properties of α-Amino Acids

• Amino acids' properties are influenced by the proximity of a basic amino group and an acidic carboxyl group within the same molecule.
• Side chains provide further properties and reactions.

Stereochemistry of Amino Acids

• All amino acids found in proteins are in the L-configuration.
• Differentiating L- and D-amino acids is vital.

This quiz covers the fundamentals of amino acids and their critical roles in protein synthesis and function. Learn about the various types of proteins, including enzymes, structural proteins, and regulatory proteins, and their significance in biological processes. Test your understanding of how proteins contribute to cellular structure and function.