Proteins and Their Characteristics

Overview of Proteins

• Proteins are unbranched polymers made from amino acids, vital for nearly all cellular functions.
• Majority of proteins are composed of carbon, hydrogen, oxygen, nitrogen, and often sulfur; some (like casein) contain phosphorus and others (like hemoglobin) contain iron.

Characteristics of Proteins

• Proteins are the most abundant molecules in cells after water.
• A zwitterion is formed when amino groups accept protons, creating a molecule with both positive and negative charges but no net charge.
• pH levels influence amino acid charge:
  • Low pH (acidic) leads to protonation of carboxyl groups.
  • High pH (basic) results in proton loss from amino groups.

Functions of Proteins

• Enzymes: Catalyze biochemical reactions.
• Defense: Protect the body against pathogens.
• Transport: Carry substances across cells and tissues.
• Regulatory: Involved in signaling pathways.
• Structural: Provide support to cells and tissues.
• Movement: Required for muscle contractions.
• Nutrient Storage: Maintain availability of amino acids.

Properties of Amino Acids

• All standard amino acids are chiral except glycine, which is achiral.
• Amino acids can bear negative, neutral, or positive charges depending on the surrounding pH.
• Functional roles include neurotransmission, serving as precursors for hormones, and energy sources.

Structural Diversity Based on Polarity

• Non-polar amino acids: Hydrophobic, often found in protein interiors.
• Polar neutral, acidic, and basic amino acids vary in water interaction; polar acids bear negative charges while polar basics are positively charged.

Specific Amino Acids

• Alanine: Important in gluconeogenesis.
• Glycine: Simplest, only achiral amino acid, important in collagen.
• Proline: Known as an imino acid and disrupts α-helix structures.
• Methionine: Start codon for protein synthesis, involved in methyl group transfers.
• Phenylalanine: Aromatic amino acid, converted to tyrosine; associated with phenylketonuria.
• Tyrosine: Precursor for catecholamines and thyroid hormones.
• Tryptophan: Precursor for serotonin and melatonin, regulates mood.
• Asparagine and Glutamine: Important nitrogen carriers.

Nutritional Requirements

• Amino acids classified as essential, non-essential, or conditionally essential based on dietary need.
• Non-essential amino acids can be synthesized in the body while essential ones must be obtained from diet.

Peptide Hormones and Neurotransmitters

• Oxytocin and Vasopressin: Nonapeptides that regulate reproductive processes and water retention.
• Enkephalins: Endogenous pentapeptide neurotransmitters involved in pain regulation.

Protein Structure

• Monomeric Proteins: Composed of a single peptide chain.
• Multimeric Proteins: Contain multiple peptide chains which can be identical or different.
• Alpha Helix: A common secondary structure stabilized by hydrogen bonds, forming a right-handed spiral.

Functions of Specific Proteins

• Glutathione: Acts as an antioxidant, preventing oxidative damage.
• Conjugated Proteins: Contain non-peptide components, such as prosthetic groups.

Metabolic Fates of Amino Acids

• Amino acids can be exclusively ketogenic, exclusively glucogenic, or both, impacting their metabolic pathways and energy production.

Summary Points

• Amino acid structure and properties significantly influence protein function and utility in biochemical processes.
• Understanding protein characteristics and amino acid properties is crucial for fields like biochemistry, nutrition, and pharmacology.### Protein Structure Overview
• Hydrogen bonds form between C=O groups of one amino acid and N-H groups of another, crucial for secondary structure stability.
• One turn of the alpha helix contains 3.6 amino acid residues; amino acid R groups extend outward, allowing varied interactions.
• Many α helices exhibit amphipathic properties with hydrophobic R groups on one side and hydrophilic R groups on the opposite side.

Levels of Protein Structure

• Primary Structure: Linear sequence of amino acids linked by peptide bonds determines a protein's unique sequence and functionality.
• Secondary Structure: Spatial arrangement of protein backbone involves common structures like:
  • Alpha helix (α helix)
  • Beta pleated sheet (β pleated sheet)
• Tertiary Structure: Overall 3D shape resulting from interactions between widely separated amino acid side chains.
• Quaternary Structure: Arrangement of multiple polypeptide chains in a protein, stabilized by hydrophobic interactions.

Protein Classification by Structure

• Fibrous Proteins: Elongated shape; provide structural support (e.g., keratin and collagen).
• Globular Proteins: Spherical shape; perform metabolic functions (e.g., enzymes and transport proteins).
• Membrane Proteins: Span cell membranes; involved in transport and signaling functions.

Specific Proteins and Their Functions

• Hemoglobin: Tetramer consisting of two α and two β subunits; transports oxygen using heme groups.
• Myoglobin: Monomer with a single heme group; stores oxygen in muscles and has a higher affinity for oxygen than hemoglobin.
• Collagen: Most abundant protein in humans; forms a triple helix structure, essential for connective tissues.

Functional Classification of Proteins

• Catalytic Proteins: Enzymes acting as biological catalysts for biochemical reactions.
• Defense Proteins: Immunoglobulins or antibodies that protect against pathogens.
• Transport Proteins: Bind small molecules for transportation, e.g., hemoglobin and transferrin.
• Messenger Proteins: Communicate signals between cells and tissues (e.g., insulin).
• Contractile Proteins: Facilitate movement, including muscle contraction (e.g., actin and myosin).
• Structural Proteins: Provide rigidity and support (e.g., collagen and keratin).
• Transmembrane Proteins: Control small molecule and ion transport across membranes.
• Storage Proteins: Store important molecules for later use (e.g., myoglobin).
• Nutrient Proteins: Essential for growth and development in early life stages (e.g., casein and ovalbumin).
• Fluid-balance Proteins: Maintain fluid balance in tissues (e.g., albumin and globulin).

Protein Hydrolysis and Denaturation

• Hydrolysis: Enzyme-catalyzed breakdown of proteins to amino acids; crucial for protein digestion.
• Denaturation: Loss of tertiary and quaternary structure; can be caused by heat, extreme pH, organic solvents, and heavy metals.
• Denaturation is generally reversible under some conditions, termed renaturation; primary structure remains intact.

Denaturation Agents and Their Effects

• Heat: Disrupts hydrogen bonding and hydrophobic interactions; often irreversible.
• Extreme pH: Disrupts ionic interactions.
• Organic Solvents/Detergents: Disrupt hydrophobic interactions.
• Mercaptoethanol: Disrupts disulfide bonds.
• Heavy Metal Salts: Disrupt disulfide bonds.

Importance of Immunoglobulins

• Crucial for immune response against antigens, with significant implications in diseases like AIDS which compromise the immune system.
• CD4 cells indicate immune function status, crucial for monitoring health in HIV patients.

Overview of Proteins

• Proteins are unbranched polymers made from amino acids, vital for nearly all cellular functions.
• Majority of proteins are composed of carbon, hydrogen, oxygen, nitrogen, and often sulfur; some (like casein) contain phosphorus and others (like hemoglobin) contain iron.

Characteristics of Proteins

• Proteins are the most abundant molecules in cells after water.
• A zwitterion is formed when amino groups accept protons, creating a molecule with both positive and negative charges but no net charge.
• pH levels influence amino acid charge:
  • Low pH (acidic) leads to protonation of carboxyl groups.
  • High pH (basic) results in proton loss from amino groups.

Functions of Proteins

• Enzymes: Catalyze biochemical reactions.
• Defense: Protect the body against pathogens.
• Transport: Carry substances across cells and tissues.
• Regulatory: Involved in signaling pathways.
• Structural: Provide support to cells and tissues.
• Movement: Required for muscle contractions.
• Nutrient Storage: Maintain availability of amino acids.

Properties of Amino Acids

• All standard amino acids are chiral except glycine, which is achiral.
• Amino acids can bear negative, neutral, or positive charges depending on the surrounding pH.
• Functional roles include neurotransmission, serving as precursors for hormones, and energy sources.

Structural Diversity Based on Polarity

• Non-polar amino acids: Hydrophobic, often found in protein interiors.
• Polar neutral, acidic, and basic amino acids vary in water interaction; polar acids bear negative charges while polar basics are positively charged.

Specific Amino Acids

• Alanine: Important in gluconeogenesis.
• Glycine: Simplest, only achiral amino acid, important in collagen.
• Proline: Known as an imino acid and disrupts α-helix structures.
• Methionine: Start codon for protein synthesis, involved in methyl group transfers.
• Phenylalanine: Aromatic amino acid, converted to tyrosine; associated with phenylketonuria.
• Tyrosine: Precursor for catecholamines and thyroid hormones.
• Tryptophan: Precursor for serotonin and melatonin, regulates mood.
• Asparagine and Glutamine: Important nitrogen carriers.

Nutritional Requirements

• Amino acids classified as essential, non-essential, or conditionally essential based on dietary need.
• Non-essential amino acids can be synthesized in the body while essential ones must be obtained from diet.

Peptide Hormones and Neurotransmitters

• Oxytocin and Vasopressin: Nonapeptides that regulate reproductive processes and water retention.
• Enkephalins: Endogenous pentapeptide neurotransmitters involved in pain regulation.

Protein Structure

• Monomeric Proteins: Composed of a single peptide chain.
• Multimeric Proteins: Contain multiple peptide chains which can be identical or different.
• Alpha Helix: A common secondary structure stabilized by hydrogen bonds, forming a right-handed spiral.

Functions of Specific Proteins

• Glutathione: Acts as an antioxidant, preventing oxidative damage.
• Conjugated Proteins: Contain non-peptide components, such as prosthetic groups.

Metabolic Fates of Amino Acids

• Amino acids can be exclusively ketogenic, exclusively glucogenic, or both, impacting their metabolic pathways and energy production.

Summary Points

• Amino acid structure and properties significantly influence protein function and utility in biochemical processes.
• Understanding protein characteristics and amino acid properties is crucial for fields like biochemistry, nutrition, and pharmacology.### Protein Structure Overview
• Hydrogen bonds form between C=O groups of one amino acid and N-H groups of another, crucial for secondary structure stability.
• One turn of the alpha helix contains 3.6 amino acid residues; amino acid R groups extend outward, allowing varied interactions.
• Many α helices exhibit amphipathic properties with hydrophobic R groups on one side and hydrophilic R groups on the opposite side.

Levels of Protein Structure

• Primary Structure: Linear sequence of amino acids linked by peptide bonds determines a protein's unique sequence and functionality.
• Secondary Structure: Spatial arrangement of protein backbone involves common structures like:
  • Alpha helix (α helix)
  • Beta pleated sheet (β pleated sheet)
• Tertiary Structure: Overall 3D shape resulting from interactions between widely separated amino acid side chains.
• Quaternary Structure: Arrangement of multiple polypeptide chains in a protein, stabilized by hydrophobic interactions.

Protein Classification by Structure

• Fibrous Proteins: Elongated shape; provide structural support (e.g., keratin and collagen).
• Globular Proteins: Spherical shape; perform metabolic functions (e.g., enzymes and transport proteins).
• Membrane Proteins: Span cell membranes; involved in transport and signaling functions.

Specific Proteins and Their Functions

• Hemoglobin: Tetramer consisting of two α and two β subunits; transports oxygen using heme groups.
• Myoglobin: Monomer with a single heme group; stores oxygen in muscles and has a higher affinity for oxygen than hemoglobin.
• Collagen: Most abundant protein in humans; forms a triple helix structure, essential for connective tissues.

Functional Classification of Proteins

• Catalytic Proteins: Enzymes acting as biological catalysts for biochemical reactions.
• Defense Proteins: Immunoglobulins or antibodies that protect against pathogens.
• Transport Proteins: Bind small molecules for transportation, e.g., hemoglobin and transferrin.
• Messenger Proteins: Communicate signals between cells and tissues (e.g., insulin).
• Contractile Proteins: Facilitate movement, including muscle contraction (e.g., actin and myosin).
• Structural Proteins: Provide rigidity and support (e.g., collagen and keratin).
• Transmembrane Proteins: Control small molecule and ion transport across membranes.
• Storage Proteins: Store important molecules for later use (e.g., myoglobin).
• Nutrient Proteins: Essential for growth and development in early life stages (e.g., casein and ovalbumin).
• Fluid-balance Proteins: Maintain fluid balance in tissues (e.g., albumin and globulin).

Protein Hydrolysis and Denaturation

• Hydrolysis: Enzyme-catalyzed breakdown of proteins to amino acids; crucial for protein digestion.
• Denaturation: Loss of tertiary and quaternary structure; can be caused by heat, extreme pH, organic solvents, and heavy metals.
• Denaturation is generally reversible under some conditions, termed renaturation; primary structure remains intact.

Denaturation Agents and Their Effects

• Heat: Disrupts hydrogen bonding and hydrophobic interactions; often irreversible.
• Extreme pH: Disrupts ionic interactions.
• Organic Solvents/Detergents: Disrupt hydrophobic interactions.
• Mercaptoethanol: Disrupts disulfide bonds.
• Heavy Metal Salts: Disrupt disulfide bonds.

Importance of Immunoglobulins

• Crucial for immune response against antigens, with significant implications in diseases like AIDS which compromise the immune system.
• CD4 cells indicate immune function status, crucial for monitoring health in HIV patients.

Overview of Proteins

• Proteins are unbranched polymers made from amino acids, vital for nearly all cellular functions.
• Majority of proteins are composed of carbon, hydrogen, oxygen, nitrogen, and often sulfur; some (like casein) contain phosphorus and others (like hemoglobin) contain iron.

Characteristics of Proteins

• Proteins are the most abundant molecules in cells after water.
• A zwitterion is formed when amino groups accept protons, creating a molecule with both positive and negative charges but no net charge.
• pH levels influence amino acid charge:
  • Low pH (acidic) leads to protonation of carboxyl groups.
  • High pH (basic) results in proton loss from amino groups.

Functions of Proteins

• Enzymes: Catalyze biochemical reactions.
• Defense: Protect the body against pathogens.
• Transport: Carry substances across cells and tissues.
• Regulatory: Involved in signaling pathways.
• Structural: Provide support to cells and tissues.
• Movement: Required for muscle contractions.
• Nutrient Storage: Maintain availability of amino acids.

Properties of Amino Acids

• All standard amino acids are chiral except glycine, which is achiral.
• Amino acids can bear negative, neutral, or positive charges depending on the surrounding pH.
• Functional roles include neurotransmission, serving as precursors for hormones, and energy sources.

Structural Diversity Based on Polarity

• Non-polar amino acids: Hydrophobic, often found in protein interiors.
• Polar neutral, acidic, and basic amino acids vary in water interaction; polar acids bear negative charges while polar basics are positively charged.

Specific Amino Acids

• Alanine: Important in gluconeogenesis.
• Glycine: Simplest, only achiral amino acid, important in collagen.
• Proline: Known as an imino acid and disrupts α-helix structures.
• Methionine: Start codon for protein synthesis, involved in methyl group transfers.
• Phenylalanine: Aromatic amino acid, converted to tyrosine; associated with phenylketonuria.
• Tyrosine: Precursor for catecholamines and thyroid hormones.
• Tryptophan: Precursor for serotonin and melatonin, regulates mood.
• Asparagine and Glutamine: Important nitrogen carriers.

Nutritional Requirements

• Amino acids classified as essential, non-essential, or conditionally essential based on dietary need.
• Non-essential amino acids can be synthesized in the body while essential ones must be obtained from diet.

Peptide Hormones and Neurotransmitters

• Oxytocin and Vasopressin: Nonapeptides that regulate reproductive processes and water retention.
• Enkephalins: Endogenous pentapeptide neurotransmitters involved in pain regulation.

Protein Structure

• Monomeric Proteins: Composed of a single peptide chain.
• Multimeric Proteins: Contain multiple peptide chains which can be identical or different.
• Alpha Helix: A common secondary structure stabilized by hydrogen bonds, forming a right-handed spiral.

Functions of Specific Proteins

• Glutathione: Acts as an antioxidant, preventing oxidative damage.
• Conjugated Proteins: Contain non-peptide components, such as prosthetic groups.

Metabolic Fates of Amino Acids

• Amino acids can be exclusively ketogenic, exclusively glucogenic, or both, impacting their metabolic pathways and energy production.

Summary Points

• Amino acid structure and properties significantly influence protein function and utility in biochemical processes.
• Understanding protein characteristics and amino acid properties is crucial for fields like biochemistry, nutrition, and pharmacology.### Protein Structure Overview
• Hydrogen bonds form between C=O groups of one amino acid and N-H groups of another, crucial for secondary structure stability.
• One turn of the alpha helix contains 3.6 amino acid residues; amino acid R groups extend outward, allowing varied interactions.
• Many α helices exhibit amphipathic properties with hydrophobic R groups on one side and hydrophilic R groups on the opposite side.

Levels of Protein Structure

• Primary Structure: Linear sequence of amino acids linked by peptide bonds determines a protein's unique sequence and functionality.
• Secondary Structure: Spatial arrangement of protein backbone involves common structures like:
  • Alpha helix (α helix)
  • Beta pleated sheet (β pleated sheet)
• Tertiary Structure: Overall 3D shape resulting from interactions between widely separated amino acid side chains.
• Quaternary Structure: Arrangement of multiple polypeptide chains in a protein, stabilized by hydrophobic interactions.

Protein Classification by Structure

• Fibrous Proteins: Elongated shape; provide structural support (e.g., keratin and collagen).
• Globular Proteins: Spherical shape; perform metabolic functions (e.g., enzymes and transport proteins).
• Membrane Proteins: Span cell membranes; involved in transport and signaling functions.

Specific Proteins and Their Functions

• Hemoglobin: Tetramer consisting of two α and two β subunits; transports oxygen using heme groups.
• Myoglobin: Monomer with a single heme group; stores oxygen in muscles and has a higher affinity for oxygen than hemoglobin.
• Collagen: Most abundant protein in humans; forms a triple helix structure, essential for connective tissues.

Functional Classification of Proteins

• Catalytic Proteins: Enzymes acting as biological catalysts for biochemical reactions.
• Defense Proteins: Immunoglobulins or antibodies that protect against pathogens.
• Transport Proteins: Bind small molecules for transportation, e.g., hemoglobin and transferrin.
• Messenger Proteins: Communicate signals between cells and tissues (e.g., insulin).
• Contractile Proteins: Facilitate movement, including muscle contraction (e.g., actin and myosin).
• Structural Proteins: Provide rigidity and support (e.g., collagen and keratin).
• Transmembrane Proteins: Control small molecule and ion transport across membranes.
• Storage Proteins: Store important molecules for later use (e.g., myoglobin).
• Nutrient Proteins: Essential for growth and development in early life stages (e.g., casein and ovalbumin).
• Fluid-balance Proteins: Maintain fluid balance in tissues (e.g., albumin and globulin).

Protein Hydrolysis and Denaturation

• Hydrolysis: Enzyme-catalyzed breakdown of proteins to amino acids; crucial for protein digestion.
• Denaturation: Loss of tertiary and quaternary structure; can be caused by heat, extreme pH, organic solvents, and heavy metals.
• Denaturation is generally reversible under some conditions, termed renaturation; primary structure remains intact.

Denaturation Agents and Their Effects

• Heat: Disrupts hydrogen bonding and hydrophobic interactions; often irreversible.
• Extreme pH: Disrupts ionic interactions.
• Organic Solvents/Detergents: Disrupt hydrophobic interactions.
• Mercaptoethanol: Disrupts disulfide bonds.
• Heavy Metal Salts: Disrupt disulfide bonds.

Importance of Immunoglobulins

• Crucial for immune response against antigens, with significant implications in diseases like AIDS which compromise the immune system.
• CD4 cells indicate immune function status, crucial for monitoring health in HIV patients.