Protein Chemistry Overview
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Questions and Answers

What structures are primarily stabilized by hydrogen bonds between carboxyl and amino groups?

  • β-sheet (correct)
  • α-helix (correct)
  • β-bends
  • Disulfide bonds

Which of the following amino acids is known to disrupt the formation of an α-helix?

  • Serine
  • Glycine
  • Alanine
  • Proline (correct)

What is the number of amino acids present per turn in an α-helix?

  • 4.0
  • 3.6 (correct)
  • 2.5
  • 3.0

Which structural characteristic differentiates a β-sheet from an α-helix?

<p>β-sheets are arranged in pleated or zigzag patterns. (A)</p> Signup and view all the answers

What type of protein structure is primarily influenced by the arrangement of disulfide bonds?

<p>Tertiary structure (B)</p> Signup and view all the answers

In which type of β-sheet are adjacent strands running in the same direction?

<p>Parallel β-sheet (C)</p> Signup and view all the answers

Which statement correctly describes the stability of an α-helix?

<p>It is a spontaneous conformation with the lowest energy. (D)</p> Signup and view all the answers

What defines the minor secondary structure known as β-bends?

<p>They connect ends of adjacent strands of anti-parallel β-pleates. (D)</p> Signup and view all the answers

Which of the following statements accurately describes oligomeric proteins?

<p>They exhibit quaternary structure. (B)</p> Signup and view all the answers

What is the primary structure of a protein primarily defined by?

<p>The sequence of amino acids from N-terminal to C-terminal. (A)</p> Signup and view all the answers

Which of the following is an example of a protein that exhibits secondary structure?

<p>Myoglobin (A), Hemoglobin (B), Keratin (C)</p> Signup and view all the answers

What characterizes the tertiary structure of proteins?

<p>It refers to the overall three-dimensional shape of a single polypeptide chain. (D)</p> Signup and view all the answers

What is a significant consequence of a change in the primary structure of a protein?

<p>It may result in loss of biological activity. (A)</p> Signup and view all the answers

Which of the following is true about the quaternary structure of proteins?

<p>It describes how multiple subunits interact and arrange. (D)</p> Signup and view all the answers

What distinguishes a monomeric protein from an oligomeric protein?

<p>Monomeric proteins consist of a single polypeptide chain. (D)</p> Signup and view all the answers

Which of the following examples correctly represents the quaternary structure?

<p>Hemoglobin (D)</p> Signup and view all the answers

What is the primary characteristic of β-bends in protein structure?

<p>They involve the formation of hydrogen bonds between the first and fourth amino acid residues. (C)</p> Signup and view all the answers

Which of the following statements is true regarding tertiary structure of proteins?

<p>It results in the formation of domains that are functionally independent. (B)</p> Signup and view all the answers

What happens to a protein during denaturation?

<p>The protein loses its secondary, tertiary, and quaternary structures. (B)</p> Signup and view all the answers

Which type of bond is primarily responsible for stabilizing quaternary protein structures?

<p>Disulfide bonds formed between distant side chains. (C)</p> Signup and view all the answers

What effect does denaturation have on the solubility of proteins?

<p>Denaturation leads to a decrease in solubility. (D)</p> Signup and view all the answers

Which of the following agents is NOT a physical denaturing agent?

<p>Acids (D)</p> Signup and view all the answers

Which feature distinguishes oligomeric proteins from monomeric proteins?

<p>Oligomeric proteins are composed of multiple polypeptide chains. (D)</p> Signup and view all the answers

Which amino acids are most likely involved in forming kinks in the polypeptide chain?

<p>Proline and Glycine (C)</p> Signup and view all the answers

What is the process called when the carboxyl group of one amino acid links with the amino group of another amino acid to form a peptide?

<p>Peptide bond formation (A), Condensation reaction (B)</p> Signup and view all the answers

What suffix do amino acid residues have when peptides are named, excluding the free C-terminal amino acid?

<p>-yl (C)</p> Signup and view all the answers

Which of the following is NOT a function of glutathione?

<p>Transporting lipids in the intestine (C)</p> Signup and view all the answers

What is the primary role of oxytocin in the body?

<p>Stimulating uterine contractions (D)</p> Signup and view all the answers

Angiotensin II is derived from which peptide and has what primary effect?

<p>Angiotensin I; hypertensive effect (A)</p> Signup and view all the answers

Which peptide is known for its opiate-like function and helps inhibit pain?

<p>Methionine enkephalin (A)</p> Signup and view all the answers

Which type of peptides are produced from plasma proteins through snake venom enzymes?

<p>Bradykinin and kallidin (D)</p> Signup and view all the answers

What is the primary effect of denaturation on the protein structure?

<p>It unfolds the secondary, tertiary, and quaternary structures. (C)</p> Signup and view all the answers

What is the primary component that makes up aspartame?

<p>Aspartic acid and phenylalanine (B)</p> Signup and view all the answers

Which type of protein is characterized as being water-soluble and spherical in shape?

<p>Globular proteins (D)</p> Signup and view all the answers

Which bonding force plays a crucial role in stabilizing the tertiary structure of proteins?

<p>Hydrogen bonds formed between polar groups. (B)</p> Signup and view all the answers

What characteristic is NOT associated with fibrous proteins?

<p>Soluble in water (B)</p> Signup and view all the answers

Which of the following agents is classified as a chemical denaturing agent?

<p>Alcohol (B)</p> Signup and view all the answers

What occurs during protein folding?

<p>The polypeptide chain acquires a biologically active 3D structure. (B)</p> Signup and view all the answers

Which type of globular protein is soluble in dilute salt solutions and heat-coagulated?

<p>Albumins (C)</p> Signup and view all the answers

In the context of β-bends, what term is used to describe the resulting structure due to specific hydrogen bonds?

<p>Hairpin turn or reverse turn (C)</p> Signup and view all the answers

Which of the following proteins is considered a conjugated protein due to the presence of a nucleic acid?

<p>Nucleoproteins (B)</p> Signup and view all the answers

What is a key feature of lectins in biological systems?

<p>Carbohydrate-binding proteins (C)</p> Signup and view all the answers

Which of the following is a type of fibrous protein found in exoskeletal structures?

<p>Keratins (A)</p> Signup and view all the answers

Which gastrointestinal hormone is involved in digestive processes?

<p>Gastrin (B)</p> Signup and view all the answers

Which of the following amino acid types is typically found in high amounts in keratin?

<p>Cysteine (B)</p> Signup and view all the answers

What is the property of proteins that is used in ion exchange chromatography?

<p>Overall charge (B)</p> Signup and view all the answers

Which technique relies on a protein's molecular size for separation?

<p>Gel filtration chromatography (D)</p> Signup and view all the answers

What does isoelectric focusing depend on for the cessation of protein movement?

<p>Charge at its isoelectric point (D)</p> Signup and view all the answers

Which property does the technique 'salting out' utilize for protein purification?

<p>Hydrophobicity (B)</p> Signup and view all the answers

In two-dimensional electrophoresis, what properties of proteins are used for their separation?

<p>Charge and molecular size (B)</p> Signup and view all the answers

What is the significance of dialysis in protein purification?

<p>Separates molecules based on size (D)</p> Signup and view all the answers

Which property is exploited in adsorption chromatography?

<p>Adsorption property (C)</p> Signup and view all the answers

What fundamental property does polyacrylamide gel electrophoresis (PAGE) utilize?

<p>Molecular size (B)</p> Signup and view all the answers

What is the main factor determining the efficiency of ultracentrifugation?

<p>Molecular weight of proteins (D)</p> Signup and view all the answers

Which method would be ineffective in separating proteins based on their molecular size?

<p>Ion exchange chromatography (B)</p> Signup and view all the answers

What is the primary determinant of a protein's biological activity?

<p>The sequence of amino acids in its primary structure (A)</p> Signup and view all the answers

Which of the following proteins represents an example of an oligomeric protein?

<p>Hemoglobin (A)</p> Signup and view all the answers

What distinguishes the tertiary structure of a protein from its secondary structure?

<p>The overall three-dimensional conformation (D)</p> Signup and view all the answers

Which characteristic accurately describes the quaternary structure of proteins?

<p>It consists of multiple polypeptide subunits (B)</p> Signup and view all the answers

What is the significance of a change in the primary structure of a protein?

<p>It may lead to a structural change resulting in loss of function (B)</p> Signup and view all the answers

Which level of protein structure is primarily determined by interactions between amino acids that are close in sequence?

<p>Secondary structure (A)</p> Signup and view all the answers

How many amino acids comprise the A chain of insulin?

<p>21 (B)</p> Signup and view all the answers

Which of the following statements is true about monomeric proteins?

<p>They only reach tertiary structure (C)</p> Signup and view all the answers

Which type of protein structure is stable due to covalent peptide bonds?

<p>Primary structure (C)</p> Signup and view all the answers

Which protein exemplifies a quaternary structure with four globin chains?

<p>Hemoglobin (B)</p> Signup and view all the answers

Flashcards

Interchain disulfide bonds

The bonds that hold two polypeptide chains together in a protein.

Intrachain disulfide bond

A disulfide bond between different parts of a single polypeptide chain.

α-helix

A common protein structure in which the polypeptide chain forms a right-handed spiral.

Hydrogen bonds (in α-helix)

Bonds that stabilize the α-helix structure by connecting the amino and carboxyl groups within the peptide backbone.

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β-sheet

A protein structure where polypeptide chains are arranged in sheets, either antiparallel or parallel.

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Antiparallel β-sheet

A β-sheet where polypeptide chains run in opposite directions.

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Parallel β-sheet

A β-sheet where polypeptide chains run in the same direction.

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β-bend

A structure that connects adjacent strands in antiparallel β-sheets.

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Monomeric protein

A protein with a single polypeptide chain.

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Oligomeric protein

A protein with more than one polypeptide chain.

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Quaternary structure

The arrangement of protein subunits in an oligomeric protein.

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Primary structure (protein)

The sequence of amino acids in a protein.

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Secondary structure (protein)

Folding of a polypeptide chain.

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Tertiary structure (protein)

The 3D shape of a protein, formed by interactions within the polypeptide chain.

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Peptide bond

The covalent bond that links amino acids together.

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Sickle cell anemia

A genetic disorder caused by a change in the primary structure of haemoglobin.

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Tertiary Structure

The 3D arrangement of a protein's amino acid chain. It brings distant parts of the linear chain closer together.

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Protein Denaturation

The process where a protein loses its complex 3D structure (secondary, tertiary, and quaternary), while the primary structure remains intact.

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Denaturing Agents

Substances that cause protein denaturation. These can be physical (heat, radiation) or chemical (acids, solvents).

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Protein Folding

The process by which a polypeptide chain assumes its functional 3D structure.

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Hydrophobic Interactions

Attraction between non-polar or water-fearing amino acid side chains. These interactions help drive protein folding by pushing hydrophobic side chains towards the inside of the protein.

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Protein Domains

Structurally connected but functionally independent units within a protein.

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Disulfide Bonds

Strong covalent bonds formed between sulfur atoms in cysteine amino acid residues, stabilizing protein structure.

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Amino Acid Residue

The remaining portion of an amino acid after it's incorporated into a peptide chain, minus the water molecule lost during bond formation.

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C-Terminal Amino Acid

The amino acid at the end of a peptide chain with a free carboxyl group.

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N-Terminal Amino Acid

The amino acid at the beginning of a peptide chain with a free amino group.

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Tripeptide

A peptide composed of three amino acids.

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Glutathione

A tripeptide (gamma-glutamyl-cysteinyl-glycine), a critical antioxidant and involved in amino acid transport.

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What are the functions of glutathione?

Glutathione protects red blood cells from damage, assists in amino acid transport, and helps detoxify harmful substances.

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Aspartame

An artificial sweetener made from aspartic acid and phenylalanine, about 200 times sweeter than sugar, used in low-calorie drinks.

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Gastrointestinal Hormones

Peptides produced in the digestive system that act as chemical messengers for regulating digestion and nutrient absorption.

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Simple Proteins

Proteins composed only of amino acid chains, without additional non-protein components.

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Conjugated Proteins

Proteins that contain a non-protein component, called a prosthetic group, in addition to amino acids.

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Derived Proteins

Modified or broken down forms of simple or conjugated proteins.

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Globular Proteins

Proteins with a spherical or oval shape, soluble in water, often involved in biological processes.

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Fibrous Proteins

Proteins with a long, fibrous shape, insoluble in water, providing structural support.

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Nucleoproteins

Conjugated proteins containing a nucleic acid (DNA or RNA) as the prosthetic group.

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Lectins

Proteins that bind to carbohydrates, helping cells interact and maintain tissue structure.

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What are denaturing agents?

Substances that cause protein denaturation, breaking down the 3D structure of a protein. These can be physical (heat, radiation) or chemical (acids, solvents).

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What are the bonds that stabilize tertiary structure?

The forces that hold the 3D shape of a protein together include hydrophobic interactions, hydrogen bonds, ionic bonds, van der Waals forces, and disulfide bonds.

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What is an Oligomeric Protein?

A protein composed of multiple polypeptide chains, or subunits.

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Hemoglobin

A protein with quaternary structure, consisting of four polypeptide chains (globins) and a heme group. It carries oxygen in the blood.

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Insulin

A protein hormone that regulates blood sugar levels. It has a primary structure consisting of two polypeptide chains linked by disulfide bonds.

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Primary Structure

The linear sequence of amino acids in a polypeptide chain. This is determined by the genetic code.

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Secondary Structure

The local folding patterns of the polypeptide chain, such as alpha-helices and beta-sheets, formed by hydrogen bonding between backbone atoms.

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Denaturation

The process where a protein loses its secondary, tertiary, and quaternary structure, but not its primary structure, due to factors like heat or pH change.

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How does a single amino acid change affect protein function?

A single amino acid change in the primary structure of a protein can disrupt its folding and therefore its function. This can lead to diseases like sickle cell anemia.

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Primary Structure of a Protein

The linear sequence of amino acids in a polypeptide chain, determining the protein's identity and function.

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β-Pleated Sheet

Another common secondary protein structure where polypeptide chains are arranged in sheets, either parallel or antiparallel, stabilized by hydrogen bonds between backbone atoms.

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Salting Out

A technique used to separate proteins based on their hydrophobicity, where increasing salt concentration decreases protein solubility, causing precipitation.

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Study Notes

Protein Chemistry

  • Proteins are the most abundant organic molecules in living systems
  • They make up approximately 50% of cellular dry weight
  • Proteins are fundamental to structure and function of life
  • Protein chemistry studies the structure, function, and properties of proteins
  • Proteins are polymers of amino acids linked by peptide bonds
  • The peptide bond is a covalent bond between the carboxyl group of one amino acid and the amino group of another
  • Peptide bonds are anhydride bonds formed by the loss of water molecule
  • Two amino acids form a dipeptide, three a tripeptide, four a tetrapeptide, etc
  • Ten to fifty amino acids form an oligopeptide. Chains with more than 50 are called proteins
  • The N-terminal end has a free alpha amino group, named after the first amino acid
  • The C-terminal end has a free alpha carboxyl group, contributed by the last amino acid
  • Peptide nomenclature involves appending a -yl suffix to all amino acid residues except the C-terminal one.
  • Examples of physiologically important peptides:
    • Glutathione (a tripeptide composed of gamma-glutamyl-cysteinyl-glycine) with functions in RBC membrane integrity, protecting hemoglobin, and amino acid transport
    • Thyrotropin releasing hormone (TRH)
    • Oxytocin
    • Vasopressin
    • Angiotensins
    • Methionine enkephalin
    • Bradykinin and kallidin
    • Peptide antibiotics (e.g., gramicidin, bacitracin, tyrocidin)
    • Aspartame
    • Gastrointestinal hormones (e.g., gastrin, secretin)

Protein Classification

  • Simple proteins: Composed only of amino acids.
    • Globular proteins (e.g., albumins, globulins, glutelins, prolamines, histones, globins, protamines, lectins, ) are generally soluble; some notable examples include serum albumin, ovalbumin, and casein in milk.
    • Scleroproteins (e.g., collagens, elastins, keratins) are insoluble and crucial for structural support.
  • Conjugated proteins: Contain a non-protein moiety (prosthetic group).
    • Nucleoproteins (e.g., nucleohistones, nucleoprotamines)
    • Glycoproteins
    • Lipoproteins
    • Phosphoproteins
    • Chromoproteins
    • Metalloproteins.
  • Derived proteins: Denatured or degraded products of simple and conjugated proteins.

Protein Classification based on function:

  • Structural: Keratin, collagen
  • Enzymes: Hexokinase, pepsin
  • Transport : Hemoglobin, serum albumin
  • Hormonal: Insulin, growth hormone
  • Contractile : Actin, myosin
  • Storage : Ovalbumin, glutelin
  • Genetic : Nucleoproteins
  • Defence: Snake venoms, Immunoglobulins
  • Receptor: For hormones, viruses

Protein Purification Techniques

  • Purifying protein from extraction buffer (e.g., ion exchange chromatography, gel filtration chromatography, affinity chromatography, adsorption chromatography)
  • Electrophoretic techniques (e.g., Polyacrylamide Gel Electrophoresis (PAGE), Isoelectric focusing,2-Dimensional electrophoresis, Gradient Gel Electrophoresis)
  • Other techniques (e.g. ultracentrifugation, salting out, dialysis)

Protein Folding

  • Proteins fold into their biologically active 3D shapes through a complex process
  • Folding influenced by various external factors including pH, temperature, chemicals, and limitations in space
  • Protein misfolding can lead to problems and diseases.
  • Protein misfolding may cause amyloid disorders (e.g. Alzheimer's disease).
  • Prion diseases are another example of protein misfolding (e.g., Creutzfeldt-Jakob disease, Kuru, scrapie, BSE)

Protein Denaturation

  • Denaturation is the process where a protein loses its native structure without breaking primary structure
  • Chemical denaturation agents include acids, alkalis, organic solvents, heavy metals, urea, and others.
  • Physical denaturation agents include heat, UV radiation, X-rays, ultrasound, and pressure.
  • Denaturation affects solubility, precipitability, and biological activity of proteins, making them more digestible.

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Description

This quiz covers the fundamentals of protein chemistry, including their structure, function, and properties. Explore concepts such as peptide bonds, amino acids, and nomenclature. Understand the significance of proteins in living systems and their classification based on amino acid chains.

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