Proteins: Occurrence and Importance
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Questions and Answers

What is the Greek word for 'holding first place or rank'?

proteios

Approximately what percentage of a cell's dry weight do proteins make up?

50%

Which of the following is NOT a function of proteins in the body?

  • Storage of energy (correct)
  • Defense against infection
  • Transport of substances
  • Catalysis of chemical reactions

    • What protein is responsible for transporting oxygen in the blood?

    <p>Haemoglobin</p> Signup and view all the answers

    What type of protein acts as a defense mechanism against bacterial or viral infections?

    <p>Immunoglobulins</p> Signup and view all the answers

    Provide an example of a hormone that is a protein.

    <p>Insulin</p> Signup and view all the answers

    What type of proteins are involved in the contraction of muscles?

    <p>Muscle proteins</p> Signup and view all the answers

    What is the name of the protein that is involved in gene expression and controls the process of translation?

    <p>Histones</p> Signup and view all the answers

    What is the name of the milk protein that serves as a nutrient?

    <p>Casein</p> Signup and view all the answers

    What is the name of the protein that stores iron in the body?

    <p>Ferritin</p> Signup and view all the answers

    What is the name of the protein found in egg white that functions as an anti-vitamin?

    <p>Avidin</p> Signup and view all the answers

    What type of protein causes mad cow disease?

    <p>Prions</p> Signup and view all the answers

    What is the name of the toxin produced by cholera bacteria?

    <p>Enterotoxin</p> Signup and view all the answers

    Provide two examples of proteins that contribute to the structural strength and elasticity of organs and tissues.

    <p>Collagen and elastin</p> Signup and view all the answers

    What protein is found in hair and skin and contributes to the structure of tissues?

    <p>α-keratin</p> Signup and view all the answers

    All proteins contain amino acids.

    <p>True</p> Signup and view all the answers

    What is the type of bond that links amino acids together in protein chains?

    <p>Peptide bonds</p> Signup and view all the answers

    The molecular weight of proteins is generally low.

    <p>False</p> Signup and view all the answers

    Proteins are typically soluble in water.

    <p>False</p> Signup and view all the answers

    All proteins have the same shape.

    <p>False</p> Signup and view all the answers

    The charge of proteins can be altered by changing the surrounding pH.

    <p>True</p> Signup and view all the answers

    What is the pH at which a protein has a net charge of zero?

    <p>Isoelectric point</p> Signup and view all the answers

    Proteins are not capable of acting as buffers.

    <p>False</p> Signup and view all the answers

    Which protein is primarily responsible for buffering action in red blood cells?

    <p>Hemoglobin</p> Signup and view all the answers

    Proteins are always classified according to their composition.

    <p>False</p> Signup and view all the answers

    Which of the following is NOT a major class of proteins based on their structure?

    <p>Synthetic Proteins</p> Signup and view all the answers

    What are simple proteins composed of?

    <p>Amino acids</p> Signup and view all the answers

    What is the non-protein component of a conjugated protein called?

    <p>Prosthetic group</p> Signup and view all the answers

    What type of linkage typically holds lipids to proteins in lipoproteins?

    <p>Hydrophobic</p> Signup and view all the answers

    Glycoproteins contain ______ as their prosthetic group.

    <p>carbohydrates</p> Signup and view all the answers

    What is the name of the protein found in milk that is a phosphoprotein?

    <p>Casein</p> Signup and view all the answers

    What is the name of the protein that forms chromatin, a complex of DNA and proteins found in the nucleus?

    <p>Nucleoproteins</p> Signup and view all the answers

    What is the name of the prosthetic group found in hemoglobin and myoglobin?

    <p>Heme</p> Signup and view all the answers

    What is the name of the protein that stores iron in the body, an example of a metalloprotein?

    <p>Ferritin</p> Signup and view all the answers

    Derived proteins are formed from smaller subunits.

    <p>False</p> Signup and view all the answers

    Proteins are always arranged in a linear fashion.

    <p>False</p> Signup and view all the answers

    What is the name of the linear sequence of amino acids in a protein?

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

    The primary structure of proteins is maintained by covalent bonds, primarily peptide bonds and disulfide bonds.

    <p>True</p> Signup and view all the answers

    What is the name of the folded structure of a protein that is held together by hydrogen bonds, such as a-helix and ẞ-pleated sheets?

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

    Proteins can have both ordered and disordered conformations.

    <p>True</p> Signup and view all the answers

    The tertiary structure of a protein is primarily maintained by covalent bonds.

    <p>False</p> Signup and view all the answers

    What is the name of the three-dimensional structure of a protein, composed of multiple polypeptide chains?

    <p>Quaternary structure</p> Signup and view all the answers

    What is the name of the process by which a protein loses its native conformation and biological activity?

    <p>Denaturation</p> Signup and view all the answers

    Which of the following is NOT a consequence of protein denaturation?

    <p>Increased structural stability</p> Signup and view all the answers

    Denaturation is always irreversible.

    <p>False</p> Signup and view all the answers

    What is the name of the non-cellular portion of blood that contains proteins?

    <p>Plasma</p> Signup and view all the answers

    Albumin is the most abundant protein in plasma.

    <p>True</p> Signup and view all the answers

    Globulins are precipitated by half-saturated ammonium sulfate.

    <p>True</p> Signup and view all the answers

    Electrophoresis is a technique used to separate proteins based on their size.

    <p>False</p> Signup and view all the answers

    Which of the following is NOT a major class of globulins?

    <p>δ-Globulins</p> Signup and view all the answers

    Study Notes

    Proteins: Occurrence and Importance

    • Proteins are found in every cell of humans, animals, plants, and microorganisms.
    • They constitute about 50% of a cell's dry weight.
    • The term "protein" comes from the Greek word "proteios," meaning "holding first place."

    Medical and Biological Importance

    • Proteins play essential roles in various bodily functions.
    • Transport: Examples include hemoglobin, which carries oxygen.
    • Enzymatic activity: Proteins catalyze chemical reactions in the body.
    • Defense: Proteins like immunoglobulins fight bacterial and viral infections.
    • Hormonal regulation: Hormones, such as insulin, control biochemical processes.
    • Muscle contraction: Muscle proteins are involved in muscle movement.
    • Gene expression: Histones control gene expression and translation.
    • Nutrients and storage: Proteins like casein and ferritin serve as nutrients and store substances.
    • Buffering: Proteins act as buffers, maintaining stable pH levels.
    • Anti-vitamins: Some proteins act as inhibitors, like avidin in eggs.
    • Infectious agents: Prions, proteins, cause diseases like mad cow disease.

    Chemical Nature of Proteins

    • Proteins are polymers of amino acids.
    • Amino acids are linked together by peptide bonds.
    • Sometimes proteins are also called polypeptides due to multiple peptide bonds.

    Properties of Proteins

    • Proteins have high molecular weights. Examples include lactalbumin (17,000) and pyruvate dehydrogenase (7 x 106).
    • Proteins are colloids.
    • Proteins have large particle sizes.
    • Solubility varies in different solvents.
    • Proteins exhibit different shapes.
    • Hydrolysis of some proteins yields only amino acids, and others yield amino acids plus additional molecules.
    • Charge properties depend on the environment (e.g., pH). Isoelectric point is where net charge is zero.
    • Proteins can act as buffers due to their amphoteric nature.
    • Hemoglobin and plasma proteins are significant buffers in blood.

    Protein Classification

    • Proteins can be classified based on composition, solubility, structure, or function.
    • Simple proteins: Composed only of amino acids. Examples include albumin, trypsin, etc.
    • Conjugated proteins: Contain non-protein components (prosthetic groups). Subclasses include lipoproteins, glycoproteins, phosphoproteins, nucleoproteins, hemoproteins/chromoproteins, flavoproteins, and metalloproteins.
    • Derived proteins: Formed from simple or conjugated proteins via processes like denaturation or hydrolysis (proteoses, peptones, gelatin, and peptides).

    Protein Structure

    • Primary structure: Linear sequence of amino acids.
    • Secondary structure: Ordered folding patterns (e.g., alpha-helices, beta-sheets).
    • Alpha-helix: Hydrogen bonds between groups along the chain. 3.6 amino acids per turn.
    • Beta-sheets: Adjacent polypeptide chains held together by hydrogen bonds.
    • Tertiary structure: Three-dimensional arrangement of the entire protein. Driven by various interactions (hydrophobic, electrostatic, hydrogen bonds, and van der Waals).
    • Quaternary structure: Arrangement of multiple polypeptide chains in a complex. Formed through various interactions like hydrogen bond, electrostatic, van der waals, and disulfide bonds.

    Denaturation of Proteins

    • Loss of native conformation.
    • Physical or chemical changes can lead to denaturation. Examples include high temperature, extreme pH, or the presence of urea, guanidine, or heavy metal salts.
    • Denaturation often results in altered solubility, biological activity, and other properties.
    • Sometimes, denaturation is irreversible. Renaturation is possible in some cases.
    • Denaturation has significance in many biological and medical processes (e.g., enzyme function, food preservation).

    Plasma Proteins

    • Plasma contains various proteins that play crucial roles.
    • Albumin is a significant plasma protein.
    • The protein concentration and subtypes in serum are clinically significant.

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