Proteins and Their Structures
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Proteins and Their Structures

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Questions and Answers

What determines the structure of proteins?

  • The sequence of amino acids (correct)
  • The temperature of the environment
  • The pH level of the solution
  • The presence of lipids

    • What is a key characteristic of α-amino acids?

  • Differentiated by different side-chains (R-group) (correct)
  • They are all negatively charged
  • They typically have 10 different types
  • They contain multiple amino groups

    • Which statement correctly describes a zwitter ion?

  • It is only positively charged
  • It carries both a positive and negative charge (correct)
  • It is a neutral molecule
  • It is only negatively charged

    • What is one primary function of proteins?

    <p>Assisting in cellular structure and function</p> Signup and view all the answers

    How are proteins typically detected in laboratory settings?

    <p>By employing specific binding assays</p> Signup and view all the answers

    What type of bonds primarily stabilize the structure of both the alpha helix and beta sheet?

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

    Which amino acids are commonly found in U-turns of protein structures?

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

    What characterizes the quaternary structure of a protein?

    <p>Multiple subunits held together by non-covalent bonds</p> Signup and view all the answers

    Which structural feature is specifically described as a right-handed helix?

    <p>Alpha helix</p> Signup and view all the answers

    What might low levels of hemoglobin indicate about a person's health?

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

    What is the significance of L-amino acid enantiomers in proteins?

    <p>They play a crucial role in the specificity of molecular recognition.</p> Signup and view all the answers

    Which amino acid is always the first in a polypeptide chain?

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

    What primarily determines the secondary structure of a protein?

    <p>Hydrogen bonding involving peptide bonds.</p> Signup and view all the answers

    Which structure of a protein is characterized by the linear sequence of amino acid residues?

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

    What type of bonding does cysteine engage in to stabilize protein structure?

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

    Which element found in methionine and cysteine contributes to their unique properties?

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

    In what way does the primary structure influence protein function?

    <p>It determines how the peptide will fold into a 3D shape.</p> Signup and view all the answers

    What is the result of hydrogen bonding in secondary protein structure?

    <p>Creation of α-helix and β-sheet patterns</p> Signup and view all the answers

    What type of mutation leads to misfolding associated with sickle cell disease?

    <p>Point mutation</p> Signup and view all the answers

    Which condition is characterized by abnormal protein accumulation that forms extracellular deposits?

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

    What role does the C-peptide play during insulin synthesis?

    <p>It aids in the formation of disulphide bonds.</p> Signup and view all the answers

    Which of the following proteins is primarily associated with Alzheimer's disease?

    <p>Amyloid-beta (Aβ)</p> Signup and view all the answers

    What is a characteristic of prion proteins?

    <p>They have a primarily alpha-helical secondary structure.</p> Signup and view all the answers

    What consequence results from premature stop codons in protein synthesis?

    <p>The formation of incomplete proteins</p> Signup and view all the answers

    In which cellular structure are insulin and its C-peptide stored?

    <p>Secretory vesicles</p> Signup and view all the answers

    Which ionic conditions in the trans Golgi network assist in protein aggregation?

    <p>Acidic pH and high Ca2+ concentration</p> Signup and view all the answers

    What is the process called when abnormal PrPC converts normal PrPC into an abnormal form?

    <p>Chain reaction</p> Signup and view all the answers

    Which disease in humans is associated with spongiform encephalopathies?

    <p>Creutzfeldt-Jakob Disease</p> Signup and view all the answers

    What is the molecular weight of ubiquitin?

    <p>8.5 kDa</p> Signup and view all the answers

    Which of the following is NOT a function of proteins?

    <p>Genetic encoding</p> Signup and view all the answers

    Which of the following techniques is used for protein detection?

    <p>SDS-PAGE</p> Signup and view all the answers

    What role does the proteasome play in the cell?

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

    Which of the following represents a structural protein?

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

    What type of modification can proteins undergo after translation?

    <p>Post-translational modification</p> Signup and view all the answers

    Which type of proteins are involved in cell signaling?

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

    What is one of the primary roles of glycosylation in proteins?

    <p>Cell recognition and signaling</p> Signup and view all the answers

    Study Notes

    Proteins

    • Complex biopolymers, whose structure is determined by the sequence of amino acids

    Alpha Amino Acids

    • Contain an asymmetric carbon
    • Two stereoisomers exist called enantiomers or optical isomers
    • Proteins in all life only contain L-amino acid enantiomers
    • The surface of proteins is asymmetric, allowing for highly specific molecular recognition
    • Play an important role in the formation of protein “secondary structure”

    Methionine and Cysteine

    • Both contain sulfur
    • Methionine is always the first amino acid in a polypeptide chain
    • The free sulfhydryl group of cysteine is highly reactive and is often used in enzyme active sites to attach various chemical groups to proteins
    • Cysteine can form disulfide bonds

    Primary Protein Structure

    • The primary structure of a peptide or protein is the linear sequence of amino acid residues from the N- to the C-terminus.

    Secondary Protein Structure

    • Dependent on hydrogen bonding involving the peptide bonds
    • Alpha Helix
    • Beta Sheets
    • U Turns
    • The secondary structure of a protein is the folding pattern of the polypeptide chain.

    Tertiary Structure

    • Specifies the special arrangements of the secondary arrangement

    Quaternary Protein Structure

    • Several subunits held together by non-covalent bonds

    Hemoglobin

    • One example of a protein with quaternary structure

    Sickle Cell Disease

    • Abnormal primary structure can affect protein function
    • Point mutations leading to misfolding
    • Point mutations leading to trapping of protein in the ER
    • Point mutations leading to premature stop codons

    Insulin

    • Proinsulin contains the amino acid sequence of insulin plus the 31-amino acid C (connecting) peptide
    • In the Golgi apparatus, disulfide bonds are established, aided by C-peptide
    • Sorting and packaging due to special surface proteins
    • Insulin is stored in vesicles in zinc-bound crystals
    • Proteases that cleave proinsulin are packaged within the secretory vesicle

    Amyloidosis

    • Accumulation of amyloid (proteins that have folded abnormally and aggregated together)
    • Folded into beta sheets, they form extracellular deposits

    Prions

    • Proteinaceous infectious particles
    • PrPC (Prion Protein) is a normal neuronal protein involved in cell adhesion, ion channel activity, and neuronal excitability
    • In abnormal form, alpha helix changes to beta sheet
    • Abnormal PrPC can convert normal PrPC into abnormal form

    Histopathology

    • Creutzfeldt-Jakob Disease (CJD)
    • Gerstmann-Straussler-Scheinker Syndrome
    • Kuru
    • Scrapie in sheep
    • Bovine Spongiform Encephalopathy (BSE) in cows
    • Transmissible Mink Encephalopathy in mink
    • Feline Spongiform Encephalopathy in cats

    Protein Detection

    • SDS Page gels – 1D and 2D
    • Staining techniques
    • Immunoblotting
    • Mass spectrometry
    • Crystallography
    • Edman sequencing

    Ubiquitination

    • Ubiquitin is an 8.5kDa protein
    • Marks proteins for degradation via the proteasome
    • Binds to lysine, cysteine, threonine residues along the length of the target molecule or to the N-terminus of the protein
    • Regulates major cellular processes such as cell division, immune responses, and embryonic development

    Protein Breakdown

    • Important way for cells to regulate expression of proteins
    • The proteasome

    Functions of Proteins

    • Structural proteins
    • Catalytic proteins – Enzymes
    • Signaling Proteins
    • Proteins involved in cell adhesion and recognition
    • Membrane transport proteins

    Functions of Proteins: Examples

    • Extracellular Matrix Proteins (ECM) like collagen, Elastin, lamin and fibronectin
    • Muscle proteins: actin and myosin
    • Cytoskeletal proteins
    • Proteins that participate in immunity (antibodies, complement system…)
    • Transport proteins including Albumin (50% of plasma protein)
    • Pro-and anti-coagulant proteins
    • DNA binding proteins

    Summary

    • Proteins are organized in four different levels (primary to quaternary structure)
    • There are several different detection levels for proteins
    • Proteins can be post-translationally modified
    • Proteins fulfill a wide array of functions

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    Description

    This quiz focuses on the fundamental concepts of proteins, including the structure and properties of alpha amino acids, and the roles of methionine and cysteine. Explore the differences between primary and secondary protein structure and test your understanding of these vital biomolecules.

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