Overview of Globular Proteins
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Questions and Answers

Most of the chemical work of the cell is mediated by which kind of proteins?

  • Fibrous proteins
  • Structural proteins
  • Enzymatic proteins
  • Globular proteins (correct)

    • What are globular proteins?

    Proteins whose three-dimensional folded shape is relatively compact.

    How is the structure of globular proteins different from fibrous proteins?

    Globular proteins have polypeptide chains folded into compact structures, unlike the extended forms of fibrous proteins.

    What is a typical example of a fibrous protein?

    <p>Myoglobin.</p> Signup and view all the answers

    What is distinct about the tertiary structure of globular proteins?

    <p>The polypeptide chain is folded into compact tertiary structures, with secondary structure regions folded on each other.</p> Signup and view all the answers

    What is the major determinant of a globular protein's functional properties?

    <p>The tertiary structure of a globular protein.</p> Signup and view all the answers

    What two methods provide structural information with atomic-level details for proteins?

    <p>X-ray diffraction and NMR.</p> Signup and view all the answers

    Globular proteins possess secondary structures and are also folded into what?

    <p>Compact tertiary structures.</p> Signup and view all the answers

    What is one of the smallest globular proteins?

    <p>Human ubiquitin, which contains only 76 amino acid residues.</p> Signup and view all the answers

    What does human ubiquitin do?

    <p>It plays a critical role in targeting other proteins for degradation.</p> Signup and view all the answers

    How do cartoon models represent proteins?

    <p>They emphasize the position of the main chain and associated secondary structure elements.</p> Signup and view all the answers

    What does a cartoon rendering allow easy identification of?

    <p>The helices and sheets, and how they are packed together.</p> Signup and view all the answers

    When is a stick model of a protein useful?

    <p>When examining specific interactions such as hydrogen bonds.</p> Signup and view all the answers

    In most cases, what is of greatest importance in defining a protein's function?

    <p>The outer surface of the protein.</p> Signup and view all the answers

    We can think of this surface as the protein's what?

    <p>&quot;skin.&quot;</p> Signup and view all the answers

    In a typical globular protein, there is no what?

    <p>No open space in the interior.</p> Signup and view all the answers

    The secondary structures of some proteins are composed almost solely of either what or what?

    <p>α helix or β sheet.</p> Signup and view all the answers

    The secondary structure of myoglobin is mostly what?

    <p>α helix.</p> Signup and view all the answers

    What is neuraminidase?

    <p>An enzyme important for viral pathogenesis.</p> Signup and view all the answers

    What is the secondary structure of neuraminidase like?

    <p>It is mostly β sheet.</p> Signup and view all the answers

    What is triosephosphate isomerase (TIM)?

    <p>An enzyme important for the utilization of glucose as a nutrient.</p> Signup and view all the answers

    What is the secondary structure of TIM like?

    <p>It has both helix and sheet structures.</p> Signup and view all the answers

    What is the first common principle about the classification of globular proteins?

    <p>We can classify a protein based on the dominant secondary structural motifs.</p> Signup and view all the answers

    What is the second common principle about the classification of globular proteins?

    <p>Many proteins are made up of more than one domain.</p> Signup and view all the answers

    What is a domain?

    <p>A compact, locally folded region of tertiary structure of roughly 150-250 amino acids.</p> Signup and view all the answers

    Domains are interconnected by what?

    <p>The polypeptide strand that runs through the whole molecule.</p> Signup and view all the answers

    Multiple domains are especially common in what?

    <p>Larger globular proteins.</p> Signup and view all the answers

    Relatively small proteins like ubiquitin tend to have what kind of domains?

    <p>Single folded domains.</p> Signup and view all the answers

    Different domains often perform differing what?

    <p>Functions.</p> Signup and view all the answers

    A given domain type may be found where?

    <p>In several different proteins.</p> Signup and view all the answers

    What is the 3rd common principle about the classification of globular proteins?

    <p>Domains may themselves be composed of repeating secondary structure motifs.</p> Signup and view all the answers

    What is an example of a type of supersecondary structure found in globular proteins?

    <p>A β-strand sequence linked to an α-helix sequence is referred to as a &quot;β / α motif.&quot;</p> Signup and view all the answers

    What is a good example of a globular protein that has supersecondary structures?

    <p>The enzyme TIM.</p> Signup and view all the answers

    What is the most common type of domain fold found in proteins?

    <p>The β-barrel.</p> Signup and view all the answers

    What is the β-barrel?

    <p>A barrel-like structure formed by eight β strands.</p> Signup and view all the answers

    What are the four basic folding patterns found in globular proteins?

    <ol> <li>Those built around α helices; 2. Those constructed on β sheets; 3. Those including both; 4. Those containing little helices or sheets.</li> </ol> Signup and view all the answers

    What is topology as it refers to protein classification?

    <p>It refers to the order in which secondary structural features are connected in the main chain.</p> Signup and view all the answers

    What is a Rossman fold?

    <p>A common domain structure for enzymes that bind NAD cofactor.</p> Signup and view all the answers

    There are 130 distinct homologous superfamilies of proteins that include a Rossman fold topology. What are they?

    <p>Homologous superfamilies.</p> Signup and view all the answers

    How do homologous superfamilies work?

    <p>Proteins within each superfamily appear to be homologous.</p> Signup and view all the answers

    The majority of globular protein structures can be broadly classified as 'mainly α,' 'mainly β,' and 'α + β.' A small number of globular proteins has little what?

    <p>α or β secondary structure.</p> Signup and view all the answers

    List the 4 things on our growing list of common principles of globular protein structure.

    <ol> <li>All globular proteins have a defined inside and outside; 2. Sheets are usually twisted into barrel structures; 3. The polypeptide chain can turn corners to go from one segment to the next; 4. Not all parts can be conveniently classified.</li> </ol> Signup and view all the answers

    If we examine the amino acid sequences of globular proteins, we find no particular distribution pattern of what?

    <p>Hydrophobic or hydrophilic residues.</p> Signup and view all the answers

    But when we look at the positions of the amino acids in the three-dimensional structure of globular proteins, we invariably find what?

    <p>Tertiary structure places hydrophobic residues mostly on the inside and hydrophilic residues on the surface.</p> Signup and view all the answers

    What is one kind of a compact turn for a polypeptide chain to go from one β segment or α helix to the next?

    <p>A β turn.</p> Signup and view all the answers

    There are several varieties of β turn, each able to accomplish what?

    <p>A complete reversal of the polypeptide chain direction in only four residues.</p> Signup and view all the answers

    Bends and turns most often occur where in globular proteins?

    <p>At the surface of proteins.</p> Signup and view all the answers

    Not all parts of globular proteins can be conveniently classified as what?

    <p>Helix, β sheet, or turns.</p> Signup and view all the answers

    What have some of the weird contorted loops and folds in the polypeptide chains of globular proteins been called?

    <p>&quot;Random coil&quot; regions.</p> Signup and view all the answers

    Study Notes

    Overview of Globular Proteins

    • Globular proteins mediate various cellular functions, including synthesizing, transporting, and metabolizing.
    • Their three-dimensional folded shape is compact, unlike the extended forms of fibrous proteins.

    Structural Characteristics

    • The polypeptide chains of globular proteins fold into compact structures, contrasting with the filamentous structures of fibrous proteins, exemplified by myoglobin (compact) vs. collagen (extended).
    • Tertiary structure is crucial as it determines a globular protein's functional properties, achieved through the folding of secondary structural elements (α helices and β sheets).

    Protein Examples and Functions

    • Human ubiquitin, containing 76 amino acids, plays a vital role in targeting proteins for degradation.
    • Myoglobin has a secondary structure predominantly composed of α helices.
    • Neuraminidase, important for viral pathogenesis, mainly consists of β sheets.
    • Triosephosphate isomerase (TIM), involved in glucose utilization, has both α and β structures.

    Domains and Classification Principles

    • Classification of globular proteins can be based on dominant secondary structural motifs, with many proteins comprising multiple domains.
    • A domain is a compact, locally folded region of tertiary structure, often consisting of 150-250 amino acids, recognizable within the protein.
    • Proteins with multiple domains are common, while smaller proteins like ubiquitin typically consist of a single folded domain.
    • Different domains may have unique functions and may recur across various proteins, like ATP-binding domains.

    Supersecondary Structures and Folds

    • Domains can feature repeating secondary structural motifs known as supersecondary structures, such as β/α motifs.
    • TIM exemplifies a protein with supersecondary structures, possessing a β-barrel configuration, which is a prevalent domain fold in proteins.

    Folding Patterns and Topology

    • Four basic folding patterns of globular proteins include packing around α helices, frameworks of β sheets, combinations of both, or minimal structures.
    • Topology refers to the specific order of the secondary structural elements in a protein chain, influencing classification.

    Homologous Superfamilies

    • The Rossman fold is a domain structure found in enzymes interacting with NAD, critical for ATP production.
    • A total of 130 distinct homologous superfamilies exhibit this topology, indicating a shared evolutionary ancestor.

    General Principles of Globular Protein Structure

    • Globular proteins possess defined interiors and surfaces, with twisted sheets often arranged in barrel structures.
    • Polypeptide chains can create turns and corners for structural transition.
    • Tertiary structures typically localize hydrophobic residues in the interior and hydrophilic residues on the surface.

    Turns and Irregular Structures

    • Compact turns like β turns enable polypeptide chains to reverse direction efficiently.
    • Not all regions of globular proteins fit neatly into classifications of helix, β sheet, or turns; some exhibit contorted loops known as "random coil," though this term misrepresents their structure, which can be well-defined.

    Additional Notes

    • Structural variations can often be seen at the protein surface, with bends and turns enhancing function and stability.

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    Description

    This quiz explores the essential characteristics and functions of globular proteins, including their structure and roles within cellular processes. It highlights the comparison between globular and fibrous proteins and delves into specific examples like myoglobin and ubiquitin. Test your knowledge on the significance of tertiary structure and the functionality of these proteins.

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