Biochemistry Proteins and Structures Quiz
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Questions and Answers

What type of secondary structure is the basic unit of keratin?

  • β-sheets
  • Triple helix
  • α-helix (correct)
  • Random Coil

Which of the following promotes α-helix formation in keratin?

  • Disulfide bonds
  • Hydrophilic amino acids
  • Hydrophobic Amino Acids (correct)
  • Proline residues

Which of these amino acids is most likely to be found in the interior of a globular protein?

  • Serine
  • Valine (correct)
  • Lysine
  • Glutamic acid

Which of the following statements is TRUE about the alpha-helix structure of a protein?

<p>The alpha-helix is stabilized by hydrogen bonds between the carbonyl group of one amino acid and the amino group of another amino acid. (B)</p> Signup and view all the answers

What is the main structural component of a single hair?

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

What is the name of the process that breaks disulfide bonds in keratin?

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

What is the difference between a parallel and an anti-parallel beta-sheet structure?

<p>The orientation of the amino acid chains. (B)</p> Signup and view all the answers

Which of the following proteins is characterized by a high proportion of alpha-helix structures?

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

What is the structural unit of collagen?

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

What is the term used to describe the interaction between two or more polypeptide chains to form a larger protein molecule?

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

What is the approximate length of a collagen molecule?

<p>3000 A (C)</p> Signup and view all the answers

Which technique was used to elucidate the structure of myoglobin?

<p>X-ray crystallography (D)</p> Signup and view all the answers

Which of the following proteins is an example of a dimer?

<p>Muscle creatine kinase (B)</p> Signup and view all the answers

What type of amino acids are typically found on the surface of globular proteins?

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

What is the primary structure of a protein?

<p>The sequence of amino acids in a polypeptide chain (C)</p> Signup and view all the answers

What is a domain in a protein?

<p>A region of the protein that folds independently (B)</p> Signup and view all the answers

What is the primary function of myoglobin?

<p>Storage of oxygen in muscle tissue (C)</p> Signup and view all the answers

What is the prosthetic group in myoglobin that allows for oxygen binding?

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

Which of the following amino acids is NOT found in the interior of myoglobin?

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

What is the significance of the 4 proline residues in myoglobin?

<p>They disrupt the formation of alpha helices. (B)</p> Signup and view all the answers

How many subunits does hemoglobin have?

<p>4 (B)</p> Signup and view all the answers

What is the difference between the alpha and beta subunits of hemoglobin?

<p>The alpha subunits have a shorter D helix while the beta subunits have a shorter H helix. (A)</p> Signup and view all the answers

What is the difference between the T (tense) and R (relaxed) structures of hemoglobin?

<p>The T structure has a higher affinity for oxygen. (B)</p> Signup and view all the answers

What is the primary reason for the difference in oxygen affinity between the T and R structures of hemoglobin?

<p>Differences in the interactions between the subunits. (E)</p> Signup and view all the answers

What is the main reason myoglobin is easy to study?

<p>It crystallizes easily and is small in size. (D)</p> Signup and view all the answers

Which of the following describes the function of the heme group in hemoglobin?

<p>It allows binding of oxygen due to the iron atom. (D)</p> Signup and view all the answers

What is the difference between the alpha and beta chains in hemoglobin?

<p>Alpha chains contain 141 amino acids; beta chains contain 146 amino acids. (A)</p> Signup and view all the answers

How many oxygen molecules can one hemoglobin molecule carry at maximum?

<p>4 (C)</p> Signup and view all the answers

What role do proline residues play in the structure of myoglobin?

<p>They break the helix structure. (A)</p> Signup and view all the answers

What is the consequence of the transition from the T to R structure in hemoglobin?

<p>Higher oxygen affinity for hemoglobin. (B)</p> Signup and view all the answers

Which of the following segments corresponds to a non-helical segment in myoglobin?

<p>NA1-NA2 (B)</p> Signup and view all the answers

What happens to the iron ion in the T structure of hemoglobin?

<p>It is pulled out of the plane, reducing accessibility for oxygen. (B)</p> Signup and view all the answers

What is the most common secondary structure found in globular proteins?

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

Which type of beta structure is generally more common in globular proteins?

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

What characterizes the quaternary structure of a protein?

<p>Interactions between two or more polypeptide chains (A)</p> Signup and view all the answers

How many amino acids are typically found in an alpha helix within a globular protein?

<p>11 on average (A)</p> Signup and view all the answers

Which amino acids are predominantly located on the surface of globular proteins?

<p>Charged and polar amino acids (A)</p> Signup and view all the answers

What percentage of a globular protein is typically composed of beta structures?

<p>23% (A)</p> Signup and view all the answers

What defines an oligomeric protein?

<p>It is composed of two or more subunits (C)</p> Signup and view all the answers

Concanavalin A is primarily characterized by which structural feature?

<p>Only beta structures (A)</p> Signup and view all the answers

What determines the tertiary structure of a protein?

<p>The primary structure of the protein (A)</p> Signup and view all the answers

What structural feature is primarily responsible for keratin's insolubility in water?

<p>Presence of disulfide bonds (D)</p> Signup and view all the answers

Which structure is formed by the twisting of two coiled-coils in keratin?

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

What type of protein is collagen primarily classified as?

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

How is the structure of myoglobin primarily described?

<p>Composed of a single polypeptide chain (D)</p> Signup and view all the answers

What is the basic unit that forms the structural component of hair?

<p>α-helix polypeptide (B)</p> Signup and view all the answers

What role do molecular chaperones play in protein folding?

<p>They assist in stabilizing newly formed structures (B)</p> Signup and view all the answers

Flashcards

Alpha Helix

A right-handed coiled structure stabilized by hydrogen bonds between peptide bonds.

Beta Structure

A secondary protein structure with hydrogen bonds forming a pleated sheet between chains.

Oligomeric Proteins

Proteins composed of two or more polypeptide chains, called subunits or monomers.

Dimer

A protein made of two identical or non-identical subunits.

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Hydrophobic Amino Acids

Amino acids that are typically found in the interior of proteins due to their non-polar nature.

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Polar Amino Acids

Amino acids that can be found on the surface or interior of proteins based on their charge.

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Quaternary Structure

The level of protein structure where multiple polypeptide chains interact to form larger molecules.

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Super Secondary Structures

Arrangements of secondary structures in a protein, like motifs or domains.

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Haemoglobin Structure

Haemoglobin is a tetramer with 2 alpha and 2 beta subunits.

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Central Dogma of Protein Folding

The primary structure determines the tertiary structure of proteins.

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Spontaneous Protein Folding

Protein folding begins with local secondary structures like α-helices or β-sheets.

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Molecular Chaperones

Proteins that assist in the correct folding of other proteins.

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Fibrous Protein Example: Keratin

Keratin is a fibrous protein that consists of α-helices and forms coiled-coils.

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Collagen Structure

Collagen is a structural protein with a triple helix of three polypeptides.

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Myoglobin Discovery

Myoglobin structure revealed by John Kendrew and Max Perutz via x-ray crystallography.

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Disulfide Bonds in Proteins

Disulfide bonds stabilize protein structure and can be cleaved by mercaptans.

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Myoglobin

A small protein that carries oxygen in muscle tissue, comprised of 153 amino acids.

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Haem

A red-colored prosthetic group in myoglobin and hemoglobin that binds oxygen; it's a tetrapyrrole.

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T and R Structures

Two forms of hemoglobin - T (tense) with lower oxygen affinity and R (relaxed) with higher affinity.

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Oxygen Binding

Each iron atom in a heme group can bind to an oxygen atom, allowing hemoglobin to transport oxygen efficiently.

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Helix Segments in Hemoglobin

Hemoglobin beta subunits have 8 helix segments while alpha subunits have 7, with one helix segment missing.

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Iron Accessibility in T State

In the tense state of hemoglobin, the iron ion is less accessible, reducing its ability to bind oxygen.

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Domain in Proteins

Distinct functional and structural units within large proteins, typically consisting of multiple secondary structures.

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Anti-parallel Beta Structure

A form of beta structure where adjacent polypeptide chains run in opposite directions.

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Subunits in Oligomeric Proteins

Polypeptide chains that combine to form larger protein molecules, called oligomers.

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Tertiary Structure

The overall three-dimensional shape of a single protein molecule, including arrangements of secondary structures.

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Right-Handed Twist

The characteristic twist of the alpha helix and some beta structures, resulting in their specific shape.

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Protein Folding Nucleus

The initial local secondary structure where folding begins.

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Coiled-Coil Structure

A structure of two α-helices twisted together, forming part of keratin.

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Keratin Function

The main structural protein in hair, nails, and skin.

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Microfibrils

Structures formed by the arrangement of protofilaments in a 9+2 manner.

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Hydrophobic Nature of Keratin

Keratin's R-groups face outward, making it insoluble in water.

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Collagen Triple Helix

A unique structure of collagen consisting of three intertwined polypeptides.

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Role of Disulfide Bonds

Stabilize protein structure; can be cleaved by reducing agents.

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Molecular Chaperones Purpose

Proteins assisting in the proper folding of other proteins.

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Myoglobin Structure

Myoglobin is a compact protein with 153 amino acids, primarily comprising alpha helices.

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Haem Group

Haem is a red-colored prosthetic group in myoglobin and hemoglobin that binds oxygen.

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Non-Helical Segments

Myoglobin has five non-helical segments connecting its helices.

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Hemoglobin Polypeptide Chains

Hemoglobin consists of four polypeptide chains: 2 alpha and 2 beta.

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Oxygen Binding Capacity of Hemoglobin

Hemoglobin can carry up to 4 oxygen molecules due to its structure.

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Tense Structure of Hemoglobin

The tense (T) structure has a lower affinity for oxygen and is less accessible.

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Relaxed Structure of Hemoglobin

The relaxed (R) structure has a greater affinity for oxygen.

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Helix Segments in Myoglobin

Myoglobin features 8 alpha helical segments in its structure.

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