Amino Acids and Proteins Overview

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Questions and Answers

Which of the following amino acids are classified as semi-essential?

  • Proline
  • Histidine (correct)
  • Glycine
  • Arginine (correct)

What distinguishes proline and hydroxyproline from other amino acids?

  • They are the only amino acids that are dispensable.
  • They contain sulfur groups.
  • They have imino groups instead of amino groups. (correct)
  • They are both essential amino acids.

Which of the following statements is true regarding the classification of amino acids?

  • The rest of the amino acids are either dispensable or nonessential. (correct)
  • Arginine and histidine are dispensable amino acids.
  • Proline and hydroxyproline are essential amino acids.
  • All amino acids are essential.

What can be said about the dispensability of proline and hydroxyproline?

<p>They are classified as nonessential amino acids. (C)</p> Signup and view all the answers

Which amino acids are considered dispensable or nonessential?

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

What primarily determines the structure of a protein?

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

What characterizes the secondary structure of a protein?

<p>Fine folding of the polypeptide chain (A)</p> Signup and view all the answers

Which of the following statements about tertiary structure is correct?

<p>It involves coarse folding and super folding. (C)</p> Signup and view all the answers

What is the correct sequence of protein structure levels from simplest to most complex?

<p>Primary, secondary, tertiary (C)</p> Signup and view all the answers

What does the term 'native protein' refer to?

<p>A protein that has achieved its correct three-dimensional structure (A)</p> Signup and view all the answers

Which type of amino acids are all included in protein structures?

<p>α-amino acids (B)</p> Signup and view all the answers

What characteristic of all amino acids in protein structure distinguishes them optically?

<p>They are all L-amino acids. (D)</p> Signup and view all the answers

Which amino acid is known to be optically inactive?

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

What is a reason why glycine is considered optically inactive among amino acids?

<p>It has a symmetrical carbon atom. (C)</p> Signup and view all the answers

Which statement regarding amino acids is false?

<p>All amino acids have a non-polar R-group. (A)</p> Signup and view all the answers

What is the definition of quaternary structure in proteins?

<p>Multiple protein subunits that can be dimeric, trimeric, or multimeric. (D)</p> Signup and view all the answers

Which of the following is an example of a protein with quaternary structure?

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

Which statement is false regarding quaternary structures?

<p>All proteins have quaternary structure. (B)</p> Signup and view all the answers

How is quaternary structure different from tertiary structure?

<p>Quaternary structure is formed by multiple polypeptide chains. (B)</p> Signup and view all the answers

What types of quaternary structures exist?

<p>Dimeric, trimeric, and multimeric structures. (A)</p> Signup and view all the answers

Flashcards

Semi-essential amino acids

Amino acids that the body can make, but may not make enough in certain conditions, so they need to be consumed in the diet to meet needs.

Nonessential amino acids

Amino acids that the body can produce in sufficient amounts on its own.

Dispensable amino acids

Amino acids that the body can produce.

Imino group

A chemical group that includes a nitrogen atom attached to two carbon atoms.

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Proline and Hydroxyproline

Amino acids containing imino groups instead of the typical amino groups, important for collagen structure.

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Amino acid structure

All amino acids in proteins are alpha-amino acids, L-amino acids, and optically active.

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Glycine

The only non-optically active amino acid, due to having hydrogen as its R-group.

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Alpha-amino acid

A type of amino acid in proteins with an amino group and a carboxyl group attached to the same carbon atom.

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L-amino acid

A type of amino acid commonly found in proteins.

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Optical activity

The ability of a molecule to rotate plane-polarized light.

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DNA's Role in Protein Structure

DNA provides the genetic code that determines the sequence of amino acids in a protein chain. This sequence ultimately dictates the protein's final shape and function.

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Secondary Structure: Fine Folding

The secondary structure of a protein refers to the initial localized folding patterns of the amino acid chain. This involves interactions between nearby amino acids, forming structures like alpha-helices and beta-sheets.

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Tertiary Structure: Course Folding

The tertiary structure describes the overall three-dimensional shape of a protein, resulting from interactions between distant amino acids. This intricate folding creates functional domains and the protein's native shape.

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Native Protein

The final, stable, functional form of a protein, achieved after all folding processes are complete.

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Protein Domains

Distinct structural and functional units within a larger protein molecule. These domains often perform specific tasks, contributing to the protein's overall function.

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Quaternary Structure

The arrangement and interaction of multiple protein subunits (polypeptide chains) in a protein complex.

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Dimeric Protein

A protein composed of two identical polypeptide chains.

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Trimeric Protein

A protein composed of three identical polypeptide chains.

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Multimeric Protein

A protein composed of multiple (more than two) polypeptide chains.

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Hemoglobin & Lactate Dehydrogenase

Examples of proteins with quaternary structure, formed by multiple subunits.

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Study Notes

Amino Acids

  • Amino acids are the building blocks of proteins
  • The structure includes an alpha carbon bonded to four groups: an amino group (-NH2), a carboxylic group (-COOH), a hydrogen atom, and an R-group (side chain).
  • The R-group differentiates amino acids.
  • Amino acids are classified into three groups based on their characteristics
    • Chemical classification: Neutral, Acidic, and Basic amino acids
      • Aliphatic, Hydroxy, Aromatic, Sulfur-containing, Heterocyclic are examples of chemical classifications
    • Metabolic classification: Glucogenic, Ketogenic, and Mixed are related to their metabolic roles
    • Biological classification: Essential, Semi-essential, and Non-essential based on the body's ability to produce them
  • Some amino acids contain an imino group instead of amino group. (e.g., Proline, Hydroxyproline).
  • The pH at which a protein carries no net electric charge is called its isoelectric point.

Proteins

  • Proteins are formed by peptide bonds between amino acids
  • These bonds lead to the formation of different structures of proteins
    • Primary structure: The linear sequence of amino acids
    • Secondary structure: Localized folding (e.g., alpha-helices and beta-sheets) caused by hydrogen bonds
    • Tertiary structure: Overall, 3D shape, stabilized by variety of bonds (hydrophobic, ionic, disulfide, hydrogen, Van der Waals forces)
    • Quaternary structure: Multiple polypeptide chains assembled into a functional unit (e.g., hemoglobin)
  • A genetic disease, Sickle Cell Anemia, is related to the primary structure
  • Protein denaturation is the unfolding of a protein without breaking the peptide bonds.
  • Hydrolysis breaks down proteins into amino acids.

Carbohydrates

  • Carbohydrates are classified by the number of sugar subunits: monosaccharides, disaccharides, oligosaccharides, and polysaccharides
  • Isomers are different versions of a molecule (e.g., D and L isomers and α and β anomers) with varying configurations around an asymmetric carbon.
  • Monosaccharides are classified by the number of carbons and the type of carbonyl group.
  • Glucose (blood sugar) and fructose (fruit sugar) are examples of monosaccharides.
  • Disaccharides and polysaccharides are formed by joining monosaccharides
  • Polysaccharides are composed of different forms, like starch, glycogen, cellulose, and pectin.
  • Some polysaccharides have other molecules attached.

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