Amino Acids and Proteins: Characteristics and Structure

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Questions and Answers

What percentage of the body weight are proteins?

  • 75%
  • 50% (correct)
  • 25%
  • 10%

What is the relationship between the 3D structure of a protein and its function?

  • No relationship
  • They are unrelated
  • The 3D structure is not related to its function
  • The 3D structure is related to its function (correct)

Where is the genetic information for the amino acid sequence of a protein encoded?

  • Cytoplasm
  • DNA (correct)
  • RNA
  • Protein structure

Which type of proteins are in contact with water and considered hydrophilic?

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

How many common amino acids are coded in DNA?

<p>20 (B)</p> Signup and view all the answers

What type of isomers do amino acids have?

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

In proteins, what type of stereoisomers are all amino acid residues?

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

What do peptide bonds form when two amino acid molecules are joined?

<p>Flat, planar structure (D)</p> Signup and view all the answers

What do nonpolar and polar amino acids lead to in a peptide chain?

<p>Insoluble and water-soluble protein, respectively (C)</p> Signup and view all the answers

What does the primary structure of a protein describe?

<p>Amino acid sequence in a polypeptide chain (D)</p> Signup and view all the answers

What is the main feature of α-helices in proteins?

<p>Right-handed, helical conformations (A)</p> Signup and view all the answers

Which type of bond stabilizes proteins through interactions between side chain functional groups?

<p>Covalent disulfide bonds (C)</p> Signup and view all the answers

What denaturing agents can lead to protein precipitation and aggregation?

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

What is the smallest unit of a quaternary structure protein called?

<p>Monomer or subunit (D)</p> Signup and view all the answers

What is the process called when an unfolded (denatured) protein is refolded to restore its native structure and function?

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

Which type of interaction is NOT involved in stabilizing proteins?

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

What is the three-dimensional structure of a multisubunit protein known as?

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

What leads to the partial or complete unfolding of the specific native conformation of a protein?

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

What do denaturing agents such as urea lead to?

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

What are two or more separate polypeptide chains, or subunits, in a multisubunit protein called?

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

What is the biologically active conformation of a protein known as?

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

Flashcards

Protein percentage in body weight

Proteins account for approximately 50% of the body's weight

Protein structure and function

A protein's 3D structure dictates its function.

Protein sequence info location

Genetic information for protein amino acid sequences is stored in DNA.

Hydrophilic proteins

Globular proteins interact well with water.

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Common amino acids

20 amino acids are commonly encoded by DNA.

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Amino acid isomers

Amino acids exist as L and D isomers.

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Protein stereoisomers

In proteins, all amino acid residues are L-stereoisomers.

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Peptide bond structure

Joining two amino acids forms a flat, planar peptide bond.

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Amino acid effects on peptide chain

Nonpolar amino acids lead to an insoluble protein, while polar ones lead to water-soluble proteins.

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Primary protein structure

The amino acid sequence in a polypeptide chain.

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α-helices in proteins

Right-handed, helical conformations in proteins.

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Protein stabilizing bonds

Covalent disulfide bonds stabilize proteins via side chain interactions.

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Protein denaturing agents

pH and heat are denaturing agents, causing protein precipitation and aggregation.

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Quaternary structure unit

The smallest unit of a quaternary structure protein is a monomer or subunit.

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Protein renaturation

Unfolded (denatured) proteins can sometimes refold to their native structure and function.

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Stabilizing interactions (excluded)

Metallic bonds are not involved in stabilizing proteins.

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Multisubunit protein structure

The 3D structure of a multisubunit protein is called quaternary structure.

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Protein Denaturation

Partial or complete unfolding of the native conformation of a protein.

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Urea's effect on proteins

Denaturing agents such as urea lead to protein aggregation.

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Oligomeric proteins

Two or more separate polypeptide chains (subunits) in a multisubunit protein.

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Native conformation

The biologically active conformation of a protein.

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Study Notes

  • Amino acids have a general structure with an α-carbon bonded to a carboxyl group, an amino group, an R group (except for glycine), and a hydrogen atom. The α-carbon is a chiral center, leading to the existence of two stereoisomers: L and D.
  • All amino acid residues in proteins are L stereoisomers, and cells can specifically synthesize L isomers through stereospecific reactions.
  • Amino acids are amphoteric molecules, capable of donating and accepting protons and functioning as acids or bases.
  • Peptide bonds form when two amino acid molecules are covalently joined, forming a flat, planar structure that is stable and can participate in hydrogen bonding.
  • Amino acid composition in a peptide chain significantly affects its physical and chemical properties, with nonpolar and polar amino acids leading to insoluble and water-soluble protein, respectively.
  • Proteins have a complex structure, consisting of primary, secondary, tertiary, and quaternary levels.
  • Primary structure describes the amino acid sequence in a polypeptide chain, which is essential for the unique function of each protein.
  • Secondary structure refers to the local spatial arrangement of the mainchain atoms, which can form various structures like α-helices and β-pleated sheets.
  • α-helices are right-handed, helical conformations of a polypeptide chain, stabilized by hydrogen bonding between peptide linkages.
  • β-pleated sheets are extended conformations of polypeptide chains, stabilized by hydrogen bonding between the carbonyl and amino groups of the polypeptide chain.
  • β turns are important in globular proteins, connecting the ends of two adjacent segments of an antiparallel β sheet through a 180° turn involving glycine and proline.
  • Tertiary structure describes the overall three-dimensional arrangement of all atoms in a protein, reflecting its biologically active conformation and overall shape.

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