Biology Proteins and Peptides Quiz

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Questions and Answers

What type of protein includes a heme unit as its prosthetic group?

Fibrous proteins

Globular proteins

Enzymatic proteins

Hemoproteins (correct)

Which of the following interactions is primarily responsible for protein stability?

Peptide bonds

Hydrophobic interactions (correct)

Disulfide bonds

Ionic interactions

What describes the spatial arrangement of the polypeptide backbone?

Configuration

Conformation (correct)

Composition

Conjugation

Which characteristic of a peptide bond contributes to its rigidity and resistance to conformational change?

Partial double bond character Signup and view all the answers

Which of the following statements about conformational changes in proteins is true?

They involve rotation about single bonds. Signup and view all the answers

Which of the following amino acids is classified as nonpolar?

Isoleucine Signup and view all the answers

What is a common characteristic of polar uncharged amino acids?

They form hydrogen bonds. Signup and view all the answers

Which amino acid is considered semi-essential for children?

Histidine Signup and view all the answers

Which groups of amino acids are positively charged at physiologic pH?

Histidine and Arginine Signup and view all the answers

What best describes zwitterions in amino acids?

Having a positive and a negative charge Signup and view all the answers

Which amino acid is categorized as acidic?

Aspartate Signup and view all the answers

Which amino acids are classified as branched-chain amino acids?

Leucine, Isoleucine, Valine Signup and view all the answers

What is the primary structure of a protein composed of?

Polypeptide chains of amino acids Signup and view all the answers

What is the primary function of the side chain group (R-group) in an amino acid?

It dictates the function of the amino acid. Signup and view all the answers

Which of the following amino acids is classified as a polar basic amino acid?

Lysine Signup and view all the answers

Which chemical group in an amino acid can accept a proton?

Amino Group Signup and view all the answers

Which amino acid is the simplest and achiral?

Glycine Signup and view all the answers

In the context of protein structure, what is an oligopeptide?

A chain consisting of 10-20 amino acids Signup and view all the answers

Which class of amino acids possesses both a carboxyl and an amino group?

All amino acids Signup and view all the answers

What is a characteristic feature of enantiomers in amino acids?

They exist in L- and D- configurations. Signup and view all the answers

Which of the following is not a common function of proteins?

Energy storage Signup and view all the answers

What element is not commonly found in proteins?

Sodium Signup and view all the answers

What role does chirality play in amino acids?

It affects how amino acids interact with each other. Signup and view all the answers

What type of amino acids are commonly found in beta turns?

Glycine and Proline Signup and view all the answers

Which type of protein is characterized by a rounded, spherical shape and typically functions in a biochemical capacity?

Globular Proteins Signup and view all the answers

Which of the following statements about keratin is true?

It can be found in hair, nails, and skin. Signup and view all the answers

What characterizes a supersecondary structure?

It has a recognizable folding pattern involving multiple secondary structures. Signup and view all the answers

What type of keratin is known for being less pliable and is found in structures like hair and nails?

HARD Keratin Signup and view all the answers

Which structure is described as having irregularities within antiparallel beta-sheets?

Beta Bulge Signup and view all the answers

What type of forces are primarily involved in maintaining the tertiary structure of proteins?

All of the above Signup and view all the answers

Which of the following is an example of a fibrous protein?

Collagen Signup and view all the answers

What definition best describes configuration in the context of molecular structure?

The geometric relationship between a given set of atoms. Signup and view all the answers

Which of the following does NOT affect the stability of a protein's conformation?

Covalent bonds between atoms. Signup and view all the answers

In the alpha helix structure, how many amino acids are typically found per turn?

3.6 Signup and view all the answers

What is the pitch of an alpha helix in angstroms (Å)?

5.4 Å Signup and view all the answers

Which statement regarding the beta-pleated sheet is correct?

Hydrogen bonds occur between neighboring strands. Signup and view all the answers

What is a primary function of torsional angles in protein folding?

To limit possible configurations of amino acids. Signup and view all the answers

Which of the following amino acids is known to act as an alpha-helix breaker?

Proline Signup and view all the answers

What type of beta sheet features hydrogen bonding chains running in opposite directions?

Antiparallel beta sheet Signup and view all the answers

Study Notes

Proteins and Peptide Bonds

Proteins are the most abundant organic molecules in the human body.
Composed of carbon, hydrogen, oxygen, nitrogen, and some contain sulfur and phosphorus.
Monomer unit of proteins is an amino acid.
Peptide bonds (amide bonds) form between amino acids.
Peptide: unbranched chain of amino acids.
Oligopeptide: 10-20 amino acid residues.

Functions of Proteins

Structural support
Enzymes
Hormones and receptors
Immunity
Fluid and acid-base balance

Amino Acid

Building block of protein.
Contains both an amino group and a carboxyl group.
α-amino acid: amino group and carboxyl group are attached to the α-carbon atom.
R denotes a side chain group.

Amino Acid Classification

Non-polar amino acids:
- Zero net charge
- Form hydrophobic interactions
- Found in the interior of the protein
- Glycine, Alanine, Valine, Leucine, Isoleucine, Phenylalanine, Tryptophan, Methionine, Proline
Polar uncharged amino acids:
- Zero net charge
- Form hydrogen bonds
- Found on the surface of the protein
- Serine, Threonine, Tyrosine (contain -OH), Cysteine (-SH), Asparagine, Glutamine (amides)
Charged amino acids:
- Positive (acidic) or negative (basic) net charge
- Form ionic interactions
- Found on the surface of the protein
- Acidic: Aspartate, Glutamate
- Basic: Arginine, Lysine, Histidine

Essential Amino Acids

Cannot be synthesized in the body.
Semi-essential amino acids: required for growth in children, but not for adults.
Barone Essential Amino Acid Mnemonic: PVT.TIM HALL
- Phenylalanine, Valine, Tryptophan
- Threonine, Isoleucine, Methionine
- Histidine, Arginine, Lysine (ketogenic), Leucine (ketogenic)

Zwitterion

Has a positive charge on one atom and a negative charge on another atom with no net charge.
Amino acids can serve as buffers in aqueous solutions.

Types of Conjugated Proteins

Hemoproteins:
- Prosthetic group: heme unit
- Hemoglobin, myoglobin
- Carrier of O2 in blood, oxygen binder in muscles

Protein Stability

Chemical Factors:
- Disulfide bonds
- Hydrophobic interactions (predominant)
- Hydrogen bonding
- Van der Waals interactions
- Increase in IMF, more stable due to decreased Gibbs free energy change (ΔG)

Peptide Bond

Rigid planar trans configuration
Partial (about 40%) double bond character between α-amino nitrogen of one amino acid to the carbonyl carbon of the next.
Keeps peptide links relatively resistant to conformational change

Torsional Angles

Ψ (psi): allowed rotation for –Cα–C=O
Ф (phi): allowed rotation for –N–Cα–
Limited rotation due to steric and torsional strains
Ramachandran diagram indicates allowed conformations of polypeptides

Conformation & Configuration

Conformation: Spatial relationship of every atom in a molecule.
- Interconversion between conformers occurs with retention of configuration.
Configuration: Geometric relationship between a given set of atoms.
- Interconversion of configurational alternatives requires breaking and reforming covalent bonds.

Protein Conformation

Spatial arrangement of atoms in a molecule (protein).
Native proteins: functional and folded conformation.
Folding must achieve a decrease in Gibbs free energy change for a protein to be stable.
Stability is the tendency to maintain a native conformation.

Secondary Structure

Conformation of the polypeptide backbone
Spatial arrangement of the polypeptide backbone.
Alpha helix:
- Right-handed coiled spring shape (helix).
- Stabilized by intramolecular hydrogen bonds.
- Hydrogen bonds are parallel to the axis of the helix.
- 3.6 amino acid residues per turn.
- Pitch: 5.4 Å (0.54nm) rise per turn.
- Amino acid side chains (R groups) project outward from the helix.
Beta pleated sheet:
- Highly extended polypeptide backbone.
- Zigzag or pleated pattern.
- R groups of adjacent amino acid residues project in opposite directions.
- Hydrogen bonds occur between neighboring polypeptide chains.
- Parallel β sheet: H-bonded chains run in the same direction.
- Antiparallel β sheet: H-bonded chains run in the opposite direction.
β-Loops:
- Short segments of amino acids that join two units of the secondary structure (e.g., two adjacent strands of an antiparallel β sheet).
- 180° turn involving 4 amino acid residues.
- Structural role.
β-Bulge:
- Irregularity in antiparallel β-sheets.
- Hydrogen bonding between 2 residues from one strand with 1 residue from the other.

Super Secondary Structure

Also known as motifs.
Intermediate in scale between secondary and tertiary structures.
A recognizable folding pattern involving 2 or more elements of secondary structure and the connection/s between them.
Examples:
- β-α-β loop
- α-α unit (helix-turn-helix)
- β-meander
- Greek key motif

Fibrous and Globular Proteins

Fibrous: - Long narrow rod. - Structural role. - Mostly insoluble in water. - Repetitive amino acid sequence. - Examples: collagen, keratin
Globular: - Rounded/spherical. - Functional role. - Mostly water soluble. - Irregular amino acid sequence. - Examples: hemoglobin, enzymes, immunoglobulins

Keratin

Occurs in all higher vertebrates.
Found in hair, nails, claws, wool, quills, feathers, horns, hooves, and skin.
α-Keratins: found in mammals.
- Right-handed α-helix.
- Two α-helices coil each other to form a left-handed supercoil.
- Rich in Cys residues that form disulfide bonds, linking filaments.
- Hard keratin: hair, horn, nail (less pliable).
- Soft keratin: skin, callus.
β-Keratins: occur in birds and reptiles.
- Provides waterproofing and prevents drying.
- β-sheet pattern in native state.

Permanent Wave in Hair

Forces Involved in 3° Structure:
- Disulfide bonds.
- Hydrophobic interactions.
- Hydrogen bonding.
- Van der Waals interactions.

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Description

This quiz explores the structure, function, and classification of proteins and peptides, focusing on amino acids and their roles in biological systems. Test your knowledge on how peptide bonds form and the diverse functions proteins serve in the human body.