Immunoglobulins and Amino Acid Structure

Questions and Answers

What characterizes free amino acids at physiologic pH of 7.4 in solution?

They exist solely as cations.

They are only in peptide linkage.

They exist as zwitterions. (correct)

They do not participate in hydrogen bonding.

How does glycine's side chain affect its function in proteins?

It minimizes steric hindrance. (correct)

It allows for extensive hydrogen bonding.

It adds significant steric hindrance.

It causes strong electrostatic interactions.

What is true about the carboxyl and amino groups in peptide linkages?

They can only form hydrogen bonds.

They are entirely free to engage in chemical reactions.

They exist as zwitterions in peptide chains.

They are unavailable for chemical reactions. (correct)

Which classification describes amino acids based on their side chains?

Based on polarity and structural features. Signup and view all the answers

What role does glycine primarily play in protein structures?

It is often found in tightly packed chains. Signup and view all the answers

Which statement about amino acids is incorrect?

Polar amino acids do not form hydrogen bonds. Signup and view all the answers

What is a major feature of zwitterionic amino acids?

They carry both a positive and negative charge simultaneously. Signup and view all the answers

Which of the following statements is accurate regarding the amino acids' side chains?

The nature of side chains dictates the functional roles of amino acids. Signup and view all the answers

What is the importance of amino acid classification?

It aids in understanding metabolic pathways and functional roles. Signup and view all the answers

At which pH value does alanine predominantly exist as form II, with a net charge of zero?

pH 7 Signup and view all the answers

What happens when the pH equals pK2 for alanine?

Forms II and III are equal in amount in solution Signup and view all the answers

Which pairs act as buffers in the titration of alanine?

-COOH/-COO- and -NH3+/-NH2 Signup and view all the answers

Which group in amino acids has a dissociable proton at the carboxyl terminal?

COOH group Signup and view all the answers

What characteristic of amino acids is described as amphoteric substances?

They can act as either an acid or a base Signup and view all the answers

Which of the following does not participate in the titration of alanine?

Side chain of alanine Signup and view all the answers

Which amino acid has a side chain that contains a hydroxyl group allowing it to engage in hydrogen bonds?

Tyrosine Signup and view all the answers

Which of the following amino acids is characterized by a nonpolar hydrophobic side chain that lacks substituents?

Phenylalanine Signup and view all the answers

What characteristic makes tryptophan more polar than phenylalanine?

It has an indole ring with nitrogen. Signup and view all the answers

Which amino acid serves as a site for attachment of oligosaccharide chains in glycoproteins?

Asparagine Signup and view all the answers

Which of the following amino acids is least likely to have its side chain located on the surface of water-soluble globular proteins?

Tryptophan Signup and view all the answers

What common feature do serine and threonine share that allows them to serve as sites of attachment?

A polar hydroxyl group Signup and view all the answers

When at alkaline pH, which property is true of tyrosine?

It can lose a proton. Signup and view all the answers

Which amino acids fall into the category of aliphatic, polar, and uncharged amino acids?

Asparagine and Glutamine Signup and view all the answers

Which property of serine makes it an important component in enzyme active sites?

It can form hydrogen bonds. Signup and view all the answers

Which of the following correctly describes the properties of hydroxyl and amide groups in amino acids?

They allow for hydrogen bonding with polar molecules. Signup and view all the answers

Which statement about histidine's side chain is correct?

It has an imidazole ring that allows for charge variation. Signup and view all the answers

What is the primary amino group location in lysine?

On the epsilon carbon. Signup and view all the answers

How does the side chain of arginine contribute to protein interactions?

Through ionic bonds with negatively charged compounds. Signup and view all the answers

Which basic amino acid is recognized for its ability to form ionic bonds effectively?

Histidine and lysine. Signup and view all the answers

What role do the positive charges of basic amino acids play in proteins?

They enable the formation of ionic bonds with negatively charged groups. Signup and view all the answers

At physiological pH, how are the side chains of lysine and arginine characterized?

Fully ionized and positively charged. Signup and view all the answers

Which of the following statements regarding hydrogen bonding in amino acids is true?

It involves basic amino acids forming bonds with acidic residues. Signup and view all the answers

What characteristic of histidine allows it to serve different roles in protein function?

Ability to exist in a charged or neutral state. Signup and view all the answers

Which amino acids primarily form ionic bonds and salt bridges with negatively charged groups?

Lysine and arginine. Signup and view all the answers

The charges on amino acid side chains at physiological pH depend on what property?

The pKa of the acidic and basic groups. Signup and view all the answers

Which of the following statements accurately describes the characteristics of branched chain amino acids?

They possess bulky, nonpolar, aliphatic side chains that cluster to form hydrophobic cores. Signup and view all the answers

What structural feature of proline contributes to its unique behavior in protein structures?

It contains a rigid ring that includes its α-carbon and α-amino group. Signup and view all the answers

How do hydrophobic amino acids primarily promote their association within proteins?

By clustering together to form hydrophobic cores via van der Waals forces. Signup and view all the answers

What is the significance of the electron sharing in the side chains of nonpolar amino acids?

It results in equal sharing of electrons, inhibiting hydrogen bonding with water. Signup and view all the answers

What type of interaction is primarily responsible for the association of branched chain amino acid side chains?

Van der Waals forces between closely packed atoms. Signup and view all the answers

Which of the following properties do aromatic amino acids share due to their structure?

Their polarity is determined by the substituents on their aromatic rings. Signup and view all the answers

What role does proline play in the structure of collagen?

It contributes to the fibrous structure by causing kinks in the backbone. Signup and view all the answers

Why are branched chain amino acids considered oily or lipid-like?

Their hydrophobic nature promotes lipid-like interactions. Signup and view all the answers

What structural characteristic distinguishes aromatic amino acids from other amino acids?

Presence of a six-membered carbon-hydrogen ring with conjugated double bonds. Signup and view all the answers

How do branched chain amino acids enhance protein stability?

By clustering to form hydrophobic environments that reduce exposure to water. Signup and view all the answers

Study Notes

Immunoglobulins and Their Function

Immunoglobulins, also known as antibodies, play a critical role in the immune system by targeting and neutralizing infectious bacteria and viruses.

Structure of Amino Acids

There are 20 amino acids that are the building blocks of proteins.
At physiological pH (7.4), free amino acids exist as zwitterions, with a dissociated carboxyl group (-COO-) and a protonated amino group (-NH3+).
Peptide linkages typically involve the amino and carboxyl groups, making them unavailable for other chemical reactions, except for hydrogen bonds.
The role of an amino acid in proteins is primarily determined by the characteristics of its side chain.

Classification of Amino Acid Side Chains

Amino acids are classified based on polarity and structural features, aiding in the understanding of their functional roles and metabolic pathways.

Nonpolar, Aliphatic Amino Acids

Glycine: Simplest amino acid with a hydrogen side chain; causes minimal steric hindrance, often found in bends or compact chains.
Alanine and Branched Chain Amino Acids: Valine, Leucine, Isoleucine; their bulky nonpolar side chains cluster to form hydrophobic cores in proteins.
Proline: Features a rigid ring structure that induces kinks in peptide backbones, affecting the formation of collagen and interrupting alpha-helices.

Aromatic Amino Acids

Side chains contain aromatic ring structures, contributing to variable polarity based on substituents.
Phenylalanine: Hydrophobic structure with a nonpolar ring; stacks on itself.
Tyrosine: Contains a hydroxyl group, making it polar and hydrophilic, allowing for hydrogen bonding and modifications.
Tryptophan: Complex indole ring that can engage in hydrogen bonding, making it more polar than phenylalanine.

Aliphatic, Polar, Uncharged Amino Acids

Asparagine and Glutamine: Have carbonyl and amide groups, engaging in hydrogen bonding.
Serine and Threonine: Contain polar hydroxyl groups for hydrogen bonding and attachment sites.
Frequent components on water-soluble globular proteins due to their hydrophilic nature.

Basic Amino Acids

Histidine: Weakly basic with an imidazole ring; can be positively charged or neutral depending on pH.
Lysine: Contains a primary amino group, contributing to its basic nature.
Arginine: Contains a guanidinium group; both lysine and arginine form ionic bonds with negatively charged residues.

Interactions and Charges of Amino Acids

Basic amino acids can form ionic bonds with negatively charged groups (e.g., phosphate groups in ATP).
They can also participate in hydrogen bonding and form salt bridges with inorganic ions.

Titration and Charge States

Titration curves illustrate how the charges of amino acids change with pH.
The isoelectric point occurs when an amino acid has a net charge of zero, common in neutral pH.
Amino acids are amphoteric; they can act as acids or bases, a property of importance in biochemical reactions.

Titrable Groups in Proteins

Only the side chains of specific amino acids, as well as the amino- and carboxyl-termini groups, have dissociable protons, affecting their behavior in different environments.

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Description

This quiz covers the roles of immunoglobulins in defending against infectious bacteria and viruses, alongside a detailed exploration of amino acids, their structure, and behavior in physiological pH. Understanding zwitterions and the peptide linkage of amino acids is essential for deeper insights into biochemistry.