Amino Acids Quiz Chapter 2

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Questions and Answers

Which statement accurately describes the side chain of glutamine?

It contains a nonpolar aliphatic group.

It allows for significant protonation at acidic pH.

It has a carbonyl and a polar amide group. (correct)

It is purely hydrophilic.

How does the side chain of serine primarily function in enzymatic reactions?

As a site for phosphorylation and attachment of other groups. (correct)

As a component of the enzyme’s structure that limits reactivity.

As a hydrophobic anchor.

By forming ionic bonds with negatively charged substrates.

What characteristic of tyrosine makes it more likely to engage in hydrogen bonding?

Its lack of a substituent on the ring.

Its purely nonpolar structure.

Its significant hydrophobic nature.

The presence of a hydroxyl group on its phenyl ring. (correct)

In what significant way does threonine's side chain differ from serine's?

Threonine can attach oligosaccharide chains, while serine cannot. Signup and view all the answers

Which aspect of glutamine's structure contributes to its nonpolar character?

Electrons being shared equally in its side chain ring. Signup and view all the answers

Which of the following amino acids has a side chain that can lose a proton at alkaline pH?

Tyrosine Signup and view all the answers

What impact does the polar hydroxyl group have on serine and threonine?

It allows them to act as effective nucleophiles. Signup and view all the answers

What role do the side chains of tyrosine and serine have in enzyme function?

Both can participate in post-translational modifications. Signup and view all the answers

Which lipid group is often attached to plasma membrane proteins?

Palmitoyl Group (C16) Signup and view all the answers

What is the main characteristic of the α-carbon in amino acids?

It is optically inactive in Glycine. Signup and view all the answers

Which statement correctly describes farnesyl and geranyl groups?

Farnesyl is C15 while geranyl is C20. Signup and view all the answers

What role do lipid groups play in membrane proteins?

They interact hydrophobically with membrane lipids. Signup and view all the answers

Which of these options correctly identifies a feature of the myristoyl group?

It is attached to proteins in intracellular vesicle membranes. Signup and view all the answers

Which of the following statements is true about palmitoyl and myristoyl groups?

Myristoyl groups typically associate with intracellular vesicles. Signup and view all the answers

What is a common feature of farnesyl and geranyl groups in membrane proteins?

They are synthesized from isopentenyl pyrophosphate. Signup and view all the answers

How do regulatory modifications impact proteins?

They change the activity of the protein. Signup and view all the answers

What happens to lysine at physiologic pH?

It is fully ionized and positively charged. Signup and view all the answers

Which structural feature distinguishes lysine and arginine?

The presence of a guanidinium group in arginine. Signup and view all the answers

How does the side chain of lysine participate in binding interactions?

By participating in hydrogen bonding and ionic interactions. Signup and view all the answers

What is a key characteristic of arginine's side chain when compared to lysine's?

It has the ability to form salt bridges. Signup and view all the answers

Which property is associated with the side chains of both lysine and arginine?

They contain nitrogen and can be positively charged. Signup and view all the answers

In terms of charge and interaction characteristics, how do lysine and arginine behave in physiological conditions?

Both are positively charged and can engage in ionic bonding. Signup and view all the answers

Which of the following describes a function of the guanidinium group in arginine?

It allows for the formation of ionic interactions with negatively charged molecules. Signup and view all the answers

What type of binding can lysine participate in due to its side chain properties?

Formation of salt bridges with inorganic ions. Signup and view all the answers

What role do calcium ions play in the carboxylation of the γ carbon of glutamate?

They mediate the attachment of proteins to a surface by binding to negatively charged groups. Signup and view all the answers

What happens to the carboxyl group (-COOH) of glutamate when the pH is elevated?

It dissociates, losing a proton to become a carboxylate group (-COO-). Signup and view all the answers

What is a key feature of hydroxyproline in collagen?

It contains an additional OH group that contributes to hydrogen bonding. Signup and view all the answers

Which characteristic defines molecules that assume a dipolar form (zwitterion)?

They contain both positively and negatively charged groups. Signup and view all the answers

Which proteins are specifically mentioned in association with the dissociation of the carboxyl group?

Certain blood clotting proteins. Signup and view all the answers

What is primarily responsible for the dipolar nature of molecules like glutamate at physiological pH?

The presence of multiple protonated and deprotonated groups. Signup and view all the answers

Hydroxylation of which amino acid is crucial for the structural integrity of collagen?

Proline. Signup and view all the answers

Which of the following is most accurate regarding the significance of the γ carbon carboxylation process?

It is critical for binding to extracellular matrix components. Signup and view all the answers

What occurs when the pH is less than the pKa of carboxylic acid groups?

All carboxylic acid groups are protonated. Signup and view all the answers

At which pH does the form II and III of alanine exist in equal amounts?

pK2 Signup and view all the answers

What characterizes alanine at its isoelectric point?

It carries a net charge of zero. Signup and view all the answers

Which buffers are associated with the pK1 and pK2 regions of alanine?

-COOH/-COO for pK1 and -NH3/-NH2 for pK2 Signup and view all the answers

What is true about amino acids at physiologic (nearly neutral) pH?

They are considered amphoteric substances. Signup and view all the answers

Which form of alanine is predominantly present at neutral pH?

Form II Signup and view all the answers

What defines an amphoteric substance in the context of amino acids?

It can donate and accept protons. Signup and view all the answers

What is the net charge of amino acids at physiologic pH?

Can be zero. Signup and view all the answers

Study Notes

Glutamine (Gln, Q) features a side chain with a carbonyl and polar amide group, contributing to its hydrophilic nature.
The side chain of glutamine possesses no substituents and can stack hydrophobically.
Serine (Ser, S) has a polar hydroxyl group on its side chain that serves as an attachment site for groups like phosphates, critical for enzyme active sites.
Tyrosine has a hydroxyl group on the phenyl ring, increasing its polarity and hydrophilicity; can participate in hydrogen bonds and attachment of phosphate groups.
Threonine (Thr, T) also contains a polar hydroxyl group for attachment, notably oligosaccharides in glycoproteins.
Lysine (Lys, K) features a positively charged side chain with a primary amino group that forms ionic bonds at physiological pH.
Arginine (Arg, R) has similar characteristics to lysine, characterized by its guanidinium group.

Properties of Acidic and Basic Amino Acids

Acidic and basic amino acids facilitate hydrogen bonding and salt bridge formation.
Salt bridges involve ionic interactions between negatively charged groups and positively charged ions, e.g., sodium.

Fatty Acylation and Prenylation

Membrane proteins can have covalently attached lipid groups that interact hydrophobically within the membrane.
Palmitoyl (C16) groups frequently attach to plasma membrane proteins.
Myristoyl (C14) groups are commonly found in lipid membranes of intracellular vesicles.
Farnesyl (C15) or Geranyl (C20) groups, synthesized from isoprene units, attach to specific cysteine residues in membrane proteins.

Optical Properties of Amino Acids

All amino acids except glycine possess a chiral α-carbon that is optically active, attached to four different groups.
Glycine is optically inactive due to having two identical substituents on its α-carbon.

Regulatory Modifications of Amino Acids

Carboxylation of the γ-carbon of glutamate plays a role in blood clotting by assisting calcium ion attachment.
Hydroxylation, as seen in collagen, adds OH groups to proline, enhancing hydrogen bonding between polypeptide chains.

Isoelectric Points and pH Effects

Amino acids exist primarily in protonated form at low pH, transitioning to carboxylate forms as pH increases.
At pH equating to pKa, different ionic forms of amino acids are equally represented.
The isoelectric point of alanine occurs at neutral pH, where it predominantly exists as a zwitterion with no net charge.
Amino acids are amphoteric, serving as ampholytes capable of acting as acids or bases depending on environmental pH.

Net Charge of Amino Acids

At physiological pH, amino acids exist as zwitterions, featuring both carboxylate (-COO-) and ammonium (-NH3+) functional groups, resulting in a neutral net charge.

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Description

Test your knowledge on glutamine, serine, tyrosine, threonine, lysine, and arginine in this quiz focusing on their properties and functions. Understand the unique characteristics of acidic and basic amino acids as well. This quiz is perfect for students studying biochemistry or related fields.