Biochem 1.3 Acid-Base Chemistry of Amino Acids
43 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the charge of an amino acid backbone at physiological pH?

  • Negative charge
  • Positive charge
  • Variable charge depending on the side chain
  • Neutral charge (correct)

Which group tends to become positively charged when the pH is low?

  • Side chain groups
  • Amino groups (correct)
  • Carboxyl groups
  • Zwitterion groups

Which of the following amino acids is classified as ionizable?

  • Arginine (correct)
  • Glycine
  • Serine
  • Alanine

What effect does increasing the pH have on the carboxyl and amino groups of an amino acid?

<p>Both groups lose protons (B)</p> Signup and view all the answers

Which statement best describes the ionization state of amino acids at high pH?

<p>They are predominantly anions (C)</p> Signup and view all the answers

Which amino acids have the potential to carry a negative charge at physiological pH?

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

What happens to amino acids at low pH?

<p>They gain protons and may become cations (D)</p> Signup and view all the answers

Which of the following options is NOT an ionizable amino acid?

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

What is the average charge of histidine at its isoelectric point of 7.8?

<p>0 (B)</p> Signup and view all the answers

What is the predominant ionization state of histidine between the pH values of 6.0 and 9.6?

<p>0 (C)</p> Signup and view all the answers

How is the isoelectric point (pI) of an amino acid determined?

<p>By averaging the pKa values of the acidic and basic groups. (C)</p> Signup and view all the answers

What happens to the average charge of histidine as the pH decreases?

<p>The average charge increases. (D)</p> Signup and view all the answers

Which of the following statements about histidine at its isoelectric point is true?

<p>The charged forms of histidine equalize, resulting in a net charge of zero. (A)</p> Signup and view all the answers

What effect does an adjacent negative charge have on a carboxyl group in terms of proton acceptance?

<p>It increases the likelihood of proton acceptance. (D)</p> Signup and view all the answers

Which ionizable amino acids are typically positively charged when protonated?

<p>Arg, Lys, His (B)</p> Signup and view all the answers

When deprotonated, which ionizable amino acids become negatively charged?

<p>Tyr, Cys, Glu, Asp (C)</p> Signup and view all the answers

Which statement about serine and threonine is true in the context of ionization?

<p>They are typically omitted from the list of ionizable amino acids. (A)</p> Signup and view all the answers

What largely determines the protonation state of an ionizable amino acid side chain?

<p>The local environmental context of the amino acid. (D)</p> Signup and view all the answers

What type of ionizable side chains can be neutral or positive depending on their protonation state?

<p>Side chains containing nitrogen. (B)</p> Signup and view all the answers

Which of the following statements is false regarding the percent ionization of a chemical group?

<p>A single ionizable site can be partially protonated. (A)</p> Signup and view all the answers

How does an alcohol group behave when placed near a positive charge?

<p>It loses a proton and becomes more acidic. (D)</p> Signup and view all the answers

Which amino acids are neutral when protonated?

<p>Tyr, Cys, Glu, Asp (B)</p> Signup and view all the answers

What is the primary factor for determining the charge of side chains that contain oxygen or sulfur?

<p>Protonation state. (D)</p> Signup and view all the answers

What occurs to the percentage of deprotonated groups as pH increases?

<p>It increases. (C)</p> Signup and view all the answers

At what pH is the population of a protonated ionizable group 50%?

<p>pH = pKa (B)</p> Signup and view all the answers

Which statement is true when pH is below the pKa of an ionizable group?

<p>More than 50% of the population is protonated. (C)</p> Signup and view all the answers

What is the approximate pKa value of the α-carboxyl group in amino acids?

<p>2.2 (C)</p> Signup and view all the answers

According to the equation pH = pKa + log[A⁻]/[HA], what does [A⁻] represent?

<p>Concentration of deprotonated form (B)</p> Signup and view all the answers

Which side chain has the highest pKa value among the ionizable side chains listed?

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

What happens to the protonation state of an amino acid when the pH is raised above its pKa?

<p>More than 50% of the population becomes deprotonated. (A)</p> Signup and view all the answers

What is the pKa value of the histidine side chain?

<p>6.0 (B)</p> Signup and view all the answers

Which factor directly affects the protonation state of an ionizable group?

<p>pH of the solution (C)</p> Signup and view all the answers

What can be concluded when the pH is exactly the same as the pKa?

<p>The concentration of protonated and deprotonated forms is equal. (C)</p> Signup and view all the answers

What does the equation $pH = pK_a + log\frac{[A^-]}{[HA]}$ express?

<p>The relationship between pH, pK_a, and the concentrations of protonated and deprotonated forms. (B)</p> Signup and view all the answers

How can the percent ionization of an amino acid be calculated?

<p>% ionization = $\frac{[HA]}{[A^-] + [HA]}$ × 100% (A), % ionization = $\frac{[A^-]}{[A^-] + [HA]}$ × 100% (C)</p> Signup and view all the answers

What does the isoelectric point (pI) of an amino acid represent?

<p>The pH at which the population of amino acids has an average net charge of 0. (A)</p> Signup and view all the answers

At what pH is histidine predominantly positive?

<p>Below pH 6.0 (B)</p> Signup and view all the answers

How does pH impact the net charge of amino acid populations?

<p>Decreasing pH can create net positive charges in amino acids. (A)</p> Signup and view all the answers

What occurs to histidine molecules at physiological pH?

<p>Most histidine molecules are neutral with a slight positive charge on average. (C)</p> Signup and view all the answers

To calculate the pI of any amino acid, you average which two values?

<p>The pKa below which the amino acid is predominantly positive and the pKa above which it is predominantly negative. (D)</p> Signup and view all the answers

In what scenario can a population of amino acids collectively have a net negative charge?

<p>By sufficiently increasing the pH. (D)</p> Signup and view all the answers

What is a characteristic of amino acids at low pH?

<p>They tend to be predominantly positively charged. (B)</p> Signup and view all the answers

When examining amino acid ionization, which is an important factor?

<p>The surrounding environmental conditions, such as pH. (A)</p> Signup and view all the answers

Flashcards

Ionizable Groups

Chemical groups that can gain or lose protons, resulting in a change in charge. These groups are crucial for acid-base reactions and can be either positively charged (cations) or negatively charged (anions).

Amino Acid Acid-Base Chemistry

Amino acids can participate in acid-base reactions by donating or accepting protons (H+). This ability is crucial for their function and depends on the surrounding environment, particularly the pH.

Zwitterion

A molecule with both a positive and a negative charge, making it electrically neutral overall. This is the typical state of amino acids at physiological pH.

Backbone Ionizable Groups

The amino group (NH2) and the carboxyl group (COOH) are both ionizable, meaning they can gain or lose protons, changing their charge at different pH values.

Signup and view all the flashcards

Ionizable Side Chains

The specific side chains of certain amino acids can also become protonated or deprotonated, contributing to their unique properties and roles in biological systems.

Signup and view all the flashcards

pH Effect on Protonation

The pH of the environment influences the protonation states of the amino acid. Low pH favors protonation, resulting in a positive charge, while high pH favors deprotonation, leading to a negative charge.

Signup and view all the flashcards

Acidic Conditions (Low pH)

At low pH, the backbone of an amino acid is more likely to be protonated, resulting in an overall positive charge. This is because there are more free protons available in the environment.

Signup and view all the flashcards

Basic Conditions (High pH)

At high pH, the backbone of an amino acid is more likely to be deprotonated, resulting in an overall negative charge. This is due to fewer free protons available in the environment.

Signup and view all the flashcards

Acidity/Basicity

The tendency of a chemical group to lose or gain protons (H+).

Signup and view all the flashcards

Protonated

The state where an ionizable group has gained a proton (H+).

Signup and view all the flashcards

Deprotonated

The state where an ionizable group has lost a proton (H+).

Signup and view all the flashcards

Environmental Influence on Acidity/Basicity

The environment around a chemical group can influence its tendency to donate or accept protons, thus affecting its acidity or basicity.

Signup and view all the flashcards

pKa

The pH at which half of a population of ionizable groups are protonated and half are deprotonated.

Signup and view all the flashcards

Nitrogen-Containing Ionizable Amino Acids

The ionizable amino acids with side chains containing nitrogen. These can be positively charged when protonated (e.g., Arg, Lys, His) or neutral when deprotonated.

Signup and view all the flashcards

Oxygen/Sulfur-Containing Ionizable Amino Acids

The ionizable amino acids with side chains containing oxygen or sulfur. These can be neutral when protonated (e.g., Tyr, Cys, Glu, Asp) or negatively charged when deprotonated.

Signup and view all the flashcards

Percent Ionization

The percentage of ionizable groups in a population that are protonated or deprotonated.

Signup and view all the flashcards

Protonation/Deprotonation

The process of changing an amino acid's charge by adding or removing a proton (H+).

Signup and view all the flashcards

pH and Protonation

Higher pH values favor deprotonation, leading to a higher proportion of the ionizable group in its deprotonated form.

Signup and view all the flashcards

Ionizable Groups in Amino Acids

The amino and carboxyl groups in the backbone of amino acids are ionizable and their protonation state depends on the pH.

Signup and view all the flashcards

pKa Values of Amino Acid Backbones

The pKa values of the backbone amino and carboxyl groups are approximately 9.6 and 2.2, respectively. These values can vary slightly depending on the side chain.

Signup and view all the flashcards

pKa Values of Ionizable Side Chains

The pKa values of ionizable side chains range from 3.7 to 12.5. These values can be used to predict the protonation state of a specific amino acid at a given pH.

Signup and view all the flashcards

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation can be used to calculate the ratio of protonated to deprotonated forms of an ionizable group at a given pH.

Signup and view all the flashcards

Below pKa

At a pH below the pKa, an ionizable group is more likely to be protonated (accept a proton).

Signup and view all the flashcards

Above pKa

At a pH above the pKa, an ionizable group is more likely to be deprotonated (lose a proton).

Signup and view all the flashcards

Protonation and Protein Function

The protonation state of an ionizable group can significantly impact the structure, function, and interactions of a protein.

Signup and view all the flashcards

Isoelectric Point (pI)

The pH at which an amino acid exists in its electrically neutral form, with an equal number of positive and negative charges.

Signup and view all the flashcards

Average Charge of an Amino Acid

The average charge of an amino acid molecule at a given pH, taking into account the protonation states of its ionizable groups.

Signup and view all the flashcards

Study Notes

Acid-Base Chemistry of Amino Acids

  • Amino acids can exchange protons with their environment
  • Protonation/deprotonation affects chemical groups
  • Ionizable groups can become positive or negative
  • Amino acids have at least two ionizable groups: backbone amino and carboxyl
  • Zwitterion: neutral state at physiological pH (protonated amino group, deprotonated carboxyl group, net charge of 0)
  • pH adjustments change protonation states
    • Lower pH: more protons available, carboxyl and amino groups more likely to be protonated, overall positive charge
    • Higher pH: fewer free protons, carboxyl and amino groups more likely to be deprotonated, overall negative charge

Ionizable Amino Acid Side Chains

  • Side chains of many amino acids are electrically neutral at physiological pH
  • Some side chains can become charged (positive or negative)
  • Ionizable amino acids: arginine, lysine, histidine, tyrosine, cysteine, glutamate, aspartate
  • Side chain ionization affected by environment
    • Negative charge nearby: carboxyl group more likely to accept a proton, becoming more basic
    • Positive charge nearby: alcohol more likely to lose a proton, becoming more acidic

Amino Acid Percent Ionization

  • Percentage of ionizable groups in a population that are protonated depends on the pKa (the pH at which 50% of the ionizable group is protonated/deprotonated) and the pH of the solution
  • Lower pH than pKa: More likely to be protonated
  • Higher pH than pKa: More likely to be deprotonated

Isoelectric Points (pI)

  • The pH at which an amino acid population has an average net charge of zero (each positive charge balances out a negative charge)
  • Calculated by averaging pKa values where amino acid is predominantly positive and negative
  • Histidine example: pI = (6.0 + 9.6) / 2 = 7.8

Amino Acid Titration Curves

  • Titration: Solution of amino acid brought to a low pH, strong base (NaOH) added gradually, pH plotted against amount of base added
  • Reveals identity of unknown amino acids
  • Buffer regions: pH ranges around pKa values where the amount of base added does not result in a large change in pH

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Acid-Base Chemistry of Amino Acids PDF

Description

Explore the intricate acid-base chemistry of amino acids and their protonation states in various pH environments. This quiz covers the characteristics of zwitterions and the ionizable side chains of amino acids, which affect their overall charge. Understand the significance of ionizable groups in biochemical contexts.

More Like This

cours de Raussens
100 questions

cours de Raussens

ExcellentObsidian639 avatar
ExcellentObsidian639
Structure of Amino Acid 1-A: Aliphatic Amino Acids Quiz
5 questions

Structure of Amino Acid 1-A: Aliphatic Amino Acids Quiz

WellMadeCadmium avatar
WellMadeCadmium
Propriétés et pI des acides aminés
8 questions

Quiz sur le pI des acides aminés

CourageousEuphoria3518 avatar
CourageousEuphoria3518
Use Quizgecko on...
Browser
Open
Browser
Browser