Amino Acids
45 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

Which amino acid is unique due to its lack of chirality?

  • Methionine
  • Glycine (correct)
  • Proline
  • Tyrosine

In what part of a protein would you most likely find amino acids with non-polar side chains?

  • Located on the ends of the protein interacting with hydrophilic molecules.
  • Concentrated in the active site for substrate binding.
  • Exposed on the protein surface interacting with water.
  • Buried in the core, away from water. (correct)

Which amino acid is commonly found in combination with glycine at polypeptide turns?

  • Alanine
  • Proline (correct)
  • Serine
  • Tryptophan

Which of the following is a post-translational modification that can occur on tyrosine?

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

Which of the amino acids listed contains sulfur in its side chain?

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

Why is it important to focus of comparing and contrasting all amino acids instead of assigning them to the specific group?

<p>Categorization results in losing the specific details of the many other ways to group amino acids. (D)</p> Signup and view all the answers

Which of the following is not an effective way to subdivide amino acids?

<p>Charged with Hydrogen (B)</p> Signup and view all the answers

What is the probable composition of amino acids with non-polar side chains?

<p>Mainly hydrocarbon side chains. (A)</p> Signup and view all the answers

Which of the following is the predominant form of the carboxyl group of an amino acid at pH 3.0, given its typical pKa is around 2.0?

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

Why do triprotic amino acids exhibit three buffering regions in their titration curves?

<p>Because they have an alpha-amino group, an alpha-carboxyl group, and an ionizable R-group. (B)</p> Signup and view all the answers

An amino acid has a pKa of 6.0. At what pH will the concentrations of the protonated and unprotonated forms of the amino acid be equal?

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

Which statement accurately describes the charge state of aspartate at physiological pH (7.4)?

<p>Aspartate carries a net negative charge. (D)</p> Signup and view all the answers

Consider an amino acid with an ionizable side chain. If the pKa of the side chain is 4.0, what would be the approximate ratio of the deprotonated form (A-) to the protonated form (HA) at pH 6.0?

<p>100:1 (A)</p> Signup and view all the answers

Which amino acids are commonly phosphorylated by kinases?

<p>Tyrosine, Serine, and Threonine (A)</p> Signup and view all the answers

What is the role of phosphatases in relation to phosphorylation?

<p>They remove phosphoryl groups from proteins. (B)</p> Signup and view all the answers

What type of bond is formed between two cysteine residues, and what process is involved in its formation?

<p>Disulfide bond; oxidation (B)</p> Signup and view all the answers

Why are disulfide bonds important for protein structure?

<p>They stabilize the protein structure. (D)</p> Signup and view all the answers

Which of the following is a characteristic of lysine and arginine at physiological pH?

<p>They always carry a +1 net charge. (B)</p> Signup and view all the answers

What property of histidine allows it to serve as a proton acceptor/donor in enzymatic reactions?

<p>Its imidazole group's pKa being near physiological pH. (B)</p> Signup and view all the answers

What is a key requirement for cysteine residues to form a disulfide bond within a protein structure?

<p>They must be in close proximity in space. (B)</p> Signup and view all the answers

Which of the following best describes post-translational modification?

<p>The covalent modification of amino acids after their incorporation into a protein. (B)</p> Signup and view all the answers

Why is the diversity of sequences important when constructing proteins from amino acids?

<p>It allows for a vast number of molecules with varying lengths and sequences, enabling a wide range of functions. (D)</p> Signup and view all the answers

What is the primary reason that proteins are constructed as polymers of smaller building blocks, such as amino acids?

<p>To simplify chemistry through common reactions for polymerization and degradation, enable recycling, and achieve vast molecular diversity. (C)</p> Signup and view all the answers

Considering the general structure of amino acids, which component is primarily responsible for the unique characteristics that differentiate each of the 20 standard amino acids?

<p>The side chain (R group). (D)</p> Signup and view all the answers

Why are proteins in living organisms almost exclusively composed of L-amino acids rather than a mix of L- and D-amino acids?

<p>The enzymes that synthesize proteins are stereospecific for L-amino acids. (B)</p> Signup and view all the answers

If a scientist is studying a protein composed of 50 amino acid residues, what is the maximum possible number of different sequences that this protein could theoretically have, assuming any of the 20 standard amino acids can be at each position?

<p>$20^{50}$ (D)</p> Signup and view all the answers

Which of the following is NOT a direct advantage of constructing biomolecules as polymers of smaller building blocks?

<p>Increased structural complexity of individual building blocks. (B)</p> Signup and view all the answers

An amino acid is in a solution where the pH is significantly higher than its pKa values for both its amino and carboxyl groups. What would be the predominant net charge of the amino acid in this solution?

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

A researcher discovers a new peptide consisting of four amino acid residues. How many different peptides can be generated using the 20 standard amino acids, considering the sequence?

<p>160,000 (C)</p> Signup and view all the answers

If an amino acid has pKa values of 2.0 and 9.0, around what pH would it have a net charge of zero?

<p>5.5 (A)</p> Signup and view all the answers

Which of the following occurs when the pH of a solution containing an amino acid is significantly lower than its pKa for the carboxyl group?

<p>The carboxyl group is predominantly protonated (COOH). (D)</p> Signup and view all the answers

What is the primary characteristic of an amino acid at its isoelectric point (pI)?

<p>It has a net charge of zero. (B)</p> Signup and view all the answers

Consider an amino acid with an ionizable side chain. How is its pI determined?

<p>By averaging the two pKa values that are on either side of the neutral species. (D)</p> Signup and view all the answers

At a pH above the pKa of an amino group, which form of the amino group will predominate?

<p>NH2 (C)</p> Signup and view all the answers

Which of the following best describes a zwitterion?

<p>A molecule with both positive and negative charges, resulting in a net charge of zero. (A)</p> Signup and view all the answers

An amino acid is in a solution where the pH is equal to its pKa. What does this indicate about the concentrations of the protonated and unprotonated forms of the relevant functional group?

<p>The concentrations of the protonated and unprotonated forms are equal. (A)</p> Signup and view all the answers

An amino acid's carboxyl group has a pKa of 2.0. If the pH of a solution containing the amino acid is 4.0, what can be concluded about the ratio of [COO-] to [COOH]?

<p>The ratio is approximately 100:1 ([COO-]:[COOH]). (B)</p> Signup and view all the answers

For a diprotic amino acid, how is the isoelectric point (pI) typically calculated?

<p>pI = (pKa1 + pKa2) / 2 (A)</p> Signup and view all the answers

What determines the similarity in titration curves and pI values between glutamate and aspartate?

<p>They both possess two titratable protons within a similar pKa range. (B)</p> Signup and view all the answers

Histidine's pI is calculated using which of the following pKa values?

<p>pKaR and pKa2 (C)</p> Signup and view all the answers

If an amino acid has pKa1 = 2.0, pKa2 = 9.0, and pKaR = 4.0, which pKa values would you use to calculate the pI?

<p>pKa1 and pKaR (C)</p> Signup and view all the answers

An unknown amino acid is titrated. The titration curve reveals pKa values of 3.1 and 8.2. What is the approximate pI of this amino acid?

<p>5.65 (D)</p> Signup and view all the answers

Consider an amino acid with a positively charged side chain. The relevant pKa values are pKa1 = 2.0, pKa2 = 9.0, and pKaR = 6.0. Which calculation correctly determines the pI?

<p>pI = (6.0 + 9.0)/2 (A)</p> Signup and view all the answers

Which characteristic of amino acids is most directly responsible for their ability to act as buffers?

<p>The presence of both an amino and a carboxyl group (B)</p> Signup and view all the answers

How would the titration curve of an amino acid with an acidic side chain (like glutamate) differ from that of an amino acid with a non-ionizable side chain (like alanine)?

<p>The acidic amino acid would display an additional buffering region. (C)</p> Signup and view all the answers

Flashcards

Amino Acids

Amino acids are the basic building blocks of proteins.

Proteins as Polymers

Proteins are linear polymers constructed from amino acids.

Standard Amino Acids

There are 20 standard amino acids that make up all proteins in living organisms.

Advantages of Polymers

Simple chemistry, recycling of components, and diversity of resulting molecules.

Signup and view all the flashcards

Amino Acid Structure

A central carbon atom bonded to a hydrogen atom, an amino group, a carboxyl group, and a variable side chain (R group).

Signup and view all the flashcards

Amino Acid Side Chain

The 'R' group attached to the central carbon atom that varies between different amino acids.

Signup and view all the flashcards

Chiral Center

A carbon atom bonded to four different groups.

Signup and view all the flashcards

Stereoisomers

L and D isomers.

Signup and view all the flashcards

Negatively Charged Amino Acids

Aspartate and glutamate have a net charge of -1 at physiological pH.

Signup and view all the flashcards

Umami and Glutamate

Umami is one of the five basic tastes and glutamate is responsible for it.

Signup and view all the flashcards

Amino Acid Acid/Base Properties

Amino acids have at least two groups that can accept or donate protons: the alpha-carboxyl group and the alpha-amino group. Triprotic amino acids have ionizable groups in their side chains.

Signup and view all the flashcards

pKa Definition

The pH at which the group changes its protonation state.

Signup and view all the flashcards

pH vs pKa

When pH < pKa, the protonated form (HA) dominates. When pH > pKa, the unprotonated form (A-) dominates.

Signup and view all the flashcards

Amino Acid Groups

Amino acids categorized by side chain properties: Non-polar aliphatic, Aromatic, Polar uncharged, Polar positively charged, Polar negatively charged.

Signup and view all the flashcards

Non-polar Aliphatic Amino Acids

Side chains mainly consist of hydrocarbons. Typically found in the protein's core.

Signup and view all the flashcards

Proline's Location

Often found at polypeptide turns, frequently paired with glycine.

Signup and view all the flashcards

Glycine's Unique Structure

Smallest amino acid, and the only one that isn't chiral.

Signup and view all the flashcards

Methionine

Contains a sulfur atom in its side chain.

Signup and view all the flashcards

Essential Amino Acid Details

Knowing full name, 3-letter code, 1-letter code, and structure diagram.

Signup and view all the flashcards

Aromatic Amino Acids

Contain ring structures. Histidine can also be considered aromatic.

Signup and view all the flashcards

Tyrosine Modification

Can undergo post-translational modification through phosphorylation.

Signup and view all the flashcards

Phosphorylation

A mechanism to regulate protein function by adding a phosphoryl group.

Signup and view all the flashcards

Kinases

Enzymes that add phosphoryl groups to specific amino acids with hydroxyl groups.

Signup and view all the flashcards

Phosphatases

Enzymes that remove phosphoryl groups.

Signup and view all the flashcards

Amino Acids for Phosphorylation

Serine, Threonine, and Tyrosine.

Signup and view all the flashcards

Post-translational Modification

Covalent modifications to amino acids after protein synthesis. Phosphorylation is a key example.

Signup and view all the flashcards

Disulfide Bond

A covalent linkage formed by the oxidation of two cysteine residues.

Signup and view all the flashcards

Function of Disulfide Bonds

Stabilize protein structures by linking parts of the protein chain.

Signup and view all the flashcards

Positively Charged Amino Acids

Lysine and Arginine.

Signup and view all the flashcards

Zwitterion

A molecule with both positive and negative charges, resulting in a net charge of zero.

Signup and view all the flashcards

Isoelectric Point (pI)

The pH at which a molecule carries no net electrical charge.

Signup and view all the flashcards

Calculating pI

The average of the pKa values that surround the neutral species (zwitterion).

Signup and view all the flashcards

Carboxylic acid at pH 7.4

At physiological pH (7.4), carboxylic acids are deprotonated, existing as negatively charged carboxylates (COO-).

Signup and view all the flashcards

Amino group at pH 7.4

At physiological pH (7.4), amino groups are protonated existing as positively charged ammonium ions (NH3+).

Signup and view all the flashcards

Titration Curve

A graph showing the change in pH of a solution as acid or base is added, revealing pKa values.

Signup and view all the flashcards

What is the isoelectric point (pI)?

The pH at which a molecule carries no net electrical charge.

Signup and view all the flashcards

How to calculate pI for diprotic amino acids?

pI = (pKa1 + pKa2) / 2

Signup and view all the flashcards

What are diprotic amino acids?

Amino acids with two titratable protons.

Signup and view all the flashcards

What is the topic name?

Amino Acids-Titration of Glutamate.

Signup and view all the flashcards

How to calculate pI for Glutamate?

pI = (pKa1 + pKaR) / 2

Signup and view all the flashcards

What is the topic name?

Amino Acids-Titration of Histidine.

Signup and view all the flashcards

How to calculate pI for Histidine?

pI = (pKaR + pKa2) / 2

Signup and view all the flashcards

Titration curves and pIs?

Titration curves and pIs would be quite similar.

Signup and view all the flashcards

Study Notes

  • Amino acids are the building blocks of proteins.
  • Proteins are linear polymers of amino acids.
  • All proteins are produced from 20 standard amino acids found in all living organisms.
  • Diversity of sequences is enabled by twenty building blocks.
  • A peptide of three residues can be produced 8000 ways.
  • A protein of 100 residues has 1.3 X 10^130 possible sequences.
  • Proteins are linear polymers of amino acid building blocks.
  • Biomolecules are created as polymers of smaller building blocks. The advantages include:
    • Simplicity of chemistry where there is one type of reaction for polymerization and a second type for degradation.
    • Recycling where Biomolecules can be digested back to component building blocks which are reusable for production of other biomolecules.
    • Diversity is present as a result of the vast number of molecules of varying lengths and sequences.
  • Common features of amino acids are Hydrogen, a Central Alpha Carbon, an Amino group, and a Carboxyl group.
  • The 20 amino acids differ in their side chain (R) groups.
  • The side chains define the unique characteristics of each amino acid.
  • For all amino acids except glycine, the alpha carbon is bonded to four different groups and creates a chiral center.
  • Stereoisomers are labelled as the L and D isomers and are the products of four different groups occupying unique spatial arrangements.
  • Proteins are made almost exclusively from L amino acids.
  • Amino acids are grouped based on the properties of their side chains:
    • Non-polar aliphatic
    • Aromatic
    • Polar, Uncharged
    • Polar, Positively Charged
    • Polar, Negatively Charged
  • While the groupings provide a way to sub-divide the amino acids, these groupings are man-made and there are many other ways to group amino acids.
  • It is important to be able to compare and contrast all the amino acids rather than assign them to specific groups.

Nonpolar, Aliphatic Amino Acids

  • Main hydrocarbon side chains.
  • The residues with non-polar chains are often buried in the core of a protein.
  • Proline if often found at polypeptide turns, usually in combination with glycine.
  • Glycine is the smallest amino acid and the only one which is not chiral.
  • Methionine is one of two amino acids with a sulfur group within its side chain.

Aromatic Amino Acids

  • Histidine can also be considered as an aromatic.
  • Tyrosine can be post-translation modified through phosphorylation.
  • Phosphorylation is a mechanism to regulate protein function.
  • Other amino acids with hydroxyl groups, Serine and Threonine, can also be phosphorylated.
  • Tryptophan, a precursor of serotonin, became a popular supplement in the 1980s.
  • Tryptophan was banned by the FDA due to a disease-outbreak among users.

Post-translational Modification of Amino Acids

  • Amino acids can be covalently modified after their incorporation into a protein.
  • Phosphorylation is a central example of post-translational modification.
  • Phosphoryl groups are added by kinases to specific, hydroxyl-group containing amino acids (Tyr, Ser and Thr).
  • Modifications are often reversible, and the phosphoryl group can be removed by phosphatases.

Polar, Uncharged Amino Acids

  • Serine and Threonine can undergo phosphorylation of their hydroxyl groups.
  • Two cysteines can form a covalent linkage called a disulfide bond.

Disulfide Bonds of Cysteine

  • Disulfide bonds form through the oxidation of the sulfhydryl groups of two cysteine residues to form a covalent linkage.
  • Disulfides stabilize protein structures.
  • Cysteine residues forming a disulfide bond must be in close proximity in space within the protein structure.
  • Disulfide bonds can be inter or intra-molecular.

Positively Charged Amino Acids

  • Lys and Arg always carry a +1 net charge at physiological pH.
  • Histidine's imidazole group has a pKa near physiological pH such that a fraction of cellular histidines will be +1 and the rest will carry a net charge of 0.
  • His serves as a proton acceptor/donor in many enzymatic reactions.

Negatively Charged Amino Acids

  • Aspartate and Glutamate carry a net charge of -1 at physiological pH.
  • Glutamate is responsible for one of the five basic tastes (umami).
  • Glutamate is used as a flavor enhancer as monosodium glutamate (MSG).

Acid/Base Properties of AA

  • Every amino acid has at least two groups that accept and donate protons (diprotic).
  • All amino acids have the alpha carbon carboxyl group and amino groups.
  • Triprotic amino acids have ionizable groups in their side chains (Lys, Arg, His, Asp, Glu, Cys and Tyr).
  • Diprotics have two buffering regions and triprotics have three buffering regions.
  • Ionizable groups in the amino acids include carboxyl group, amino group, and side chains of the triprotic amino acids.
  • Each ionizable group has a specific pKa. This is the pH at which that group changes its protonation state.
  • When pH is below the pKa, the protonated form predominates (HA).
  • When pH is above the pKa, the unprotonated form predominates (A-).
  • All amino acids have both carboxyl (pKa ~2.0) and an amino (pKa ~10.0) groups.
  • At pH 7.4 these groups will be in the COO- and NH3+ forms.
  • The dipolar ion of an amino acid is called a zwitterion.
  • The isoelectric point (pI) of an amino acid is the pH at which the net charge on the molecule is equal to zero.
  • pI is the average of the pKas on either side of where the net charge is equal to zero.
  • All diprotics would have similar titration curves and pIs.

Studying That Suits You

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

Quiz Team

Related Documents

Chapter 3 Amino Acids, Peptides and Proteins - Lecture Slides PDF

Description

Questions about amino acids, their properties, and behavior in proteins. Includes chirality, post-translational modifications, and titration curves. This set of questions covers the core concepts of amino acids.

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser