Biology: Proteins and Amino Acids

Questions and Answers

What is the primary structural feature that differentiates amino acids from one another?

The R group (correct)

The carboxyl group

The amino group

The α carbon

Which of the following statements about amino acids is true?

All amino acids contain two chiral carbon atoms.

Glycine is the most complex amino acid.

Amino acids have no functional groups.

L-amino acids are the only type manufactured in cells. (correct)

What type of bond links amino acids together in proteins?

Hydrogen bond

Ionic bond

Peptide bond (correct)

Covalent bond

How many amino acids does a tripeptide consist of?

3 Signup and view all the answers

What is the correct classification of a protein that contains 75 amino acids?

Polypeptide Signup and view all the answers

Which amino acid is optically inactive due to its structure?

Glycine Signup and view all the answers

What is the range of amino acids typically found in proteins?

100 to 10,000 Signup and view all the answers

What does the term 'α' in alpha-amino acid refer to?

The position of the amino group relative to the α carbon Signup and view all the answers

Which of the following amino acids is considered essential?

Tryptophan Signup and view all the answers

What characterizes non-essential amino acids?

They can be synthesized by the body. Signup and view all the answers

Which amino acid is achiral?

Glycine Signup and view all the answers

Which group of amino acids does not form hydrogen bonds with water?

Non-polar Amino Acids Signup and view all the answers

What is a characteristic of polar neutral amino acids?

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

Which of the following is true about L-alpha alanine and L-alpha valine?

They possess chiral centers. Signup and view all the answers

Which amino acid has the polar hydrophilic group -OH?

Serine Signup and view all the answers

What distinguishes the properties of polar neutral amino acids from non-polar amino acids?

Polar neutral amino acids contain hydrophilic groups. Signup and view all the answers

Which of the following amino acids is classified as a polar, positively charged amino acid?

Arginine Signup and view all the answers

Which of these amino acids is considered an acidic, polar, negatively charged amino acid?

Glutamic Acid Signup and view all the answers

What type of interaction is mainly exhibited by hydrophobic amino acids like alanine and valine?

Hydrophobic interaction Signup and view all the answers

Which of the following amino acids cannot be synthesized in the body and is therefore essential for nutrition?

Lysine Signup and view all the answers

Which amino acid is characterized by a cyclical amino group and is often found at the beginning of proteins?

Proline Signup and view all the answers

What is the metabolic precursor for cysteine?

Methionine Signup and view all the answers

Which of these amino acids is not classified as a basic amino acid?

Tyrosine Signup and view all the answers

Which interaction occurs when an ionic bond is formed between a basic amino acid and an acidic amino acid?

Ionic interaction Signup and view all the answers

What type of bond is formed when two cysteine molecules are oxidized?

Disulfide bond Signup and view all the answers

Which amino acids are categorized as aromatic?

Phenylalanine, Tryptophan, Tyrosine Signup and view all the answers

At physiological pH, which form do amino acids predominantly take?

Zwitterion form Signup and view all the answers

What is the result of a peptide bond formation?

A covalent bond and the release of water Signup and view all the answers

What happens to the carboxylic group of amino acids at a lower pH?

It gains a proton and becomes positively charged Signup and view all the answers

Which charge do amino acids have at their isoelectric point (pI)?

No overall charge Signup and view all the answers

In electrophoresis, what direction do positively charged amino acids move?

Toward the anode Signup and view all the answers

Which interaction is characterized as a weak attractive force between aromatic rings?

Stacking interaction Signup and view all the answers

Study Notes

What are Proteins?

Large molecules composed of long chains of amino acids.
Proteins play key roles in various body functions and processes.
Name originates from the Greek word "Proteios," meaning "holding first place."

Structure of Proteins

Proteins are chains of amino acids, classified by their length:
- Peptides: fewer than 50 amino acids
- Dipeptides: 2 amino acids
- Tripeptides: 3 amino acids
- Polypeptides: more than 10 amino acids
- Proteins: more than 50 amino acids, commonly 100 to 10,000.

Amino Acids

Comprised of carbon, hydrogen, oxygen, and nitrogen; contain an amino group (-NH2) and a carboxyl group (-COOH).
All amino acids, except glycine, have at least one chiral carbon and exhibit optical activity.
Only L-amino acids are incorporated into proteins; essential for various biological functions.

Classification of Amino Acids

Essential Amino Acids: Cannot be produced by the body and must be obtained through diet (e.g., lysine, arginine, histidine).
Non-Essential Amino Acids: Synthesized by the body (e.g., alanine, asparagine, glutamic acid).

Polar and Non-Polar Amino Acids

Non-Polar Amino Acids: Hydrophobic, unable to hydrogen bond with water (e.g., alanine, valine, phenylalanine).
Polar Neutral Amino Acids: Contain polar groups capable of forming hydrogen bonds (e.g., serine, threonine).
Polar, Positively Charged Amino Acids: Basic amino acids with positively charged side chains (e.g., lysine, arginine).
Polar, Negatively Charged Amino Acids: Acidic with negatively charged side chains (e.g., aspartic acid, glutamic acid).

Optical Activity of Amino Acids

Glycine is the only optically inactive amino acid due to the presence of two hydrogen atoms on its asymmetric carbon.
L-α Alanine and L-α Valine are optically active due to their chiral centers.

Interactions Exhibited by R-Groups

Hydrophobic Interactions: Occur with amino acids having hydrocarbon R-groups.
Ionic Interactions: Involve deprotonation of acidic amino acids and protonation of basic amino acids (e.g., lysine and aspartic acid).
Hydrogen Bonding: Formed by hydroxyl or sulfhydryl-containing amino acids (e.g., serine, cysteine).
Disulfide Bonds: Strong covalent bonds formed from the oxidation of cysteine molecules.
Stacking Interactions: Non-covalent interactions between aromatic rings (e.g., phenylalanine, tryptophan).

Acid-Base Properties and Isoelectric Point

Amino acids are amphoteric: can act as both acids (donors) and bases (acceptors).
At physiological pH (7.38), carboxylic groups lose protons forming zwitterions, neutral molecules with both positive and negative charges.
At the isoelectric point (pI), amino acids have no net charge and do not migrate during electrophoresis.

Peptide Bond

Known as amide bond, formed through the reaction between the carboxyl group of one amino acid and the amino group of another, releasing water.

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Description

This quiz delves into the structure and function of proteins and amino acids. Understand the classification of amino acids, their roles in biological processes, and the significance of proteins in the body. Test your knowledge on the essentials of these vital molecules.