135 Questions
Which of the following is NOT a component of an α-amino acid?
Hydrogen atom
At neutral pH, amino acids in solution exist predominantly as:
Dipolar ions
Which of the following is true about the optical activity of amino acids?
Only amino acids with four different groups connected to the α-carbon are optically active
Why are cells able to specifically synthesize the L isomers of amino acids?
Because L-isomers are more stable than D-isomers
What is the role of proline in peptide chains?
Proline stabilizes the 3-dimensional shape of peptide chains
What is the significance of the hydroxyl groups in serine and threonine?
The hydroxyl groups make serine and threonine more reactive
What is the function of glycine in proteins?
Glycine is particularly abundant in structural proteins
Which of the following statements about amino acids is NOT true?
Amino acids are the monomeric subunits of proteins.
Which of the following amino acids is NOT commonly found in proteins?
Proline
Which of the following amino acids is optically active?
Serine
Which of the following amino acids is NOT hydrophilic?
Alanine
Which of the following amino acids is an essential amino acid?
Serine
Which of the following amino acids is commonly found in collagen and gelatin?
Glycine
Which of the following amino acids has a cyclic structure in its side chain?
Proline
Which of the following amino acids has a hydroxyl group in its side chain?
Serine
Which of the following amino acids can engage in H-bonding and ester formation?
Serine
Which of the following amino acids is an important component of the active site of many enzymes?
Serine
Which of the following is true about the structure of an α-amino acid?
It consists of a central carbon atom, an amino group, and a carboxylic acid group
Which of the following is true about the R group of an α-amino acid?
It is often referred to as the side chain
What is the predominant form of amino acids in solution at neutral pH?
Dipolar ions
What is the isoelectric point (IEP) of an amino acid?
The pH at which the net ionic charges are balanced
Which of the following is true about the optical activity of amino acids?
Only L isomers of α-amino acids are optically active
Why are cells able to specifically synthesize the L isomers of amino acids?
L isomers have a higher stability
What is the significance of the hydroxyl groups in serine and threonine?
They can undergo post-translational modifications
Which of the following is true about the structure of glycine?
It is not an α-amino acid
What is the role of proline in peptide chains?
It disrupts the secondary structure of proteins
What is the function of glycine in proteins?
It is a non-essential amino acid
all amino acids of animal proteins are ______ isomers
L
D-amino acid residues have been found only in ______ and a few, generally small peptides, including some peptides of bacterial cell walls
plants
D-alanine and D-glutamic acid occur in ______ cell wall
bacteria
some antibiotics contain D-______ acids
amino
D-alanine, D-glutamic acid and D-ornithine are present in bacitracin-an active agent against a variety of ______ positive and a few ______ negative bacteria (in vitro)
Gram, Gram
polymyxins contain D-______
phenylalanine
why are cells able to specifically synthesize the L ______ of amino acids
isomers
the remarkable range of functions exhibited by proteins result from the diversity and versatility of the 20 kinds of building ______-amino acids
blocks
glycine (Greek glykos, “sweet”) was so named because of its ______ taste
sweet
alanine has ______ group as its side chain
methyl
An α-amino acid consists of a central carbon atom, called the α carbon, an amino group, a carboxylic acid group, a hydrogen atom, and a distinctive ______.
R group
The R group is often referred to as the ______.
side chain
Amino acids in solution at neutral pH are predominantly dipolar ions (Zwitterions) rather than ______ molecules.
unionised
In the dipolar state, the amino group is ______ and the carbonyl group is ______.
protonated, dissociated
The pH at which the net ionic charges are balanced is the ______.
isoelectric point (IEP)
Amino acids are ______.
optically active
With four different groups connected to the tetrahedral α-carbon atom, α-amino acids are chiral – they are ______.
optically active
The α-carbon of all amino acids are asymmetric, so there are two ______ of each except glycine.
stereoisomers
The two mirror-image forms are called the ______ and ______ isomers.
L, D
By convention, if the α-NH3+ is projected to the left, the α-amino acid has an absolute ______ configuration.
L configuration
Phenylalanine, tyrosine & tryptophan have ______ side chains
aromatic
The aromatic side chains make them relatively ______ (hydrophobic)
nonpolar
All can participate in ______ interactions
hydrophobic
Tyrosine and tryptophan are significantly more ______ than phenylalanine
polar
because of the tyrosine ______ group and the nitrogen of the tryptophan ______ ring
hydroxyl, indole
Aromatic amino acids are exploited in the ______ of proteins
characterization
Tyrosine was first isolated from ______ (its name is derived from the Greek tyros, “cheese”)
cheese
Phenylalanine & tyrosine are important constituents of ______
proteins
Are precursors for the synthesis of important regulatory proteins as neurotransmitters and ______
hormones
Which of the following is true about the aromatic side chains of phenylalanine, tyrosine, and tryptophan?
They are nonpolar (hydrophobic)
Which of the following amino acids is significantly more polar than phenylalanine?
Tyrosine
Which amino acid can be converted to tyrosine by the enzyme phenylalanine Hydroxylase?
Phenylalanine
Which of the following amino acids are important constituents of proteins?
Phenylalanine, tyrosine, and tryptophan
Which amino acids are precursors for the synthesis of important regulatory proteins such as neurotransmitters and hormones?
Phenylalanine, tyrosine, and tryptophan
Which amino acids are the starting point for the synthesis of catecholamines?
Phenylalanine and tyrosine
Which enzyme is absent in the congenital disease phenylketonuria?
Phenylalanine Hydroxylase
Which amino acid was first isolated from cheese?
Tyrosine
Which amino acids can participate in hydrophobic interactions?
Phenylalanine, tyrosine, and tryptophan
Which of the following statements about amino acids is true?
D-alanine and D-glutamic acid occur in bacterial cell walls
Which amino acid is commonly found in collagen and gelatin?
Proline
What is the role of serine and threonine in proteins?
They can serve as attachment sites for oligosaccharide chains in glycoproteins
Which of the following amino acids is NOT hydrophilic?
Phenylalanine
Which amino acid is an important reactive amino acid in proteins because the pka of the nitrogen in the imidazole ring of histidyl residues in proteins is in the range of pH of the tissues?
Histidine
Which amino acid is an important component of proteins due to the reactivity of the amino group on the side chain?
Lysine
Which amino acid is the precursor of nitric oxide?
Arginine
Which amino acid has a nonpolar thioether group in its side chain and acts as a methyl donor in biochemical processes?
Methionine
Which of the following amino acids contains a sulfhydryl group in its side chain?
Cysteine
Which amino acid can form a covalent cross-link called a disulfide bond?
Cysteine
Which amino acid is a constituent of myosin?
Methionine
Which of the following uncommon amino acids is found in prothrombin (factor II)?
carboxyglutamate
Which of the following is NOT a type of protein mentioned in the text?
Polysaccharides
Which of the following is the correct formula for haemoglobin mentioned in the text?
C2952H4664O832N812S8Fe4
What is the function of albumin in the body?
Regulation of water balance
What does the sedimentation of a protein containing solution indicate?
Protein aggregation
Which of the following best describes the structure of an α-amino acid?
A central carbon atom, an amino group, a carboxylic acid group, and an R group
Which of the following is true about the optical activity of amino acids?
All α-amino acids are optically active
Which of the following best describes the predominant form of amino acids in solution at neutral pH?
Dipolar ions (Zwitterions)
By convention, if the α-NH3+ is projected to the left, the α-amino acid has an absolute ______ configuration.
L
Which of the following is NOT a general function of proteins?
Catalysts
Which of the following is a dynamic function of proteins?
Metabolic control
Which proteins are involved in enzymatic catalysis?
Enzymes
Which proteins are involved in transport of molecules?
Transferrin and albumin
Which proteins provide structural strength and elasticity to organs?
Collagen and elastin
Which proteins are involved in the control and regulation of gene transcription and translation?
Histone proteins
Which category do nonpolar, aliphatic amino acids belong to?
Nonpolar, aliphatic
What is the general configuration of the peptide bond?
Trans
What are the charged groups present in polypeptides?
N-terminal α-amino group, C-terminal α-carboxyl group, and ionized groups in the side chains of amino acids
What are proteins classified based on?
Composition, molecular weight, molecular shape, function, source, and physicochemical properties
Which amino acid is an important precursor of the pharmacologically active substance histamine?
Histidine
Which amino acid has a lipotropic action and prevents fatty infiltration of the liver?
Methionine
What is the most abundant excitatory neurotransmitter in the vertebrate nervous system?
Glutamate
Which amino acid is involved in the synthesis of urea and stimulates the secretion of insulin and growth hormone?
Arginine
What is the general structure of an α-amino acid?
An α-amino acid consists of a central carbon atom, called the α carbon, an amino group, a carboxylic acid group, a hydrogen atom, and a distinctive R group.
What are the two mirror-image forms of amino acids called?
The two mirror-image forms are called the L isomer and D isomer.
What is the predominant form of amino acids in solution at neutral pH?
Amino acids in solution at neutral pH are predominantly dipolar ions (Zwitterions) rather than unionised molecules.
What is the pH at which the net ionic charges are balanced called?
The pH at which the net ionic charges are balanced is the isoelectric point (IEP).
What are the different categories in which amino acids are classified?
nonpolar, aliphatic; aromatic; polar, uncharged; and charged
What is the function of a peptide bond?
covalently joining amino acids in proteins
What is the naming convention for a polypeptide?
changing the suffixes of amino acid residues
What are the charged groups present in polypeptides?
N-terminal α-amino group, C-terminal α-carboxyl group, and ionized groups in the side chains of amino acids
What is the significance of the hydroxyl groups in serine and threonine?
The hydroxyl groups in serine and threonine make them much more hydrophilic (water loving) and reactive than alanine and valine.
What is the role of proline in peptide chains?
Proline is an important determinant of the 3-dimensional shape of peptide chains.
Which amino acids are commonly found in collagen and gelatin?
Hydroxy derivatives of proline are found only in collagen and gelatin.
What are the aromatic amino acids and what makes them different from each other?
The aromatic amino acids are phenylalanine, tyrosine, and tryptophan. Tyrosine and tryptophan are significantly more polar than phenylalanine due to the hydroxyl group in tyrosine and the nitrogen of the tryptophan indole ring.
What is the role of cysteine in proteins?
Cysteine plays a role in determining the tertiary structure of proteins and can form disulfide bonds.
What is the difference between cysteine and cystine?
Cysteine is the monomeric form with a sulfhydryl group, while cystine is the dimeric form with a disulfide bond.
What are some examples of uncommon amino acids?
Some examples of uncommon amino acids are 4-hydroxyproline, 5-hydroxylysine, 6-N methyllysine, carboxyglutamate, desmosine, and selenocysteine.
What is the role of methionine and acetylcysteine in the liver?
Methionine increases conjugation reaction in the liver, while acetylcysteine increases GSH formation in the liver.
What are the properties and functions of proteins?
Proteins are extremely large natural polymers with molecular weights reaching several million. They are too large to pass through cell membranes and remain trapped in the cells where they are made. Proteins can interact with one another and with other biological macromolecules to form complex assemblies. They contain a wide range of functional groups, which accounts for the broad spectrum of protein function. The function of a protein is directly dependent on its three-dimensional structure.
How do proteins fold into three-dimensional structures?
Proteins spontaneously fold up into three-dimensional structures that are determined by the sequence of amino acids in the protein polymer.
What is the significance of sedimentation in protein analysis?
Sedimentation is a process in which a protein-containing solution is centrifuged at a high speed to separate the molecules based on their molecular weight.
What is the role of pH in determining protein properties?
The pH of the environment determines the solubility, viscosity, and enzymatic activity of a protein.
What are the general functions of proteins in living systems?
Proteins serve crucial functions in essentially all biological processes such as catalysts, transport and storage of molecules, mechanical support and immune protection, generation of movement, transmission of nerve impulses, and control of growth and differentiation.
What are the three dynamic functions of proteins?
The three dynamic functions of proteins are enzymatic catalysis, transport, and protective role.
Give an example of a protein involved in enzymatic catalysis.
Enzymes are dynamic proteins and almost all biological reactions are enzyme catalyzed.
Give an example of a protein involved in transport.
Haemoglobin and myoglobin transport oxygen in blood and in muscle respectively.
Give an example of a protein involved in protective role.
Immunoglobulins and interferons act against bacterial or viral infection.
What are the structural functions of proteins?
Proteins provide structural strength and elasticity to organs and play a 'brick-and-mortar' role in forming the matrix for bone, ligaments, connective tissue, and skin.
Proteins are the most versatile macromolecules in living systems and serve crucial functions in all biological processes.
True
Almost all biological reactions are enzyme catalyzed.
True
Haemoglobin and myoglobin transport oxygen in blood and in muscle, respectively.
True
Fibrin is formed where required to stop the loss of blood on injury to the vascular system.
True
Many hormones are proteins, including insulin, thyrotropin, and somatotropin.
True
Myosin and actin function in muscle contraction.
True
Histone proteins are closely associated with DNA and control gene expression.
True
Collagen and elastin form the matrix for bone, ligaments, connective tissue, and skin.
True
Proteins provide structural strength and elasticity to organs.
True
Keratin is the primary component of human hair, nails, skin, and tooth enamel.
True
Study Notes
Classification and Properties of Peptides and Proteins
- Ornithine and citrulline are metabolites involved in the biosynthesis of arginine and the urea cycle.
- Amino acids are classified into nonpolar, aliphatic; aromatic; polar, uncharged; and charged categories.
- Peptide bonds covalently join amino acids in proteins, and can be hydrolyzed non-enzymatically under certain conditions.
- A polypeptide is an unbranched chain of amino acids linked through peptide bonds, and its naming convention involves changing the suffixes of amino acid residues.
- The peptide bond has a partial double-bond character, conferring rigidity and preventing free rotation.
- The peptide bond is generally in the trans configuration.
- The peptide bond is uncharged, and the charged groups present in polypeptides are the N-terminal α-amino group, C-terminal α-carboxyl group, and ionized groups in the side chains of amino acids.
- Small peptides may contain D-amino acids or be linked by bonds other than the standard peptide bond.
- Glutathione is a tripeptide with biochemical importance, acting as a coenzyme and undergoing oxidation under certain conditions.
- Proteins are classified based on their composition, molecular weight, molecular shape, function, source, and physicochemical properties.
- Proteins can be classified as simple (containing only amino acids) or conjugated (containing additional substances).
- Albumins are a type of simple protein that are water soluble and precipitated with full saturation in ammonium sulfate.
Classification and Properties of Peptides and Proteins
- Ornithine and citrulline are metabolites involved in the biosynthesis of arginine and the urea cycle.
- Amino acids are classified into nonpolar, aliphatic; aromatic; polar, uncharged; and charged categories.
- Peptide bonds covalently join amino acids in proteins, and can be hydrolyzed non-enzymatically under certain conditions.
- A polypeptide is an unbranched chain of amino acids linked through peptide bonds, and its naming convention involves changing the suffixes of amino acid residues.
- The peptide bond has a partial double-bond character, conferring rigidity and preventing free rotation.
- The peptide bond is generally in the trans configuration.
- The peptide bond is uncharged, and the charged groups present in polypeptides are the N-terminal α-amino group, C-terminal α-carboxyl group, and ionized groups in the side chains of amino acids.
- Small peptides may contain D-amino acids or be linked by bonds other than the standard peptide bond.
- Glutathione is a tripeptide with biochemical importance, acting as a coenzyme and undergoing oxidation under certain conditions.
- Proteins are classified based on their composition, molecular weight, molecular shape, function, source, and physicochemical properties.
- Proteins can be classified as simple (containing only amino acids) or conjugated (containing additional substances).
- Albumins are a type of simple protein that are water soluble and precipitated with full saturation in ammonium sulfate.
Test your knowledge of amino acid structure and physicochemical properties with this quiz! Learn about the building blocks of peptides and proteins, the composition of α-amino acids, and the unique R group. Challenge yourself and expand your understanding of amino acids.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
