Amino Acids Overview

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Questions and Answers

Which statement accurately describes the configuration of amino acids in proteins?

Glycine is the only amino acid that is chiral.

Stereoisomers cannot exist in amino acids.

L-configuration is found in all amino acids in proteins. (correct)

All amino acids in proteins are in D-configuration.

At what pH does an amino acid mostly exist as a zwitterion?

At the isoelectric point. (correct)

At a pH above the isoelectric point.

At a pH below its isoelectric point.

Zwitterions never occur at any specific pH.

Which of the following amino acids is classified as essential?

Histidine

Glutamine

Threonine (correct)

Arginine

What characterizes the primary structure of a protein?

The sequence of amino acids linked by peptide bonds. Signup and view all the answers

Which type of bond primarily stabilizes the secondary structure of proteins?

Hydrogen bonds. Signup and view all the answers

Which amino acid is characterized by having an achiral carbon?

Glycine Signup and view all the answers

Which of the following amino acids is involved in the transfer of methyl groups?

Methionine Signup and view all the answers

Which amino acid is associated with the condition known as Maple Syrup Urine Disease (MSUD)?

Valine Signup and view all the answers

What is the main function of Cysteine in proteins?

Forming disulfide bonds Signup and view all the answers

Which amino acid is a precursor for Serotonin and Melatonin?

Tryptophan Signup and view all the answers

Which of the following amino acids is positively charged at physiological pH?

Lysine Signup and view all the answers

What type of group characterizes aromatic amino acids?

Hexose Structures Signup and view all the answers

Which amino acid is primarily linked to O-linked glycosylation in the Golgi apparatus?

Serine Signup and view all the answers

What is the role of Glutamine in the body?

Formation of Ammonia Signup and view all the answers

Which amino acid is known for contributing to the fibrous structure of collagen?

Proline Signup and view all the answers

What represents the unique aspect of each amino acid in its fundamental structure?

The R group Signup and view all the answers

Which of the following is NOT a type of amino acid based on the nature of its side chain?

Amino acids with acid-base chains Signup and view all the answers

What is the primary function of enzymes in living organisms?

Regulate metabolism Signup and view all the answers

What is the term for the set of all proteins expressed by a cell at a specific time?

Proteome Signup and view all the answers

Which of the following statements best describes the relationship between isoelectric pH and amino acids?

Isoelectric pH indicates the neutral net charge of amino acids. Signup and view all the answers

What role do contractile proteins play in muscular systems?

They facilitate movement. Signup and view all the answers

Which bond in a peptide backbone is free to rotate, affecting conformation?

Phi and psi bonds Signup and view all the answers

Why is the study of proteomics significant in understanding cellular functions?

It identifies proteins under varying conditions. Signup and view all the answers

What is the general shape of an alpha helix?

R-handed spiral Signup and view all the answers

Which of the following amino acids is known to disrupt the formation of an alpha helix?

Proline Signup and view all the answers

What type of bonding predominantly stabilizes tertiary structures of proteins?

All of the above Signup and view all the answers

What is the key difference between alpha helices and beta sheets in terms of hydrogen bond direction?

Alpha helices have bonds parallel to the helix; beta sheets have bonds in a perpendicular direction. Signup and view all the answers

Which type of secondary structure appears as a flat, pleated sheet?

Beta sheet Signup and view all the answers

What role do domains play in protein structure?

They are fundamental structural and functional units formed by motifs. Signup and view all the answers

What causes denaturation in proteins?

Heat Signup and view all the answers

What type of structure is formed by proteins consisting of more than one polypeptide chain?

Quaternary structure Signup and view all the answers

Study Notes

Amino Acids

There are over 300 amino acids but only 20 are commonly found in mammalian proteins
All amino acids have the same fundamental structure: a central carbon atom, an amino group (NH2), a carboxyl group (COOH) and a hydrogen atom
The R group or side chain differentiates amino acids
Amino acids can be classified into 6 categories: aliphatic side chains, OH groups, SH groups, basic groups, acidic groups, aromatic side chains

Aliphatic Side Chains

Glycine (Gly, G) is the only amino acid with an achiral carbon due to its hydrogen side chain
Glycine is used in heme synthesis, purine synthesis, and is a major inhibitory neurotransmitter in the SPINAL CORD
Alanine (Ala, A) carries nitrogen from peripheral tissues to the liver
Valine (Val, V), Isoleucine (Ile, I), and Leucine (Leu, L) are branched-chain amino acids whose metabolites accumulate in MSUD (Maple Syrup Urine Disease)

OH Groups

Serine (Ser, S) is a phosphorylation site for enzyme modification
Threonine (Thr, T) is linked to carbohydrate groups in glycoproteins
Tyrosine (Tyr, Y) is a precursor of thyroxine and melanin

SH Groups

Cysteine (Cys, C) contains a sulfhydryl group that is an active part of many enzymes
Two cysteines can be connected by a covalent Disulfide bond to form Cystine
Methionine (Met, M) transfers methyl groups as SAM

Basic Groups

Histidine (His, H) is a precursor of histamine and is used in the diagnosis of Folic Acid Deficiency
Arginine (Arg, R) is a precursor of Urea, Creatinine and Nitric Oxide
Lysine (Lys, K) is involved in the production of collagen and elastin

Acidic Groups

Aspartic acid (Asp, D) and Glutamic acid (Glu, E) are proton donors
Asparagine (Asn, N) and Glutamine (Gln, Q) are involved in amino acid metabolism

Aromatic Groups

Tryptophan (Trp, W) has the largest aromatic side chain
Phenylalanine (Phe, F) accumulates in phenylketonuria

Imino Groups

Proline (Pro, P) is a non-standard amino acid because its side chain is linked to the nitrogen group of the amino group
Proline's structure contributes to the fibrous structure of collagen and interrupts α-helices in globular proteins

Nonpolar Side Chains

Nonpolar side chains have a net charge of zero at physiologic pH
They are not acidic or basic and do not bind or give off protons
Nonpolar side chains promote hydrophobic interactions and cluster in the interior of proteins

Uncharged, Polar Side Chains

Uncharged, polar side chains have a net charge of zero at physiologic pH
They can form hydrogen bonds
They are often found on the surface of proteins where they can interact with water molecules

Acidic Side Chains

Acidic side chains are negatively charged at physiologic pH because of the carboxylate group
They are proton donors and participate in ionic reactions
Glutamate (Glu, E) is the precursor of GABA and Glutathione

Basic Side Chains

Basic side chains are positively charged at physiologic pH because of the amine group
They are proton acceptors and participate in ionic reactions

Selenocysteine, the 21st Amino Acid

Selenocysteine is an L-α amino acid found in proteins such as peroxidases, reductases, selenoprotein P, and iodothyronine deiodinases

Optical Properties of Amino Acids

All amino acids except Glycine are chiral
L-configuration is found in proteins
D-configuration is found in bacterial walls and antibiotics
Stereoisomers/Isomers/Enantiomers are exact mirror images of each other

Charge of Amino Acids

Amino acids can have a positive, negative, or zero charge depending on the pKa values and pH of the environment
Zwitterion Molecule is a chemical compound with a total net charge of zero
Isoelectric pH or Isoelectric Point is the pH where the zwitterion predominates

Essential Amino Acids

Essential amino acids cannot be synthesized by the body and must be obtained from the diet
Essential amino acids include: Phenylalanine, Valine, Tryptophan, Threonine, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine

Conditionally Essential Amino Acids

Conditionally essential amino acids are not typically required but can become necessary under certain conditions
Conditionally essential amino acids include: Arginine and Histidine

Protein Structures

Proteins have four levels of structure: primary, secondary, tertiary, and quaternary

Primary Structure

Primary structure refers to the linear sequence of amino acids in a polypeptide chain
Peptide bonds connect the α-amino group of one amino acid to the α-carbonyl group of another
Peptide bonds are very stable and can only be disrupted by hydrolysis or prolonged exposure to a strong acid/base at elevated temperatures

Secondary Structure

Secondary structure refers to the local folding of the polypeptide chain into three-dimensional structures
Two main types of secondary structure are α-helix and β-pleated sheets
Secondary structure is stabilized by hydrogen bonding

Alpha-Helix

The α-helix is a right-handed spiral structure with the polypeptide backbone core side chains extending outward
The α-helix is stabilized by hydrogen bonds between the carbonyl and amino groups of the polypeptide backbone
Proline, large R groups, and charged R groups disrupt the α-helix

Beta-Pleated Sheet

The β-pleated sheet is formed by two or more polypeptide chains that are parallel to each other
The β-pleated sheet is stabilized by hydrogen bonds between the carbonyl and amino groups of the polypeptide backbone
The β-pleated sheet can be either parallel or antiparallel

Tertiary Structure

Tertiary structure refers to the overall three-dimensional shape of a protein
It refers to the folding of domains and their final arrangement in the polypeptide
Tertiary structure is stabilized by disulfide bonds, hydrophobic interactions, and hydrogen bonds
Examples of tertiary structures include globular proteins and fibrous proteins

Domains

Domains are fundamental functional and three-dimensional structural units of a polypeptide
Domains are formed by a combination of motifs

Quaternary Structure

Quaternary structure refers to the arrangement of multiple polypeptide chains (subunits) in a protein complex
Quaternary structure is stabilized by noncovalent bonds

Denaturation

Denaturation is the disruption of a protein’s structure
When a protein becomes unfolded and disorganized, they become dysfunctional
Denaturation can be reversible
Causes of denaturation include heat, organic solvents, mechanical mixing, and heavy metal ions

Prion Diseases

Prion diseases are caused by the misfolding of a protein called the prion protein
Misfolded prion proteins can convert other normal prion proteins into misfolded forms
Misfolded prion proteins aggregate and form amyloid plaques, which can damage brain tissue

Alzheimer's Disease

Alzheimer's disease is caused by the accumulation of amyloid-beta plaques and neurofibrillary tangles in the brain
Amyloid-beta plaques are formed by misfolded amyloid-beta proteins
Neurofibrillary tangles are formed by misfolded tau proteins
Both amyloid-beta plaques and neurofibrillary tangles contribute to the death of brain cells and the symptoms of Alzheimer's disease

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Description

Explore the fundamental structures and classifications of amino acids in this quiz. Learn about the 20 essential amino acids commonly found in mammalian proteins and their various functional groups. Enhance your understanding of their roles in biological processes and diseases.