STOKER

What is a naturally-occurring, unbranched polymer in which the monomer units are amino acids?

A protein

What are the most abundant molecules in cells after water?

Proteins

What percentage of a cell's overall mass do proteins account for?

15%

What is the average nitrogen content of proteins by mass?

15.4%

What is an organic compound that contains both an amino NH2 and carboxyl (COOH) groups attached to the same carbon atom?

Amino acid

What is the position of the carbon atom in an amino acid where the functional groups are attached?

Alpha

What part of an amino acid varies in size, shape, charge, acidity, functional groups present, hydrogen-bonding ability, and chemical reactivity?

R side chain

How many amino acids are currently known?

more than 700

How many standard amino acids are there based on common "R" groups?

20

Into how many groups are standard amino acids divided based on the properties of R-groups?

Four

What is the property of R-groups in non-polar amino acids?

Non-polar

What term describes non-polar amino acids that are insoluble in water?

Hydrophobic

How many of the 20 standard amino acids are non-polar?

8

Where are non-polar amino acids located when present in proteins?

Interior of protein

What are the three types of polar amino acids?

Polar neutral, acidic, and basic

What type of polar amino acid contains polar but neutral side chains?

Polar neutral

How many standard amino acids belong to the polar-neutral category?

Seven

What functional group do polar acidic amino acids contain as part of their side chains?

Carboxyl group

How many standard amino acids belong to the polar acidic category?

Two

What functional group do polar basic amino acids contain as part of their side chain?

Amino group

How many standard amino acids belong to the polar basic category?

Two

What type of abbreviations are widely used for naming amino acids?

Three letter abbreviations

Which three amino acids have three-letter abbreviations where the next two letters after the first are different from how they are spelled?

Asparagine (Asn), Glutamine (Gln) and tryptophan (Trp)

What are commonly used for comparing amino acid sequences of proteins?

One-letter symbols

Which amino acid is the only standard amino acid that does not have four different groups attached to the alpha-carbon atom?

Glycine

What is the R-group in glycine?

Hydrogen

How many of the 20 standard amino acids contain a chiral center?

19

What do chiral centers exhibit?

Enantiomerism

Which isomer form of amino acids is found in nature and in proteins?

L isomers

Which organism contains some D-amino acids?

Bacteria

Which isomer form of monosaccharides does nature favor?

D-isomers

In a Fischer projection formula for an amino acid, where is the -COOH group positioned?

top

In a Fischer projection formula for an amino acid, where is the -NH2 group positioned if it is an L isomer?

On the left

What are amino acids in pure form?

White crystalline solids

What is an ion with positive and negative charges on the same molecule with a net zero charge?

Zwitterion

What happens to carboxyl groups in a zwitterion?

They give-up a proton to get negative charge

What happens to amino groups in a zwitterion to become positive?

They accept a proton

In solution, what three different species of amino acids exist in equilibrium?

Zwitterions, positive ion, and negative ion

What is the pH at which the concentration of zwitterion is maximum and the net charge is zero?

Isoelectric point (pI)

Why are amino acids at their isoelectric point not attracted towards an applied electric field?

Net zero charge

Which standard amino acid is the only one with a sulfhydryl group (SH group)?

Cysteine

What is formed when cysteine dimerizes in the presence of mild oxidizing agents?

Cystine molecule

What consists of two cysteine residues linked via a covalent disulfide bond?

Cystine

What is an unbranched chain of covalently-linked amino acids?

A peptide

What are the covalent bonds between amino acids in a peptide called?

Peptide bonds

What is a bond between two amino acids?

Dipeptide

What is a bond between approximately 10 to 20 amino acids?

Oligopeptide

What is a bond between a large number of amino acids?

Polypeptide

What are the two ends that every peptide possesses?

N-terminal end and a C-terminal end

In peptide nomenclature, which amino acid residue keeps its full amino acid name?

The C-terminal amino acid residue

What suffix replaces the -ine or -ic acid ending of all amino acid residues except the C-terminal one and tryptophan?

-yl

At which residue does the amino acid naming sequence begin?

The N-terminal amino acid residue

What term refers to peptides that contain the same amino acids but present in a different order?

Isomeric peptides (constitutional isomers)

What type of small peptides are oxytocin and vasopressin?

Hormones

Where are oxytocin and vasopressin produced?

The pituitary gland

How many amino acid residues are in a nonapeptide?

Nine

What type of bond holds six of the residues in oxytocin and vasopressin in the form of a loop?

Disulfide bond

What are enkephalins?

Pentapeptide neurotransmitters

What is the function of enkephalins produced by the brain?

Help reduce pain

What is the amino acid sequence for Met-enkephalin?

Tyr-Gly-Gly-Phe-Met

What is the amino acid sequence for Leu-enkephalin?

Tyr-Gly-Gly-Phe-Leu

What tripeptide is present in high levels in most cells as an antioxidant?

Glutathione (Glu-Cys-Gly)

What is the unusual structural feature of glutathione?

Glu is bonded to Cys through the side-chain carboxyl group

What is the specific definition of a protein based on the number of amino acid residues?

A peptide in which at least 40 amino acid residues are present

What terms are often used interchangeably to describe a protein?

Polypeptide and protein

How many amino acid residues do common proteins contain?

400-500

What is a protein called if it contains only one peptide chain?

Monomeric

What is a protein called if it contains more than one peptide chain?

Multimeric

What is a protein in which only amino acid residues are present?

Simple protein

What is a protein that has one or more non-amino acid entities present in its structure?

Conjugated protein

What are the non-amino acid components of a conjugated protein called?

Prosthetic groups

What type of conjugated proteins contain lipid prosthetic groups?

Lipoproteins

What type of conjugated proteins contain carbohydrate groups?

Glycoproteins

What type of conjugated proteins contain a specific metal as a prosthetic group?

Metalloproteins

What refers to the order in which amino acids are linked together in a protein?

Primary structure

Who sequenced and determined the primary structure for insulin in 1953?

Frederick Sanger

What was the first protein to have its primary structure sequenced?

Insulin

From what source is human insulin now produced?

Genetically engineered bacteria

What refers to the arrangement of atoms of the protein backbone in space?

Secondary structure

What are the two most common types of secondary structure?

Alpha-helix and the beta-pleated sheet

Why are peptide linkages essentially planar?

Six atoms lie in the same plane

Which isomer is the preferred orientation for the planar peptide linkage?

Trans isomer

What type of hydrogen bonding occurs in an alpha-helix?

Intramolecular

Where are the R-groups located in an alpha-helix structure?

Outside of the helix

What characterizes the amino acid chains in beta-pleated sheets?

Completely extended

What is the overall three-dimensional shape of a protein called?

Tertiary structure

From what do tertiary structures result?

Interactions between amino acid side chains (R groups)

What strong, covalent interaction occurs between two cysteine groups in a tertiary structure?

Disulfide bond

What interaction involves a salt bridge between charged side chains of acidic and basic amino acids?

Electrostatic interactions

Between which types of R groups does hydrogen bonding occur in tertiary structures?

Polar, acidic and/or basic

Between which types of side chains do hydrophobic interactions occur?

Non-polar

What refers to the organization among the various peptide chains in a multimeric protein?

Quaternary structure

What are proteins with quaternary structure often referred to as?

Oligomeric proteins

What are the three types of proteins classified based on shape?

Fibrous, globular, and membrane

What shape do fibrous proteins have?

Elongated shape

Which type of protein is generally insoluble in water and has a single type of secondary structure?

Fibrous proteins

What shape do globular proteins have?

Spherical or globular shapes

Which type of protein generally functions as enzymes and intracellular signaling molecules?

Globular proteins

Which type of protein is associated with cell membranes and helps in the transport of molecules?

Membrane proteins

What is the major protein constituent of hair, feathers, nails, and horns?

Alpha-Keratin