4. Amino Acids and Proteins

Question 1

What is an α-amino acid?

Answer 1

an amino acid in which the amino group is attached to the carbon atom adjacent to the carboxyl group

Question 2

What is aggregation?

Answer 2

Several things grouped together or considered as a whole

Question 3

What is chymotrypsin?

Answer 3

a digestive enzyme thatcleaves peptide bonds of proteins where the amide side of the bond is an aromatic amino acid like tyrosine, phenylalanine or tryptophan. Used to sequence amino acids

Question 4

What us cyanogen bromide?

Answer 4

an inorganic compound used to sequence amino acids by cleaving the C-terminus of methionine

Question 5

What is a D-configuration?

Answer 5

a compound that when represented as a Fischer projection with the carboxyl group pointing up, has its amine group on the right

Question 6

What is a disulfide bridge?

Answer 6

a covalent bond between two sulfur atoms, i.e. an - S - S - bond

Question 7

What is Edman degradation?

Answer 7

a method of sequencing amino acids in a peptide. In this method, the amino-terminal residue is labeled and cleaved from the peptide without disrupting the peptide bonds between other amino acid residues

Question 8

What is a Fischer projection?

Answer 8

two-dimensional representations that show the configuration of a stereocentre; horizontal lines represent bonds projecting forward from the stereocentre, vertical lines represent bonds projecting to the rear

Question 9

What is gel electrophoresis?

Answer 9

a method for separation and analysis of macromolecules (DNA,RNAandproteins) and their fragments, based on their size and charge

Question 10

What is the hydrophobic effect?

Answer 10

the observed tendency of nonpolar substances to aggregate in aqueous solution and exclude water molecules.

Question 11

What is an isoelectric point?

Answer 11

the pH at which an amino acid, a polypeptide or protein has no net charge

Question 12

What is an L-configuration?

Answer 12

a compound that when represented as a Fischer projection with the carboxyl group pointing up, has its amine group on the left

Question 13

What are peptidases?

Answer 13

any enzyme that performs proteolysis; protein catabolism by hydrolysis of peptide bonds

Question 14

What is a peptide?

Answer 14

a short polymer of amino acids

Question 15

What is a primary structure?

Answer 15

the sequence of smaller molecular components that are assembled to make a biopolymer; thus for proteins and peptides it is the specific amino acids in a polypeptide chain read from the N-terminal amino acid to the C-terminal amino acid

Question 16

What is a quaternary structure?

Answer 16

the arrangement of polypeptide monomers into a noncovalently bonded aggregation

Question 17

What is a secondary structure?

Answer 17

the ordered arrangement (conformation) of a biopolymer; this the organised shaped of the chain of amino acids in localised regions of a polypeptide or protein, seen as sheets or coils.

Question 18

What is a tertiary structure?

Answer 18

the three-dimensional arrangement in space of all atoms in a single polypeptide chain

Question 19

What is trypsin?

Answer 19

a chemical used to sequence amino acids by cleaving the polypeptide chain at points where a arginine or lysine are present

Question 20

What is zwitterion?

Answer 20

an ionic salt in which both cation and anion are part of the same molecule

Question 21

What determines the behaviour of the amino acid in water and how the peptide folds?

Answer 21

The nature of the amino acid r-group

Question 22

Are all amino acids chiral?

Answer 22

No - glycine is not chiral but the others are

Question 23

What do horizontal lines on a Fischer projection represent?

Answer 23

Bonds projecting forward

Question 24

What do vertical lines on a Fischer projection represent?

Answer 24

Bonds projecting to the rear

Question 25

Which configuration is most amino acids in?

Answer 25

L-configuration

Question 26

Which amino acid is the only R configuration using the R,S system?

Answer 26

Cysteine - the rest are S, except glycine which is achiral

Question 27

What does cyanogen bromide do?

Answer 27

It is a molecule specific for cleavage of peptide bonds formed by the carboxyl group of methionine

Question 28

Which amino acids does trypsin cleave?

Answer 28

Arginine and lysine

Question 29

Which amino acids does chymotrypsin cleave?

Answer 29

Phenylalanine, tryptophan and tyrosine

Question 30

What does edman degradation do?

Answer 30

Cleaves the n-terminal amino acid allowing it to be identified