Amino Acids and Proteins- Lecture 2

Question 1

Which amino acids are considered to have non-polar side chains?

Answer 1

Glycine, Alanine, Valine, Leucine, Isoleucine, Phenylalanine, Methionine, and Proline

Question 2

Which amino acids do not always fit into one category?

Answer 2

Tryptophan (can be non-polar due to the hydrophobic phenyl ring or polar due to N that can H bond)
Histidine (charged if side chain is protonated, but its pKa is close to physiological pH so it is often found uncharged)
Cysteine (contains slightly electronegative sulfur so it can be non-polar or uncharged polar)

Question 3

Which amino acids are considered to have uncharged polar side chains?

Answer 3

Serine, Threonine, Tyrosine, Asparagine, and Glutamine

Question 4

Which amino acids are considered to have acidic side chains (negatively charged at physiological pH)?

Answer 4

Aspartic acid and Glutamic Acid

Question 5

Which amino acids are considered to have basic side chains?

Answer 5

Lysine and Arginine

Question 6

What is the difference between a peptide and a protein?

Answer 6

peptide contains a chain less than 50 amino acids long and proteins are 50 amino acids long or greater

Question 7

What is the primary structure of a protein?

Answer 7

its amino acid sequence/ the linear order of amino acids in the chain starting at the N-terminus and ending at the C-terminus

Question 8

What is the secondary structure of a protein?

Answer 8

its local three-dimensional conformation; normally either alpha-helix or beta-sheet (loops are less common)

Question 9

What three groups can proteins be classified in based on their relative content of secondary structures?

Answer 9

mainly alpha, mainly beta, mixed alpha-beta

Question 10

What is the tertiary structure of a protein?

Answer 10

folding; overall three dimensional conformation which is determined by its amino acid sequence (interactions between the backbone and amino acid side chains)

Question 11

What is one of the main driving forces of tertiary structure?

Answer 11

the hydrophobic effect (consequence of disruption of water H bonds by the presence of hydrophobic groups); one of the main reasons why proteins have a hydrophobic core

Question 12

What is quaternary structure of a protein?

Answer 12

the arrangement of protein subunits in a complex that contains more than one polypeptide chain

Question 13

What mutation causes Sickle Cell Anemia?

Answer 13

Glu6 - Val in hemoglobin

Question 14

What are post-translational modifications?

Answer 14

changing the chemical characteristics of amino acids after a protein has been translated; most often adding a chemical group to the side chain of an amino acid

Question 15

Which amino acid(s) can be phosphorylated?

Answer 15

Serine, Threonine, and Tyrosine (those that have hydroxyl groups)

Question 16

Which amino acid(s) can undergo glycosylation (sugars added)?

Answer 16

Serine, Threonine, and Asparagine

Question 17

What amino acid(s) can undergo acetylation?

Answer 17

Lysine