Proteins

Question 1

What are proteins?

Answer 1

• large molecules, polymers of amino acids

Question 2

What enzyme catalyses formation of peptide bonds ?

Answer 2

• peptidyl transferase

Question 3

What are peptides?

Answer 3

• between 2 and 50 amino acids

Question 4

What are 3 methods of post-translational modification of proteins?

Answer 4

• Proteolysis = polypeptide chain cleaved into fragments
• glycosylation = addition of sugars
• phosphorylation

Question 5

What kind of hormone is insulin + where is it produced?

Answer 5

• Peptide hormone produced in 𝛃 of pancreas

Question 6

function of proteins ?

Answer 6

• enzymes
• structural support
• hormones
• cell signaling

Question 7

what do amino acids form at low and high pH’s ?

Answer 7

• form cations in low pH
• anions in high pH

Question 8

how many amino acids does a polypeptide chain contain ?

Answer 8

• polypeptide chain between 50 and 2000 amino acids

Question 9

what is the primary structure of a protein ?

Answer 9

• sequence of amino acids in polypeptide chain

Question 10

What is the secondary structure of a protein ?

Answer 10

• localized folding patterns within the polypeptide chain
• stabilized by H bonds
• α-helix and β-pleated sheets

Question 11

What is the α-helix (𝛼-helix), and how is it structured?

Answer 11

• right-handed spiral structure
• each C=O forms a H bond with the NH of the amino acid four residues earlier

Question 12

What is the β-pleated sheet (𝛃-sheet) ?

Answer 12

• 2 or more lengths of the polypeptide chain lie parallel to each other
• R groups of the amino acids point above and below the sheets
• NH and C=O parts of the peptide bond point towards each other
• H-bonds between these sections

Question 13

What is the tertiary structure of a protein?

Answer 13

• final 3D shape, which is determined by the interactions between the R-groups

Question 14

What are the four main types of interactions that stabilize the tertiary structure of proteins?

Answer 14

• Ionic bonds
• Hydrophobic interactions
• Hydrogen bonds
• Disulphide bridges = (covalent)

Question 15

What is the quaternary structure of a protein?

Answer 15

• two or more polypeptide chains interact
• Forces between these chains, SAME AS TERTIARY structure

Question 16

which bond is strongest out of disulfide, ionic, H bonds, van der waals ?

Answer 16

• disulfide bonds

Question 17

what is the role of insulin ?

Answer 17

• lowers blood glucose level
• promotes absorption of glucose from blood into liver +fat + muscle cells

Question 18

insulin therapy ?

Answer 18

• porcine insulin close to human version
• used to treat type 1 diabetes by injection

Question 19

why is insulin administered via injection ?

Answer 19

• too big to pass through PLB

Question 20

difference between structures of human and porcine insulin ?

Answer 20

• only 1 amino acid differs in sequence
• folded and twisted differently

Question 21

2 Factors affecting insulin activity ?

Answer 21

• folding = correct folding pattern allows protein to bind adequately, makes insulin more stable
• hydration = H2O molecules attached in correct places = affects solubility
• hydrophobic amino acids cluster in interior form hydrophobic protein core

Question 22

why was insulin measured in IU ?

Answer 22

• impossible to dry and rehydrate into correct 3D structure

Question 23

process of genetic engineering of insulin ?

Answer 23

• isolate human insulin gene
• plasmid cut by enzyme
• insert human insulin gene into plasmid
• plasmid inserted into new bacterium
• bacterium divides + produces insulin