3.1.4.1 General properties of proteins

Question 1

what are the monomers from which proteins are made?

Answer 1

amino acids

Question 2

what is the general structure of an amino acid (draw it out)?

Answer 2

NH2 represents an amine group, COOH represents a carboxyl group and R represents a side chain

Question 3

what element does the R group in an amino acid generally contain?

Answer 3

carbon

Question 4

which amino acid’s R group only contains hydrogen?

Answer 4

glycine

Question 5

which amino acid’s R group contains sulfur?

Answer 5

cysteine

Question 6

how many amino acids are common in all organisms?

Answer 6

20

Question 7

what is the only way that the amino acids differ from each other?

Answer 7

the R (side) groups can differ

Question 8

what reaction joins two amino acids?

Answer 8

a condensation reaction

Question 9

what bond is formed when two amino acids combine?

Answer 9

a peptide bond

Question 10

where is the peptide bond formed between two amino acids?

Answer 10

one amine group joins to a carboxyl group from another amino acid

Question 11

how are dipeptides formed?

Answer 11

by the condensation reaction between the amine and carboxyl group of two amino acids

Question 12

how are polypeptides formed?

Answer 12

by the condensation reaction between 2 or more amino acids

Question 13

draw the formation of a dipeptide and circle the peptide bond?

Question 14

what does a functional protein contain?

Answer 14

may contain one or more polypeptides

Question 15

what is the structure of a protein determined by?

Answer 15

the position of amino acids / R groups / interactions

Question 16

how many structural levels are there to proteins?

Answer 16

4 (primary, secondary, tertiary and quaternary)

Question 17

what is the primary structure of a protein?

Answer 17

the sequence and number of amino acids

Question 18

what is the secondary structure of a protein?

Answer 18

• hydrogen bonds
• forming an α-helix or a β-pleated sheet

Question 19

where do hydrogen bonds form in the secondary structure of a protein?

Answer 19

between NH group of one amino acid and C=O group

Question 20

what is the tertiary structure of a protein?

Answer 20

• formed by interactions between R groups
• the 3D shape of a polypeptide chain
• this determines the function of the protein

Question 21

which bonds are involved in the tertiary structure of a protein?

Answer 21

• hydrogen bonds
• ionic bonds
• disulfide bridges
• covalent bonds
• hydrophobic interactions
  –> these are all known as ‘interactions’

Question 22

which bonds maintain the tertiary structure of a protein?

Answer 22

• hydrogen bonds
• ionic bonds
• disulfide bridges

Question 23

what is the property of hydrogen bonds in proteins?

Answer 23

they are numerous but easily broken

Question 24

what is the property of ionic bonds in proteins?

Answer 24

they are weaker than disulfide bonds and are easily broken by changes in pH

Question 25

where do ionic bonds form?

Answer 25

between R groups of different amino acids

Question 26

what is the property of disulfide bridges in proteins?

Answer 26

they are resistant to chemical and physical attack and therefore cannot be easily broken

Question 27

where do disulfide bridges form?

Answer 27

between R groups of different amino acids

Question 28

what is the quaternary structure of a protein?

Answer 28

• more than one polypeptide chain
• other non-protein groups can also be associated
• formed by interactions between polypeptides

Question 29

what is the function of fibrous proteins?

Answer 29

structural (collagen)

Question 30

what is the function of globular proteins?

Answer 30

metabolic (haemoglobin / enzymes)

Question 31

what does it mean if a protein is denatured?

Answer 31

• bonds which hold the secondary and tertiary structure break
• unique 3D shape is lost

Question 32

what are the conditions that denature a protein?

Answer 32

• too high a temperature (too much kinetic energy can break intermolecular bonding)
• too high / low a pH (too many H+ or OH- ions can disrupt ionic charges in R groups)

Question 33

what happens if one amino acid changes in the primary structure of a protein?

Answer 33

• different sequence of amino acids
• causes hydrogen / ionic / disulfide bonds to form in a different place
• this results in a different 3D shape

Question 34

what is the food test for proteins?

Answer 34

• add biuret’s solution to sample
• if protein is present, colour change from blue to purple