General properties of proteins (3.1.4.1)

Question 1

what are amino acids?

Answer 1

the monomers from which proteins are made

Question 2

what is the general structure of an amino acid?

Answer 2

C atom bonded to R, COOH, H and H2N

Question 3

what does NH2 represent?

Answer 3

an amine group

Question 4

what does COOH represent?

Answer 4

a carboxyl group

Question 5

what does R represent?

Answer 5

a side chain - the twenty amino acids that are common in all organisms differ only in their side group.

Question 6

what does a condensation reaction between two amino acids form?

Answer 6

a peptide bond

Question 7

what is formed from the condensation of two amino acids?

Answer 7

a dipeptide

Question 8

what is formed from the condensation of three or more amino acids?

Answer 8

a polypeptide

Question 9

what may a functional protein contain?

Answer 9

one or more polypeptides

Question 10

how does a polypeptide become a protein?

Answer 10

it folds into a complex, 3D structure which allows it to carry out its function

Question 11

what are the four levels of protein structure?

Answer 11

primary, secondary, tertiary and quaternary

Question 12

what is the primary structure of proteins?

Answer 12

the sequence of amino acids in a polypeptide chain

Question 13

what is primary structure determined by?

Answer 13

the DNA sequence of the gene that encodes that polypeptide

Question 14

why is primary structure important?

Answer 14

it determines the protein’s shape (tertiary structure) and therefore function, because if one amino acid is changed it will change the whole shape

Question 15

what is the secondary structure of proteins?

Answer 15

hydrogen bonds form between amino acids so the protein twists and folds into a 3D shape eg. alpha helix, beta pleated sheet

Question 16

how do the hydrogen bonds form in secondary structure?

Answer 16

the -NH group has an overall positive charge and the -C=O group has an overall negative charge so they form between them

Question 17

what is the tertiary structure of proteins?

Answer 17

the overall 3D shape of a polypeptide chain - the secondary structure twists and folds to give a more complex structure

Question 18

what is tertiary structure important for?

Answer 18

how the protein functions eg. the active site of an enzyme depends on it forming a specific tertiary structure and if this changes it can’t function properly

Question 19

what is the quaternary structure of proteins?

Answer 19

when proteins consist of several polypeptide chains linked together to form a large molecule

Question 20

what are prosthetic groups?

Answer 20

non-protein molecules which form part of the quaternary structure of proteins and help it to carry out its role eg. haem in haemoglobin

Question 21

what is a conjugated protein?

Answer 21

a protein with a prosthetic group

Question 22

what are subunits?

Answer 22

the individual polypeptide chains which make up the quarternary structure of a protein

Question 23

what two thing does quaternary structure show?

Answer 23

1. how individual subunits are arranged
2. the position of any prosthetic groups

Question 24

how do you carry out the test for proteins?

Answer 24

1. place 3cm^3 of food solution into a test tube
2. add 3cm^3 of dilute sodium hydroxide (alkali) solution and mix
3. add 10 drops of dilute copper sulphate solution and mix
4. positive test will show purple colour, negative will remain blue

Question 25

what does the type of bonding in a protein depend on?

Answer 25

the specific amino acids present in the polypeptide (bonds form between R groups on amino acids)

Question 26

when do hydrogen bonds form in a polypeptide chain?

Answer 26

when two amino acids have R groups containing a hydroxyl (OH) - forms due to slight positive and negative charges present on it

Question 27

what are non-polar amino acids?

Answer 27

amino acids with uncharged R groups which are hydrophobic

Question 28

what are hydrophobic interactions?

Answer 28

when non-polar amino acids cluster together, excluding water molecules (often found in centre of proteins)

Question 29

where are hydrophilic amino acids usually found?

Answer 29

on the surface of proteins where they can interact with water molecules

Question 30

where are ionic bonds found in proteins?

Answer 30

between amino acids with oppositely charged R groups

Question 31

what is the role of an ionic bond?

Answer 31

to hold different parts of the polypeptide chain together, contributing to the protein’s overall structure

Question 32

how do ionic bonds relate to the nature of enzymes?

Answer 32

ionic bonds break due to changes in pH, which is a reason for enzymes denaturing in alkaline/acidic conditions

Question 33

what is a disulphide bond?

Answer 33

a covalent bond formed between two sulphur atoms in the R groups of two different amino acids

Question 34

what are the different strengths of the bonds found in proteins?

Answer 34

hydrogen - weak
hydrophobic and hydrophilic interactions - weak
ionic - weak
disulphide - strong

Question 35

when are the bonds in proteins involved in tertiary structure?

Answer 35

when they form between different amino acids on the same polypeptide chain

Question 36

when are the bonds in proteins involved in quarternary structure?

Answer 36

when they form between different subunits