Proteins (3.1.4)

Question 1

Define a dipeptide

Answer 1

Forms from a condensation reaction between 2 amino acids

Question 2

Define a polypeptide

Answer 2

Forms from the condensation of more than 2 amino acids

Question 3

What are the monomers of proteins?

Answer 3

Amino acids

Question 4

How many polypeptides form a protein?

Answer 4

1 or more

Question 5

Describe the primary structure of a protein

Answer 5

-The sequence of amino acids in the structure
-sequence differs in each chain

Question 6

Describe the secondary structure of a protein

Answer 6

-Sequence of amino acids causes parts of a protein molecule to bend into an alpha helix or fold into a beta pleated sheet
-Hydrogen bonds form between the carbon to oxygen double bond groups of the carboxyl group of 1 amino acid and the H in the amine group of another to hold the secondary structure together

Question 7

Describe the tertiary structure of a protein

Answer 7

-Further folding of the structure forms a unique 3D shape held together by hydrogen, ionic and or disulphide bonds
-Ionic bonds or disulphide bridges form between the R groups, must be a sulphur present in the R group for a disulphide bridge to form

Question 8

Describe the quaternary structure of a protein

Answer 8

-Protein made up of more than one polypeptide chain
-Only occurs in some proteins such as haemoglobin

Question 9

What happens if one amino acid in the sequence of the primary structure is different?

Answer 9

Bonds holding structure together will form in a different location during the secondary structure resulting in a different 3D shape, causing the protein to change function or lose it

Question 10

What happens to the structure when a protein is denatured?

Answer 10

The bonds holding the secondary and tertiary structure break, therefore losing its unique 3D shape

Question 11

When will a protein denature?

Answer 11

-When the temperature is too high (too much KE)
-too high/low pH (too many H+ or OH- ions)

Question 12

Explain the food test for proteins?

Answer 12

1) Add biuret solution (blue) to protein sample
2) If proteins are present = solution turns to purple

Question 13

Many proteins are enzymes, what do enzymes do?

Answer 13

Catalyse (speed up) reactions by lowering activation energy

Question 14

How do enzymes lower activation energy?

Answer 14

Lowered when the substrate binds the the active site of the enzyme

Question 15

Describe the stages of the induced fit model

Answer 15

1) Substrate isn’t complimentary to the active site (cannot bind) as it does not have the correct tertiary structure
2) substrate can induce a conformational change in the tertiary structure of the active site allowing substrate to bind and form and enzyme - substrate complex

Question 16

What is a conformational change?

Answer 16

A change in shape

Question 17

What is a substrate?

Answer 17

The molecule that the enzyme reacts with

Question 18

Explain enzyme specificity

Answer 18

-Tertiary structure of the active site is extremely specific
-Only complimentary substrates can bind to the active site to form an enzyme - substrate complex

Question 19

What factors can effect enzyme activity?

Answer 19

-temperature
-pH
-enzyme concentration
-substrate concentration
-enzyme inhibition (competitive and non competitive)

Question 20

How does temperature effect enzyme activity?

Answer 20

Temperature increases = Kinetic energy of the molecules increases = more likely the substrate and enzyme with bind to form an enzyme - substrate complex

Question 21

Describe the optimum temperature for enzymes

Answer 21

-Temperature most enzyme - substrate complexes are formed is 40°C
-If the enzyme denatures H bonds are hydrolysed, changing the tertiary structure of the active site

Question 22

How does pH effect enzyme activity?

Answer 22

-Activity will rise as pH increases and will peak
-If there is an imbalance of pH (H+ and OH- ions) this can disrupt the tertiary structure = substrate can no longer compliment active site

Question 23

What effect does enzyme concentration have on enzyme activity?

Answer 23

-rapidly increases as more active sites are available for complementary substrates
-plateau’s as there’s not enough substrates, some active sites are left empty

Question 24

What effect does substrate concentration have on enzyme activity?

Answer 24

-increases rapidly as there is more substrates for active sites
-plateau’s similar to enzyme conc as there are not enough active sites available for the substrates

Question 25

Explain competitive inhibition

Answer 25

-Competitive inhibitors have a similar structure to the complimentary substrate, and can bind to the active site instead = enzyme - substrate complexes can’t be formed = decreased rate of reaction
-Increasing substrate conc helps to decrease the effect of competitive inhibition

Question 26

Explain non - competitive inhibition

Answer 26

Enzymes have other sites which non - competitive inhibitors aim to bind to = tertiary structure of the active site changes = enzyme - substrate complex cannot be formed