2b. Protein and enzymes

Question 1

what elements do proteins contain

Answer 1

C H O N

Question 2

What is a protein

Answer 2

A polymer made of one or more chains of amino acid monomers - a polypeptide
Some proteins are conjugated - have other chemicals within their structures

Question 3

What are amino acids made of

Answer 3

An amine
A carboxyl group
A side chain

Question 3

what is the general structure of an amino acid

Answer 3

R
H2N- C - COOH
H

Question 3

What is a polypeptide

Answer 3

Many amino acids linking together by a condensation reaction

Question 4

How do amino acids form chains

Answer 4

By linking together.
2 Amino acids join to form a dipeptide
The bond between amino acids is a dipeptide bond
Condensation reaction

Question 5

What is the primary structure of proteins

Answer 5

The sequence of amino acids in a polypeptide chain

Question 6

What is the secondary structure of proteins

Answer 6

The folding of regions of the polypeptide chain due to the formation of many weak H-bonds.
Produces either an alpha helix or a beta-pleated sheet

Question 7

What is the tertiary structure of a protein

Answer 7

The further folding of the whole chain into a specific shape.
Stabilised by ionic bonds, hydrogen bonds, and disulphide bonds.
It’s the specific shape of the tertiary structure that determines its function

Question 8

What happens to a protein is subjected to high temperatures or extreme pH

Answer 8

It can become denatured.
H-Bonds break first as they are very weak
Disulphide bonds are stronger and can withstand higher temperatures.
When bonds break the tertiary stucture is lost and the protein loses its function

Question 9

What is the quaternary structure of a protein

Answer 9

Found in proteins made out of more than one polypeptide chain

Question 10

What are the different types of protein shape

Answer 10

Globular
Fibrous

Question 11

What is a fibrous protein

Answer 11

Form long chains running parallel to each other with cross-bridges between the chains.
Produces very stable molecules like collagen.
Tend to have a structural role in organisms

Question 12

What are globular proteins

Answer 12

Carry out metabolic functions
e.g enzymes and haemoglobin

Question 13

How do you test for proteins

Answer 13

Biuret test

Question 14

What is the biuret test

Answer 14

• Add biuret solution to a sample of the solution to be tested
  -Pale blue -> Lilac

Question 15

What is chromatography used for

Answer 15

Used to separate mixtures of monosaccharides or amino acids.
Molecules have a different molecular size and solubilities.
The smaller or more soluble the molecule, the further is will move

Question 16

What is an Rf value used for and what is the calculation

Answer 16

To identify the spots that appear on the chromatogram and compare with different chromatographs with the same solvents.
Rf = Distance from origin to solute / Distance from origin to solvent front

Question 17

What is activation energy

Answer 17

The minimum amount of energy required for a chemical reaction to take place

Question 18

What are enzymes

Answer 18

biological catalysts which increase the rate of a reaction by lowering the activation energy

Question 19

What happens to cells without enzymes

Answer 19

The temperature in living cells would be too low for chemical molecules to react fast enough to support life

Question 20

What are the different types of enzymes

Answer 20

Intracellular (inside cells) and extracellular (outside cells)

Question 21

How does ezymes structure relate to its function

Answer 21

Globular protein molecules so each enzyme and its active site has a specific tertiary structure and shape

Question 22

How do enzymes bind

Answer 22

Enzymes usually only work on the substrate which molecular shape is complementary to the active site.
They combine reversibly to form an enzyme-substrate complex

Question 23

What did the lock and key model suggest

Answer 23

The substrate combines with the enzymes active site precisley.
The active site is always the exact complementary shape at optimum temp so reactions are fastest in these conditions.

Question 24

What proved the lock and key model false

Answer 24

The enzyme is considered a rigid structure however later proved to be flexible

Question 25

What does the induced fit model suggest

Answer 25

The substrate and active site are not exactly complementary to begin.
But when the substrate binds to an enzyme, it induces a change in the enzymes structure and moulds to the substrate to form an E-S complex. It causes particular bonds in the substrate to undergo stress and distortion, thus reducing the activation energy needed to break the bond.
The active site changes shape to become complementary

Question 26

Why is the induced fit model a better explanation of enzyme action

Answer 26

It explains how the binding of other molecules can affect enzymes shape and activity and also explains how the activation energy is lowered

Question 27

What is the rate of reaction

Answer 27

The amount of product made per unit time

Question 28

What are factors effecting enzyme action

Answer 28

Subtible temperature
Subtible pH
adequate supply of substrate and enzyme
Inhibitors

Question 29

How does temperature effect enzyme action

Answer 29

As temperature increases, enzyme and substrate molecules gain more kinetic energy so move about more quickly.
They collide more frequently and so a greater number of enzyme-substrate complexes are formed so more product is made leading to an increased rate of reaction.

Question 30

What happens to enzymes after optimum temperature

Answer 30

Enzymes are denatured.
H-Bonds break
Tertiary structure changes
Active site changes and substrate is no longer complementary
ES Substrates can no longer form
They higher the temperature the more enzyme molecules will denature

Question 31

How does pH affect enzyme action

Answer 31

pH alters the charges on the amino acids of the active site
H-Bonds and ionic bonds in tertiary stucture may break and reform in different places
Alters shape of active site
substrate doesnt fit and no ES complexes form
Enzyme is denatured

Question 32

How do you calculate pH

Answer 32

pH = -log10(H+)

Question 33

How can pH of a solution be controlled

Answer 33

A buffer solution

Question 34

How does substrate conc affect the rate of reaction

Answer 34

As conc of substrate increases, RoR increases.
There are more substrate molecules so more collisions and more ES complexes.
RoR reaches a max and remains constant at a certain conc of substrate. All the active sites are occupied/saturated – maximum number of ES complexes

The conc of enzyme is a limiting factor

Question 35

What are the types of inhibitors

Answer 35

Competitive and non-competitive

Question 36

What is a competitive inhibitor

Answer 36

Have a similar shape of active site.
Binds to active site which blocks any substrates from binding
Fewer ES Complexes
RoR is reduced

Question 37

What is a non-competitive inhibitor

Answer 37

Bind to some other region of the enzyme, changes its tertiary sturcture and shape of active site
Fewer ES complexes form
RoR decreases