Proteins and enzymes

Question 1

Describe the structure of an amino acid

Answer 1

One carboxyl group, an amino group, a hydrogen atom and a variable R group bonded to a central carbon atom.

Question 2

What is a dipeptide?

Answer 2

Two amino acids joined by a peptide bond

Question 3

What type of bond joins two amino acids together?

Answer 3

A peptide bond

Question 4

What type of reaction forms a peptide bond?

Answer 4

A condensation reaction

Question 5

What happens during a condensation reaction?

Answer 5

A bond is formed and a molecule of water is released.

Question 6

What is a polypeptide?

Answer 6

A polymer made from multiple amino acid monomers joined by peptide bonds in condensation reactions.

Question 7

What is the primary structure of a protein?

Answer 7

The sequence of amino acids in a polypeptide, held by peptide bonds

Question 8

What is the secondary structure of a protein?

Answer 8

Local interactions of the polypeptide chain to form 3D structures like alpha helices and beta pleated sheets. It’s held together by hydrogen bonding.

Question 9

State two types of secondary structure in a protein

Answer 9

Alpha helices, beta pleated sheets

Question 10

What is the tertiary structure of a protein?

Answer 10

The further coiling of a protein into its functional 3D shape. Held by hydrogen, ionic and disulphide bonds, and hydrophobic interactions.

Question 11

How does the primary structure affect the tertiary (3D) structure?

Answer 11

R group variations produce different bonds. Sulfur atoms form disulfide bridges, oppositely charged groups form ionic bonds. Hydrogen bonds are always present.

Question 12

What is the quaternary structure of a protein?

Answer 12

-Not always applicable
-Describes the interactions of multiple polypeptide chains
-Held together by hydrogen, ionic and disulphide bonds, and hydrophobic interactions.

Question 13

Give one example of a protein with a quaternary structure

Answer 13

Haemoglobin

Question 14

Give 5 uses of proteins in the body

Answer 14

-Membrane proteins for transport
-Receptors
-Hormones
-Antibodies
-Enzymes

Question 15

What roles do globular proteins have in the body?

Answer 15

Metabolic roles

Question 16

What roles do fibrous proteins have in the body?

Answer 16

Structural roles

Question 17

Describe how the structure of fibrous proteins relates to their function.

Answer 17

Long polypeptide chains, folded in parallel. Very little tertiary and quaternary structure aside from cross-linkages for strength. This makes them soluble and useful for providing structure.

Question 18

Give an example of a fibrous protein and explain how its properties relate to its use.

Answer 18

Collagen - hydrogen and covalent bonds make it strong. Polypeptide fibers form a triple helix which creates fibers. This makes it useful in bones, cartilage and other connective tissue.

Question 19

Describe how the structure of globular proteins relates to their function.

Answer 19

Compact, highly folded with complex tertiary/quaternary structures. Soluble, forms colloids in water. They are useful for hormones, antibodies, etc.

Question 20

Give an example of a globular protein and explain how its properties relate to its use.

Answer 20

Hemoglobin - Water-soluble, with quaternary structure. Contains four haem groups that oxygen can bind to. Used to carry oxygen in the blood to respiring tissues.

Question 21

What are enzymes?

Answer 21

Biological catalysts that speed up the rate of metabolic reactions without being used up or permanently altered.

Question 22

Define catalysis

Answer 22

The process where a substance speeds up a chemical reaction by lowering activation energy without being used up itself.

Question 23

What are enzymes made of?

Answer 23

Protein

Question 24

What class of proteins are enzymes generally made up of?

Answer 24

Globular proteins

Question 25

How do enzymes work?

Answer 25

The active site is specific to a certain substrate. When the enzyme and substrate bind they form a complex, which lasts until the reaction is complete.

Question 26

What is meant by a specific active site?

Answer 26

The 3D structure of each enzyme is unique because of the side chains and branches. This makes the active site unique as well, so only substrates that match the active site can bind there.

Question 27

Differentiate between intracellular and extracellular enzymes

Answer 27

Intracellular: catalyse restions inside the cells.
Extracellular: catalyse reactions outside of cells.

Question 28

Describe the lock and key model.

Answer 28

1. Substrate and active site come into contact. 2. Substrate binds and the enzyme-substrate complex is formed.
2. Reaction takes place, products are formed. 4. Products are released from the active site and the site can bind to another substrate.

Question 29

Describe the induced fit hypothesis

Answer 29

1. Enzyme approaches the substrate.
2. Enzyme binds
3. The substrate induces a subtle change in the active site so that it fits the substrate precisely.
4. The enzyme catalyses reaction and creates an enzyme product complex
5. The enzyme releases the products.

Question 30

Describe the effect of t° on the rate of an enzyme controlled reaction.

Answer 30

As t° increases, so does rate of reaction. Once t° exceeds the optimum, the enzyme denatures and the rate of reaction decreases.

Question 31

Why does the rate of an enzyme-controlled reaction increase when the t° increases?

Answer 31

As t° increases, the particles have more kinetic energy. This increases chances of collisions between molecules being successful and leading to a reaction.

Question 32

If t° increases above the optimum, how does this affect enzyme function?

Answer 32

As the atoms in the active site gain more energy, they vibrate more which disrupts the bonds. The active site will be distorted and the bonds are broken. This denatures the enzyme and so it will no longer fit the substrate and can’t catalyse the reaction.

Question 33

Describe the effect of pH on the rate of an enzyme-controlled reaction.

Answer 33

-The rate of an enzyme catalysed reaction is faster at the optimum pH.
-If pH is too high or low, the enzyme will work less efficiently and the active site may be denatured at extremes of pH

Question 34

How does substrate concentration affect the rate of an enzyme-controlled reaction?

Answer 34

If enzyme concentration is fixed, the rate of reaction increases proportionally to the substrate concentration. Once all active sites become full, the rate no longer increases. It’s a limiting factor.

Question 35

How does enzyme concentration affect the rate of an enzyme-controlled reaction?

Answer 35

If substrate concentration is fixed, rate of reaction increases proportionally to the enzyme concentration. When all the substrates occupy active sites, the rate no longer increases. It’s a limiting factor.