chapter 4- Enzymes

Question 1

what is the difference between anabolic and catabolic reactions?

Answer 1

anabolic= chemical reactions required for growth are anabolic and are all catalysed by enzymes. (building up reactions)
catabolic= energy is released from large organic molecules like glucose in metabolic pathways. (breaking down reactions)

Question 2

what is the Vmax?

Answer 2

enzymes can only increase the rate of reaction up to a certain point. This is called the Vmax.

Question 3

what is needed by molecules for a reaction to happen?

Answer 3

molecules need to collide in the right orientation and have frequent successful collisions.

Question 4

what is a limitation of the lock and key hypothesis?

Answer 4

assumes that enzymes have a rigid structure and do not change shape

Question 5

describe the induced fit hypothesis

Answer 5

• the active site of the enzyme changes slightly as the substrate enters
• active site will undergo a conformational change of shape when exposed to the substrate to improve binding

Question 6

what is a metabolic pathway

Answer 6

a series of consecutive reactions, with the use of specific enzymes in certain steps. Reactants and products are known as metabolites

Question 7

examples of enzymes involved in the digestive system

Answer 7

amylase= involved in carbohydrate digestion. it hydrolyses starch into simple sugars. It is secreted by the salivary glands (mouth) and pancreas ( small intestine)

trypsin= used in the digestion of proteins into smaller peptides which can be broken down further into amino acids, produced in the pancreas.

Question 8

why is digestion usually carried out by extracellular enzymes?

Answer 8

Because macromolecules being digested are too large to enter the cell

Question 9

Is thermal denaturation reversible?

Answer 9

no

Question 10

Is PH denaturation reversible?

Answer 10

often reversible

Question 11

what is temperature coefficient?

Answer 11

the ratio between the activities of a process , at two different temperatures. If the the two temperatures are 10 degrees apart, then the temperature coefficient is written as Q10.

Question 12

what is the equation to find the temperature coefficient?

Answer 12

Temperature coefficient= ( rate of reaction at (x+10) °C ÷ ( rate of reaction at x°C )

Question 13

why does the rate of reaction of enzymes decrease at high PH.

Answer 13

hydrogen and ionic bonds hold the tertiary structure of a protein ( e.g. enzyme) together. the breaking of bonds due to PH alters the shape of the active site, which leads to less enzyme substrate complexes or denaturation.

Question 14

what is a buffer?

Answer 14

something that resists changes in PH. These donate or accept hydrogen ions to maintain the PH.

Question 15

what are the two type of inhibitors?

Answer 15

• competitive
• non- competitive

Question 16

examples of competitive inhibitors

Answer 16

• statin= regularly prescribed to help people reduced their blood cholesterol concentration
• aspirin= inhibits the active site of COX enzymes, preventing the synthesis of chemicals responsible for producing pain and fever

Question 17

examples of non- competitive inhibitors

Answer 17

PPI’s= used to treat long term indigestion, irreversibly blocks enzymes from producing excess acid in the stomach.

Question 18

how does competitive inhibition work?

Answer 18

• a molecule that has a similar shape to the substrate of an enzyme can fit into the active site of an enzyme.
• this blocks the substrate from entering the active site of an enzyme, slowing down the rate of reaction
• does not affect the Vmax
  -most only bind
  temporarily, except aspirin.

Question 19

how does non-competitive inhibition work?

Answer 19

• inhibitor binds the enzyme at a location other than the active site called the allosteric site.
• this changes the shape of the active site, so it is no longer complementary to the substrate
• increasing enzyme/ substrate concentration will not overcome the effect of a non- competitive inhibitor

Question 20

what is end product inhibition?

Answer 20

the term used for enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it. this serves as negative feedback

Question 21

what are cofactors?

Answer 21

• inorganic non-protein substances that enzymes require in order to function properly
• they may help to stabilize the structure of an enzyme or take part in a reaction at the active site
• for example, chloride ions act as a cofactor for amylase, as chloride ions are necessary for the formation of a correctly shaped active site
• inorganic cofactors are obtained via the diet as minerals, including iron and calcium

Question 22

what are coenzymes?

Answer 22

• organic (carbon- containing) non- protein cofactors
• some coenzymes can bind permanently to the enzyme they assist or temporarily
• coenzymes contribute to enzyme catalysed reactions, by accepting or donating hydrogen ions or chemical groups
• many co enzymes are derived from vitamins found in the diet

Question 23

what are prosthetic groups?

Answer 23

• cofactors, which are required by certain enzymes to carry out their catalytic function
• prosthetic groups are tightly bound and permanent on the protein

Question 24

what is precursor activation?

Answer 24

• many enzymes are produced in an inactive form

Question 25

Give an example of an intracellular enzyme

Answer 25

Hydrogen peroxide is formed as a byproduct of many metabolic reactions. It is harmful to cells. Catalase converts hydrogen peroxide into water and oxygen to avoid damage.

Question 26

Give examples of 2 extracellular enzymes

Answer 26

Amylase= digestion is usually carried out by extracellular enzymes. This is because the macromolecules being digested are too large to enter the cell. Amylase is involved in carbohydrate digestion. It hydrolyses starch into simple sugars. It is secreted by the salivary glands and pancreas for digestion in the mouth and small intestine. Trypsin= protease enzyme that breaks down larger proteins into smaller peptides which can then be broken down further into amino acids. It is used in the digestion of proteins into smaller peptides. Trypsin is produced in the pancreas.

Question 27

What is the effect of PH on enzyme activity

Answer 27

A change in ph refers to a change in hydrogen ion concentration-acidic or alkaline The more H ions present (low PH), the less R groups are able to interact with each other. This leads to bonds breaking and the shape of the enzyme changing. All enzymes have an optimum pH Enzymes are denatured at extremes of pH Hydrogen and ionic bonds hold the tertiary structure of the protein (ie. the enzyme) together The breaking of bonds alters the shape of the active site, which means enzyme-substrate complexes form less easily or can no longer form at all (denaturation)

Question 28

What is a buffer?

Answer 28

something that resists changes in PH. These donate or accept hydrogen ions to maintain the PH. In lab experiments you will use the buffer solutions to maintain the desired PH.

Question 29

what is End-product inhibition?

Answer 29

when the final product inhibits an enzyme involved in the initial reactions. At the end of the metabolic pathway, the final product may be able to inhibit the enzyme responsible for catalysing the initial reaction. This causes the whole metabolic pathway to stop.

Question 30

Describe percursor activation

Answer 30

many enzymes are produced in an inactive form, known as an inactive precursor enzyme. Precursor enzymes typically consist of enzymes that can cause damage within the cells that produce them or tissues where they are released. They often need to undergo a change in their tertiary structure to be activated. This can be achieved by the addition of a co-factor. Before the cofactor is added the precursor enzyme is called an apoenzyme. After the cofactor is added and the enzyme is activated it is called a holoenzyme. Sometimes the change in the tertiary structure is brought about by the action of another enzyme. In other cases, a change in conditions such as pH or temperature can cause a change in the tertiary structure.