Unit 1: Human Cells - Key Area 6 - Metabolic Pathways

Question 1

What are examples of degradation reactions in the human body?

Answer 1

HPCOW: hydrogen peroxide + catalyse = oxygen + water
SAM: starch + amylase = Maltose

Question 2

What are examples of synthesis reactions in the human body?

Answer 2

GPS - glucose + phosphorylase = starch

Question 3

What is cell metabolism?

Answer 3

The collective term for all the biochemical reactions that occur in a living cell.

Question 4

What are metabolic pathways?

Answer 4

Metabolic pathways are integrated and controlled pathways of enzyme-catalysed reactions within a cell. They can have REVERSIBLE steps, IRREVERSIBLE steps and ALTERNATIVE ROUTES.

Question 5

What do metabolic pathways involve?

Answer 5

metabolic pathways involve BIOSYNTHETIC PROCESSES (anabolism) and the break down of molecules (catabolism) to provide energy and building blocks.

Question 6

What are the two types of metabolic pathways?

Answer 6

Anabolic and catabolic.

Question 7

What do anabolic reactions do?

Answer 7

Anabolic reactions BUILD UP molecules from small molecules and REQUIRE ENERGY.

Question 8

What do catabolic reaction do?

Answer 8

Catabolic reactions BREAK DOWN large molecules into smaller molecules and RELEASE ENERGY.

Question 9

In a metabolic pathway, what controls each step?

Answer 9

Enzymes.

Question 10

What are enzymes?

Answer 10

Biological catalysts.

Question 11

What is a catalyst?

Answer 11

A catalyst is a substance that speeds up the rate of a reaction by lowering the energy needed to make the reaction proceed but is not used up in the reaction and can be used again after the reaction.

Question 12

What do enzymes speed up?

Answer 12

Biochemical reactions (chemical reactions inside living things).

Question 13

What is every biochemical reaction catalysed by?

Answer 13

A catalyst.

Question 14

What are enzymes that work inside the cells?

Answer 14

Intracellular enzymes.

Question 15

What are enzymes that work outside the cell?

Answer 15

Extracellular enzymes (pepsin in the stomach).

Question 16

During a chemical reaction what is energy needed for?

Answer 16

Energy is needed to break chemical bonds during a chemical reaction.

Question 17

What is the energy needed to break the chemical bonds in a chemical reaction called?

Answer 17

The activation energy.

Question 18

What do enzymes do to the activation energy needed for a reaction to proceed?

Answer 18

Enzymes lower/decrease the activation energy needed for a reaction to take place.

Question 19

What is induced fit?

Answer 19

Induced fit is when the active site can change shape slightly when it comes in contact with a substrate molecule for a better fit.

Question 20

What does affinity mean?

Answer 20

An attraction for something.

Question 21

If a substrate has a high affinity for the active site, what does the active site do?

Answer 21

The active site works by holding the reactants together together in an induced fit. This acts to weaken the chemical bonds in the reactants. This allows the reaction to take place.

Question 22

Once the reaction has taken place what do the products have and what does this cause to happen?

Answer 22

The products have a low affinity for the active site and are therefore released.

Question 23

What can enzyme activity be affected by?

Answer 23

Temperature, pH, Substrate concentration, Concentration of product, Inhibitors.

Question 24

As the concentration of a substrate increases, what also increases?

Answer 24

The reaction rate.

Question 25

When all of the enzyme’s active sites have become occupied with substrates (as substrate concentration is increased), what is now the limiting factor?

Answer 25

Enzyme concentration.

Question 26

When all of the enzymes are occupied by substrates what is this called?

Answer 26

The point of saturation.

Question 27

What are most metabolic pathways?

Answer 27

Reversible

Question 28

What can an enzyme often catalyse a reaction in?

Answer 28

Both a forward and a reverse direction.

Question 29

What does the direction an enzyme catalyses a reaction depend on?

Answer 29

The concentration of the reactants and the products.

Question 30

When does E.coli only produce β-glactosidase?

Answer 30

When lactose (it’s substrate) is present in the cell.

Question 31

What is enzyme induction?

Answer 31

The process by which a gene is switched on only when the enzyme is needed.

Question 32

When the enzyme β-glactosidase is not needed due there being no lactose, what happens to the production of the enzyme?

Answer 32

The repressor protein is produced by the regulator gene, which then binds to the operator gene. This then blocks the operator gene from telling the structural gene to produce the β-glactosidase (the structural gene is off) and no β-glactosidase will be produced.

Question 33

When the enzyme β-glactosidase is needed due to lactose being present, what happens to the production of the enzyme?

Answer 33

The regulator gene still produces the repressor protein but the lactose binds to the repressor protein, which then prevents the protein from binding to the operator gene. This allows the operator gene to tell the structural gene to produce the enzyme β-glactosidase (the structural gene is on).

Question 34

What is the advantage to the bacterium of this switching mechanism?

Answer 34

To prevent enzyme being produced which prevents resources from being wasted.

Question 35

What is an inhibitor?

Answer 35

An inhibitor is a substance that decreases the rate of an enzyme-controlled reaction.

Question 36

What are the two types of enzyme inhibitor?

Answer 36

Competitive and non-competitive.

Question 37

What does a competitive inhibitor do and what does this cause?

Answer 37

Competes with the substrate for the active site. The inhibitor has a similar shape that is similar to the substrate, and so when it binds to the active site of the enzyme it prevents the substrate the substrate from binding lowers the reaction rate.

Question 38

How can competitive inhibition be reversed?

Answer 38

By increasing substrate concentration.

Question 39

What does a non-competitive inhibitor do and what does this cause?

Answer 39

Non-competitive inhibitors do NOT combine with the active site of the enzyme. Instead they bind to another part of the enzyme (called the allosteric site) and indirectly change the shape of the active site. This means the substrate cannot bind to the active site and the reaction rate decreases.

Question 40

Will increasing substrate concentration have any effect on reaction rate in non-competitive inhibition?

Answer 40

No.

Question 41

Will increasing substrate concentration reverse non-competitive inhibition?

Answer 41

No.

Question 42

How does feedback inhibition do and how does this work?

Answer 42

Feedback inhibition occurs when the end product of a series of reactants binds to to an enzyme that catalyses a reaction early in the pathway, reducing that enzyme’s activity. This slows down the series of reactions, preventing the production of more of the end product until its concentration falls and the inhibition is removed.

Question 43

What property of a competitive inhibitor allows it to compete with the substrate?

Answer 43

They have similar shaped substrates which are complementary to the active site, which allows it to bind to the enzymes active sites.