c1.1-Enzymes and Metabolism

Question 1

What are enzymes?

Answer 1

Globular proteins that are biological catalysts that speed up chemical reactions without being changed

Question 2

Metabolism

Answer 2

Complex network of independent and interacting chemical reactions occurring in a living organism.
Each chemical reaction is controlled by a specific enzyme

Question 3

Anabolism

Answer 3

Energy used in metabolic reactions that BUILD macro molecules (and release water) by condensation reactions
-Requires energy
-Example- synthesis of protein

Question 4

Catabolism

Answer 4

The breaking down of macro molecules into simple molecules (monomers) by hydrolysis (addition of water)
-Energy is released
-example- digestion

Question 5

Active site

Answer 5

-region on enzyme where substrate binds to
-has a complimentary shape to one substrate
-composed of a few amino acids but the 3D shape of the enzyme ensures the active site can catalyse the reaction

Question 6

Where enzymes can be found

Answer 6

-inside cell
-outside cell (secreted)
-in membranes (integral proteins)

Question 7

Induced fit model

Answer 7

-The substrate approaches and enters the active site of the enzyme. Substrate induces the active site of the enzyme to change shape for an optimal fit (modified to fit each other)
-Enzyme substrate complex is formed
-Substrate=product

Question 8

Affect of molecular motion in substrate active site collision

Answer 8

Enzymes and substrates are in constant motion.
Enzymes can only catalsyse a reaction when substrate collides with active site
More frequent collisions=faster rate of reactions

Question 9

Ways to increase reaction rate in enzymes

Answer 9

(factors increasing number of collisions)
1. increase temp= particles move faster
2.increasing substrate conc = increasing chance of collision
3. Immobilisation of substrates= allows for repeated enzymatic reactions

Question 10

Denaturation of enzymes

Answer 10

=the permanent change of an enzyme that results in loss of biological function.
When denatured the shape and chemistry of active site changes and substrate can no longer bind.

Question 11

Factors affecting enzyme activity (graph and explanation)

Answer 11

1. temp; low temps= KE is low, low rate of reaction as temp increases gain KE, rate increases until optimum temp. Above optimum temp (37 degrees c)= denatured
2. PH; enzymes have an optimal PH (8) decrease in PH from optimum results in decreased activity. Large change will denature protein.
3. Substrate concentration; when substrate conc rises collisions become more frequent until a plateau is reached. Active sites are all taken before freed again.

Question 12

Equation for rate of reaction and how it can be found on a graph

Answer 12

change in reactant/product / time
can be found on a graph by calculating gradient at any point.

Question 13

Activation energy

Answer 13

Minimum amount of energy required for a chemical reaction to occur

Question 14

Why enzymes lower activation energy

Answer 14

Enzymes provide an alternative pathway where less activation energy is required. It positions substrate correctly making/ breaking new bonds so reaction needs less energy to start.
Lowering it allows reactions to occur at body temperature

Question 15

Intracellular enzymes and example

Answer 15

Active within the cell they are produced in
Examples of metabolism involving intracellular enzymes= glycolysis and Krebs cycle

Question 16

Extra cellular enzymes and examples

Answer 16

Active outside of cell synthesised in cell, secreted by exocytosis. Example= digestion in gut

Question 17

Multi enzyme complexes

Answer 17

A group of enzymes working together to catalyse essential life reactions both inside/ outside cell

Question 18

Metabolic efficiency

Answer 18

Heat generation is inevitable as metabolic reactions are not 100% efficient in anergy transfer. For endotherms this heat is essential to maintain a constant body temp
Endotherm- animals which maintain a constant body temperature.

Question 19

Cyclical and linear metabolic pathways

Answer 19

Linear pathway=chain of reactions that convert initial substrate into end product.
Example= glycolysis
Cyclical pathway= use and regenerate sequences of intermediates.
Example= Krebs cycle and Calvin cycle

Question 20

Metabolic pathways

Answer 20

Chains/cycles of enzyme controlled reactions in a specific sequence

Question 21

What is enzyme inhibition?

Answer 21

Chemicals that bind to enzymes and stop or slow down activity of enzyme by altering active site (non competitive inhibitors and competitive inhibitors)

Question 22

Similarities of non competitive inhibitors and competitive inhibitors

Answer 22

-inhibitors that bind to enzymes
-slow down/stop activity

Question 23

Non competitive inhibitors

Answer 23

Inhibitors that do not complete for enzymes active site rather, bind to alloseteric sites of enzymes
-must have specific shape and chemistry to bind to alloseteric site
-different chemistry/structure to substrate

Question 24

Competitive inhibition

Answer 24

Bind to the active site to prevent substrate from entering
-have similar shape/chemistry to substrate
-reduces reaction rate

Question 25

Statins as competitive inhibitors

Answer 25

Statins= drugs used to lower cholesterol levels. -A metabolic pathway of reactions produces cholesterol in the liver -enzyme HMG/COA reductase converts HMG/COA into melavonic acid (which is later converted in cholesterol) -statins are competitive inhibitors of enzyme HMG/COA reductase, binds to active site and inhibits production of melavonic acid= less cholesterol produced

Question 26

End product inhibition

Answer 26

The last product in a metabolic pathway when produced in high quantity acts as a non competitive inhibitor of the first step in pathway. It is used to prevent over supply of end product. Pathway begins again when conc of final product is low and no longer inhibits first reaction in pathway.

Question 27

Isoleucine inhibiting threonine deaminase

Answer 27

Amino acid threonine is converted into amino acid Isoleucine through enzyme reactions. If there is an excess of Isoleucine it binds to the allosetric site of threonine deaminase causing active site to change and pathway to stop working.

Question 28

Mechanism based inhibitors

Answer 28

Competitive inhibitors which permanently, covalently bond to active site. Irreversible reaction, substrate can no longer enter.

Question 29

Penicillin as mechanism based inhibitor

Answer 29

Penicillin= anti biotic which inhibits synthesis of bacterial cell wall -mechanism based inhibitor binds to transpeptidase (enzyme involved in making cell wall of bacteria) and prevents cell wall from being built -irreversibly inhibits transpeptidase