enzymes

Question 1

define enzyme

Answer 1

biological catalysts that interact with a substrate to facilitate chemical reactions

Question 2

what type of protein usually makes up an enzyme?

Answer 2

globular proteins

Question 3

define substrate

Answer 3

chemical reactants that enzymes bind to

Question 4

define product

Answer 4

substance formed from a chemical reaction

Question 5

explain why enzymes are necessary for life

Answer 5

• most important metabolic reactions are slow
• would need to happen at very high temp + pressures to be fast enough to match demand
• these conditions would damage cell components + impossible to reach in living cells
• enzymes speed up metabolic reactions w/o needing harsh environmental conditions

Question 6

define an anabolic reaction

Answer 6

metabolic reactions that construct molecules from smaller units
- require energy

Question 7

define a catabolic reaction

Answer 7

metabolic reactions that break molecules down into smaller units
- release energy

Question 8

define digestion

Answer 8

process where large biomolecules are hydrolysed into smaller constituent molecules so can be absorbed across cell membranes

Question 9

define metabolism

Answer 9

sum of all of the different reactions and reaction pathways happening in a cell or an organism

Question 10

define intracellular enzyme + example

Answer 10

enzymes that act within cells
- eg. catalase

Question 11

define extracellular enzyme + example

Answer 11

enzymes that act outside of cells (released from cells to act outside them)
- eg. amylase, trypsin

Question 12

state the substrates and products of amylase, trypsin and catalase

Answer 12

• amylase (starch –> maltose)
• trypsin (protein –> peptide)
• catalase (hydrogen peroxide –> H2O + O2)

Question 13

explain the role of extracellular enzymes in general

Answer 13

digest nutrients into smaller molecules so that they can be absorbed and used by cells

Question 14

summarise the digestion of starch as an example of the role of extracellular enzymes.

Answer 14

• starch polymers partially broken down into maltose (disaccharide) using amylase (released in saliva, produced by salivary glands and pancreas)
• maltose is broken down into glucose (monosaccharide that can be absorbed by cells) using maltase (present in small intestine)

Question 15

summarise the digestion of proteins as an example of the role of extracellular enzymes.

Answer 15

• proteins digested into smaller peptides using trypsin (produced in pancreas and released into small intestine)
• peptides further broken down into aa by other proteases
• aa are absorbed by cell lining of digestive system, then absorbed into bloodstream

Question 16

define active site

Answer 16

area of an enzyme with a shape complementary to a specific substrate so enzyme can bind to a substrate with specificity

Question 17

define specificity

Answer 17

term that describes how each enzyme catalyses one biochemical reaction

Question 18

explain why an enzyme only catalyses one type of reaction.

Answer 18

• different enzymes have differently shaped active sites
• each active site is complementary to a specific substrate shape
• so each enzyme will only be able to catalyse a specific substrate + only one type of reaction

Question 19

state the sequence of events in an enzyme-controlled reaction.

Answer 19

1. molecules move and randomly collide
2. when substrate binds to specific enzyme, it forms enzyme-substrate complex
3. substrates react and products are formed in enzyme-product complex
4. products are released, leaving enzyme unchanged and able to catalyse more

Question 20

describe the lock and key hypothesis

Answer 20

• idea of a specific key fitting into a specific lock
• active site shape is exactly complementary to the shape of the substrate
• enzyme does not change shape

Question 21

describe the induced-fit hypothesis

Answer 21

• enzyme changes shape slightly as the substrate enters
• weak interactions between substrate and enzyme induce change in tertiary structure that strengthen bind, putting strain on substrate molecule
• bonds weaken in the substrate, lowering the activation energy

Question 22

define activation energy

Answer 22

energy required to initiate a reaction.

Question 23

suggest how R-groups of amino acids are involved in catalysing reactions.

Answer 23

• R-groups interact with substrate, forming temporary bonds
• the bonds put strain on bonds within substrate which helps lower the activation energy

Question 24

state what the presence of an enzyme does to the activation energy for the reaction and explain why this increases the rate of reaction.

Answer 24

• enzymes lower activation energy
• so lowers minimum amount of energy required in particles for them to react
• higher proportion of particles are able to react = more reactions happen during a given time interval = higher rate