save my exams enzymes

Question 1

Enzymes

Answer 1

biological catalysts
they speed up the rate of chemical reactions without being used up or changed
globular proteins
be intracellular or extracellular

Question 2

intracellular

Answer 2

are produced and function inside the cell

Question 3

Extracellular enzymes

Answer 3

secreted by cells and catalyse reactions outside cells (eg. digestive enzymes in the gut)

Question 4

denaturation

Answer 4

Extremes of heat or pH can change the shape of the active site, preventing substrate binding

Question 5

specificity of an enzyme

Answer 5

result of the complementary nature between the shape of the active site on the enzyme and its substrate

shape of the active site (and therefore the specificity of the enzyme) is determined by the complex tertiary structure

Question 6

how enzymes 3d shape is formed

Answer 6

Proteins are formed from chains of amino acids held together by peptide bonds
The order of amino acids determines the shape of an enzyme
If the order is altered, the resulting three-dimensional shape changes

Question 7

Enzyme reactions can either be

Answer 7

catabolic or anabolic

Question 8

Catabolic

Answer 8

involve the breakdown of complex molecules into simpler products, which happens when a single substrate is drawn into the active site and broken apart into two

cellular respiration and hydrolysis

Question 9

Anabolic reactions

Answer 9

building of more complex molecules from simpler ones by drawing two or more substrates into the active site, forming bonds between them and releasing a single product

protein synthesis and photosynthesis

Question 10

Activation energy

Answer 10

amount of energy needed by the substrate to become just unstable enough for a reaction to occur and for products to be formed
Enzymes speed up chemical reactions because they influence the stability of bonds in the reactants
The destabilisation of bonds in the substrate makes it more reactive

Question 11

why enzymes lower activation energy

Answer 11

provide an alternative energy pathway

Question 12

lock-and-key hypothesis

Answer 12

Enzymes are globular proteins
This means their shape
is determined by the complex tertiary structure of the protein that makes up the enzyme and is therefore highly specific

Question 13

induced-fit hypothesis

Answer 13

the enzyme and substrate interact with each other
The enzyme and its active site can change shape slightly as the substrate molecule enters the enzyme
These changes in shape are known as conformational changes
This ensures an ideal binding arrangement between the enzyme and substrate is achieved
This maximises the ability of the enzyme to catalyse the reaction

Question 14

low temp and enzymes

Answer 14

Lower temperatures either prevent reactions from proceeding or slow them down:
Molecules move relatively slow
Lower frequency of successful collisions between substrate molecules and active site of enzyme
Less frequent enzyme-substrate complex formation
Substrate and enzyme collide with less energy, making it less likely for bonds to be formed or broken (stopping the reaction from occurring)

Question 15

high temp

Answer 15

Molecules move more quickly
Higher frequency successful collisions between substrate molecules and active site of enzyme
More frequent enzyme-substrate complex formation
Substrate and enzyme collide with more energy, making it more likely for bonds to be formed or broken

Question 16

enzyme begins to denature

Answer 16

-Bonds holding the enzyme molecule in its precise shape start to break
-tertiary structure of the protein to change
-permanently damages the active site, preventing the substrate from binding
-Denaturation has occurred if the substrate can no longer bind

Question 17

ph and enzymes

Answer 17

Below and above the optimum pH of an enzyme, solutions with an excess of H+ ions (acidic solutions) and OH- ions (alkaline solutions) can cause these bonds to break
This alters the shape of the active site, which means enzyme-substrate complexes form less easily
Eventually, enzyme-substrate complexes can no longer form at all
At this point, complete denaturation of the enzyme has occurred

Question 18

Enzyme concentration on ph

Answer 18

higher the enzyme concentration in a reaction mixture, the greater the number of active sites available and the greater the likelihood of enzyme-substrate complex formation
initial rate of reaction increases linearly with enzyme concentration

Question 19

when Enzyme conc becomes a limiting factor

Answer 19

amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate as the amount of substrate becomes a limiting factor

Question 20

substrate conc

Answer 20

greater the substrate concentration, the higher the rate of reaction:

number of substrate molecules increases, the likelihood of enzyme-substrate complex formation increases

all available active sites eventually become saturated and any further increase in substrate concentration will not increase the reaction rate

any substrate molecules that are added have nowhere to bind in order to form an enzyme-substrate complex

Question 21

Enzyme Inhibitors

Answer 21

two types of reversible inhibitors
An enzyme’s activity can be reduced or stopped, temporarily, by a reversible inhibito

Question 22

two types of reversible inhibitors

Answer 22

Competitive inhibitors
Non-competitive inhibitors

Question 23

Competitive inhibitor

Answer 23

have a similar shape to that of the substrate molecules and therefore compete with the substrate for the active site

Question 24

Non-competitive

Answer 24

inhibitors bind to the enzyme at an alternative site, which alters the shape of the active site and therefore prevents the substrate from binding to it
the inhibitor changes the conformation of enzymes after binding so that substrate cannot bind to enzymes
the results inna decrease of Xmas
depends on inhibitor concentration

Question 25

Increasing the concentration of an inhibitor

Answer 25

reduces the rate of reaction and eventually, if inhibitor concentration continues to be increased, the reaction will stop completely

Question 26

competitive inhibitors ncreasing the substrate concentration

Answer 26

can increase the rate of reaction once more (more substrate molecules mean they are more likely to collide with enzymes and form enzyme-substrate complexes)

Question 27

non-competitive inhibitors, increasing the substrate concentration

Answer 27

cannot increase the rate of reaction once more, as the shape of the active site of the enzyme remains changed and enzyme-substrate complexes are still unable to form

Question 28

evidence to support the induced fit mode

Answer 28

X-ray diffraction techniques allow for 3D pictures of molecules to be formed

produce pictures of the enzyme hexokinase before and after it bound to its substrate glucose

confirmed that the active site of the enzyme changed shape after the substrate bound

Question 29

Experiments showed

Answer 29

proteins are not rigid structures
multiple regions of an enzyme molecule moved in response to the environment
larger movements occurred when the substrate bound to the enzyme

Question 30

sucrose

Answer 30

sucrase hydrolyses glycoside bond in this molecule to form 2 monosaccharides , glucose and fructose

Question 31

lactose

Answer 31

lactase hydrolyses glycosidic bond in this molecules to form 2 minosaccharides, glucose and galactose