enzymes

Question 1

how does the structure of enzymes determine its function

Answer 1

• some enzymes may need cofactors to help catalyse some reactions
• if a gene for the enzyme has a mutation that alters the amino acid sequence, this may alter the enzyme’s tertiary structure and prevent it functioning
• if an enzyme that catalyses a metabolic reaction is deficient than a metabolic disorder results

Question 2

key features of the active site

Answer 2

• an indentation or cleft in the enymes surface
• consists of about 6-10 amino acids
• the tertiary structure of the active is crucial as its shape is complementary to the substrates shape
• each enzyme is highly specific in function as it can only catalyse a reaction with a specific substrate
• the shape of the active site can be altered by temperature or pH

Question 3

where do enzymes work

Answer 3

in a range of intracellular and extracellular reactions

Question 4

how do intracellular enzymes work

Answer 4

• through a metabolic pathway
• each metabolic pathway in a living cell is ne series of censecutive reactions
• various reactants and intermediates act as substrates for specific enzymes

Question 5

whats a metabolite

Answer 5

the reactants, intermediates and products

Question 6

whats a catabolic pathway

Answer 6

metabolites are broken down to smaller molecules and release energy

Question 7

whats an anabolic pathway

Answer 7

energy is used to synthesise larger molecules from smaller ones

Question 8

whats catalase

Answer 8

• an enzyme which protects cells from damage by reactive oxygen by quickly breaking down hydrogen peroxide (a potentially harmful by-product of metabolic pathways) to water and oxygen
• consists of 4 polypeptide chains and contains a haem group with iron
• is the fastest-acting enzyme
• white blood cells use catalase to help kill invading microbes
• the optimum pH is around pH 7

Question 9

extracellular enzymes

in our digestive system how are enzymes secreted

Answer 9

• from cells lining the alimentary canal into the gut lumen
• they then extracellulary digest the large molecules (proteins, lipids, carbohydrates and nucleic acids) found in food
• the products of the digestion are then absorbed into the blood stream to be used for respiration, grouth and repair

Question 10

whats a prothetic group

Answer 10

a cofactor that is permanently bound, by covalent bonds, to an enzyme molecule

Question 11

whats carbonic anhydrase

Answer 11

• an enzyme which contains a zinc ion permanently bound )its prosthetic group) to its active site
• is found in erythrocytes (red blood cells)
• catalyses the interconversion of carbon dioxide and water to carbonic acid which then breaks down to protons and hydrogencarbonate ions
• the reaction is vitally important as it enables carbon dioxide to be carried in the blood from respiring tissue to the lungs

Question 12

whats a cofactor

Answer 12

a substance that has to be present to ensure that an enzyme catalysed reaction occurs at the appropriate rate

Question 13

what are the roles of cofactors

Answer 13

• some may act as a co-substrate and with the substrate form the correct shape to bind to the active site of the enzyme
• others may change the charge distributiong on the surface of the substrate molecule or on the surface of the enzyme’s active site and make the temporary bonds in the enzyme-substrate complex form

Question 14

what does amylase need to digest startch into maltose

Answer 14

chloride ions

Question 15

what are coenzymes

Answer 15

• small organic non-protein molecules that bind temporarily to the active site of enzyme molecules wither before or after the substrate binds
• they are chemically charged during the reaction and sometimes need to be recycles to their original state by a different enzyme

Question 16

whats the lock-and-key hypothesis

Answer 16

• the tertiary structure of the active site has a shape which is complementary to the substrate molecules shape
• a large substrate molecule can fit in the active site and form an enzyme-substrate complex where it is broken into smaller product molecules
• two smaller substrate molecules can fit in the active site and form a enzyme-substrate complex which then turns into an enzyme-product complex

Question 17

what happens during the lock-and-key hypothesis

Answer 17

• the substrate and enzyme molecules constantly move around
• if a substrate molecule successfully collided with and enzyme, it forms an enzyme-substrate complex (ES complex) as the substrate fits into the complementary active site
• the substrate molecules are either broken down or built up into the product molecule forming enzyme-product complex whilst in the active site
• the product molecules leave the active site

Question 18

whats the induced-fit hypothesis

Answer 18

• suggests that the active site is not a rigid fixed structure but the presence of the substrate molecule induces a shape change

Question 19

what happens during the induced-fit hypothesis

Answer 19

• when the substrate molecules fit in the active site and then the active site changes shape slightly to mould itself around the substrate molecule
• the moulding allows the substrate to bind more effectively to the active site
• an enzyme-substrate complex is formed and non-covalent forces (e.g. hydrogen bonds and hydrophobic interactions) bind the substrate to the active site
• forms a enzyme-product complex whilst in active site
• the product molecules have a slightly different shape from the substrate molecule so detaches from the active site

Question 20

whats the outcome of an increase in temperature causing the molecules to vibrate

Answer 20

• may break some weak bonds (hydrogen and ionic bonds) that hold the tertiary strructure of active site
• active site shape can change which means substrate molecules will not fit and rate of reaction will decrease
• as more heat is applied, the active site denatures and the reaction cannot proceed at all

Question 21

whats a buffer

Answer 21

something that resists a change in pH

Question 22

how does a change in pH affects bonds within molecules

Answer 22

• excess hydrogen ions will interfere with the hydrogen bonds and ionic forces so the active site will change shape (rate of reaction that enzymes catalyse will decrease)
• increasing the conc of hydrogen ions will alter the charges on the active sit as more protons will cluster around negatively charged groups - will interfere with the binding of the substrate molecule to the active site

Question 23

extracellular enzymes

what are the different pHs through the digestion system

Answer 23

• amylase enzymes that digest starch into maltose work best at pH 6.8
• hydrochloric acid is used to kill pathogens so has a ver low pH
• the protease enzyme, pepsin, digests large peptide molecules and works best at pH 1 or 2
• as the partly digested food moves into the intestines the pH raises to 7.8 which is ideal for trypsin and enterokinase

Question 23

what happens to enzyme molecules when there is a change in pH

Answer 23

• small changes of pH (either side of the optimum pH) - slows rate ofe reaction as the shape of active site is disrupted, if normal pH is restoredd the hydrogen bons can re-form and active sites shape restored
• extreme changes of pH - the active site may be permanently damaged, enzyme is denatured

Question 23

whats the optimum pH for enzymes that work intracellularly

Answer 23

pH 7

Question 24

why will rate of reaction increase when the conc of substrate molecules increase

Answer 24

* because more ES complexes can form which means more product molecules form * substrate conc is a limiting factor

Question 25

what happens when the reaction reaches its maximum rate

Answer 25

* adding more substrate molecules will not increase the rate of reaction * as all enzyme active sites are occupied by substrate molecules

Question 26

what are some advantages of enzyme degradation

Answer 26

* it eliminates abnormally shaped proteins which could accumulate and harm cells * regulates metabolism in cells by eliminating and superfluous enzymes

Question 27

what happens as enzyme conc increases

Answer 27

* more active sites of the enzyme become available * more successful collisions between the enzyme and substrate occur * more ES complexes can form per unit time - rat of reaction increases

Question 28

when is the rate of reaction fastest

Answer 28

at the initial rate (the beginning)

Question 29

whats an inhibitor

Answer 29

a substance that reduces or stops a reaction

Question 30

whats a competitive inhibitor

Answer 30

a substance whose molecules have similar shape to an enzymes substrate molecules

Question 31

how to competitive inhibitors work

Answer 31

* the competitive inhibitor fits into active site so the substrate molecule cant enter * they form an enzyme-inhibitor complex that is catalitically inactive * once on the active site, the inhibitor does not change

Question 32

whats an inactivator inhibitor

Answer 32

* when the competitive inhibitor binds irreversibly to the active site * most competitive inhibitors are reversible

Question 33

whats a non-competitive inhibitor

Answer 33

* when the inhibitor molecule binds to the enzyme somewhere other than the active site * attach to allosteric site

Question 34

how do non-competitive inhibitors work

Answer 34

* bind to the allosteric site which changed the enzymes tertiary structure and its shape * the change of shape means the active site is no longer complementary to the shape of the substrate molecule * means the maximum rate of reaction decrease * some are reversible whilst others are irreversible

Question 35

what does cyanide do

Answer 35

* when ingested cyanide (KCN) is hydrolysed to produce hydrogen cyanide which is a very toxic gas that can dissolve into H+ ions and CN- ions * the CN- ions bind irreversibly to and enzyme found in mitochondria and inhibit the final stage of aerobic respiration

Question 36

# the venom of the green samba snake what happens due to snake venom

Answer 36

* contains a chemical that inhibits the enzyme acetylcholinesterase which is important at neuromucular synapses to break down the transmitter acetylcholine * if the enzyme is inhibited it acetylcholine stay attached ti the receptors on the muscle membrane and keeps muscles contracted - causing paralysis

Question 37

how does aspirin act as an enzyme inhibitor

Answer 37

* salicylic acid binds to the enzymes that catalyse the formation of prostaglandins (which are cell signalling molecul;es produced by cells when tissues are infected or damaged) and thus stopping the production * prostaglandins make nerve cells nire sensitive to pain and increase swelling

Question 38

how do ATPase inhibitors work

Answer 38

* inhibit the sodium potassium oump in cell membranes of the heart muscle cells and allow more calcium ions to enter the cells * calcium ions increase muscle contraction and strengthens the heartbeat

Question 39

how do ACE inhibitors work

Answer 39

inhibit the angiotensin converting enzyme (ACE) which operates in a metabolic pathway that increases blood pressure

Question 40

why are ACE inhibitors used

Answer 40

* to lower blood pressure in patients with hypertension who cannot take beta-blockers * to treat heart failure * to minimise risk of second heart attack or stroke in patients who suffered myocardial infarction

Question 41

what do protease inhibitors do

Answer 41

* used to treat viral infections * prevent the replication of the virus particles within the host cells by inhibiting protease enzymes so the viral coats cannot be made * often inhibit through competitive inhibition