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biology - module 2 > enzymes > Flashcards

enzymes Flashcards

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1
Q

how does the structure of enzymes determine its function

A
  • 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
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2
Q

key features of the active site

A
  • 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
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3
Q

where do enzymes work

A

in a range of intracellular and extracellular reactions

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4
Q

how do intracellular enzymes work

A
  • 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
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5
Q

whats a metabolite

A

the reactants, intermediates and products

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6
Q

whats a catabolic pathway

A

metabolites are broken down to smaller molecules and release energy

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7
Q

whats an anabolic pathway

A

energy is used to synthesise larger molecules from smaller ones

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8
Q

whats catalase

A
  • 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
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9
Q

extracellular enzymes

in our digestive system how are enzymes secreted

A
  • 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
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10
Q

whats a prothetic group

A

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

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11
Q

whats carbonic anhydrase

A
  • 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
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12
Q

whats a cofactor

A

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

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13
Q

what are the roles of cofactors

A
  • 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
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14
Q

what does amylase need to digest startch into maltose

A

chloride ions

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15
Q

what are coenzymes

A
  • 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
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16
Q

whats the lock-and-key hypothesis

A
  • 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
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17
Q

what happens during the lock-and-key hypothesis

A
  • 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
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18
Q

whats the induced-fit hypothesis

A
  • suggests that the active site is not a rigid fixed structure but the presence of the substrate molecule induces a shape change
19
Q

what happens during the induced-fit hypothesis

A
  • 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
20
Q

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

A
  • 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
21
Q

whats a buffer

A

something that resists a change in pH

22
Q

how does a change in pH affects bonds within molecules

A
  • 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
23
Q

extracellular enzymes

what are the different pHs through the digestion system

A
  • 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
23
Q

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

A
  • 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
23
Q

whats the optimum pH for enzymes that work intracellularly

A

pH 7

24
Q

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

A
  • because more ES complexes can form which means more product molecules form
  • substrate conc is a limiting factor
25
Q

what happens when the reaction reaches its maximum rate

A
  • adding more substrate molecules will not increase the rate of reaction
  • as all enzyme active sites are occupied by substrate molecules
26
Q

what are some advantages of enzyme degradation

A
  • it eliminates abnormally shaped proteins which could accumulate and harm cells
  • regulates metabolism in cells by eliminating and superfluous enzymes
27
Q

what happens as enzyme conc increases

A
  • 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
28
Q

when is the rate of reaction fastest

A

at the initial rate (the beginning)

29
Q

whats an inhibitor

A

a substance that reduces or stops a reaction

30
Q

whats a competitive inhibitor

A

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

31
Q

how to competitive inhibitors work

A
  • 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
32
Q

whats an inactivator inhibitor

A
  • when the competitive inhibitor binds irreversibly to the active site
  • most competitive inhibitors are reversible
33
Q

whats a non-competitive inhibitor

A
  • when the inhibitor molecule binds to the enzyme somewhere other than the active site
  • attach to allosteric site
34
Q

how do non-competitive inhibitors work

A
  • 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
35
Q

what does cyanide do

A
  • 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
36
Q

the venom of the green samba snake

what happens due to snake venom

A
  • 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
37
Q

how does aspirin act as an enzyme inhibitor

A
  • 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
38
Q

how do ATPase inhibitors work

A
  • 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
39
Q

how do ACE inhibitors work

A

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

40
Q

why are ACE inhibitors used

A
  • 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
41
Q

what do protease inhibitors do

A
  • 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

biology - module 2 (2 decks)

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