2.1.4 Enzymes Flashcards
Suggest 2 reasons why students chose potato rather than liver as a source of catalase
- easier to control SA
- less chance of ethical objection
- lower risk of infection
Potato cylinders were cut to equal lengths. Suggest a further precaution that students should have taken when preparing them, to ensure investigation was valid.
consistent potato variety/ same age
Suggest 2 reasons why the value the students recorded for the volume of oxygen collected might not accurately reflect the volume of oxygen produced
- some oxygen dissolved in solution
- gas other than oxygen collected
- some gas escaped
Explain how induced fit mechanism of enzyme action observed in chitinase increases the rate of chitin breakdown
- stronger bonds between chitin and chitinase
- bonds in chitin are WEAKENED
- lowers activation energy
Explain which type of pipette would reduce the uncertainty when transferring solution?
- one with fewer uses required
- fewer random errors
- highest resolution
- lowest percentage error
what are co-enzymes?
small, organic non protein molecules that bind TEMPORARILY to active site of enzyme molecules, and assist/activate them
chemically changed so need to be recycled to their original state
what is the role of amylase?
- extracellular
- produced in salivary glands and acts in mouth to digest starch into maltose.
- also produced in pancreas and acts in duodenum to catalyse same reaction
- must have Cl-
What are protease inhibitors?
treat viral infections
prevent replication of virus particles by competitively inhibiting protease enzymes so viral coats cant be made
Why are enzymes so efficient?
Small amount of catalyst can catalyse a large number of reactions. they are able to function in conditions that sustain life.
What is a buffer? What is an example of one?
resist changes in pH by accepting or donating H+ ions
certain chemicals in blood so blood pH is close to 7.4
Which vitamin is thiamine pyrophosphate derived from? What is the human deficiency disease if this vitamin is insufficient?
thiamine, B1
beriberi
What happens as enzyme conc increases?
more active sites available
more successful collisions
more ES complexes can form per unit time = rate increases
limiting factor initially
however, it will then not be the limiting factor. all substrates will end up occupying an active site or are now products
if enzyme conc increases further, no inc in rate since lack of substrate molecules is preventing this
what is the effect of substrate conc on rate of reaction?
more substrate added = more ESC can form = more product molecules formed = inc rate.
substrate conc is limiting factor
as conc increases more, maximum rate will be reached
adding more substrate will NOT increase the rate, since all active sites are occupied, so it is no longer the limiting factor.
Which vitamin is co enzyme A derived from? What is the human deficiency disease if this vitamin is insufficient?
pantothenate
elevated blood plasma triglyceride levels
What are the roles of enzymes?
- biological catalysts: speed up metabolic reactions in living organisms, remaining unchanged.
what is the temperature coefficient?
Temperature coefficient = (rate of reaction at (T + 10) °C) ÷ (rate of reaction at T°C)
Why is aspirin (salicylic acid) used as a medicinal drug?
binds to enzymes that catalyse formation of prostaglandins (cell signalling molecules) which are produced by cells when tissues get infected or damaged and make nerve cells more sensitive to pain
can reduce risk of blood clots
What are co-factors? What are their roles?
small, non protein molecules that ensure the reaction occurs at the appropriate rate by changing tertiary structure
inorganic ions may bind temporarily to ease formation of ESC and rate of reaction
- acting as co-substrates (them and substrate form correct shape to bind to active site)
- changing charge distribution on surface of enzymes a.s or on substrate and make temporary bonds in the complex easier to form.
What is needed for enzymes to catalyse some reactions?
cofactors or coenzymes
what is the effect of increasing temperature on enzyme activity?
molecules have more KE = move faster
more frequent collisions + increases force with which they collide
rate of ESC formed increases and rate of reaction increases TO A POINT.
Why are ACE inhibitors used?
inhibit ACE which normally operates in a metabolic pathway that ultimately increases blood pressure
used to lower blood pressure in those with hypertension, to treat a heart failure, and minimise risk of 2nd heart attack in those who have suffered a myocardial infarction.
Why are ATPase inhibitors used?
treat heart failure or abnormal heart beat -> inhibit Na+/K+ in cardiac muscle membrane -> More Ca2+ ions enter to inc muscle contraction
what happens if an enzyme that catalyses a reaction is deficient?
metabolic disorder results
what is a holoenzyme vs an apoenzyme?
holoenzyme:enzyme bound to cofactor/coenzyme
apoenzyme:inactive enzyme, just protein
What do enzymes affect?
- both structure and function within cells, tissues and organs
what is turnover number?
no. of reactions an enzyme can catalyse per second
what happens if a gene has a mutation?
alters amino acid sequence in protein = may alter tertiary structure = prevents function
what do enzymes also catalyse?
formation of structural components. some genetic disorders can cause malformations e.g. of connecticve tissue.
role of intracellular enzymes
- each metabolic pathway is a series of consecutive reactions, each one catalysed by a specific enzyme, producing a specific product.
- reactants, intermediates + products = metabolites
- if one enzyme cannot function in a metabolic pathway, then it cannot run
what is the role of catalase?
protects cell from damage by reactive oxygen by quickly breaking down hydrogen peroxide into water and oxygen
4 chains and a haem group with iron
found inside peroxisomes
when white blood cells ingest pathogens they use catalase to help kill invading microbe
what is the role of trypsin?
- extracellular
- made in pancreas and acts in duodenum to digest polypeptides into smaller peptides by hydrolysing peptide bonds
How do fungi use enzymes?
release hydrolytic enzymes from hyphae which digest molecules in bread + products are absorbed into them for growth and respiration
When do enzymes usually require co factors?
- esp those in oxidation - reduction reactions
what is a prosthetic group?
a co-factor that is permanently bound by covalent bonds to an enzyme
What is the role of carbonic anhydrase? What must it have?
found in RBC’s and catalyses interconversion of CO2 and H2O to carbonic acid (which then breaks down to protons and hydrogen carbonate ions). Enables CO2 to be carried in the blood from respiring tissues to lungs.
Contains Zn2+ ion
where are many coenzymes derived from?
- water-soluble vitamins
Which vitamin are cobalamin coenzymes derived from? What is the human deficiency disease if this vitamin is insufficient?
B12
pernicious anaemia
Which vitamin is tetrahydrofolate derived from? What is the human deficiency disease if this vitamin is insufficient?
Folic acid
megablastic anaemia
Which vitamin is NAD and NADP derived from? What is the human deficiency disease if this vitamin is insufficient?
nicotinamide, B3
pellagra (dementia, diarrhoea, weakness)
Which vitamin is thiamine pyrophosphate derived from? What is the human deficiency disease if this vitamin is insufficient?
thiamine, B1
beriberi (confusion, paralysis, irregular heartbeat)
what is the lock and key hypothesis?
tertiary structure of active site = EXACT complementary shape to that of substrate. specificity.
what is the induced fit hypothesis?
active site isn’t a fixed, rigid structure.
still has a complementary shape but the presence of substrate in it INDUCES a shape change - explains how ESC is stabilised. active site changes shape slightly to mould itself around substrate so it’s a more precise conformation.
what do enzymes do regarding activation energy?
lower activation energy
what are some examples of enzymes in organisms that work best at cooler/warmer temperatures?
- cool temps: psychrophilic bacteria in very cold conditions
- high temps: thermophilic bacteria ( their enzymes are heat stable due to more disulfide bridges that dont break with heat)
What if the temperature is increased too much?
may break some of weak bonds such as H bonds = changes to tertiary structure and active site since its the hydrogen bonds that hold it together.
substrate no longer complementary + rate of reaction decreases
more heat applied = active site IRREVERSIBLY changes = denaturation.
what if temp is decreased?
reduces KE = less frequent collisions = fewer ESC form = decrease in rate
effects of low temp though are REVERSIBLE
how do you calculate rate of reaction?
1/time
what is the general trend for temp coefficient for reactions in test tubes and metabolic reactions catalysed by enzymes??
(0-40 degrees celsius)
rate of reaction is doubled for every 10 degree celsius rise
for enzymes at temps above optimum, what happens to temp coefficient?
it decreases
How does increasing/decreasing pH affect rate of reaction?
conc of H+ ions outside optimum range will interfere with the ionic and H bonds between amino acids, so the tertiary structure will be disrupted= active site will change shape = not complementary = rate of reaction decreases.
H+ ions attracted to neg parts of molecule
alter charges on active site too, as more protons cluster around neg R groups = interferes with binding
- small changes in pH can disrupt shape of active site slightly
-if normal pH is restored, H bonds can reform + active site = restored. - extreme pH = may be permanent change = denatured
how can cells adapt to their needs?
genes for synthesising particular enzymes can be switched on/off
why do cells continuously degrade old enzyme molecules to their amino acids and synthesis new enzyme molecules?
- elimination of abnormally shaped proteins that might accumulate and harm cell
- regulation of metabolism by eliminating excess enzymes
why is initial rate of reaction used as a standardised comparison?
fastest due to lots of substrate and lots of empty active sites = lots of collisions that are successful
so maximum rate for an enzyme under an experimental situationis given
How does cyanide act as an inhibitor?
CN- ions bind irreversibly to enzyme in mitochondria, inhibiting final stage= aerobic respiration stops
How does snake venom act as an inhibitor?
green mamba snake venom contains chemical that inhibits AChE
acetylcholine neurotransmitter stays attached to receptors on muscle membrane + keeps it contracted
causes paralysis: if muscles involved in breathing are paralysed, victims die from suffocation
What are nucleoside reverse transcriptase inhibitors?
used to treat HIV
inhibit enzymes involved in making DNA using viral RNA
Enzymes digest insects into Heliamphora traps. Is the mode of action of these extracellular or intracellular? Explain your answer (3)
Extracellular
- Digestion occuring in trap
- Not inside cells
- Enzymes released by plant cells into trap
- May also come from bacteria in trap
