Enzymes Flashcards
What are enzymes?
Enzymes are globular proteins with a specific tertiary structure that catalyses metabolic reactions in living organisms
- They speed up chemical reactions and remain unchanged at the end
- small amount of catalyst can catalyse a large number of substrate molecules
- turn over number (second)
Describe the active site
Large, 100 of amino acids = specific tertiary structure, active site shape (indentation)
- tertiary structure complementary to substrate
- highly specific only catalyses reaction for substrate fits into active site
- shape (so ability) can be altered by changes in temperature, pH as affects bonds in tertiary
Explain intracellular enzymes in a metabolic pathway
Some reactions within cells and organelles are part of a metabolic pathway
- metabolites are reactants, intermediates and products
- catabolic = metabolites broken down to smaller and release energy
- anabolic = metabolites make larger molecules out of smaller (energy used)
- metabolites act as substrates for specific enzymes
Respiration and photosynthesis
Explain extracellular enzymes
Some enzymes secrete out of the cell
- Fungi mucor release hydrolytic enzymes from hyphae, digest carbs, proteins, lipids and the products absorb into hyphae for respiration and growth
- Digestive system: cells lining alimentary canal into gut lumen, digest products of digestion via epithelial cells into blood stream for respiration, growth, tissue repair
- some examples:
- amylase salivary gland digest polysacc starch into disacc maltose, made in pancreas (lumen of small intestine)
- trypsin made in pancreas digest proteins into peptides by hydrolysing peptide bonds 7.5 and 8.5 pH
Explain catalase
Protects cells from damage by reactive O2 by breaking down H2O2 harmful by-product to H2O and O2
- 4 polypeptide chains + haem iron
- fastest acting enzyme
- found in peroxisomes
- WBC to kill microbe
- pH 7 45 C optimum human
What is a cofactor?
A small,non protein molecule that must be present in an enzyme catalysed reaction
What is a prosthetic group and give an example
A cofactor that is permanently bound by covalent bonds to an enzyme
Carbonic anydrase and zinc ion = erthrocytes
CO2 + H2O = H2CO3 = H+ + HCO3-
Enables CO2 to be carried in blood stream from respiring tissues
Describe inorganic ion cofactors
Some enzymes work in the presence of ions that are not attached to them
- they bind to substrate or enzyme, easing the formation of ES, increase rate of enzyme reaction
- cosubstrates form correct shape for AS
- change charge distribution on enzyme or substrate temp bonds easier form
Amylase = starch to maltose Cl-
What are coenzymes?
Small, organic non protein bind temp to AS changed then recycled
Carry chemical groups between enzymes
What vitamins are important for enzyme reaction?
B1 thiamine thiamine pyrophosphate = beriberi B3 nicotinamide NAD NADP = pellagra B6 pantothenate coenzyme A = triglyceride high levels B12 cobalamin = pernious anemia Folic acid tetrahydrofolate = megablastic anemia
Describe and draw the lock and key hypothesis
Kinetic energy
- shape of AS is complementary and specific to substrate
- substrate successfully collides with active site substrate is they key and AS is lock forms an ES complex hold by temp H bonds
- products formed becomes enzyme-product no longer fit so are released
- small no. of enzyme molecules therefore can convert a large no. of substrate = product
Describe the induced fit hypothesis
- substrate molecule collides with complementary and specific AS, enzyme changes shape so AS fits more closely, held by H bonds, ionic bonds, VDW
- ES formed change in enzyme shape destabilises substrate converts to product
- products made EP no longer fit so are released
How do enzymes lower the activation energy?
Ea minimum level of energy required to enable reaction to take place
Enzymes lower the Ea so speed up metabolic reactions
Without the need for high temp (denature and melt)
Bring the substrate and molecules close enough to react
Less energy required
How does temperature effect the collisions between enzyme and substrate?
As temp increases, kinetic energy increases so the molecules move more quickly, this increases the rate of successful collisions, rate of formation of ES increases, so rate of product formation
What effect does heat have on proteins?
Heat makes molecules vibrate, breaks h bonds and ionic bonds, the tertiary structure of AS will change therefore substrate will no longer fit and reaction can’t proceed, the enzyme is denatured
What is the optimum temperature?
The temp at which enzymes works best, it works at maximum rate of reaction
Thermophilic bacteria contain more disulfide bonds that do not break with heat and keep shape stable
What is the temperature coefficient?
The increase in rate of a process when the temperature is increased by 10C
Q10 = rate of reaction (T+ 10)
rate of reaction at T
Draw a graph showing the effect of temperature on enzyme rate
Between A and B increasing temperature increases the rate of reaction due to increased kinetic energy
B is optimum temp gives maximum rate of reaction
Increasing temp beyond B reduces RoR due to breaking of the bonds holding the enzyme’s tertiary structure
C there is no reaction because enzyme is denatured
Describe how an enzyme breaks down a substrate
- substrate is complementary to enzyme’s active site
- substrate fits into the active site of enzyme
- forms ES complex
- destabilises bonds in substrate then forms enzyme-product complex
- products leave active site
What is a buffer?
Something that resists changes in pH, this is to ensure that blood pH remains in narrow limits, they donate or accept hydrogen ions
Used to maintain pH in experiments
How does pH affect molecules?
- H+ holds tertiary structure of active site
- excess H+ ions interfere with H bonds and ionic forces so AS will change shape (RoR decrease if substrate doesn’t fit)
- increasing conc of H+ alters charge on AS protons go to negatively charged R groups interfere with binding of the substrate
How do enzymes work in pH? Draw a graph and label
- work in a narrow pH range
- small changes slow down RoR as shape is disrupted
- permanently changed denatured
How do other enzymes work with examples? Show on a graph
- Amylase starch to maltose pH 6.8
- pepsin (protease) pH 1 and 2
- typsin and enterokinase pH 7.8 salts in bile in liver
Explain the effect of substrate concentration on initial rate of reaction
Substrate conc increases so does RoR
- more ES complexes
- more product molecules form
- limiting factor becuase as it increases so does RoR
- max rate: more substrate won’t increase RoR
- all enzymes AS are occupied with substrate
- if more is added they can’t successfully collide with and fit into AS
Explain the effect of enzyme concentration on initial rate of reaction
Enzyme conc increases so does RoR
- more active sites become available
- more successful collisions between E and S
- more ES complexes form RoR increases
- enzyme conc limiting factor
What happens if substrate conc is fixed or limited? Draw a graph and label
- if enzyme conc is increased further then there will be no increase in RoR AS will not be occupied by substrate molecules
- enzyme conc no longer limiting factor as enzyme conc increases RoR does not increase
- substrate conc limiting factor
What is enzyme degradation?
Protein component, cells degrade old enzymes to amino acids and synthesising new enzymes
- elimination of abnormal proteins may accumulate and harm the cell
- regulation of metabolism by removing excess enzymes
Degradation = synthesis
Explain how the initial rate of reaction changes over time
- at start there is a great chance of successful collisions
- as it proceeds substrate molecules used up as converted so conc substrate drops
- frequency between enzyme and substrate decreases because some enzymes collide with product so RoR slows
- initial reaction rate is max rate
Tangents
What is a competitive inhibitor?
Inhibition of an enzyme where inhibitor has a similar shape to substrate to AS and competes with substrate and blocks the AS prevents ES forming so reduces rate of products/reaction
Can be reversible and irreversible (inactivator)
What effect does this have on substrate concentration? Draw a graph
More inhibitor = more collisions with AS
More substrate = at a fixed conc of inhibitor they will be unlikely to form EI complexes more chance
What is non-competitive inhibition?
Inhibition of enzyme where inhibitor attaches to allosteric site and disrupt the tertiary structure and changes the AS so it is not complementary to substrate so can no longer bind prevents ES complexes form
It is also reversible and non reversible
What effect does non competitive have on substrate concentration? Draw a graph
The max RoR is reduced by NCI adding more substrate maintain lower rate but even high conc won’t allow RoR to return to normal
More inhibitors = greater more enzymes are distorted can’t form ES
What is end product inhibition?
At completion substrate remains so can’t form more of the product than cell needs, regulation called negative feedback
Describe the control of metabolic sequences
- product one one reaction becomes substrate for next enzyme
- don’t accumulate too much of product, substrate E attaches to enzyme 1 (not AS)
- changes shape of enzyme 1 preventing pathway reversible
- when product conc falls substrate E is released allow pathway to run again
- increases efficiency without increases substrate conc
Explain how metabolic poisons act as enzyme inhibitors
Cyanide
KCN is highly toxic inhibits aerobic respiration and catalase, ingested produces HCN gas H+ CN- binds to enzyme it mitochondria inhibits final stage of aerobic respiration
Snake venom
inhibits AChE nucleotransmitter ACh breaks down synapses in muscles stays on receptors muscle stays contracted = paralysis, breathing muscles then die
Explain how medicinal drugs act by enzyme inhibition
Aspirin
Salicylic acid binds to enzymes that catalyse prostaglandins (nerves more sensitive to pain and increase swelling) can reduce risk of blood clots forming reduce risk of stroke
ATPase
purple focgloves treat heart failure and atrial arrhythmia inhibit NaK allow more Ca ions to enter cuase muscle contraction = strength (digitoxin)
Explain how more medicinal drugs act by enzyme inhibition
ACE
operates in pathway that increases blood pressure they’re used to lower b.p hypertension (no beta blockers)
heart failure low dose and checked
minimise second heart attack or myocardial infarction
Protease
Amprenavir treat viral infections prevent replication of virus so virus coats can’t be made
Nucleoside reverse transcriptase
Zidovudine treat HIV inhibit enzymes making DNA and using viral RNA as a template
