Enzymes (LOIL 2) Flashcards
Enzymes can occur in 2 different forms. State, and explain, what these 2 forms are
- Holoenzymes - contain a prosthetic group
2. Apoenzymes - don’t contain a prosthetic group
state what it is meant by the key term - co-factors
co-factors are non-protein factors which are essential for enzyme activity, can be organic or inorganic (eg - metallic ions)
state what it is meant by the key term - co-enzymes
co-enzymes are substances that enhance the action of an enzyme (organic co-enzymes are derived from water soluble vitamins; fat soluble vitamins do no form co-enzymes)
state what it is meant by the key term - co-substrates
co-substrates are loosely and transiently bound co-factors
state what it is meant by the key term - prosthetic group
a prosthetic group is a non-protein group forming part of, or is combined with, a protein
state 2 facts about prosthetic groups
- usually a small inorganic molecule or atom
2. usually tightly bound to the enzyme
state 2 facts about co-enzymes
- large organic molecule
2. loosely bound to the apoenzyme
state the function of the following enzyme - Riboflavin/B2
forms part of the coenzyme - FAD (flavin adenine dixnucleortide)
state the function of the following enzyme - Niacin/B3
forms part of the coenzyme - NAD (nicotinamide adenine dinucleotide)
state the function of the following enzyme - Pantothenic Acid/B5
forms part of the coenzyme - CoEnzyme A
state the function of the following enzyme - Biotin/B7
forms part of the - Biotin coenzyme
state the function of the following enzyme - Thiamine/B1
forms part of the coenzyme - Thiamine Pyrophosphate TTP
state the function of the following enzyme - Pyridoxine/B6
forms part of the coenzyme - Pyridoxal Phosphate
what is the term for a deficiency in Niacin/B3 ?
Pellagra
what is the term for a deficiency in Thiamine/B1 ?
BeriBeri
state the functions for the following deficiency - Riboflavin/B2 Deficiency
- itching and burning eyes
- sluggishness
- oily skin
- night blindness
- mouth/lip sores
- sore throat
- skin disorders
- fatigue
- anaemia
- development deformities (eg - cleft lip)
state the functions for the following deficiency - Pellagra (Niacin/B3 deficiency)
- neurological impairments
- skin inflammation
- nausea
- decreased appetite
- watery diarrhoea
state the functions for the following deficiency - Pantothenic Acid/B5 deficiency
- vomiting
- fatigue
- stomach pain
- irritability
state the functions for the following deficiency - Pyridoxine/B6 deficiency
- sore glossy tongue
- cracked and sore lips
- skin rashes
state the functions for the following deficiency - Biotin/B7 deficiency
- scaly skin
- skin lesions
- dry and dull hair
- scruffy appearance
- lethargy
- alopecia
- reduced growth rate
- diarrhoea
state the functions for the following deficiency - BeriBeri (This,ine/B1 deficiency)
- shortness of breath
- swelling of feet
- increased heart rate
- tingling in hands and feet
when is a steady state of a reaction reached ?
a steady state is reached a short time after the initial mixing of an enzyme and a substrate
explain what it is meant by the key term - V (velocity)
V = the quantity of reactant which disappears in a given time frame
explain what it is meant by the key term - activity/velocity
umol/min (depends on the amount of protein)
explain what it is meant by the key term - specific activity
umol/min.mg
explain what it is meant by the key term - ‘enzyme unit’
amount which gives 1 umol product/min
explain what it is meant by the key term - Katal (SI)
about which gives 1 Mol/sec
what is a first order reaction ? (5 points)
- A —–> P
- reactions that are directly proportional to the reactant concentration
- the rate of the reaction is directly related to the concentration of A by a proportionality constant - k (the rate constant)
- V = k[A]
- units = s-1
explain second order reactions (3 points)
- two reactants: A + B —-> P
- V = k[A][B]
- units = M-1 s-1
state what it is meant by the key term - Pseudo First Order Reactions (2 points)
- when a second order reaction can appear to be a first order reaction
- eg - if B is in excess and A and low conc^, the reaction rate will be 1st order with respect to A and will not appear to depend on [B]
how do you measure reaction rate ? (2 points)
- follow each reaction over time
2. measure [P] or [S] and time
what are the two equations for reaction rate ?
- V = Δ[P] / Δt
2. V = Δ[S] / Δ
state the 3 phases of an enzyme reaction
- Pre-steady state (micro second equilibration, too short to measure)
- steady state
- substrate depletion
state what it is meant by the key term - ‘direct assay’
assay has a way of detecting P or S directly due to some property off either - can be measured continuously
state what it is meant by the key term - ‘discontinuous direct assay’ (2 points)
- the reaction is stopped at set time points to measure P or S
- the assay to measure P or S may quench the enzyme
explain what a ‘Couples Assay’ is (4 points)
- sometimes P or S can’t be measured
- P can be consumed in another reaction
- the product of the 2nd reaction can be measured
- 2nd enzyme must be in excess to ensure that the rate limiting step is the one to be measured
state the 4 factors which effect enzyme rate
- enzyme concentration - [E]
- substrate concentration - [S]
- temperature
- pH
reaction rate is proportional to [E] providing what 2 things ?
- the substrate is not rate limiting
2. the product is not in excess
what is Vo ?
Vo is the initial velocity of a reaction at t = 0 (as close as measurable)
state 2 introductory facts about Michaelis and Menten
- in 1913, Leonor Michaelis and Maud Menten proposed a simple method to account for the kinetic characteristics
- the critical feature in their treatment in that a specific ES complex is a necessary intermediate in catalysis
what is a steady state system ?
in a steady state system, the concentrations of the intermediaries stay the same, even though the concentrations of products and substrates are changing
finish the sentence:
E + S = ES complex….
E + S = ES complex, with a rate constant
The ES complex has 2 possible fates. What are they ?
- it can dissociate to E and S, with a rate constant - k
2. it can proceed to form P, with a rate constant - k2
explain what can also occur with the ES complex
The ES complex can also be reformed from E and P by the reverse reaction with a rate constant - k-2. However, as before, we can simplify these reactions by considering the rate of reaction at time close to 0 (Vo) when there is negligible product formation, and thus no back reaction (no k-2)
state the 3 main assumptions of ‘Michaelis-Menten Kinetics’
- the step of (ES —-> E + P) is irreversible - no K-2
- [ES] is in steady state (K1 = K-1 + K2)
- E < km
state the ‘Michaelis Menten Equation’
Vo = (Vmax[S]) / (km + [S])
what enzymes don’t follow MM kinetics, and why ?
allosteric enzymes as they consist of multiple sub-units and multiple active sites
explain the characteristics of an enzyme with a high km
enzymes with a high km have a low affinity for its substrate and requires a greater concentration of substrate to achieve its Vmax
km (Michaelis Constant) varies for each enzyme with what 3 things ?
- Substrate
- pH
- Ionic Interactions
explain what km (Michaelis Constant) is using 3 points
- provides a measure of the [S] required for significant catalysis to take place
- the higher the km of an enzyme, the lower its affinity for its substrate
- a higher km means that it takes a lot of substrate before the enzyme gets to Vmax/2
what is the reason for the ‘Line-Weaver Burk Plot’ (2 points)
- linearised data gives straight forward regression analysis to yield kinetic parameters
- a line-weaver burk plot is widely used to transform a MM graph into linear form to make it easy to find the km and Vmax
explain, using 4 points, what it is meant by the key term - Kcat
- kcat = rate of catalysis = turnover number
- kcat = Vmax / [E]
- number of substrate molecules transformed per minute by a single enzyme molecule when the enzyme is the rate limiting factor
- units = ms-1
what do allosteric enzymes often display ?
allosteric enzymes often display ‘Sigmoidal Plots’ of the reaction velocity
