Download BOCE2626(BIOCHEMISTRY) Test 1 2017 MEMO

UNIVERSITEIT VAN DIE VRYSTAAT
UNIVERSITY OF THE FREE STATE
HOOFKAMPUS / MAIN CAMPUS
BOCE2626
DEPARTEMENT MIKROBIESE, BIOCHEMIESE & VOEDSELBIOTEGNOLOGIE
DEPARTMENT OF MICROBIAL, BIOCHEMICAL & FOOD BIOTECHNOLOGY
KONTAKNOMMER / CONTACT NUMBER: 051 401 ????
SEMESTER TOETS 1 / SEMESTER TEST 1 – 2 September 2017
ASSESSOR(E)/ASSESSOR(S):
TYD / TIME: 1 ½ UUR / HOURS
Question 1 / Vraag 1
1. Dr. E.D. Cason
PUNTE / MARKS: 50
[19]
1.1
As catalysts, enzymes are / As kataliste is ensieme
a. significantly less effective than non-enzymatic catalysts / aansienlik
minder effektief as nie ensiematiese kataliste
b. slightly less effective than non-enzymatic catalysts / effens minder
doeltreffend as nie ensiematiese kataliste
c. significantly more effective than non-enzymatic catalysts / aansienlik
meer effektief as nie-ensiematiese kataliste
d. slightly more effective than non-enzymatic catalysts / effens meer effektief
as nie-ensiematiese kataliste
1.2
Enzymatic activity has an optimum temperature because / Ensiematiese
aktiwiteit het 'n optimum temperatuur omdat
a. the amino acids have varying melting points / die aminosure het
verskillende smeltpunte
b. the rate of reactions is thermodynamically controlled / die tempo van
reaksies is termodinamies beheer
c. the side chains of essential amino acids are chemically degraded at
higher temperatures / die sykettings van noodsaaklike aminosure verval
chemies by hoër temperature
d. raising the temperature speeds up the reaction until protein
denaturation sets in / die verhoging van die temperatuur versnel die
reaksie totdat die protein begin denatureer
1.3
The main difference between a catalyzed and an uncatalyzed reaction is that /
Die belangrikste verskil tussen 'n gekataliseer en ongekataliseerde reaksie is
dat
a. the activation energy of the catalyzed reaction is lower. / die
aktiveringsenergie van die gekataliseerde reaksie is laer.
1.4
b. the catalyzed reaction has a more favourable free energy change. / die
gekataliseerde reaksie het 'n meer gunstige vrye energie verandering.
c. the catalyzed reaction has a more favourable enthalpy change. / die
gekataliseerde reaksie het 'n meer gunstige entalpie verandering.
d. the catalyzed reaction has a more favourable entropy change. / die
gekataliseerde reaksie het 'n meer gunstige entropie verandering.
Which of the following is true? / Watter van die volgende is waar?
a. The E-S complex often dissociates with no reaction taking place. / Die E-S
kompleks dissosieer dikwels met geen reaksie wat plaasvind nie.
b. The E-S complex must form before a reaction can take place / Die E-S
kompleks moet vorm voordat 'n reaksie kan plaasvind
c. Once the E-S complex forms, it can go on to form product or dissociate to
E + S / Sodra die E-S kompleks vorm, kan dit gaan na produk of dit kan
dissosieer na E + S
d. All of these / Al hierdie
1.5
The active site of an enzyme / Die aktiewe setel van 'n ensiem
a. is frequently located in a cleft in the enzyme. / dikwels geleë in 'n kloof in
die ensiem.
b. is the portion of the enzyme to which the substrate binds. / is die deel van
die ensiem waar die substraat bind.
c. contains the reactive groups that catalyze the reaction. / bevat die
reaktiewe groepe wat die reaksie kataliseer.
d. all of these / al hierdie
1.6
In the induced-fit model of substrate binding to enzymes / In die geïnduseerde
passing model van substraat binding in ensieme
a. the substrate changes its conformation to fit the active site / die substraat
verander sy konformasie om die aktiewe setel te pas
b. the active site changes its conformation to fit the substrate / die aktiewe
setel verander sy konformasie om die substraat te pas
c. there is a conformational change in the enzyme when the substrate
binds / daar is 'n konformasie verandering in die ensiem wanneer die
substraat bind
d. there is aggregation of several enzyme molecules when the substrate
binds / daar is aggregasie van verskeie ensiem molekules wanneer die
substraat bind
1.7
The active site of an enzyme is the place where the following happens: / Die
aktiewe setel van 'n ensiem is die plek waar die volgende gebeur:
a. The enzyme substrate complex forms here. / Die ensiem substraat
kompleks vorm hier.
b. The catalytic reaction happens here. / Die katalitiese reaksie gebeur hier.
c. Allosteric regulation of enzyme rate occurs here. / Allosteriese regulering
van ensiem tempo gebeur hier.
d. The enzyme-substrate complex forms and the reaction occurs at the
active site. / Die ensiemsubstraat-komplekse vorm en die reaksie
vind plaas by die aktiewe setel.
e. All of these are correct. / Al hierdie korrek is.
1.8
Most enzyme reactions display first order kinetics for the individual substrates
when the substrate concentration is low. / Die meeste ensiemreaksies vertoon
eerste-orde kinetika vir die individuele substrate wanneer die substraat
konsentrasie laag is.
a. True / Waar
b. False / Vals
1.9
It is important that at physiological conditions, enzymes work at Vmax. / Dit is
belangrik dat by fisiologiese toestande ensieme teen V max werk.
a. True / Waar
b. False / Vals
1.10
The KM of hexokinase for glucose = 0.15 mM and for fructose, K M = 1.5 mM.
Which is the preferred substrate? / Die KM van hexokinase vir glukose = 0,15
mM en fruktose, KM = 1,5 mM. Wat is die voorkeur substraat?
a. Glucose. / Glukose.
b. Fructose. / Fruktose.
c. Neither substrate is preferred over the other. / Geen substraat word
verkies bo die ander nie.
d. You cannot tell from the data given. / Jy kan nie sê van die data gegee.
e. None of these answers is correct. / Nie een van hierdie antwoorde is
korrek.
1.11
A velocity curve (V vs. [S]) for a typical allosteric enzyme will be / 'n Snelheid
kurwe (V teen [S]) vir 'n tipiese allosteriese ensiem sal wees
a. a rectangular hyperbola. / 'n reghoekige hiperbool.
b. a sigmoid curve. / 'n sigmoidale kurwe.
c. a straight line. / 'n reguit lyn.
d. a parabola. / 'n parabool.
1.12
Homotrophic effects for allosteric enzymes involve / Homotrofiese effekte vir
allosteriese ensieme betrek
a. the same molecule binding to different sites in the enzyme. /
dieselfde molekuul bind aan verskillende plekke in die ensiem.
b. different molecules binding to the same site in an enzyme. / verskillende
molekules bind aan dieselfde plek in 'n ensiem.
c. different molecules binding to different sites in the same enzyme. /
verskillende molekules bind aan verskillende plekke in dieselfde ensiem.
d. All of these are homotrophic effects. / Al hierdie is homotrofiese effekte.
1.13
Which of the following is true? / Watter van die volgende is waar?
a. Allosteric enzymes are rarely important in the regulation of metabolic
pathways. / Allosteriese ensieme is selde belangrik in die regulering van
metaboliese weë.
b. Michaelis-Menten kinetics describe the reactions of allosteric enzymes /
Michaelis-Menten kinetika beskryf die reaksies van allosteriese ensieme
c. Allosteric enzymes have a hyperbolic plot of reaction rate vs. substrate
concentration / Allosteriese ensieme het 'n hiperboliese plot van
reaksietempo teen substraatkonsentrasie
d. none of these is true / Nie een van hierdie is waar
1.14
Allosteric enzymes must exhibit which of the following? / Allosteriese ensieme
moet watter van die volgende toon?
a. feedback inhibition / terugvoerinhibisie
b. a phosphorylation site / 'n fosforilering setel
c. general acid-base catalysis / algemene suur-basis katalise
d. a quaternary structure / 'n kwaternêre struktuur
1.15
The sequential model for allosteric behaviour / Die opeenvolgende model vir
allosteriese gedrag
a. cannot account for reactions that display negative cooperativity. / kan nie
reaksies verklaar wat negatiewe koöperatiwiteit vertoon nie.
b. postulates binding of substrates and inhibitors by the induced-fit
model. / postuleer binding van substrate en inhibeerders deur die
geïnduseerde passing model.
c. requires that the conformation of all subunits change simultaneously. /
vereis dat die konformasies van alle subeenhede gelyktydig verander.
d. is mathematically simpler than the concerted model. / wiskundig makliker
as die gesamentlike model.
1.16
Important mechanisms of enzymatic catalysis include / Belangrike
meganismes van ensiematiese katalise sluit in
a. nucleophilic reactions / nukleofiele reaksies
b. general acid-base catalysis / algemene suur-basis katalise
c. Lewis acid-base catalysis / Lewis suur-basis katalise
d. all of these / al hierdie
1.17
A transition-state analog is likely to bind to an enzyme / 'n Oorgang-staat
analoog is geneig om 'n ensiem te bind
a.
more tightly than the substrate. / stywer as die substraat.
b.
less tightly than the substrate. / minder styf as die substraat.
c.
about as tightly as the substrate. / omtrent so styf as die substraat.
d.
at a site other than the catalytic site. / op 'n ander plek as die katalitiese
setel.
1.18
Which of the following statements about coenzymes is true? / Watter van die
volgende stellings oor koënsieme is waar?
a. They are commonly derived from vitamins. / Hulle word algemeen verkry
vanaf vitamiene.
b. They bind to the active site on specific types of enzymes./ Hulle bind aan
die aktiewe setel of spesifieke tipes ensieme.
c. They can be metal ions, such as Zn(II)./ Hulle kan metaalione soos Zn(II)
wees.
d. NAD+ and FAD are both examples of coenzymes. / NAD+ and FAD is
beide voorbeelde van koënsieme
e. All of these statements are true./ Al hierdie stellings is waar.
Question 2 / Vraag 2
[2 x 4]
Define the following concepts/terms / Definieer die volgende konsepte/terme:
2.1
Steady-state / Bestendige toestand
The condition in which the concentration of an enzyme-substrate complex
remains constant in spite of continuous turnover
OR
The rate of formation of the enzyme-substrate complex is equal to the rate of
the breakdown of ES
2.2
Coenzyme / Koensiem
A nonprotein substance that takes part in an enzymatic reaction and is
regenerated for further reaction
2.3
Catabolism / Katabolisme
The breakdown of larger molecules into smaller ones, an oxidative process
that releases energy
2.4
Zymogen / Zymogeen
Inactive precursor of enzyme, irreversibly transformed to active enzyme by
cleavage of covalent bonds/Peptide Bonds
Question 3 / Vraag 3
[5]
Consider the Michaelis-Menten model to enzyme kinetics for the following reaction: /
Oorweeg die Michaelis-Menten model tot ensiemkinetika vir die volgende reaksie:
k1
E+S
k2
ES
E+P
k-1
3.1 Define the steady state in terms of the rate constants (k1, k-1 and k2) – this is
the starting point of the model derivatisation / Definieer die bestendige toestand
in terme van die snelheidskonstantes (k1, k-1 and k2) – dit is die beginpunt van
die model se afleiding
(3)
k1[E][S] (√) = k-1[ES] (√) + k2[ES] (√)
3.2 Give the Michaelis-Menten equation that relates initial velocity to substrate
concentration / Gee die Michaelis-Menten vergelyking wat die verband gee
tussen aanvanklike snelheid tot substraatkonsentrasie
(1)
V = Vmax [S] / (KM + [S])
3.3 How is Vmax defined? / Hoe word Vmax gedefineer?
V init
= V max =
k 2[E]T
Question 4 / Vraag 4
Competitive inhibition / Kompeterende inhibisie:
4.1
(1)
What is a competitive inhibitor? / Wat is ‘n kompeterende inhibitor?
[6]
(2)
Reversible Inhibitor
- Compound similar in structure to substrate
- Binds to active sit and blocks (competes) active site
4.2
How does a competitive inhibitor influence the KM and Vmax of an enzyme? /
Hoe beïnlvoed ‘n kompeterende inhibitor die KM en Vmax van ‘n ensiem? (2)
Vmax Unchanges
Km Increase
4.3
Sketch a Line-Weaver Burk plot to demonstrate your answer in 4.2 / Skets 'n
Line-Weaver Burk plot om jou antwoord in 4.2 te demonstreer.
(2)
Question 5 / Vraag 5
[6]
Discuss the concerted model for allosteric behaviour of enzymes / Bespreek die
gesamentlike model vir allosteriese gedrag van ensieme
-
Protein has 2 conformations
R -> Relaxed: Binds S Tightly
T -> Taut: Binds S Less Tightly
All Subunits Changes Simultaneosly
In Equilibrium Ratio (with high Temp)
Binding of S to R form causes shift, removes free R form and T form
Changes to R (LE Chateliers Principles)
-
Inh. Bind to T form, Act. Bind to R form => Also shirt to re-establish
equilibrium ratio.
Question 6 / Vraag 6
[7]
Sketch AND describe the intermediate step in the first stage of the reaction
mechanism of chymotrypsin where the active site Histidine acts as a base / Skets
EN beskryf die stap in die eerste deel van die reaksie meganisme van chimotripsien
waar die aktiewe setel Histidien dien as 'n basis.
-
His acts as base and abstracts proton from Ser, Ser (O-) potent nucleophile
Nucleophilic attack on carbonyl, double bond break
Tetrahedral intermediate forms
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