Davina Jugnarain
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Degree (Enzyme Kinetics) Biochemistry Test sobre Enzyme Kinetics 2, creado por Davina Jugnarain el 26/05/2016.

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Davina Jugnarain
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Enzyme Kinetics 2

Pregunta 1 de 27

1

Which are true about bisubstrate reactions?

Selecciona una o más de las siguientes respuestas posibles:

  • They use one substrate to yield two products

  • They use two substrates to yield two products

  • The two types of bisubstrate reactions are transferase and redox reactions

  • The two types of reactions are transferase and substitution reactions

  • 10% of reactions are bisubstrate

  • 60% of reactions are bisubstrate

  • 80% of reactions are bisubstrate

Explicación

Pregunta 2 de 27

1

A transferase reaction is one where the functional group on one substrate is transferred to another substrate

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 3 de 27

1

In redox reactions, oxidising equivalents are transferred between substrates

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 4 de 27

1

In bisubstrate reactions with a sequential mechanism, all substrates must combine with the enzyme before the reaction can occur and products are released. Which of the following are also true of sequential bisubstrate reactions?

Selecciona una o más de las siguientes respuestas posibles:

  • Ordered sequential means that the substrates must bind in a particular order

  • Ordered sequential means that the substrates must bind and be released in a particular order

  • Random sequential means that the products may be released in any order

  • Random sequential means the substrates and products may be released in any order

  • A Bi Bi reaction is bisubstrate

  • A Bi Bi reaction has 2 substrates and 2 products

  • The Lineweaver-Burk plot will be like that of uncompetitive inhibition

  • The Lineweaver-Burk plot will be like that of competitive inhibition

Explicación

Pregunta 5 de 27

1

In Ping-Pong reactions, one or more products are released before all substrates have combined with the enzyme. Which of the following are also true of Ping-Pong reactions?

Selecciona una o más de las siguientes respuestas posibles:

  • They are also referred to as "double displacement" reactions

  • They are also referred to as "transient displacement" reactions

  • Functional groups are transferred to the substrate directly

  • Functional groups are sometimes transferred to the enzyme

  • Enzyme intermediates in Ping-Pong are stable and can be purified and characterised

  • Enzyme intermediates in Ping-Pong are transient and can't be purified or characterised

  • The Lineweaver-Burk plots are like those for competitive inhibition

  • The Lineweaver-Burk plots are like those for uncompetitive inhibition

  • Binding of one substrate will encourage binding of a second substrate

  • Binding of one substrate will inhibit binding of another one

Explicación

Pregunta 6 de 27

1

Pancreatic triacylglycerol lipase catalyses the hydrolysis of the esters of fatty acids into free esters and is involved in protein digestion.

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 7 de 27

1

Pancreatic triacylglycerol lipase is secreted by the pancreas and also found in saliva and the stomach

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 8 de 27

1

Free esters released from lipid digestion of fatty acids, are more soluble than fatty acids.

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 9 de 27

1

Pancreatic triacylglycerol lipase catalyses the hydrolysis of triacylglycerols at position 1 and 2 on the glycerol molecule, and formation of 1,2-diacylglycerols and 2-acylglycerols

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 10 de 27

1

Which are true about lipase?

Selecciona una o más de las siguientes respuestas posibles:

  • It is only present in an aqueous form

  • It is present in aqueous solution and as a micelle

  • It requires an Mg co-factor for activity

  • It requires a procolipase co-factor for activity

  • Lipase is a zymogen

  • Procolipase is a zymogen

  • The active site is permanently open

  • There is a flap that masks and closes the active site

Explicación

Pregunta 11 de 27

1

What residues compose the catalytic triad of pancreatic triacylglycerol lipase?

Selecciona una o más de las siguientes respuestas posibles:

  • His

  • Asp

  • Glu

  • Pro

  • Ser

  • Thr

  • Phe

  • Leu

Explicación

Pregunta 12 de 27

1

The mechanism of triacylglycerol lipase:

Asp . His can then to increase its nucleophilicity. Then Ser is able to launch a nucleophilic attack on the (the glycerol backbone). This forms a , which is stabilised by (with residues ). The negative charge collapses as and the carbonyl reforms, releasing the first product, .

His then abstracts a proton from a molecule of water, forming a reactive . can than attack the , forming another intermediate, which is stabilised in an oxyanion hole. The negative charge collapses when , reforming the catalytic Ser and allowing release of a 2nd product, .

Arrastra y suelta para completar el texto.

    H-bonds to His, to increase its basicity
    launches attack on glycerol
    coordinates an Mg ion
    abstract a proton from Ser
    abtract a proton from Asp
    abstract a proton from water
    ester carbonyl of the fatty acids
    glycerol backbone
    carboxylic acids
    tetrahedral intermediate
    planar intermediate
    octahedral intermediate
    an oxyanion hole
    a Mg ion
    the active site
    Phe and Leu
    Asp, Ser and His
    Glu and Asp
    His protonates the glycerol backbone
    water donates a proton to the glycerol
    1,2-diacylglycerol
    2-acylglycerol
    a free fatty acid
    1-acylglycerol
    hydroxyl anion
    proton
    hydroxyl radical
    This OH
    This H
    This OH radical
    carbonyl carbon of the lipid
    free fatty acid chain
    carboxylic acid
    His protonates Ser
    His protonates Asp
    Ser abstracts a proton from water
    Ser abstracts a proton from Asp
    a 1-acylglycerol
    free fatty acid or monoglyceride
    free fatty acid

Explicación

Pregunta 13 de 27

1

PLCA2 (phospholipase A2) requires a conformational change to function.

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 14 de 27

1

In PLCA2, the hydrophobic binding pocket is blocked by an inhibitor

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 15 de 27

1

The active site of PLCA2, consists of which of the following catalytic residues?

Selecciona una o más de las siguientes respuestas posibles:

  • His

  • Asp

  • Ser

  • Water

  • Glu

Explicación

Pregunta 16 de 27

1

The active site contains a bound Mg.

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 17 de 27

1

PLCA2 mechanism: His is to activate for nucleophilic attack, so there is a which will later attack the scissile carbonyl carbon. Asp makes His more basic, His abstracts a proton from water. The activated water can nucleophilically attack the , forming a tetrahedral intermediate. The role of Ca2+ is to coordinate the activated water molecule and eletrostatically stabilise negative charge on the oxygen of the tetrahedral intermediate (). Then there is the collapse of the tetrahedral intermediate. The to the hydroxyl group, causing it to abstract a proton from the lipid and reform water

Arrastra y suelta para completar el texto.

    too far
    too weak
    too basic
    second water
    Ser residue
    carbonyl carbon
    phosphate group
    His residue
    metal catalysis
    electrostatic catalysis
    acid-base catalysis
    His H-bonds
    Ser abstracts a proton
    His donates a proton

Explicación

Pregunta 18 de 27

1

Which are true of monotopic enzymes?

Selecciona una o más de las siguientes respuestas posibles:

  • They tend to bind hydrophobic substrates

  • Subtrates tend to be lipid-soluble and can diffuse through the lipid bilayer

  • Some oxidoreductases are monotopic and so are some peptidases

  • All transferases reactions are catalysed by monotopic enzymes

  • They bind hydrophilic, aqueous substrates

Explicación

Pregunta 19 de 27

1

Which are true of multi-span enzymes?

Selecciona una o más de las siguientes respuestas posibles:

  • Many peptidase are multispan and cleave peptides for transloaction

  • Transferases are a type of multispan enzyme

  • Multispan enzyme have multiple TMs

Explicación

Pregunta 20 de 27

1

The gram negative cell wall is less robust and lacks mechanical strength as there is less peptidoglycan.

Selecciona uno de los siguientes:

  • VERDADERO
  • FALSO

Explicación

Pregunta 21 de 27

1

LpxC is an essential zinc-dependent deacetylase of bacterial lipid A synthesis producing UDP-3-O-N-glucosamine. Which of the following are true about it?

Selecciona una o más de las siguientes respuestas posibles:

  • It is only present in gram-negative bacteria

  • It catalyses the reaction from UDP-3-O-N-acetylglucosamine (UDP-GlcNac) --> UDP-3-O-N-glucosamine + acetate

  • It catalyses the reaction from UDP-3-O-N-acetylglucosamine (UDP-GlcNac) --> 3-O-N-acetylglucosamine + UDP

  • The key residues involved are Asp and His

  • The key residues involved are Glu and His

  • A bound Mg ion is required

  • A bound Zn ion is required

Explicación

Pregunta 22 de 27

1

1 proposed mechanism for LpxC action:

binds the active site. Glu acts as a base and , making a good nucleophile to attack the . His stabilises the that develops. The negative charge collapses and and the lipid. is also formed which loses a to form . The product leaves and the Zn-lipid complex is displaced by water molecule and a new substrate.

Arrastra y suelta para completar el texto.

    Zn
    Mg
    deprotonates water
    deprotonates Glu
    protonates water
    carbonyl carbon
    hydroxyl group
    alpha carbon
    negative charge
    positive charge
    Glu acts as an acid
    Glu acts as a base
    donates a proton back to
    abstracts a proton from
    Acetic acid
    UDP
    proton
    phosphate
    acetate
    UTP

Explicación

Pregunta 23 de 27

1

Why is mechanism 1 for LpxC thought to be incorrect? What is the correct mechanism?

Selecciona una o más de las siguientes respuestas posibles:

  • The mechanism suggests His is just stabilising, when it is actually acting as an acid by donating a proton to the tetrahedral intermediate as shown by mutagenesis

  • The correct mechanism is that the His is initially protonated, and then later protonates the lipid, and another water will bind Zn and be used

  • Mutating Glu to Ala, reduced activity, supporting the alternative mechanism

  • Mutating Glu to Ala, reduced activity, supporting both mechanisms

  • Mutating His to Ala, reduced activity, supporting both mechanisms

  • Mutating His to Ala, reduced activity, supporting the alternative mechanism

  • The mechanism suggests Asp is just stabilising, when mutagenesis shows that it is involved in the reaction as its mutation gives reduced activity

Explicación

Pregunta 24 de 27

1

In terms of bacterial cell wall biosynthesis, which are true of transglycosylation?

Selecciona una o más de las siguientes respuestas posibles:

  • The cell wall is purely an immune system physical barrier

  • The cell wall is an essential structure in scaffolding the cytoplasmic membrane and maintaining structural integrity of the bacteria

  • Glycosyltransferase (GT) and transpeptidase (TP) enzymes are involved in cell wall biosynthesis

  • There are antibiotics that inhibit the activity of GTs, such as beta-lactams (e.g. penicillin), glycopeptides (e.g., vancomycin) and glycolipopeptides

  • There are antibiotics that inhibit the activity of TPs, such as beta-lactams (e.g. penicillin), glycopeptides (e.g., vancomycin) and glycolipopeptides

  • Bacteria gain resistance to these antibiotics by accumulating mutations in the TP enzymes

  • Bacteria gain resistance to these antibiotics by mutating their cell wall

  • GT enzymes catalyse transfer of a sugar glycosyl nucleotide donor substrate to a specific hydroxyl group of another sugar, or to other acceptors (e.g. lipids)

  • GT enzymes transfer a glycosyl substrate to a tertiary hydroxyl on nucleotide sugar acceptors (e.g. lipids)

  • Peptidoglycan transglycosylation by the enzyme GT takes place through polymerization of lipid II substrates

Explicación

Pregunta 25 de 27

1

To form peptidoglycans, enzymes exist to make trans additions of sugars. Which are true?

Selecciona una o más de las siguientes respuestas posibles:

  • Glycosyltransferase catalyses the transfer of a sugar glycosyl to a nucleotide

  • Glycosyltransferase catalyses the linking of sugar molecules to other sugars or lipids

  • Transpeptidase links L-ala residues to other L-ala residues, cross linking them

  • Transpeptidase links D-ala residues to other D-ala residues, cross linking them

  • Transpeptidase is linked to glycosyltransferase by a linker and glycosyltransferase is partially embedded in the membrane

  • Lipids for cell wall composition are fed through the plasma membrane and deposited in the periplasmic space

  • Lipids for cell wall composition are derived from the cytoplasm and transported to the periplasm by active transport

Explicación

Pregunta 26 de 27

1

Transglycosylation mechanism of glycosyltransferases (GTs):

Lipid binds to the membrane protein in a pocket and another lipid is fed through the membrane.
The E114 residue acts as a , abstracting a proton from the group of the .
Oxygen activates to act as a good nucleophile and can make attack on of sugar moiety.
Glu E171 stabilises the negative charge forming (phosphate groups), coordinating that form on the donor.
Stabilisation is either directly or indirectly, mediated by a to stabilise negative charge.
Upon attack on sugar, leaving group can diffuse out of active site to give higher oligomeric state of lipid (through addition of more sugar to the incoming lipid).
Must go from conformation (because SN2 attack)

Arrastra y suelta para completar el texto.

    bronsted base
    bronsted acid
    4-OH
    3-OH
    2-OH
    lipid II acceptor
    lipid I acceptor
    C1 position
    C2 position
    pyrophosphate groups
    phosphate groups
    divalent metal cation (e.g. Mg)
    Lys residue
    monovalent metal cation (e.g. Li+)
    lipid-pyrophosphate
    lipid-phosphate
    boat to chair
    chair to boat

Explicación

Pregunta 27 de 27

1

Mechanism for lipid II polymerisation by TG (transglycosylase):

Glu acts as bronsted base and on of a lipid II molecule at the .
This is followed by a simultaneous reaction with the C1 of another lipid II at S2 site with Glu.
stabilise the negative charge of phosphate and facilitate its diffusion as a leaving group.
Then there is the to growing chain.
Essentially, the lipid II’s glycosyl reacts with the acceptor site (S1) of lipid II to form a linked glycan chain.
Lipid keeps growing until certain length before leaving.

Arrastra y suelta para completar el texto.

    deprotonates 4-OH
    deprotonates 3-OH
    protonates H2O
    GlcNAc
    Acetate
    UDP
    acceptor site (S1)
    donor site (S2)
    Lys and Arg
    Glu and Asp
    His and Lys
    transfer of the sugar and phosphate
    elimination of the sugar and phosphate
    S2 site
    S1 site
    β1–4-
    α1-4-
    β2-4

Explicación

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