Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biochemistry I > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What are cofactors?

Differentiate.

A

needed by some enzymes in order to function

  • prosthetic groups: organic mol. covalently bound to an enzyme → non-dissociable
  • coenzymes: organic mol. non-covalently bound to an enzyme → dissociable
  • metall ions: bound to sec. interactions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the native conformation of enzymes?

A

maximal catalytic activity at distinct ph and temp.

  • pH: optimum is NEVER at IP
  • T: ↑ T → ↑ Ekin → ↑ activity, but if T too high, denaturation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do enzymes change reaction kinetics?

A

change reaction mechanism
BUT: catalyze in both direction

  • decreased Ea
  • unchanged ΔG
  • unchanged EQ-state, but decreased time to reach EQ
  • unchanged thermodynamics (half life, reaction order, etc.)

REMEMBER diagram

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is enzyme activity?

Formula + unit.

A

amount of substrate converted to product per unit time

EA = -Δ[S]/Δt = Δ[P]/Δt

measured in [Catal] = [mol/sec], [μmol/min]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is specific enzyme activity?

Unit.

A

amount of product formed in a given amount of time per mg of total protein

→ enzyme activity per per mg of total protein

in [kat/mg]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Define turnover number.

Formula + unit.

A

max. amount of products that is formed by a single catalytic site per second

kcat = np / nE * t

in [mol(P) / mol(E)*sec]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is an important medical application of enzyme activity measurements?

A

measurement of non-functional plasma enzymes

⇒ marker enzymes for blood plasma indicate died tissue cells → information abt tissue problems

ex: after heart attack

  • creatine kinase CPK
  • lactate dehydrogenase LD
  • α-hydroxbutyrate dehydrogenase HBDH
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Explain the 2 different enzyme models.

A

enzyme-substrate complex ES stabilized by sec., ionic, covalent bonds

lock and key model:

S + E have specific shape → fit exactly into one another

induced fit model:

E changes slightly its shape as S binds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Distinguish btw different enzyme mechanisms.

A
  • catalysis by proximity: enzyme brings together substrates in proper orientiation, incr. the prob of succesfull collisions
  • acid-base catalysis: enzyme transfers H+/OH- from one substrate to another
  • covalent catalysis: enzyme forms covalent bonds substrates, providing an energetically more favorable reaction partner
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are proteases?

What is the most important group among proteases?

List some examples.

A

cuts proteins by hydrolysis of peptide bonds

Ser-proteases = Ser in active center

  • trypsin, chymotrypsin
  • elastase
  • thrombin + other blood coag. factors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is DIPF?

Why is it pretty cool?

A

diisopropylphosphofluoridate

  • *irreversible inhibitor of Ser-enzymes**
  • (ex: chymotrypsin + acetylcholinesterase)*

→ used as biochemical weapon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are zymogens?

A

proenzymes = inactive enzyme precursors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are trypsinogen and chymotrypsinogen?

Explain their proteolytic activation pathway.

A

trypsinogen + chymotrypsinogen stored as zymogens to protect pancreas from autodigestion

  1. activation of trypsinogen → trypsin
  2. activates chymotrypsinogen → π​-chymotrypsin
  3. cut each other into shorter fragments → α-chymotrypsin = active peptidase
  4. trypsin inactivated by inhibitor → chymotrypsinogen activation ceases
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the catalytic triad in case of chymotrypsin?

What type of catalysis is it?

A

proton shuttle in active center of Ser-proteases

here: 102Asp 57His 195Ser

→ covalent catalysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Explain the reaction mechanism of chymotrypsin.

A

catalysis of peptide bond

  1. S binds to 195Ser, shifts -OH H+ to 102Asp
  2. nucleophilic attack of Ser O on C of peptide bond → acyl-enzyme intermediate
  3. H+ shuttled to peptide → H2N-R pinches off (= 1st product) when replaced by H20
  4. H20 withdraws H+ to 102Asp
  5. OH- attacks acyl-enzyme intermediate → H+ shuttled back to 195Ser
  6. original conformation restored → COOH-R pinches off (= 2nd product)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Explain the specificity of the Ser-proteases chymotrypsin, trypsin and elastase.

A

depends on R-side chain

  • chymotrypsin: big, non-polar pocket
    → only aromatic rings: Phe, Tyr, Trp
  • trypsin: negatively charged pocket
    → only pos. charged: Arg, Lys
  • elastase: small pocket
    → only small -R: Gly, Ala, Ser

REMEMBER: chY, tYr. And just know the rest

17
Q

What is the vi of enzyme kinetics?

Which conditions must be fulfilled in order to measure it correctly?

A

initial reaction rate
rate (approx. linear) where highest amount of products is formed by enzyme

conditions for the measurement:

  • rel. short time
  • molar excess of S over E
  • reverse reaction negligible
18
Q

What is the Michaelis-Menten equation?

Consequences?

A

describes enzyme kinetics
→ the lower KM, the greater vi

consequences:

  • low substrate conc: vi = vmax*[S]/KM
  • substrate conc = Km: vi = vmax/2
  • high substrate conc: vi approaches vmax
    → all E in ES complex
19
Q

What does the Michaelis constant describe?

A
  • low KM = enzyme has high affinity for substrate
  • high KM = enzyme has low affinity for substrate
20
Q

What is the Lineweaver-Burk plot?

Another name.

A

double reciprocal plot
instead of Vi vs [S], 1/Vi vs 1/[s]

  • y-intercept = 1/Vmax
  • x-intercept = -1/Km
  • slope = KM/Vmax

​⇒ used to determine KM, Vmax

21
Q

What are isoenzymes?

Characteristics?

A

enzymes that differ in AA sequence but catalyze the same reaction

  • coded by diff. genes
  • may have diff. kinetic parameters (v, KM)
  • same substrate specificity, BUT may also catalyze other substrates
  • activated under diff. circumstances
22
Q

Compare the Km of btw glucokinase and hexokinase.

A
  • hexokinase: always active to supply O2 dependent tissues w/ glucose (↓ KM → ↑ affinity)
  • glucokinase: only active when hyperglycaemia, e.g. after meal (↑ KM → ↓ affinity)
23
Q

What is lactate dehydrogenase?

A

tetrameric enzyme consisting of 2 monomer types:
H (heart) and M (muscle) → 5 LDH isozymes:

  • HHHH predominates in heart tissue
  • HHHM, HHMM, HMMM,
  • MMMM in the liver

→ LDH levels rise in blood plasma, injured tissue type can recognized by isozyme pattern (marker enzyme)

24
Q

Differentiate btw mechanisms of irreversible inhibitors like poisons.

Examples.

A
  • action on active center: covalent bond on act. center (e.g. DIPF)
  • nonspecific inhibitors: denaturation (e.g. heavy metals, heat)
25
Q

What is competitive inhibition?

What are its effects on enzyme kinetics?

A

substrate analogue binds to active site
→ prevents [ES]-complex formation

  • *Vmax** unchanged (when S binds to E, E still functioning properly)
  • *KM ↑** → affinity ↓ (more molecules present, competition for S to bind)
26
Q

How can competitive inhibition be overcome?

Depends on… ?

A

can be overcome by increasing [S], exact amount depends on:

  • [I]
  • KI (affinity of I for E)
  • KM (affinity of E to bind to S)
27
Q

What is non-competitive inhibition?

What are its effects on enzyme kinetics?

A

bind to E (not on active site), but affect E’s catalysation activities during the time of binding

  • *↓ V**<strong>max</strong> (due to decr. activity)
  • *KM unchanged** (no competition for S binding to act. site)
28
Q

What is uncompetitive inhibition?

What are its effects on enzyme kinetics?

A

inhibitor binds only to ES-complex

  • *Vmax ↓** (takes longer for substrate/prod. to leave act. site)
  • *KM ↓** → affinity ↑ (b/c less active enzyme complexes present, less competition)
29
Q

What is allosteric regulation?

A

substance binds to allosteric binding site and induces a conformational change

30
Q

What are K, V type inhibitors?

How do they effect enzyme kinetics?

A

​types of allosteric inhibitors, can be activating/inactivating

  • K type: change KM
  • V type: change Vmax
31
Q

What is a cooperative enzyme?

What are the 2 types of cooperativity?

A

multimeric enzyme that binds substrate at 2+ sites

  • homotropic cooperativity
  • heterotropic cooperativity
32
Q

What is homotropic cooperativity?

A

S binds to catalytic subunit → activates other cat. subunits

tense (low affinity) → relaxed (high affinity) state

ex: hemoglobin when O2 binds

33
Q

What is heterotropic cooperativity?

Example.

A

activation or inactivation of further cat. subunits upon ligand binding changes w/ different ligands

ex: ATCase resp. for 1st step of synthesis of pyrimidine is activated by ATP,
inactivated by CTP

Biochemistry I (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions