Brainscape's Knowledge GenomeTM

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


See full index

EoM > Enzymes: Mechanisms Of Action and membrane function > Flashcards

Enzymes: Mechanisms Of Action and membrane function Flashcards

1
Q

Enzymes

A
  • catalyze reversible reactions
  • the specificity of each reaction is established through the use of specific enzymes that catalyze each reaction.
  • diverse mechanisms of catalysis have evolved to solve the unique problems of synthesis, degradation, transport, replication, motility, and communication
  • study through kinetic analysis of their behaviors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why are enzymes over inorganic catalysts?

A
  • greater reaction specificity: avoids side products
  • milder reaction conditions: (37C, pH 7)
  • higher reaction rates: in a biologically useful timeframe
  • ## Capacity for regulation: control biological pathways
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Proteins (enzymes)

A
  • oxireductase
  • transferase
  • hydroplane
  • leases
  • isomerases
  • ligase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

RNA enzymes (Ribozymes)

A
  • ribosomes

- hammerhead, hepatitis delta virus RNA, group I intron ribozymes

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

Oxireductases

A
  • transfer of electrons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Transferases

A

-group transfer reactions

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

Hydrolases

A

-hydrolysis reactions (transfer of functional groups to water)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Lyases

A
  • cleavage of C-C, C-O, C-S, and C-N bonds by condensation reactions coupled to cleavage of ATP or similar cofactor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Isomerases

A

-transfer of groups within molecules to yield isomeric forms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Ligases

A

-Formation of C-C, C-S, C-O, and C-N bonds by condensation reactions coupled to cleavage of ATP or similar cofactor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Enzyme Nomenclature

A
  • some are still known by traditional names : pepsin, kinase, trypsin
  • a numeric system of nomenclature
  • first digit denotes class name
  • the second digit denotes subclass
  • third digit denotes the acceptor atom
  • fourth digit denotes the acceptor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Prosthetic group

A
  • tightly and stably incorporated into a protein’s structure by covalent or no covalent forces
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Cofactors

A

-bind in a transient, dissociable manner either to the enzyme or to a substrate such as ATP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Coenzymes

A
  • serve as group transfer as group transfer agents and transport many substrates from one point within the cell to another
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Apoenzyme

A
  • enzyme without the factor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Holoenzyme

A

-complete enzyme with prosthetic group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Pyruvate dehydrogenase Complex

A
  • Enzymes:
    1) E1- pyruvate dehydrogenase
    2) E2- dihydrolipoyl transacetylase
    3) E3 - dihydrolipoyl dehydrogenase
  • Coenzymes
    1) TPP - bound to E1
    2) Lipoate-covalently linked to E2
    3) Coenzyme A - substrate for E2
    4) FAD - bound to E3
    5) NAD - substrate for E3 - reduced by FADH2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

FAD and FMN

A
  • flavin nucleotides are tightly bound to flavoproteins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

NAD+ and NADP+

A
  • contains vitamins B3 niacin
  • involved in redox reactions, carrying electrons from one reaction to another. The coenzyme is found in two forms. NAD+ is an oxidizing agent - accepts electrons from other molecules and becomes reduced.
  • Niacin deficiency causes pellagra
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Tetrahydrofolate

A
  • carrier of one C group

- deficiency causes low birth weight infant and spina bifida

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Models of Enzyme-Substrate Interaction

A
  • enzyme catalyzed reactions, a strong interaction is formed between a substrate and a cleft or pocket on the enzyme’s surface that forms part of a region called the active site.
  • Lock and Key
  • Induced Fit
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Lock and Key

A

The enzyme dihydrofolate reductase with its substrate NADP+ , NADP+ binds to a pocket that is complementary to it in shape and ionic properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Induced fit

A

-conformational changes induced by binding of a substrate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Catalysis by Proximity

A
  • effective molarity concentration and orientation of substrate molecules in the active site of enzymes will enhance the rate of reactions. Eg. Substrate channeling by multi-enzyme complexes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Acid-base Catalysis

A
  • ionizable functional groups of amino acid side chains and prosthetic groups contribute to catalysis by acting as acids of bases
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Catalysis by Strain

A
  • enzymes bind their substrates in an favorable conformation to weaken the bond that will undergo cleavage. Eg. Stickies model
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Covalent Catalysis

A

-formation of a covalent bond between the enzyme and one or more substrates to create a more reactive enzyme. Eg. Group transfer reactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

AA in General in Acid-Base catalysis

A
  • many organic reactions are promoted by proton donors or proton acceptors
  • the active sites of some enzymes contain amino acid functional groups that can participate in the catalytic process as proton donors or acceptors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Example of Acid Base catalysis

A
  • enzymes of the aspartic protease family, which includes the digestive enzyme pepsin, the lysosomal cathepsins, and the protease produced by HIV share this common catalytic mechanism
  • two conserved aspartic acid residues are involved in acid-base catalysis
30
Q

Example of Covalent Catalysis

A
  • catalysis serine protease, chymotrypsin, involves prior formation of a covalent acyl-enzyme intermediate
  • AA residues at the active sit, Asp 102-His 57- Ser 195, functions as a proton shuttle during the proteolysis
31
Q

Structure of Chymotrypsin

A
  • protein consists of 3 polypeptide chains linked by S-S bonds
  • active-site AA residues are groups together in the 3D structure
32
Q

Recombinant DNA technology and Site-Directed mutagenesis

A
  • overproduction of recombinant proteins using recombinant DNA technology provides an important tool for studying enzyme structure and function
  • Recombinant proteins can be readily purified by affinity chromatography in large quantities
  • generation of mutant recombinant proteins by site-directed mutagenesis provides mechanistic insights
33
Q

Isozymes

A
  • catalyze the same reaction but may differ in reaction rate, inhibition by various substances, electrophoretic mobility, or immunologic properties.
  • some is oxygen may also enhance survival by providing a backup copy of an essential enzyme.
  • their pattern in serum may indicate organ damage. Eg. Alkaline phosphatase, lactate dehydrogenase, creating kinase
34
Q

Detection of Enzymatic activities

A
  • Enzyme assays that produce a chromagenic or fluorescent product are ideal for rapid analysis of multiple samples

1) NAD(P) - dependent dehydrogenases
- spectrophotomeric assays
- assay at saturating [S], so that v is proportional only to [E]
- coupled assays
2) Enzyme-linked immunosorbent assays

35
Q

NAD(P) dependent dehydrogenases

A
  • coupled assays

- hexokinase assay coupled with glucose-6-phosphate dehydrogenase assay

36
Q

Detection of Lactate Dehydrogenase Activity

A

-coupled colorimetric assay to measure liver disease/damage in serum

37
Q

ELISA

A

1) coat surface with sample antigen
2) block unoccupied sites
3) incubate with primary antibody against specific angtigens
4) incubate with antibody-enzyme complex that binds primary antibody
5) add substrate

-used in detection of: Mycobacterium antibodies in TB, Rotavirus in feces, Hep B markers, Enterotoxin of E. Coli in feces, HIV antibodies in blood samples

38
Q

Membrane Function

A

1) Barrier
- plasma membrane separates cytoplasm from external environment
2) Compartmentalize
- organizes internal components into separate organelles with specialized functions

39
Q

Biological problems with membrane function

A

1) Communication - mediates communication with environment, transmembrane receptors transfer extracellular signals into the cell to influence cellular function
2) transport of molecules - selective permeability across membranes- regulates cellular composition- acquire nutrients, excretes wastes, maintain intracellular pH, ion concentration and water balance
3) Exchange of molecules with external environment and between organelles - membrane transporters, vesicular transport

40
Q

Permeability

A
  • solubility in bilayer
  • gradients
  • selectivity depends on: solubility in lipid bilayer, specificity of transport proteins
  • permeable molecules are readily soluble in lipid bilayer
  • impermeable molecules have low solubility in the lipid bilayer
41
Q

Gradients

A
  • concentration gradients affect the rate of diffusion
  • for ions the rate of diffusion is also affected by electrical potential difference
  • concentration gradient + electrical gradient = electrochemical gradient
42
Q

Passive Transport

A

1) Simple Diffusion - down concentration gradient
2) Facilitated Diffusion
- down concentration gradient
- protein mediated by: rate greater than expected based on solubility in lipid bilayer, selective - specific carriers for each solute, saturable - reaches maximal rate

43
Q

Active Transport

A

1) Primary
- pumps salutes up a concentration gradient
- requires hydrolysis of ATP: ion pumps (ATPases), ABC transporters
2) Secondary
- Coupled transport of two salutes provides the energy: symporters and antiporters

44
Q

Secondary Active Transport

A
  • coupled transport:
  • co-transport of two molecules
  • uses energy from moving one solute down its gradient to drive movement of second solute up it its grand inept
  • symporters and antiporters
45
Q

Transport Proteins

A
  • transporters or carrier proteins
  • pumps : ATPases
  • Ion channels
46
Q

Characteristics of transporters of carrier proteins

A
  • bind one or more salutes
  • conformational change
  • passive or secondary active transport
47
Q

How carrier proteins change conformation

A
  1. Ligand binding site is exposed on one side of the membrane
  2. Ligand binding changes the shape of the carrier so that the ligand binding site is exposed on the other side of the membrane and the ligand is released
  3. Without the ligand bound the conformation returns to the original position so a new ligand can bind and the cycle repeats
48
Q

Characteristics of Ion Pumps

A
  • ATPases: primary active transport, up concentration gradients, hydrolysis of ATP
49
Q

Types of Ion Pumps

A

1) P-type: autophosphorylate, multipass transmembrane proteins
2) V-type (Vacuolar): multi-subunit proton pumps
3) F-type: multi-subunit proton pumps
4) ABC transporters : ATP Binding Cassette

50
Q

The Na+ K+ Pump

A
  • p-type
    1. Na+ binds
    2. Binding initiates phosphorylation by ATP and binding of Pi
    3. induces a conformational change that releases Na+ extracellularly and
    4. Exposes binding sites for extracellular K+
    5. Binding of K+ induces release of Pi that allows the conformation to
    6. change back, release K+ in the cytosol and
    7. The transporter is ready for another cycle
51
Q

Na+ K+ ATPase Cycle

A
  • cardiac glycosides oubain and digitalis inhibit the Na+/K+ ATPase and are used to treat cardiac failure
  • slowing the Na+/K+ ATPase decreases the sodium grandient
  • Ca++ transport out of the cell by the Na+/Ca++ antiporters is reduced
  • higher intracellular Ca++ levels increase the force of contraction
52
Q

P-type ATPases

A

1) Ca++ ATPase
- plasma membrane and sarcoplasmic reticulum
- maintains low Ca++ concentration inside cell, which is important for signal transduction and muscle contraction
2) H+/K+ ATPase
- secretion of H+ from gastric cells
- Proton pump inhibitors block acid secretion (Prilosec, Prevacid)

53
Q

V-Type ATPases

A

1) H+ ATPase
- use energy from ATP hydrolysis to move H+ across membrane up a concentration gradient
- lysosomes: acidification to maintain optimal pH for hydrolysis
- some plasma membranes: osteoclasts(bone resorption) and Renal cells (acid base balance)

54
Q

Transporters

A

1) ABC transporters
- ATP Binding cassette, highly conserved
- transport many types of molecules:
- sugars, AA’s, lipids, proteins, and peptides
- MDR: removes toxic compounds from cells, implications for treatment
- CFTR: Cl- transporter

55
Q

P-type ATPases disease and health

A

H+ ATPase - gastric ulcers

Na+/K+ ATPase - heart failure treatment

56
Q

ABC transporters in health and disease

A
  • ABCR - macular degeneration
  • MDR - drug resistance ( cancer, TB)
  • CFTR - cystic fibrosis
  • ABCA1- hypercholesterolemia
57
Q

V-type ATPases in health and disease

A

H+ ATPase- Bone resorption

H+ ATPase - lysosomes acidification

58
Q

F-type Proton Pump in health and disease

A

ATP synthesis in mitochondria

59
Q

CFTR mutations

A
  • Class I - defective protein production
  • Class 2 - defective processing
  • Class 3 - defective regulation
  • Class 4 - defective conduction
60
Q

Characteristics of Ion channels

A

1) transport ions
- rapid movement
- passive transport
2) Selective
- narrow channels restrict passage ( on size and charge)
3) Gated
- regulated opening to permit transport

61
Q

Electrochemical Gradients

A
  • passive transport
  • flow depends on gradients established by ion pumps:
  • concentration gradient
  • electrical gradient
62
Q

Ion Channels: Structure

A
  • multi-subunit, multi-pass transmembrane proteins

- K+ channel is prototype: 4 subunits with 6 transmembrane domains

63
Q

Ion channel selectivity: Size

A
  • K+ channels can distinguish between K+ and Na+ based on size
    1) Opening in the K+ channel seen from the end
    2) the opening is too small for either hydrated K+ or Na+ ions to pass
    3) Carbonyl oxygen lines the channel
    4) the oxygens are placed to exactly match those attached to K+, and H2O is displaced
    5) the K+ is seen shedding its H2O for carbonyl O, passing through the filter, and picking up H2O on the other side
    6) Hydrated Na+ doesn’t match the spacing and is blocked
64
Q

Ion channel selectivity: Charge

A
  • Acetylcholine receptor:
  • cation channel
  • negative charge on residues inside pore
  • Na+ and K+ permeable
  • Cl- impermeable
65
Q

Ion Channels: Gating

A
  • most ion channels are gated
  • opening and closing of the gate mechanism regulates entry of ions: mechanically gated, ligand gated, voltage gated
  • Few are not gated: Leak channels
66
Q

Ligand - gated Channels

A
  • converts chemical signal to electrical signal
  • triggers an action potential by causing a local change in membrane polarization that stimulates the opening of voltage-gated channels
  • binding of a specific ligand causes a conformational change and triggers opening ( can be extracellular or intracellular)
  • removal of ligand closes channel
67
Q

Acetylcholine Receptor

A

1) Specificity
- selective for specific ion
- binds a specific ion
2) inhibitors
- Competitive - bungarotoxin, curare
- Non-competitive - valium

68
Q

Voltage-Gated

A

1) 3 conformational states determined by membrane potential (polarity charge)
- resting = closed
- activated = open
- inactivated = blocked by inactivation loop (gate is still open)
- return to rest = closed

69
Q

Leak Channels

A
  • open all the time
  • K+ channels
  • K+ transported down its concentration gradient out of the cell
  • increase inside negativity of the cell
70
Q

Establishing the Electrochemical Gradient

A
  • leak channel lets K+ ions out down the concentration gradient
  • excess possible ions outside creates an electrical potential difference across the membrane
  • the electrical potential opposes the efflux of K+ and will reach a point where it balances the concentration gradient - this is the equilibrium potential
  • the Na+ K+ pump maintains the concentration gradients
71
Q

Resting Membrane Potential

A
  • Electrical gradient with inside negative relative to outside
  • Chemical gradient : Na+ and Cl- high outside, low inside. K+ high inside, low outside
  • K+, Na+, Cl- contribute to the resting potential, but the influence of Na+ and Cl- are small
  • resting potential is close to the equilibrium potential for K+

EoM (17 decks)

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