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Cell Bio > Week 6 > Flashcards

Week 6 Flashcards

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1
Q

What can ROS also function as

A

Essential physiological regulators

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2
Q

What happens if ROS is high

A

Phagocytes has vital antimicrobial functions can also have deleterious effects on the host tissue injury and hyper-inflammatory response

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3
Q

What happens if ROS is low

A

NOX1 activated in epithelia cells affecting the cellular redox status and physiologically important cell proliferation differentation and motility

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4
Q

How is the redox regulation by ROS modulated

A

Specific reactive cysteine reisude within redox sensitive target protiens

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5
Q

What leads to the reversible modification of enzymatic activity

A

Oxidation of thiol groups SH of the cysteines

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6
Q

What is the first step of cysteine biochemistry

A

Formation of intra molecular and intermolecular disulfide bonds.

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7
Q

How are disulfide bonds formed

A

When two adjacent thiol groups are oxidized releasing proton and electron to form a covalent disulfide bond they can also be formed when reactive sulfenic acid interacts with nearby cysteines

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8
Q

What is the steps of oxidation of reactive thiol groups

A

Start with the thiol group move to the sulfenic form then fulfinic form and then finally sulfonic form which is not reversible

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9
Q

What is Glutahinoylation

A

A post translational protein modification it is a binding of glutathione tripeptide to a via the formation of a disulfide bond with a protien thiol

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10
Q

What can ROS regulate with critical singaling molecules

A

Cell proliferation, survival differenitation and metabolism

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11
Q

What do these critical signaling moelcules contain

A

Redox-reactive cysteine residues

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12
Q

What is there also potentinal for

A

DNA damage Iron homeostasis and Anti-oxidant and anti inflamatory repsonse

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13
Q

What is the key molecules of the redox regulation

A

Transcription factors Nrf2 and enzymes that control the thiol-disulfide exchange and levels of ROS (peroxiredoxin,thiroedoxin and sulfiredoxin)

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14
Q

What does Keap1 serve as and why

A

Oxidative stress sensor and it is a cysteine-rich protein and when modifications of thiol groups in this protein induce significant conformational changes and interactions with other proteins

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15
Q

What happens to Nrf2 in unstressed conditions

A

Nrf2 is associated with the Keap1 dimer and will undergo constans ubiquitination by Cul3 so Nrf2 is short lived

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16
Q

What hapens to Nrf2 under oxidative stress conditions

A

ROS will induce oxidation/chemical modifications of the cysteine reisudes which inactive Keap1 Nrf2 translocates to the nucleus and heterodimerizes with sMaf and now will bind to the antioxidant response elements that will now induce the expression of genes encoding antioxidant enzymes and cytoprotective protiens

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17
Q

What can Nrf2 do

A

Antioxiant enzymes are upregulation of genes encoding the enzymes that control thiol/disulfide and the intracellular leves of ROS

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18
Q

What are Peroxiredoxins

A

Reduce and inactivate hydrogen peroxide and organix peroxides and are small protiens and present in all biological kingsoms

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19
Q

What do Prxs usually contain

A

Two cysteine residues

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20
Q

What are the difference between the two cysteine residues

A

One is specifically oxidizes by hydrogen peroxide to cysteine sulfenic acid and this is called peroxidatic Cp the other cysteine is involved in the formation of a disulfide linkage with CP and is called the resolving Cys CR

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21
Q

Do all peroxiredoxins contain Cr

A

NO

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22
Q

What do Prxs function as

A

Homodimers arangend in a head to tail orientation from Cp and Cr cysteines

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23
Q

How many members are in the human family of perociredoxins

A

6

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24
Q

What are the three subfamiles of prx enzymes

A

Typical 2 cys
Atypical 2-cys
1-cys

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25
Q

What occurs in the Typical 2-cysteine peroxiredoxins

A

contains both Cp and Cr resudues

26
Q

What happens to Typical 2-cys if H202 is present

A

Oxidizes the thiol group of CP to form the sulfenic acid intermediate this will then recat with the Cr forming an intermolecular disulfide bond 2 H202 can be used to generate two disulfide bonds

27
Q

How do Typical 2 cys reverse back

A

Trx is needed to act as a biological reducing agent

28
Q

What happens when Prxs recat with additional H202

A

They can become hyperoxidized to cysteine sulfinc acit before the disulfide bonds can form what can cause inactivation of peroxidase activity and protien aggregation

29
Q

What can fix herpoxidized Prxs

A

Sulfiredoxin Srx reducing the sulfinic group in an ATP-dependent recation

30
Q

What is the different between Typical 2-cys and Atypical 2-cys

A

Atypical forms intramolecular disulfide linkage

31
Q

What is different abotu 1-cys

A

Contains only one cysteine residue Cp so no disulfide bond is made

32
Q

How is 1-cys regenerated

A

It can be reduced by glutathione GSH cataylzyed glutathione S-transferase not by thioredoxin

33
Q

What are the two enzymes the thioredoxin system consists of

A

Thioredoxin and thioredoxin reducates and NADPH

34
Q

How do thioredoxin catalyzing the reduction of other proteins

A

Thiol-disulfide exhange disulfide bond into two Sh groups

35
Q

What is the pathway of the Thioredoxin system

A

Thioredoxin reducates is a selenoenzyme which gets reduced by NADPH and then reduces the disulfide bond

36
Q

What is the electron transfer process

A

NADPH–> TrxR –> Trx so you have a reduced level of thioredoxin which will catalyze disulfide bond in many protien such as peroxiredoxins

37
Q

Why else might cells produce hydrogen peroxide

A

Purpose of intracellular signaling in response to stimulation through various cell surface receptors required for propagation of growth factor singaling

38
Q

What are growth factors give examples

A

PDGF and EGF

39
Q

How do growth factors work

A

Activate PTKS which then phosphorylation of effector proteins and the steady state level of PTP

40
Q

What do PTPS do

A

Remove phosphate groups from a protien

41
Q

How are PTP blocked

A

PTP can be induced by hydrogen peroxide which is produced by the NOX enzymatic complexems

42
Q

What does blocking PTP also do

A

Assembly of various signaling protiens like PTKS and Src family which is phosphorylated by PTKs in response to growth factors which then results in NoX activation and Src activation (inhibiting perociredoxin)

43
Q

Why is peroxiredoxin need to be inhibited by Src

A

To avoid hydrogen peroxide degradation so that in can inhibit PTP and activate Src kinase

44
Q

What protiens are produced in H202

A

Wound healing and tissue regenration

45
Q

What is a redox pair

A

One acts as an electron donor and one as an electron acceptor

46
Q

What are examples of redox pairs

A

NAD+/NADH
NADP+/NADPH
GssG/2GSH
Cys/CYSSCy
AA/DHAA

47
Q

What is the key molecules of redox regulation

A

GSH/GSSG

48
Q

What is the ratio of GSH.GSSG

A

High and varry intracellular levels is 3-10mM and the ratio is 100/1 GSH 2-10 uM GSH 5/1 (lower antioxidant capacity)

49
Q

What can the redox state be characterized by

A

Redox potentional using the nernst equation

50
Q

What is the Nernst equation

A

E= -E0 - (2.3RT/zF)log(red/ox)

51
Q

What is the equation for GSH

A

It needs to be squared because two GSH molecules to form one GSSG moelcuels

52
Q

In the case of glutathione was does the redox potential depend on

A

The ration and the GSH concnetration

53
Q

In different parts of the cell what is the redox potentinal

A

Negative so the homeostatic redox balance is shifted to reduced molecules reduced molecules is higher than oxidized molecules

54
Q

What is the most reduced microenvinronment

A

Mitochondria than the nuclees then the cytoplasm followed by the extracellular space

55
Q

What is microenvinronment oxidized in association with

A

Proliferation to differentation growth arrest and apoptosis

56
Q

What does redox potentinal of tissues depend on

A

GSH/GSSG and cysteine and cystine

57
Q

What did the study show

A

Wide distribution of human blood plasma redox potential GSH/GSSG and Cys/CysSScys there was a linear increase of cysteine/cystine redox potential with age which indiccates age dependent oxisation of cysteine in blood

58
Q

What was the results

A

Continous linear increase in oxidative events the capacity of GSH is mainitained until 40-50 then declines rapdily

59
Q

What would you see in people not taking antioxidants, smokers dirnker and indviduals with dieases

A

A higher redox potentinal

60
Q

What could be an assement of oxidative stress anc predictive markers of health

A

GSH/GSSG and Cys/Cyss but need to take into account other redox couples

Cell Bio (13 decks)

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