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year 1 flash cards > TOPIC 4 - enzymes > Flashcards

TOPIC 4 - enzymes Flashcards

1
Q

do enzymes change the position of equilibrium ?

A

NO

increase the rate at which equilibrium reached NOT the position

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2
Q

what are the 3 ways/ which enzymes reduce Ea

A
  • providing catalytically component groups for a specific reaction
  • bing substrates in an orientation optimised for the reaction
  • preferentially binding and stabilising the transition state of the reaction
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3
Q

what is the transition state?

A

state of forward and backward reaction

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4
Q

what does stabilsing the transition state mean?

A

highest energy barrier that needs to be overcome to make/break bonds is lowered (i.e. stabilising the transition state of the reaction), thereby making the reaction faster

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5
Q

what is the active site of an enzyme ?

A

3D space w/ crucial AA residues that are there to fold substrate/do reaction

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6
Q

what is the most important complex that is made in the reaction

A

Enzyme-substrate complex

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7
Q

what is trypsin?

A

proteolytic digestive enzyme

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8
Q

how many AA are in the active site of trypsin and how are they arranged

A

3

the residues come togther to make the active site ‘niche’ for binding substrate

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9
Q

what is the equation for Michaelis constant ?

A

Km= (K2+K3)/K1

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10
Q

what is the assumption made for the Michaelis constant

A

K3 &laquo_space;K2

so K3 becomes unimportant

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11
Q

what is the Michaelis-Menten equation and what do the symbols stand for?

A

V= Vmax* [S]/([S]+Km)

V- rate of reaction
Vmax- max theoretical rate of reaction

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12
Q

what happens if [S]»Km

A

highest rate of reaction

value close to 1

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13
Q

what happens if [S]

A

slow/no reaction

value close to 0

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14
Q

what happens if [S]=Km

A

rate of reaction becomes half V max

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15
Q

what factors affect enzyme-catalysed reactions ?

A
  • substrate/enzyme conc
  • temp
  • pH
  • inhibitors
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16
Q

what are the 4 types of inhibitors?

A
  • reversible (usually non-covalent)
  • irreversible (usually covalent)
  • competitive
  • non-competitive (or uncompetitive)
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17
Q

does the Vmax and Km value stay the same in completive inhibition?

A

Vmax stays the same

Km not the same

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18
Q

does the Vmax and Km value stay the same in non completive inhibition?

A

Vmax not the same

Km the same (as its a measure of the affinity of enzyme for the substrate )

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19
Q

what does methotrexate inhibit?

A

dihydrofolate

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20
Q

what is methotrexate used for at high conc and why

A

cancer drug

reduces dihydrofolate = reduces amount of DNA replicated

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21
Q

what kind of inhibition does aspirin have

A

competitive and irreversible (covalent modification)

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22
Q

what kind of inhibition does ibuprofen have

A

competitive and reversible (non-covalent binding )

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23
Q

what are the 2 classes of co factors essential for enzyme function

A

metal ion

coenzymes

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24
Q

what metal ions are cofactors?

A 
Mg2+
Ca2+
Cu2+
Zn2+
Fe (2+/3+)
Mn 2+
Mo 4+
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25
Q

how can metal ions be involved in enzyme action

A
  • part of active sites
  • involved in catalysis
    involved in electrostatic substrate binding
  • act as REDOX agents (Fe2+/3+)
  • regulating activity of enzyme (Ca2+ in calpain)
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26
Q

what electrostatic substrate binding is Zn2+ involved in?

A
  • Carbonic anhydrase needs Zn2+ as cofactor

- Zn2+ in active site and binds to water

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27
Q

explain how Zn2+ is used as a cofactor in carbonic anhydrase

A
  • Zn2+ in carbonic anhydrase active site binds to H2O and activates it for reaction with CO2
  • CO2 transported as bicarbonate as it reacts with water (can’t really bind on its own)
  • Carbonic anhydrase uses zinc to convert CO2 and H2O to carboxylic acid
  • Carboxylic acid then dissociates a H+ which binds to Hb
  • Hb is protonated = causes release of oxygen in tissues
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28
Q

what are essential components of coenzymes?

A

water soluble vitamins

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29
Q

what vitamin and coenzyme function is stomatitis due to?

A
  • Riboflavin (B2)

- FAD,FMN

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30
Q

what vitamin and coenzyme function is pellagra due to?

A

Niacin

- NAD+, NADP+

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31
Q

what vitamin and coenzyme function is WKS/high output heart failure due to?

A

Thiamine

Thiamine pyrophosphate

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32
Q

what does Biotin deficiency cause and problems with what co enzyme?

A
  • biotinylated carboxylates

- alopecia, dermatitis, herding and vision problems

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33
Q

what 2 vitamin deficiency cause anaemia?

A
  • cobalamin (B12) (cob amide coenzymes)

- folic acid (tetrahydrofolate)

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34
Q

what vitamin and coenzyme function is peripheral neuropathy due to?

A
  • pyridoxal (B6)

- pyridoxal phosphate

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35
Q

what is tryptophan?

A

precursor for niacin

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36
Q

what are the molecules involved in the steps in the production of NAD+?

A

1- tryptophan
2- Niacin (B3/nicotinic acid)
3- nicotinamide (intermidiate for NAD+ production)
4- NAD+

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37
Q

what is the presentation of pellagra

A

3 D’S

dementia, diarrhoea, dermatitis

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38
Q

what’s another condition where we see pellagra

A

chronic alcoholicism

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39
Q

what does pellagra cause?

A

malnutrition / malabsorption

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40
Q

highlight the steps in which alcohol/ethanol is broken down to acetate

A

1- ethanol broken down by alcohol dehydrogenase
2- reduction reaction : NAD+ –> NADH
3- = acetaldehyde
4- this is broken down by acetaldehyde dehydrogenase
5- reduction reaction
6- = acetate

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41
Q

what organ metabolises ethanol?

A

liver

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42
Q

why does acetaldehyde need to be broken down?

A

reacts with our own proteins and causes headaches

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43
Q

what is the most common enzyme deficiency ?

A

G6PDH deficiency

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44
Q

is G6PDH deficiency a sex linked disease?

A

yes

X-linked (most carries asymptomatic0

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45
Q

what is G6PDH used for?

A

production of NADPH needed for biosynthesis

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46
Q

what are the symptoms of G6PDH

A

most carries asymptomatic

  • where symptomatic:
  • haemolytic crisis
  • jaundice
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47
Q

what 2 pathways can oxidised glucose (Glucose-6-phosphate) go down?

A
  • glycolysis

- pentose phosphate pathway

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48
Q

what 2 things do the Pentose phosphate pathway produce?

A

NADH

ribose-5-phosphate (nucleic acids)

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49
Q

what is needed to make glutathione

A

NADPH

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50
Q

what is glutathione used for

A

repairs oxidatively damaged rbc membranes

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51
Q

explain the process which glutathione breaks down organic hydroperoxides

A

1- glutathione peroxidase breaks down/reduces organic hydroperoxides
2- produces oxidised glutathione (glutathione reductase), water and an alcohol
3- glutathione reductase is then reduced by NADPH into reduced glutathione
4- returns back to glutathione peroxidase

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52
Q

why does oxidised glutathione have to be broken down

A

can oxidise lipids

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53
Q

why are RBC dependent on G6PDH?

A

needs it to make NADPH as has no mitochondria

54
Q

what metabolises the pro drug 6-MP and what is produces

A
  • TPMT/ Thiopurine methyl transferase

- 6-methyl MP

55
Q

what does the activated pro drug 6-MP cause

A

cell death due to blockade of DNA synthesis

56
Q

what is the pro drug 6-MP used in

A

cancer

57
Q

what are the 4 main ways we control enzyme activity?

A
  1. Inhibition (reversible or irreversible)
  2. Feedback regulation
  3. Covalent modification-post translational modification
  4. Proteolytic activation
58
Q

what are the enzymes called that phosphorylate other enzymes

A

protein kinases

59
Q

which AA are phosphorylated most common

A

seriene
thr
tyr

60
Q

what do phosphatase do?

A

remove phosphate groups from enzymes

61
Q

what does phosphorylation and dephosphorlyation cause

A

conformational changes in enzymes which decrease or increase their activity

62
Q

what is proteolytic activation?

A

Irreversible activation of enzyme after removal of part of peptide chain

63
Q

what is important in proteolytic activation and why

A

tight control by natural inhibitors (eg. antitrypsin and antithrombin III) so enzymes don’t become active in the wrong place at the wrong time

64
Q

what is chymotrypsin

A

a serine protease: digestive enzyme

65
Q

what is the structure of chymotrypsin?

A

3 polypeptide chains in active form- all linked by disulphide bonds
(Zymogen precursor is a single polypeptide)

66
Q

what AA are in the active site of chymotrypsin

A

aspartate
histamine
serine

67
Q

highlight the steps in the activation of chymotrypsin

A

1- inactive zymogen chymotrypsinogen activated by trypsin through cleavage of peptide bonds- proteolysis
2- chymotrypsinogen then undergoes further proteolysis to further activate itself into fully active form a-chymotrypsinogen

68
Q

what is the precursor for trypsin

A

trypsinogen

69
Q

how is trypsinogen converted to trypsin

A

1- removal of 1-6 AA in trypsinogen

2- by enteropeptidase (duodenal enzyme)

70
Q

what are the most common enzymes in blood clotting cascade ?

A

serine proteases

71
Q

what does antithrombin III bind to

A

thrombin

serine proteases

72
Q

what does plasmin do

A

lysis of blood clots

73
Q

highlight the steps from which a blood clot is dissolved

A

-TPA (tissue type plasminogen activator) binds to plasminogen
2-serine protease activity of TPA cleaves plasminogen to activated plasmin
3- Plasmin digests fibrin clot to small peptides = dissolves blood clot

74
Q

when we measure for enzyme activity do we use the serum or the whole blood, and why?

A

serum- has no blood clotting

75
Q

how can tissue specific enzymes be used as markers

A

if they are found in serum = indicates damage = shouldn’t be there

76
Q

what are enzyme isoforms ?

A

enzymes with similar function, and sometimes similar amino acid sequence, but expressed from different genes

77
Q

how can Differential tissue distribution of enzyme isoforms be used as markers

A

Some isoforms more abundant in particular point in blood- can trace to see where damage is

78
Q

in what condition are enzymes amylase and lipase used as markers? and why do we use the 2 enzymes together

A

acute pancreatitis

- amylase gets degraded quickly

79
Q

in what condition are enzymes alkaline phosphatase used as markers?

A

liver disease

osteoblastic bone disease

80
Q

in what condition are enzymes glutamate-oxaloactetate transaminase (GOT) used as markers?

A

myocardial infarction

liver cell damage

81
Q

in what condition are enzymes glutamate-pyruvate transaminase (GPT) used as markers?

A

liver cell damage

82
Q

in what condition are enzymes Creatine kinase (CK) used as markers?

A

crush injuries

83
Q

why are the times you do enzyme tests important?

A

different enzymes have different half-life in blood (for example: in acute pancreatitis, lipase remains elevated for longer than amylase)

84
Q

what is the standard measure of enzyme activity

A

International Unit (IU)

85
Q

what is the IU

A

amount of activity that will convert 1 micromole (µmole, or 10-6 moles) of substrate per minute under standard defined conditions, in specific temp, place, certain buffers

86
Q

what are the products of the reaction when GPT catalyses glutamate + pyruvate ?

A

alanine + a-ketoglutarate

87
Q

what are the products of the reaction when GOT catalyses glutamate + oxaloacetate ?

A

aspartate + a-ketoglutarate

88
Q

what is jaundice in liver damage due to

A

high levels of bilirubin

89
Q

what 3 enzymes increase in levels due to liver damage

A

GPT,GOT,BILIRUBIN

90
Q

what 6 things are measured in a liver function test

A
  • albumin
  • GOT
  • GPT
  • total transaminase (GOT+GPT)
  • alkaline phospahtase (ALP)
  • direct and total bilirubin
91
Q

what do low levels of albumin suggest?

A

general loss of secretory function/ kidney disease

92
Q

what do elevated levels of GOT suggest

A

acute liver damage, but could originate from red blood cells or muscle, so not liver-specific

93
Q

what do elevated levels of GPT suggest

A

more specific indicator of liver damage - high levels rules out muscle damage

94
Q

what do high levels of total transaminase but normal ALP suggest?

A

liver necrosis

95
Q

what do elevated levels of ALP suggest?

A

large bile duct obstruction (Caution: also high in Paget’s Disease of Bone, growing kids and 3rd trimester pregnancy)

96
Q

if direct and total bilirubin levels are normal but we are still presented with jaundice what does this suggest?

A

problem upstream of the liver (some form of haemorrhage causing high total bilirubin)

97
Q

what do elevated direct bilirubin suggest?

A

normal conjugation function in the liver, but failure to excrete (bile duct obstruction)

98
Q

what test other than transaminases is sensitive to minor changes in liver function?

A

Gamma glutaryl transpeptidase (GGT)

99
Q

what does slow Prothrombin time (INR) suggest?

A

indicates failure of the liver to synthesise and secrete blood clotting proteins such as prothrombin

100
Q

what is INR/prothrombin time used to monitor?

A
  • livers ability to produce blood clotting proteins
  • warfarin usage
  • Vitamin K status
101
Q

what are the 3 markers of cardiac injury?

A
  • CK (in MB form)
  • Cardiac troponin-I (cTnI)
  • lactate dehydrogonase
102
Q

what reaction does CK catalyse

A

creatine + ATP —-(CK)—> Creatine phosphate + ADP

103
Q

what is Creatine phosphate

A

sore of high energy phosphate groups in muscles

104
Q

what 2 polypeptides isoforms is CK made from

A

M and B

105
Q

what CK isoform is predominant in skeletal muscle?

A

-MM

106
Q

what causes increased levels of MM isoform of CK

A

AMI(myocardial infarction) but also with skeletal muscle injury, intensive training, thyroid deficiency

107
Q

what CK isoform is predominant in myocardium ?

A

MB

108
Q

what causes increased levels of MB isoform of CK

A

AMI

109
Q

what CK isoform is predominant in brain ?

A

BB

110
Q

what causes increased levels of BB isoform of CK

A

neurological disorders, some cancers

111
Q

why is CK levels measured in crush injuries?

A

determine severity of muscle tissue breakdown

112
Q

what’s is rhabdomyolysis

A

muscle tissue breakdown

113
Q

how can rhabdomyolysis lead to brown urine

A
  • Muscle tissue breakdown with the release of intracellular contents, Myoglobin, into circulation
  • Elevated CK levels
  • Dark reddish brown urine due to Mb
114
Q

why can Rhabdomyolysis be dangerous

A

-Mb may occlude structures of the kidney and break down into toxic compounds leading to acute tubular necrosis or acute renal failure

115
Q

what can paracetamol poisoning lead to?

A

liver damage

116
Q

up to what time can one gain full recovery from paracetamol poisoning? what happens after this tie?

A

12hrs

after 12hrs = irreversible liver damage - transplant?

117
Q

what is pracetomal poisoning treated with

A

N-acetylcysteine/methionine

118
Q

what does paracetamol inhibit?

A

the COX’s

cycloxygenase-1 and 2

119
Q

what’s do COX’s activate?

A

prostaglandins which cause inflammation

120
Q

highlight the steps in the breakdown of paracetamol

A

1- some paracetamol leaves first by real excretion
2- cytochrome P450 breaks paracetamol down to Quinone derivative
3- Quinone derivative then broken down by glutathione 4- excretion

121
Q

biochemically, what happens in paracetamol poisoning?

A

too much paracetamol = too much Quinone derivative = insufficient glutathione to break it all down = toxicity

122
Q

how does N -acetlycysteine work

A

same mechanism at glutathione : breaks down Quinone derivative

123
Q

does hypo or hyper glycemic cause long term damage ?

A

hyper

hypoglycaemia= immediate danger

124
Q

how does hyperglycaemia cause long term damage

A

damage tissues with microvasculature (portion of the circulatory system composed of the smallest vessels), eg. Heart

125
Q

what is the significance of asparagine in cancer cells?

A

Tumor cells deficient in Asn synthetase, therefore Asn essential

126
Q

how do tumour cells obtain their asparagine

A

take it from healthy cells, diet

127
Q

is asparagine essential to normal healthy cells?

A

no

128
Q

how can we use asparaginase to treat childhood acute lymphoblastic leukaemia

A

Asparaginase can convert asparagine to aspartate and starve tumour = stop them growing
meanwhile normal cells unaffected

129
Q

what is urease used for

A

in kidney dialysis to remove urea

130
Q

what does urease break urea down into

A

2NH3 (removed by carbon) and CO2 (returned to lungs)

year 1 flash cards (23 decks)

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