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Medical Cell Biology And Genetics > Topic 6: Energy production - Carbohydrates > Flashcards

Topic 6: Energy production - Carbohydrates Flashcards

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1
Q

What type of molecules does catabolism break down

A

amino acids, glucose, fatty acids, alcohol

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2
Q

what intermediate metabolite is formed

A

acetyl coA

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3
Q

what is acetyl coA further metabolised into

A

CO2

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4
Q

what are the 4 stages of catabolism

A
  1. breakdown of fuel to building blocks for absorption (GI tract). breakage of C-N AND C-O bond, no energy released
  2. breakdown into intermediates through many pathways (cytosol or mitochondria). this is oxidative (some energy released), C-C bond broken
  3. krebs cycle in mitochondria. this is oxidative, acetyl coA to C02
  4. electron transport chain and oxidative phosphorylation, reducing power into ATP
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5
Q

what does oxidative mean

A

release of reducing power + energy

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6
Q

describe stage 1 of catabolism

A
  • extracellular (GI tract)
  • so nutrients are converted into a form that can be taken up by cells (carbs etc too big -> monosaccharides, amino acids etc)
  • forms building block molecules which absorbed from GI tract
  • no energy released
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7
Q

describe stage 2 of catabolism

A
  • intracellular (cytosolic or mitchondrial)
  • many pathways
  • building blocks into simpler molecules. many to few molecules
  • oxidative so requires coenzymes like NAD+ -> NADH
  • some energy released
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8
Q

describe stage 3 of catabolism

A
  • in mitochondria
  • cyclic, single pathway - KREBS CYCLE
  • oxidative pathway (requires NAD+ and FAD)
  • some energy produced as GTP
  • acetyl to 2CO2
  • produces precursors
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9
Q

describe stage 4 of catabolism

A
  • in mitochondria
  • electron transport chain and ATP formed
  • NADH and FADH2 re-oxidised
  • O2 required
  • lots of ATP produced
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10
Q

how much carbs in an adult

A

1% in comparison of 15% intake

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11
Q

what are the 3 main dietary monosaccharides

A

glucose
fructose
galactose

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12
Q

what is the concentration of glucose in the blood

A

5mM

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13
Q

which cells have an absolute requirement for glucose

A

red blood cells
neutrophils
innermost cells of kidney medulla
lens of the eye

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14
Q

what does CNS use as fuel

A

glucose

can use ketone bodies if required

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15
Q

how are dietary carbohydrates broken down in stage 1 of catabolsim

A

saliva - amylase breaks down starch and glycogen -> dextrins
pancrease - amylase breaks down monosacchardies
small intestine - disccharidases break down disaccharides -> monosaccharides

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16
Q

what are the different disaccharidases

A

lactose
sucrase
pancreatic amylase (alpha 1-4)
isomaltase (alpha 1-6)

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17
Q

why can’t the body break down cellulose

A

no enzymes to break down beta 1-4 linkages

can not hydrolyse as beta glycosidic bonds are different

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18
Q

how does lactose intolerance occur

A

Primary lactose deficiency-
absence of lactase persistence allele as mature, can not produce lactase as adults
secondary -
caused by injury to small intestine (gastroenteritis, coeliac disease, crohn’s, ulcerative colitis\0
in infants and adults, can be reversible
congenital -
autosomal recessive defect in lactase gene, cannot digest breast milk

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19
Q

how are monosacharide absorbed into the GI tract in stage 1 of catabolism

A
  1. active transport into intestinal epithelial cells by sodium dependent glucose transport 1 (SGLT1)
  2. passive transport via GLUT2 into bloody supply
  3. travels in blood to tissues
  4. glucose taken up in target cells via faciliated diffusion using transport proteins (GLUT1-GLUT5)
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20
Q

what are the different glucose transporters and where are they found (not really need)

A

GLUT1 - fetal tissues, adult erythroctyes, blood-brain barrier
GLUT2** - kidney, liver, pancreatic beta cells (insulin dependent), small intestine
GLUT3 - neurons, placenta
GLUT4** - adipose tissue, striated muscle
GLUT5 - spermatazoa, intestine

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21
Q

what is the main feature of stage 2 of catabolism

A

glycolysis

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22
Q

what are the functions of glycolysis in stage 2

A

aim to breakdown glucose into 2 x3C pyruvate
oxidation of glucose so NAD+ reduced
NADH production (2 for every glucose)
synthesis of ATP (2ATP per glucose, 4 results but 2 used to activate)

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23
Q

what are the features of glycolysis in stage 2

A 
in all tissues which is cytosolic
exergonic, oxidative - releases energy with oxidation of substrates
no loss of CO2
lactate dehydrogenase is also formed
irreversible
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24
Q

what enzymes are involved in glycolysis in stage 2

A

Hekokinase (glucosekinase in liver)
Phosphofructokinase-1
Pyruvate kinase

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25
Q

why are there so many steps and enzymes in glycolysis

A

effienct energy conservation
gives versatility because allows interconnections with other pathways to produce other metabolic intermediates
allows fine control
allows part to be used in reverse

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26
Q

what is phase 1 of glycolysis

A
  1. glucose enters the cell
    phosphorylated by ATP and forms ADP to form glucose-6-phosphate. the phosphate group is negatively charged so prevents backflow into membrane into blood flow
  2. an isomeration step to form fructose - 6 - phosphate
  3. ATP used to phosphorylation to form fructose 1, 6- bis phosphate
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27
Q

how much energy is formed during glycolysis

A

2ATP per glucose
reaction 1 and 2 of phase 1 has large delta G reaction so irreversible
after step 3 the substrate must move on to the rest of glycolysis

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28
Q

what is phase 2 of glycolysis

A
  1. fructose 1,6 bisphosphate is cleaved into 2 x 3C units(isomerised first to DHAP and forms two glyceraldehyde 3-phosphate)
  2. NAD+ is reduced to oxidise glyceraldehyde 3-phopshate to 1,3 bis phosphoglycerate (a phosphate is also added)
  3. large negative delta G of hydrolysis, so irreversible. substrate level phosphorylation occurs to form ATP and 3-phosphoglycerate
  4. further isomeration to form 2-phosphoglycerate and then phosphoenolypyruvate
  5. large negative delta G of hydrolysis, so irreversible. ATP formed and converts to pyruvate
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29
Q

how do you make glucose from pyruvate

A

using reversible reactions

gluconeogenesis

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30
Q

what does glycolysis porduce

A

2 moles of ATP

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31
Q

what happens when rate of glycolysis increases

A

up to 200 times faster in cancer

measured using radioactive marker and PET

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32
Q

what other intermediates can be formed from glycolysis

A
  1. fat is formed at cleavage
    from DHAP instead of forming glyceraldehyde 3 phosphate. the enzyme, glycerol 3 -phophate dehydrogenase which reduces it (accompanied by the oxidation of NAD) forms glycerol phosphate
    which can then synthesis triglyceride and phospholipid biosynthesis
    glycerol phosphate + fatty acids -> fat
  2. 2,3 - bisphosphoglycerate produced from 1,3-bisphosphoglycerate via bisphosphoglycerate mutase. this molecule is important to regulate haemoglobin oxygen affinity
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33
Q

why is NAD+ so important to glycolysis

A

2 moles of NADH produced per glucose
also uses NAD+
if all NAD+ converyed to NADH, glycolysis would stop
normally regenerated by oxidation in metabolism but wont be in RBC as no stage 3/4 of metbaolism and if no oxygen…thus need a supply of oxygen

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34
Q

what enzymes regenerates NADH

A

lactate dehydrogenase

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35
Q

why would NAD+ run out/how is lactate formed

A

NO OXYGEN - pyruvate to lactate and no NAD+ formed
without major exercise
strenuous exercise
pathological conditions such as shock or congestive heart disease

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36
Q

what happens in the lactate dehydrogenase reaction

A

no oxygen:
increased levels of NADH and pyruvate and H+ -> NAD+ + lactate, so NAD+ regenerated for glycolysis

the NAD+ is used to restore lactate to low levels:
lactate released into blood by RBC and muscles, to liver and heart where metabolised
as there is oxygen present in these tissues, NAD+ present which with the addition of lactate can form NADH + H+ + pyruvate. NADH can then be reoxidised as oxygen present

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37
Q

what happens in the liver when lactate is detected

A

converted to pyruvate and then glucose via gluconeogenesis

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38
Q

if enzyme, lactate dehydrogenase is not produced

A

built up of lactate in the blood (lactatemia)

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39
Q

why would there be no lactate dehydrogenase present

A

vitamin deficiency
impaired in liver disease
alcohol which converts NAD+ -> NADH, then lactate could not be converted as no NAD+ present
enzyme deficiencies

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40
Q

where is lactate disposed fo

A

kidney

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41
Q

what is the normal concentration of lactate in the blood

A

below 1mM

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42
Q

if lactate concentration increases in the blood to 2-5mM what happens

A

hyperlactaemia
below renal threshold so not excreted in the urine
no change in blood pH as have enough buffering capacity

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43
Q

if lactate concentration increases above 5mM

A

lactic acidosis - critical marker in the acutely unwell
above renal threshold, appear in urine
blood pH lowered as buffering capacity not strong enough

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44
Q

what other sugars are metabolised in glycolysis

A

fructose

galactose

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45
Q

how is fructose metabolised in glycolysis

A

in liver -
acted upon by fructokinase and ATP -> ADP so phosphorylated to fructose 1-phosphate
then acted upon by aldolase to form either glyceraldehyde or DHAP
DHAP isomerised to glyceraldehyde-3-phosphate
Glyceraldehyde phosphorylated with ATP and use of triose kinase to form glyceraldehyde 3 - phospjaye so two form—-> glycolysis

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46
Q

what are the clinical importance of fructose

A
  1. essential fructosuria - fructokinase missing which is then means fructose is found in urine, no clinical signs
  2. fructose intolerance - aldolase B missing so fructose 1 - phophate builds in the liver causing damage. must be removed from diet
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47
Q

how is galactose metabolised in glycolysis

A

acted upon by galactokinase and phophorylated by ATP to form galactose 1 -phosphate
which is acted upon by uridyl transferase and the use of UDP glucose to form glucose 1-phosphate to be converted to glucose 6-hposphate -> glycolysis

UDP glucose gives one phosphate to form glucose 1 -phosphate and then galactose given as substrate to form UDP galactose, UDP galactose is then converted back to UDP glucose via UDP galactose 4-epimerase

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48
Q

how does galactosaemia come about

A

defiency in any of the enzymes involved in galactose metabolism such as galactokinase, uridyl transferase, UDP-galactose epimerase

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49
Q

what is galactosaemia

A

deficiency in galactokinase (rare) - galactose conc increase

other two enzymes deficient (common) - galactose 1 phosphate and galactose accumulates

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50
Q

what happens if galactosaemic and what is used as treatment

A

Galactose then enters other pathways. Aldose reductase converts it to galactitol and oxidised NADH to NAD+, less NADPH and structure damages caused such as cateracts
accumulation of galactose - affects liver, kidney and brain
no lactose in diet

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51
Q

how does galactosaemia cause cateracts

A

enters new pathway
levels of NADPH decrease
disulfide bridges maintained using NADH so inappropriate formation occurs, loss of structural integrity, eg: lens of eye

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52
Q

what is the pentose phosphate pathway

A

when energy levels are high and intermediatery levels of glycolysis build up glucose 6 phophate can divert out of glycolysis

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53
Q

what happens int he pentose phosphate pathway

A

glucose 6-phosphate converted to 5c sugar phosphates via glucose 6 phosphate dehydrogenase. NADP+ reduced to NADPH to oxidise reaction. Co2 is formed so irreversible = oxidative decarboxylation
then rearrangement to form glycolytic intermediates, so 3 5c sugars form 2 fructose 6-phosphate + 1 glyceraldehyde 3 phosphate
(if 5c sugar not utilised can be converted back to fructose 6-phosphate or galactose-3-phosphate and enter glycolysis)
no atp produced
controlled by coenzymes

54
Q

why is NADPH important

A

NADPH used for providing reducing equivalent for biosynthesis
fatty acid, lipid and steroid biosynthesis - liver and adipose tissue
GSH regeneration
detoxification reactions

55
Q

what can ribose 5-phosphate (5C sugar) be used for

A

nucleotides - lots of pathway in dividing tissue
DNA
RNA
coenzymes

56
Q

what are the functions of pentose phosphate pathway

A
  1. produce NADPH in cytoplasm for biosynthesis and maintain free SH
  2. produce C5 sugar for nucleotides needed for nucleic acid synthesis
57
Q

what happens if someone is glucose 6-phosphate dehydrogenase deficient

A

can not form 5C sugar phosphate

and NADPH levels fall as not being converted by reduction as no oxidation reaction

58
Q

what are the affects if G6PDH deficient

A

NADPH not formed so not maintaining SH group of proteins
structural intergrity decreases and crossbridges inappropriate
commonly inherited
in RBC’s, aggregated proteins (misfolded) - heinz bodies - haemolysis - split so anaemia
and lens of eye

59
Q

how are metabolic pathways regulated

A

by regulating enzymes

60
Q

how does allosteric regulation of enzymes work

A
  1. the activator/inhibitor binds to another site
    not to catalytic site but to regulatory site. regulatory molecule binds, confirmational change, affects catalytic activity either inhibition or activation
  2. covalent modification - phosphorylation or dephosphorylation, alters protein conformation, alters activity
61
Q

what are the principles of metabolic pathway regulation (inhibition)

A

i) reversible steps are not regulated, as reaction in equilibrium so levels of product unaffected. However, product inhibition can occur, if lots of product formed less substrate, so reaction reverses so more of other product formed. so reduces rate of reaction in forward direction so binding rate and catalysis reduced
ii) irreversible steps are regulated. when reduced activity - reduces flux of substrates - reduce level or product
iii) feedback pathway - prevents build up of intermediates when reaction reversed, so pathway can continue
iv) inhibition of committing step - no diversion of substrate in or out of the pathway. so if inhibited allows substate to be diverted into other pathways

62
Q

catabolic pathways are inhibited by

A

high energy signals such as ATP, NADH, FAD2H

63
Q

catabolic pathways are activated by

A

low energy signals such as ADP, AMP, NAD+, FAD

64
Q

what is the process of hormonal regulation

A
  1. hormone receptor binding
  2. activates signalling pathway
  3. protein kinase (phosphorylation) or protein phosphotase (dephosphorylation) activated
  4. either phosphorylates or dephosphorylates enzyme
  5. alters protein conformation - either in a good or bad way
65
Q

what are some examples of phosphoregulation

A

adrenaline - activates protein kinase A, phopshorylation activates phosphorylase kinase to form glycogen phosphorylase to stimulate glycogen breakdown
insulin - stimulates signalling pathway which activates protein phosphatase 1.
either causing dephosphorylation and activation of pyruvate dehydrogenase which stimulates glucose utilisation or dephosphorylation of glycogen phosphorylase to inhibit glycogen breakdown

66
Q

what are the principles of metabolic pathway regulation (activation)

A

Feed forward - high levels of substrate feeds forward to pathways to activate entry of substrate into pathway by removal of intermediates

67
Q

what is the key regulator of glycolysis

A

phosphofructokinase-1

68
Q

what does PFK do

A

if lots of ATP and NADH - and want to store glucose as glycogen
converts fructose 6-phosphate to fructose 1,6-bisphospjate via phopshorylation of ATP -> ADP
1. when ATP levels are high and glycolysis should be inhibited, uses ATP as an allosteric site binds to it and causes inhibition (vice versa will cause activation if stimulated by high AMP when energy levels low
2. when glucose levels are high, enzyme stimulated by insulin to increase its activity (vice versa inhibited when glucagon)

69
Q

what other inhibition is available for regulation of glycolysis

A

Hexokinase - allosteric inhibition by glucose-6-phosphate
metabolic regulation (feedback product inhibition)- high NADH or low NAD+ = high energy level signal, causes inhibition of step 5 and stops glycolysis, so flux of glucose reduced (not need it)
hormonal activation - PFK and pyruvate kinase - also sensitive to allosteric regulators. inhibited by PEP and citrate and H+ ions. Activated by fructose 2.6-bisphosphate

70
Q

how is PFK regulated

A

phophoregulation

allosteric

71
Q

how does phosphoregulation of PFK work

A

glucagon -> protein kinase A -> phosphorylation -> inhibition
insulin -> protein phosphatase 1 -> phosphorylation -> activation

72
Q

how does phosphoregulation of pyruvate kinase work

A

glucagon -> protein kinase A -> phosphorylation -> inhibition
insulin -> protein phosphatase 1 -> phosphorylation -> activation

73
Q

how does allosteric regulation of hexokinase work by glucose 6-phosphate

A

forms glucose 6 phophate is irreversible but inhibits the enzyme that forms it to prevent glucose entering glycolysis
inhibition of step 5 - high NADH = high energy level signal
inhibition of step 4 PKR in response to high energy levels
thus acts as a negative regulator of hexokinase

74
Q

what are the two types of pathway regulation

A

metabolic

hormonal

75
Q

metabolic regulation occurs when

A

high NADH or low NAD+ = high energy level signal -> inhibits step 5
high ATP inhibits PFK
high AMP stimulates PFK

76
Q

hormonal regulation occurs when

A

PFK and pyruvate kinas

increase by high insulin but when glucagon high enzymes inhibited

77
Q

where is the commiting step in glycolysis

A

phosphofructokinase inhibited
energy levels high - build up of glucose and glucose 6-phosphate to form glycogen
or to pentose phosphate pathway for biosynthesis to use ATP

78
Q

whats the link reaction, what happens before krebs cycle

A

2 pyruvates converted to 2 acetyl coA using pyruvate dehydrogenase (made of 5 enzymes) - these require cofactors such as FAD, thiamine pyrophosphate and lipoid acid - provided by B vitamins. so reaction is sensitive to vitmain B1 defiency
in matrix, transporter from cytoplasm across matrix
pyruvate + coA + NAD+ -> acetyl coA + NADH + H+
reversible as CO2 formed so key regulatory step

79
Q

what is pyruvate dehydrogenase activated and inhibited by?

A

activated by low energy compounds = pyruvate, coASH, NAD+, ADP, insulin - dephosphorylation of enzyme
inhibited by high energy compounds = acetyl coA, NADH, ATP, Citrate - phosphorylation of enzyme

80
Q

what would happen in a deficiency of pyruvate dehydrogenase

A

pyruvate would build up - lactate dehydrogenase pathway - lactate - lactate acidosis

81
Q

what are some key features of the krebs cycle

A

in mitocondria
single pathway
acetyl coA oxidised to 2CO2
requires NAD+ + FAD (pick up hydrogen atoms)
some energy produced
also produces precursors for biosynthesis

82
Q

what is the krebs cycle pathway

A

2 acetyl coA + oxaloacetate = citrate (C6)
isomerised
isocitrate - oxidised and NAD+ reduced to NADH, and loss of CO2 (irreversible)
Decarboxylated further to 5C
5C + coA and oxidised so NADH forms (irreversible as CO2 formed)
C4 -> C4 (GDP->GTP - substrate level phosphorylation)
C4 oxidised to C4 so FAD-> FADH2
C4 -> C4 with water
C4-> oxaloacetate with NAD+ -> NADH

83
Q

what is formed from the krebs cycle

A

3NADH (x2)
1 FAD2H (x2)
1 GDP per cycle (x2)
but 2 acetyl coA so 2 cycles

84
Q

how is the krebs cycle regulated

A

inhibited by high energy compounds, activated by low energy compounds - at irreversible points (where CO2 released)

i) isocitrate dehydrogenase: inhibited allosterically by NADH and ATP, activated by ADP,
ii) alpha-ketoglutarate dehydrogenase: inhibited by NADH and ATP and succinyl coA, activated by ADP

85
Q

whats the importance of the krebs cycle

A

biosynthetic processes - hub for metabolism

amino acids, glucose, fatty acids, haem, sugars, ketone body, alcohol (diff pathways in and out)

86
Q

does krebs cycle function without o2

A

no

87
Q

where is the energy carried

A

within NADH and FAD2H

88
Q

how is water formed in metabolism

A

NADH is oxidised to NAD+ and in turn reduces O to H2O

89
Q

what are the key features of the E.T.C and ATP synthesis?

A

NADH + FADH2 re oxidised
O2 required
lots of energy formed

90
Q

what are the 2 process of step 4 of catabolism?

A
  1. electrons on NADH and FADH2 transferred through a series of carrier molecules to oxygen - ETC
  2. Oxidative phosphorylation - free energy to drive ATP synthesis
91
Q

what is the structure of a mitochondria

A

outer mitochondrial membrane
intermembrane space
inner mitocondrial membrane
mitochondrial matrix

92
Q

how does the electron transport chain work?

A
  1. NADH -> 2H+ + 2e-. electrons are picked up by protein translocating complexes on inner mitochondrial membrane. the complexes are arrnaged in sequence so electrons can be passed
  2. electrons passed onto next complex, and in doing so release some energy which can be used to drive protons from the mitochondrial matrix to the intermembrane space (2H+) - proton motive force due to H+ gradient
  3. more energy released, more protons translocated
  4. electron reaches third PTC, the electrons are used to form bonds between hydrogen ions and oxygen to form water
93
Q

what happens after the ETC?

A

ATP is synthesized using proton translocating ATPase/F1F0 ATPase or ATP synthase
ATP is synthesised by energy from proton motive force when 2 protons travel back to matrix as favoured by electrochemical gradient
these protons return across membrane via ATP synthase which is what drives ATP synthesis

94
Q

energy in NADH is …

A

more than in FAD2H (so uses 3 PTC’s in comparison to 2 as enters late)

95
Q

the greater the proton motive force

A

more ATP synthesized

96
Q

oxidation of 2 moles of NADH

A

5 moles of ATP (p:o 2.5)

97
Q

oxidation of 2 moles of FADH2

A

3 moles of ATP (p:o 1.5)

98
Q

ATP synthase uses

A

2 protons to drive synthesis of ATP

99
Q

how is oxidative phosphorylation regulated

A

when lots of ATP and little ADP - no substrate for ATP synthase -> inward flow of H+ slows -> H+ accumulates in intermitochondrial space -> prevents further H+ PUMPING -> stops ETC
vice versa with low ATP

100
Q

which inhibitors block oxidative phosphorylation

A

like cyanide prevents acceptance of electrons by O2 and carbon monoxide so no proton motive force so not drive ATP synthesis

101
Q

what is uncoupling of oxidative phosphorylation

A

like dinitrophenol, disnitrocresol and fatty acids. uncouplers increase the permeability of mitochondrial inner membrane to protons, dissipate proton gradient, thus reducing PMF so no drive for ATP synthesis. ETC continues but gradient does not form

102
Q

how do you inhibit ATP synthesis

A
  1. block ETC

2. prevent PMF

103
Q

what genetic disorders are associated with ETC

A

genetic defects in proteins encoded by mitochondrial DNA

104
Q

what happens to the rest of the energy

A

lost as heat
could lose if tightness of coupling reduced
can vary in different tissues
eg: brown adipose tissue - degree of coupling controlled by fatty acids (uncouplers) - more heat generated

105
Q

what happens in brown adipose tissue

A

contains thermogenin - uncoupling protein
in response to cold - noradreanline activates a lipase which releases fatty acids from triacylglycerol, which releases lots of NADH/FADH2 for ETC. also activates UCP1 which transports H+ back into mitochondria matrix bypassing ATP synthases. so electron trasnprot uncoupled from ATP synthesis - energy of pmf released as heat

106
Q

where is brown adipose tissue found

A

newborn to maintain heat around vital organs

hibernating animals

107
Q

what are the differences between oxidative phosphorylation and substrate level phosphorylation

A

ox - requires membrnae complexes, energy coupling occurs indirectly, cannot occur in presence of O2, major process for ATP synthesis, requires lots of energy
sub - requires soluble enzymes, energy coupling occurs directly, can occur without O2, minor process for ATP synthesis, requires lots of energy

108
Q

how many molecules of ATP are formed from glucose

A

32

109
Q

If no oxygen

A

Only glycolysis - substrate level phosphorylation

Has to oxides baCK NADH

110
Q

Under anaerobic conditions, the pyruvate produced by glycolysis in skeletal muscle may be reduced to lactate. What advantage is this to the muscle cells?

A

There is a fixed amount of NAD+ & NADH in the cell. The reactions of glycolysis require the presence of NAD+ which is converted to NADH. If all of the NAD+ is converted to NADH, glycolysis would stop because of lack of NAD+. This does not normally occur because, in the presence of oxygen, NADH is converted back to NAD+ by the electron transport chain in the mitochondria. However, in the absence of oxygen (anaerobic conditions) or mitochondria (red blood cell) electron transport cannot occur. Under these condition pyruvate is converted to lactate via the enzyme lactic dehydrogenase (LDH) using NADH which is oxidised to NAD+ :
CH3COCOOH + NADH + H+ ↔CH3CHOHCOOH + NAD+
This enables glycolysis to continue so that it can provide the cell with ATP via substrate level phosphorylation.

111
Q

What are the possible fates of the lactate produced by skeletalmuscle under anaerobic conditions?

A

Lactate is released from muscle cells and carried in the blood to the liver and heart muscle. In both tissues it is converted back to pyruvate by LDH. In heart muscle the pyruvate is converted to acetyl~CoA that is subsequently oxidised via the TCA cycle to provide energy. In the liver pyruvate may also be oxidised to provide energy but most will be converted to glucose via the gluconeogenic pathway. A third possibility in the liver is oxidation to acetyl~CoA which may be used for lipid biosynthesis (fatty acids, ketone bodies or cholesterol)

112
Q

Define lactic acidosis and explain why it may occur.

A

Lactic acidosis is an elevation of plasma lactate that affects the buffering capacity of the plasma i.e. there is a fall in plasma pH due to the accumulation of lactic acid. Situations in which there may be a marked increase in plasma lactate due to increased production include strenuous exercise (up to 10g/min), hearty eating, shock and congestive heart disease. Increases due to decreased utilisation occur in liver disease, thiamine deficiency and during alcohol metabolism.

113
Q

Interpret the observation that the enzyme phosphofructokinase in skeletal muscle is inhibited by high concentrations of ATP and activated by high concentrations of AMP.

A

Key catabolic enzymes are activated by low energy signals (signals that indicate a low energy status in the cell) and inactivated by high- energy signals (signals that indicate a high energy status in the cell). Opposite for key anabolic (biosynthetic) enzymes. AMP is a low-energy signal that activates phosphofructokinase and speeds up glycolysis so that more ATP can be produced. ATP is high-energy signal that inhibits phosphofructokinase and slows down glycolysis as enough ATP is available.

114
Q

Compare and contrast the functions of glycolysis in adipose tissue,
skeletal muscle and red blood cells.

A

Glycolysis is used to produce ATP by substrate level phosphorylation in all three tissues:
• In red blood cells it is the only mechanism for ATP production.
• In skeletal muscle it enables ATP production to occur under
anaerobic conditions. • In adipose tissue it is a minor route for ATP production.
Glycolysis is used to produce useful intermediates in red blood cells and adipose tissue:
• 2,3-bisphosphoglycerate is produced from 1,3-
bisphosphoglycerate in red blood cells and is important in regulating (decreases) the oxygen affinity of haemoglobin.
• Glycerol phosphate is produced from dihydroxyacetone
phosphate in adipose tissue and is used in the esterification of fatty acids to produce triacylglycerol.

115
Q
  1. List the end-products of glycolysis under aerobic and anaerobic
    conditions in red blood cells and skeletal muscle.
A

Aerobic conditions Anaerobic conditions
Lactate Lactate red blood cells
PyruvateLactate skeletal muscle

116
Q

Outline the important roles of pyruvate dehydrogenase in glucose metabolism.

A

The PDH reaction cannot be reversed in the cell. There are two major consequences of this: • The loss of CO2 from pyruvate is irreversible. • Acetyl~CoA cannot be converted to pyruvate and therefore cannot be
converted to glucose. The reaction is therefore subject to control mechanisms that ensure: • Acetyl~CoA from the b-oxidation of fatty acids rather than from glucose is
used in stage 3 of catabolism (acetyl~CoA inhibits the enzyme
allosterically). • The reaction is sensitive to the energy status of the cell (ATP and NADH
inhibit and ADP activates the enzyme allosterically). • The enzyme is activated when there is plenty of glucose to be catabolised
(insulin activates the enzyme by promoting its dephosphorylation).

117
Q

What happens if not had dairy for a while

A

lactase deficiency.
Some adults suffer from this disease due to the loss of lactase (ß-
galactosidase) activity and hence the ability to hydrolyse lactose (milk
sugar) to glucose and galactose. As a result, the unhydrolysed lactose is
fermented by gut bacteria to form various organic acids that irritate the
gastro-intestinal tract, causing cramps and diarrhoea. These symptoms
last until all of the lactose has been metabolised and the products
removed, i.e. about 24 hr.

118
Q

what are the symptoms of galactosaemia

A 
vomiting after drinking milk
cataracts
damaged liver
urine has high sugar
jaundice
119
Q

what tissue is responsible for the major part of galactose metabolsim

A

galactokinase
uridly transferase
UDP-galactose epimerase

120
Q

if no galactokinase, build up of…..which causes…

A

just galactose
cataracts
sugar in urine
no damage to liver

121
Q

if no uridyl or epimerase, build up of….which causes

A

Galactose and galactose 1 P
cataracts
liver function lost

122
Q

how to distinguish if the body has not got uridyl or epimerase

A

epimerase - rare and if do not have then can not undergo glycogenesis so can’t make galactose from glucose

123
Q

how would you determine which enzyme was missing in a person

A 
blood sugar test
enzyme assay (blood sample)
124
Q

why would galactose be present in the urine

A

no enzyme present so won’t be broken down

if damage liver + reaches kidney threshold

125
Q

what are the metabolic consequences of the absence of galactose 1-P transferase

A

build up of galactose - conversion of galactose to galactilol - results in galactasamia

126
Q

why do galacatosaemic patients develop cataracts

A

increased activity of aldose reductase -> NADPH less -> defences worst -> oxidative damage -> crystallin protein in eye damaged -> cataracts

127
Q

why does a galactosaemic patient become jaundiced

A

RBC’s broken down in spleen -> forms billirubin which is taken to the liver. due to damage of liver - unable to be excreted so builds up and causes yellowing

128
Q

is there an alternative source of tissue galactose for patients on a galactose free diet

A

galactose can be formed from glucose

glucose -> glucose BP -> glucose 1P -> UDP glucose -> UDP galactose -> galactose

129
Q

would a mother who is galactosaemic be able to produce lactose in her milk

A

can form lactose from glucose

UDP galactose + glucose (lactose synthase) ->lactose + UDP

130
Q

what happens in pesticide poisoning

A

2,4-DNP penetrates the mitochondrial inner membane and act as uncoupling agents. less energy from ox Ph so energy lost as heat and body temp rises. to combat - increased sweating -> coma-> death

131
Q

why is cyanide toxic to cells

A

blocks NADH and FAD2H oxdiation- no proton motive force - no ATP synthesis - cell death

132
Q

compare and contrast oxidative phosphorylation and substrate level phosphorylation

A

Oxidative phosphorylation
• Produces ATP from ADP and Pi
• Requires membrane associated complexes (inner mitochondrial
membrane) • Energy coupling occurs indirectly through generation and
subsequent utilisation of a proton gradient (p.m.f). • Cannot occur in absence of oxygen. • Efficiency of energy conservation ~33% - considerable heat
production • Major process for ATP synthesis in cells that require large amounts
of energy.
Substrate level phosphorylation
• Produces ATP from ADP + phosphorylated organic compound.
• Requires soluble enzymes (cytoplasmic and mitochondrial matrix)
• Energy coupling occurs directly through formation of a high energy
of hydrolysis bond (phosphoryl-group transfer). • Can occur to a limited extent in absence of oxygen. • Efficiency of energy conservation ~60% - low heat production. • Minor process for ATP synthesis in cells that require large amounts
of energy.

Medical Cell Biology And Genetics (36 decks)

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