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MEH unit > S1) Energy Production I — Carbohydrates > Flashcards

S1) Energy Production I — Carbohydrates Flashcards

1
Q

Define the terms endergonic and exergonic

A
  • Exergonic: a reaction where the energy released is greater than the energy input
  • Endergonic: a reaction where the energy input is greater than the energy released
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2
Q

What is the ATP-ADP cycle?

A

The ATP-ADP cycle is the cycle that couples endergonic reactions with exergonic reactions

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3
Q

What does the ATP-ADP cycle do?

A
  • It allows for the controlled release of energy by oxidation
  • Some of the energy is conserved by the formation of ATP from ADP and Pi and the remainder is lost as heat
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4
Q

What is cell metabolism?

A

Cell metabolism is the highly integrated network of chemical reactions in distinct metabolic pathways that occur within cells

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5
Q

Define the terms catabolism and anabolism

A
  • Catabolism involves the breakdown of larger molecules to smaller ones
  • Anabolism involves the synthesis of larger molecules from smaller ones
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6
Q

Compare and contrast catabolic and anabolic pathways

A
  • Catabolic pathways are oxidative, release large amounts of free energy, and produce some intermediary metabolites
  • Anabolic pathways are reductive, and use energy and intermediary metabolites from catabolism to synthesise cell components
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7
Q

Identify the 3 major carrier molecules

A
  • NAD
  • NADP
  • FAD
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8
Q

Represent the 3 major carrier molecules in their oxidised and reduced forms

A
  • Oxidised forms: NAD+, NADP+, FAD
  • Reduced forms: NADH + H+, NADPH + H+, FAD2H
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9
Q

Why must carrier molecules cycle between oxidative and reductive processes to maintain cell function?

A

To allow for both oxidation reactions (require NAD+) and reduction reactions (require NADH + H+) to occur

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10
Q

What is Free Energy?

A

Free Energy is the energy released in an exergonic reaction that is available to do work (ΔG)

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11
Q

What are the four steps in carbohydrate metabolism?

A
  • Stage 1: Breakdown to monomers
  • Stage 2: Breakdown to metabolic intermediates
  • Stage 3: TCA (Kreb’s) cycle
  • Stage 4: Oxidative phosphorylation
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12
Q

In stage 1 of metabolism, carbohydrates are digested at the salivary glands, pancreas and small intestines

Identify the respective enzymes involved

A
  • Saliva: amylase
  • Pancreas: amylase
  • Small intestine: lactase, sucrase, pancreatic amylase, isomaltase
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13
Q

Why can’t cellulose be digested by humans?

A

No enzymes to break down the β 1-4 linkages present in dietary fibres i.e. no cellulase

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14
Q

Identify 3 clinical features of primary lactase deficiency

A
  • Absence of lactase persistence allele
  • Only occurs in adults
  • Highest prevalence in Northwest Europe
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15
Q

Identify 3 clinical features of secondary lactase deficiency

A
  • Caused by injury to small intestine
  • Occurs in both infants and adults
  • Generally reversible
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16
Q

Identify four clinical conditions which could cause injury to the small intestine, leading to secondary lactase deficiency

A
  • Gastroenteritis
  • Coeliac disease
  • Crohn’s disease
  • Ulcerative colitis
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17
Q

Describe 3 features of congenital lactase deficiency

A

- Extremely rare

  • Autosomal recessive defect in lactase gene
  • Cannot digest breast milk
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18
Q

What foods should someone with a lactase deficiency abstain from?

A
  • Milk
  • Cream
  • Yoghurt
  • Cheese
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19
Q

Identify 4 symptoms associated with lactase deficiency?

A
  • Bloating/cramps
  • Flatulence
  • Diarrhoea
  • Vomiting
  • Rumbling stomach
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20
Q

How are monosaccharides absorbed?

A
  • Active transport by SGLT1 into intestinal epithelial cells
  • Active transport by GLUT2 into blood supply
  • Facilitated diffusion by transport proteins GLUT1-GLUT5 into cells
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21
Q

Identify 4 tissues which have an absolute requirement for glucose

A
  • Neutrophils
  • Lens of eye
  • Red blood cells
  • Innermost cells of kidney medulla
22
Q

Describe the glucose dependency of the brain

A

The CNS prefers glucose as a fuel but can use ketone bodies for some energy requirements in times of starvation

23
Q

Where does glycolysis occur?

A
  • Occurs in all tissues
  • Occurs in cytosol
24
Q

What kind of process is glycolysis?

A
  • Exergonic process
  • Oxidative process
25
Q

Identify the 4 functions of glycolysis

A
  • Oxidation of glucose
  • NADH production
  • Synthesis of ATP (2 ATP per glucose molecule)
  • Produces C6 and C3 intermediates (no loss of CO2)
26
Q

Identify the enzymes at point 1, 3 and 10

A

1 - Hexokinase

3 - Phosphofructokinase-1

10 - Pyruvate kinase

27
Q

Describe Phase 1 of Glycolysis (reactions 1-3)

A
  • Phosphorylation of glucose to G-6-P
  • Polarised glucose is more reactive & cannot return down plasma membrane
  • Input: 2 moles ATP per mole glucose
28
Q

Describe Phase 2 of Glycolysis (reactions 4-10)

A
  • Reaction 4: C6 –> 2C3 units
  • Reaction 6: Reducing power captured (NADH)
  • Reaction 7&10: ATP synthesis (substrate level phosphorylation)
29
Q

Identify the irreversible reactions in glycolysis

A

Large -ΔG:

  • Reactions 1
  • Reaction 3
  • Reaction 10
30
Q

Explain the allosteric regulation of glycolysis by phosphofructokinase

A

Allosteric regulation (muscle):

  • Inhibited by high ATP
  • Stimulated by high AMP
31
Q

Explain the hormone regulation of glycolysis by phosphofructokinase

A

Hormonal regulation (liver):

  • Stimulated by insulin
  • Inhibited by glucagon
32
Q

Describe the regulation of glycolysis through hexokinase and pyruvate kinase

A
33
Q

Explain the dependency of glycolysis on NAD+

A
  • Glycolysis pathway requires NAD+ (NADH is produced)
  • NAD+ and NADH is constant in cells, so glycolysis would end when all NAD+ is converted to NADH
  • Hence, NAD+ is regenerated in stage 4 of metabolism
34
Q

In light of the dependency of glycolysis on NAD+, explain why lactic acid (lactate) production is required

A
  • RBC have no stage 4 to regenerate NAD+
  • Stage 4 requires oxygen (limited in muscles and gut)
  • NAD+ is regenerated using Lactate Dehydrogenase (LDH)
35
Q

Explain how the blood concentration of lactate is controlled

A
36
Q

Which three factors account for elevations of plasma lactate concentration?

A
  • Rate of production
  • Rate of utilisation
  • Rate of disposal
37
Q

Identify 3 clinical features of hyperlactaemia

A
  • Lactate concentration 2-5 mM
  • Below renal threshold
  • No change in blood pH (buffering capacity)
38
Q

Identify 3 clinical features of lactic acidosis

A
  • Lactate concentration above 5 mM
  • Above renal threshold
  • Blood pH lowered
39
Q

Outline galactose metabolism

A
  • Dietary lactose is hydrolysed by lactase to release glucose + galactose which absorbed into the blood stream
  • Galactose is metabolised largely in the liver:

Galactose + ATP → Glucose 6-phosphate + ADP

40
Q

What is galactosaemia?

A

Galactosaemia is a clinical condition wherein one cannot use galactose obtained from the diet because of a lack of the kinase or transferase enzyme

41
Q

Describe the galactosaemia that occurs when the kinase enzyme is absent

A

Kinase absence:

  • Rare
  • Build-up of galactose in tissues
42
Q

Describe the galactosaemia that occurs when the transferase enzyme is absent

A

Transferase absence:

  • Common and more serious
  • Build-up of galactose and galactose-1-P
43
Q

What happens when galactose accumulates in the tissues?

A

Accumulation of galactose in tissues leads to its reduction to galactitol by the activity of the enzyme aldose reductase

44
Q

Outline fructose metabolism

A
  • Dietary sucrose is hydrolysed by sucrase to release glucose + fructose which are absorbed into the blood stream
  • Fructose is metabolised largely in the liver and is converted to glyceraldehyde 3-phosphate (an intermediate of glycolysis)
45
Q

Describe the clinical features of essential fructosuria

A
  • Fructokinase missing
  • Fructose in urine, no clinical signs
46
Q

Describe the clinical features of fructose intolerance

A
  • Aldolase missing
  • Fructose-1-P accumulates in liver (leads to liver damage)
  • Treatment: remove fructose from diet
47
Q

Describe the input and output of the pentose phosphate pathway

A
  • Input: Glucose-6-Phosphate
  • Output:

I. CO2

II. Ribose – synthesis of nucleotides, DNA and RNA

III. No ATP

48
Q

What is the rate limiting enzyme for the pentose phosphate pathway?

A

Glucose-6-phosphate dehydrogenase (G6PDH)

49
Q

The pentose phosphate pathway is an important source of NADPH for which processes?

A
  • Reducing power for biosynthesis
  • Maintenance of GSH levels
  • Detoxification reactions
50
Q

Where does the pentose phosphate pathway occur?

A

In the cytosol

51
Q

what does the pentose phosphate sugar pathway produce

A

NADPH

MEH unit (6 decks)

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