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Session 1 (B) Flashcards

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1
Q

Stage 1 of dietary carbohydrate metabolism involves the breakdown of carbohydrates into…

A

Monosaccharides

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2
Q

In which parts of the body does stage 1 breakdown of dietary carbohydrates take place and using which enzymes?

A

Saliva - Amylase

Pancreas - Amylase

Small intestine contains disaccharidases attached to the brush border membrane of epithelial cells - lactase, sucrose, pancreatic amylase, isomaltase

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3
Q

What does amylase in saliva break down?

A

Starch/glycogen into dextrins

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4
Q

What does amylase in the pancreas break down?

A

Sugars into monosaccharides

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5
Q

What do pancreatic amylase and isomaltase respectively break down?

A

Alpha 1-4 bonds

Alpha 1-6 bonds

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6
Q

What are three reasons for lactose intolerance?

A

Primary lactase deficiency

Secondary lactase deficiency

Congenital lactase deficiency

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7
Q

What monosaccharides is lactose composed of?

A

Galactose + Glucose

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8
Q

What are common symptoms of lactose intolerance?

A 
Bloating/cramps 
Flatulence
Diarrhoea 
Vomiting 
Rumbling stomach
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9
Q

What is the cause of primary lactase deficiency?

A

Absence of lactase persistence allele

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10
Q

In which group of people does primary lactase deficiency occur? Where in the world does it have the highest prevalence?

A

Adults

Northwest Europe

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11
Q

What causes secondary lactase deficiency?

A

Injury to the small intestine e.g. Gastroenteritis, Crohn’s, UC

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12
Q

What ages does secondary lactase deficiency affect? Is it generally reversible or irreversible?

A

Both infants and adults

Reversible

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13
Q

Congenital lactase deficiencies are extremely rare, what causes them and what effect will it have on a newborn child?

A

An autosomal recessive defect in lactase gene

Won’t be able to digest breast milk

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14
Q

How are monosaccharides absorbed from the gut lumen?

A

By active transport by the SDGT1 into intestinal epithelial cells

Then via GLUT2 into the blood supply

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15
Q

How does glucose get from the bloodstream into cells?

A

Via facilitated diffusion using transport proteins (GLUT1 - GLUT5)

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16
Q

Where is GLUT2 found?

A

On the membranes of kidney, liver, pancreatic beta cells and the small intestine

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17
Q

GLUT4 transporters are ______ regulated

A

Insulin

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18
Q

Where are GLUT4 transporters found?

A

Adipose tissue

Striated muscle

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19
Q

All tissues can metabolise glucose but which cells have an absolute requirement for glucose as their source of energy?

For what reasons?

A

Red blood cells
Neutrophils
Innermost cells of kidney medulla
Lens of the eye

Either have a poor oxygen supply or no mitochondria so can’t rely on the later stages of respiration and largely use glycolysis

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20
Q

CNS (brain) prefers glucose as a fuel but can use __________ _______ in times of ___________

A

Ketone bodies

Starvation

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21
Q

Stage 2 of carbohydrate metabolism involves the break down of glucose into metabolic intermediates. These metabolic intermediates release… (2)

A

Reducing power and energy

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22
Q

Where does glycolysis take place?

A

In the cytoplasm of cels

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23
Q

Glycolysis consist of which two main phases? What does each phase consist of?

A

Investment (involves investment of ATP)

Payback (release of more ATP than was invested)

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24
Q

What are the starting and ending molecules of glycolysis?

A

Glucose

2 x Pyruvate

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25
What are the functions of glycolysis? (3)
Oxidation of glucose NADH production (2 per glucose) Synthesis of ATP from ADP (net gain of 2 per ATP)
26
Glycolysis can operate anaerobically with the addition of which enzyme?
Pyruvate dehydrogenase
27
What are some key enzymes in glycolysis? (3)
Hexokinase (glucokinase in liver) Phosphofructokinase Pyruvate kinase
28
What role does hexokinase (glucokinase in the liver) play in glycolysis?
It's the first step | Converting glucose to glucose-6-phosphate
29
What role does phosphofructokinase play in glycolysis?
A key control enzyme in glycolysis | Converts fructose-6-phosphate to fructose-1,6-bisphosphate
30
What role does pyruvate kinase play in glycolysis?
The last step of glycolysis | Phosphoenolpyruvate ---> Pyruvate
31
What is the difference between glucokinase and hexokinase?
Glucokinase has a lower affinity for glucose and is not inhibited by its product
32
What happens to glucose in phase 1 of glycolysis? (3 steps)
Phosphorylation of glucose to G-6-P then conversion to fructose-6-phosphate and phosphorylation to fructose-1,6-bisphosphate
33
What is the reason for phosphorylation of glucose? (2)
Makes glucose negatively charge preventing passage back across the plasma membrane Increases reactivity of glucose for further steps of glycolysis
34
How many moles of ATP are used in phase 1 of glycolysis per glucose?
2 moles of ATP
35
Which reactions in phase 1 of glycolysis are irreversible and why?
(1) Glucose ---> G-6-P (2) F-6-P ---> Fructose-1,6-bisphosphate These reactions have a large -ve deltaG value (too much energy would be required to carry out the reverse reaction)
36
What reaction of glycolysis commits glucose to metabolism via glycolysis?
Step 3 in Phase 1 F-6-P ---> Fructose-1,6-bisphosphate
37
The rate of glycolysis in cancer cells is...
Up to 200x greater than normal
38
What happens at the start of phase 2 of glycolysis?
There is cleavage of 6C in to two 3C units
39
Reducing power is produced in which form in phase 2 of glycolysis? How many molecules are produced per glucose?
NADH 2 per glucose
40
ATP is synthesised by which process in glycolysis?
Substrate level phosphorylation - production of ATP from ADP + Pi
41
Which reaction in phase 2 of glycolysis is irreversible and why?
Last step - Phosphoenolpyruvate ---> Pyruvate Large -ve delta G value
42
What is the main regulator for glycolysis and in which 2 main ways is it regulated?
Phosphofructokinase Hormonally Allosterically
43
How is PFK allosterically regulated in muscle?
Inhibited by high ATP | Stimulated by high AMP
44
How is PFK hormonally regulated in the liver?
Stimulated by insulin | Inhibited by glucagon
45
What is glycerol phosphate? What is it formed from? What is it used for? Where is it produced?
Important intermediate of glycolysis Formed from DHAP Important to TAG/phospholipid biosynthesis Produced by glycolysis in the liver (can also be made directly) and in adipose tissue (essential here)
46
Which enzyme catalyses the production of glycerol phosphate?
Glycerol 3-phosphate dehydrogenase
47
What is 2,3-bisphosphoglycerate? Where is it produced? What is its function?
Important intermediate of glycolysis RBCs Regulates haemoglobin oxygen affinity
48
Which enzyme catalyses the production of 2,3-BPG?
Bisphosphoglycerate mutase
49
How many moles of NADH are produced per mole of glucose in glycolysis?
2
50
Total [NAD+] and [NADH] in a cell are __________. So if NAD+ is all reduced glycolysis will _______. How is this prevented?
Constant Stop
51
How is NAD+ typically regenerated in most cells? In which cells is this not possible and why?
NAD+ is regenerated from NADH in the last stage of carbohydrate metabolism RBCs (or other cells with a reduced oxygen supply) There are no stages 3 and 4 of carbohydrate metabolism in RBCs as they have no mitochondria
52
How is NAD+ regenerated in RBCs and cells with an insufficient oxygen supply?
Through the action of lactate dehydrogenase
53
What reaction does lactate dehydrogenase catalyse?
NADH + H+ + pyruvate NAD+ + Lactate Converts pyruvate to lactate instead of passing it on to the link reaction
54
What does the presence of lactate dehydrogenase allow a cell to do?
Regenerate NAD+ so glycolysis can continue
55
Name some tissues more reliant on glycolysis and two reasons why this may be the case.
RBCs, skeletal muscle, skin, brain and GI Low oxygen, no mitochondria
56
What happens to the lactate produced in tissues in the heart?
Enters the blood and can be converted back to pyruvate and used directly as a source of energy
57
What happens to any lactate produced in the tissues, in the liver and kidneys?
Converted back to pyruvate and used for gluconeogenesis
58
What is the normal plasma lactate concentration?
Less than 1.6 mM
59
What plasma lactate concentration is defined as hyperlactaemia? Is there a change in blood pH at this point and why?
2-5 mM No, still below renal threshold
60
What plasma lactate concentration is defined as lactic acidosis? How does this affect blood pH?
Above 5mM Lowers blood pH, above renal threshold
61
Galactose produced by the breakdown of dietary lactose can be used in which 2 ways?
To start glycolysis To produce glycogen
62
Which enzyme catalyses the phosphorylation of galactose to galactose-1-phosphate?
Galactokinase
63
Deficiencies in which 3 enzymes can cause galactosaemia?
Galactokinase Uridyl transferase UDP-galactose epimerase
64
What reaction does uridyl transferase catalyse?
Conversion of galactose-1P to glucose-1P (on its way to be used in glycolysis)
65
What reaction does UDP-galactose epimerase catalyse?
Conversion of galactose-1P to UDP-galactose (on its way to forming glycogen)
66
Where in the body is fructose metabolised? What can fructose be used for in the body?
In the liver Can be modified for use in glycolysis
67
What is the cause, features and clinical signs of essential fructosuria?
Fructokinase missing Fructose in urine No clinical signs
68
What is the cause, result and treatment for fructose intolerance?
Adolase missing Fructose-1-phosphate accumulates in the liver causing liver damage Remove fructose from the diet
69
The pentose phosphate pathway starts from...
Glucose-6-phosphate
70
The pentose phosphate pathway is an important source of _________ and ________
NADPH C5-sugar ribose
71
The NADPH produced in the pentose phosphate pathway is required for... (3)
Reducing power for biosynthesis Maintenance of GSH levels Detoxification reactions
72
The C5-sugar ribose produced in the pentose phosphate pathway is required for the synthesis of... (3)
Nucleotides DNA RNA
73
Is ATP synthesised in the pentose phosphate pathway?
No
74
Is carbon dioxide produced in the pentose phosphate pathway?
Yes
75
What is the rate limiting enzyme of the pentose phosphate pathway?
Glucose-6-phosphate dehydrogenase

MEH (9 decks)

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