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SfM topics > Carbohydrates 2 > Flashcards

Carbohydrates 2 Flashcards

1
Q

What does isomaltase do?

A

hydrolyses (α1→6) bonds

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2
Q

What does glucoamylase do?

A

removes Glc sequentially from non-reducing ends

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3
Q

What do lactase and sucrase do?

A

Hydrolyse lactose and sucrose

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4
Q

where is starch found in diet?

A

cereals, potatoes, rice

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5
Q

where is glycogen found in diet?

A

meat (when animal dies, enzymes in tissue degrade most of glycogen stores)

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6
Q

where is cellulose and hemicellulose found in diet?

A

plant cell walls (humans don’t digest it)

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7
Q

where are oligosaccharides (containing alpha 1-> 6 linked to galactose) found in the diet?

A

peans, beans, lentils

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8
Q

where are lactose, sucrose and maltose found in the diet?

A

milk, table sugar, beer

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9
Q

where are glucose and fructose found in the diet?

A

fruit and honey

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10
Q

what digestion of carbohydrates occurs in the mouth?

A

Salivary amylase hydrolyses (α1→4) bonds of starch into glucose

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11
Q

what digestion of carbohydrates occurs in the stomach?

A

no carbohydrtae digestion (mainly proteins are broken down)

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12
Q

what digestion of carbohydrates occurs in the duodenum?

A

pancreatic amylase works as in mouth

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13
Q

what digestion of carbohydrates occurs in the jejunum?

A

final digestion by mucosal cell-surface enzymes (most carbohydrate breakdown occurs there)

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14
Q

what draws glucose molecules from intestinal lumen into the epithelial cells?

A

Na concentration inside cells (Na flows into cell down its conc. gradient, taking glucose along with it) . Na is constantly pumped out and therefore glucose can be transported

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15
Q

what sort of process is glucose transport?

A

Na dependant process

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16
Q

does glucose transport require ATP?

A

No; only the Na pump is ATP-driven which maintains low cellular Na so glucose can continually be moved in to epithelial cell

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17
Q

does the glucose transport through Na dependent process occur even against its conc. gradient ? (when blood glucose is high)

A

Yes

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18
Q

what other saccharide has a similar mode of absorption as glucose?

A

galactose (utilises gradients to facilitate its transport)

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19
Q

what does fructose bind to when it enters the cells down its conc. gradient (high in gut lumen and low in blood)

A

binds to channel protein GLUT5

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20
Q

regardless of blood glucose concentration, will glucose always be pumped out of the cell?

A

yes

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21
Q

why can’t oligosaccharides likes cellulose and hemicellulose be broken down by the gut?

A

they have dense structures which we can’t break down

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22
Q

what gases are produced by breakdown of oligosaccharide polymers by gut bacteria?

A

CH4 and H2 gases

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23
Q

what are disaccharide deficiencies caused by?

A

enzymes needed for breakdown are not produced

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24
Q

what can disaccharide infections result from?

A
  1. genetic
  2. severe intestinal infection
  3. other inflammation of the gut lining
  4. drugs injuring the gut wall
  5. surgical removal of the intestine
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25
Q

what enzymes are checked when a disaccharide deficiency is investigated?

A

usually checking for:

  • lactase
  • maltase
  • sucrase activity
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26
Q

what is the most common disaccharide deficiency?

A

lactose intolerance (not enough lactase in the body)

27
Q

what gives the lactose intolerance symptoms? (2)

A
  1. indigested lastose is broken down by gut bacteria causing gas build up and irritant acids
  2. lactose is osmotically active, thus drawing water from the gut into the lumen causing diarrhoea
28
Q

how can symptoms of lactose intolerance be avoided?

A
  1. avoiding milk products
  2. using milk products treated with fungal lactase
  3. supplementing diet with lactase (useless, since it can be easily digested, not good for long term)
29
Q

overall, why are the symptoms caused? (link it to bacteria)

A

bacteria are osmotically active

30
Q

what happens to glucose during its absorption until they are found in the cells?

A
  1. glucose diffuses through intestinal epithelium cells into blood and travels to liver
  2. glucose is immediately phosphorylated to glucose-6-phosphate by hepatocytes
  3. G6P can’t now diffuse out of the cell because GLUT transports can’t recognise it
  4. glucose is trapped inside hepatic cells
31
Q

where is glucokinase active?

A

in liver

32
Q

where is hexokinase active?

A

in other tissues

33
Q

when does glucokinase act?

A

only when glucose levels are VERY high (flood of glucose), liver “grabs” glucose, otherwise it’s inactive

34
Q

when does hexokianse act?

A

all the time, when glucose levels are normal, other tissues have the glucose

35
Q

what does high Vmax mean?

A

efficient enzyme

36
Q

what does low Km mean?

A

enzyme has high affinity for substrate

37
Q

What is Vmax and Km for glucokinase?

A

High Vax

High Km

38
Q

what is Vmax and Km for hexokianse?

A 
low Vmax (tissues are easily satisfied) 
low Km (even at low glucose conc. tissues can still "grab" it effectively)
39
Q

what are the 3 possible fates of G6P (glucose-6-phosphate)?

A
  1. pentose phosphate pathway (to generate pentoses or NADPH)
  2. glycogen (storage in the liver or other tissues if high conc. of glucose)
  3. glycolysis and CAC (energy production)
40
Q

what happens in the liver if blood glucose falls?

A
  1. glycogen is converted to G6P

2. G6P is then converted to glucose in blood by glucose-6-phosphatase

41
Q

what happens in the skeletal muscle if blood glucose falls?

A
  1. liver has no glucose-6-phosphatase
  2. glycogen is converted to G6P
  3. G6P is then converted straight to lactate (glycolysis since no enzyme present)
42
Q

what does glucose-6-phosphotase do?

A

chops off the phosphate group (to convert G6P to glucose)

43
Q

does glycogen form directly from glucose monomers?

A

no

44
Q

what enzyme begins the glycogen formation process by covalently binding glucose from UDP-glucose to form chain of 9 glucose residues? (sticks glucose together)

A

Glycogenin (sticks glucose molecules together)

45
Q

what enzyme takes over after glycogenin to extend the long glucose chain?

A

glycogen synthase (synthesises glycogen by taking glucose from UDP to make a long chain of glucose residues)

46
Q

what two bonds are required in synthesis of glycogen?

A
  1. alpha (1-4) glycosidic bonds

2. alpha (1-6) branches

47
Q

every how many glucose residues are alpha (1-6) branches formed?

A

every 8-10 residues

48
Q

glycogen synthase adds the glucosyl residues from UDP-glucose to which end of the glycogen chain?

A

the non-reducing end

49
Q

what is the overall step 1 of glycogen formation?

A

transfer of glucosyl units from UDP-glucose to the non-reducing ends of glycogen chains by glycogen synthase (enzyme) which attached glucosyl residues in alpha(1-4) bonds

50
Q

what is the overall step 2 of glycogen formation?

A

chains formed by glycogen synthase are then broken by glycogen -branching enzyme and re-attached via alpha(1-6) bonds to give branching points.
- enzyme chops off branches and reattaches them to other molecules

51
Q

in degradation of glycogen, what enzyme is used to cleave G1P groups from glycogen chain one at a time to make a shortened glycogen molecules?

A

glycogen phosphorylase

52
Q

what are the two de-branching enzymes involved in glycogen degradation?

A
  1. transferase activity

2. glucosidase activity

53
Q

what does transferase do?

A

removes a set of 3 glucose residues and attaches them to the nearest non-reducing end via alpha(1-4) bond

54
Q

what does glucosidase do?

A
  • removes the final glucose by breaking a alpha(1-6) linkage to release a free glucose
  • this then leaves an unbranched chain which can be further degraded or built upon as needed
55
Q

what does glycogen phosphorylase do?

A

removes glucose monomers in the form of G1P from the glycogen chain to shorten it

56
Q

what happens to G1P which is cleaved off the glycogen chain during glycogen degradation?

A
  • G1P is converted to G6P
  • in the liver, G6P can be converted to glucose by glucose-6-phosphatase and travels into blood
  • in the skeletal muscle, G6P is converted to lactate through substrate level phosphorylation
57
Q

what is the order of glycogen ending up as glucose/lactate again?

A
  1. glycogen
  2. G1P
  3. G6P
  4. glucose (in liver) OR lactate (in muscle)
58
Q

what is a famous G6P deficiency?

A

Von Gierke’s disease

59
Q

what 3 organs are affected by Von Gierke’s disease?

A
  • liver
  • kidneys
  • intestines
60
Q

what are 2 main symptoms of Von Gierke’s disease?

A
  • high liver glycogen (normal structure maintained)

- low blood glucose (fasting hypoglycemia)

61
Q

what causes the symptoms to Von Gierke’s disease?

A

glucose can’t be used as an energy source and all energy must come from dietary carbohydrates (glycogen CANNOT be utilised)

62
Q

what is the famous skeletal muscle phosphorylase deficiency?

A

McArdle’s disease

63
Q

what is the main symptoms of McArdle’s disease?

A
  • high muscle glycogen

weakness and cramps after exercise

SfM topics (21 decks)

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