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Science for Medicine > Carbohydrates 2 > Flashcards

Carbohydrates 2 Flashcards

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1
Q

What are some carbohydrates in the diet?

A

Starch (cereals, potatoes)

Glycogen (meat)

Cellulose and hemicellulose (plant cell walls)

Oligosaccharides containing a1-6 linked galactose (peas, beans)

Lactose, succrose, maltose (milk, sugar, beer)

Glucose, fructose (fruit, honey)

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2
Q

Where are 3 places that carbohydrates are digested?

A

Mouth

Duodenum

Jejanum

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3
Q

How are carbohydrates digested in the mouth?

A

Salivary amylase hydrolyses a1-4 bonds of starch

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4
Q

How are carbohydrates digested in the duodenum?

A

Pancreatic amylase works as in the mouth (hydrolyses a1-4- bonds)

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5
Q

How are carbohydrates digested in the jejunum?

A

Final digestion by mucosal cell surface enzymes

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6
Q

What are enzymes that digest carbohydrates in the jejunum and what do they do?

A

Isomaltase (hydrolysis a1-6 bonds)

Glucoamylase (removes glucose from non reducing end)

Sucrase (hydrolysis sucrose)

Lactase (hydrolysis lactose)

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7
Q

What is the deudenum and jejunum part of?

A

Small intestine

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8
Q

Are any carbohydrates digested in the stomach?

A

No

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9
Q

Where are glucose transporters found?

A

In the microvilli of epithelial cells facing the lumen of the intestine

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10
Q

What does our high intake os salt cause?

A

High Na concentration outside of cells

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11
Q

What is the glucose transporter driven by?

A

Na, it takes in 2 Na and 1 glucose

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12
Q

What maintains the concentration gradient of Na that can drive glucose into the cells?

A

Na+/K+ pumps

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13
Q

How is glucose then pumped from within the cell into the blood?

A

Pump on the basal surface of the cell move glucose to blood, only transporting glucose due to the high concentration gradient

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14
Q

What the exact process for the absorption of glucose?

A
  1. High [Na+] out of the cell due to high salt intake
  2. Na+/K+ pump maintains the concentration gradient
  3. Transporters on microvilli bring in 2 Na+ and 1 glucose
  4. Transporter on basal surface lets 1 glucose leave into blood due to concentration gradient
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15
Q

Why can the absorption of glucose be described as an indirect ATP process?

A

Because of the use of the Na+ pump

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16
Q

Why will glucose be pumped in the cell even if its up its concentration gradient?

A

Because of the Na+ concentration which drives the pump

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17
Q

How is galactose absorbed?

A

Similarly to glucose utilising gradients

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18
Q

How is fructose absorbed?

A
  1. Binds to channel protein GLUT5
  2. Simply moves down its concentration gradient
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19
Q

What happens to cellulose and hemicellulose?

A

Cannot be digested by the gut, are broken down into methane and hydrogen by gut bacteria

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20
Q

What do cellulose and hemicellulose do?

A

Increase facial bulk and decrease transit time

Cause smelly farts (broken down into methane)

21
Q

What be disaccaride deficiencies be caused by?

A

Genetic

Severe intestinal infection

Inflammation of the gut lining

Drugs injuring the gut wall

Surgical removal of part of the intestine

22
Q

What does diagnosis of disaccaride defficiencies require?

A

Enzyme tests of intestinal secretions for lactose, maltose or sucrose activity

23
Q

What is the most common disaccharide deficiency?

A

Lactose intolerence

24
Q

What causes the symptoms of lactose intolerence?

A

Undigested lactose broken down by gut bacteria causing gas build up and acid

Lactose is osmotically active, drawing water into the lumen from the gut causing diarrhoea

25
Q

What is the fate of absorbed glucose?

A
  1. Diffuses through intestinal epithelium cells into blood and then the liver
  2. Immedietely phosphorylated into glucose-6-phosphate by the hepatocytes
26
Q

Why is glucose converted into glucose-6-phosphate?

A

Because glucose-6-phosphate cannot escape the cell as GLUT transporters don’t recognise it

27
Q

What enzymes control the reaction of glucose to glucose-6-phophate?

A

Glucokinase (liver)

Hexokinase (skeletal muscle)

28
Q

Where is glucokinase found?

A

In the liver

29
Q

Where is hexokinase found?

A

In skeletal muscle

30
Q

What are the kenetic properties of glucokinase and hexokinase?

A

Glucokinase has high KM and high vmax

Hexokinase has low KM and low vmax

31
Q

What happens when the concetration of blood glucose is low, in terms of glucokinase and hexokinase?

A

Liver doesn’t grab all of it (due to high KM of glucokinase) so other tissues can use it

32
Q

What happens when glucose concentration is high, in terms of glucokinase and hexokinase?

A

The liver grabs a lot more of it

33
Q

Why would glucose-6-phosphate be converted back to glucose in the liver?

A

To enter the blood stream and travel to where it is needed

34
Q

What is substrate level phosphorylation?

A

Formation of ATP by direct transfer of a phosphoryl group (PO3) to ADP from another phosphorylated compound

35
Q

What is oxidative phosphorylation?

A

ATP is formed from the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers

36
Q

What does the pathway of glycogen in the liver to glucose in the blood look like?

A
37
Q

What does the fate of glycogen in skeletal muscle look like?

A
38
Q

Where is the enzyme glucose-6-phosphotase found?

A

In the liver, not the skeletal muscle as the genes that code for it are not active

39
Q

What does glucose-6-phosphatase do?

A

Breaks down glucose-6-phosphate into glucose

40
Q

What is the exact process of the synthesis of glycogen?

A
  1. Glycogenin begins process by covalently binding glucose from uracil diphosphate (UDP) glucose to form a chain of about 8 monomers
  2. Glycogen synthase takes over and extends the glucose chain
  3. Chains formed are broken by glycogen branching enzymes and reattacthed via a1-6- bonds to give branching points
  4. Glycogen synthase extends the chain and repeat
41
Q

How does glycogenin catalyse the synthesis of glycogen?

A

Producing a tiny amount of glucose to start the chain

42
Q

What is uracil diphospahte (UDP)?

A

A carrier molecule that allows the cell to defferentiate what glucose is to be used for the synthesis of glycogen

43
Q

What is the exact process of the degradation of glycogen?

A
  1. Glucose monomers are removed one at a time from the non reducing end by glycogen phophorylase to produce G-1-P
  2. Branch is removed by debranching enzyme
  3. Transferase removes 3 glucose monomers and attatches them to nearest non reducing end via a1-4 bonds)
  4. Glucosidase removes final glucose monomer by breaking a1-6 bond and releases a free glucose
  5. Process repeats
44
Q

What is G-1-P readily converted to and what does this look like?

A

G-6-P

45
Q

What are some common diseases associated with glycogen storage?

A

van Gierke’s disease

McArdle’s disease

46
Q

What is van Gierke’s disease caused by?

A

A G-6-P defficiency in the liver, kidney and intestine

47
Q

What are the symptoms of van Gierke’s disease?

A

High [liver glycogen]

Low [blood glucose]

High [blood lactate]

48
Q

What is the treatment of van Gierke’s disease?

A

Regular carbohydrate feeding

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