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Gastrointestinal Biology > GB 12. Post-Absorption Processing of Carbohydrates > Flashcards

GB 12. Post-Absorption Processing of Carbohydrates Flashcards

1
Q

In the “fed” state what is the plasma levels of glucose, amino acids and triglycerides (chylomicrons)?

A

they are ALL increased

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2
Q

What are the control mechanisms (secretions) in the fed state? [2]

A

[1] increase secretion of insulin by pancreas

[2] decrease secretion of glucagon

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3
Q

What type of response does the body have in the fed state? (one word)

A

anabolic

- building big things from small things

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4
Q

What happens in the liver, adipose tissue, muscle and tissue in the fed state?

A

LIVER:
- makes glycogen, proteins + triglycerides (VLDL)

ADIPOSE TISSUE:
- makes triglycerides

MUSCLE:
- makes protein

TISSUE:
- uses glucose as “fuel”

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5
Q

In the “fasting” state what is the plasma levels of glucose, amino acids and triglycerides (chylomicrons)?

A

they are ALL decreased

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6
Q

What are the control mechanisms (secretions) in the fasting state? [2]

A

[1] decreased secretion of insulin

[2] increased secretion of glucagon + adrenaline

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7
Q

What type of response does the body have in the fed state? (one word)

A

catabolic

- the breakdown of larger molecules

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8
Q

What happens in the liver, adipose tissue, muscle and brain in the fed state?

A

LIVER:

  • glycogenolysis
  • gluconeogenesis
  • beta oxidation
  • ketogenesis

ADIPOSE TISSUE:
- lipolysis

MUSCLE:

  • uses FAs + ketone bodies as “fuel”
  • proteolysis supplies AAs to liver

BRAIN:
- uses glucose + ketone bodies as “fuel”

ketone bodies are transported from the liver to other tissues where they can be reconverted to acetyl coa

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9
Q

What are the 2 types of simple dietary carbohydrates? Give examples of each.

A

[1] monosaccharides

  • glucose
  • fructose

[2] disaccharides

  • sucrose
  • lactose
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10
Q

What are some examples of complex dietary carbohydrates?

A
  • starch (plant sources)
  • glycogen (animal)
  • cellulose
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11
Q

What are the 2 overarching categories of dietary carbohydrates?

A

[1] Simple Carbs

[2] Complex Carbs

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12
Q

Where does absorption of carbohydrates mainly occur?

A

duodenum + upper jejunum

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13
Q

What are the enzymes involved in digesting carbohydrates in the gut?

A

[1] SALIVA

  • contains Alpha-Amylase
  • breaks down starch + glycogen
  • however, pH restricted

[2] PANCREAS
- contans Pancreatic Alpha-Amylase

[3] GUT MUCOSA
- contains Oligosaccharidases + Disaccharidases (such as isomaltase, maltase, sucrase, lactase)

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14
Q

How long can liver glycogen support blood glucose levels for in the absence of food?

A

10 to 18 hours

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15
Q

What is gluconeogenesis?

A

synthesis of glucose from lactate, pyruvate, glycerol and so on

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16
Q

During over-night fasting, where does gluconeogenesis primary occur?

A

90% in the liver

10% in the kidneys

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17
Q

How does glucagon stimulate gluconeogenesis?

A

(normally stimultes glycogenolysis)

  • glucagon opposes insulin and works to increase blood glucose levels
  • it stimulates gluconeogenesis (which is increasing glucose blood levels)
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18
Q

List the 3 main substrates for gluconeogenesis.

A

[1] Lactate

  • released into blood by exercising muscle
  • gluconeogenesis in liver converts lactate to glucose

[2] Glycerol
- from fat stores (triglycerides)

[3] Amino Acids
- from tissue protein breakdown

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19
Q

What are the 3 irreversible reactions in glycolysis?

A

[1] Glucose to Glucose-6-Phosphate

[2] Fructose-6-Phosphate to Fructose-1,6-Bisphosphate

[3] Phosphoenolpyruvate to Pyruvate

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20
Q

What are the 4 special reactions that are used in gluconeogenesis to make glucose from pyruvate? (specific enzymes)?

A

[1] Pyruvate Carboxylase

[2] PEP Carboxykinase

[3] Fructose 1,6 Bisphosphatase

[4] Glucose-6-Phosphatase
- glucose-6-phosphate translocase

21
Q

What is the structural unit of glycogen? Where are the main glycogen stores located? What is glycogen?

A

Structure: a polymer made of glucose (analagous to starch in plants)

Main Glycogen Stores:

  • Liver: 10% by weight
  • — used to maintain blood glucose
  • Muscle: 1 to 2% by weight
  • — used as a fuel reserve for ATP synthesis during muscle contraction

What is it?

  • a rapidly mobilizable storage form of glucose
  • when glycogen depleted, some tissues synthesize glucose via gluconeogenesis using amino acids
22
Q

At what time of the day is the liver glycogen at its highest?

A

SLIDE 16 + 17**

23
Q

What is the structure of glycogen?

A
  • branched polymer of alpha-D-glucose units
  • the chain is formed by alpha-1,4 glycosidic bonds
  • the “branch points” are formed by alpha-1,6 glycosidic bonds
24
Q

What enzymes (and protein) are involved in glycogen synthesis? (e.g. making the chain longer, creating the chain and making branches in the chain)

A

[1] Glycogen Synthase

  • adds successive glucose units to the non reducing ends of growing chains, forming the alpha-1,4 bonds
  • it can only make existing glycogen chains longer

[2] Glycogenin
- if there is no glycogen left, the protein Glycogenin acts as a primer accepting glucose units to form a new chain

[3] Branching Enzyme

  • branches are made by this enzyme
  • amylo-alpha (1-4) to alpha (1-6) transglucosidase
25
Q

What is UDP-Glucose? What is the structure of UDP-Glucose?

A

UDP-Glucose: it is a precursor of glycogen

It has 2 parts:

  • glucose
  • uridine diphosphate
26
Q

What enzymes are involved in glycogenolysis?

A

[1] Glycogen Phosphorylase

  • cleaves alpha-1,4 glycosidic bonds
  • cleaves successive glucose units off the chains (starting at non-reducing ends), then releases them as glucose-1-phosphate
  • enzyme stops 4 glucose residues before each branch point
  • —- this eventually produces a structure called a LIMIT DEXTRIN

[2] Debranching Enzyme
- branches are removed

[3] Phosphoglucomutase
- glucose-1-phosphate is then converted to glucose-6-phosphate

[4] Glucose-6-phosphatase (LIVER)
- converts glucose-6-phosphate to glucose for release into blood stream

[5] Glucose-6-Phosphate Translocase (LIVER)
- along with Glucose-6-Phosphatase to release free glucose from glucose-6-phosphate

then in MUSCLE, glucose-6-phosphate goes into glycolysis directly to produce energy

27
Q

What is a limit dextrin?

A

after GLYCOGEN PHOSPHORYLASE cleaves the successive glucose units off of chain, they stop 4 glucose residues before each branch point…
- this produces the LIMIT DEXTRIN structure

28
Q

What are the 2 key enzymes in the regulation of glycogen metabolism?

A

[1] Glycogen Synthase

[2] Glycogen Phosphorylase

29
Q

What are the 2 levels of regulation in glycogen metabolism?

A

[1] Allosteric Regulation

[2] Hormonal Regulation

30
Q

In the fed state, what happens to synthesis and degradation levels?

A
  • increase synthesis

- decrease in degradation

31
Q

In the fasting state, what happens to synthesis and degradation levels?

A
  • decrease synthesis

- increase degradation

32
Q

What are some examples of allosteric regulation in glycogen metabolism?

A

[1] Glucose-6-Phosphate*

  • activates glycogen synthase
  • inhibits glycogen phosphorylase

[2] Ca2+
- that is released by muscle during contraction, acts indirectly to activate Glycogen Phosphorylase

[3] High AMP
- in the muscle as a result of anoxia and ATP depletion, activates Glycogen Phosphorylase

33
Q

How do hormones have a controlling effect on glycogen metabolism (general statement)? What mechanism do hormones use to control the activity of enzymes?

A

they act by controlling the activity of the enzymes

Mechanism: Reversible Phosphorylation/Dephosphorylation

  • Protein Kinases = Phosphorylation
  • Phosphatases = Dephosphorylation

Hormones (such as glucagon, insulin + adrenaline) act through this mechanism

34
Q

How does phosphorylation and dephosphorylation affect both glycogen synthase and glycogen phosphorylase?

A

GLYCOGEN SYNTHASE:

  • phosphorylated: less active
  • dephosphorylated: active

GLYCOGEN PHOSPHORYLASE:

  • phosphorylated: active
  • dephosphorylated: less active
35
Q

How does glucagon and adrenaline affect glycogen metabolism?

A
  • they activate cAMP-dependent Protein Kinase A promoting phosphorylation
  • net effect: glycogen breakdown
  • glycogen synthase decreased
  • glycogen phosphorylase increased
36
Q

How does insulin affect glycogen metabolism?

A
  • activates another protein kinase that causes dephosphorylation
  • net effect: glycogen synthesis
  • glycogen synthase increased
  • glycogen phosphorylase decreased
37
Q

Overall, in the FED state, insulin promotes…[2]

A

[1] glycogen synthesis

[2] triglyceride synthesis

38
Q

Overall, in the FASTING state, glucagon and adrenaline promotes…[2]

A

[1] Glycogenolysis

[2] Lipolysis

39
Q

What type of control is Adipose Tissue Lipase controlled by?

A
  • it is hormone-sensitive
  • controlled by phosphorylation and dephosphorylation
  • it is ACTIVE, when PHOSPHORYLATED by PKA (lipolysis)
40
Q

What are Glycogen Storage Disorder (GSDs)? What are they caused by?

A
  • they are due to abnormal synthesis or degradation of glycogen
  • due to a defect in the genes coding for enzymes involved in glycogen metabolism
41
Q

What do GSD’s mainly affect? [2]

A

[1] liver
[2] muscle

  • disease presentation + severity depend on the role played by the enzyme and its tissue specificity
42
Q

What are the signs of Glycogen Storage Disorders (GSDs)?

A
  • hypoglycaemia
  • muscle pain
  • muscle cramps
  • weakness
43
Q

What is another name for GSD V?

A

McArdle Disease

44
Q

What is another name for McArdle Disease?

A

GSD V

45
Q

What is another name for GSD I?

A

Von Gierke’s Disease

46
Q

What is another name for Von Gierke’s Disease?

A

GSD I

47
Q

What is the cause of GSD V and what happens?

A
  • muscle glycogen phosphorylase deficiency
  • muscle fatigue
  • myoglobinuria
48
Q

What is the cause of GSD I and what happens?

A
  • glucose-6-phosphatase deficiency
  • hypoglycaemia
  • lactic acidosis (accumulation of glycolysis intermediates, phosphorylated glucose cannot leave the cell and is converted to lactate)
  • ketosis
  • hepatomegaly (accumulation of glycogen and fat)
49
Q

What is the most common glycogen storage disorder? (accounts for 25% of all GSD cases)

A

GSD I (Von Gierke’s Disease)

Gastrointestinal Biology (15 decks)

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