Carbohydrate metabolism Flashcards

1
Q

types of carbohydrates: Monosaccharides:

A

Glucose
Fructose
Galactose

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2
Q

types of carbohydrates: Disaccharides (2 monosaccharides joined together):

A

Sucrose (Glucose+Fructose)
Maltose (Glucose+Glucose)
Lactose (Glucose+Galactose)
Isomaltose (Glucose+Fructose)

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3
Q

types of carbohydrates: Oligosaccharides (a carbohydrate whose molecules are composed of a relatively small number of monosaccharide units.) and Polysaccharides

A

Oligosaccharides:
Maltodextrin

Polysaccharides:
Amylose
Amylopectin

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4
Q

Glucose homeostasis: hypo and hyperglycaemia?

A

Blood glucose level:
Normal: ~4-5 mM
HYPOglycaemia: < 3.9 mM
Shakiness, palpitations, increased heart rate, sweating, coldness, clamminess

< 3.6 mM: reduced mental efficiency
< 2.2 mM: impaired action and judgment / seizures
< 0.6 mM: brain cells stop working / coma

Hyperglycaemia: > 7 mM
frequent urination, excessive thirst, frequent hunger

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5
Q

what are the sources of Glucose in humans?

A

So, where does the glucose come from?

Glycogen in Skeletal Muscle
Directly available

Blood Glucose
Directly from food (absorbed from intestine)
Liver Glycogen
Liver Gluconeogenesis (glucose produced from lactate / glycerol / amino acids)

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6
Q

to produce Glycogen from Glucose?

A

Glucose—>Glucose-6-P (hexokinase) —->Glucose-1-P (Phosphoglucomutase)—>Glycogen (Glycogen synthase)

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7
Q

to produce Glucose from Glycogen?

A

Glycogen—>Glucose-1-P (Glycogen phosphorylase) —>Glucose-6-P (Phosphoglucomutase)

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8
Q

Glucose Homeostasis: energy stores and utilisation?

A

Fat is the preferred form of energy for storage AND oxidation

~10-25% of body weight

~66% of energy supply at rest

Glucose is needed by the brain and during exercise

~100 g in liver and ~500 g in muscle

100% of energy supply to brain, and main source of energy during intense exercise

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9
Q

Hormones and glucose homeostasis: blood levels?

A

Blood insulin levels:

increase when blood glucose levels increase

stimulate tissue uptake of glucose

Blood glucagon levels:

increase when blood glucose levels decrease

stimulate release of glucose from the liver

Blood adrenaline levels:

increase before and during exercise

stimulate release of glucose from the liver

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10
Q

Glucose homeostasis is under hormonal control: insulin and glucagon: if glucose is low (fasted)?

A

Insulin (and glucagon) levels vary throughout the day to:

Regulate the breakdown / storage of carbohydrates (and fats)

Keep blood glucose levels within a tight range (4-7 mmol/L)

Low insulin levels / high glucagon levels

Fat is broken down to provide the main fuel as hormone sensitive lipase is active / not inhibited.

Some liver glycogen is broken down and glucose produced (gluconeogenesis) to keep blood glucose stable

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11
Q

Glucose homeostasis is under hormonal control: insulin and glucagon: if glucose is high (fed)?

A

High insulin levels / low glucagon levels

Breakdown of fat is inhibited as hormone sensitive lipase is inhibited

Glycogen is stored in muscle AND liver as glycogen synthase is activated

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12
Q

The pancreas and its role in hormone control?

A

Islets of Langerhans:
α-cells: glucagon
β-cells: insulin

Insulin:
stimulates storage of energy

Glucagon:
stimulates release of glucose from the liver

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13
Q

Effects of insulin: Stimulation of:

A

Glucose uptake: muscle and adipose

Glycogenesis: liver and muscles

Lipogenesis: liver and adipose

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14
Q

Effects of insulin: inhibition of:

A

Protein degradation: liver, muscle and adipose

Lipolysis: liver and adipose

Glycogenolysis: Liver and muscle

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15
Q

Effects of insulin on key enzymes?

A

Insulin promotes energy storage / anabolism!

Inhibits glycogen breakdown
by inhibiting glycogen phosphorylase

Stimulates glycogen storage
by stimulating glycogen synthase

Inhibits fat breakdown
by inhibiting hormone sensitive lipase

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16
Q

what is skeletal muscle responsible in relation to insulin and glucose uptake?

A

Skeletal muscle is responsible for the majority (~80%) of insulin-stimulated glucose uptake following a high carbohydrate meal

17
Q

Skeletal Muscle glucose uptake?

A

Glucose cannot cross the muscle cell membrane!

Transport proteins are required

The main muscle glucose transporter (GLUT):
GLUT4

GLUT4 is stored in the cell
But needs to be attached to the cell-membrane to work!

Insulin tells the muscle to transport GLUT4 to the cell-membrane

Exercise has the same effect (does not need insulin)!

18
Q

Glycolysis: what is its function?

A

Function:

take one 6-carbon sugar (glucose)
split it into two 3-carbon sugars
rearrange the atoms (to pyruvate)

Some energy is released in the process

Pyruvate can be converted into:
acetyl-CoA!
lactate

19
Q

what is the process of Glycolysis?

A

GLUCOSE—>Glucose-6-P—>Fructose-6-P—>Fructose-1,6-bis-P—> (broken into 2 sections of) Glyceraldehyde-3-P—>1,3-bis-P-Glycerate—>3-P-Glycerate—>2-P-Glycerate—>P-Enolpyruvate—>PYRUVATE

20
Q

what are the two (possible) Fates of Pyruvate? Acetyl-CoA

A

Pyruvate to Acetyl-CoA is the preferred pathway!

Full oxidation of glucose:
18 times more ATP than conversion into lactate!

To lactate: 2 ATP
To acetyl CoA: ~36 ATP

No accumulation of products that are associated with fatigue!

BUT – during high-intensity exercise the rate of oxidative metabolism cannot keep up with ATP demand!

21
Q

what are the two (possible) Fates of Pyruvate?: Lactate

A

Converting lactate to pyruvate is important for two reasons:
Remove negative feedback from accumulated pyruvate

Resynthesise NAD+ concentrations which are required for glycolysis!

Converting pyruvate to lactate is important for two reasons:

Remove negative feedback from accumulated pyruvate

Resynthesise NAD+ concentrations which are required for glycolysis!

This reaction allows glycolysis to keep going and producing a small amount of ATP when oxygen availability is ‘insufficient’.