Carbohydrate metabolism Flashcards
types of carbohydrates: Monosaccharides:
Glucose
Fructose
Galactose
types of carbohydrates: Disaccharides (2 monosaccharides joined together):
Sucrose (Glucose+Fructose)
Maltose (Glucose+Glucose)
Lactose (Glucose+Galactose)
Isomaltose (Glucose+Fructose)
types of carbohydrates: Oligosaccharides (a carbohydrate whose molecules are composed of a relatively small number of monosaccharide units.) and Polysaccharides
Oligosaccharides:
Maltodextrin
Polysaccharides:
Amylose
Amylopectin
Glucose homeostasis: hypo and hyperglycaemia?
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
what are the sources of Glucose in humans?
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)
to produce Glycogen from Glucose?
Glucose—>Glucose-6-P (hexokinase) —->Glucose-1-P (Phosphoglucomutase)—>Glycogen (Glycogen synthase)
to produce Glucose from Glycogen?
Glycogen—>Glucose-1-P (Glycogen phosphorylase) —>Glucose-6-P (Phosphoglucomutase)
Glucose Homeostasis: energy stores and utilisation?
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
Hormones and glucose homeostasis: blood levels?
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
Glucose homeostasis is under hormonal control: insulin and glucagon: if glucose is low (fasted)?
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
Glucose homeostasis is under hormonal control: insulin and glucagon: if glucose is high (fed)?
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
The pancreas and its role in hormone control?
Islets of Langerhans:
α-cells: glucagon
β-cells: insulin
Insulin:
stimulates storage of energy
Glucagon:
stimulates release of glucose from the liver
Effects of insulin: Stimulation of:
Glucose uptake: muscle and adipose
Glycogenesis: liver and muscles
Lipogenesis: liver and adipose
Effects of insulin: inhibition of:
Protein degradation: liver, muscle and adipose
Lipolysis: liver and adipose
Glycogenolysis: Liver and muscle
Effects of insulin on key enzymes?
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
what is skeletal muscle responsible in relation to insulin and glucose uptake?
Skeletal muscle is responsible for the majority (~80%) of insulin-stimulated glucose uptake following a high carbohydrate meal
Skeletal Muscle glucose uptake?
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)!
Glycolysis: what is its function?
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
what is the process of Glycolysis?
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
what are the two (possible) Fates of Pyruvate? Acetyl-CoA
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!
what are the two (possible) Fates of Pyruvate?: Lactate
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’.
