carbohydrate metabolism Flashcards
too high blood glucose
release of water from tissues due to osmotic pressure
dehydration and death
too low blood glucose
lack of fuel to produce ATP
brain/CNS depend on glucose
red blood cells low on ATP unable to provide oxygen to tissues
what regulates blood glucose
insulin
glucagon
adrenaline
ratio of blood homrones
more glucagon, less insulin
- release of glucose when blood glucose levels fall
vise versa
uptake of glucose, stored as glycogen
sourcseof glucose
diet
glycogen degredation
gluconeoensis
fatty acid oxidation provides energy
breakdown of dietary carbs
Breakdown with saliva, a amylase in the saliva/mouth
- breaks down amylose and other components of carbohydrates into a- dextrins
- further broken down by a amylase from the pancreas into oligo/tri saccharides, disaccharides (maltose), isomaltose
- These can be taken up upon the brush border of the small intestine/gut
Maltase and isomaltase can help breakdown maltose in the gut
Sucrase and lactase can break down substituents to allow absorption of the monomers (sucrose)
carbs in form of fibre
fibre fermented in gut
gut can absorb as short chain fatty acids
sources of glucose during fasting
glucose stores
no dietary carbs being absroed
where are glycogen stores
liver
muscles
structure of glycogen
branche chains glucose
1-4 alpha glycosidic linkages
branching via the linkages
carbon joined to glycogenin
function of glycogen
sore of carb
source of glucose for aTP
synthesis of glycogen
- requires energy in form of UTP
- starts of as glucose 1 phosphate combines with UTP
- forms UDP glucose
- glucose is transferred from UDP glucose to the priming protein glycogenein
- glycogen synthase transfers glucose from UDP glucose to growing chain
- this forms a1-4 linkages
- when the 11 residues (glucose molecules) is reached, 6-8 are cleaved off and rejoined by a1-6 linkaged by branching enzyme
which enzymes are involeved in glycogen degredation
glycogen phosphoryalse
debranchig enzyem
debranching enzyme
acts as transferase removes glucose near branch point
cleaves at branch point
glycogen phsophorylase
removes glucose at ends of chains
types of deb ranching enzymes
4,4 transferase and a1-6 glucosidase
regulation of metabolism in each part
In liver
- glycogen regulates blood glucose levels
- supply glucose to other tissues
in muscle
- responds to changes in energy (ATP) needs
- useful as muscles are high energy, don’t need to wait for energy to be supplied
regulation of metabolism in the liver
- Regulated by hormones involved in blood glucose homeostasis, responds to changes in environment to release glucose
hormones involved in regulation of liver metabolism
insulin
glycagon
adrenaline
regulation of metabolism in muslce
simple feedback-
glycogen supplies glucose for ATP generation
- Low ATP (=high AMP) stimulates glycogen degradation,
- Calcium (indicates muscle fibre activity) and adrenaline also stimulate glycogen degradation
disorders of metablism
caused by mutations of enzymes
may only affect liver or muscle enzymes therefore differing severity
gluconeogensis
1) fed state taken up into tissues
2) then break down the glycogen
3) gluconeogenesis then slowly increases, to provide energy
produces glucose from non carb sources
which pathway will dominate if there is lots of glucose
glycolysis will dominate
what regulation is involved in the glycolysis pathway
allosteric regualtion
what is fructose 6 phosphate converted into and what enzyme
fructose 1 6 bisphosphate
- phosphofructose kinase
regulation of the cnversio of fructose 6 phosphate into fructose 1-6 bisphospahse
- when there is a lot of fructose 6 phosphate there is another enzyme which can generate a different product to speed up the pathway
fructose 2,6 bisphosphate increases PFK 1 action (glycolysis) and also switches off the F1, 6BP which goes the opposite way (i.e. inhibiting gluconeogenesis)
-forces reaction in the glycolysis pathway
steps undergo if blood glucose drops
1) drop in blood glucose (decrease in insulin and increase in glucagon), tells the body to increase blood glucose level
2) this stimulates the liver to breakdown some glycogen to generate glucose (see glycogen degredation)
3) glucose is released into the blood to reach the tissues requiring it eg brain, RBC
4) RBC can undergo anaerobic respiration producing lactate, which can go back to the liver
steps to form energy from fat
2) adipose tossue releases fatty acids in form of lipids
3) Glyerol is also released to the liver to be used as a substrate to form glucose for gluconeogenesis
4) lactate is also substrate for gluconeogenesis (RBC)
5) fatty acids can be burnt in the muscle and liver to generate ATP
6) if starvation is occurring, blood glucose has been low for a while
7) muscle can start to breakdown protein, can be used as a substrate for gluconeogenesis (amino acid) generateing glucose
8) urea is erected through kidney
ketone bodies are produced from
acetyl Co A in liver
only produced when gluconeogensis is taking place
- can be converted back into acetyl co A to enter TCA cycle for ATP
what occurs during fasting
ketone bodies produced by liver
fuel for Brian and muscl
excess can lead to ketosis
ketosis signs
acetone smell on breath
