carbohydrate metabolism Flashcards
Why is the regulation of blood glucose important?
Too high- release of water from tissues into blood due to osmotic pressure =dehydration, death
Too low- lack of fuel to make ATP, brain depends on glucose as fuel =coma
-RBCs low on ATP so can’t provide oxygen to tissues =death
How is blood glucose regulated?
Ratio of hormones Fight or flight overrides system Insulin- takes glucose out of blood and into tissues Glucagon- releases fuels from tissues Others (adrenaline)
What are the three main sources of glucose?
Diet
Glycogen degradation
Gluconeogenesis
Fatty acid oxidation provides energy but not glucose
How are carbs digested?
Broken down by salivary alpha amylase into polysaccharides, oligosaccharides, alpha dextrins etc
Broken down further by pancreatic amylase into disaccharides (maltose, isomaltose etc)
Enzymes in the brush border of enterocytes break down into monosaccharides (glucose, fructose etc)
Transport proteins take into cells
Bacteria in large intestine ferment fibre to generate short chain fatty acids (butyrate, propionate etc)
What is glycogen?
Storage in liver and muscle
Muscle- source of glucose for ATP generation for itself + lactate
Liver- source of ATP but mainly used to supply other tissues via blood
Branched chains of glucose joined by alpha 1-4 linkages w branching of alpha 1-6 linkages
One carbon is joined to glycogenin (protein)
How is glycogen synthesised?
Phosphorylated glucose + UTP is used to generate uridine diphosphate glucose (UDP)
This is transferred to glycogenin
Glycogen synthase adds glucose to the growing chain forming alpha 1-4 linkages
When 11 residues are reached, a branching enzyme cleaves off 6-8 and rejoins it w alpha 1-6 linkages
How is glycogen degraded?
Glycogen phosphorylase- removes glucose from ends of chains Debranching enzyme (transferase etc)- removes glucose near branch point and cleaves branch point
How is glycogen regulated in the liver and muscle?
Liver- hormones regulate blood glucose levels (less insulin, more glucagon and adrenaline=more degradation)
Muscle- responds to changes in ATP needs (low ATP, more calcium and adrenaline=more degradation)
What are some disorder of metabolism that affect glycogen?
Mutations in enzymes (some specific to liver/muscle)
Differing severity
What happens when glycogen levels are low in the stores?
Gluconeogenesis
~produces glucose from non-carb sources (amino acids [alanine] and lactate from muscle, glycerol from adipose, propionate from fermentation)
~in liver usually unless extreme starvation
~regulated by substrate availability and activity of key enzymes
How is gluconeogenesis regulated by enzymes?
3 key regulatory steps (allosteric and gene expression) ~pyruvate—>phosphoenolpyruvate ~fructose 1,6-bisphosphate—>fructose 6-phosphate ~glucose 6-phosphate—>glucose Enzymes- •glucose 6-phosphatase •fructose 1,6-bisphosphatase •phosphoenolpyruvate carboxykinase •pyruvate carboxylase
What are ketone bodies?
Generated from acetyl coA from fatty acid in liver for gluconeogenesis
Can be converted back into acetyl coA in muscle and brain
Excess production= ketosis= pear drop breath
