Carbohydrate metabolism Flashcards
Roles of CHO in the body
Storage - liver/muscle
Glycated proteins - Glycosaminoglycans eg -
Hyaluronic acid - for skin
Keratan sulfate - cornea, cartilage, bone
Heparan sulfate - animal tissue
Chondroitin sulfate - blood vessels, heart valves, tendons
Glucose uptake definition
Glucose being taken from the blood into tissue
Glycogen synthesis definition
Making glycogen from glucose (in muscle/liver)
Glycogen breakdown definition
Liver/muscle allows glucose to be used (liver glycogen is moveable muscle isn’t)
Glycolysis definition
breaking down of glucose
Gluconeogenesis definition
making glucose from carbon sources (liver)
Fructose metabolism key points
Happens in the liver - used to make liver glycogen, glucose, lactate & TG synthesis (bad if not active leads to lipid accumulation & insulin resistance)
Taken up in other cells by GLUT 5
How is CHO removed from blood (hormonal)
Pancreas secretes insulin into blood during eating and as glucose enters blood
Insulin increases glucose uptake & promote glycogen storage
Glucose in blood removal
Taken up by liver cells (facilitated transport down conc grad) through GLUT 2
Insulin receptor detects insulin in blood - increases Glucokinase so glycogen is produced (glucose conc grad maintained)
Glucose returning to blood
Enzyme is present to remove phosphate group and release glucose back into blood stream (Glucose -6- phosphatase)
Importance of glucose to the brain
Glucose provides energy for turnover and neurotransmitter synthesis
brain 2% body weight uses 20% of total glucose
How does glucose get into the brain
Glucose cross blood brain barrier through GLUT 1 then into a neuron through GLUT 3 or Astrocyte (support cell) via GLUT 1 then into the TCA cycle
What happens if there is too much pyruvate in the brain cells
it is converted into lactate in the neuron and transported through the extracellular fluid to the astrocyte which prevents new glucose being oxidised instead it is turned into glycogen and stored
Positron emission tomography shows? (where is gluicose)
Glucose mainly present in brain, heart, bladder
How does glucose get into skeletal muscle
Facilitated transport via GLUT 4
Insulin receptor stimulate hexokinase creating glucose 6 P (conc grad maintained)
Glucose cant leave once phosphate is attached - stored or oxidised
Liver is better at storage but much more is held in muscle due to mass
What is the role of insulin in the skeletal muscle
Can increase amount of GLUT 4 on the membrane (via intracellular signalling - reaction to insulin detection) = more glucose in
How does exercise increase the glucose in muscle cells
Contractions release calcium which translocate GLUT 4 to the membrane increasing glucose uptake
Process is independent of insulin
Glycogen synthesis
Glucose -> glucose 6 phosphate -> glucose 1 phosphate -> UPD glucose -> glycogen
How is glycogen constructed
UPD glucose attaches to glycogenin core
8-10 units attached = pro glycogen
Glycogen synthase (insulin regulated) takes over = macro glycogen
Branching enzyme = branched structure (1-6 bonds (1-4 straight))
Glycogen synthase regulation
GS normal is inactive (P group attached blocking catalytic site)
Insulin activates protein phosphates removing the p group making GS active - glycogen is made
Adreneline/calcium (from exercise) stimulate protein kinase A = more inactive GS (adding P group)
Glycogen breakdown enzyme & regulation
Glycogen phosphorylase a (active w/ P group)
Glycogen phosphorylase b (inactive no P group)
regulated by glycogen phosphorylase kinase (GPK) it adds to the P group & Glycogen phosphorylase phosphatase (GPP)
Glycogen breakdown stimulatuion
Glucagon (from pancreas), Calcium & adrenaline (exercise) stimulates GPK to make active glycogen phosphorylase a
Insulin (during rest) stimulates GPP to remove the P group making glycogen phosphorylase b inactive
When is glycogen breakdown inhibited
When there is lots of ATP or G-6-P they both inhibit glycogen phosphorylase a
High AMP levels inhibit GPP
Key CHO processes during exercise
lots of glycolysis (stimulated by calcium/adrenaline)
Reduced insulin (less storage)
Glycogenolysis
Glucose uptake
