Carbohydrates (Lecture 2) Flashcards
why is the whole system not at equilibrium if most metabolic reactions are?
first step is a committed step
open system that has waste along the way and the products are consumed
starch
polymer of glucose bound by alpha bonds (1,6)
glycogen
polymer of glucose bound by alpha bonds with increased branching relative to starch
cellulose
polymer of glucose bound by (1,4) beta bonds
sucrose
glucose + fructose
lactose
glucose + galactose
what are the 2 methods of glucose uptake in intestine absorption to the blood? (explain)
active transport: taking glucose against its concentration gradient, thus rewiring an input of energy
i.e. in the intestinal villi, the Na+/glucose symporter acts as a secondary active transporter, since its combined with the Na+/K+ ATPase anti porter
passive transport: taking glucose down its concentration gradient
i.e. glucose uniport in the bush border cell will pass glucose forms he cytosol into the capillaries, since [glucose in the blood] < [glucose in cell]
which cells uptake glucose in the pancreas?
pancreatic beta cells
when is insulin released into the blood?
when [glucose]> 5.5 mM
what occurs between meals in the pancreatic beta cell?
this is a basal blood glucose circumstance, thus [glucose] < 5.5 mM
glucose will be imported into the beta cell via the Glut2 transporter
this will allow for the generation of pyruvate via glycolysis, which in turn will feed into the OxPhos cycle and generate some ATP
low levels of ATP allow K+ to be pumped out of the cell via a K-ATP channel, thus resulting in hyperpolarization
what occurs in the beta cell after a meal?
this is under stimulatory blood glucose conditions , where [glucose] > 5.5 mM
the increased amount of glucose will enter the Glut2 transporter and increase the rate of glycolysis, and OxPhos, thus generating a large yield of ATP
increased amounts of ATP will inhibits the K-ATP channel, thus resulting in membrane depolarization
this will activate a calcium influx and stimulate the vesicular release of insulin to decrease the blood glucose
how is glucose taken up by adipose tissue?
Glut4 receptors will be recruited to the cell to uptake glucose, which will be used to form lipids via lipogenesis
how is glucose taken top by the muscle?
Glut4 will uptake glucose and transform glucose into glycogen, which is used as an energy source for muscle contraction.
how is glucose taken up by the liver?
Glut2 transporters will uptake glucose to promote glycogen synthesis and lipogenesis (for storage purposes).
upon treatment with insulin…
Glut4 is recruited to the plasma membrane
why are there so man y glucose transporters?
transport tailored to the need of the tissue
tissues often express more than one glucose transporter, and these levels re controlled by their expression
sugar specificity
where is glucose managed?
liver
what is the order of energy expenditure during exercise?
- ATP
- creatine-phosphate
- anaerobic glycolysis
- aerobic glycolysis
- aerobic lipolysis
how is creatine-phosphate used for energy?
P-creatine + ADP –> creatine +ATP
what does oxidative phosphorylation generate ?
ATP out of NADH, FADH2 and O2
these substrates provide electrons to the ETC which provides energy to pump H+ across the inner mitochondrial membrane and create a proton gradient to activate the ATPase for energy production
what does the citric acid cycle generate ?
produces NADH and FADH2 (and CO2) out of Acetyl-CoA
what does glycolysis generate ?
generates 2 ATPs, 2 NADH, 2 pyruvate out of 1 glucose
no oxygen required
how is glycolysis negatively regulated?
increased ATP and decreased NAD+
how is glycolysis positively regulated?
decreased ATP
how is the CAC negatively regulated?
increased NADH
how is OxPhos negatively regulated?
high ATP, low O2, low NADH/FADH2
how is OxPhos positively regulated?
low ATP
tumour cells use which method to obtain energy?
mainly use (aerobic) glycolysis as a source of ATP
seeing that glycolysis is less efficient that Ox Phos, cancer cels must use a lot of glucose to compensate
what are the 3 potential pathways of pyruvate?
- int he presence of O2, pyruvate will enter CAC to generate NADH (excess NADH will replenish the NAD+ pool)
- without O2 homolactic fermentation may occur, where NADH is converted to NAD+ in order to generate lactate
- without O2, NADH is converted into NAD+ to generate CO2 and ethanol
