Carbohydrates (Lecture 2)

Question 1

why is the whole system not at equilibrium if most metabolic reactions are?

Answer 1

first step is a committed step

open system that has waste along the way and the products are consumed

Question 2

starch

Answer 2

polymer of glucose bound by alpha bonds (1,6)

Question 3

glycogen

Answer 3

polymer of glucose bound by alpha bonds with increased branching relative to starch

Question 4

cellulose

Answer 4

polymer of glucose bound by (1,4) beta bonds

Question 5

sucrose

Answer 5

glucose + fructose

Question 6

lactose

Answer 6

glucose + galactose

Question 7

what are the 2 methods of glucose uptake in intestine absorption to the blood? (explain)

Answer 7

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]

Question 8

which cells uptake glucose in the pancreas?

Answer 8

pancreatic beta cells

Question 9

when is insulin released into the blood?

Answer 9

when [glucose]> 5.5 mM

Question 10

what occurs between meals in the pancreatic beta cell?

Answer 10

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

Question 11

what occurs in the beta cell after a meal?

Answer 11

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

Question 12

how is glucose taken up by adipose tissue?

Answer 12

Glut4 receptors will be recruited to the cell to uptake glucose, which will be used to form lipids via lipogenesis

Question 13

how is glucose taken top by the muscle?

Answer 13

Glut4 will uptake glucose and transform glucose into glycogen, which is used as an energy source for muscle contraction.

Question 14

how is glucose taken up by the liver?

Answer 14

Glut2 transporters will uptake glucose to promote glycogen synthesis and lipogenesis (for storage purposes).

Question 15

upon treatment with insulin…

Answer 15

Glut4 is recruited to the plasma membrane

Question 16

why are there so man y glucose transporters?

Answer 16

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

Question 17

where is glucose managed?

Answer 17

liver

Question 18

what is the order of energy expenditure during exercise?

Answer 18

1. ATP
2. creatine-phosphate
3. anaerobic glycolysis
4. aerobic glycolysis
5. aerobic lipolysis

Question 19

how is creatine-phosphate used for energy?

Answer 19

P-creatine + ADP –> creatine +ATP

Question 20

what does oxidative phosphorylation generate ?

Answer 20

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

Question 21

what does the citric acid cycle generate ?

Answer 21

produces NADH and FADH2 (and CO2) out of Acetyl-CoA

Question 22

what does glycolysis generate ?

Answer 22

generates 2 ATPs, 2 NADH, 2 pyruvate out of 1 glucose

no oxygen required

Question 23

how is glycolysis negatively regulated?

Answer 23

increased ATP and decreased NAD+

Question 24

how is glycolysis positively regulated?

Answer 24

decreased ATP

Question 25

how is the CAC negatively regulated?

Answer 25

increased NADH

Question 26

how is OxPhos negatively regulated?

Answer 26

high ATP, low O2, low NADH/FADH2

Question 27

how is OxPhos positively regulated?

Answer 27

low ATP

Question 28

tumour cells use which method to obtain energy?

Answer 28

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

Question 29

what are the 3 potential pathways of pyruvate?

Answer 29

1. int he presence of O2, pyruvate will enter CAC to generate NADH (excess NADH will replenish the NAD+ pool)
2. without O2 homolactic fermentation may occur, where NADH is converted to NAD+ in order to generate lactate
3. without O2, NADH is converted into NAD+ to generate CO2 and ethanol