Topic 5: Glycolysis

Question 1

What is the major source of carbs?

Answer 1

Sun –> Plants make carbs with light + CO2 + H2O

Question 2

How is glycogen organized?

Answer 2

alpha-1,4 linkages with alpha-1,6 branches roughly every 10 residues

Question 3

What is “normal” glucose levels in non-ruminants?

Answer 3

70-120 mg/dl or 4.16-6.66 mM

Question 4

What is normal glucose for Bovines and other ruminants?

Answer 4

40-75mg/dl AND they don’t normally have a glucose spike after a meal since microbes get it all

Question 5

What is more condensed? Starch or glycogen?

Answer 5

Glycogen. They branch roughly every 10 residues whereas Starch branches every 30 residues.

Question 6

How is starch organized?

Answer 6

alpha-1,4 linkages with alpha-1,6 branches roughly every 30 residues

Question 7

What is the advantage of storing in polymeric forms such as starch and glycogen?

Answer 7

Reduces OSMOTIC pressure. Remember osmotic pressure depends on number of molecules not size.

Question 8

What glucose transporters are insulin sensitive and what tissues are they in?

Answer 8

GLUT-4 and they are in: Skeletal Muscle, Heart, and Fat Cells

Question 9

Which tissues have GLUT 2?

Answer 9

Liver and Pancreas and they have a SHITLOAD. Liver is considered freely permeable to glucose. These are always present an essential for normal metabolism.

have a High Km for Glucose

Question 10

Which tissues have GLUT 1 and 3 and why is it significant?

Answer 10

Brain (GLUT 1 and 3), Placenta (GLUT 1 and 3), RBCs (GLUT 1), Colon (GLUT 1)

They have a lower Km for glucose than the other GLUTs which means they will MUCH MORE readily take up glucose.

Question 11

What is the definition of Km?

Answer 11

The concentration of solute at which an enzyme will be 50% saturated. A lower Km means the enzyme will take up more solute at lower concentrations.

Question 12

Which tissues have GLUT 5?

Answer 12

GLUT 5 is a fructose transporter so you see it in the small intestines and testis but also less extensively in skeletal muscle, kidney, adipose and the brain.

Question 13

Where do you see SGLTs and what are they?

Answer 13

Glucose/Na+ Symports

Seen in the gut and kidney.

Question 14

What is the difference between hexokinase and glucokinase with respect to Km for glucose and tissue location?

Answer 14

Hexokinase has a lower Km and is EVERYWHERE.

Glucokinase has a higher Km and is in the Liver, Pancreas, Brain and Gut. It is activated in higher concentrations of glucose

Question 15

What happens in Step 1 of Glycolysis?

Answer 15

Glucose is phosphorylated via hexokinase or glucokinase (tissue and [Glucose] dependent) to Glucose-6-phosphate

ATP is used here.

Question 16

What happens in Step 2 of Glycolysis?

Answer 16

Glucose-6-phosphate via phosphoglucose isomerase is slightly rearranged to Fructose-6-phosphate

Question 17

What happens in Step 3 of Glycolysis?

Answer 17

Fructose-6-phosphate is phosphorylated by Phosphofructokinase (PFK) to become Fructose-1,6-bisphosphate

ATP is used here.

Question 18

What happens in Step 4 of Glycolysis?

Answer 18

F-1,6-P via Aldolase split up into 2 units: Dihydroxyacetone (DHAP) and Glyceraldehyde-3-Phosphate (GA3P)

The two can be converted interchangeably by triose phosphate isomerase. (triose for 3 C sugars involved, phosphate for each having a single phosphate, isomerase since they are isomers)

Question 19

What happens in Step 5 of Glycolysis?

Answer 19

GA3P via GA3P-Dehydrogenase is phosphorylated into 1,3-bisphophoglycerate

NADH and a free H+ are generated here.

Question 20

What happens in Step 6 of Glycolysis?

Answer 20

1,3-BPG loses a phosphate to ATP via phosphoglycerate kinase to become 3-Phosphoglycerate.

ATP is generated here.

Question 21

What happens in Step 7 of Glycolysis?

Answer 21

The phosphate on 3-Phosphoglycerate is rearranged via phosphoglyeromutase to become 2-phosphoglycerate.

Question 22

What happens in Step 8 of Glycolysis?

Answer 22

2-Phosphoglycerate has an H2O removed by ENOLASE to become Phosphoenolpyruvate (PEP).

H2O is yielded here.

Question 23

What happens in Step 9 of Glycolysis?

Answer 23

PEP via Pyruvate Kinase loses a phosphate to ATP to become pyruvate.

ATP is generated here.

This step is TOTALLY IRREVERSIBLE and considered the rate limiting step.

Question 24

What is the significance of the action of hexokinase and glucokinase?

Answer 24

Glucose Trapping! Once glucose is phosphorylated by one of these enzymes it cannot get out of the cell.

Hexokinase is constitutive while Glucokinase has a much higher Km.

Glucokinase is also induced by insulin –> Double Trap!
Insulin isn’t released until high [glucose] is detected at the same time high [glucose] triggers its activation.

Question 25

Compare and Contrast Hexokinase and Glucokinase

Answer 25

Hexokinase: Low Km for glucose; in EVERY tissue; unaffected by insulin; feedback inhibition by its product, Glucose-6-Phosphate

Glucokinase: High Km for glucose; only in Liver, Pancreas, Brain and Gut; NO feedback inhibition; induced by insulin!

Question 26

Why is HYPERGLYCEMIA bad?

Answer 26

Glucose is an ALDEHYDE SUGAR – VERY Reactive

In the CNS, because they are highly reactive, they tend to form crosslinks –> they Bind and will spontaneously add themselves to molecules especially PROTEINS

Glycosylated Proteins at a rate faster than can be corrected. Changing their structure changes their function. Extremeties take the biggest hit, FEET most common and Fingers.

Glycosylated axons will no longer carry depolarizations ==> NEUROPATHY

Kidneys will also take a hit -> Kidney failure in diabetics. Mess up endothelium of capillary surfaces.

Reduced circulation and innervation can lead to no sensation of gangrene onset

Question 27

Why is hypoglycemia bad?

Answer 27

Glucose is fuel for the body. Everyone needs it. Not enough = you’re fucked. Have a nice day!