Lecture 20

Question 1

During glycolysis, 1 molecule of glucose is converted into what? what type of process is glycolysis?

Answer 1

2 molecules of pyruvate and 2 ATP molecules

Glycolysis can occur in anaerobic or aerobic ways

Question 2

Explain why aerobic conditions generate more ATP than anaerobic conditions

Answer 2

Under aerobic conditions, Pyruvate from glycolysis can become Acetyl Coa

Acetyl Coa can then enter the TCA cycle and creates more ATP via the ETC.

Question 3

What “fuel” is used by the brain under conditions of non-starvation? what other human cells exclusively use this “fuel”?

Answer 3

glucose

RBC’s ONLY use glucose

Question 4

Pyruvate and lactate can be salvaged and resynthesized into glucose via what process?

Answer 4

gluconeogenesis

this process is only used when our diet is not providing sufficient levels of glucose

Question 5

State 3 sources of glucose in the diet

Answer 5

1. disaccharides (especially sucrose and lactose)
2. Starch (this is a polysaccharide)
3. Glycogen (complex version of glucose ; basically lots of glucose molecules that are bound to one another)

Question 6

GLUT’s are protein transporters that uptake glucose by helping it cross the membrane of a cell. State the places in the body where the following type of GLUT can be found. Also include the affinity this GLUT exhibits and it’s Km value.

GLUT1:

Answer 6

GLUT1: ubiquitous (in all cell types) but HIGHLY expressed in the brain and RBC’s
High affinity
Km = 1 mM

(Low affinity = there needs to be a lot of glucose around for it to cross the membrane ; High affinity = there DOES NOT need to be a lot of glucose around for it to cross the membrane)

Question 7

GLUT’s are protein transporters that uptake glucose by helping it cross the membrane of a cell. State the places in the body where the following type of GLUT can be found. Also include the affinity this GLUT exhibits and it’s Km value.

GLUT2:

Answer 7

GLUT2: Main transporter in the Liver
Low affinity
Km = 10 mM

(Low affinity = there needs to be a lot of glucose around for it to cross the membrane ; High affinity = there DOES NOT need to be a lot of glucose around for it to cross the membrane)

Question 8

GLUT’s are protein transporters that uptake glucose by helping it cross the membrane of a cell. State the places in the body where the following type of GLUT can be found. Also include the affinity this GLUT exhibits and it’s Km value.

GLUT3:

Answer 8

GLUT3: Main transporter in Neurons
High affinity
Km = 1 mM

(Low affinity = there needs to be a lot of glucose around for it to cross the membrane ; High affinity = there DOES NOT need to be a lot of glucose around for it to cross the membrane)

Question 9

GLUT’s are protein transporters that uptake glucose by helping it cross the membrane of a cell. State the places in the body where the following type of GLUT can be found. Also include the affinity this GLUT exhibits and it’s Km value.

GLUT4:

Answer 9

GLUT4: Present in skeletal muscle, heart, and adipose tissue
It’s affinity is Insulin-dependent
KM = 5 mM

(Low affinity = there needs to be a lot of glucose around for it to cross the membrane ; High affinity = there DOES NOT need to be a lot of glucose around for it to cross the membrane)

Question 10

State the 2 stages of glycolysis. What structures in the glycolysis pathway separate these 2 stages?

Answer 10

1. Trapping of glucose and it’s cleavage into 2 interconvertible 3-carbon molecules
2. Generation of ATP

Glyceraldehyde-3-phosphate (and Dihydroxyacetone phosphate) is at the end of stage 1

1,3-Bisphosphoglycerate represents the beginning of stage 2

Question 11

State, in order, the enzymes that are involved in stage 1 of glycolysis (ID the rate limiting step as well)

Answer 11

1. Hexokinase and Glucokinase
2. Phosphoglucoisomerase
3. Phosphofructokinase (rate limiting step)
4. Aldolase
5. Triose phosphate isomerase

Question 12

State, in order, the enzymes that are involved in stage 2 of glycolysis

Answer 12

1. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH)
2. Phosphoglycerate kinase
3. Phosphoglycerate mutase
4. Enolase
5. Pyruvate Kinase

Question 13

Sucrose is a disaccharide of glucose and _____. Lactose is a disaccharide of glucose and _____. What is the relationship between these 2 blanks?

Answer 13

Fructose (intermediate = Glucose-6-phosphate)

Galactose (intermediate = Fructose-6-phosphate)

Fructose and galactose are converted into glycolytic intermediates (so that they can be processed by the body)

Question 14

Describe the fructose metabolism pathway (including enzymes)

Answer 14

Fructose (via fructokinase and ATP consumption) becomes Fructose-1-phosphate

Fructose-1-phosphate (via Fructose-1-phosphate aldolase) becomes Glyceraldehyde AND Dihydroxyacetone phosphate

Glyceraldehyde (via Triose kinase and ATP consumption) becomes Glyceraldehyde-3-phosphate

Question 15

Describe the galactose metabolism (including enzymes)

Answer 15

Galactose (via Galactokinase) becomes Galactose-1-phosphate

Galactose-1-phosphate and UDP-glucose (via Galactose-1-phosphate uridyl transferase) interact and transfer a phosphate in order to glucose-1-phosphate

Glucose-1-phosphate (via phosphoglucomutase) becomes glucose-6-phosphate

Question 16

State the 3 major regulatory enzymes of glycolysis and include where they can be found in the pathway.

Answer 16

Hexokinase: creates glucose-6-phosphate from Glucose

Phosphofructokinase (rate limiting step): Creates Fructose-1,6-bisphosphate from fructose-6-phosphate

Pyruvate kinase: creates pyruvate from phosphoenolpyruvate

Question 17

Compare the regulation of glycolysis in muscle and in the liver (state the goal, what regulates glycolysis in the tissue, and which enzyme initiates it)

Answer 17

Muscle: generates ATP during activity
ATP levels regulate glycolysis (levels directly affect Phosphofructokinase enzyme)
Hexokinase is the enzyme (inhibited by glucose-6-phosphate)

Liver: Maintains blood glucose levels
Phosphofructokinase is ACTIVATED by F-2,6-BP and INHIBITED by citrate
Glucokinase is the enzyme (glucose permanently trapped)

Question 18

Explain why excessive fructose (High fructose corn syrup) can lead to pathologies

Answer 18

The actions of fructokinase and triose kinase (the 2 main enzymes in fructose metabolism) bypass the “rate limiting step of glycolysis” (the phosphofructokinase-catalyzed reaction)

This leads to excess Acetyl CoA that is stored in adipose tissue (as triglycerols) and leads to obesity and fatty organs

Question 19

A defect in what enzyme causes lactose intolerance?

Answer 19

lactase (which breaks lactose down into glucose and galactose)

Question 20

____ ______ is caused by a deficiency in galactose-1-phosphate uridyl transferase activity. Describe how this condition presents itself physically and in diagnostic tests

Answer 20

classic galactosemia

Afflicted infants fail to thrive (vomiting/diarrhea after drinking milk, liver enlargement, cataracts, retarded mental development, etc)

Diagnostic tests will show an absence of transferase in RBC’s

Question 21

Explain how the presence of aldose reductase in the eye can cause cataracts to form in a pt with galactosemia that is consuming galactose.

Answer 21

If the transferase in the eye is not active, as it will be in a pt with galactosemia, the presence of aldose reductase will convert accumulating galactose to galactitol (forms cataract)

Question 22

Describe the Warburg Effect and what it has to do with Tumor formation

Answer 22

Warburg Effect: preference that tumor cells show for an anaerobic version of glycolysis (glucose to lactate) occurring even IN THE PRESENCE OF OXYGEN

Tumors that are able to conduct the Warburg effect are particularly aggressive due to their high glucose uptake