Carbohydrates 1

Question 1

Amylose bonds

Answer 1

alpha-1,4 bond

Question 2

Amylopectin bonds

Answer 2

Alpha-1,4 bonds w/ alpha-1,6 branch bonds

Question 3

Cellulose bonds

Answer 3

Beta-1,4 bonds

Question 4

Glycoproteins

Answer 4

• More protein than sugar
• Membrane bond
• Secreted

Question 5

Proteoglycans

Answer 5

• More sugar than protein
• Mucins (mucus)
• Lectins (cell-cell interactions)

Question 6

Glycolipids

Answer 6

• 3 genes encode 3 glycosyltransferases (A, B, O)

- Inherited from each parent

Question 7

SGLT-1 active transporter

Answer 7

• Transports glucose in the same direction as Na+ (symporter)
• Enzyme itself doesnt use energy but is coupled w/ ATPase which pumps Na+ out of cell in exchange for K+

Question 8

Glut-1

Answer 8

• Glucose facilitated transport
• Lower KM (and higher affinity) for glucose than GLUT-2
• Present in most tissues
• Basal transporters of glucose at a constant rate into tissues that are metabolically dependent on glucose (e.g., brain and erythrocytes)

Question 9

Glut-2

Answer 9

• Glucose facilitated transport
• Distinctive in having a very high KM value for glucose (15-20 mM)
• Present in liver, kidney, pancreatic beta cells
• Glucose enters these tissues at a biologically significant rate only when the concentrations of glucose in the blood are higher
• Functional GLUT-2 is needed for proper insulin secretion; pancreas can sense the glucose level and adjust the rate of insulin secretion accordingly
• The high KM value of GLUT-2 also ensures that glucose rapidly enters liver cells only in times of plenty of glucose are available.

Question 10

Glut-3

Answer 10

• Glucose facilitated transport
• Lower KM (and higher affinity) for glucose than GLUT-2
• Present in brain, placenta, fetal muscle
• Present in many cell membranes
• Basal transporters of glucose at a constant rate into tissues that are metabolically dependent on glucose (e.g., brain and erythrocytes)

Question 11

Glut-4

Answer 11

• Glucose facilitated transport
• Insulin dependent
• Km= 5mM
• Insulin ⬆️Vmax
• Present in skeletal, heart, muscle, adipocytes
• Without insulin, it resides in the membrane enclosed intracellular vesicles; fed state, leads to a rapid increase in the number of GLUT-4 transporters to the plasma membrane
• Defects in GLUT-4 can result in insulin resistance
• Insulin raises the apparent Vmax by increasing the number of GLUT-4 transporters on the plasma membrane

Question 12

Glut-5

Answer 12

• Fructose facilitated transport
• Km= 5mM
• Present in small intestines, located in both the luminal and basolateral sides of the intestinal epithelial cells

Question 13

The rate of glucose transport is relatively independent of the extra-cellular glucose conc. for which transporters?

Answer 13

• Glut-1 and 3

Question 14

The rate of glucose transport is almost proportional to the extra-cellular glucose conc. for which transporter?

Answer 14

• Glut-2 (liver)

Question 15

Salivary alpha-amylase

Answer 15

• Hydrolyzes the internal α-1,
  4 glycosidic bonds
• Action stops in the stomach

Question 16

Brush border enzymes

Answer 16

• Maltase, iso-maltase, sucrase and lactase
• digest oligo-, di- and tri saccharides and generate mono-saccharide
• These enzymes are on the membranes of the intestinal epithelial cells with α-helix transmembrane domains and longer extracellular domains, extending out from the cells

Question 17

3 regulatory enzymes in glycolysis

Answer 17

1) Glucokinase (liver)/hexokinase (the other tissues)
2) Phosphofructokinase-1
3) Pyruvate kinase

Question 18

Hexokinase inhibitor

Answer 18

Glucose-6-P

Question 19

Glucokinase inhibitor

Answer 19

Fructose-6-P

Question 20

PFK-1 inhibitors

Answer 20

Allosteric

• ATP
• Citrate

Question 21

PFK-1 activators

Answer 21

Allosteric

• AMP
• Fructose-2,6-P

Question 22

Pyruvate kinase inhibitors

Answer 22

Allosteric

• ATP
• Alanine (allosteric)
• cAMP-dependent (hormonal)

Question 23

Pyruvate kinase activators

Answer 23

Allosteric

• Fructose-1,6-P
• (Liver pyruvate kinase) Insulin-inducible and its activity is also hormonally regulated by covalent modification (phosphorylation dephosphorylation)

Question 24

Hexokinase activators

Answer 24

• Constitutive activation

Question 25

Glucokinase activators

Answer 25

- 100-fold lower affinity for glucose and is inducible | - Only active w/ high glucose levels

Question 26

Tissues expressing glucokinase

Answer 26

- Liver | - Pancreatic beta cells

Question 27

Fructose-2,6-phosphate regulates

Answer 27

- Liver where it regulates both glycolysis and gluconeogenesis - Adipose tissue where it regulates glycolysis

Question 28

Pyruvate metabolic fate

Answer 28

- Acetyl-CoA through pyruvate dehydrogenase enzyme (one directional: produces CO2 and NADH) - Lactate through lactate dehydrogenase enzyme recycling NAD+ from NADH (bi-directional: works in the opposite direction when O2 demands met; Cori cycle) - Oxaloacetate through pyruvate carboxylase (one directional: biotin cofactor and consumes 1 ATP) - Alanine through pyridoxal phosphate (bi-directional: works in opposite direction through alanine aminotransferase)

Question 29

Glucose-Alanine cycle

Answer 29

- Pyruvate can be translocated as alanine from muscle to the liver where it is converted back to glucose (gluconeogenesis) - 6 ATP molecules are needed for synthesis of a glucose molecule

Question 30

Pyruvate enters mitochondria through

Answer 30

- Monocarboxylate transporter (an | anti-porter) with exchange of H+

Question 31

Oxidation of acetyl CoA in the TCA cycle can go only as fast...

Answer 31

- Electrons from NADH and FAD(2H) enter the electron transport chain - The rate of the TCA cycle is adjusted to the rate of oxidative phosphorylation

Question 32

Citrate is an important allosteric inhibitor of

Answer 32

Allosteric - Citrate synthase - PFK-1

Question 33

TCA cycle regulated by

Answer 33

- Inhibitory: ATP and NADH | - Stimulatory: ADP and NAD+

Question 34

Citrate synthase regulated by

Answer 34

- Inhibitors: citrate, succinyl CoA | - Activators: oxaloacetate, acetyl CoA

Question 35

Isocitrate dehydrogenase regulated by

Answer 35

- Inhibitors: NADH | - Activators: ADP, Ca2+

Question 36

α-Ketoglutarate dehydrogenase regulated by

Answer 36

- Inhibitors: NADH, succinyl CoA, GTP | - Activators: ADP, Ca2+

Question 37

Mannose metabolism

Answer 37

● Hexokinase converts mannose to mannose-6-P | ● Mannose-6-P can be converted to fructose-6-P by an isomerase

Question 38

Fructose metabolism

Answer 38

● Fructokinase converts fructose to fructose-1-P ● Aldolase B cleaves the 6-carbon sugar into two 3-carbon sugars, dihydroxyacetone-P and glyceraldehyde ● Glyceraldehyde kinase is needed to get glyceraldehyde-3-P for glycolysis ● Over consumption of fructose leads to fatty liver or hyperglycemia

Question 39

Galactose metabolism

Answer 39

● Galactokinase converts galactose to galactose-1-P. ● A transferase utilizes a high energy form of glucose (UDP-glucose) to exchange galactose for glucose. Finally, an epimerase converts UDP-galactose to UDP-glucose.

Question 40

Too much glucose can lead to

Answer 40

● No-enzymatic glycosylation (for example, formation of HbA1C) ● Conversion to fructose (and cause high-fructose toxicity) ● Leads to accumulation of sorbitol in tissues (Schwann cells, lens, retina and kidneys; since these tissues lack sorbitol dehydrogenase) and cause cataracts, retinopathy and peripheral neuropathy

Question 41

Warburg Effect

Answer 41

- Aerobic Glycolysis in cancer cells - Tumor cells have higher glucose uptake and enhanced glycolysis - Increases the acidity of the microenvironment which helps cancer cell invasion and escape from immune system attacks - Can aide in diagnosis through 2-F18-2-D-deoxyglucose (FDG, an indigestible glucose analogue) and positron emission tomography (PET) and computerized tomography (CT) scan