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CMBM Exam 2 > Carbohydrates 1 > Flashcards

Carbohydrates 1 Flashcards

1
Q

Amylose bonds

A

alpha-1,4 bond

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2
Q

Amylopectin bonds

A

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

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3
Q

Cellulose bonds

A

Beta-1,4 bonds

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4
Q

Glycoproteins

A
  • More protein than sugar
  • Membrane bond
  • Secreted
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5
Q

Proteoglycans

A
  • More sugar than protein
  • Mucins (mucus)
  • Lectins (cell-cell interactions)
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6
Q

Glycolipids

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

- Inherited from each parent

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7
Q

SGLT-1 active transporter

A
  • 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+
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8
Q

Glut-1

A
  • 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)
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9
Q

Glut-2

A
  • 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.
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10
Q

Glut-3

A
  • 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)
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11
Q

Glut-4

A
  • 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
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12
Q

Glut-5

A
  • Fructose facilitated transport
  • Km= 5mM
  • Present in small intestines, located in both the luminal and basolateral sides of the intestinal epithelial cells
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13
Q

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

A
  • Glut-1 and 3
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14
Q

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

A
  • Glut-2 (liver)
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15
Q

Salivary alpha-amylase

A
  • Hydrolyzes the internal α-1,
    4 glycosidic bonds
  • Action stops in the stomach
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16
Q

Brush border enzymes

A
  • 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
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17
Q

3 regulatory enzymes in glycolysis

A

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

18
Q

Hexokinase inhibitor

A

Glucose-6-P

19
Q

Glucokinase inhibitor

A

Fructose-6-P

20
Q

PFK-1 inhibitors

A

Allosteric

  • ATP
  • Citrate
21
Q

PFK-1 activators

A

Allosteric

  • AMP
  • Fructose-2,6-P
22
Q

Pyruvate kinase inhibitors

A

Allosteric

  • ATP
  • Alanine (allosteric)
  • cAMP-dependent (hormonal)
23
Q

Pyruvate kinase activators

A

Allosteric

  • Fructose-1,6-P
  • (Liver pyruvate kinase) Insulin-inducible and its activity is also hormonally regulated by covalent modification (phosphorylation dephosphorylation)
24
Q

Hexokinase activators

A
  • Constitutive activation
25
Q

Glucokinase activators

A
  • 100-fold lower affinity for glucose and is inducible

- Only active w/ high glucose levels

26
Q

Tissues expressing glucokinase

A
  • Liver

- Pancreatic beta cells

27
Q

Fructose-2,6-phosphate regulates

A
  • Liver where it regulates both glycolysis and gluconeogenesis
  • Adipose tissue where it regulates glycolysis
28
Q

Pyruvate metabolic fate

A
  • 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)
29
Q

Glucose-Alanine cycle

A
  • 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
30
Q

Pyruvate enters mitochondria through

A
  • Monocarboxylate transporter (an

anti-porter) with exchange of H+

31
Q

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

A
  • 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
32
Q

Citrate is an important allosteric inhibitor of

A

Allosteric

  • Citrate synthase
  • PFK-1
33
Q

TCA cycle regulated by

A
  • Inhibitory: ATP and NADH

- Stimulatory: ADP and NAD+

34
Q

Citrate synthase regulated by

A
  • Inhibitors: citrate, succinyl CoA

- Activators: oxaloacetate, acetyl CoA

35
Q

Isocitrate dehydrogenase regulated by

A
  • Inhibitors: NADH

- Activators: ADP, Ca2+

36
Q

α-Ketoglutarate dehydrogenase regulated by

A
  • Inhibitors: NADH, succinyl CoA, GTP

- Activators: ADP, Ca2+

37
Q

Mannose metabolism

A

● Hexokinase converts mannose to mannose-6-P

● Mannose-6-P can be converted to fructose-6-P by an isomerase

38
Q

Fructose metabolism

A

● 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

39
Q

Galactose metabolism

A

● 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.

40
Q

Too much glucose can lead to

A

● 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

41
Q

Warburg Effect

A
  • 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

CMBM Exam 2 (13 decks)

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