Lecture 13 Flashcards

1
Q

Cyclization of monosaccharides

A
  • former carbonyl carbon becomes new chiral center –> anomeric carbon
  • carbonyl oxygen becomes hydroxyl group
  • position of hydroxyl determines whether a/b
  • if trans to CH2OH of the ring = a (alternative sides)
  • if cis to CH2OH of the ring = b (same side)
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2
Q

a arrangement of sugar

A

OH is trans to CH2OH

a = alternative

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3
Q

b arrangement of sugar

A

oh on same side as CH2OH

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4
Q

Oligosaccharides

A

2-10 monosacharides linked by glycosidic bonds

  • often covalently bonded to proteins and lipids on cell surfaces and act as recognition signals
  • human blood groups get specificity from oligosaccharide chains
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5
Q

polysaccharides

A
  • consist of more than ten (sometimes hundreds of) monosaccharides joined through dehydration sunthesis

–> starch, glycogen, cellulose are polymers of glucose that are covalently bonded differently

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6
Q

glucose structires

A

a –> starch and glycogen, twists and packs tightly, for energy

b –> cellulose, linear strands, good for structure

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7
Q

What are the 4 main fates fo glucose?

A
  1. synthesis of complex polysaccharides
  2. storage as glucose polymers
  3. oxidation to ribose 5-phosphate via the pentose phosphate pathway
  4. oxidation to pyruvate via glycolysis
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8
Q

Preparatory stage of glycolysis

A
  • need to thermodynamically destabilize the ring twice
  • converts it from a 5 carbon to a 4 carbon structure
  • 2 ATP invested
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9
Q

Energy conserving stage of glycolysis

A
  • 2 G3P molecules are oxidized to 2 pyruvic acids

Net 2 ATP produced

(4 total - 2 used in preparatory)

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10
Q

Importance of hexokinase

A
  • adds Pi to glucose so it cannot pass back trhough plasma membrane
  • substrate-induced conformation
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11
Q

phosphohexose isomerase

A

step 2

makes 5 carbon ring into a 4 carbon ring

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12
Q

phosphofructokinase

A

setp 3

major allosteric enzyme that sets the pace

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13
Q

Aldolase

A
  • seems unfavorable but mass action allows it
  • concentrations are not that of standard conditions
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14
Q

triose phosphate isomerase

A

a and b structure, very simple

uses Hist and Glu

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15
Q

Glyceraldehyde 3 phosphate dehydrogenase

A

coupled reaction of oxidation and acyl-phosphate formation

huge Ae between steps 1 and 2

thioester intermediate bridges

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16
Q

What 3 steps of gluconeogenesis are irreversible

A
  1. conversion of pyruvate to PEP via oxaloacetate
  2. dephosphorylation of fructose 1,6-bisphosphate
  3. dephosphorylation og glucose 6-phosphate