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1

Cyclization of monosaccharides

- 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)

2

a arrangement of sugar

OH is trans to CH2OH

a = alternative

3

b arrangement of sugar

 

oh on same side as CH2OH

4

Oligosaccharides

 

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

 

5

polysaccharides

 

- 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

6

glucose structires

 

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

b --> cellulose, linear strands, good for structure

7

What are the 4 main fates fo glucose?

 

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

8

Preparatory stage of glycolysis

- need to thermodynamically destabilize the ring twice

- converts it from a 5 carbon to a 4 carbon structure

- 2 ATP invested

9

Energy conserving stage of glycolysis

 

- 2 G3P molecules are oxidized to 2 pyruvic acids

 

Net 2 ATP produced

 

(4 total - 2 used in preparatory)

10

Importance of hexokinase

 

- adds Pi to glucose so it cannot pass back trhough plasma membrane

- substrate-induced conformation

11

phosphohexose isomerase

 

step 2

makes 5 carbon ring into a 4 carbon ring

 

12

phosphofructokinase

 

setp 3

major allosteric enzyme that sets the pace

13

Aldolase

 

- seems unfavorable but mass action allows it

- concentrations are not that of standard conditions

14

triose phosphate isomerase

 

a and b structure, very simple

uses Hist and Glu

15

Glyceraldehyde 3 phosphate dehydrogenase

 

coupled reaction of oxidation and acyl-phosphate formation

huge Ae between steps 1 and 2

thioester intermediate bridges

16

What 3 steps of gluconeogenesis are irreversible

1. conversion of pyruvate to PEP via oxaloacetate

9. dephosphorylation of fructose 1,6-bisphosphate

11. dephosphorylation og glucose 6-phosphate