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BIOC 311 > Carbohydrates (Lecture 4) > Flashcards

Carbohydrates (Lecture 4) Flashcards

1
Q

what are the metabolic consequences of hexokinase and glucokianse?

A

since hexokinase has a higher affinity for glucose than glucokinase, hexokinase will bind to most of the glucose to promote glycolysis and glucokinase ill onlyinteract with the remaining circulating glucose, which will be converted into glycogen in the liver.

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2
Q

what is the 4th step in glycolysis?

A

F1,6BP will be converted into GAP and DHAP via the enzyme,e aldolase.

it is important tot note that GAP and DHAP can be interconverted

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3
Q

how are GAP and DHAP related?

A

these two molecules are interconvertible with the enzyme Triose phosphate isomerase

the consumption of GAP during glycolysis pushes the generation of more GAP

in cells, there’s a higher concentration fo DHAP, since GAP is quickly con summed by glycolysis

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4
Q

how many GAP molecules are generated per glucose?

A

2

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5
Q

what’s the 6th step of glycolysis?

A

GAP is converted to 1,3 Bisphosphoglycerate via GAPDH

this step generates NADH

the product is a high energy intermediate due to the presence of two Pi groups

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6
Q

what’s the 7th step of glycolysis?

A

1,3 BPG is converted to 3PG via PGK

this step generates ATP

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7
Q

why does substrate channeling occur and which compounds are involved in this process?

A

1,3 bisphosphoglycerate is a high energy intermediate with a short half life, it is rapidly passed along 2 enzymes to ensure that it does not accumulate.

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8
Q

which step is involved with PGM, phsophoglycerate mutase.

A

the 8th step, where 3PG is converted into 2PG

transfer of the phosphate form position 3 to position 2

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9
Q

how is PEP formed?

A

2PG is transformed into PEP via an enolase, which dehydrates the 2PG to phsophoenolpyruvate

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10
Q

explain the importance of PEP

A

PEP is a high energy intermediate

before making ATP , PEP is hydrolyzed to supply energy

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11
Q

how is pyruvate kinase involedi n glycolysis?

A

PK is the last step of glycolysis, as for it generates pyruvate

this step generates two ATPs per glucose molecule

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12
Q

how is pyruvate kinase activated?

A

allosterically via a feed forward mechanism with Fructose 1,6 bisphosphate

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13
Q

how is pyruvate kinase inhibited?

A

allosterically via ATP

hormonally via glucagon (cAMP and PKA)

PKA phosphorylates PK to inactivate the enzyme

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14
Q

name the 3 committed steps:

A
  1. HK
  2. PFK1
  3. PK
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15
Q

how man y ATPare generated from aerobic glycolysis?

A

7 ATP

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16
Q

how man y ATPare generated from anaerobic glycolysis?

A

2 ATP

17
Q

what is the importance of NAD+?

A

NAD+ must be regenerated for glycolysis

18
Q

how is NAD+ replenished?

A

in the citric acid cycle (need for O2)

homolactic fermentation, NADH is invested to generate lactate ans NAD+

alcoholic fermentation generated CO2 and ethanol via the investment of NADH

19
Q

homolactic fermentation

A

does not require O2

lactate dehydrogenase (LDH) converts NADH and pyruvate into lactate

the NAD+ will then refill the pool for glycolysis

20
Q

explain the Cori cycle

A

lactate in the muscle will be transported into the liver via this cycle

when exercising, pyruvate is converted into lactate

lactate circulates the blood, but when blood glucose levels are low, gluconeogenesis will occur with the lactate supplied by the muscle to the liver

the glucose synthesized will be released not the blood

when there is an accumulation of glucose, it will be converted into glycogen for storage in the muscle

to access the glucose, glycogen will be transformed into lactate

21
Q

why is fructose metabolized in the liver?

A

the fructose consumed by our diets will enter the hepatic vein, thus it will pass through the liver before reaching any other organ

22
Q

what is the role of fructokinase?

A

once fructose enters the liver, it will be converted into fructose-1-phospahte via fructokinase

this process requires the investment of 1 ATP

the ring structure is opened to form a chain

23
Q

how is glyceraldehyde formed?

A

F1P chain is converted into glyceraldehyde via fructose-1-phospahte aldolase

24
Q

what are the two options for glyceraldehyde?

A

1.
glyceraldehydeis converted into glyceraldehyde-3-phosphate (GAP) via glyceraldehyde kinase

thuis requires 1 ATP

G3P can then be used for glycolysis

  1. with the investment of 1 NADH, glyceraldehyde can generate glycerol via alcohol dehydrogenase

glycerol is then converted into glycerol-3-phosphate via glycerol kinase

glycerol-3-phosphate is used as a precursor for glycerophospholipids

with NAD+, DHAP is generated via glycerol phosphate DH

this supplies 1 NADH

DHAP is converted to GAP via TIM to enter glycolysis

25
Q

why are there 2 options for glyceraldehyde, if both processes se the same amount of energy?

A

the pathway converting glyceraldehyde into glycerol is favoured when the liver needs to synthesize glycophospholipids

when this is not the case, glyceraldehyde will be directly converted into GAP

26
Q

when does fructose enter the muscle tissue and that happens?

A

only about 5% of the time

in the muscle, hexokinase converts fructose into F6P with the investment of 1ATP

F6P is converted to F1,6BP via PFK

F1,6BP is converter to GAP/DHAP to enter glycolysis via fructose-1,6-phosphate aldolase

27
Q

how does fructose enter glycolysis in the liver?

A

GAP

28
Q

how does fructose enter glycolysis in the muscle ?

A

F6P

29
Q

fructose metabolism in the fed state:

A

bypasses the PFK 1 control in anabolic liver and it is converted into fatty acids instead (via accumulation of acetyl coa)

30
Q

explain the Leloir pathway

A

with the investment of 1 ATP, galactose can be converted into galactose-1-phosphate via galactokianse

galactose-1-phosphate is converted unto a UDP-galactose with a free floating UDP

UDP galactose is converted into UDP glucose via UDP-galactose-4-epimerase

the UDP glucose is then converted into G1P (via galactose-1-phosphate uridylyl transferase) and then further into G6P via phosphoglucomutase

the G6P will then be used for glycolysis

31
Q

what causes galactosemia?

A

mutations in enzymes that prevent the conversion of galactose into G6P

this causes patients to not be able to consume dairy products

32
Q

type 1 galactosemia

A

mutation in uridylyl transferase

UDP glucose -> G1P

33
Q

type 2 galactosemia

A

mutation in galactokinase

galactose -> galactose-1-phosphate

34
Q

type 3 galactosemia

A

epimerase

UDP galactose -> UDP glucose

35
Q

mannose is a substrate for ____ and converted into___

A

hexokinase, mannose-6-phosphate

36
Q

how is mannose-6-phosphate converted into F6P?

A

phosphomannose isomerase

BIOC 311 (33 decks)

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