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BIOSCI106 2017 SEM 2 > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

How can you find out how many stereoisomers there are in a molecule?

A

2^n where n is the number of chiral carbons

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2
Q

What are the 2 types of stereoisomers?

A
  1. Enantiomer - non-superimposable mirror images

2. Diasteromer - superimposable non-mirror images

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3
Q

What are the 2 types of diastereomer?

A
  1. Epimer - differ at one of the several asymmetric carbons
  2. Anomer - isomers that differ at a new asymmetric carbons on the ring structure i.e a (OH pointing down) or b (OH pointing up)
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4
Q

Fructose and glucose have the same molecular formula, why is glucose a 6 membered ring and fructose 5?

A

Because fructose is a ketone so it just has the extra carbon not included in the ring

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5
Q

What are oligosaccharides?

A

Disaccharides with monosaccharide subunits linked together by a glycosidic bond

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6
Q

What are 3 examples of oligosaccharides?

A
  1. Sucrose (glucose + fructose) with alpha 1,2 glycosidic bonds
  2. Lactose (galactose + glucose) with alpha 1,4 glycosidic bond
  3. Maltose (glucose + glucose) with alpha 1,4 glycosidic bonds
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7
Q

What is high fructose corn syrup made up of?

A

Glucose + fructose

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8
Q

What are the 2 most abundant polysaccharides?

A

Cellulose and starch

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9
Q

Alpha linkages lead to ____ structures that can be broken down by ______. Beta structures lead to _______ that can be broken down by _______.

A
  1. Helical (hydrophilic) - humans

2. Linear (hydrophobic) - animals

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10
Q

What is an example of a type of starch with alpha 1,4 linkages?

A

Amylose which is a helical shape and is soluble and humans can break it down

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11
Q

What are 2 examples of polysaccharides with alpha 1,4 and alpha 1,6 linkages?

A

Glycogen - branched form of glucose

Amylopectin - branched form of starch

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12
Q

Which is more highly branched - amylopectin or glycogen?

A

Glycogen

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13
Q

What is 2 examples of molecules made up of beta 1,4 linkages?

A
  1. Cellulose - strong and insoluble made up of glucose

2. Chitin - nitrogen containing appendage on each glucose

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14
Q

Describe glycolysis:

A

Occurs in the cytoplasm in the absence of oxygen and breaks down glucose (6carbons) into 2 pyruvates (3 carbons). Produces 2 ATP and 2 NADH

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15
Q

Why do we have irreversible steps, what makes them irreversible?

A

They have such large negative delta G values

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16
Q

What are the 3 irreversible steps of glycolysis?

A

Hexokinase (step 1)
Phosphofructokinase (step 3)
Pyruvate kinase (step 9 - last one)

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17
Q

List the process of glycolysis with each enzyme and name of intermediate etc:

A
  1. Glucose is turned into glucose-6-phosphate by hexokinase and it uses 1 ATP
  2. Glucose-6-phosphate is turned into fructose-6-phosphate by phosphoglucose isomerase
  3. Fructose-6-phosphate is turned into fructose-1,6-bisphosphate by phosphofructokinase and it uses 1 ATP
  4. Fructose-1,6-bisphsphate is tuned into glyceraldehyde-3-phosphate which is in equilibrium with dihydroxyactetonephosphate by alsolase. They can interconvert in the presence of troise phosphate isomerase.
  5. Glyceraldehyde-3-phosphate is turned into 2x 1,3 bisphoshphoglycerate by glyceraldehyde-3-phosphate dehydrogenase and produces 2x NADH
  6. 1,3-bisphoshphoglycerate is tuned into 2x 3-phosphoglycerate by phosphoglycerate kinase and produces 2 ATP
  7. 3-phosphoglycerate is turned into 2-phosphoglycerate by phosphoglycerate mutase
  8. 2-phosphoglycerate is urned into 2x phosphoenol pyruvate by enolase and it produces 2 H20
  9. Phosphoenol pyruvate is turned into 2x pyruvate by pyruvate kinase and produces 2 ATP
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18
Q

What is pyruvate kinase inhibited by?

A

High levels of ATP and acetyle-CoA

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19
Q

What is pyruvate kinase activated by?

A

Fructose-1,6-bisphosphate

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20
Q

Describe the energy investment phase:

A

When 2 ATP’s are used in glycolysis

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21
Q

Describe the energy payoff phase:

A

When 4 ATP are produced by glycolysis (2 net)

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22
Q

What is the ATP yield when breaking down glycogen to glucose then doing glycolysis compared to normal glycolysis?

A

It produces 3 ATP as opposed to only 2

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23
Q

Describe the regulation of glycolysis during exercise i.e if there not much ATP and the cell needs energy:

A

AMP activates and stimulates PFK and fructose-1,6-bisphosphate stimulates pyruvate kinase which increases the rat of glycolysis, ATP and NADH.

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24
Q

Describe the regulation of glycolysis if there too much ATP:

A

Citrate inhibited PFK and pyruvate kinase is also inhibted which decreases glycolysis, ATP and NADH

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25
Q

What happens when PFK is inhibited by citrate?

A

Glucose-6-phosphate builds up and inhibits hexokinase by a feedback loop

26
Q

What are the 5 fates of pyruvate?

A
  1. Pyruvate to ethanol - when no oxygen
  2. Lactate fermentation/corti cycle - no oxygen
  3. Pyruvate/alanine cycle
  4. Conversion of pyruvate to oxoloacetate - gluconeogenesis
  5. Conversion of pyruvate to acetyl-CoA - when theres oxygen
27
Q

Describe the process of the conversion of pyruvate to acetyl-CoA:

A

2 pyruvates in the cytoplasm get converted to 2 acetyl-CoA’s in the mitochondria by pyruvate dehydrogenase which works by firstly taking off CO2 from each pyruvate then adding a cofactor A then producing a NADH.

28
Q

What is pyruvate dehydrogenase regulated by?

A
  1. Inhibited by acetyl-CoA, NADH and ATP
  2. High levels of acetyl-CoA stimulates the conversion of pyruvate to oxoloacetate by stimulating the enzyme pyruvate carboxylase.
29
Q

What are the net products of TCA cycle for 1 glucose?

A

6 NADH
2 FADH2
2 ATP

30
Q

What are the net products of the TCA cycle for one molecule of acetyl-CoA?

A

3 NADH
1 FADH2
1ATP

31
Q

List all of the steps in the TCA cycle:

A
  1. When acetyl-CoA is added to oxoloacetate it is turned into citrate by citrate synthesase.
  2. Citrate is turned into isocitrate by aconitase
  3. Isocitrate is turned into alpha ketogluterate by isocitrate dehydrogenase and produces 1 NADH and a Co2
  4. Alpha ketogluterate is turned into succinyl CoA by alpha ketogluterate dehydrogenase complex and produces a NADH and Co2
  5. Succinyl CoA is tunred into succinate by succinyl CoA synthetase and produces 1 ATP
  6. Succinate is turned into fumerate by succonate dehydrogenase and produces 1 FADH2
  7. Fumerate is turne into malate by fumerase
  8. Malate is turned into oxoloacetate by malate dehydrogenaseand produces a NADH
32
Q

How much ATP does 1 NADH make?

A

2.5

33
Q

How much ATP does one FADH2 make?

A

1.5

34
Q

What is the total net of NADH, FADH2 and ATP from glycolysis, pyruvate dehydrogenase and TCA cycle?

A

4 ATP
10 NADH
2 FADH2

35
Q

Where does the electron transport chain happen?

A

In the inner mitochondrial membrane

36
Q

Where are the hydrogens pumped in the electron transport chain?

A

From the mitochondrial matrix to the intermembrane space

37
Q

For the following complex, say its name, how many protons it pumps and any special features: complex I

A 
NADH-Q oxidoreductase
Pumps 4H+
Contains Fe-S clusters
Protons then go to ubiqinone
NADH transfered electrons
38
Q

For the following complex, say its name, how many protons it pumps and any special features: complex II

A 
Succinate Q reductase
No protons pumped
Contains succinate dehydrogenase
Electron are transferred to ubiquinone 
FADH2 transferred electrons
39
Q

For the following complex, say its name, how many protons it pumps and any special features: complex III

A

Q-cytochrome C oxidoreductase
Pumps 4H+
Transfers electrons to cytochrome C

40
Q

For the following complex, say its name, how many protons it pumps and any special features: complex IV

A

Cytochrome C oxidase
Pumps 2H+
Where O2 accepts electrons to form H2O
Inhibited by cyanide

41
Q

Describe chemiosmosis:

A

An energy coupling mechanism that uses cellular energy in the form of an H+ gradient across a membrane to produce ATP

42
Q

What is the total number of ATP’s produced in the whole cycle and where do they go?

A

32

34% is captured and 64% are lost as heat

43
Q

Where does gluconeogenesis occur and why?

A

In the liver because skeletal muscle cannot undergo gluconeogenesis as it can only use hexokinase to store it (liver uses glucokinase).

44
Q

What would happen if there was a futile cycle i.e both glycolysis and gluconeogenesis happens at the same time?

A

Glycolysis produces 2 ATP and gluconeogenesis uses 6 ATP so there would be a waste of 4 ATPs

45
Q

What are the 3 bypasses used in gluconeogenesis?

A
  1. Pyruvate carboxylase/phosphoenolpyruvate carboxykinase
  2. Fructose-1,6-bisphosphotase
  3. Glucokinase
46
Q

Describe how this bypass works: Pyruvate carboxylase/ phosphoenolpyruvate carboxykinase

A

Pyruvate carboxylase is activated by acetyl-coA and converts pyruvate to oxoloacetate. Phosphoenolpyruvate carboxykinase converts oxoloacetate to phosphoenol pyruvate and uses 1 ATP. If you increase the amount of this enzyme, oxoloacetate decreases so does the TCA cycle so acetyl-CoA builds up and stimulates pyruvate carboxykinase

47
Q

Describe how this bypass works: fructose-1,6-bisphosphotase (2)

A

It converts fructose-1,6-bisphosphate to fructose-6-phohphate

48
Q

Describe how this bypass works: glucokinase (3)

A

Converts glucose-6-phosphate into glucose using H20

49
Q

Why does the liver have glucokinase and skeletal muscle have hexokinase?

A

Glucokinase has a much lower affinity for glucose because the liverd does both gluconeogenesis and glycolysis where as skeletal muscle has hexokinase that has a high affinity for glucose because it can only do glycolysis and the glucose is trapped.

50
Q

What are the 3 types of hormonal regulation?

A

Glucagon
Epinephrine
Insulin

51
Q

Which hormone has no effect on skeletal muscle?

A

Glucagon

52
Q

What does glucagon do to bypass 1 in the liver?

A

It inhibits pyruvate kinase so no pyruvate is made when blood sugar levels are low. It also increases the action of PEPCK which draws more oxoloacetate away from the TCA cycle which raises acetyl-CoA levels and stimulates the conversion of pyruvate to make more oxoloacetate

53
Q

What does glucagon and epinephrine do to bypass 2?

A

They regulate the production of fructose-1,6-bisphosphotase which stimulates the activity of phosphofructokinase and can override the inhibtion by ATP and inhibits fructose-1,6-bisphosphotase

54
Q

Overall glucagon and epinephrine favour?

A

Gluconeogenesis

55
Q

Overall insulin favours?

A

Glycolysis

56
Q

Why can acetyl CoA not be used to make glucose in animals?

A

Acetyl CoA has to enter the TCA cycle and in doing this it loses 2 Co2. In order to make glucose you need these 2 carbons so thats why you can’t make sugar from fat

57
Q

Describe the structure of glycogen:

A

It contains alpha 1,4 linnkages and alpha 1,6 linkages at the branch points (every 8-10 units)

58
Q

What are the 4 steps in glycogen synthase?

A
  1. Conversion of glucose to glucose-6-phosphate by hexokinase or glucokinase
  2. Formation of glucose-6-phosphate to glucose-1-phosphate by phosphoglucomutase
  3. Activation of glucose-1-phosphate by UDP catalysed by UDP- glucose phosphorylase
  4. UDP glucose is the added to the glycogen polymer by glycogen synthase which catalyses the formation of alpha 1,4 bonds and the alpha 1,6 bonds are formed by a branching enzyme
59
Q

Describe the process of glycogenolysis (glycogen breakdown):

A

The alpha 1,4 bonds are cleaved by glycogen phosphorylase so a free phosphate is added to make glucose-1-phosphate. The debranching enzymes breaks the alpha 1,6 linkages. The glucose-1-phosphate is then turned into glucose-6-phosphate by phosphoglucomutase for use in glycolysis

60
Q

Describe the regulation of glycogen synthesis and breakdown

A

Regulated by glycogen synthase and glycogen phosphorylase. When one is on the other is off. When a phosphate is added, phosphorylase is activated and synthase is inactivated

61
Q

How do the hormones epinephrine, glucagon and insulin affect glycogen synthase?

A

It adds a phosphate group so it is not active, due to a decrease affinity for UDP-glucose. Inulin has the opposite affect. The inhibition effect of epinephrine or glucagon can be reversed by high levels of glucose-6-phosphate which can bind to the less active form of glycogen synthase to restore its affinity. This means that the cell can still drive glycogen synthesis under conditions where glycolysis is inhibited. This can happen when PFK is inhibted by high levels of ATP in skeletal muscle causing an increase in glucose-6-phosphate

62
Q

Describe glycogen phosphorylase

A

It exists in 2 main forms the active phosphorylase a form and the less active phosphorylase b form where both exist in equilibrium with an active R state and less active T state. In the liver the R state is converted into the T state in the presence of glucose

BIOSCI106 2017 SEM 2 (7 decks)

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