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Year 2 - Endocrinology > Carbohydrate Metabolism > Flashcards

Carbohydrate Metabolism Flashcards

1
Q

In what three ways can ATP be replenished?

A

Creatinine phosphate
Anaerobic metabolism
Aerobic metabolism

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2
Q

Give some examples of polysaccharides.

A

Starch

Cellulose

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3
Q

Name some disaccharides.

A

Maltose
Sucrose
Lactose

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4
Q

Name some monosaccharides.

A

Glucose

Fructose

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5
Q

What is the difference between D-glucose and L-glucose?

A

D-glucose rotates the plane of polarised light to the right.

L-glucose is the mirror image enantiomer of this and is not found naturally.

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6
Q

What constitutes whether a glucose molecule is alpha or beta?

A

Alpha-glucose refers to the -OH being below the first carbon atom.
Beta-glucose is the -OH being above the first carbon atom

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7
Q

What is the glycosidic bond found in starch?

A

Alpha-1,4- glycosidic bond

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8
Q

What breaks down starch into glucose, maltose and dextrins?

A

Salivary amylase

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9
Q

What breaks down dextrins into more disaccharides?

A

Pancreatic amylase

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10
Q

What brush border enzymes break down maltose, sucrose and lactose respectively?

A

Maltase breaks down maltose into glucose
Lactase breaks down lactose into glucose and galactose
Sucrose breaks down sucrose into glucose and fructose

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11
Q

Which starches are slowly digested and why?

A
  • trapped inside intact starch granules/plant cell wall structure
  • resistant to amylase as 3D structure is too tightly packed
  • associated with dietry fibre, which slows the absorption and digestion by making the gut contents viscous
  • CHO food containing high levels of fat
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12
Q

How do humans process cellulose?

A

We can’t because we don’t have the enzymes to break down the beta-1,4 links in cellulose

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13
Q

SGLUT-1 transporters are found where and have what characteristics?

A

Found on the intestinal mucosa and kidney tubules.

Cotransports one molecule of glucose or galactose along with two sodium ions. NO FRUCTOSE

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14
Q

GLUT-1 transporters are found where and have what characteristics?

A

It’s found on all cells
It transports glucose (high affinity) and galactose.
NO FRUCTOSE

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15
Q

GLUT-2 transporters are found where and have what characteristics?

A

These are found on liver and pancreatic beta cells

Transports glucose, galactose and fructose. A low affinity, high capacity glucose transporter.

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16
Q

GLUT-3 transporters are found where and have what characteristics?

A

Found in the placenta, brain and testes.
Transports glucose (high affinity) and galactose, and is the primary glucose transporter for neurons.
NO FRUCTOSE

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17
Q

GLUT-4 transporters are found where and have what characteristics?

A

It’s found on skeletal muscle, cardiac muscle and adipose tissue
It’s the insulin-responsive glucose transporter with a high affinity for glucose

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18
Q

GLUT-5 transporters are found where and have what characteristics?

A

Found in small intestine and sperm

Transports fructose, but not glucose or galactose

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19
Q

Give some ways glucose can enter the bloodstream.

A

From the diet, glycogen stores in the liver and gluconeogensis by the liver.

20
Q

Give some ways glucose can be removed from the blood.

A

It can be taken up by tissues, turned into glycogen in the liver, turned into glycogen in the muscle, be used to synthesis FAs and triglycerides and be used to synthesis pentoses.

21
Q

What can happen to glucose once it enters a cell

A

Produce ATP, be stored as glycogen, be stored as a lipid, be made into pentoses and be made into glycolipids/glycoproteins.

22
Q

What is done to all glucose molecules in every possible pathways within a cell?

A

There is phosphorylation of the glucose into glucose-6-phosphate

23
Q

What is the physiological function of immediately phosphorylating glucose to G6P?

A

It prevents the glucose from being transported out, trapping it within the cell.

24
Q

What catalyses the glucose to G6P phosphorylation reaction?

A

Hexokinases I-IV, depending on the tissue type.

25
Q

What does glycolysis require to be completed?

A

Glucose
2ATP
2NAD+

26
Q

What does glycolysis yield?

A

2 pyruvates
2ATP
2NADH
4 H+

27
Q

Name the first three enzymes needed in the glycolysis pathway.

A

Hexokinase (glucokinase)
Phosphoglucose isomerase
Phosphofructokinase-1

28
Q

Name the first four molecules in the glycolysis pathway.

A

Glucose
Glucose-6-phosphate
Fructose-6-phosphate
Fructose-1,6-bisphosphate

29
Q

Which hexokinase is glucokinase and in which cells is it used?

A

Hexokinase IV

Found in the beta-cells of the pancreas and liver.

30
Q

Where are hexokinases I-III expressed, and what is different about them?

A

They are expressed in all other tissues and are inhibited by G6P (negative feedback)

31
Q

Describe the kinetics of the hexokinases and glucokinase.

A

Hexokinases are immediately active when there is any glucose in the blood, until it reaches its peak at a relatively low glucose concentration.
Glucokinase isn’t active until a slightly higher glucose concentration, and takes a while to reach its peak activity levels.
This is so the tissues can be supplied with the energy they need right now, and THEN the glucose can be used for storage.

32
Q

What determines the activity of phosphofructokinase?

A

Activity depends on whether G6P is used for glycolysis or other purposes.
It’s inhibited by ATP and citrate (so the more glycolysis is performed, the less this enzyme acts)

33
Q

Which step is the committed step for glycolysis?

A

The action of phosphofructokinase.

34
Q

Why is lactate formed in anaerobic conditions, despite it not producing any more ATP?

A

Because the formation of lactate allows the NADHs to be used, so replenishing the NAD+ stores, and allowing glycolysis to be repeated and make another two ATP.

35
Q

How is fructose introduced to glycolysis?

A

It’s converted to fructose-1-phosphate (F1P) by fructokinase.
F1P is converted into glyceraldehyde-3-phosphate and DHAP, both of which are intermediates in glycolysis.

36
Q

How is galactose introduced to glycolysis?

A

It’s converted to glucose-1-phosphate, and then glucose-6-phosphate by a number of steps

37
Q

What two things can happen to pyruvate once it’s been formed?

A

It can be converted to lactate in anaerobic conditions.

It can also be converted into acetyl-CoA to be used in the TCA cycle

38
Q

Pyruvate is converted to lactate using what enzyme and which coenzyme?

A

It’s converted by lactate dehydrogenase and it converted NADH back to NAD+ to be used in glycolysis again.

39
Q

How many ATPs does anaerobic metabolism of glucose create?

A

2ATPs

40
Q

How and where is pyruvate converted to acetyl-CoA?

A

It’s converted in the mitochondria, using the enzyme pyruvate dehydrogenase during aerobic respiration.

41
Q

What cofactor is used during pyruvate conversion to acetyl-CoA, and what products does this process yield?

A

It uses NAD+

It creates NADH, H+ and CO2

42
Q

What are the products of the TCA cycle?

A 
3NADH
FADH2
GTP
CoA
2CO2
43
Q

How many ATPs does one NADH molecule produce?

A

3

44
Q

How many ATPs does one FADH2 produce?

A

2

45
Q

How many ATPs does one GTP produce?

A

One

46
Q

How many ATPs are normally produced from one glucose molecule during aerobic respiration?

A

36 ATPs

Year 2 - Endocrinology (14 decks)

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