BMS1030 - CHO Metabolism

Question 1

When the change in G (Gibbs free energy) is smaller than 0, this is called…

And when it’s greater than 0?

Answer 1

Exergonic

Endergonic

Question 2

Enzymes can act as gatekeepers for pathways - inhibiting or encouraging them. What else can they determine?

Answer 2

The direction of the pathway.

Question 3

Where is Ribose found in?

Answer 3

Meat, fish and pultry (flavour precursor)

Question 4

Galactose is ____ in free form in foods.

Answer 4

Rare

Found in milk products after lactose hydrolysis

Question 5

What is the sweetest natural sugar?

Answer 5

Fructose

Question 6

What is the majority of free sugars in food found as?

Answer 6

Sucrose (glucose + fructose)

Question 7

Whatprocess is maltose produced in?

Answer 7

The brewing process

Question 8

What is the difference between amylose and amylopectin?

Answer 8

Amylose - long, unbranched, 1-4 linkages
Amylopectin - branched chains, 1-4 and 1-6 linkages

Question 9

What is the main example of a non starch polysaccharide?

Answer 9

Cellulose –> dietary fibre
Beta glucose, 1,4 linkages

Question 10

Give some examples of other non starch polysacchrides (NSPS) in food.

Answer 10

B-glucan (oats and barley) - helps to reduce cholesterol

Pectin (jam, fruit)

Aliginate (brown seaweed) -used as thickener/gelling agent

Question 11

All sugars absorbed in the gut (_______, ________, ________) go straight to the ______ before being exported into the blood as _______.

Answer 11

Glucose, Galactose, Fructose

Liver
Glucose

Question 12

How is D-glucose diffferent to a-D-glucose?

Answer 12

Question 13

What are the 2 stages of glycolysis called?

Answer 13

Investment stage (uses ATP)
Pay off stage (Creates ATP)

Question 14

What overall happens in glycolysis? (beginning and ending)

Answer 14

1 x 6 Carbon glucose is split into 2 x 3 Carbon Pyruvate

Question 15

What is the overall equation for Glycolysis?

Answer 15

Glucose + 2NAD+ + 2ADP + 2Pi –> 2 Pyruvate + 2NADH + 2 ATP

Question 16

What are the 5 steps of the investment stage of glycolysis? (names of steps and molecules)

Answer 16

Glucose
[Priming]
Glucose 6-Phosphate
[Isomeration]
Fructose 6-Phosphate
[Priming]
Fructose 1,6-Phosphate
[Cleavage]
Glyceraldehyde 3-phosphate + DHAP
[Interconversion]
2 x Glyceraldehyde 3-Phosphate (2 x GAP)

Question 17

What is the enzyme that primes glucose to form glucose 6-phosphate?

What type of enzyme is it?

Answer 17

Hexokinase
- allosteric enzyme (so prevents uptake at low glucose concs)
- irreversible

Question 18

How does glucokinase comapre to hexokinase?

Answer 18

Both: glucose is substrate
Differences:
- Glucokinase = not allosteric - so ensures utilization
of glucose even at low conc.
- Hexokinase = allosteric - so only takes up a little glucose at low glucose concs.

Question 19

What enzyme converts glucose 6-phosphate to fructose 6-phosphate?

Answer 19

Phosphohexose isomerase

Question 20

What enzyme converts Fructose 6-Phosphate to Fructose 1,6-bisphosphate?

What do I need to remember about this reaction?

Answer 20

PFK1 (phosphofructokinase-1)

It’s Irreviersible and is the committed step/key switch for glycolysis.
Controlled by many things.

Question 21

What is PFK1 inhibited by?

Answer 21

ATP

Question 22

What enzyme splits Fructose 1,6-bisphosphate into two molecules?

Answer 22

Aldolase

Question 23

What enzyme converts DHAP into the second Glyceraldehyde-3-phosphate molecule?

Answer 23

Triose phosphate isomerase

Question 24

Which enzymes in the Investment stage of Glycolysis use ATP?

Answer 24

The irriversible ones - Hexokinase and PFK1

Question 25

What are the 5 steps of the pay off stage of glycolysis? (names of steps and molecules)

Answer 25

Glyceraldehyde-3-Phosphate [Oxidation] 1,3-Bisphosphoglycerate [1st ATP production] 3-Phosphoglycerate + ATP [Rearrangement] 2-Phosphoglycerate [Dehydration] Phosphoenolpyruvate (PEP) [2nd ATP production] Pyruvate + ATP

Question 26

What enzyme converts GAP into 1,3 Bisphosphoglycerate? What extra molecule is produced in this step?

Answer 26

GAP dehydrogenase NADH produced. This is the first energy yielding step of glycolysis.

Question 27

What enzyme converts 1,3 Bisphosphoglycerate into 3-Phosphoglycerate?

Answer 27

Phosphoglycerate kinase

Question 28

What enzyme rearranges 3-Phosphoglycerate into 2-Phosphoglycerate?

Answer 28

Phosphoglyceromutase

Question 29

WHat enzyme dehydrates 2-Phosphoglycerate into PEP?

Answer 29

Enolase

Question 30

What enzyme converts PEP into Pyruvate?

Answer 30

Pyruvate Kinase - highly regulated enzyme, irreversible

Question 31

Where does glycolysis occur?

Answer 31

In the cytosol of the cell

Question 32

How many ATPs are invested and gained in Glycolysis? Net gain?

Answer 32

2 ATP invested 4 ATP gained Net gain of 2 ATP

Question 33

What are the 3 irreviersible steps in glycolysis?

Answer 33

Hexokinase (1) PFK1 (2) Pyruvate Kinase (10)

Question 34

How does galactose enter into glycolysis?

Answer 34

It's first converted to Galactose-1-Phosphate by galactokinase using ATP. Then its onverted to Glucose-1-Phosphate and then Glucose-6-phosphate which enters glycolysis.

Question 35

How does fructose enter into glycolysis?

Answer 35

First its converted to fructose-1-phosphate by fructokinase using ATP. Then converted into either Glyceraldehyde or Dihydroxyacetone phosphate. DHP reversibly and Glyceraldehyde irreversibly converted into Glyceraldehyde 3-phosphate -> glycolysis

Question 36

The entry of ______ into glycolysis bypasses the key control steps of the pathway and can lead to an 'overload' of _____________.

Answer 36

Fructose Carbohydrate [So overload happens when we eat fructose and glucose (pure sugar) together]

Question 37

What can overdosing in CHO lead to? What sugar is more likely to cause this issue than fructose alone?

Answer 37

Fatty liver synthesis and excess export of glucose back out into the system. Sucrose

Question 38

How many ATP molecules can be generated per glucose anaeobicaly?

Answer 38

2 ATP

Question 39

In Anaerobic catabolism, what needs to be recyled? By what reaction? What else does it form?

Answer 39

NAD+ -> used in conversion of Glyceraldehyde 3-phosphate to 1,3 bisphosphoglycerate. Recycled by dehydration reaction - forming lactate

Question 40

How is Pyruvate converted to Lactate in anaerobic catabolism?

Answer 40

Reduced by the action of lactate dehydrogenase, using NADH.

Question 41

What is the overall equation for anaerobic catabolism?

Answer 41

Glucose + 2 Pi + 2 ADP -> 2 Lactate + 2 ATP + 2 H2O

Question 42

The liver recycles lactate back to glucose via the ____ Cycle.

Answer 42

Cori Cycle

Question 43

How is glycolysis controlled?

Answer 43

With irriversible reactions with 3 key enzymes: - Hexokinase, - Phosphofructokinase (PFK-1) - Pyruvate Kinase The activity of these enzymes are controlled by hormones and other metabolites

Question 44

What inhibits PFK1 enzyme? WHat is inhibition reversed and enhanced by?

Answer 44

ATP Reversed by: - Insulin, AMP, Fructose-6-phosphate, Catecholamines (in muscle) Enhanced by: - Glucagon, Citrate, Catecholamines (in liver) Catecholamines - e.g. adrenalin, noradrenalin)

Question 45

What is pyruvate kinase activated and inhibited by?

Answer 45

Activated by: - Fructose 1,6 Bisphosphate - Insulin Inhibited by: - ATP - Glucagon - Alanine (signalling an abundance of building blocks)

Question 46

What are the possible fates of pyruvate?

Answer 46

Anaerobic catabolism -> lactate Aerobic catabolism -> Acetyl CoA -> TCA cycle and oxidative phosphorylation Synthetic --> Alanine Gluconeogenic --> converted back to glucose