Carbohydrates

Question 1

What are the advantages to carbohydrates being hydrophilic?

Answer 1

water soluble
attract water
cannot pass easily across membranes
already partially oxidised so take less oxygen than fatty acids for complete oxidation

Question 2

Name the 3 disaccharides

Answer 2

lactose, maltose, sucrose

Question 3

What are oligosaccharides?

Answer 3

Carbohydrates that are 3-12 units in length

Question 4

Where is glycogen stored in the body?

Answer 4

Liver and muscle

Question 5

Which enzymes are attached to the brush border of epithelial cells in the small intestine?

Answer 5

lactase, sucrase, amylase, isomaltase

Question 6

How do monosaccharides enter cells?

Answer 6

Via facilitated diffusion using transport proteins (GLUT1-GLUT5)

Question 7

Which tissues can metabolise glucose?

Answer 7

All tissues

Question 8

What is the normal blood glucose concentration?

Answer 8

5mM

Question 9

Which tissues have an absolute requirement for glucose?

Answer 9

red blood cells
white blood cells
kidney medulla 
lens of eye
brain

Question 10

What is the net ATP production of glycolysis?

Answer 10

2 ATP molecules (net) per glucose

Question 11

Why are there so many steps in glycolysis?

Answer 11

the chemistry is easier in smaller stages
allows for efficient energy conservation
gives versatility (interconnections to other pathways)
can be controlled

Question 12

What is different about glycolysis in cancer?

Answer 12

The rate of glycolysis can be up to 200 times faster

Question 13

What is DHAP and what can it be converted to?

Answer 13

DHAP is an intermediate of glycolysis (one of the C3 molecules produced after cleavage)
DHAP can be converted to glycerol phosphate

Question 14

Where and for what is glycerol phosphate used?

Answer 14

adipose tissue and liver

important for triglyceride and phospholipid biosynthesis

Question 15

What is the role of 2,3-bisphosphoglycerate?

Answer 15

important regulator of oxygen affinity of haemoglobin present in RBCs

Question 16

What are allosteric effectors?

Answer 16

Activators or inhibitors that bind to enzymes at a different site to the active site

Question 17

What product inhibits hexokinase in glycolysis?

Answer 17

glucose-6-phosphate

Question 18

Under what conditions is phosphofructokinase-1 increased in activity?

Answer 18

high AMP levels

high insulin levels

Question 19

Does a high insulin level increase or decrease the activity of pyruvate kinase?

Answer 19

It increases the activity (dephosphorylation so that ADP can be phosphorylated)

Question 20

Why can’t RBCs perform oxidative phosphorylation?

Answer 20

They don’t have any mitochondria

Question 21

Which enzyme converts pyruvate to lactate?

Answer 21

Lactate dehydrogenase

Question 22

Where is lactate normally metabolised?

Answer 22

In the liver and heart

Question 23

Define lactic acidosis

Answer 23

A high concentration of lactate in the blood (>5mM) which lowers the pH of the blood.

Question 24

Where is fructose metabolised?

Answer 24

In the liver

Question 25

What is the pathway for fructose metabolism and what are the enzymes that catalyse each stage?

Answer 25

Fructose -> Fructose-1-P (Fructokinase) Fructose-1-P -> 2-Glyceraldehyde-3-P (Aldolase)

Question 26

What disease do we have if fructokinase is missing and how would we spot it?

Answer 26

essential fructosuria | fructose in the urine

Question 27

What disease do we have is aldolase missing and what does this lead to?

Answer 27

Fructose intolerance | Fructose-1-P accumulates in the liver and causes liver damage

Question 28

Where is galactose metabolised?

Answer 28

In the liver

Question 29

What 3 enzymes are involved in galactose metabolism?

Answer 29

galactokinase galactose-1-P uridyl transferase UDP-galactose 4'-epimerase

Question 30

Which enzymes can be deficient to cause galactosaemia?

Answer 30

``` galactokinase deficiency (rare) transferase deficiency (common) ```

Question 31

In people with galactosaemia, what pathway does galactose enter?

Answer 31

galactose -> galactitol (aldose reductase) NADPH reoxidised to NADP+

Question 32

Which organs are affected by the accumulation of galactose-1-P?

Answer 32

liver kidney brain

Question 33

Why is it a bad thing that the NADPH levels are depleted in galactosaemia?

Answer 33

lowered NADPH prevents the maintenance of free sulphdryl groups so inappropriate disulphide bonds are formed this causes loss of structural and functional integrity in some proteins Also more susceptible to oxidative damage as cannot reduced GSSG back to GSH as efficiently

Question 34

Which enzyme catalyses the conversion of glucose-6-P to a five carbon sugar?

Answer 34

glucose-6-P dehydrogenase

Question 35

What are the functions of the pentose phosphate pathway?

Answer 35

produce NADPH in the cytoplasm | produce five carbon sugars for nucleotides

Question 36

What is the general formula of a carbohydrate?

Answer 36

(CH2O)n

Question 37

What does pyruvate dehydrogenase deficiency lead to?

Answer 37

Lactic acidosis | Because the pyruvate is converted into lactate instead

Question 38

How many oxidative steps does the TCA cycle have and how many of those steps release CO2?

Answer 38

4 oxidative steps | 2 of them release CO2

Question 39

How are Krebs cycle enzymes inhibited?

Answer 39

Allosterically

Question 40

Does the Krebs cycle function in the absence of oxygen?

Answer 40

No | NADH and FAD2H will build up and allosterically inhibit the action of the enzymes

Question 41

At the electron transport chain the majority of the electrons' energy is...

Answer 41

released as heat

Question 42

Which hydrogen carrier has a higher energy yield?

Answer 42

NADH

Question 43

What do uncouplers do?

Answer 43

Increase the permeability of the inner mitochondrial membrane to protons the protons no longer need to pass through ATP synthase to move down their electrochemical gradient

Question 44

Give 2 examples of electron transport inhibitors

Answer 44

cyanide | carbon monoxide

Question 45

Give 3 examples of uncouplers

Answer 45

dinitrophenol fatty acids dinitrocresol

Question 46

Which protein is most significant in brown adipose tissue and what does it do?

Answer 46

Thermogenin (UCP-1) | It is a natural uncoupling protein that is used when the body requires extra heat generation

Question 47

How many molecules of ATP are synthesised from glucose in normal aerobic respiration?

Answer 47

32 moles ATP per glucose