Metabolism

Question 1

What is the basic reaction by which food is converted to ATP?

Answer 1

Oxidation

Question 2

1. Which enzyme(s) are responsible for initial glucose phosphorylation after entry into the cell?
2. Which enzyme reverses this reaction?

Answer 2

1. Glucokinase - liver

Hexokinase - other tissues

2. Glucose-6-phosphatase

Question 3

GLYCOGENESIS

Answer 3

glucose 6-phosphate is converted to glucose-1-phosphate and then uridine diphosphate glucose before becoming glycogen.

Question 4

Which is the important enzyme involved in glycogenolysis?

Answer 4

Glycogen phosphorylase

Question 5

How many moles of ATP are formed from a single mole of glucose?

Answer 5

38

Question 6

What is the end product of the glycolytic pathway?

Answer 6

Two pyruvic acid molcules

Question 7

How many ATPs are formed from glycolysis?

Answer 7

4 are formed but 2 are required in the initial phosphorylation of glucose so the net gain is two ATP

Question 8

What vitamin is acetyl-CoA a derivative of?

Answer 8

Vitamin B5 - patothenic acid

Question 9

What is the net reaction of the CAC following the processing of one molecule of glucose?

Question 10

What is the starting molecule of the CAC?

Answer 10

Oxaloacetate

Question 11

Which vitamin is required to form NADH?

Answer 11

Nicotinamide (vitamin B3)

Question 12

What group of enzymes splits hydrogen from substrates in glucose breakdown pathways?

Answer 12

Dehydrogenases

Question 13

What group of enzymes splits away CO₂ in the various glucose breakdown pathways?

Answer 13

Decarboxylases

Question 14

What is oxidation vs. reduction?

Answer 14

Oxidation = removal of electrons

Reduction = addition of electrons

Question 15

What is the role of cytochrome oxidase in the electron transport chain?

Answer 15

To reduce oxgen by combining it with H20.

Question 16

Summarise ATP formation during the breakdown of glucose

Answer 16

1. Glycolysis - formation of net 2 ATP
2. CAC - 2 ATP
3. 24 hydrogens produced from the above, which are then oxidised in the mitochondrial chemiosmotic mechanism.

= 38 ATP molecules

Question 17

What is the importance of the enzyme phosphofructokinase in the glucose metabolic pathway?

Answer 17

It is involved in the formation of fructose 1,6-diphosphate (early stage in glycolysis).

PPK can be inhibited by ATP and this represents a feedback mechanism by which cellular energy metabolism is regulated.

Citrate also inhibits PPK

Question 18

What are the most common fatty acids present in human triglycerides?

Answer 18

1. Stearic acid
2. Oleic acid
3. Palmitic acid

Question 19

What is the plasma T½ of a chylomicron?

Answer 19

Approz. 1h

Question 20

What is the role of lipoprotein lipase and where is it located?

Answer 20

Its role is to release triglycerides from chylomicrons so that they can diffuse into cells.

Location = capillary wall (particularly of adipose tissues)

Question 21

What is the role of apoliprpteins (e.g. Apo E and Apo B) in lipid metabolism?

Answer 21

They mediate clearance of chylomicron remnants from the blood by the liver.

Question 22

Which type of lipoproteins transport TG to the following:

1. Adipose tissue
2. Liver

Answer 22

1. VLDL transport TG to adipose tissue
2. IDL transported to liver in an ApoE mediated process and LDLs are trasported by ApoB mediated transport

Question 23

What are the liver’s roles in fat metabolism?

Answer 23

1. Generation of energy from triglycerides
2. Synthesis of fatty acids from carbodydrates +/- amino acids
3. Production of other lipid compounds e.g. cholesterol and phospholipids from fatty acids

Question 24

Which molecule is required to transport fatty acids into the mitochondria prior to beta-oxidation?

Answer 24

Carnitine

Carnitine is a derivative of lysine

Question 25

What are the end products of each cycle of beta-oxidation of fatty acids?

Answer 25

Acetyl-CoA and 4H⁺

Question 26

How is acetoacetic acid formed chemically?

Answer 26

2xacetyl-CoA + H₂O

Question 27

What ketones are detected by a urine dipstick pad?

Answer 27

Predominantly acetoacetate and acetone

Question 28

What are the three main steps in TG synthesis from excess carbohydrate?

Answer 28

1. Formation of melanyl-CoA from acetyl-CoA by *acetly-CoA carboxylase* 2. The above starts to form a fatty acid which is elongated by the addition of succusive acetyl-CoA molecules using NADPH and H⁺ 3. Glycerol is synthesised from alpha-glycerophosphate (a product of glycolysis)

Question 29

Which phospholipid is choline required for the syntehsis of?

Answer 29

Sphingomyelin (amoung others)

Question 30

Which phospholipids is inositol involved in the synthesis of?

Answer 30

Cephalins

Question 31

List 5 main processes phospholipids are required for

Answer 31

1. Formation of cell membranes 2. Formation of lipoproteins 3. Nervous development/funciton (sphinomyelin) 4. Thromboplastin formation (cephalin) 5. Chemical reactions - donation of phosphate radicals

Question 32

Which enzyme is responsible for cholesterol synthesis?

Answer 32

*3-hydroxy-3-methylglutaryl CoA reductase*

Question 33

Which enzyme is required for the transformation of one amino acid into another?

Answer 33

Aminotransferase (aka. transainase)

Question 34

Which amino acids can be used in transamination?

Answer 34

Asparaginine Aspartic acid **Glutamine**

Question 35

Which vitamin is important in the formation of transaminases?

Answer 35

*Vitamin B6 - pyroxidine*

Question 36

What are the main amino acids found in the *urea cycle?*

Answer 36

Ornithine Citrulline Arginine - this is actually the only one on the list of the 20 amino acids in the human body.

Question 37

What are *Kupffer cells?*

Answer 37

Reticuloendothelial cells of the liver (macrophages).

Question 38

The presence of which compoud in the liver allows storage of iron?

Answer 38

**Apoferritin** + Fe --\> ferritin

Question 39

Explain the formation and excretion of bilirubin

Answer 39

Question 40

Where are the feeding and satiety centres of the hypothalamus located?

Answer 40

Feeding centre = *lateral nuclei* Satiety centre = *ventromedial nuclei*.

Question 41

What are the main neurons in the *arcuate* nucleus of the hypothalamus that result in increased/decreased hunger signals?

Answer 41

1. Increase: *agouti-related protein (AGRP)* and *neuropeptide Y* producing neurons 2. Decrease: *proopiomelanocortin (POMC) and cocain-amphetamine related transcript* (*CART*) neurons -these produce alpha-MSH.

Question 42

Which MCRs are most important in the regulation of feeding behaviours? What is the effect of activation of these receptors?

Answer 42

MCR-3 and MCR-4 MCR-3 is present on POMC/CART (increases activity) and NYP/AGRP (decreases activity) neurons MCR-4 is presnt in the paraventricular nucleas of the hypothalamus These effects all act to decrease appetite.

Question 43

Where is MCR-4 activated with regards to its role in energy expenditure?

Answer 43

The PVN of the hypothalamus is where the MCR-4 receptor is present and to some degree it is present int the *nucleus tractus solitarius*.

Question 44

What is thought to be the role of AGRP in hunger signalling?

Answer 44

It antagonises the MCR-4 receptor.

Question 45

Which neurotransmitter is released to increase hunger? Which receptor does it act on?

Answer 45

Neuropeptide Y (NYP), the NYP₁

Question 46

Ways in which leptin may impact on energy storage

Answer 46

Inhibition of the feeding centre and stimulation of the satiety centre Increase production of CRH (an anorexigenic hormone) Increase sympathetic tone (increasing BMR) Decrease insulin production (reducing energy storage)

Question 47

What is the enzyme that activates the vitamin K dependent co-facotors? Bonus = what is the action of this enzyme?

Answer 47

Carboxylase epoxidase Carboxylates glutamic acid residues on inactive coagulation factors. (II, VII, IX, X, C, S, Z)

Question 48

How much of bodily iron (as a fraction) is in the form of haemoglobin?

Answer 48

2/3

Question 49

*Michaelis-Menten equation*

Answer 49

Question 50

Which area of the hypothalamus detects temperature changes?

Answer 50

Temperature sensitive neurons in the **anterior pre-optic area**

Question 51

Which area of the hypothalamus integrates temperature sensing afferents?

Answer 51

The posterior hypothalamus

Question 52

Where in the brain is the motor centre for shivering located?

Answer 52

Dorsomedial hypothalamus next to the wall of the third ventricle

Question 53

Which interleukin is important in increasing the hypothalamic set point in fever?

Answer 53

IL-1