Metabolism Flashcards
What is the basic reaction by which food is converted to ATP?
Oxidation
- Which enzyme(s) are responsible for initial glucose phosphorylation after entry into the cell?
- Which enzyme reverses this reaction?
- Glucokinase - liver
Hexokinase - other tissues
- Glucose-6-phosphatase
GLYCOGENESIS
glucose 6-phosphate is converted to glucose-1-phosphate and then uridine diphosphate glucose before becoming glycogen.
Which is the important enzyme involved in glycogenolysis?
Glycogen phosphorylase
How many moles of ATP are formed from a single mole of glucose?
38
What is the end product of the glycolytic pathway?
Two pyruvic acid molcules
How many ATPs are formed from glycolysis?
4 are formed but 2 are required in the initial phosphorylation of glucose so the net gain is two ATP
What vitamin is acetyl-CoA a derivative of?
Vitamin B5 - patothenic acid
What is the net reaction of the CAC following the processing of one molecule of glucose?
What is the starting molecule of the CAC?
Oxaloacetate
Which vitamin is required to form NADH?
Nicotinamide (vitamin B3)
What group of enzymes splits hydrogen from substrates in glucose breakdown pathways?
Dehydrogenases
What group of enzymes splits away CO2 in the various glucose breakdown pathways?
Decarboxylases
What is oxidation vs. reduction?
Oxidation = removal of electrons
Reduction = addition of electrons
What is the role of cytochrome oxidase in the electron transport chain?
To reduce oxgen by combining it with H20.
Summarise ATP formation during the breakdown of glucose
- Glycolysis - formation of net 2 ATP
- CAC - 2 ATP
- 24 hydrogens produced from the above, which are then oxidised in the mitochondrial chemiosmotic mechanism.
= 38 ATP molecules
What is the importance of the enzyme phosphofructokinase in the glucose metabolic pathway?
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
What are the most common fatty acids present in human triglycerides?
- Stearic acid
- Oleic acid
- Palmitic acid
What is the plasma T½ of a chylomicron?
Approz. 1h
What is the role of lipoprotein lipase and where is it located?
Its role is to release triglycerides from chylomicrons so that they can diffuse into cells.
Location = capillary wall (particularly of adipose tissues)
What is the role of apoliprpteins (e.g. Apo E and Apo B) in lipid metabolism?
They mediate clearance of chylomicron remnants from the blood by the liver.
Which type of lipoproteins transport TG to the following:
- Adipose tissue
- Liver
- VLDL transport TG to adipose tissue
- IDL transported to liver in an ApoE mediated process and LDLs are trasported by ApoB mediated transport
What are the liver’s roles in fat metabolism?
- Generation of energy from triglycerides
- Synthesis of fatty acids from carbodydrates +/- amino acids
- Production of other lipid compounds e.g. cholesterol and phospholipids from fatty acids
Which molecule is required to transport fatty acids into the mitochondria prior to beta-oxidation?
Carnitine
Carnitine is a derivative of lysine
What are the end products of each cycle of beta-oxidation of fatty acids?
Acetyl-CoA and 4H+
How is acetoacetic acid formed chemically?
2xacetyl-CoA + H2O
What ketones are detected by a urine dipstick pad?
Predominantly acetoacetate and acetone
What are the three main steps in TG synthesis from excess carbohydrate?
- Formation of melanyl-CoA from acetyl-CoA by acetly-CoA carboxylase
- The above starts to form a fatty acid which is elongated by the addition of succusive acetyl-CoA molecules using NADPH and H+
- Glycerol is synthesised from alpha-glycerophosphate (a product of glycolysis)
Which phospholipid is choline required for the syntehsis of?
Sphingomyelin (amoung others)
Which phospholipids is inositol involved in the synthesis of?
Cephalins
List 5 main processes phospholipids are required for
- Formation of cell membranes
- Formation of lipoproteins
- Nervous development/funciton (sphinomyelin)
- Thromboplastin formation (cephalin)
- Chemical reactions - donation of phosphate radicals
Which enzyme is responsible for cholesterol synthesis?
3-hydroxy-3-methylglutaryl CoA reductase
Which enzyme is required for the transformation of one amino acid into another?
Aminotransferase (aka. transainase)
Which amino acids can be used in transamination?
Asparaginine
Aspartic acid
Glutamine
Which vitamin is important in the formation of transaminases?
Vitamin B6 - pyroxidine
What are the main amino acids found in the urea cycle?
Ornithine
Citrulline
Arginine - this is actually the only one on the list of the 20 amino acids in the human body.
What are Kupffer cells?
Reticuloendothelial cells of the liver (macrophages).
The presence of which compoud in the liver allows storage of iron?
Apoferritin + Fe –> ferritin
Explain the formation and excretion of bilirubin
Where are the feeding and satiety centres of the hypothalamus located?
Feeding centre = lateral nuclei
Satiety centre = ventromedial nuclei.
What are the main neurons in the arcuate nucleus of the hypothalamus that result in increased/decreased hunger signals?
- Increase: agouti-related protein (AGRP) and neuropeptide Y producing neurons
- Decrease: proopiomelanocortin (POMC) and cocain-amphetamine related transcript (CART) neurons -these produce alpha-MSH.
Which MCRs are most important in the regulation of feeding behaviours?
What is the effect of activation of these receptors?
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.
Where is MCR-4 activated with regards to its role in energy expenditure?
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.
What is thought to be the role of AGRP in hunger signalling?
It antagonises the MCR-4 receptor.
Which neurotransmitter is released to increase hunger? Which receptor does it act on?
Neuropeptide Y (NYP), the NYP1
Ways in which leptin may impact on energy storage
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)
What is the enzyme that activates the vitamin K dependent co-facotors?
Bonus = what is the action of this enzyme?
Carboxylase epoxidase
Carboxylates glutamic acid residues on inactive coagulation factors. (II, VII, IX, X, C, S, Z)
How much of bodily iron (as a fraction) is in the form of haemoglobin?
2/3
Michaelis-Menten equation
Which area of the hypothalamus detects temperature changes?
Temperature sensitive neurons in the anterior pre-optic area
Which area of the hypothalamus integrates temperature sensing afferents?
The posterior hypothalamus
Where in the brain is the motor centre for shivering located?
Dorsomedial hypothalamus next to the wall of the third ventricle
Which interleukin is important in increasing the hypothalamic set point in fever?
IL-1
