meh metabolism bb quiz and sm

Question 1

energy requirement for males and females

Answer 1

Question 2

how much food does the average adult eat in a year

Answer 2

500kg

Question 3

A 56 year old man who has been drinking heavily over the past month has developed alcoholic fatty liver disease. The triglyceride synthesis in his liver is dependent on the activity of the enzyme glycerol-3-phosphate dehydrogenase to form glycerol phosphate from an intermediate metabolite of glycolysis.

Which intermediate of glycolysis is the substrate of this enzyme?

Answer 3

Question 4

Which of the following is a feature of oxidative phosphorylation?

Answer 4

Oxidative phosphorylation utilises a proton gradient to synthesise ATP

Question 5

A 21 year old woman sits down in her seat on a train to rest. She has just run down the platform to avoid missing her train home. The majority of the ATP generated within her muscles to provide the energy required for contraction was generated by a rapid increase in the rate of glycolysis. Now she is resting, the rate of glycolysis in her muscles has declined again.

What would cause a decrease in the rate of this metabolic pathway?

Answer 5

A low cellular concentration of NAD+
The conversion of NAD+ to NADH occurs in step 6 of glycolysis (glyceraldehyde 3-phosphate to 1.3-bis phosphoglycerate). If NAD+ is not regenerated from the NADH then glycolysis would stop due to product inhibition of step 6.

Question 6

GLUT 1

Answer 6

GLUT1 is expressed at highest levels in erythrocytes and also in endothelial cells of the blood–brain barrier. It is responsible for the low level of basal glucose uptake required to sustain respiration. GLUT1 is not regulated by insulin.

Question 7

GLUT2

Answer 7

GLUT2 is a bidirectional transporter, allowing glucose to flow in both directions (both out of and into the cell). GLUT2 is the major transporter in liver allowing the hepatocytes to export glucose made by gluconeogenesis into the blood. It is also the primary glucose transporter in pancreatic beta cells allowing the glucose entry that ultimately regulates insulin synthesis and release by casuing an increase in ATP concentration. GLUT2 is not regulated by insulin

Question 8

GLUT3

Answer 8

GLUT3 is the main transporter in brain. It has a high affinity isoform for glucose allowing transport even in times of low plasma glucose concentrations (to ensure brain has enough glucose). GLUT3 is not regulated by insulin

Question 9

GLUT4

Answer 9

GLUT4 is the insulin-regulated glucose transporter expressed by skeletal muscle and adipose tissue. It is responsible for insulin-regulated glucose uptake.

Question 10

Answer 10

Glucose-6-phosphate

Question 11

The Krebs cycle occurs within the mitochondrial matrix.

Which enzyme links glycolysis to this cycle by catalysing the formation of acetyl-CoA?

Answer 11

Pyruvate dehydrogenase
Correct. Pyruvate dehydrogenase catalyses the formation of acetyl-CoA from pyruvate. This is a key reaction that you should know. The reaction is irrversible.

Question 12

Glucose is the most important source of energy for cells.

Which process produces the most energy in the form of ATP during the oxidation of this carbohydrate?

Answer 12

The electron transport chain
Correct. By far the most ATP is produced by the electron transport chain. This is an immportant point to understand. One molecule of glucose would yield 10 NADH and 2 FAD(2H) from glycolysis, pyruvate dehydrogenase and the citric acid cycle. Each NADH is capable of driving the synthesis of 2.5 ATP by the electron transport chain and each FAD(2H) 1.5 ATP molecules.

Question 13

NADPH is an important metabolite in red blood cells as is protects against cellular damage resulting from oxidative stress.

Which metabolic pathway is the major source of this metabolite in these cells?

Answer 13

Pentose phosphate pathway
The pentose phosphate pathway. Since red blood cells lack mitochondria, other pathways producing NADPH are not available. Note the pentose phosphate pathway is also important for production of C5 sugars required for nucleotide synthesis (in other cells types) but since red blood cells also do not contain a nucleus, the main function of the pentose phosphate pathway in red blood cells in NADPH production

Question 14

A 5 month old boy is diagnosed with galactosaemia due to deficiency in the enzyme galactokinase.

Which substance would accumulate in the boy’s tissues as a result of this enzyme deficiency?

Answer 14

Galactitol

Question 15

The Krebs cycle occurs within the mitochondrial matrix.

Which molecule combines with acetyl-CoA to form citrate in the first step of this cycle?

Answer 15

Oxaloacetate

Question 16

Lipases are enzymes that hydrolyse the ester linkages of triacylglycerol allowing the fatty acids to be released for energy production.

After two additional reactions, the glycerol also released upon this hydrolysis can enter which pathway?

Answer 16

Glycolysis
Correct. After phosphorylation to glycerol phosphate and conversion to dihydroxyacetone phosphate, glycerol can enter glycolysis. It can also act as a precursor for gluconeogenesis by these same reactions.

Question 17

A 21 year old male rugby player has gained 8 kg in weight over the summer, mainly from an increased consumption of pasta and pizza. The excess carbohydrates in his diet have been converted to fat in his liver, a process promoted by the actions of the hormone insulin.

The activity of which key regulatory enzyme in the process of lipogenesis is increased by this hormone?

Answer 17

Acetyl-CoA carboxylase
Correct. Well done! Acetyl-CoA carboxylase produces malonyl-CoA from acetyl-CoA which is needed for synthesis of fatty acids

Question 18

As part of a routine NHS health check a 56 year old man is found to have a total plasma cholesterol level of 15 mM (normal less than 5 mM). The majority of cholesterol transported around the body in lipoprotein particles is in the form of cholesterol ester.

Which enzyme catalyses the formation of these esters?

Answer 18

Lecithin Cholesterol Acyltransferase (LCAT)
Correct. Well done! Cholesterol is converted into cholesterol esters by the enzyme Lecithin Cholesterol Acyltransferase. Acyl-coenzyme A:cholesterol acyltransferases also fulfil this role. Even if you could not remember the name of LCAT you could have worked out the correct option from the name of the enzyme and a process of elimination….a good technique for SBA questions!

Question 19

A 12 year old boy completes a 100m race at school. During the race the process of glycogenolysis resulted in the production of glucose-6-phosphate in his skeletal muscles.

What would be the fate of this metabolite in this tissue under these conditions?

Answer 19

enters glycolysis

Question 20

Lipoprotein particles function to transport hydrophopbic lipid molecules in the aqueous environment of the blood.

Which of the different types of these particles have the shortest half life?

Answer 20

IDL
Correct. IDL is a short lived precursor leading to the formation of LDL particles from VLDL particles released from the liver (VLDL → IDL → LDL)

Question 21

A newborn baby boy has his routine NHS blood spot screening test at 5 days old. The results show that he has homoystinuria.

What is the mode of inheritance of this condition?

Answer 21

Autosomal recessive
Correct. Well done! The majority of inborn errors of metabolism show this form of inheritance although there are some exceptions to this rule. With autosomal recessive diseases both parents of an affected person are carriers. Not typically seen in every generation.

Question 22

Oxidants are reactive molecules that are produced both inside the body and in the environment. They can react with cellular components (e.g. protein, DNA, lipids) resulting in damage to molecules leading to disease and inflammation.

What is a common endogenous source of this type of reactive molecule?

Answer 22

Electron transport chain
Correct. Well done!
Occasionally electrons can escape from the electron transport chain and react with dissolved O2 to form superoxide (which is an reactive oxygen species).

The other answers were incorrect as they are exogenous sources.

Question 23

comparison of FA synthesis and Beta oxidation

Answer 23

Question 24

fatty acid synthesis and oxidation difference

Answer 24

Fatty acid synthesis occurs in the cytoplasm. Fatty acid oxidation however occurs in mitochondria.

Question 25

A 20 year old male student drinks a bottle of wine over the course of a meal in a restaurant. He wakes the next morning with a slight headache but after breakfast feels back to normal. During the metabolism of the ethanol that he had consumed the toxic metabolite acetaldehyde was produced in his liver.

What property of the enzyme aldehyde dehydrogenase limited the toxic effects of this metabolite?

Answer 25

Has a low Km for acetaldehyde
CORRECT. Acetaldehyde toxicity is normally kept to a minimum by aldehyde dehydrogenase because this enzyme has a low Km for acetaldehyde

Question 26

A 5 day old baby boy is identified as having Homocystinuria from his routine NHS blood spot test.

What vitamin supplement could potentially help control the levels of homocysteine in this patient?

Answer 26

B6

Question 27

Reactive oxygen species (ROS) damage to proteins can result in protein glycosylation. (TRUE or FASE?)

Answer 27

False
CORRECT. Glycosylation is a normal post-translational modification to some proteins not a consequence of oxidative damage. Oxidative damage to proteins by free radicals includes hydroxylated adducts, di-tyrosine dimers, inappropriate disulphide bond formation and the formation of ring open species.

Question 28

A 33 Year old male goes on hunger strike as a political protest whilst in prison. He has not eaten any food for 30 days and over this period has lost 50% of his skeletal muscle mass through the process of proteolysis.

Which hormone would promote this process thus providing amino acids to be used as an energy source?

Answer 28

Cortisol
Correct. Well done! One of the actions of cortisol is to promote proteolysis

Question 29

A 25 year old man who was born in Albania is referred to the neurological unit due to a history of seziures and behavioural difficulties including frequent temper outbursts and episodes of self-harm. He also experiences tremors and jerking movements in his arms and legs and has an odd musty smell to his breath and skin. Further investigation reveals that the man has Phenylketonuria (PKU) which had gone undetected due to him being born in a country without a neonatal screening programme in place.

Which enzyme is deficient in this patient?

Answer 29

Phenylalanine hydroxylase

Question 30

A 20 year old male with Phenylketonuria (PKU) has been on a modified diet since a few days after birth when he was found to have this autosomal recessive condition by a routine NHS blood spot (“heel prick”) test. By altering and monitoring his diet throughout his life he has been able to avoid the devastating detrimental consequences of this disease.

What would be the appropriate dietary modification for this patient?

Answer 30

Low phenylalanine with enriched tyrosine

Question 31

A 38 year old woman presents to the emergency department with severe vomiting (emesis), abdominal cramps and diarrhoea after ingesting some death cap mushrooms which she had mistaken for an edible species. Blood tests show that her plasma ALT enzyme levels are twenty times above normal.

What is the normal function of this enzyme?

Answer 31

Converts alanine to glutamate.

Question 32

time course of glucose utilisation

Answer 32

Question 33

A 19 year old male medical student skips breakfast to avoid being late for a lecture. In his rush he forgets his wallet so is also unable to buy lunch. In order to maintain blood glucose levels, thus avoiding hypoglycaemia, later that day his liver starts to generate glucose through the metabolic pathway of gluconeogenesis.

Which enzyme is a major control point for this pathway?

Answer 33

Fructose 1,6-bisphosphatase
Yes that’s correct. The two major control enzymes for gluconeogenesis are Phosphoenolpyruvate carboxykinase (PEPCK) and Fructose 1,6-bisphosphatase

Question 34

A 16 year old boy with type 1 diabetes starts to experience weakness and nausea and is unable to concentrate. He has developed hypoglycaemia as a result of taking his insulin injection prior to leaving his house but then skipping lunch and not eating for the past few hours.

What effect would the hormone in the boy’s injection normally have on his metabolism?

Answer 34

Dephosphorylates glycogen synthase
Correct. Well done, this was a tricky distinction level question! When blood-glucose levels are high, insulin stimulates the synthesis of glycogen by triggering a signalling pathway that activates the enzyme protein phosphatase 1 which dephosphorylates glycogen synthase increaseing activity.

Question 35

A 19 year old man starts to feel hungry after not eating anything since his lunch 8 hours ago. His liver begins to undergo the process of gluconeogenesis after its glycogen stores are depleted.

Which molecule is not a possible substrate for this process?

Answer 35

Acetyl-CoA
Correct. Well done!
The reaction converting pyruvate (3C) to acetyl-CoA(2C) via pyruvate dehydrogenase is irreversible, therefore acetyl CoA cannot be converted to glucose in humans. If the acetyl-CoA were to enter the citric acid cycle there can still be no net synthesis of glucose from acetyl-CoA because acetyl-CoA (a 2 carbon molecule) enters the citric acid cycle by reacting with oxaloacetate (a 4 carbon molecule) to produce citrate (a 6 carbon molecule). During the citric acid cycle 2 carbons are lost as carbon dioxide so there is no net gain of carbon to make glucose from oxaloacetate entering gluconeogenesis.

Question 36

A dietitian analysing the diet of a 56 year old man who had recently recovered from a myocarial infarction found that he was consuming an unusually high amount of triacylglycerol.

What class of lipoprotein particle transports this type of nutrient from the intestine to tissues such as muscle and adipose?

Answer 36

Correct. Chylomicrons transport dietary triacylglycerol from the intestine to peripheral tissues

Question 37

Name two sources of free radicals (oxidants) inside cells (i.e. endogenous sources)?

Answer 37

The electron transport chain is a major source of free radicals since electrons can occasionally accidently escape the chain and react with dissolved O2 to form superoxide. Other postential sources include peroxidase enzymes, nitric oxide synthase (nitric oxide is a free radical) lipooxygenases, NADPH oxidase enzyme (used in “respiratory burst”), Xanthine oxidase and Monoamine oxidase.

Question 38

A 5 day old baby boy is diagnosed with phenylketonuria (PKU) after his routine NHS “heel prick” test. If left untreated his condition could result in a significant inhibition of brain development through disturbances in energy metabolism and neurotransmitter synthesis. Dietary modifications however can prevent the vast majority of the detrimental effects of this disease.

Which amino acid would become dietary essential in patients with this condition?

Answer 38

Tyrosine
Correct! PKU is a deficiency in phenylalanine hydroxylase, meaning phenylalanine cannot be converted into tyrosine. Defective phenylalanine hydroxylase means that excess dietary phenylalanine cannot be degraded via the normal pathway. Instead it accumulates in the blood until its concentration exceeds the renal threshold and it is excreted in the urine. In addition, as its plasma concentration increases it is metabolised via alternate pathways. The most significant of these is transamination to produce phenylpyruvate, the major phenylketone found in the urine of patients suffering from PKU. PKU along with other inborn errors of metabolism are tested for in the blood test all new-born babies must undergo, called the heel prick test.

Question 39

Answer 39

C
Correct. Well done!
After absorption of fatty acids and diglycerides, triglycerides are resynthesised and packaged into chylomicrons within enterocytes before entering lacteals and draining into the lymphatic system. The chylomicrons subsequently enter the bloodstream at the left subclavian vein when the lymphatic system connects with the bloodstream at the thoracic duct.

Within cells FAs are converted to acetyl-CoA by beta oxidation. Acetyl-Co A then enters the krebs cycle where NADH, FADH2 and GTP made. NADH and FADH2 are then used in oxidative phosphorylation forming ATP (energy for the cell).

Question 40

A 5 day old baby has lost weight since birth, is vomiting after every breastfeed and has yellow discoloration of his sclera and skin. He is referred to the paediatric unit and subsequent investigations reveal that he has galactosaemia due to galactose-1-phosphate uridylyltransferase deficiency.

What would be the metabolic consequence of an increased activity of the enzyme aldose reductase in this patient as a result of his condition?

Answer 40

Lowered NADPH concentration
Correct. Well done! Aldose reductase forms Galactitol from Galactose, in the process using NADPH. This leads to lowered NADPH concentrations in the cell

Question 41

metabolic responses to chronic alcohol consumption

Answer 41

Question 42

A 5 day old baby girl is diagnosed with PKU following the results of a Heel Prick Test. The doctor advises that the child follows a strict low phenylalanine diet, avoiding high protein foods in order to avoid the risk of abnormalities in brain development.

If left untreated how would this condition disrupt normal brain development?

Answer 42

Saturation of the Large Neutral Amino Acid Transporter (LNAAT) by phenylalanine limits neurotransmitter synthesis
Correct. Well done! This was a distinction level question. Phenylalanine is a large neutral amino acid (LNAA) and competes for transport across the blood brain barrier via LNAAT. Excess phenylalanine in PKU can therefore saturate this transporter and the levels of other LNAA in the brain are decreased leading to protein/neurotransmitter synthesis being inhibited and brain development affected.

Question 43

A 5 day old baby boy tests positive for homocystinuria in his routine NHS Newborn blood spot test. Subsequent investigations confirm that he has indeed inherited this autosomal recessive disorder of amino acid metabolism and he is placed on a modified diet to limit the effects of the disease.

A diet low in which amino acid would be most appropriate for this patient?

Answer 43

methionine

Question 44

Which reactive oxygen species is produced when molecular oxygen (O2) gains an electron?

Answer 44

superoxide

Question 45

trace elements

Answer 45

copper, zinc, iodine, selenium and chromium.

Question 46

A worried mother brings her child to A&E for the third time in four months. The child has broken their wrist, and suffered previously with a broken arm, collarbone and multiple finger fractures. You examine the child and find that they are short in stature. What vitamin deficiency has caused these effects?

Answer 46

vitD rickets

Question 47

What type of bond is the main bond within fats?

Answer 47

ester

Question 48

What are the main purposes of the Pentose Phosphate Pathway?

Answer 48

The main purposes of the pentose pathway are to provide 5C sugar phosphates for DNA / RNA synthesis, but also to produce NADPH, used to help maintain the structure of proteins, DNA and the lipid bilayer, especially in red blood cells, via the maintenance of glutathione (GSH). It contributes a small amount of 5C sugar phosphates for glycolysis but this is a very minor role.

Question 49

A deficiency in which molecule will cause Heinz bodies in red blood cells?

Answer 49

NADPH is produced mainly through the pentose phosphate pathway, and is used to maintain the SH groups on proteins in their reduced state, which is important for maintaining protein function and preventing aggregation. This process is especially important in red blood cells because they cannot perform the electron transport chain due to having no mitochondria. If proteins in red blood cells aggregate, Heinz bodies form, causing the red blood cell to be destroyed by the spleen.

Question 50

Which of these would increase the action of phosphofructokinase through allosteric regulation?

Answer 50

Phosphofructokinase is allosterically regulated, inhibited by high concentrations of ATP, and stimulated by insulin. This is because if there is lots of ATP, glycolysis needs to slow down, but if insulin is present, it means that there is lots of glucose that needs to be metabolised or stored.

Question 51

Which of these reactions in glycolysis are irreversible?

Answer 51

1 3 10

Question 52

Which of the following enzymes is the enzyme used to catalyse stage 10 of glycolysis?

Answer 52

pyruvate kinase

Question 53

Which of the following enzymes is the enzyme used to catalyse stage 1 of glycolysis in the liver?

Answer 53

Glucokinase is the correct answer here, because it catalyses the 1st stage of glycolysis in the liver only. Hexokinase catalyses this reaction in the rest of the body. Pyruvate kinase catalyses the 10th stage of glycolysis. Lactate dehydrogenase catalyses the reaction turning pyruvate into lactate.§

Question 54

What co-factors does pyruvate dehydrogenase need to work?

Answer 54

Vitamin B and NAD+

Question 55

Why is the Link Reaction irreversible?

Answer 55

releases co2

Question 56

Which of the following is produced in beta oxidation of fatty acids?

Answer 56

NADH

Question 57

how glycerol metabolism can be used to produce ATP?

Answer 57

The correct answers here are that glycerol metabolism produced DHAP and NADH which can be used in respiration. Glycerol metabolism uses up NAD+ when it forms the NADH, and glycerol metabolism does not produce cartinine.

Question 58

how do you go between LDL and HDL

Answer 58

To turn LDL into HDL, add TAG

To turn HDL into LDL, add cholesterol esters

Question 59

Which of these amino acids is used for the production of serotonin?

Answer 59

Tryptophan is the correct answer in this case. Histidine is used for the production of histamine. Glycine is used in the production of haem. Threonine has no special function.

Question 60

Which of the following amino acids is also used for glutathione production?

Answer 60

Cysteine is the correct answer to this question. Glutamate is used in the production of GABA, tyrosine is used in the production of melanin, and alanine has no special function.

Question 61

Describe the molecular basis for Re-feeding Syndrome.

Answer 61

The correct answer here is that ammonia toxicity causes harm to the patient when protein is consumed because the enzymes of the urea cycle have been downregulated in times of low protein intake. Ammonia causes damage because it interferes with the Krebs Cycle, the blood-brain barrier, protein synthesis and pH in high concentrations.

Question 62

In which of these common diseases does oxidative damage play a part in the disease process?

Answer 62

Oxidative damage is a part of the disease process in many diseases, like cancer, chronic obstructive pulmonary disease, cardiovascular disease, multiple sclerosis and Parkinson’s Disease. It does not play a part in asthma or epilepsy.

Question 63

What is the function of the enzyme glycogen synthase?

Answer 63

Glycogen synthase adds glucose molecules to existing branches on glycogen through the formation of α1-4 bonds

Question 64

Which of the following signs and symptoms would you expect to see in a baby with Von Gierke’s Disease?

Answer 64

The protuberant abdomen (meaning an abdomen looking like a tuber like a potato) is correct; it occurs due to hepatomegaly, as glycogen is deposited but cannot be fully broken down, so it remaining in the liver.

Sweating and pallor relieved by feeding is also correct; this is due to hypoglycaemia, as glycogen cannot be broken down into glucose to raise blood glucose levels.

High blood fatty acid levels occur because the body performs gluconeogenesis to compensate for the low blood glucose.

Question 65

Life threatening hypothermia

Answer 65

Life threatening hypothermia is classified as a core body temperature below 28°C.

Question 66

Life threatening hypothermia

Answer 66

Life threatening hypothermia is classified as a core body temperature below 28°C.

Question 67

Which of these diseases commonly affect thermoregulation?

Answer 67

MS and DM

Question 68

risk factors for gestational diabetes

Answer 68

Risk factors include maternal BMI over 25, maternal age over 25, and a family history of any sort of diabetes or macrosomia.