Glucose Metabolism Flashcards
What is the difference between catabolic and anabolic reactions and pathways
In catabolic reactions and pathways, substances are broken down to release energy needed for chemical and mechanical processes in the body. In anabolic reaction or pathways, larger molecules are synthesised from smaller substances, which requires energy, to build molecules needed for storage or structures in the cell and the body.
What are the three main stages of glucose metabolism and where do they occur
Glycolysis (cytoplasm), TCA/Krebs cycle (mitochondrial matrix), oxidative phosphorylation (mitochondrial inner membrane)
How is the activation energy in glucose breakdown overcome
The enzymes involved in the step-by-step breakdown of glucose can lower the activation energy required for each step to such extent that the body temperature suffices to provide this energy
How efficient is glucose metabolism and how can you calculate this
Roughly 40%, calculated by dividing the energy stored in 38 ATP molecules (38 x 31 kJ/mol) by energy in glucose (2872 kJ/mol)
How much energy is released in hydrolysis of ATP
31 kJ/mol
In what six types of reaction can all metabolic reaction be categorised
Redox reaction, litigation requiring ATP cleavage, isomerisation, group transferring, hydrolysation, group addition or removal
Where does glycolysis occur and how much net ATP and NADH does it produce
In the cytoplasm, produces net 2 ATP and 2 NADH
In what two stages can glycolysis be divided
Formation of high energy compound requiring ATP investment (step 1-5), breakdown/splitting of high energy compound resulting in ATP production (step 6-10)
What enzyme commits glucose to the cell metabolism
Hexokinase, converts glucose to glucose-6-phosphate unable to be transported across membrane
Why is glucose-6-phosphate isomerised
Fructose-6-phosphate can in glycolysis be split into more equal parts than glucose-6-phosphate
What enzyme is key in the control of the rate of glycolysis
Phosphofructokinase, converts fructose-6-phosphate into fructose-1,6-biphosphate, controls entry of sugars into glycolysis
What is the substrate of aldolase and what are the product
Aldolase splits fructose-1,6-biphosphate (substrate) into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate
What enzyme is cause of the only fatal glycolytic enzymopathy and what does it catalyse
Triose phospate isomerase, converts dihydroxyacetone phosphate to glyceraldehyde 3-phosphate
What are the cofactors for glyceraldehyde-3-phosphate dehydrogenase and product
NADH and inorganic phosphate (cofactors), 1,3-biphosphoglycerate (product)
In what steps of glycolysis are ATP produced
In step 7 and step 10, conversion of 1,3-biphosphoglycerate to 3-phosphoglycerate and conversion of phosphoenolpyruvate to pyruvate
What enzyme isomerises 3-phosphoglycerate and what is the product
phosphoglycerate mutase, 2-phosphoglycerate (product)
What type of reaction does enolase catalyse and what is the product
Hydrolisation/group transfer, phosphoenolpyruvate
What is the enzyme involved in production of pyruvate in last step glycolysis
Pyruvate kinase
Which two enzymes are involved in alcohol fermentation of pyruvate
Pyruvate decarboxylase and alcohol dehydrogenase, pyruvated converted sequentially into acetaldehyde and ethanol
Which types of organisms is alcohol fermentation characteristic of
Yeasts
What enzyme is involved in lactate generation from pyruvate
Lactate dehydrogenase
Which types of organisms use lactate generation
Animals and certain bacteria
How is NAD+ replenished in hypoxic state of cell
By reducing pyruvate to lactate, oxidising NADH to NAD+ to allow glycolysis to continue
What is creatine phosphate in cell used for
To provide an ATP buffer during strenuous exercise, storing high energy phosphate which can be converted to ATP by creatine kinase
How is ATP generated and used during different stages of exercise
In first second, existing ATP concentration is used up. In first four seconds, creatine phosphate releases phosphate to ATP to buffer drop in ATP levels. Then anaerobic respiration (glycolysis) takes over ATP production while level of aerobic respiration slowly increases and takes over
Why do athletes use creatine as dietary supplement
Because this can increase the amount of creatine phosphate in cells and thus provide more energy for the first few seconds of strenuous excercise in muscle cells
Which enzyme is needed to enter TCA cycle and what substrates are needed
Pyruvate dehydrogenase complex, pyruvate and HS-coenzyme A are needed
What origin does Coenzyme A have and why
The RNA basis of coenzyme A suggest that it originates from RNA
How can acetyl-CoA donate acetate to oxaloacetate and what is the linkage called
The thioester bond between acetate and the sulphuratom in coenzyme A is easily hydrolysed, since it is a high energy bond
Which cofactor is needed for pyruvate dehydrogenase complex and what is its mechanism
Thiamine, easily protonates and subsequently attacks the pyruvate molecule
What is name of deficiency of thiamine and the symptoms
Beri-Beri, peripheral nerve damage, weakened muscles and decreased cardiac output
How many steps are involved in the TCA cycle
8 steps
What are the products of the reaction of the TCA cycle
3 NADH, 1 FADH2, 1 GTP/ATP, 2 CO2
Where are the enzymes for Krebs cycle found and what is the exception
In the mitochondrial matrix, except succinate dehydrogenase (complex II ETC) that converts succinate to fumarate
What can differ between certain cell types regarding the TCA cycle
Some cells first create GTP in substate-level phosphorylation step involving succinyl-coA, other cells ATP directly
In what two categories can amino acids be divided when metabolism is concerned
Glucogenic and ketogenic
In how many skeletons can the 20 amino acids be broken down
7 carbon skeletons
What reactions and enzymes are needed for protein metabolism
Transaminations, carried out by transaminases
What two substance groups are required for this reaction
A ketonic acid and an amino acid
How is the amino group from amino acids removed from the body
By transferring the amino group to urea
Which two shuttles are used to transport high energy electrons into mitochondrion
Glycerol phosphate shuttle and malate aspartate shuttle
Where are the two different electron shuttles found in the body
Glycerol phosphate shuttle is predominantly found in brain cells (neurons) and skeletal muscles, malate aspartate shuttle predominantly in cardiac muscle, liver and kidney cells
Which enzyme is required for glycerol phosphate shuttle
glycerol-3-phosphate dehydrogenase
What are the two substrates involved in cytosolic reaction of glycerol shuttle
dihydroxyacetone and NADH
What are the two substrates involved in mitochondrial reaction of glycerol shuttle
glycerol 3-phosphate and FAD
What happens to the electrons after shuttling through glycerol shuttle
Electrons in FADH2 are directly passed on to coenzyme Q/ubiquinone
Which substance is shuttled in and which out in malate aspartate shuttle and what is intermediate compound
Malate is shuttled in, aspartate is shuttled out, oxaloacetate is intermediate compound
Which two enzymes are needed for malate aspartate shuttle
malate dehydrogenase and aspartate transaminase
What are high energy electrons transported to in malate aspartate shuttle
To NADH
What antiporters are involved in the malate aspartate shuttle
The malate antiporter also transports a-ketoglutarate, the aspartate antiporter also transports glutamate
What is the Warburg effect in cancer and what causes this
Because of genetic mutations in TCA cycle enzymes rendering the enzymes ineffective, cancer cells often preferentially use glycolysis over oxidative phosphorylation
How can cancer potentially be treated targeting the Warburg effect
By reinstating the TCA cycle by administering effective enzymes, maybe cancerous cells can become normal again
Which amino residues are used by kinases to activate or deactivate proteins in cells
Serine, threonine, tyrosine by adding phosphate group to hydroxygroup
What is the difference between substrate-level and oxidative phosphorylation
Substrate-level phosphorylation requires the transfer of phosphate groups by kinases, oxidative phosphorylation requires an electron transport chain
How can LDH be used as a diagnostic tool
lactate dehydrogenase can be an indicator that cells have died and lysed, releasing the enzyme into the blood. By measuring LDH concentration in blood, cell damage can be estimated and monitored
How can glucose metabolism in cancers be used as treatment target or as diagnostic tool
Because cancer cells often require more glucose for ATP synthesis by merely glycolysis, the transporter proteins can be inhibit to inhibit energy supply to these cells and labeled glucose can be used to locate tumours in the body
