Cell metabolism I

Question 1

What 6 types of metabolic reactions are present?

Answer 1

Redox
Group transfer
Isomerisation
Hydrolytic
Ligation requiring ATP cleavage
Addition/removal of functional groups

Question 2

What are oxidation-reduction reactions?

Answer 2

Transfer of electrons between molecules

Question 3

What are ligation reactions?

Answer 3

Formation of covalent bonds

Question 4

What are isomerisation reactions?

Answer 4

Rearrangement of atoms to form isomers

Question 5

What are group transfer reactions?

Answer 5

Transfer of a functional group from one molecule to another

Question 6

What are hydrolytic reactions?

Answer 6

Cleavage of bond via addition of water

Question 7

What are the reduction reactions?

Answer 7

Addition of hydrogen
Addition of electrons
Removal of oxygen

Question 8

What are oxidation reactions?

Answer 8

Addition of oxygen
Removal of hydrogen
Removal of electrons

Question 9

What is NAD?

Answer 9

Nicotinamide adenine dinucleotide
Coenzyme hydrogen acceptor

Question 10

What is FAD?

Answer 10

Flavin adenine dinucleotide

Question 11

What is the first step of glycolysis?

Answer 11

Glucose is phosphorylated by ATP to glucose-6-phosphate via hexokinase-4
Proton released
Group transfer

Question 12

Why is glucose phosphorylated?

Answer 12

Addition of high-energy phosphate makes glucose more reactive
Unable to bind to glucose transporter
Negatively charged
Trapped within cell (irreversible/ committed to glycolysis)

Question 13

What is the second step of glycolysis?

Answer 13

Glucose-6-phosphate is converted into fructose-6-phosphate via phosphoglucoisomerase
Isomerisation

Question 14

What is the third step of glycolysis?

Answer 14

Fructose-6-phosphate is phosphorylated into fructose-1,6-bisphosphate via phosphofructokinase
Group transfer

Question 15

What is the fourth step of glycolysis?

Answer 15

Fructose-1,6-bisphosphate is hydrolysed into glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP) via aldose
Hydrolytic cleavage

Question 16

What is the fifth step of glycolysis?

Answer 16

DHAP is converted into G3P via triosephosphate isomerase (TPI)
Isomerisation

Question 17

What is the glycolytic enzymopathy that is fatal?

Answer 17

TPI deficiency

Question 18

What is the sixth step of glycolysis?

Answer 18

G3P is converted into 1,3-bisphosphoglycerate via glyeraldehyde-3-phosphate dehydrogenase
NADH is generated from NAD+
Redox and group transfer

Question 19

What is the seventh step of glycolysis?

Answer 19

1,3-bisphosphoglycerate is converted into 3-phosphoglycerate via phosphoglyceratekinase
ATP produced from ADP and Pi
Group transfer

Question 20

What is the eighth step of glycolysis?

Answer 20

3-phosphoglycerate is converted to 2-phosphoglycerate via phosphoglycerate mutase
Isomerisation

Question 21

What is the ninth step of glycolysis?

Answer 21

2-phosohoglycerate is converted into phosphoenolpyruvate via enolase
Dehydration

Question 22

What is the last step of glycolysis?

Answer 22

Phosphoenolpyruvate is converted into pyruvate via pyruvate kinase
ATP is produced
Group transfer

Question 23

Where does glycolysis occur?

Answer 23

In the cellular cytoplasm

Question 24

What is glycolysis?

Answer 24

Substrate level phosphorylation of respiratory substrate glucose to synthesize pyruvate, ATP, and reduced NAD to generate ATP

Question 25

How many gross ATP molecules are made?

Answer 25

Four 2 via 1,3bisphosphoglycerate --> 3-bisphosphoglycerate 2 via phosphoenolpyruvate --> pyruvate

Question 26

What is the destination of the 2 NADH molecules under aerobic conditions?

Answer 26

They pass through the outer mitochondrial membrane into the electron transport chain

Question 27

What are the three fates of the 2 molecules of pyruvate made?

Answer 27

Acetyl CoA formation Alcohol fermentation (plants, microorganisms) Lactate production (anaerobic conditions only)

Question 28

What property of acetyl CoA makes it useful to respiration?

Answer 28

It has a high-energy thioester bond that is readily hydrolysed It is picks up and donates the acetate group to the TCA cycle

Question 29

How is acetyl CoA formed from pyruvate?

Answer 29

Actively transported to mitochondrial matrix Link reaction Pyruvate is decarboxylated and dehydrogenated to form acetate via pyruvate dehydrogenase complex (PDH) Coupled with CoA to form acetyl CoA (and CO2)

Question 30

How is Beri Beri caused and what are the symptoms?

Answer 30

Thiamine deficiency (vitamin B1 derivative) Thiamine pyrophosphate is a co-factor of the PDH complex It is easily deprotonated and the resulting carbanion attacks pyruvate so that acetyl CoA can't form Results in damage to PNS, muscle weakness, decreased cardiac output Brain is vulnerable as it is heavily reliant on glucose metabolism

Question 31

How is lactate formed from pyruvate?

Answer 31

Pyruvate is reduced to lactate via lactate dehydrogenase NADH is re-oxidised to NAD+ to allow glycolysis to continue Occurs in mammalian muscle when oxygen is unavailable to be the final hydrogen accept during oxidative phosphorylation

Question 32

What happens to the lactate that is formed?

Answer 32

Transported back to the liver and converted into pyruvate via LDH

Question 33

Where is LDH predominantly located?

Answer 33

Liver, kidneys, skeletal muscle, heart, blood and lungs

Question 34

What is the neural response to lactate production?

Answer 34

Release of hydrogen ions enter into the blood (from acid) subsequently dropping blood pH Detected by chemoreceptors within the carotid sinus and aortic arch Triggers CNS to reduce muscle contraction, muscle have time to recover and return to aerobic respiration.

Question 35

How is alcohol formed from pyruvate?

Answer 35

Pyruvate is decarboxylated to ethanal (acetaldehyde) via pyruvate decarboxylase Ethanal is then reduced to ethanol via ethanal dehydrogenase NAD+ is regenerated Occurs under anaerobic conditions

Question 36

Why is the regeneration of NAD+ important?

Answer 36

NAD+ is required for step 6 of glycolysis (glyceraldehyde-3-phosphate is dehydrogenated into 1,3-bisphosphoglycerate) This is the first step in glycolysis where ATP is made

Question 37

Why is creatine phosphate important in the body?

Answer 37

It acts as a buffer for ATP concentration in muscles It is a reservoir of phosphate groups which are transferred to ADP to form ATP via creatine kinase when [ATP] falls too low

Question 38

What is the equation for creatine phosphate?

Answer 38

Creatine phosphate + ADP --> ATP + creatine

Question 39

What is produced by the link reaction per glucose molecule?

Answer 39

2 acetyl CoA 2 CO2 2 NADH

Question 40

What is the overall equation for the link reaction?

Answer 40

Pyruvate + NAD + CoA --> AcetylCoA + CO2 + NADH