energy metabolism

Question 1

example of anabolic process

Answer 1

bonding of amino acids to make proteins

Question 2

example of catabolic process

Answer 2

glucose breakdown

Question 3

where do cells get energy from

Answer 3

nutrients or fuels such as carbohydrates lipids or proteins

Question 4

what is the structure of ATP

Answer 4

adenine base
ribose sugar
3 phosphate groups
it has high energy bonds

Question 5

what happens when ATP is hydrolysed

Answer 5

Phosphate and heat energy is released
The reaction is energetically favourable - negative gibbs freee energy

Question 6

What is glycolysis

Answer 6

anaerobic breakdown of glucose to pyruvate
small amount of ATP generated by substrate level phosphorylation

Question 7

what is Krebs cycle

Answer 7

Oxidation of acetyl CoA to Co2
Generates co enzymes NADH and FADH2
generates ATP

Question 8

what is oxidative phosphorylation

Answer 8

transduction of energy derived from fuel oxidation to high energy phosphate
generates large amounts of ATP

Question 9

what pathways is glucose metabolism linked to

Answer 9

Glycolysis
Krebs cycle
Oxidative phosphorylation

Question 10

where does glycolysis occcur

Answer 10

in cytosol under anaerobic conditions

Question 11

why does glycolysis occur (2)

Answer 11

it’s an emergency energy production pathway when oxygen is limited

it generates precursors for biosynthesis
- G-6-P converted to ribose 5-P via pentose phosphate pathway
- G-1-P for glycogen synthesis
- pyruvate is transaminated to alanine
- substrate for fatty acid synthesis
- glycerol -3-P is backbone of triglycerides

Question 12

what are the products of glycolysis

Answer 12

2 molecules of pyruvate (C3H4O3)

2NADH + H+

2 ATP

Question 13

Overview of glycolysis

Answer 13

Glucose enters cells through diffusion
Glucose is phosphorylated on 6th carbon
Phosphate group has come from ATP hydrolysis
This is catalysed by hexokinase
This produces glucose 6 phosphate
This is isomerised to fructose 6 phosphate by glucose isomerase
Another phosphate is added to carbon 1 to produce fructose 1,6 biphosphate
Catalysed by phosphofructokinase
Produced fructose 1,6 biosphopate
this is an unstable molecule that will split spontaneously to form two 3 carbon molecule and consumes the second molecule of ATP
fructose-1,6-bisphosphate is converted into dihydroxyacetone phosphate and glyceraldehydr 3- phosphate, catalysed by fructose-bisphosphate aldolase
DHAP is converted into a second molecule of GA3P.

1 NADH and 2 ATP are produced per molecule of GA3P entering the pathway.
As our first molecule of glucose has generated two molecules of GA3P, the total payout from the payout phase is 2 NADH + 4 ATP.
As we used 2 ATP in the investment phase, the net gain from our first molecule of glucose is 2 NADH and 2 ATP

6, GA3P is converted into 1,3-bisphosphoglycerate (1,3-BPG) by glyceraldehyde phosphate dehydrogenase - yields a molecule of NADH, formed by the reduction of NAD+

1,3-BPG is converted into 3-phosphoglycerate (3PG) by phosphoglycerate kinase - generates a molecule of ATP

3PG is converted into 2PG by phosphoglycerate mutase

2PG is converted into phosphenolpyruvate by enolase.

Phosphenolpyruvate is converted into pyruvate by pyruvate kinase, which yields our second molecule of ATP. This is irreversible, and is therefore another key regulatory step

Question 14

what is allosteric regulation

Answer 14

binds to a non catalytic site
conformational change
increases or decreases affinity for the substrate

Question 15

what is hormonal regulation

Answer 15

increases or decreases gene expression of the enzyme
indirect route - through affecting regulatory molecules (usually kinases or phosphatases)
increases or decreases enzyme activity

Question 16

how are proteins broken down

Answer 16

protein –> amino acids –> amine –> urea

Question 17

how are carbohydrates broken down

Answer 17

carbohydrates –> glucose –> glycolysis –> acetyl coA –> krebs cycle

Question 18

what is the equation for glycolysis

Answer 18

Glucose + 2ADP + 2Pi + 2NAD+ > 2 Pyruvate + 2ATP + 2NADH + 2H+ + 2H20

Question 19

what are the methods for generating ATP (6)

Answer 19

• Glycolysis
• Kreb’s cycle
• Oxidative phosphorylation
• Substrate level phosphorylation
• Electron transport chain
• Beta oxidation

Question 20

what does the enzyme kinase do

Answer 20

enzyme that adds/removes phosphate group to things from an ATP

Question 21

what does the enzyme isomerase do

Answer 21

enzyme that rearranges structure of substrate without changing the molecular formula

Question 22

what does the enzyme adolase do

Answer 22

enzyme that creates or breaks carbon-carbon bonds

Question 23

what does the enzyme dehydrogenase do

Answer 23

enzyme that moves hydride ion (H-) to an electron acceptor e.g. (NAD+ of FAD+)

Question 24

what does the enzyme enolase do

Answer 24

enzyme that produces a carbon=carbon double bond by removing a hydroxyl group

Question 25

how does ATP provide energy

Answer 25

When the phosphate bonds are broken energy is released BUT to ‘break’ bonds an input of energy is required. As bonds reform in the products of the reaction of the hydrolysis of ATP energy is released. The energy released making the new bonds is greater than the energy required to hydrolyse the bonds (since they are relatively weak) thus meaning the hydrolysis of ATP gives out energy

Question 26

what are the regulators of glycolysis and PFK

Answer 26

Adenosine monophosphate (AMP) Adenosine triphosphate (ATP) citrate fructose 2,6 biphosphate

Question 27

what does Adenosine monophosphate (AMP) regulate

Answer 27

it is an allosteric activator of phosphofructokinase-1 (PFK-1). it binds to PFK-1 resulting in a conformational change - increasing the affinity of PFK-1 for fructose-6-phosphate

Question 28

what does Adenosine triphosphate (ATP) regulate

Answer 28

it is an allosteric inhibitor for PFK-1 this means it modifies the active site of the enzyme so that the affinity for the substrate decreases at low ATP levels = fast reaction speed of PFK-1 > fructose 1,6 bisphosphate, and at high ATP levels = slow reaction speed of PFK-1 > fructose 1,6 bisphosphate AMP opposes the allosteric inhibition by ATP

Question 29

how does citrate regulate glycolysis

Answer 29

it is the first product of the Krebs cycle acts as an allosteric inhibitor for PFK-1 increased citrate levels is a signal that the cycle does not need more fuel

Question 30

how does fructose-2,6-biphosphate regulate glycolysis

Answer 30

it is generated from fructose 6 phosphate is the most important allosteric activator of PFK 1 it mediates the effect of insulin and glycogen

Question 31

what is the fate of pyruvate in anaerobic conditions

Answer 31

it is converted to lactate using lactate dehydrogenase because it cannot enter the Kreb’s cycle or undergo Oxidative Phosphorylation since these processes require oxygen this leads to regeneration of NAD+

Question 32

what is the equation for the fate of pyruvate in anaerobic conditions

Answer 32

glucose + 2 ADP + 2 Pi > 2 Lactate + 2 ATP + 2 H2O

Question 33

what is the fate of pyruvate in aerobic conditions

Answer 33

it enters the mitochondria is converted to Acetyl CoA and Co2 by pyruvate dehydrogenase - this is an irreversible reaction Acetyl CoA can enter the TCA cycle for more energy production

Question 34

what inhibits pyruvate dehydrogenase

Answer 34

high concentrations of acetyl CoA and NADH

Question 35

what inactivates pyruvate dehydrogenase

Answer 35

phosphorylation

Question 36

what activates pyruvate dehydrogenase

Answer 36

phosphate removal

Question 37

what is the equation for the fate of pyruvate in aerobic conditions

Answer 37

pyruvate + CoA + NAD+ ----------> acetyl CoA + CO2 + NADH + H+ catalysed by pyruvate dehydrogenase

Question 38

what are 2 other names for the Krebs cycle

Answer 38

citric acid cycle tricarboxylic acid (TCA) cycle

Question 39

where does the krebs cycle occur

Answer 39

in the mitochondrial matrix in aerobic conditions

Question 40

why does krebs need to occur in aerobic conditions

Answer 40

since oxidative phosphorylation is required to covert NADH & FADH2 back to NAD+ and FAD to be used in the conversion of Isocitrate to a-Ketoglutarate and a-Ketoglutarate to Succinyl coenzyme A & Succinate to Fumarate & Malate to Oxaloacetate.

Question 41

what are the 3 reasons the krebs cycle occurs

Answer 41

1) generates lots of ATP 2) provides final common pathway for oxidation of carbohydrates, fat and protein via acetyl CoA 3) produces intermediates for other metabolic pathways

Question 42

what are the 3 ways of making acetyl CoA

Answer 42

1) from pyruvate 2) the beta-oxidation of fatty acids 3) from amino acid breakdown

Question 43

what is acetyl CoA derived from

Answer 43

the B vitamin pantothenic acid

Question 44

what is the primary function of acetyl CoA

Answer 44

functions primarily to transfer acetyl groups (2 carbons), from one molecule to another.

Question 45

what is the overall equation for the Krebs cycle

Answer 45

Acetyl CoA + 3NAD+ + FAD + GDP + ADP + Pi + 2H2O > 2CO2 + CoA + 3 NADH + 3H+ + FADH2 + GTP + ATP

Question 46

give a brief overview of the krebs cycle

Answer 46

acetyl CoA condenses oxaloacetate with acetate oxaloacetate regenerated in krebs cycle

Question 47

what are the products of each stage in the krebs cycle

Answer 47

“Can I Keep Selling Socks For Money, Officer ?” - C - Citrate - Can - I - Isocitrate - I - K - a-Ketoglutarate - Keep - S - Succinyl CoA - Selling - S - Succinate - Socks - F- Fumarate - For - M - Malate - Money - O - Oxaloacetate - Officer?

Question 48

what are the regulators of the krebs cycle

Answer 48

- pyruvate dehydrogenase - citrate synthase - isocitrate dehydrogenase - a-ketoglutarate dehydrogenase

Question 49

what is the role of pyruvate dehydrogenase

Answer 49

converts pyruvate to acetyl CoA an irreversible and tightly regulated reaction to control how much fuels enters the krebs cycle

Question 50

what inhibits pyruvate dehydrogenase

Answer 50

ATP and NADH negatively inhibit pyruvate dehydrogenase acetyl CoA (its product) inhibits it to make sure its only made when its needed

Question 51

what activates pyruvate dehydrogenase

Answer 51

ADP activates pyruvate dehydrogenase as well as its substrate pyruvate

Question 52

what inhibits citrate synthase (4)

Answer 52

ATP and NADH allosterically inhibit citrate synthase they reduce the affinity of citrate synthase for its substrates succinyl CoA competitively inhibits citrate synthase citrate inhibits citrate synthase and increased citrate reduces the speed of the cycle

Question 53

what activates citrate synthase

Answer 53

ADP

Question 54

what is isocitrate DH

Answer 54

a key rate-limiting enzyme of Krebs cycle

Question 55

what causes the rate of krebs cycle to increase

Answer 55

in states of increased oxidative phosphorylation demands

Question 56

what inhibits isocitrate DH

Answer 56

ATP and NADH

Question 57

what activates isocitrate DH

Answer 57

ADP

Question 58

what inhibits a - ketoglutarate DH

Answer 58

its products NADH and succinyl - coA also inhibited by GTP, ATP and reactive oxygen species (ROS)

Question 59

what activates a - ketoglutarate DH

Answer 59

Ca2+ may be useful in generating ATP during intense muscle exercise

Question 60

where does oxidative phosphorylation occur

Answer 60

in the inner mitochondrial membranes in aerobic conditions

Question 61

when does oxidative phosphorylation release the majority of energy

Answer 61

during cellular respiration

Question 62

what happens in oxidative phosphorylation briefly

Answer 62

- reduced NADH or FADH2 from glycolysis and krebs cycle are oxidised - their electrons are passed to components of electron transport chain (ETC) - these are a series of carriers embedded in the inner mitochondrial membrane - the final electron acceptor is O2 - energy released is trapped to generate ATP

Question 63

what forms the components of the ETC

Answer 63

cytochromes (contain iron and copper co-factors, structure resembles the red iron- congaing haemoglobin) and associated proteins embedded in the inner mitochondrial membrane surface

Question 64

describe process of oxidative phosphorylation

Answer 64

* Two electrons from hydrogen atoms are initially transferred either from NADH + H+ or FADH2 to one of the protein in the electron transport chain. These electrons are then successively transferred to other compounds in the chain redox reactions, until the electrons are finally transferred to molecular oxygen, which then combines with hydrogen ions (protons) to form water. * These hydrogen ions, like the electrons, come from free hydrogen ions and the hydrogen-bearing coenzymes (NADH and FADH2), that had been released earlier in the electron transport chain when the electrons from the hydrogen atoms were transferred to the cytochromes. * IMPORTANTLY in addition to transferring the coenzyme hydrogens to water, this process also regenerates the hydrogen-free forms of the coenzymes (NAD+ & FAD), which can then become available to accept two more hydrogens from intermediates in the Kreb’s cycle, glycolysis or beta-oxidation. * Thus, the electron transport chain provides the aerobic mechanism for regenerating the hydrogen-free form of the coenzymes * At certain steps along the electron transport chain, small amounts of energy are released. As electrons are transferred from one protein to another alone the chain, some of the energy released used by the cytochromes to pump hydrogen ions from the matrix into the intermembranal space - the compartment between the inner and outer mitochondrial membranes * This creates a source of potential energy in the form of a hydrogen-ion- concentration gradient across the membrane. * Embedded in the inner mitochondrial membrane are enzymes called ATP synthase. This enzyme forms a channel in the membrane, allowing hydrogen ion to flow back into the matrix via chemiosmosis - moving from an area of high concentration of hydrogen ions to an area of low concentration. During this process, the energy of the concentration gradient is converted into chemical bond energy by ATP synthase, which then catalyses the formation of ATP from ADP and Pi. * The transfer of electrons to oxygen produces on average around 2.5 and 1.5 molecules of ATP for each molecule of NADH + H+ & FADH2 respectively.