Metabolism and its controll

Question 1

What is metabolism?

Answer 1

is the sum of the chemical processes that occur within an organism to maintain life

Question 2

What is catabolism

Answer 2

Breaking down of complex molecules into smaller ones releasing energy

Question 3

What is anabolism?

Answer 3

building up of a complex molecule from two smaller ones requiring energy input

Question 4

What is oxidation

Answer 4

Oxidation is loss of electrons

Question 5

What is reduction

Answer 5

gain of electrons

Question 6

What are the functions of NAD+ and FADH

Answer 6

Are coenzymes act as hydrogen carriers transport hydrogen to the ETC to release e and allow generation of ATP

Question 7

What are some of the specialisation’s of the mitochondria

Answer 7

double membrane
forms inter-membrane space to allow accumulation of protons

lots of cristae increase the SA for ETC and ATP synthases

matrix contains specific enzymes for TCA cycle as well as for B oxidation . these are encoded for by the mitochondria’s own plasmid

Question 8

Where does glycolysis occur

Answer 8

in the cytosl

Question 9

What are the inputs and the outputs of hlycolysis

Answer 9

Inputs:
Glucose, 2ATP, 4ADP, 2Pi, 2NAD+

Outputs
2 pyruvate, 2NADH, 2 net ATP

Question 10

What is the priming phase

Answer 10

conversion of glucose into fructose 1-6-bisphosphate required 2 ATP.

Question 11

What are the two irreversible enzymatically controlled steps in the priming phase

Answer 11

conversion of glucose to glucose 6 phosphate via hexokinase (uses an ATP)

conversion of fructose 6 phosphate to fructose 1-6-bisphosphate via 6 phosphofructokinase
this directs molecules to ATP production

Question 12

What are the final major two phases of glycolysis

Answer 12

splitting phase conversion of F1-6BP to 2GA3P

oxidoreduction phase whereby 2G3P is converted to pyruvate via pyruvate kinase this is irreversible

Question 13

What then happens to the pyruvate produced from glycolysis

Answer 13

shuttled into mitochondrial matrix

Question 14

What is pyruvate decarboxylation and where does it occur.

Answer 14

occurs in the mitochondrial matrix
pyruvate dehydrogenase converts pyruvate and CoA to aCoA and CO2.
also produces a NADH
this happens twice as there are 2 pyruvates produced from one glucose!

Question 15

why is the control of pyruvatedecarboxylase so essential?

How is it controlled?

Answer 15

this is an irreversible step. A gaseous product is produced that cannot be trapped
this directs pyruvate into generation of ATP

is inhibited by high [ATP], high [NADH], and high [aCoA]
tightly controlled enzymatic feedback mechanism

Question 16

citric acid cycle
Where does it occur
what is produced in one turn?

Answer 16

in the mitochondrial matrix

1 turn produces:
3NADH
1FADH2
1GTP
2CO2

Question 17

what are the important irreversible control points in the citric acid cycle?

What are they controlled/inhibited by?

Answer 17

citrate synthase (adds aCoA to oxaloacetate to produce citrate and CoA)

isocitrate dehydrogenase which converts isocitrate to alpha ketoglutarate

a ketoglutarate dehydrogenase
that producess succinyl-CoA

All are inhibited by high [ATP] and high [NADH]

Question 18

what happens to molecules in the TCA cycle when there is no need for the TCA cycle to turn?

Answer 18

can be filtered off for use in anaplertoic reactions
e.g. pyruvate can be used to produce alanine
or oxaloacetate can be used to produce aspartate

Question 19

Outline the Electron transport chain

Answer 19

reduced hydrogen carriers bind to enzyme complexes embedded in the inner mitochondrial membrane

causes oxidation of h carrier and reduction of enzyme e- are donated and H+ are release into matrix

e- are passed from carrier to carrier passing into a lower energy state each time. release of energy as they pass from carriers allows pumping of H+ into inter-membrane space
generating a proton motive force

each H carrier will enter at different points and therefore pump a different amount of ATP across the membrane

O2 acts as the final electron acceptor taking e-, and using H+ from matrix forming H2O . Essential to allow ETC to continue

Question 20

What is chemisomosis

Answer 20

H+ that have accumulated in the inter-membrane space may then move back through ATP synthases done a electrochemical gradient causing a conformational change in the enzyme allowing for the production of ATP via oxidative phosphorylation

Question 21

What happens in brown adipose tissue

Answer 21

Mitochondria are uncoupled
therefore H+ that are pumped into inter-membrane space pass freely through UCP1 channels –> this releases heat energy allowing for thermogenesis in neonates

Question 22

What is anaerobic respiration and what occurs?

Answer 22

Oxidative phosphorylation cannot occur as there is not enough O2 getting to respiring tissues.

To allow glycolysis to continue and some ATP to be generated there must be a supply of NAD+ (is no longer being oxidised in the ETC)

as such Pyruvate is converted to lactate and in this process pyruvate accepts e- from NADH to produce NAD+ and lactate. This allows Glycolysis to continue

Question 23

What is the fate of lactate

Answer 23

lactate build up cause lactic acidosis so majority of it is transported to the liver
It is converted back to pyruvate via lactate dehydrogenase
this pyruvate can then be used by hepatocytes to produce new glucose molecule via gluconeogenesis this is known as the Cori cycle

Question 24

What is gluconeogenesis? what does it require?

Answer 24

Production of glucose form non carbohydrate soucres

costly process requires:
Pyruvate
4ATP
2GTP
2NADH
to make a single glucose

Question 25

how do glycolysis and gluconeogenesis differ

Answer 25

similar reaction to glycolysis however (hexokinase, phosphofrutokinase, and pyruvate kinase are unidirectional for glycolysis )

Question 26

What causes the cell to degrade or synthesis glucose?

What two key enzymes control this process?

Answer 26

phosphofrutokinase and fructose-1-6-bisphosphate

When [ATP] is high phosphofructokinase is inhibited by ATP. Fructose 1-6- bisphospahte activated as convertes fructose-6-phosphate which can be used in gluconeogenesis

When [ATP] is low [AMP], [ADP] are high this activate phsophofructokinase glycolysis is triggered
fructose 1-6- bisphosphate is inhibited thus stopping gluconeogeneisis

Question 27

Glycogen control mechanisms

Answer 27

gluconeogenisis isn’t always most efficient can use glycogen stores first

Glycogen phsophorylase that hydrolyses glycogen to glucose-1-phsophate which can be converted to glucose 6 phosphate for use in glycolysis

High Glucose-6-phsophate, and high [ATP] inhibit the activity of glycogen phosphorylase
yet will increase the synthesis of new glycogen via activation of glycogen synthase

Question 28

citrate synthase control point
Where
What is the control mechanism?

Answer 28

TCA cycle - irreversible step

citrate synthase convertes oxaloacetate and ACoA to citrate

inhibited by high [ATP], [ACoa], [NADH]

Question 29

isocitrate dehydrogenase control point?
Where
What is the control mechanism?

Answer 29

TCA cycle irreversible step

convertes isocitrate to alpha ketoglutarate

inhibited by high [ATP], [NADH]

simulated by high [ADP]

Question 30

alpha ketoglutarate control point?
Where?
What is the control mechanism?

Answer 30

TCA cycle irreversible step

produces succinyl-CoA

inhibited by high [ATP], [NADH]

stimulated by high [ADP]

Question 31

pyruvate dehydrogenase control point?
Where
What is the mechanism?

Answer 31

occurs in the mitochondrial matrix

converts pyruvate to ACoa
via oxidative decarboxylation reaction
must be tightly controlled as convertes pyruvate to ACoa and produces CO2 therefore is totally irreversible

inhibited by [ATP] ,[NADH], [ACoa]

Question 32

What is Beriberi?

What is the cause and how does it effect the cell?

Answer 32

Beriberi
TCA cycle is switched off as essential thiamine pyrophosphate cofactor is not present
pyruvate dehydrogenase and a ketoglutarate rely on this TPP coenzyme to function
this if this is not present the flow of pyruvate into the TCA cycle and the movement of the TCA cycle itself stops.