Metabolism Flashcards
Anabolism
Absorption of molecules
- requires ATP (endergonic)
- reductive
Eg. ADP + Pi —> ATP
Catabolism
Breakdown of molecules
- releases energy (exergonic)
- oxidative
eg. ATP —> ATP + Pi
Where is glycogen stored
Muscle and liver
What are human’s primary energy source
Glucose
Oxidised to CO2 and H2O
Structure of ATP
- 3 phosphate groups
- One ribose sugar
- One adenine
Adenosine triphosphate
What is glucose used for
- Storage by glycogen/conversion to lipids
- Pyruvate
- Lactate
- Ribose-5-phosphate
How does glucose get transported into cells
Via Na+/glucose symporters
Via passive facilitated diffusion glucose transporters
Where is GLUT1 present
Brain
Where is GLUT2 present
Liver
Beta-cells
Where is GLUT3 present
Brain
Where is GLUT4 present
Muscle
Adipose (fat) tissue
Where is GLUT5 present
Gut
Where does glycolysis occur
Cytoplasm
Phase 1 of glycolysis
Glucose —> fructose-1,6-biphosphate
2ATP—>2ADP
Phase 2 of glycolysis
Fructose-1,6-biphosphate —> 2x triose phosphates
Phase 3 of glycolysis
2x triose phosphates —> 2x pyruvate
4ADP—>4ATP
2NAD+—>2NADH + 2H+
Overall reaction of glycolysis
Glucose + 2ADP + 2Pi + 2NAD+ —> 2 pyruvate + 4ATP + 2H2O + 2NADH + 2H+
Not efficient for ATP production
Fast
What are the 3 control points in glycolysis
Hexokinase - substrate entry (glucose)
Phosphofructokinase - rate of flow (intermediate)
Pyruvate kinase - product exit (pyruvate)
Fate of pyruvate
Provides carbon to fuel TCA cycle in mitochondria
Fate of NADH
Carries H+ and e- to electron transport chain for ATP synthesis
Stages of respiration
Glycolysis
TCA cycle
Electron transport chain
Glycolysis ATP net gain
2
What happens if oxygen isn’t present
Lactic acid cycle
Only glycolysis
- 2 pyruvate converted to 2 lactic acid by NADH
Can we cells produce energy by …
High rate of glucose —> lactic acid
Where does TCA cycle take place
Matrix of mitochondria
Where does the electron transport chain take place
The inner membrane of mitochondria
Role of dehydrogenase enzymes
Remove H+ and e- from glycolysis intermediates and pass them to NAD (forming NADH)
How is acetyl-CoA formed
Pyruvate (3C) enters the matrix —> CO2 released —> acetyl group (2C) combines with coenzyme A to form acetyl coenzyme A
Describe stage 1 of TCA cycle
Acetyl-CoA (2C) + oxaloacetate (4C) —> Citrate (6C)
6C —> 4C (yields 2CO2 + 2NADH)
4C undergoes oxidation - yields NADH, FADH2 and GTP (energy)
Oxaloacetate (4C) recreated - cycle repeats
All enzymes of TCA cycle are located in the mitochondrial matrix except succinate dehydrogenase located in …
The inner mitochondrial membrane
If supply of pyruvate/oxaloacetate is limited (eg. no glycolysis), what is acetyl-CoA diverted to
Ketones - emergency energy supply for brain during fasting/starvation/diabetes
Long term accumulation—> death, coma
Each turn of the TCA cycle results in transfer of … to NAD+ to form NADH + H+
And the transfer of … to reduce FAD to FADH2
3 pairs of e-
1 pair of e-
One substrate level phosphorylation reaction results in the formation of …
GTP from GDP and Pi
Each molecule of glucose yields … (up to TCA cycle)
10NADH + 10H+ + 2FADH2 + 6CO2 + 4ATP
2ADP made in glycolysis (-2)
2ATP for each pyruvate made (2 made = 4)
Total in glycolysis = 2
1GDP forms 1 ATP. 2 pyruvate means 2GDP
Total in TCA cycle = 2
Net gain of how many ATP in TCA cycle
2
What is the final hydrogen ion and electron acceptor
Oxygen
Electrons from NADH and FADH2 are used to reduce O2 to …
H2O
The energy of electron transport is used to pump protons (H+) from the … to …
Mitochondrial matrix to the intermembrane space
pH decreases in the intermembrane space, increases in matrix
Energy of electron flow is used to phosphorylate ADP to ATP
True/false
False
Energy of PROTON (H+) flow is used to phosphorylate ADP to ATP
When does oxidative phosphorylation stop
Without the presence of O2
That’s why we need to breathe oxygen
In oxidative phosphorylation, the phosphoryl transfer potential of NADH+ and FADH2 is converted into the electron transfer potential of ATP
True/false
False
In oxidative phosphorylation, the electron transfer potential of NADH+ and FADH2 is converted into the phosphorl transfer potential of ATP
A negative E’o means that the reduced form of X has a lower affinity for electrons than H2, and a positive E’o means the opposite
True/false
True
Strong reducers = more -ve
Strong oxidisers = more +ve
How is the energy of electrons converted into the energy of ATP
Oxidative phosphorylation
Consists of:
- electron transport
- ATP synthesis
Electron transport and ATP synthesis are catalysed by the same proton pumps
True/false
False
Different proton pumps
Describe electron transport
- electrons flow from NADH and FADH2 to O2
- respiratory chain
- energy is used to pump H+ out of the matrix
Describe ATP synthesis
- electrochemical gradients of H+ across inner membrane
- energy stored in this gradient can be used to synthesise ATP
What are cytochromes
Proteins which contain a haem group as a functional co-factor
Haem contains Fe(II) which can take up/release electrons
How many multisubunit complexes are present in the inner membrane, and how many of these pump H+
4 present, 3 pump H+
Describe the electrochemical gradient between the intermembrane space and matrix
- more H+ in intermembrane space than matrix
- electrical field forms. Matrix more -ve
- H+ want to flow back into matrix
- flow back is coupled to ATP synthesis
What do protons flow back into the inner membrane from intermembrane space via?
ATP synthase
Intermembrane —> inner membrane —> matrix
What can inhibit the electron transport chain
Cyanide, azide and CO inhibit transfer of e- to O2
No ATP made
What is oxidative phosphorylation in simple words
- H+ is pumped through ATP synthase
- O2 electrons and H+ flow to make H2O
- flow of H+ makes ATP from ADP
How much ATP is yielded from 1 glucose molecule
30 to 32
Glycolysis = 2
TCA cycle = 2
Electron transport chain = 26 to 28
What metabolic properties of cancer are relevant to PET scans
High glucose up-take
Lactate/lactic acid production
