Metabolism Flashcards
What is metabolism?
Metabolism is the sum of all the chemical reactions that take place within an organism to maintain life
What are the two types of metabolism?
- Anabolism: The building up of complex molecules from simpler ones (e.g., protein synthesis). This usually requires energy (+🔼G, non spontaneous)
- Catabolism: The breaking down of complex molecules into simpler ones (e.g. digestion). This usually releases energy (-🔼G, spontaneous)
What are the benefits of metabolic pathways? (4)
- Make complex transformations kinetically possible
- Allow multiple energy production sites by releasing free energy in manageable ‘packets’
- Generate a diverse range of chemical structures
- Allow a high level of control
What are the benefits of compartmentalisation? (3)
- Substrate channelling - the substrate is moved directly from the enzyme of one active site to the next sequentially without releasing it into the bulk solution
- This increases the rate by increasing the effective concentration of enzyme and reactants
- Compartmentalisation also avoids unwanted side reactions and futile cycling
How are pathways discovered and studied?
- Cell fractionation
- Inhibitors
- Radiolabelling
- Mutants
What must the overall free energy change for a pathway be?
Must be negative
Why is ATP less stable than ADP and Pi? (3)
- the -ve charges on the phosphate groups repel one another
- Entropy is increased, 2 molecules for 1
- Water stabilises the products - more interactions between H2O interactions with Pi and ADP than with ATP alone
- free Pi stabilised by resonance structures not possible when bound to ATP
What is the formula that includes mass action ratio (Γ)?
T = temp in Kelvin often 298K (room temp) 310 K (body temp)
ln = natural log (i.e. log to base e)
Γ = mass action ratio (actual concentration ratio of products to reactants under a particular condition)
🔼G = RT ln (Γ/K)
Give me 4 co-factors
FADH2, NADH, ATP, A-CoA
When can 2 reactions be coupled?
If they share one or more intermediates
Where does glycolysis occur?
Glycolysis takes place in the cytoplasm
What does glycolysis produce?
Oxidises 1 glucose to get 2 pyruvate while producing 2 ATP and 2 NADH
(Involves hydrolysing 2 ATP molecules)
What is the first step of glycolysis? And explain
Glucose phosphorylation - Glucose is phosphorylated by hexokinase.+ ATP
The -ve charges on the Pi keeps G6P inside cell since charged molecules do not cross membrane easily
How does hexokinase do it?
- Binding of glucose causes a conformational change
- the effect of the cleft closing is that the active site around glucose and ATP becomes more non-polar
- This favours direct transfer of the Pi group from ATP to glucose and prevents hydrolysis of ATP
What is step 2 of glycolysis? And explain
Step 2: Isomerisation to fructose
Glucose- 6- phosphate is isomerised by phopsphoglucose isomerase to fructose -6 - phosphate
This forms a ketone sugar from an aldose sugar
What is the 3rd step of glycolysis ?
3rd step: The second phosphorylation
- F6P is phosphorylated by phosphofructokinase to fructose - 1, 6-biphosphate ( F1, 6BP) using ATP
- Entry of sugars into glycolysis is controlled at this step via allosteric regulation of phosphofructokinase
What happens in step 4 (cleavage)?
- F1, 6BP is cleaved by Aldolase to yield DHAP and GAL (3 carbon sugar)
- Only GAP can proceed through glycolysis, DHAP is converted to GAP
What happens in step 5 of glycolysis?
Conversion of DHAP: DHAP is converted to a second molecule of GAP by triose phosphate isomerase
What is step 6 of glycolysis?
Oxidation of GAP:
Glyceraldehyde 3- phosphate dehydrogenase (GAPDH) uses the co-enzyme NAD+ to oxidise GAP, forming NADH (2 electron carrier)
- GADPH uses Pi to form 1,3 BPG - a compound with high phosphorylation transfer potential
- This is the first energy generating step of glycolysis where an activated carrier molecule is formed (NADH)
What is step 7 of glycolysis?
First phosphate transfer to ADP:
Pi transferred from 1,3 BPG to ADP by phosphoglycerate kinase to form 3- phosphoglycerate + ATP
- Transfer of a Pi group from a phospho-sugar such as 1,3 BPG to ADP is known as ‘substrate level phosphorylation’
(Phosphate stolen from 1 position to make ATP)
What happens in step 8 of glycolysis?
Isomerisation to 2- phosphoglycerate:
Phosphoglycerate mutate transfers phosphorescent linkage from carbon 3 to carbon 2 forming 2- phosphoglycerate
What happens in step 9 of glycolysis?
Removal of water:
Removal of water from 2-phosphoglycerate by enclose creates a molecule of phosphoenolpyruvate
What happens in the final step of glycolysis?
Second phosphate transfer to ADP:
Pyruvate kinase forms a molecule of ATP and pyruvate from phosphoenolpyruvate
- Third energy generating step and another example of substrate level phosphorylation
What is the output product of glycolysis with/without O2?
In the presence of O2, pyruvate will be converted to Acetylene Co-enzyme A (CoA)
In the absence of O2, output product of glycolysis (pyruvate) is fermented to lactate
What happens in fermentation?
- NADH is used to reduce pyruvate to either lactate or ethanol to regenerate NAD+
- NAD+ is thus regenerated to restore redox balance, crucially allowing ATP production via glycolysis to continue without O2
