Johnson (Cellular Respiration) Flashcards
What is the difference between anabolism and catabolism?
- anabolism = making stuff, mainly endergonic (+ΔG)
- catabolism = breaking stuff down, mainly exergonic
(-ΔG)
What is the relationship between catabolism and anabolism?
- catabolism provides energy for anabolism
What is cellular respiration?
- catabolic breakdown of red C derived from fats and sugars to gain energy
What is glycolysis?
- central ATP prod pathway
- in cytosol
- involves 10 enzymatic reactions
Where do heterotrophs obtain energy from?
- ox red C sources, eg. sugars and fats
Why are reactions in respiration carried out stepwise?
- to release energy in controlled way, so it can be captured and stored in activated carrier molecules
How does ox of C compounds provides energy?
- C-H bonds less stable than C-O and C=O
- so energy yielded to env when C-H bonds replaced by them –> so ox of C provides energy
Which part of respiration is common to animals, plants and many bacteria?
- glycolysis
To what extent is O involved in glycolysis?
- not req
- but involved as e-s removed from C to NADH
What is the net gain from glycolysis?
- 2 ATP
- 2 NADH
- 2 pyruvate
What are the 10 steps of glycolysis?
1) Glucose phosphorylation
2) Isomerisation to fructose
3) 2nd phosphorylation
4) Cleavage
5) Conversion of DHAP
6) Oxidation of GADP
7) 1st phosphate transfer to ADP
8) Isomerisation to 2-phosphoglycerate
9) Removal of water
10) 2nd phosphate transfer to ADP
What occurs during glucose phosphorylation, and what is the role of the negative charge on the Pi? (1st step glycolysis)
- glucose to glucose-6-phosphate
- by hexokinase
- req ATP input
- negative charge on Pi traps G6P inside cell
- also keeps glucose conc low, promoting uptake via glucose transporter proteins
- charge destabilises molecule, facilitating further metabolism
Why is ATP less stable than ADP + Pi?
- negative phosphate charges repel
- lower entropy
- less interactions w/ water
- free Pi stabilised by resonance structures, not poss when bound to ATP
In terms of equilibrium, which is favoured, ATP or ADP + Pi?
- ADP + Pi greatly favoured
What happens to reaction in terms of ATP prod, depending on ΔG value?
- at equilibrium reaction has no capacity to do work
- when ΔG-ve, hydrolysis of ATP favourable under cellular conditions
- when ΔG+ve, synthesis of ATP req energy under cellular conditions
Why is there no such thing as a high energy bond, what is really meant?
- simply extent conc of products to reactants (Γ) displaced from equilibrium
- this defines capacity of reaction to do work
- not attribute of any single component
What is req for 2 reactions to be coupled?
- must share 1 or more intermediates
What is the ΔG of coupled reactions?
- sum of 2 individual reactions
What occurs during isomerisation to fructose, what kind of sugars are converted and is it reversible? (2nd step glycolysis)
- G6P to F6P
- by phosphoglucose isomerase
- aldose sugar converted to ketose sugar (necessary for step 4)
- readily reversible under cellular conditions
What occurs during 2nd phosphorylation, and how is entry of sugars into glycolysis controlled at this step? (3rd step glycolysis)
- F6P to fructose-1,6-bisphosphate
- phosphofructokinase
- req ATP input
- 2nd Pi further destabilises sugar, promoting cleavage in step 4
- entry of sugars into glycolysis controlled via allosteric reg of phosphofructokinase by ATP levels in cell, ATP binds to enzyme downregulating it
What occurs during cleavage? (4th step glycolysis)
- F1,6BP to DHAP + GADP
- by aldolase
- only GADP can progress through glycolysis
- isomerisation to fructose ensures 3:3 split of C, rather than 2:4 which would req 2 separate pathways to metabolise
What occurs during conversion of DHAP? (5th step glycolysis)
- DHAP –> GADP
- K greatly in favour of DHAP, but reaction proceeds as GADP constantly removed by glycolysis pathway
What occurs during oxidation of GADP? (6th step glycolysis)
- GADP to 1,3-bisphosphoglycerate (compound w/ high phosphoryl transfer pot)
- by glyceraldehyde-3-phosphate dehydrogenase
- NADH formed
- 1st energy gen step
What are the common activated carrier molecules?
- NADH
- FAD/FADH2
- CoASH