1.16. Cell respiration 1 Flashcards
cell respiration
metabolic pathway with many steps with the purpose of harvesting chemical energy from food molecules
- the oldest metabolic process in living organisms on Earth
substrates and products in CR
substrates: glucose, O2 (optional - only if aerobic), NAD^+
products: CO2, H2O, ATP and NADH + H^+ (chemical energy)
which living organisms perform CR?
all - Animalia, Plants, Funghi, Protocstists, Archea, Bacteria
where does CR occur
in cytoplasm and in mitochondria (in most organisms - except Archea ad Bacteria)
why is the presence of an oxidizing agent needed for cell respiration?
glucose is a very stable molecule (it’s inert/self-satisfied) - it needs to be destabilized to react/interact which can be achieved either by heating it, providing an enzyme or providing an oxidizing agent to oxidize it
- catabolic reaction analogy: rock rolling downhill - initial push (E invested) and then reaction continues spontaneously providing much more E than invested (2 ATP invested, 38 released)
providing thermal E to glucose:
products CO2, H2O, light E and heat (useless for organisms)
in organisms, E from glucose is released as… (efficiency?)
ATP (chemical energy) and heat (thermal energy) - efficiency is 40% (rest is lost as heat)
ATP is…
universal energy transfer molecule
glucose gets oxidized by…
oxygen
redox reactions
reduction and oxidation reactions are coupled processes (one causes the other):
glucose + O2 into CO2 + H2O (ox.)
ADP + P into ATP (red.)
or
ATP into ADP + P (ox.)
a-a into polypeptide chain (red.)
- oxidation of ATP creates E for a-a polymerization
oxidation
- similar to hydrolysis
- E released
- gain of O2
- loss of e-
- loss of H+
- results in many C-O bonds
- yields a compound with lesser potential energy
reduction
- similar to dehydration
- E has to be invested
- loss of O2
- gain of e-
- gain of H+
- results in many C-H bonds
- yields a compound with higher potential energy
high electronegativity
affinity of a substance to gain electrons (susceptible to reduction)
how does oxidation release energy
transfer of electrons from a less electronegative towards the more electronegative atom releases E
organic compounds store chem E in ___ (___) because…
chemical bonds, covalent bonds, they are shared e- pairs so e- in the bond are the ones possessing energy
if cell respiration is anaerobic, it happens in…
cytoplasm (no mitochondria)
energy within glucose is stored in…
chemical bonds: C-O, C-H, C-C - covalent bonds=electrons whose transfer produces energy - they absorb E jump to excited state and when spontaneously going back to the ground state emit light/heat
two most important products of gradual oxidation of glucose (state full equations)
glucose -> (oxidizing agent) …
1|…-> (energy) P + ADP -> ATP
2|…-> (H) NAD^+ + 2H -> NADH + H^+
NADH + H^+ is the ___ form and the NAD^+ ___ form of the electron/hydrogen carrier
reduced, oxidized
why is NAD^+ an oxidizing agent?
because of it’s high electronegativity - it’ s hungry for electrons so it steals them from other substances
electron/hydrogen carrier meaning
it carries electrons and/or hydrogen atoms/protons (H^+=p+)
what can be done with the two products of gradual (step-by-step) oxidation of a food molecule
1|ATP can immediately be used to obtain energy to power anabolic processes
2|H atoms are joined with NAD^+ and NADH + H^+ is formed - little boxes storing potential energy which accumulate and get transferred to a specific site in mitochondria where they are opened in controlled way and the E released is used to create ATP - majority of E is stored in this way
gradual oxidation also called
stepwise or regulated - meaning, it has multiple steps
when is O2 used as oxidizing agent
only in the last step of cell respiration - in its place the cell uses NAD^+ (found in cell)
why does oxygen have to be introduced as an oxidizing agent
because once NAD^+ is reduced, it is very stable so an even stronger oxidizing agent has to be introduced to turn it back to its oxidized form - this is O2
how is water one of the products of CR? (show equations)
O2->2O^2-
O^2- + 2H^+->H2O
the main electron carrier in CR is…
NAD^+ (nicotinamide adenine dinucleotide)
what is the aim of many steps of CR?
to generate NADH+H^+ molecules because in the final step of CR they will accumulate and release energy for ATP
molecule that stores E in the cell
ATP?
most common CR substrates
carbohydrates (glucose - any hexose sugars), lipids, proteins (once c-h and lipids are used up)
