Download Respiration Intro.

Respiration Intro.
Energy: required by all living systems for: SYNTHESIS,
TRANSPORT & MOVEMENT; much of that energy is obtained
via Cellular Respiration (CR)
- The breakdown of glucose is exergonic, having a free energy
change that has a –ΔG value = indicates that the products of
the chemical reaction stores less energy than the reactants;
(because energy was released to to cell).
Remember… The more - ∆G, more work can be done.
 Chemical Energy: stored in chemical bonds
- combustion: breaking of bonds to release energy
- controlled combustion: when that energy is harnessed via
coupled reactions.
coupled reactions: energy from an exergonic reaction can drive an
endergonic reaction.
Cellular Respiration: process of converting food energy to ATP
ATP: a usable form of energy (“energy currency”)
 ATP provides the cell with the free energy to drive
endergonic reactions so exergonic reactions can take place…
 Exergonic reactions (from CR) provide the energy to
regenerate ATP…
- The release of energy during the hydrolysis of ATP comes
from the chemical change to a state of lower free energy,
not from the phosphate bonds themselves.
Exergonic
- The cell taps this energy source by using enzymes (kinases)
to transfer phosphate groups from ATP to other compounds,
which are said to be phosphorylated…
phosphorylation: a
is transferred to a molecule (increased E)
MAKES IT MORE REACTIVE.
-
Release of
P
used to drive SYNTHESIS, TRANSPORT &
MOVEMENT
 Two types of phosphorylation creating ATP:
1. Substrate-level phosphorylation = transfer of a
from a
substrate molecule (usually an intermediate sugar) to ADP
making/recharging ATP.
2. Oxidative phoshorylation = a mode of ATP synthesis powered
by redox reactions.
In order to understand the process of making energy (ATP), we
must review redox reactions:
 Oxidation-Reduction: REDOX reactions in which energy is
transferred between molecules.
Electron’s energy associated with stability:
 with highly electronegative atom (ex: O of O2):
- more tightly held
- more stable
- less energy to be extracted

-
with less electronegative atom (like C-H bond in glucose):
less tightly held
less stable
energy can be yielded if moved to lower energy state
(from a more electronegative atom taking e- from C-H)
 Organic molecules that have an abundance of hydrogen are
excellent fuels because their bonds are a source of electrons
with high potential energy.
 They also have the the potential to “drop” the energy when
they move closer to oxygen.
 The change in covalent status of electrons as hydrogen (and
associated e-) is tranferred to oxygen is what liberates the
energy.
OXIDATION:
- removal of electrons from a compound/atom
- sometimes removing whole H atoms = (dehydrogenation)
[e- + proton]
- may also happen with addition of oxygen (inorganically =
"rusting")
releases energy
lowers energy in compound which is oxidized
- compound doing the oxidizing (the compound taking the
removed e- (or removed H) = oxidizing agent; when it takes
the e-, it becomes reduced.
REDUCTION:
- addition of electrons (reduces the amount of + charge of
that atom.)
- also, addition of whole H atoms
- may also happen with the removal of oxygen
requires energy
raises energy in compound which is reduced
- compound doing the reducing (the compound giving up the e-)
= reducing agent; when it loses e- it becomes oxidized
 Oxidation-reduction always occurs together = redox rxns
- if reduction requires energy, oxidation must supply it
- reactions can be coupled to transfer energy
-G = spontaneous = exergonic
oxidation
+G = not spontaneous (requires E from exergonic rxns) = endergonic =
reduction
 Oxidation & reduction refer not to isolated substances
but to changes occurring to a substance during a rxn.
o compounds have lower energy after oxidization
o so, if we can reduce them again they'll be "recharged"
(capable of yielding electrons and energy again)
Importance to CR = A redox reaction that relocates ecloser to oxygen releases chemical energy which can be put
to work.
 In CR, e- “fall” from glucose to oxygen in a series of
steps in creating ATP.
 During the combustion of glucose, glucose is oxidized and
oxygen is reduced. Meanwhile, e- lose potential energy
along the way.
- So,… what are these compounds from where these e- “fall
from and to” in the transfer of energy stored in glucose in
forming ATP?
- In other words, what compound carry these e- from glucose
to the final e- acceptor (oxygen), in forming the final
energy storage molecule = ATP?
= Electron Carriers!
 Think of it as a game of “hot potato” as electrons move from
one reaction to the next in each process of CR.
 Electron carriers in biological systems (the players in the game
of hot potato):
 NAD+ & NADH
- NAD+: nicotinamide adenine dinucleotide (oxidized form)
- NADH: reduced NAD
 carries electrons (and Energy ) from glycolysis & citric acid
cycle (CAC) to elctron trasport system/chain (ETS)
 oxidation of NADH will ultimately yield ATP at the end of CR
(≈3 ATP / NADH)
 FAD & FADH2:
 carry e-'s from (one step) of CAC to ETS
(≈2 ATP / FADH2)
 NADP+ & NADPH: involved in photosynthesis (more to
come…)
CR in a nut shell: Glycolysis
Junction rxn
Citric Acid
Cycle (Kreb’s)
Electron Transport Chain (system) [ETS]
Chemiosmosis
ATP