catabolic pathways
occur when molecules are broken down and their energy is released
two important catabolic pathways to know
fermentation and aerobic respiration
fermentation
the partial degradation of sugars without the use of oxygen
aerobic respiration
the most prevalent and efficient catabolic pathway
energy from biological macromolecules is used to produce ATP
oxygen is consumed as a reactant
term cellular respiration will be used to refer to this
in cellular respiration...
carbohydrates, fats, and proteins can all be broken down to release energy
chemical rxn for cellular respiration
C6H12O6 + 6O2 -> 6 CO2 + 6 H2O + energy
exergonic release of energy from glucose...
is used to phosphorylate ADP to ATP
life processes...
constantly consume ATP
cellular respiration burns fuels and...
uses the energy to regenerate ATP
oxidation-reduction (redox) reactions
electrons and transferred from one reactant to another
the reactions of cellular respiration
oxidation
loss of one or more electrons from a reactant
loses electrons and loses energy
reduction
the gain of one or more electrons
gains electrons and gains energy
at key steps in cellular respiration...
electrons are stripped from glucose
electrons and protons travel together, forming hydrogen atoms
how are hydrogen atoms transferred to oxygen?
NAD+
NAD+
electron carrier
coenzyme
derivative of the B vitamin niacin
NAD+ accepts...
two electrons + stabilizing hydrogen ion
forms NADH
NADH has been reduced, gained energy
glycolysis
glucose is broken down into two pyruvate molecules
six-carbon glucose -> two three-carbon sugars -> two three-carbon acids (pyruvate)
where does glycolysis occur?
the cytosol
ATP-consuming phase of glycolysis
two ATP molecules are consumed
helps destabilize glucose and make it more reactive
ATP-producing phase of glycolysis
four ATP molecules are produced
glycolysis results in a net gain of how many ATP molecules?
2
products of glycolysis
2 NADH
2 ATP (net gain)
2 pyruvate - which head to the Krebs Cycle
most of the potential energy of glucose molecules resides where, after glycolysis occurs?
in the remaining two pyruvates
what happens after glycolysis?
pyruvate is oxidized to Acetyl CoA
how does pyruvate move from the cytosol into the matrix of the mitochondria?
via a transport protein
what happens in the matrix of the mitochondria when the pyruvate is moved in?
an enzyme complex catalyzes three reactions
1) CO2 molecule is removed
2) electrons are stripped from pyruvate to convert NAD+ to NADH
3) coenzyme A joins with remaining two-carbon fragment to form acetyl CoA
how many acetyl CoA molecules are produced per glucose molecule?
2
where does the acetyl CoA produced go?
it enters the citric acid cycle
citric acid cycle
the job of breaking down glucose is completed with CO2 released as a waste product
where does the citric acid cycle occur?
the mitochondrial matrix
each turn of the citric acid cycle requires the input of how many acetyl CoA?
1
how many turns must the citric acid cycle make before glucose is completely oxidized?
2
each turn of the citric acid cycle produces...
2 CO2
3 NADH
1 FADH2
1 ATP
the total products of the citric acid cycle are...
(needs two turns to fully oxidize glucose)
4 CO2
6 NADH
2 FADH2
2 ATP
at the end of the citric acid cycle...
the six original carbons in glucose have been released as CO2
why have only 2 ATP molecules been produced at the end of the citric acid cycle when all of the 6 original carbons have been released as CO2?
the energy is held in the electrons in the electron carriers, NADH and FADH2
where is the electron transport chain located?
it is embedded in the inner membrane of the mitochondria
what is the electron transport chain composed of?
three transmembrane proteins - work as hydrogen pumps
two carrier molecules - transport electrons between hydrogen pumps
*thousands of these are present in the inner mitochondrial membrane
what is the electron transport chain powered by?
electrons from electron carrier molecules NADH and FADH2
how does the electron transport chain work?
as the electrons flow through the electron chain, the loss of energy by electrons is used to power the pumping of protons across the inner membrane
what happens at the end of the electron chain?
the electrons combine with two hydrogen ions and oxygen to form water
what is the final electron acceptor?
O2
what happens if oxygen isn't available at the end of the electron transport chain?
the transport of electrons comes to a screeching halt
no hydrogen ions are pumped, no ATP is produced
how do hydrogen ions flow back down their gradient?
ATP synthase
what is ATP synthase?
a channel in the transmembrane protein
harnesses the electrochemical gradient to to phosphorylate ADP, forming ATP
what is an electrochemical gradient?
gradient of hydrogen ions
stores potential energy by a diffusion gradient and an electric charge gradient across a membrane
where are electrochemical gradients found in cellular respiration?
across the inner membrane of mitochondria
where are electrochemical gradients found in photosynthesis?
across the inner membrane of chloroplasts
chemiosmosis
an energy-coupling mechanism
uses stored energy in the form of an H+ gradient across a membrane to drive cellular work
ie. ATP synthesis
the electron transport chain and chemiosmosis together result in...
oxidative phosphorylation
why is the term oxidative phosphorylation used to describe electron transport chain and chemiosmosis?
ADP is phosphorylated
oxygen is necessary to keep the electrons flowing
fermentation
an expansion of glycolysis
ATP is generated without oxygen
fermentation consists of...
glycolysis
reactions that regenerate NAD+
what molecule accepts electrons in glycolysis?
NAD+
oxygen is not needed to accept electrons
alcohol fermentation
pyruvate is converted into ethanol
CO2 is released -> NADH oxidized in the process
creates more NAD+
lactic acid fermentation
pyruvate is reduced by NADH
NAD+ formed in the process
lactate produced as a waste product
what else can be used to generate ATP during cellular respiration other than glucose and other sugars?
proteins and fats
phosphofructokinase (PFK)
allosteric enzyme
functions in early pathway of glycolysis
acts as a regulator of respiration
with adequate ATP...
the breakdown of glucose to pyruvate is not required
when ATP is needed in higher concentrations...
a product of ADP acts as an allosteric regulator on PFK
increases ATP production
PFK is considered...
the pacemaker of respiration
controls the rate of the entire process of cellular respiration
PFK is a great example of...
the regulation of an enzymatic process by negative feedback