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