Energy flows
Into an ecosystem as sunlight and leaves as heat
Catabolic pathways yield
Energy by oxidizing organic fuels. Catabolic pathways release stored energy by breaking down complex molecules
The breakdown of organic molecules is
Exergonic
Fermentation
A partial degradation of sugars that occurs without O2
Aerobic respiration
Consumes organic molecules and O2 and yields ATP
Anaerobic respiration
Similar to aerobic respiration but consumes compounds other than O2
Autotrophs
Are able to produce their own organic molecules through photosynthesis (plants, algae, some bacteria)
Heterotrophs
Live on organic compounds produced by other organisms
All organisms use
Cellular respiration to extract energy from organic molecules. Energy is contained within bonds of molecules
Electrons can be
Transferred from one atom to another during some chemical reactions. Still retain the energy of their position in the atom
Oxidation
LOSS of electrons
Reduction
GAIN of electrons
OIL RIG
Oxidation is loss, reduction is gain
Reduction:
Reduces the positivity of an atom/ion
Reducing agent
The electron donor
Oxidizing agent
The electron receptor
Cellular respiration is a series
Of reactions that are oxidation and also dehydrogenations. What is lost is a hydrogen atom
Dehydrogenations
Lost electrons are accompanied by hydrogen ions
NAD+
An electron carrier, accepts 2 electrons and 1 proton to become NADH. This reaction is reversible
NADH will later
Pass the electrons to the electron transport chain
Harvesting of energy from glucose has 3 stages
Glycolysis, pyruvate oxidation & citric acid cycle, and oxidative phosphorylation
Glycolysis
Breaks down glucose into two molecules of pyruvate
Pyruvate oxidation and Citric acid cycle
Complete the breakdown of glucose
Oxidative phosphorylation
Accounts for most of the ATP synthesis because it is powered by redox reactions
Substrate level phosphorylation
A smaller amount of ATP is formed in glycolysis and the Citric acid by this
32 molecules of ATP
For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to this many
ATP powers
Cellular work
ATP hydrolysis
Drives endergonic reactions in two way: by coupling or by phosphorylating
Coupling
Exergonic reactions with endergonic reactions so overall Delta G < 0
Phosphorylating
By phosphorylating substrates and making them more reactive
When glucose is oxidized yo CO2,
It ‘loses’ electrons. So glucose loses the potential energy that is associated with those electrons
Glycolysis breaks down
6-carbon glucose into two 3-carbon molecules of pyruvate and occurs in the cytoplasm
Glycolysis occurs
In the cytoplasm and occurs whether or not O2 is present
Glycolysis consists of two phases:
Energy investment phase and energy payoff phase
Energy investment phase
Two molecules of ATP are consumed. Glucose is phosphorylated twice.
Energy payoff phase
- Sugar is split to form 2 pyruvate molecules
- 2 molecules of NAD+ are reduced to NADH
- 4 molecules of ATP are formed by substrate level phosphorylation (net gain of 2 ATP)
For glycolysis to continue
NADH must be recycled to NAD+ by either aerobic respiration or fermentation
Aerobic respiration occurs
When oxygen is available as the final electron acceptor
Fermentation occurs
When oxygen is not available or when an organic molecule is the final electron acceptor
When oxygen is present
Pyruvate is oxidized to acetyl-CoA which enter the Citric Acid cycle
Without oxygen, pyruvate is
Reduced to oxidize NADH back to NAD+
Before the Citric acid cycle can begin,
Pyruvate must be converted to acetyl CoA.
Acetyl-CoA
Consists of 2 carbons from pyruvate attached to coenzyme A. Proceeds to the Citric Acid Cycle
The Citric acid cycle
Completes the breakdown of pyruvate to CO2
The Citric acid cycle oxidized organic fuel derived from
Pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn
First step of Citric Acid Cycle
Acetyl-CoA (2 carbons) +
Oxaloacetate (4 carbons) —>
Citrate (6 carbons)
Remaining steps of Citric Acid Cycle
- release 2 molecules of CO2
- reduce 3 NAD+ to 3 NADH
- reduce 1 FAD (electron carrier) to FADH2
- produce 1 ATP
- regenerate oxaloacetate
Have to run Citric Acid Cycle
Twice for each glucose. Produce 2 acetyl-CoA per glucose
After glycolysis, pyruvate oxidation, and the Citric Acid Cycle, glucose has been oxidized to:
- 6 O2
- 4 ATP
- 10 NADH
- 2 FADH2
NADH & FADH2 (electron carriers) proceed to the electron transport chain