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Pathways that harvest chemical energy

Part I: Redox Reactions and Glycolysis

Where does the Energy for Life come from?

Where does the Energy for Life come from?

Phototrophs

(via photosynthesis)

Chemotrophs & Phototrophs

6 CO 2 + 6 H 2 O + energy  C 6 H 12 O 6 + 6 O 2 D G = C 6 H 12 O 6 + 6 O 2  6 CO 2 + 6 H 2 O + energy for life processes D G = Assume that the change in free energy for these two reactions is 686 kcal/mol.

Assign the proper sign for each.

Release of energy from glucose: why not do it all in one step?

Combustion of glucose is a highly

exergonic

reaction… so how come living organism don ’ t harvest its energy in one single step?

Release of Energy from glucose: why not do it in one step?

Release of energy from glucose: why not do it all in one step?

1.

Allows for energy to be captured in “ packets ” . More practical. Harvest energy from small steps and store it in carrier molecules (ATP and NADH).

1.

A multistep pathway can be more efficiently regulated.

2.

Metabolic intermediates

from one pathway can feed into other metabolic pathways.

Cells obtain energy from glucose by oxidizing it Nutrients + 6O 2 O-R Reactions, catabolic reactions 6CO + 6H 2 + Extract energy from nutrient molecules, used for cellular activity Cell

Pathways that harvest the energy in glucose

Where in the cell do major energy pathways take place?

Where in the cell do major energy pathways take place?

Redox reactions • •

One substance transfers electrons to another substance

Reduction: Gain of one or more electrons by

an atom, ion, or molecule

• Oxidation: Loss of one or more electrons • Another way to think about it.

– hydrogen atoms are gained or lost (H = H + + e )

Redox reactions

During combustion, glucose is the reducing agent (electron donor), O 2 is the oxidizing agent (electron acceptor)

One carbon compounds with different energy concept

One carbon compounds with different free energy

Meet an Essential Electron Carrier

NAD + /NADH Is an Electron Carrier in Redox Reactions

• Example 1: Biological Oxidation-Reduction Reactions oxidation reduction 5 H • Example 2: C 6 H 12 O6 + 6O 2 4 H oxidation 6CO 2 + 6H 2 O reduction

Cellular respiration The two energy producing pathways

Both pathways start with glycolysis • •

Converts six-carbon glucose to two 3-carbon pyruvate Takes place in cytosol

What happens in glycolysis

1,3 bisphosphate glycerate 3-phospho glycerate 2-phospho glycerate

Which two rxns are endergonic & require free energy from ATP? ___, ___ Which reaction cleaves the 6-carbon backbone? ____ Which is the redox reaction? ______ Which reactions harvest energy for the cell? _______________ Which of these two intermediates are more oxidized: Glyc-3-P or 1,3 Bisphosphate glycerate Which glycolysis intermediates are NOT phosphorylated?

glyceraldehyde-3 phosphate

Pathway

Glycolysis

Notes

Glucose  2 pyruvate; 10 rxn in cytosol Prep Reaction Citric Acid Cycle Electron Transport & ATP synthase

ATP or GTP NADH FADH 2

+2 2 -