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How Cells Harvest Energy: Chapt. 7. food substances are energy-rich molecules cells oxidize food to release energy. Oxidation. removal of electrons (often as hydrogen atoms) as one molecule is oxidized another is reduced (Red-Ox reactions) Text pg 116. + electron.

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how cells harvest energy chapt 7
How Cells Harvest Energy:Chapt. 7
  • food substances are energy-rich molecules
  • cells oxidize food to release energy
oxidation
Oxidation
  • removal of electrons (often as hydrogen atoms)
  • as one molecule is oxidized another is reduced (Red-Ox reactions)
  • Text pg 116

+ electron

oxidized reduced

(electron acceptor)

(electron donor)

cellular redox reactions
Cellular Redox Reactions
  • Typically Exergonic reactions
  • DG is negative
  • Reactants Products + E.
  • E. (in the form of e-) is used for initiating other reactions
cell oxidation reduction reactions performed by
Cell Oxidation-ReductionReactions Performed by:
  • Cell molecules such as NAD, NADP, FAD, FMN …termed coenzymes
  • each of these work with specific enzymes to catalyze redox reactions
  • Text pg 116
  • when reduced (ie. NADH, NADPH) each gains energy for use elsewhere in the cell
storage sources of cell energy
Storage Sources of Cell Energy:
  • Triglycerides (fats)
  • Carbohydrates (glycogen, starch)

Both end up following the breakdown

pathway for glucose.....

glucose breakdown an oxidation process
Glucose Breakdown-an oxidation process

Occurs as two separate processes:

1. Glycolysis

2. Cellular respiration

1 glycolysis
1. Glycolysis
  • occurs in cytoplasm
  • evolutionary primitive energy creating system
  • may occur in anaerobic environments

Summary: One (6-carbon glucose) goes to form

Two (3- carbon pyruvate) molecules

produces 2 ATP & 2 NADH

Low energy yield (~3% Potential)

glycolysis
Glycolysis

+

(2) Pyruvate

Glucose

glycolysis energy yield
Glycolysis Energy Yield

~700 Kcal of energy stored in 1 glucose sugar...

Glycolysis produces 2 ATPs from glucose

Each ATP is worth ~7-10 Kcal

Therefore, ~20 Kcal produced

20/700 = ~3% efficiency

part 1 uses atp energy

Glycolysis:

Part 1- Uses ATP Energy

Glucose (6C)

Glyceraldehyde 3-phosphate (3C)

2 ATP

5 Steps

2 ADP

part 2 generates atp nadh

Glycolysis:

Part 2- Generates ATP + NADH

G3P (3C)

Pyruvate (3C)

4 ADP

2 NADH

4 ATP

5 Steps

slide13

Glycolysis: Summary

  • 10 enzymes act in sequence to:
  • Convert 1 Glucose (6C) --> 2 Pyruvate (3C)
  • 2 ATP’s produced
  • 2 NADH produced
  • Reactions occur in cytoplasm
slide14
When Oxygen is available to the cell, glycolysis is followed by cellular respiration…
    • Text pg 117
  • When O2 is unavailable, glycolysis will lead to Fermentation steps…
    • Text 117
fermentation
Fermentation

When inadequate oxygen is present, for example, in a muscle cell undergoing

vigorous contraction, the pyruvate produced by glycolysis is converted to lactate.

This reaction uses NADH produced in glycolysis, and the whole pathway yields

much less energy overall than complete oxidation.

fermentation16
Fermentation

In some organisms that can grow anaerobically, such as yeasts, pyruvate is converted via acetaldehyde into carbon dioxide and ethanol. Again, this pathway regenerates NAD+ from NADH, as required to enable glycolysis to continue.