Chapter 7 – The Working Cell:
Energy from Food
College Prep Biology
Mr. Martino
7.1 How Cells Make ATP
 Cellular Respiration: harvesting of E from
food molecules by cells

2 types of respiration:
Aerobic: requires oxygen (harvests 40% of E in glucose)
 Anaerobic: does not require oxygen (harvests 2% of E
in glucose)
 Evolved about 3.8 billion years ago - before oxygen


C6H12O6 + 6 O2

6 CO2 + 6 H2O + E
Glucose is the example carbohydrate
Glycolysis:
(exergonic) splits
glucose into 2 pyruvic
acid
 Occurs in
cytoplasm
 Oxygen is final
electron acceptor
= water
 Enzymes catalyze
 First stage of all
respiration
Overview of Aerobic Respiration
 Aerobic Respiration is
continuous – but occurs in 3
main stages
 Glycolysis: (exergonic)
splits glucose into pyruvic
acid
 Occurs in cytoplasm
 Kreb’s Cycle: (exergonic)
completes glucose
breakdown - pyruvic acid
becomes CO2
 ETC: (endergonic) NADH
and FADH2 shuttle e- and
generates most of cell’s ATP
by chemiosmosis
Two Mechanisms Generate ATP
 Chemiosmosis: cells
use the potential E of
concentration
gradients to make ATP



Depends upon
membranes and ATP
synthase
ETC makes this E
transport possible
Cells generate most of
their E this way
 Substrate-level
phosphorylation: an
enzyme transfers a Pgroup from a substrate
to ADP
 No membrane
involved
 Only generates a
small percentage of
a cell’s ATP
7.3 Second Stage – Pyruvic Acid
Conversion and Kreb’s Cycle
 2 pyruvate molecules from glycolysis enter mitochondrion
 Pyruvic acid from glycolysis does not enter the Kreb’s cycle
+
 1. It is oxidized while NAD is reduced to NADH
 2. 1 C is released in the form of CO2
 3. Coenzyme A + fragment = acetyl CoA
 Each glucose produces 2 acetyl CoAs for Kreb’s
Kreb’s Cycle
 Only the acetyl part of
acetyl CoA participates
 Each turn of Kreb’s
produces:
 1 ATP by substrate
level phosphorylation
 3 NADH
 1 FADH2
 Turns twice per
glucose
7.4 Third Stage – Electron
Transport System
 Final stage of respiration is ETC & ATP formation

1.
2.
3.
4.
The fold of the cristae provide space for many ETC’s and
ATP synthases
NADH is shuttled down the e- carriers
Oxygen is the final e- (H) acceptor forming H2O
Proteins shuttle H+ across the membrane
 The greater the gradient the more potential E
H+ are passed through ATP synthase which catalyzes the
formation of about 34 ATP
7.5 Anaerobic Respiration
 2 forms of anaerobic respiration
1.
Alcoholic fermentation: anaerobic respiration in which
pyruvic acids form ethyl alcohol
 Performed by yeasts and bacteria
 Releases CO2
 Ethanol is toxic to the organisms who produce it – if
too concentrated
7.5 – con’t
2.
Lactic Acid Fermentation: anaerobic
fermentation in which pyruvic acids form
lactic acids



Used to make cheese and yogurt
Occurs in muscle cells – causing pain and fatigue
No CO2 is released