Download Lecture 6

Cellular respiration
and fermentation
04/18/2016
BI102
Announcements
• Exam 1 after lecture
• Don’t forget to do the online assignments every
week!
• Quiz 2 and lab 2 review
Cellular Respiration
Cells require lots of energy
• Cell require a constant supply of energy to
perform metabolic reactions
• Energy is transferred from energy-storage
molecules like glucose to energy-carrier
molecules like ATP
• The energy used on earth comes almost entirely
from the Sun
Energy storage
• Plants convert glucose to
sucrose or starch
• Animals convert glucose to
glycogen and fat
• We will not cover the
conversion of storage
molecules to glucose
• We will cover the
breakdown of glucose
during respiration
The energy carrier molecule,
ATP
• A nucleoside with three phosphates
• AMP is a nucleotide in RNA
• Paired with endergonic reactions 
dephosphorylation of ATP
Electron (energy) carriers
• FAD (vitamin B2) and NAD (vitamin B3) are electron carriers
• They can be easily reduced (add e-) or oxidized (give out e-)
Oxidative phosphorylation –
chemiosmosis in the cell for ATP
production
• In eukaryotes, oxidative phosphorylation takes place in
mitochondria. In prokaryotes, this process takes place in the
plasma membrane.
Photosynthesis
6 CO2 + 6 H2O + light energy  C6H12O6 + 6 O2
Cellular respiration
C6H12O6 + 6 O2  6 CO2 + 6 H2O + 38 ATP + heat
Cellular respiration
• Animals do this too
• We just bypass photosynthesis by eating,
breathing
(exhaled)
Cellular Respiration
Cellular respiration
• Glycolysis – generates 2 ATP
• Kreb’s cycle – generates 2
ATP
 Identified in 1937 by Hans
Adolf Krebs
• Electron Transport Chain –
generates 34 ATP
 38 ATP total (in theory)
Glycolysis
• Glyco – sweet
• Lysis – split apart
• Happens outside the mitochondria
• Cytoplasm
• One glucose molecule is converted to
two pyruvate molecules
• 2 ATP and 2 NADH are generated
Kreb’s or Citric acid cycle
• If oxygen is available, the 2 pyruvate will be
broken down into 6 CO2 and ATP
• Takes place in the matrix
Oxidation of pyruvate
• First, each pyruvate is split, releasing a CO2,
leaving an acetyl behind
• Acetyl reacts with CoA, transferring two
electrons to NAD+
• The CO2 has
two of the
original six
carbons from
glucose
Kreb’s or Citric acid cycle
• Start with one molecule of Acetyl CoA
• By the end of the cycle, two CO2 will be
generated and chemical energy will be stored in
1 ATP, 3 NADH, and 1 FADH2
• CO2 diffuses from the mitochondrial matrix
into your blood where it is transported finally
to your lungs
Kreb’s or Citric acid cycle
• If oxygen is available, the 2 pyruvate will be
broken down into 6 CO2 and ATP
Energy inventory
• Glycolysis
• Each glucose  2 pyruvate + 2 ATP
• Kreb’s cycle
• Each pyruvate  3 CO2 + 1 ATP
• Total is 4 ATP per glucose
• But the cell has charged up 10 NADH and 2
FADH2 per glucose
• These will release electrons during the electron
transport chain
• The depleted energy carriers can be recharged again
Electron Transport Chain (ETC)
• High-energy electrons jump from molecule to
molecule releasing small amounts of energy
• Energy is used to pump H+ across the inner
membrane into the intermembrane space
Electron Transport Chain (ETC)
• The concentration gradient of H+ across the
membrane is used to drive ATP production by
ATP synthase
• The electrons, the H+, and O2 combine to form
water (1 water molecule/2 electrons)
Electron Transport Chain (ETC)
ATP is recycled by the cell
• A protein carrier takes the ATP molecules to
the intermembrane space (and then the ADP
molecules to the matrix)
• The ATP molecules diffuse through the large
pores in the outer membrane and enter the
cytosol
• Then, ADP molecules diffuse back into the
intermembrane space
Fermentation
What happens when oxygen is unavailable?
• Cells must generate ATP without oxygen
• Fermentation
• Less efficient – 2 ATP per glucose
• Waste products
• Lactic acid (animals, bacteria (yogurt))
• C6H12O6
2 Lactic acid + 2 ATP +
heat
•
Lactic acid fermentation
Fermentation
•
Waste products in yeast: ethanol and CO2
C6H12O6
2 CO2 + 2 Ethanol + 2 ATP + heat
Alcoholic fermentation
Cellular respiration - summary
Amino acids can be sent to
glucose canabolism
Glycogen, fats, and proteins
can be fed into cell respiration