Download Chapter 7 Cellular Respiration

Chapter 7
Cellular Respiration
Glycolysis and Fermentation
• Cellular respiration: cells make ATP by
breaking down organic compounds
• Both autotrophs and heterotrophs undergo
cellular respiration
– Break down organic compounds into simple
molecules and energy
– Some energy used to make more ATP, some is
used by the cells to do work
Overview of Cellular Respiration
Cellular Respiration Overview
Overview of Cellular Respiration
1. Glycolysis
– Organic compounds are converted into carbon
molecules of pyruvic acid, which makes a small
amount of ATP and NADH (electron carrier)
– Anaerobic process = does not require oxygen
– Occurs outside of the mitochondria
Overview of Cellular Respiration
2. Aerobic Respiration (oxygen present)
– Pyruvic acid is broken down and NADH is used to
make a large amount of ATP
Note: pyruvic acid can enter other pathways when
no oxygen is present. Glycolysis and other anaerobic
pathways = fermentation
Overview of Cellular Respiration
Glycolysis
• Series of chemical rxns
catalyzed by specific
enzymes to create
pyruvic acid from 6carbon molecules
1. Phosphate groups are
attached to glucose to
form a 6-carbon molecule
2. 6-carbon molecule
splits into two G3P
molecules
3. G3P molecules are
oxidized and receive a
phosphate group
– NAD+ to NADH
4. Phosphate groups (4)
added in step 1 and 3 are
removed, forming pyruvic
acid, produce 4 ATP
Glycolysis
Glycolysis
• Two ATP molecules used, but four are
produced
• Glycolysis has a net yield of 2 ATP molecules
Fermentation
• In anaerobic environments some cells can still
produce carbon compounds
• Using glycolysis and additional pathways to
generate NAD+ is called fermentation
– Lactic acid fermentation
– Alcoholic fermentation
Fermentation
• Lactic acid fermentation: pyruvic acid is
converted into lactic acid
• Involves transfer of one hydrogen atom from
NADH and the addition of one proton (H+) to
pyruvic acid (NADH  NAD+)
• NAD+ is used in glycolysis, and helps keep this
process going
• Why is this process important?
Lactic Acid Fermentation
Fermentation
• Alcoholic fermentation: converts pyruvic acid
into ethyl alcohol
• Two steps:
– 1.) CO2 molecule removed from pyruvic acid
• Leaves a two carbon compound
– 2.) Two hydrogen atoms are added to the twocarbon compound to form ethyl alcohol
– The hydrogen atoms come from NADH and H+,
and regenerates NAD+ for glycolysis
Aerobic Respiraton
• Aerobic = Uses oxygen
• Two major stages:
– Krebs Cycle
– Electron Transport Chain
• Krebs cycle involves completing the oxidation
of glucose in glycolysis. NAD+  NADH
• Electron transport chain uses NADH to make
large quantities of ATP
Aerobic Respiraton
• In prokaryotes, occurs in the cytosol of the cell
• In eukaryotes, occurs inside the mitochondria
– Pyruvic acid produced in glycolysis diffuses across
mitochondria’s double membrane and into the
matrix
Aerobic Respiration
• Pyruvic acid enters the mitochondrial matrix
and reacts with a molecule called coenzyme A
to form acetyl coenzyme A, acetyl CoA
The Krebs Cycle
• Biochemical pathway
that breaks down acetyle
CoA, producing CO2,
hydrogen, and ATP
The Krebs Cycle
1. Acetyl CoA combines with oxaloacetic acid to
produce citric acid
– Regenerates coenzyme A
2. Citric acid releases CO2 and hydrogen forming
a five carbon compound
– NAD+  NADH
3. Five carbon molecule releases CO2 and
Hydrogen forming a four carbon molecule
The Krebs Cycle
4. Four carbon compound from step three
creates another four carbon compound by
releasing a hydrogen
– FADFADH2
5. Step four molecule releases a hydrogen to
regenerate oxaloacetic acid to keep krebs cycle
going
– NAD+ NADH
Electron Transport Chain
• Second stage of aerobic respiration
• Couples with chemiosmosis
• ETC and ATP synthase are embedded into the
membrane of the mitochondria
– In prokaryotes this occurs on the cell membrane
• ATP is produced when NADH and FADH2
release hydrogen, regenerating NAD+ and FAD
Electron transport chain
1. NADH and FADH2 give up electrons
2. electrons passed down chain, losing energy
moving from molecule to molecule
3. energy from electrons pumps protons from
the matrix building a concentration gradient
between inner and outer membranes
Electron transport chain
• 4. concentration gradients of protons drive
the synthesis of ATP by chemiosmosis (same
as photosynthesis)
• 5. Oxygen is the final acceptor of electrons
that pass down the ETC
– Protons, electrons and oxygen all combine to form
water