Download 8 Glycolysis and Fermentation

Glycolysis and
Fermentation
Chapter 8
Cellular Respiration and
Photosynthesis
0 Things to know in these chapters
0 Names and order of the processes
0 Reactants and products of each process
0 How do they relate to the overall equations?
0 What environmental factors are needed to run the process?
0 Where will these processes occur? (organisms and
organelles)
0 The occasional important “step” within the process
Cellular Respiration
0 Cellular respiration is the process of breaking down sugars to
provide cells with energy
0 Cellular Respiration Equation:
0 C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy
0 Cellular respiration allows for a molecule of glucose to be broken
down as slowly as possible
0 If glucose was broken down quickly, much of the energy it holds
would be lost as heat
0 Cellular respiration is able to harness 39% of the energy
available in a glucose molecule
0 Photosynthesis is 55% efficient
0 The average gasoline automobile is 25% efficient
Cellular Respiration
0 Cellular respiration is 3 separate processes that combine to
maximize the energy output in various conditions
0 1. Glycolysis.
0 Slowly convert glucose into pyruvic acid.
0 Obtain small quantity of energy; very little wasted though
0 Designed to maximize energy production later
0 2. Aerobic Respiration
0 Takes place when cell has access to oxygen
0 Citric Acid Cycle and Electron Transport Chain
0 Large amounts of ATP produced
0 3. Anaerobic Respiration (Fermentation)
0 Takes place when cell has no access to oxygen
0 Alcohol or lactic acid produced
0 Maintains life temporarily until oxygen can be maintained
Glycolysis Summary
0 Each process in photosynthesis and respiration is a machine.
0 The machine takes a reactant and, throughout a series of
steps, builds products.
0 Like man-made machines, each of these steps creates waste
material
0 Unlike man-made machines, the waste materials just happen
to be molecules the cell needs
0 Sometimes, the products also are needed. Sometimes they aren’t.
0 As long as the cell keeps these machines working, the
machines will keep churning out these “waste” products
Glycolysis Summary
0 Glycolysis takes place in the cytoplasm
0 Glycolysis is ten steps long
0 Glycolysis requires an input of energy
0 “Glyco” = glucose; “lysis” = “to split”
0 For the processes in these chapters, I will provide all the
information so you know what is happening. The essential info
for memorizing will be underlined
Glycolysis
0 Step 1
0 Begins with a molecule of glucose
0 Energy from an ATP is consumed
0 At this point, the cell has used energy and hasn’t harnessed any.
It’s in debt.
0 By spending energy now, it can invest the energy and get MUCH
more energy later.
0 The cell forms a molecule of glucose-6-phosphate
Glycolysis
0 Step 2
0 Glucose-6-phosphate is rearranged to form a molecule
of fructose-6-phosphate
Glycolysis
0 Step 3
0 Another input of ATP is required
0 At this point the cell has spent two high-energy
molecules and has made none.
0 The cell is even more in debt now.
0 Fructose-6-Phosphate is rearranged to form Fructose-
1,6-Bisphosphate
Glycolysis
0 Step 4 and Step 5
0 The glucose molecule is split from one 6-carbon molecule
into two 3-carbon molecules
0 The amount of carbon, hydrogen, oxygen and phosphorus hasn’t
changed. But now there’s two molecules instead of one.
0 One molecule immediately forms a glyceraldehyde-3-phosphate
(PGAL, or G3P)
0 The other forms a different molecule temporarily, then
immediately forms a second PGAL
0 From this point on, there are two identical molecules that
enter each step of cell respiration, which means we will
double the products we make from here on out.
0 Without the input of energy at the beginning, we couldn’t have
done this.
Glycolysis
0 Step 6
0 The PGAL is phosphorylated (a free-floating
phosphate is attached)
0 This phosphate will eventually be attached to an ADP to
form an ATP
0 PGAL also donates a Hydrogen to an NAD+ to become
an NADH
0 NADH is a waste product in glycolysis, but NADH will be
used later in the electron transport chain as a reactant
0 The PGAL rearranges to form a molecule of 1,3-
bisphosphoglycerate (PGAP)
Glycolysis
0 Step 7
0 The PGAP donates one of it’s phosphates to an ADP to
form ATP
0 The ATP is a “waste” product in glycolysis—but the cell
can use it somewhere else
0 *Remember: we’ve actually made TWO ATP’s (one for
each PGAL we made earlier)
0 PGAP is rearranged to form a 3-phosphoglycerate
(PGA)
Glycolysis
0 Step 8
0 PGA is rearranged to form a 2-phosphoglycerate
Glycolysis
0 Step 9
0 2-phosphoglycerate loses a water molecule
0 2-phosphoglycerate is rearranged to form
Phosphoenolpyruvate (PEP)
Glycolysis
0 Step 10
0 PEP donates a phosphate to form an ATP
0 The final molecule of glycolysis is a 3-carbon pyruvate.
Glycolysis Summary
0 Inputs
0 1 glucose molecule
0 2 ATP
0 Outputs
0 2 pyruvate molecules
0 2 NADH
0 4 ATP
0 Net Gain
0 2 pyruvate molecules
0 2 NADH
0 2 ATP
Fermentation
0 After glycolysis, the pyruvic acid will enter either aerobic or
anaerobic respiration
0 Aerobic respiration: if oxygen is available
0 Anaerobic respiration: if oxygen is not available
0 Anaerobic respiration, or fermentation, comes in two forms
0 Alcoholic fermentation: Yeasts and other microorganisms
0 Pyruvic acid + NADH  Alcohol + CO2 + NAD+
0 Lactic Acid fermentation: muscle cells
0 Pyruvic acid + NADH  Lactic Acid + NAD +
Fermentation
0 Fermentation for humans is not ideal at all. It’s a life-support
system.
0 Without oxygen, the only process for cells to obtain energy
from is glycolysis.
0 In order for glycolysis to occur, it needs three reactants
0 Glucose, which is obtained from food. This is not a problem
0 ADP, to form ATP. This is not a problem
0 NAD+ to form NADH. NADH is consumed and transformed back
to NAD+ during aerobic respiration
0 But…we can’t go through aerobic respiration right now. So we can’t
turn the NADH back to NAD+. So we don’t have any NAD+ to use in
glycolysis. So we can’t run glycolysis.
0 THIS is the problem.
Fermentation
0 The sole purpose of fermentation is to remove the “H” off of
the NADH and turn it back to NAD+.
0 The NAD+ can then re-enter glycolysis, and the cell can get
another net gain of 2 ATP.
0 2 ATP is pathetic, but it is something. So why do we do it?
0 Fermentation gives the organism a few extra precious minutes to
find some oxygen again
0 Without it, organisms would die the instant their cells are
without oxygen.
Cell Respiration Summary
0 C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy
0 C6H12O6 : For glycolysis
0 6 O2 : To collect the electron in the ETC
0 6 CO2 : Given off in intermediate step and Citric Acid Cycle
0 6 H2O : Given off in the ETC
0 Energy : In the form of ATP