For CAPE Biology unit 2 specification

1. Objectives

2. Objectives

3. Relationship between ATP and ADP

4. ATP has two key functions within the cell:
• It functions as the energy currency of the cell by releasing energy
when hydrolysed to ADP (powers cell metabolism)
• It may transfer the released phosphate group to other organic
molecules, rendering them less stable and more reactive
•
ATP is synthesised from ADP using energy derived from one of two
sources:
• Solar energy – photosynthesis converts light energy into chemical
energy that is stored as ATP
• Oxidative processes – cell respiration breaks down organic
molecules to release chemical energy that is stored as ATP

5. Redox Reactions
• When organic molecules are broken down by cell respiration, the
chemical energy is transferred by means of redox reactions
• Redox reactions involved the reduction of one chemical species
and the oxidation of another (redox = reduction / oxidation)

6. • Cell respiration breaks down organic molecules and transfers
hydrogen atoms and electrons to carrier molecules
• As the organic molecule is losing hydrogen atoms and electrons,
this is an oxidation reaction
• Energy stored in the organic molecule is transferred with the
protons and electrons to the carrier molecules
•
The carrier molecules are called hydrogen carriers or electron
carriers, as they gain electrons and protons (H+ ions)
• The most common hydrogen carrier is NAD+ which is reduced to
form NADH (NAD+ + 2H+ + 2e– → NADH + H+)
• A less common hydrogen carrier is FAD which is reduced to
form FADH2 (FAD + 2H+ + 2e– → FADH2)

7. Summary of the Stages of Aerobic
Respiration

8. Structure and Function of a
Mitochondrion

9. The structure of the mitochondrion is adapted
to the function it performs:
• Outer membrane – the outer membrane contains transport
proteins that enable the shuttling of pyruvate from the cytosol
• Inner membrane – contains the electron transport chain and
ATP synthase (used for oxidative phosphorylation)
• Cristae – the inner membrane is arranged into folds (cristae)
that increase the SA:Vol ratio (more available surface)
• Intermembrane space – small space between membranes
maximises hydrogen gradient upon proton accumulation
• Matrix – central cavity that contains appropriate enzymes and a
suitable pH for the Krebs cycle to occur

10. Mitochondrion Diagrams

11. Glycolysis
Process:
Invest 2 ATP to start the reaction and a Glucose
molecule
Split glucose molecule in half to create two molecules of
Pyruvic Acid (each having 3-Carbons)
Produces two molecules of NADH from NAD+
Produces 4 new ATP molecules
NET GAIN: 2 ATP (4 Produced - 2 Invested)

12. Krebs Cycle (Citric Acid Cycle)
Location: in the Mitochondrial Matrix
Main Goal: To Break down pyruvate (pyruvic acid) into carbon dioxide
and Acetyl Co-A and release more energy
Process:
-Each pyruvate loses one carbon and makes a 2
carbon molecule called Acetyl CoA
-The carbon joins with the oxygen (aerobic) that breathe
in to create the carbon dioxide we exhale
-The Acetyl Co-A can then diffuse into the matrix of the
mitochondria

13. Krebs Cycle (Citric Acid Cycle)
Reactants:
Products from glycolysis
Pyruvate to Acetyl CoA
ADP
Oxygen
FAD
NAD+
Products:
4 Carbon Molecule to be recycled
ATP
Carbon Dioxide
FADH2
NADH

14. Electron Transport Chain
• Location: Inner Membranes of
Mitochondria
• Main Goal: Use hydrogen ions and
electrons to make
• up to 34 ATP
• Process:
• -All NADH and FADH2 are
electron carrier molecules
• - Made from glycolysis and Krebs
cycle
• NADH and FADH2 donate
electrons and
• hydrogen ions to make
ATP

15. Electron Transport Chain
Reactants:
ALL NADH and FADH2
from glycolysis and the
Krebs cycle
ADP
Products:
NAD+ and FAD
ATP

16. Stages of Cellular Respiration
C6H12O6 + O2  6CO2 + 6H2O + ATP
Oxidative Phosphorylation (aka Electron Transport)
Chemiosmosis ATP Synthesis
Citric Acid Cycle (aka Krebs Cycle)
Oxidize Pyruvate to Acetyl CoA Regenerate C molecules, give off CO2
Glycolysis
Oxidize Glucose Make Pyruvate
Cytosol
Mitochondrial matrix
Inner Mitochondrial Membrane
2 ATP
2 ATP
32 ATP

17. Fig. 9-6-3
Mitochondrion
Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH
Substrate-level
phosphorylation
ATP
Electrons carried
via NADH and
FADH2
Oxidative
phosphorylation
ATP
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis

18. What is Glycolysis?
• Glycolysis is the process in which glucose is broken down to
produce energy. It produces two molecules of pyruvate, ATP,
NADH and water. The process takes place in the cytoplasm of a
cell and does not require oxygen. It occurs in both aerobic and
anaerobic organisms.

19. • Glycolysis is the primary step of cellular respiration, which
occurs in all organisms. Glycolysis is followed by the Krebs
cycle during aerobic respiration. In the absence of oxygen, the
cells make small amounts of ATP as glycolysis is followed
by fermentation.

20. Glycolysis is a 10-step process
• Stage 1
• ATP is used to phosphorylated Glucose forming Glucose ,6-
phosphate .in the cell cytoplasm, by the action of enzyme
hexokinase.
• Nb. a more reactive form of glucose. This reaction prevents the
phosphorylated glucose molecule from continuing to interact
with the GLUT proteins. It can no longer leave the cell because
the negatively-charged phosphate will not allow it to cross the
hydrophobic interior of the plasma membrane.

21. Glycolysis
• Stage 2
• Glucose-6-phosphate is isomerised into fructose,6-phosphate
by an enzyme .
• Stage 3
• A second ATP molecule is used to phosphorylate fructose 6-
phosphate and converts it into fructose 1,6-bisphosphate.

22. Glycolysis
• Stage 4
• The fructose 1,6-bisphosphate is split into glyceraldehyde 3-
phosphate and dihydroxyacetone phosphate, which are isomers
of each other.
• Step 5
• dihydroxyacetone phosphate gets converted into
glyceraldehyde 3-phosphate.
• Nb steps 6-10 will occur twice because we now have two
molecule of glyceraldehyde 3-phosphate.

23. Glycolysis
• Step 6
• The sixth step in glycolysis oxidizes the sugar (glyceraldehyde-3-phosphate), extracting high-energy
electrons, which are picked up by the electron carrier NAD+, producing NADH. The sugar is then
phosphorylated by the addition of a second phosphate group, producing 1,3-bisphosphoglycerate. Note that
the second phosphate group does not require another ATP molecule.
• Step 7
• In the seventh step, 1,3-bisphosphoglycerate donates a high-energy phosphate to ADP, forming one
molecule of ATP and 3 phospoglycerate. (This is an example of substrate-level phosphorylation.)

24. Glycolysis
• Step 8
• The phosphate of the phosphoglycerate molecules is relocated
from the third to the second carbon to produce a molecule of 2-
phosphoglycerate.
• Step 9
• 2-phosphoglycerate to lose water from its structure;(dehydration reaction), becoming phosphoenolpyruvate
(PEP). PEP is an unstable molecule (high energy compound)
• Step 10
• In last step in glycolysis PEP readily donates its phosphate group to ADP, making a second molecule of ATP. As
it loses it phosphate , PEP is converted to pyruvate, the end product of glycolysis

26. Glycolysis: breaking glucose into two 3 C
pyruvate molecules
• Substrate Level Phosphorylation
• small amounts of ATP, made by
transferring P group from substrate to
ADP
• Occurs in the cytosol
• Used in fermentation and respiration,
ancient process
• Converts glucose (6C)  2 pyruvate
(3C) (pyruvic acid)
• Uses 2 ATP – energy investment
• Produces 4 ATP + 2 NADH – energy
payoff
• NET production = 2 ATP + 2 NADH

28. Summary of
the Stages of
Aerobic
Respiration

29. The link reaction
• Pyruvate is then decarboxylated to form acetyl-coA. Acetyl-coA is the
intermediate that enters the Krebs/TCA cycle.
• In the link reaction, pyruvate enters the matrix of a mitochondrion and is:
• decarboxylated: CO2 is removed from the pyruvate and then diffuses out of the
mitochondrion and out of the cell.
• dehydrogenated: Hydrogen is removed from the pyruvate (The pyruvate
molecules are oxidized in this reaction), and is picked up by NAD, producing
reduced NAD (NADH). This converts pyruvate into a 2-carbon compound.
• combined with coenzyme A to give acetylcoenzyme A (ACoA).

31. Link Reaction
• - Second stage of respiration.
• - Takes place in the matrix of mitochondria.
• - No gain or loss of ATP.
• - Only takes place aerobically

32. Fates of Pyruvate
• If oxygen is available, each pyruvate now moves into a mitochondrion,
where the link reaction and the Krebs cycle take place. During these
processes, the glucose is completely oxidized.
• Pyruvate is a versatile molecule which feeds into numerous pathways.
After glycolysis, it can be converted to acetyl-CoA, which has
numerous metabolic destinations, including the TCA cycle. It can also
be converted into lactate, which enters the Cori cycle in absence of
mitochondria or oxygen.

33. oxidative phosphorylation/electron
transport chain
• The final stage of aerobic respiration is the electron transport chain, which is located on the inner mitochondrial membrane
• The inner membrane is arranged into folds (cristae), which increases the surface area available for the transport chain
•
The electron transport chain releases the energy stored within the reduced hydrogen carriers in order to synthesise ATP
• This is called oxidative phosphorylation, as the energy to synthesise ATP is derived from the oxidation of hydrogen carriers
•
Oxidative phosphorylation occurs over a number of distinct steps:
• Proton pumps create an electrochemical gradient (proton motive force)
• ATP synthase uses the subsequent diffusion of protons (chemiosmosis) to synthesise ATP
• Oxygen accepts electrons and protons to form water

35. Step 1: Generating a Proton Motive
Force
• The hydrogen carriers (NADH and FADH2) are oxidised and
release high energy electrons and protons
• The electrons are transferred to the electron transport chain,
which consists of several transmembrane carrier proteins
• As electrons pass through the chain, they lose energy – which
is used by the chain to pump protons (H+ ions) from the matrix
• The accumulation of H+ ions within the intermembrane space
creates an electrochemical gradient (or a proton motive force)
•

37. Step Two: ATP Synthesis via
Chemiosmosis
• Step Two: ATP Synthesis via Chemiosmosis
• The proton motive force will cause H+ ions to move down their
electrochemical gradient and diffuse back into matrix
• This diffusion of protons is called chemiosmosis and is
facilitated by the transmembrane enzyme ATP synthase
• As the H+ ions move through ATP synthase they trigger the
molecular rotation of the enzyme, synthesising ATP

39. Step Three: Reduction of Oxygen
• In order for the electron transport chain to continue functioning, the
de-energised electrons must be removed
• Oxygen acts as the final electron acceptor, removing the de-
energised electrons to prevent the chain from becoming blocked
• Oxygen also binds with free protons in the matrix to form water –
removing matrix protons maintains the hydrogen gradient
• In the absence of oxygen, hydrogen carriers cannot transfer
energised electrons to the chain and ATP production is halted
•

41. Types of Aerobic Reactions
Aerobic respiration involves three main types of reactions – decarboxylation, oxidation and
phosphorylation
The following table organises these reactions according to the different stages of aerobic
respiration

43. Glycolysis
• Glycolysis is a series of enzymatic reactions occurring in the cytoplasm. It is also known as the EMP pathway (Embden
Meyerhof Parnas pathway). It is the first step in cellular respiration. Plants and animals derive energy from the
breakdown of carbohydrates. Sucrose stored in the plants get converted to glucose and fructose. These
monosaccharides enter the glycolytic pathway to generate energy.
• Two molecules of pyruvate are produced by partial oxidation of glucose.
• There are two phases; Preparatory phase, where ATP is consumed and Pay off phase where ATP is produced. There is
a net yield of 2 ATPs and 2 NADH.
• It is a series of ten enzymatic reactions, where 6C Glucose is converted to 2 molecules of 3C pyruvate.
• In the first phase Glucose is phosphorylated to form fructose-1,6-bisphosphate in the three step process and then
broken down to 3C compound G3P (Glyceraldehyde-3-phosphate) and DHAP (Dihydroxyacetone phosphate). The
latter generates G3P. In this phase 2 ATPs are utilized.
• The second phase, which is an energy capturing phase. G3P is converted into pyruvate in five steps. Here we get 4
ATPs and 2 NADH are formed.
• In eukaryotic aerobic respiration, the pyruvate enters mitochondria, where it undergoes oxidative decarboxylation to
form acetyl CoA, which enters Krebs cycle or Citric acid cycle. In aerobic prokaryotes, this reaction takes place in
cytosol.
• In anaerobic respiration, pyruvate is converted into lactate, e.g. in muscles or acetaldehyde, which is converted into
ethanol and CO2 in bacteria and yeast

44. 2017

45. 2017

47. Measuring respiratory rate can be done by
using a respirometer.

48. Measuring respiratory rate can be done by
using a respirometer.
• The potassium hydroxide solution acts to remove carbon dioxide from
the surrounding air. This means that any carbon dioxide, which is
produced by respiration, is immediately absorbed so that it does not
affect the volume of air remaining. Therefore, any changes in volume,
which do take place, must be due to the uptake of oxygen. A
manmeter and the calibrated scale measure these changes. Tube B
acts as a control.

49. 7.5 Fermentation
• Fermentation
• Occurs when O2 is not available
• Animal cells convert pyruvate to lactate
• Other organisms convert pyruvate to alcohol and CO2
• Fermentation regenerates NAD+ which keeps glycolysis going

50. Krebs
Cycle

52. Humans

53. Anaerobic Respiration (ETC) Fermentation (no ETC)
CYTOSOL
• Anaerobic Respiration
• Uses Glycolysis and the ETC, but
O2 is not the final e- acceptor
• One ex: sulfate reducing bacteria
use the SO4
2- ion at the end of the
ETC, a by-product is H2S (icky
smell, thermal vent bacteria)
• Not as efficient as aerobic
respiration
• Fermentation
• Oxidizes food w/out O2 & w/out
Cellular Respiration.
• Still uses glycolysis & NAD+ to
generate ATP from food source
• Alcoholic or Lactic Acid
Fermentation are most common

54. Fermentation: Glycolysis then:
• Alcoholic
1. CO2 released from pyruvate then
converted to acetaldehyde
2. Acetaldehyde reduced by NADH to
ethanol
Summary
• Glycolysis – glucose  2 pyruvates
• 2 Pyruvate  Ethanol + CO2
• Lactic Acid
1. Pyruvate is reduced directly by NADH to
form lactate (lactate is the form lactic
acid takes when it gains e-)
2. Human muscle cells do this when
O2 is scarce
Summary
• Glycolysis – glucose  2 pyruvate
• 2 pyruvate  2 Lactate
• 09_18FermentationOverview_A.swf

55. What is the evolutionary significance of
Glycoysis?
• Glycolysis: a metabolic pathyway that breaks down glucose to
produce pyruvate and ATP w/out O2 and w/out a membrane bound
organelle, it just takes place in the cytosol of a cell.
• Likely the first way to generate cellular energy from food sources.
• Would have worked when earth did not have an O2 rich atmosphere
and when eukaryotic cells didn’t exist! How cool is that?

56. Respiration vs. Fermentation
• Aerobic Respiration
• O2
• Mitochondria
• Electron Acceptor is O2
• ~36-38 ATP (depends on
amt of O2 available to the
cell.)
• Free Energy becomes
available for metabolism
by the converstion of ATP
to ADP & inorganic
phosphate
• Anaerobic Respiration
• No O2
• Cytosol
• ETC w/ alternative final
electron acceptors
• ATP production variable
• Fermentation (a type of
anaerobic metabolism)
• No O2
• Cytosol
• Electron Acceptors are Ethanol
or Lactate
• 2 ATP

57. Heterotrophs don’t eat just glucose
• Proteins, Lipids and Carbs
may enter the process of
respiration at various
locations
• Glucose provides the
most direct ATP
Amino
acids
Sugars Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
NH3
Citric
acid
cycle
Oxidative
phosphorylation
Fats
Proteins Carbohydrates
Figure 9.19

58. Feedback Mechanisms & Respiration
Regulation
• Allosteric regulation of enzymes
control cellular respiration by
either preventing an enzyme
from catalyzing a reaction OR by
allowing an enzyme to catalyze a
reaction.
Glucose
Glycolysis
Fructose-6-phosphate
Phosphofructokinase
Fructose-1,6-bisphosphate
Inhibits Inhibits
Pyruvate
ATP
Acetyl CoA
Citric
acid
cycle
Citrate
Oxidative
phosphorylation
Stimulates
AMP
+
– –
Figure 9.20