Download Cellular respiration

• Cellular respiration is the set of the
metabolic reactions and processes that take
place in the cells of organisms to convert
biochemical energy from nutrients into
(ATP),
• The reactions involved in respiration are
catabolic reactions, which break large
molecules into smaller ones, releasing energy
(Saccharomyces cerevisiae).
• yeast is a living organism that requires a warm,
moist environment and a food source to grow and
thrive.
• unicellular, faculative anaerobic fungi
• In this lab, you will be using yeast to measure
the rate of cellular respiration.
• Yeast is a single-celled eukaryotic organism
that utilizes carbohydrates for ATP production
in the same way that plant and animal cells
utilize carbohydrates.
• Yeast will convert a carbohydrate into water
and carbon dioxide during cellular respiration.
• The greater the carbon dioxide production, the
greater the rates of cellular respiration.
Copyright Cmassengale
• Glycolysis is takes place in the cytosol of cells in all living
organisms.
• This pathway can function with or without the presence
of oxygen.
• process converts one molecule of glucose into two
molecules of pyruvate (pyruvic acid),
• generating two net molecules of ATP.
• Four molecules of ATP per glucose are actually produced,
• however, two are consumed as part of the preparatory
phase.
• The overall reaction can be expressed this way:
1. As pyruvate enters the mitochondrion,a modifies
pyruvate to acetyl CoA which enters the Krebs cycle in the
matrix.
2. A carboxyl group is removed as CO2.
3. A pair of electrons is transferred from the to NAD+ to
form NADH
• When oxygen is present, the mitochondria will undergo
aerobic respiration which leads to the Krebs cycle.
• However, if oxygen is not present, fermentation of the
pyruvate molecule will occur.
• In the presence of oxygen, when acetyl-CoA is
produced, the molecule then enters the citric acid cycle
(Krebs cycle)
• inside the mitochondrial matrix, and gets oxidized to
CO2.
• while at the same time reducing NAD to NADH.
• NADH can be used by the electron transport chain to
create further ATP as part of oxidative
phosphorylation.
• The citric acid cycle is an 8-step process involving
different enzymes and co-enzymes.
• This is also called the citric acid or the
tricarboxylic acid cycle
• Takes place in
• Requires Oxygen (Aerobic)
• Each cycle produces 1 ATP, 3 NADH, and
1 FADH
Pathway
Substrate-Level
Phosphorylation
Oxidative
Phosphorylation
Total
ATP
Glycolysis
2 ATP
2 NADH = 4 - 6
ATP
6-8
CoA
2 NADH = 6
ATP
6
Citric Acid Cycle
2 ATP
6 NADH = 18
ATP
2 FADH2 = 4
ATP
24
TOTAL
4 ATP
32 ATP
38 - 36
• The mitochondria has two membranes the outer one
and the inner membrane
• The H+ which are brought to mitochondria
accumulate between these two membranes.
• The electrons move from molecule to molecule until they
combine with oxygen and hydrogen ions to form water.
• As they are passed along the chain, the energy carried by
these electrons is stored in the mitochondrion in a form that
can be used to synthesize ATP
1. Electrons carried by NADH are transferred to the first
molecule in the electron transport chain
2. The electrons continue along the chain that includes
several cytochrome proteins and one lipid carrier.
3. The electrons carried by FADH2 added to a later point in
the chain.
4. Electrons from NADH or FADH2 ultimately pass to
oxygen.
5. The electron transport chain generates no ATP directly.
• Anaerobic respiration
• Alcoholic fermentation
• The rate of fermentation can be affected by
several factors:
Concentration of yeast
Concentration of glucose
Temperature
• For the yeast cell, this chemical reaction is
necessary to produce the energy for life. The
alcohol and the carbon dioxide are waste
products produced by the yeast. It is these
waste products that we take advantage of.
The chemical reaction, known as
fermentation can be watched and measured
by the amount of carbon dioxide gas that is
produced from the break down of glucose.
• S cerevisiae can live in both aerobic as well as
anaerobic conditions.
• In the presence of oxygen, yeast can undergo
aerobic respiration, where glucose is broken to CO2
and ATP is produced by protons falling down their
gradient to an ATPase.
• When oxygen is lacking, yeast only get their energy
from glycolysis and the sugar is instead converted
into ethanol, a less efficient process than aerobic
respiration.
• The main source of carbon and energy is glucose,
and when glucose concentrations are high enough,
gene expression of enzymes used in respiration are
repressed and fermentation takes over respiration.
• However, yeast can also use other sugars as a
carbon source. Sucrose can be converted into
glucose and fructose by using an enzyme called
invertase, and maltose can be converted into two
molecules of glucose by using the enzyme mannase.
• Respirometer is a device used to measure the
rate of respiration of a living organism by
measuring its rate of exchange of oxygen
and/or carbon dioxide.
Consist of test tube, graduated pipette,
aquarium tubing flask and blinder clips
1. Obtain 5 flasks and fill with approximately 200 ml
of tap water label the flasks
2. Place the water filled flasks into separate beakers
3. Obtain 5 test tubes and label them add solutions
as follows to the appropriate tubes:
Tube
Water ml
Yeast
suspension
ml
Glucose
solution ml
1
4
0
3
2
6
1
0
3
3
1
3
4
1
3
3
5
2
2
3
4. Attach a piece of aquarium tubing to the end
of each 1 ml graduated pipette
5. Then place the pipette with attached tubing
into each test tube containing fermentation
solutions.
6. Attach the pipette pump to the free end of the
tubing on the first pipette.
7. Use the pipette pump to draw the fermentaion
solution up into the pipette.
8. Fill it past the calibrated portion of the tube
but do not draw the solution into the tubing.
9. Fold the tubing over and clamp it shut with the
binder clip so the solution does not run out.
10. Open the clip slightly and allow the solution to
drain down to the 0 ml calivration line or
slightly bellow
11. Quickly do the same for the other four pipette
12. Record your intial reading for each
pipette(initial time)
13. 2 mints after the initial readings for each
pipette record the actual readings A in ml for
each pipette in the acual A column.
14. Subtract I form a to determine the total
amount of co2 evolved A – I
15. Record this value in the co2 evolved a-I
column
16. From now on you will subtract the initial
reading from each actual reading to determine
the total amount of co2 evolved
17. Continue taking readings every 2 minutes for
each of the solutions for 20 minutes
18. Remember take the actual reading from the
pipette and subtract the initial reading to get
the total amount of co2 evolved in each test
tube.