All answers to questions should go in your notebook. Be sure to number all
questions correctly and answer using COMPLETE SENTENCES!
Title- Reading: Cell Respiration
CELLULAR RESPIRATION
Respiration at the cellular level is known as internal
(cellular or tissue) respiration and can be divided into
four stages. In the first, glycolysis, glucose is broken
down to two pyruvate molecules. This does not
require oxygen and is a form of anaerobic respiration.
In the second step (Link Reaction) these two
pyruvates are then broken down further, releasing
Carbon and attaching to Coenzyme A to make the
molecule Acetyl-CoA. In the second stage, the Krebs (Citric Acid) cycle, Acetyl-CoA is attached to four
existing carbons and Carbons are slowly broken off and released. This is the main energy-yielding stage
and requires oxygen. The carbons are then rearranged, causing the release of more and more hydrogens.
These hydrogens are picked up by electron carriers known as NAD+ and FADH. The final stage of cell
respiration is Oxidative phosphorylation. This step includes the Electron Transport Chain, which takes all
the collected hydrogens from NADH and FADH2 and separates the hydrogens from their electrons. The
positively charged hydrogens are then used to power ATP Synthase, an enzyme that produces ATP from
ADP and phosphate. These processes are common to all plants and animals that respire aerobically. Even
though plants go through photosynthesis, they are also using cell respiration to process their own food
into usable energy for growth and repair. We will learn about photosynthesis in the next unit.
After reading the PINK section:
1. List the 4 steps of cell respiration.
2. Explain, using as much detail as possible, what NAD+ and FADH are used for.
3. Do plants go through cell respiration?
4. What is the starting molecule in cell respiration?
5. What is the final, most important molecule in cell respiration?
Mitochondria
Mitochondria are membrane-enclosed organelles distributed through
the cytoplasm of most eukaryotic cells. Their number within the cell
ranges from a few hundred to, in very active cells, thousands. Their
main function is the conversion of the potential energy of food
molecules into ATP. Mitochondria have:
● A small number (some 5–10) of circular molecules of DNA
○
These came from your mother!
● An outer membrane that encloses the entire structure
● An inner membrane that encloses a fluid-filled matrix
● Between the two is the intermembrane space
○
inter means between
● The inner membrane is elaborately folded with shelflike cristae projecting into the matrix.
After reading the AQUA section and looking at the diagram:
6. If the structures of the mitochondria are not working properly, what will our body NOT be able to
do?
Glycolysis, the Universal Process
Glycolysis literally means "splitting sugars." Glucose, a six carbon sugar, is split into two molecules of a
three carbon sugar. During glycolysis, two molecules of ATP, two molecules of pyruvic acid (another
name for pyruvate) and two "high energy" electron carrying molecules of NADH are produced. Glycolysis
can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular
respiration. Without oxygen, glycolysis allows cells to make small amounts of ATP. This process is called
fermentation.
During glycolysis, 2 ATP are converted into ADP,
inputting energy into the reaction as well as attaching
a phosphate to the glucose. Later, 4 ADP are converted
back into the higher energy ATP and 2 NAD+ are
converted into NADH + H+. The end result of the
glycolysis process yields two pyruvic acid (3 Carbon)
molecules, and a net gain of 2 ATP and 2 NADH per
glucose.
Glucose + 2 NAD+ + 2 Pi + 2 ADP → 2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O
After reading the RED section:
7. List the molecules (including how many you net [net means how many do you get when you
subtract the ones you used…]) that are produced during glycolysis
Anaerobic Pathways
When oxygen is not present, many organisms will ferment pyruvic acid into other chemicals, such as
lactic acid. Humans ferment lactic acid in muscles when oxygen becomes depleted, resulting in muscles
that are full of lactic acid. This lactic acid causes the muscle stiffness couch-potatoes feel after beginning
exercise programs. The stiffness goes away after a few days since stopping strenuous activity allows
aerobic conditions to return to the muscle, and the lactic acid can be converted into ATP via the normal
aerobic respiration pathways.
After reading the YELLOW section:
8. Why do my muscles feel stiff and sore after I try a new exercise?
Acetyl CoA: The Link Reaction
Pyruvic acid is first altered in the transition reaction (another name for
Link Reaction) by removal of a carbon and two oxygens (which form
carbon dioxide). When the carbon dioxide is removed, energy is given
off, and 1 NAD+ is converted into the higher energy form NADH.
Coenzyme A attaches to the remaining 2 Carbon (acetyl) unit, forming
acetyl CoA. It is important to remember that this process occurs twice,
since there are two molecules of pyruvic acid. This means the number
of NADH and CO2 molecules will double. This process is will lead into
the Kreb's Cycle.
After reading the TEAL section:
9. Name a molecule that is considered waste from this reaction.
10. How many pyruvates need to be processed during the link reaction?
11. So how many Acetyl-CoA’s will be produced in total?
Kreb's Cycle (aka Citric Acid Cycle)
The Acetyl CoA (2-C or 2 Carbons) is attached to a 4
Carbon chemical (oxaloacetic acid). The CoA is released
and returns to await another pyruvic acid. The 2-C and
4-C make another chemical known as Citric acid, a 6-C
molecule. Kreb's Cycle is also known as the Citric Acid
Cycle. The process after Citric Acid is essentially
removing carbon dioxide, getting out energy in the form
of ATP, NADH and FADH2, and lastly regenerating the
cycle. Acetyl-CoA gets oxidized to CO2 in a series of
reactions while at the same time reducing NAD+ to
NADH. To fully oxidize the equivalent of one glucose
molecule, two acetyl-CoA must be metabolized by the Krebs cycle. Two waste products, H2O and CO2, are
created during this cycle. The net energy gain from one cycle is 3 NADH, 1 FADH2, and 1 ATP. Thus, the
total amount of energy yield from one whole glucose molecule (2 pyruvate molecules → 2 Acetyl-CoA
molecules) is 6 NADH, 2 FADH2, and 2 ATP. The carbon dioxide released by cells is generated by the
Kreb's Cycle, as are the energy carriers (NADH and FADH2) which play a role in the next step.
Summary of the Krebs' (or citric acid) cycle. Image from Purves et al., Life: The Science of Biology,
4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
After reading the GOLD section:
12. What does 2-C, 4-C and 6-C mean?
13. What are two waste products released from this reaction?
14. Why is this called the Citric Acid Cycle?
15. How many NADH, FADH2 and ATP are produced from this cycle in total?
Electron Transport Chain/Oxidative Phosphorylation
Kreb's cycle completely oxidized the carbons in the pyruvic acids, producing a small amount of ATP, and
reducing NAD+ and FADH into higher energy forms. In the ETC (Electron Transport Chain) those higher
energy forms are cashed in, producing ATP. The mechanism for the oxidative phosphorylation process is
the gradient of H+ ions moving across the inner mitochondrial membrane. This mechanism is known as
chemiosmosis. This involves both chemical and transport processes. NADH and FADH2 enter the ETC,
creating 3 ATP per NADH and 2 ATP per FADH2.
After reading the PURPLE section:
16. Where do NADH and FADH2 go with all those hydrogens we collected along the way?
17. Do the math… and SHOW YOUR WORK! How many ATP were made from NADH (from Glycolysis,
Link and CAC)?
18. Do the math… and SHOW YOUR WORK! How many ATP were made from FADH2?
ATP: Cellular Energy
Energy Forms: Chemical Energy is stored in biological molecules (ATP) and is converted when needed.
ATP – Adenosine triphosphate – is a multipurpose storehouse of
adenine (nucleic acid- the same adenine that is found in your DNA),
ribose sugar, and three phosphate groups. One molecule of ATP
contains three phosphate groups, and it is produced by ATP
synthase from inorganic phosphate and adenosine diphosphate
(ADP) or adenosine monophosphate (AMP). ATP is therefore
continuously recycled in organisms.
After reading the GREY section:
19. When I remove one phosphate from ATP, it becomes ________
20. When I add a phosphate to AMP, it becomes ________
21. Which molecule (AMP, ADP or ATP) contains the most stored energy?
Cellular respiration is the process of oxidizing food molecules, like glucose, to carbon dioxide and water.
The energy released is trapped in the form of ATP for use by all the energy-consuming activities of the
cell. In eukaryotic cells, glycolysis occurs in the cytoplasm. The remaining processes take place in
mitochondria.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP)
After reading the GREEN section AND looking at the diagram:
22. List two types of cellular respiration
23. What is the main idea of cell respiration?
24. What are 3 pieces of evidence you could use to support the main idea of what is occurring during
cell respiration (feel free to use any section in this document to support your main idea)?