Chapter 9: Cellular Respiration

Chemical Energy and Food

Food = chemical building blocks living things need to grow and reproduce

Broken down gradually

Capture little bits of energy at key steps

Use energy stored in chemical bonds of foods to produce ATP which powers the activities of the cell

Overview of Cellular Respiration:

It is the process that releases energy by breaking down food molecules in the presence of oxygen

6O2 + C6H12O6 6CO2 + 6H2O + energy (ATP)

oxygen + glucose carbon dioxide + water + energy (ATP)

A cell needs to trap those little pieces of energy to make ATP

Takes 3 main steps Glycolysis Krebs Cycle (Citric Acid Cycle) Electron Transport System

Step 1: Glycolysis = “sugar breaking”

Glucose Pyruvate (pyruvic acid)

The beginning of the energy pathway in respiration

Takes place in the CYTOPLASM

One molecule of glucose is broken in half, producing 2 molecules of pyruvic acid (a 3-carbon compound) Uses 2 ATP molecules to get

the process started In the end 4 molecules will

have been produced Net gain = 2 molecules of ATP

(a relatively small amount)

Step 1: GlycolysisGlucose Pyruvate Produces

2 molecules of pyruvate 2 molecules of ATP

Advantages Happens quickly – can produce 1000s

of ATPs in a few milliseconds Does not require oxygen

If oxygen is present leads to 2 other pathways that release lots of energy = aerobic respiration

If no oxygen, a different pathway is followed = anaerobic respiration

Aerobic Respiration (oxygen present)

Step 2: Krebs Cycle(Citric Acid Cycle) Occurs in the mitochondria

Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions

1st step – citric acid production Pyruvic acid passes

through the mitochondrial membrane into the matrix

Pyruvic acid – CO2 = Acetyl CoA

Acetyl CoA + 4-C compound = Citric Acid

Step 2: Krebs Cycle(Citric Acid Cycle)

2nd step – stepwise energy extraction, release of CO2 at each step 4-C molecule

replenished at end, cycle can continue

Cha-Ching –O- Meter

ATP NADH FADH2

Step 3: Electron Transport Chain

Occurs in the MITCHONDRIAL MEMBRANE High energy electrons arrive in NADH and FADH2 from Krebs and Gylcolysis Movement of electrons down the ETC moves H into the mitochondrial membrane, establishes a concentration gradient Hydrogen moves back out through ATP synthase, spinning

the turbine and creating ATP (massive amounts of ATP!!!)

Requires O2; oxygen is

the final electron acceptor at the end of the ETC

Approximately 32-34 ATPs are generated for every glucose

Cha-Ching –O- Meter

ATP NADH FADH2

Overview of Cellular Respiration It is the process that releases energy by breaking

down food molecules in the presence of oxygen 6O2 + C6H12O6 6CO2 + 6H2O + Energy oxygen + glucose carbon dioxide + water +

energy A cell needs to trap those little pieces of energy to

make ATP Takes 3 main steps – glycolysis, krebs cycle, electron

transport system

Step 1: Glycolysis The beginning of the energy pathway in respiration The process in which one molecule of glucose is broken in half, producing

2 molecules of pyruvic acid (a 3-carbon compound) Uses 2 ATP molecules to get the process started In the end 4 molecules will have been produced Net gain = 2 molecules of ATP (a relatively small amount)

If oxygen is present leads to 2 other pathways that release lots of energy = aerobic respiration

If no oxygen, a different pathway is followed = anaerobic respiration

Aerobic Respiration – oxygen present

Step 2: Krebs Cycle/Citric Acid Cycle

90% of the chemical energy available in glucose is still unused at the end of glycolysis

It is locked in the pyruvic acid

Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions

1st step – citric acid production

2nd step – energy extraction

Step 3: Electron Transport Chain Uses the high energy electrons

from the Krebs cycle to convert ADP into ATP

Don’t worry about all the steps Produces 34 more ATP

molecules per glucose

Summary of ATP totals

Why do we need all this ATP? Cells need energy to work Primary fuel is ATP (adenosine

triphosphate) ATP = nitrogen containing compound

(adenine), 5-carbon sugar (ribose), and 3 phosphate groups

ADP = same as ATP but with 2 phosphate groups

The 3rd phosphate is the key to how cells store energy – when the cell has extra energy available it adds a phosphate to make 3 and when it needs energy it can take a phosphate away

Releasing Energy from ATP Energy is released from ATP when ATP is

changed into ADP + phosphate ATP = compressed spring (unstable) ADP = relaxed spring (stable)

Using Biochemical Energy Active transport Powers movement of organelles within the

cell ATP and Glucose Cells only contain a small store of ATP

because it is not efficient Sugar can store up to 90 times the energy

than ATP Cells use the energy in carbohydrates to

generate ATP form ADP as needed

Anaerobic Respiration – no oxygen present

Alcoholic Fermentation Used by yeasts and a few other

microorganisms Pyruvic acid + NADH

alcohol + CO2 + NAD+ Cause bread dough to rise When the yeast runs out of oxygen ,

it begins to ferment, giving off carbon dioxide

Makes the bread rise by forming small air pockets in the bread

Alcohol evaporates when the bread is baked

Lactic Acid Fermentation If pyruvic acid accumulates it can be

converted to lactic acid Pyruvic acid + NADH

lactic acid + NAD+ Lactic acid is produced in your

muscles when you exercise when the body can’t supply enough oxygen to the tissues

Your muscles start to produce ATP by lactic acid fermentation and lactic acid builds up in your muscles causing a painful burn

Photosynthesis vs. Respiration

Almost opposite reactions Photosynthesis deposits energy Respiration withdraws energy The products of photosynthesis

are the reactants for respiration Respiration takes place in all

eukaryotes and some prokaryotes Photosynthesis takes place in

plants, algae, and some bacteria