Cellular Respiration

Section 5-3

Cellular Respiration Produces ATP

Before you can use the energy you obtain from food, it has to be transferred to ATP.

Glucose’s energy (and other organic compounds) is transferred to ATP through cellular respiration.

Oxygen makes the production of ATP more efficient, but some ATP is produced without oxygen.

Aerobic Respiration – metabolic processes that require oxygen

Anaerobic respiration – metabolic processes that do not require oxygen

Overview of Cellular Respiration

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

Figure 5-10 p. 104

STAGE 1: Glucose is converted to pyruvate, producing a small amount of ATP and NADH.

STAGE 2: When oxygen is present, pyruvate and NADH are used to make a large amount of ATP (aerobic respiration). Aerobic respiration occurs in the mitochondria in eukaryotic cells and in the cell membrane of prokaryotic cells. When oxygen is not present, pyruvate is converted to either lactate or ethanol and CO2 (anaerobic respiration).

STAGE 1: Glycolysis

Glycolysis – the breakdown of glucose The primary fuel for cellular respiration is

glucose. Glucose formed when carbohydrates

(starch and sucrose) are broken down. If too few carbohydrates are available,

other molecules such as fats can be broken down to make ATP. (1 gram of fat = 2 grams carbohydrates)

STAGE 1: Glycolysis

Glycolysis – glucose is being broken down in the cytoplasm. It is an enzyme-assisted anaerobic process that breaks down one 6-carbon molecule of glucose to two 3-carbon pyruvates.

Pyruvate – the ion of a 3-carbon organic acid called pyruvic acid

As glucose is broken down, some of its hydrogen atoms are transferred to an electron acceptor called NAD+. This forms the electron carrier called NADH.

STAGE 1: Glycolysis

For cellular respiration to continue, the electrons carried by NADH are eventually donated to other organic compounds. This recycles NAD+ making it available to accept more electrons.

STAGE 1: Glycolysis Summary of Glycolysis Figure 5-11 p. 105 Step 1: Phosphate groups from 2 ATP molecules

transferred to a glucose molecule Step 2: Resulting 6-carbon compound broken

down to 2 3-carbon compounds, each with a phosphate group.

Step 3: 2 NADH molecules produced. 1 more phosphate group transferred to each 3-carbon compound.

Step 4: Each 3-carbon compound is converted to a 3-carbon pyruvate. Produces 4 ATP molecules.

Process uses 2 ATP, produces 4 ATP, so… NET GAIN OF 2 ATP.

Glycolysis is followed by another set of reactions that use the energy temporarily stored in NADH to make more ATP.

STAGE 2: Aerobic Respiration When oxygen is present, pyruvate

produced during glycolysis enters a mitochondrion. Then pyruvate is converted to a 2-carbon compound.

When pyruvate is converted to a 2-carbon compound – 1 CO2, 1 NADH, and 2-carbon acetyl group is produced.

Acetyl group is attached to a molecule called coenzyme A (CoA) – forms acetyl-CoA

STAGE 2: Aerobic Respiration – Kreb’s Cycle

Acetyl-CoA enters a series of enzyme-assisted reactions – Kreb’s cycle

Step 1: Acetyl-CoA combines with a 4-carbon compound, forming a 6-carbon compound and releasing coenzyme-A

Step 2: CO2 released from 6-carbon compound, forming 5-carbon compound. Electrons transferred to NAD+, making a molecule of NADH.

STAGE 2: Aerobic Respiration – Kreb’s Cycle

Step 3: CO2 released from 5-carbon compound, forming a 4-carbon compound. 1 ATP and 1 NADH made.

Step 4: 4-carbon compund converted to a new 4-carbon compound. Electrons transferred to an electron acceptor FAD, making a molecule of FADH2 (another type of electron carrier).

Step 5: New 4-carbon compound then converted to the 4-carbon compound that began cycle. Another NADH is produced.

STAGE 2: Aerobic Respiration – Kreb’s Cycle

NADH and FADH2 now contain much of the energy that was previously stored in glucose and pyruvate.

Recycles the 4-carbon compound.

STAGE 2: Aerobic Respiration – Electron Transport Chain

The electrons donated by NADH and FADH2 pass through an electron transport chain.

Figure 5-13 p. 107 Occurs in the inner membranes of

mitochondria Energy of the electrons used to pump H+

out of inner mitochondrial compartments H+ accumulates in outer compartment –

produces a concentration gradient across the inner membrane

STAGE 2: Aerobic Respiration – Electron Transport Chain

H+ diffuses back into inner compartment through a carrier protein that adds a phosphate group to ADP to make ATP.

At end of electron transport chain, H+ and spent electrons combine with O2 to form H2O – oxygen is final electron acceptor.

Fermentation Fermentation follows glycolysis in the

absence of oxygen. – anaerobic respiration

When enough oxygen is not present for aerobic respiration to occur, electron transport chain does not function. Why? Oxygen is not able to serve as final electron acceptor. Also, NADH electrons not transferred, so NAD+ cannot be recycled.

Fermentation Anaerobic Respiration – NAD+ recycled in

a different way. Electrons carried by NADH are transferred to pyruvate that is produced in glycolysis. This recycles NAD+ so it can continue making ATP through glycolysis.

Fermentation – recycling NAD+ using an organic hydrogen acceptor

Lactic Acid Fermentation 3-carbon pyruvate converted to a 3-

carbon lactate. NAD+ recycled. Lactate – ion of organic acid called lactic

acid During vigorous exercise, pyruvate in

muscles converted to lactate when muscles operate without enough oxygen.

Causes soreness because it builds up in muscles – blood does not remove it fast enough

Alcoholic Fermentation 3-carbon pyruvate converted to a 2-

carbon ethanol molcule. CO2 is released. 2 Step Process:

1. Pyruvate converted to a 2-carbon compound – CO2 released.2. Electrons transferred from NADH to

the 2-carbon compound producing ethanol.

o NAD+ recycled o Yeast or fungi – foods and beverages

(wine, beer, rising of bread dough)

http://programs.northlandcollege.edu/biology/Biology1111/animations/glycolysis.html

http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html