CELL RESPIRATION

The Big Picture This lesson meets the following DoE Specific Curriculum Outcomes for Biology 11: 314-2 and 314-9

MITOCHONDRIA

• Mitochondria (singular: mitochondrion) are round or sausage-shaped organelles that are usually scattered throughout the cytoplasm of eukaryotic cells.

• Prokaryotic cells have no mitochondria they carry out cellular respiration within the cytoplasm.

MITOCHONDRIA

• Mitochondria possess a double membrane (referred to as an envelope) composed of a smooth outer membrane and a highly folded inner membrane.

• The folds of the inner membrane are called cristae (singular: crista).

• The outer membrane plays a role similar to that of the cell membrane • The inner membrane is associated with cell respiration.

MITOCHONDRIA

• The inner membrane creates two compartments within the mitochondrion.

• The mitochondrial matrix is a protein rich liquid that fills the innermost space of a mitochondrion.

• A fluid-filled intermembrane space lies between the inner and outer membrane.

• Both these compartments play a critical role in aerobic respiration.

CELL RESPIRTION

• Def - the process in which a cell breaks down sugar or other organic compounds to release energy used for cellular work; may be anaerobic or aerobic, depending on the availability of oxygen.

•

Aerobic

can be summarized by the following formula: C 6 H 12 O 6 + 6O 2  6H 2 0 + 6CO 2 + energy (36 ATP)

GOALS of CELL RESPIRATION

C 6 H 12 O 6 + 6O • Cell respiration has three goals: 1. Break the bonds between the six carbon atoms of glucose, resulting in six carbon dioxide molecules.

2. Move hydrogen atom electrons from glucose to oxygen, forming six water molecules.

2  6CO 2 + 6H 2 O + 36ATP 3. Trap as much of the free energy released in the process as possible in the form of ATP .

STAGES of CELL RESPIRATION

• Stage 1: Glycolysis - a 10-step process occurring in the cytoplasm.

• Stage 2: Pyruvate oxidation - a one step process occurring in the mitochondrial matrix.

STAGES of CELL RESPIRATION

• Stage 3: The Krebs cycle (also called the tricarboxylic acid cycle, the TCA cycle, or the citric acid cycle) - an eight-step cyclical process occurring in the mitochondrial matrix.

• Stage 4: Electron transport and chemiosmosis (oxidative phosphorylation) - a multistep process occurring in the inner mitochondrial membrane.

Stage 1

Glycolysis

GLYCOLYSIS

• For each molecule of glucose, glycolysis creates two molecules of Pyruvate (Pyruvic Acid).

• All reactions (steps) take place in the cytoplasm.

• The process is anaerobic - does not require oxygen.

GLYCOLYSIS

• Two ATP molecules phosphorylates glucose by adding phosphate groups to both ends of the sugar molecule.

• The glucose molecule then splits into two PGAL molecules.

• Each of the two PGAL molecules is oxidized to BPG.

• The hydrogen each gives up is used to form a NADH molecule.

GLYCOLYSIS

• Each of the BPG molecules is further oxidized to form 3PG molecules.

• The phosphate groups they give up are used to form ATP.

• Each 3PG molecule is finally oxidized to form Pyruvate (Pyruvic Acid) molecules and yield another ATP molecule.

GLYCOLYSIS ENERGY YIELD

• In the process of converting one glucose molecule to two Pyruvate molecules… • Four ATP are produced but two are required resulting in a net gain of two ATP.

• Two NADH are produced.

FERMENTATION

• Cells that contain mitochondria (Eukaryotes) normally carry out Aerobic Cell Respiration.

• Pyruvate produced by Glycolysis enters the mitochondria and is catabolised by the Kreb ’ s Cycle and Electron Transport Chain.

• The latter process requires the presence of free oxygen.

FERMENTATION

• Prokaryotic cells do not have mitochondria.

• Their cell respiration is anaerobic and takes place in the cytoplasm.

• Unlike glycolysis that produces Pyruvate molecules, anaerobic cell respiration produces either ethyl alcohol or lactic acid.

• This process is called Fermentation.

ALCOHOL FERMENTATION

• In alcohol fermentation, glucose is split into two Pyruvate molecules using two ATP ’ s.

• Each Pyruvate is then converted to ethanol yielding two ATP ’ s (net) and releasing CO 2 .

• Alcohol fermentation takes in yeast and is used to make beer, wine and bread.

LACTIC ACID FERMENTATION

• In lactic fermentation, pyruvate is converted to lactic acid and two ATP ’ s (net).

• Takes place in bacteria cells.

• Can happen in eukaryotic cells during periods of excess exercise.

• Muscle cells demands for ATP outstrips O 2 supply (oxygen dept).

• Cell switches to anaerobic respiration and produces lactic acid but reverses after rest.