Cellular Respiration

Chapter 6

Autotrophs

• Autotrophs are organisms that can use basic energy sources (i.e. sunlight) to make energy containing organic molecules from inorganic raw materials.

• 2 Types– Photosynthetic autotrophs– Chemosynthetic autotrophs

Chemosynthesis

• Chemosynthesis is a process used by prokaryotic organisms to use inorganic chemical reactions as a source of energy to make larger organic molecules.

Heterotrophs

• Heterotrophs require organic molecules as food.

• They get their energy from the chemical bonds in food molecules such as carbohydrates, fats, and proteins.

Prokaryotic Cells

Prokaryotic Cells

• Prokaryotic cells have no nuclei.• Prokaryotic cells lack mitochondria and

chloroplasts.• They carry out photosynthesis and cellular

respiration within the cytoplasm or on the inner surfaces of the membranes.

Eukaryotic Cells

Eukaryotic Cells

• Eukaryotic cells contain nuclei, mitochondria, and in the case of plant cells chloroplasts.

• Plant cells, animal cells, fungi and protists are all eukaryotic.

Cellular Respiration

• Cellular respiration is the controlled release of chemical-bond energy from large, organic molecules.

• This energy is utilized for many activities to sustain life.

• Both autotrophs and heterotrophs carry out cellular respiration.

Aerobic Vs. Anaerobic

• Aerobic respiration requires oxygen.• Anaerobic respiration does not require

oxygen.

Aerobic Respiration

• Aerobic cellular respiration is a specific series of enzyme controlled chemical reactions in which oxygen is involved in the breakdown of glucose into carbon-dioxide and water.

• The chemical-bond energy is released in the form of ATP.

• Sugar + Oxygen carbon dioxide + water + energy (ATP)

Aerobic Respiration

• Simplified Reaction:• C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) ΔHc -

2880 kJ• Covalent bonds in glucose contain large

amounts of chemical potential energy.• The potential energy is released and utilized

to create ATP.

Glycolysis

• Glycolysis is a series of enzyme controlled anaerobic reactions that result in the breakdown of glucose and the formation of ATP.

• A 6-carbon sugar glucose molecule is split into two smaller 3-carbon molecules which are further broken down into pyruvic acid or pyruvate.

• 2 ATP molecules are created during glycolysis and electrons are released during the process.

Krebs Cycle

• The Krebs cycle is a series of enzyme-controlled reactions that take place inside the mitochondrion.

• Pyruvic acid formed during glycolysis is broken down further.

• Carbon dioxide, electrons, and 2 molecules of ATP are produced in this reaction.

Electron Transport System

• The electrons released from glycolysis and the Krebs cycle are carried to the electron-transport system (ETS) by NADH and FADH2.

• The electrons are transferred through a series of oxidation-reduction reactions until they are ultimately accepted by oxygen atoms forming oxygen ions.

• 32 molecules of ATP are produced.

Aerobic Respiration Summary• Glucose enters glycolysis.– Broken down into pyruvic acid.

• Pyruvic acid enters the Krebs cycle.– Pyruvic acid is further broken down and carbon-dioxide is

released.• Electrons and hydrogen ions from glycolysis and the

Krebs cycle are transferred by NADH and FADH2 to the ETS.– Electrons are transferred to oxygen to form oxygen ions.– Hydrogen ions and oxygen ions combine to form water.

Anaerobic Cellular Respiration

• Anaerobic respiration does not require oxygen as the final electron acceptor.

• Some organisms do not have the necessary enzymes to carry out the Krebs cycle and ETS.

• Many prokaryotic organisms fall into this category.

• Yeast is a eukaryotic organism that performs anaerobic respiration.

Fermentation

• Fermentation describes anaerobic pathways that oxidize glucose to produce ATP.

• An organic molecule is the ultimate electron acceptor as opposed to oxygen.

• Fermentation often begins with glycolysis to produce pyruvic acid.

Alcoholic Fermentation

• Alcoholic fermentation is the anaerobic pathway followed by yeast cells when oxygen is not present

• Pyruvic acid is converted to ethanol and carbon-dioxide.

• 4 ATPS are generated from this process, but glycolysis costs 2 ATPs yielding a net gain of 2 ATPs.

Lactic Acid Fermentation

• In Lactic acid fermentation, the pyruvic acid from glycolysis is converted to lactic acid.

• The entire process yields a net gain of 2 ATP molecules per glucose molecule.

• The lactic acid waste products from these types of anaerobic bacteria are used to make fermented dairy products such as yogurt, sour cream, and cheese.

Lactic Acid Fermentation

• Lactic acid fermentation occurs in the human body in RBCs and muscle cells.

• Muscle cells will function aerobically as long as oxygen is available, but will function anaerobically once the oxygen runs out.

• Nerve cells always require oxygen for respiration.• RBCs lack a nucleus and mitochondria and

therefore must always perform anaerobic, lactic acid fermentation.

Fat Respiration

• A triglyceride (neutral fat) consists of a glycerol molecule with 3 fatty acids attached to it.

• A molecule of fat stores several times the amount of energy as a molecule of glucose.

• Fat is an excellent long-term energy storage material.

• Other molecules such as glucose can be converted to fat for storage.

Protein Respiration

• Protein molecules must first be broken down into amino acids.

• The amino acids must then have their amino group (-NH2) removed (deamination).

• The amino group is then converted to ammonia. In the human body ammonia is converted to urea or uric acid which can then be excreted.