Monthly Archives: December 2011

8.1 Mitochondrial structure & function: chemiosmosis & ATP production

Mitochondria

Mitochondria are found in the cytoplasm of most eukaryotic cells. They were found using a light microscope by Carl Benda. They have a smooth outer membrane. The mitochondria are 1.2 μm in size. The outer membrane separates the contents inside the mitochondrion from the rest of the cell and it is very useful for aerobic respiration. The inner membrane contains the electron chains and the enzyme ATP synthase that carries out oxidative phosphorylation. The matrix is the fluid inside the mitochondria and it contains enzymes for the Krebs cycle and link reaction. The cristae are the projections of the inner membrane that increase the surface area. The space between the inner and outer membranes is where the electron transport chain pumps protons. The space is very small so high proton concentrations can be formed easily in chemiosmosis.

The structures of the parts of living organisms and the functions they preform have a clear relationship. This can be explained by natural selection and evolution. If there were different mitochondrial structures, the organisms with the mitochondria that produce ATP most efficiently would have an advantage. They would have a higher chance of survival and would produce more offspring. These offspring would inherit the type of mitochondria and make ATP efficiently as well and if this continued, gradually the structure of mitochondria would evolve to become more efficient. This is known as adaption, a change in the structure so that something carries out its functions more efficiently.

Chapter 8 Questions

1. D

2. C

3. B

4. D

5. B

6. D

7ai. glucose

7aii. pyruvate

7aiii. acetyl CoA

7aiv. carbon dioxide

7av. oxygen

7bi. Krebs cycle

7bii. Krebs cycle

7ci. NAD

7cii. ADP

8a. Oxidation involves the loss of electrons and reduction involves the gain of electrons. Oxidation is when hydrogen atoms are lost while reduction is the gain of hydrogen atoms.

8b. Glycolysis is the process of converting glucose into pyruvates. In glycolysis, no oxygen is used and only a small amount of ATP is produced (2 ATPs).  If no oxygen is available then this is the only ATP that can be produced. In these anaerobic conditions, glycolysis only continues if the pyruvate is converted into other substances. In humans, it is concerted into lactase which is lactic acid. However in yeast, pyruvates are converted into ethanol and carbon dioxide. These substances are toxic when there is too much produced so it must be removed from the cells or produced in small quantities.

8c. ATP is produced using energy from oxidation. Substances are oxidized by removing hydrogen or electrons which creates NADH + H+. In anaerobic respiration, 2 ATPs are produced per glucose. However in aerobic respiration substances are fully oxidized. There is energy remaining in pyruvates and so more NADH +H+ is formed. Also, the energy from NADH + H+ is released in aerobic respiration. 3 ATPs are formed per NADH + H+ so more than 30 ATPs are formed in aerobic respiration.

Exam Questions on Topic 8

1a.

1b.

1ci. The Krebs cycle takes place in the intermembrane space.

1cii. ATP synthase is located in the inner membrane.

1ciii. Glycolysis takes place in the cytoplasm of the cell.

8.1 Aerobic respiration: oxidative phosphorylation & ETS

Oxidative Phosphorylation

Oxidative phosphorylation is the last part of aerobic respiration because ADP is phosphorylated to produce ATP using energy that is released by oxidation. In this process NADH + H+ is oxidized. The energy is released in many steps carried out by a chain of electron carriers. This way, more energy is trapped in ATP. The process of energy released by oxidation for ATP production is known as chemiosmosis. This happens in the inner membrane of the mitochondria and is known as chemiosmosis because H+, a chemical substance, is moved across the membrane and down its concentration gradient and this process releases energy needed for ATP synthase to make ATP.

In this process, NADH + H+ supplies hydrogen atoms to the first carrier in the electron transport chain and the NAD+ returns to the matrix. Next, the hydrogen atoms are split to release two electrons, which pass through the carriers in the chain. Energy is released as electrons pass through the carriers and this energy is used to transfer protons across the inner membrane from the matrix to the intermembrane space. As the electrons flow along the chain and more protons are pumped across the inner membrane, a concentration gradient of protons is built up. This gradient stores potential energy. To allow the electrons to continue flowing, they have to be transferred to a terminal electron acceptor that is at the end of the chain. In aerobic respiration, this acceptor is Oxygen. This bonds with two H+ ions from the matrix and form water. Some protons pass back form the intermemrbane space to the matrix through ATP synthase/ As they move down the concentration gradient, energy is released and ATP synthase uses this energy to phosphorylated ADP to create ATP.

Data-based question: oxygen consumption by mitochondria

1a. Before

1b.

2.

3.