Cellular Respiration II

Topics Review

Q: In the electron transport chain, the energy from high-energy electrons is transformed into ___________ before being used to generate ATP.

A: A proton gradient

Lecture Question(s)

Q.1: What are the differences between aerobic respiration and anaerobic respiration (fermentation)?

A.1: aerobic respiration requires oxygen and can produce large amounts of ATP while anaerobic respiration only requires the pyruvate produced by glycolysis and produces no TP

Q.2: What about the organisms living in the environment without oxygen?

A.2:

Core Concepts

1. Anaerobic Metabolism: glucose can be broken down in the absence of oxygen by fermentation, producing a modest amount of ATP

2. Fermentation is a process for extracting energy from fueled molecules that does not rely of oxygen or an electron transport chain, but instead uses an organic molecule as an electron acceptor

3. Metabolic Integration: metabolic pathways are integrated, allowing control of the energy level of cells

The Flow of Energy in Cellular Respiration

Glycolysis

glucose → 2 pyruvate

Substrate-Level Phosphorylation: 2 ATP

Oxidative Phosphorylation: 2 NADH = 5 ATP

Total ATP: 7

Pyruvate Oxidation

2 pyruvate → 2 Acetyl-CoA

Substrate-Level Phosphorylation: 0 ATP

Oxidative Phosphorylation: 2 NADH = 5 ATP

Total ATP: 5

Citric Acid Cycle

2 turns, 1 for each Acetyl-CoA

Substrate-Level Phosphorylation: 2 ATP

Oxidative Phosphorylation: 6 NADH =15 ATP, 1 FADH₂ = 3 ATP

Total ATP: 20

Total

Substrate-Level Phosphorylation: 4 ATP

Oxidative Phosphorylation: 28 ATP

Total ATP: 32

• some energy is released by substrate-level phosphorylation, and some is transferred to the electron carriers NADH and FADH₂

• the energy of the electron carriers is transformed into energy stored in a proton electrochemical gradient

• electron carriers become oxidized again by the electron transport chain after dropping off electrons which fuel the production of ATP

Q: Energy flow without oxidative phosphorylation

A: not enough ATP (28) will be produced at once

Fermentation

• glycolysis is anaerobic - it does not require oxygen to produce pyruvate

• aerobic cellular respiration requires oxygen to occur

• fermentation does not require oxygen to occur but instead uses an electron acceptor to carry itself out

• all fermentation begins with glycolysis

• fermentation does not produce any ATP

Lactic Acid Fermentation

• produced pyruvate from glycolysis is used to produce lactic acid

• pyruvate serves as the electron acceptor

• NAD⁺ produced in fermentation is used in glycolysis

• lactic acid will be produced by animals and bacteria

Ethanol Fermentation

• produced pyruvate from glycolysis is converted to acetaldehyde is used to produce ethanol

• acetaldehyde serves as the electron acceptor

• NAD⁺ produced in fermentation is used in glycolysis

• this produces a two carbon molecule

• ethanol is produced by plants

Rising Levels of Atmospheric Oxygen

• before the presence of atmospheric oxygen, the earliest organisms likely used one of the fermentation pathways to generate the ATP necessary to power cellular processes

• fermentation can provide a quick burst of ATP

• higher efficiency in certain environments

Glucose Storage

• metabolic pathways are integrated, allowing control of the energy level of cells

• glucose can be stored as glycogen in humans and as starch in plants

Glycogen

• has a core protein surrounded by branches of glucose units

• is stored in muscle cells and liver cells

  • stored in muscle cells for the use of the muscles

  • stored in liver cells for use by the whole body

• glucose molecules at the end of glycogen chains can be cleaved one at a time in the form of glucose 1-phosphate, which is then converted into glucose 6-phosphate, the intermediate in glycolysis

How Other Sugars Contribute to Glycolysis

• Disaccharides - two sugar molecules;

  • lactose

  • maltose

  • sucrose

  • have diverse functions

• Monosaccharides - single sugar molecules

  • galactose

  • fructose

  • mannose

• Polysaccharides - large chain of sugar molecules

  • starch

  • cellulose

  • plant cell walls are made up of cellulose

Ruminants and Microbes

• cows do not have the enzyme that allows their bodies to breakdown and digest plants - instead they have microbes in their ruminants to do this

• the cow microbiome is incredibly important to their survival

Evolution of the Mitochondria

• all known eukaryotes probably diverged after the symbiotic development of mitochondria

• eukaryotes with typical aerobic mitochondria are shown in black

• those containing potential mitochondrion-related organelles are shown in red, with an indication of organelle function

• dashed lines indicate uncertainty in branching order

Hydrogenosomes in Anaerobic Fungi

• H₂ producing mitochondrial homologs found in some anaerobic microbial eukaryotes

• are small, spherical or variously elongate organelles

Regulation of Cellular Respiration

• high concentration of substrates such as ADP and NAD⁺ indicate a low-energy state in the cell and stimulate the respiratory pathways

• high concentration of products such as ATP and NADH indicate a high-energy state in the cell and inhibit the respiratory pathways