Cellular Respiration and Glycolysis

Cellular Respiration

• Cells create ATP from organic compounds (foods) through oxidation (removal of electrons)
• The respiration formula is: glucose + oxygen turns into carbon dioxide + water + energy
• Stages include: Glycolysis, Pyruvate oxidation, Citric Acid Cycle / Krebs Cycle, and the Electron Transport Chain
• Molecules needed are ATP, NADH, and FADH2

Glycolysis

• Glycolysis means splitting sugar
• Makes NADH and ATP, and converts glucose into pyruvate
• Results in a net gain of 2 ATP and 2 NADH molecules
• This process occurs in the cytoplasm of the cell
• Needs one molecule of glucose and two ATP molecules as input
• Produces 2 ATP, 2 NADH, and 2 pyruvate molecules per glucose molecule
• Energy conserved as NADH and ATP through substrate-level phosphorylation
• This is an anaerobic process and does not require/use oxygen
• It is also an exergonic process

Pyruvate Oxidation

• Pyruvate molecules made during glycolysis are converted into acetyl CoA in the mitochondrial matrix
• This results in the formation of acetyl CoA

Fate of Pyruvate

• Aerobic conditions need air or free oxygen
• Anaerobic environments lack molecular oxygen
• This process results in the regeneration of NAD+

Citric Acid Cycle / Krebs Cycle

• Generates energy as ATP through oxidation
• Oxidation of acetyl-CoA is derived from carbohydrates, fats, proteins, and alcohol
• Location is the mitochondrial matrix of eukaryotic cells
• Needs 2 Acetyl-CoA, 6 NAD+, 2 FAD, 2 ADP, and 2 Pi as the inputs
• Produces three NADH, one FADH2, one GTP (or ATP), and two CO2 molecules per acetyl-CoA molecule that enters the cycle
• Each glucose completes two cycles

Electron Transport Chain

• Protein complexes transfer electrons between electron donors and acceptors through redox reactions
• Location is on the inner mitochondrial membrane in eukaryotic cells
• Inputs include NADH, FADH2, ADP, and inorganic phosphate (Pi)
• Products are water and ATP

Chemiosmosis

• Chemiosmosis moves ions like protons across a biological membrane
• This creates an electrochemical gradient used to drive ATP synthesis
• ATP synthase is needed

ATP Yield of Respiration

• Required inputs are 2 ATP from glycolysis, and 10 NADH / 2 FADH2 from the electron transport chain
• Products of respiration are 4 ATP (net of 2 ATP) / 2 NADH from glycolysis
• The Kreb’s Cycle creates 2 ATP / 6 NADH / 2 FADH2 / 4 CO2
• The electron transport chain makes a max of 34 ATP
• Total ATP created is 2 (glycolysis) + 2 (Kreb’s Cycle) + 34 (ETC) = 38 ATP (maximum theoretical yield)

Regulation of Respiration

• Glycolysis primarily occurs at the first two steps and the seventh step of three key enzymatic steps
• Pyruvate oxidation / citric acid cycle converts pyruvate into acetyl-CoA
• This process is crucial in cellular respiration

Respiration Without Oxygen

• Anaerobic respiration creates energy without oxygen

Anaerobic Respiration

• Methanogens are anaerobic archaea and produce methane as a product of their energy metabolism
• Sulfur prokaryotes play a crucial role in the sulfur cycle by metabolizing sulfur and its compounds
• Fermentation is a biochemical process that breaks down organic molecules anaerobically
• It produces energy in the form of ATP and organic end products like ethanol, hydrogen gas, or lactic acid

Fermentation

• Ethanol fermentation is a biological process that converts sugars into cellular energy, producing ethanol and carbon dioxide as by-products
• Lactic acid fermentation is a metabolic process where six-carbon sugars are converted into cellular metabolite lactate, which is lactic acid in solution

Introduction to Photosynthesis

Photosynthesis vs cellular respiration

• Photosynthesis occurs in autotrophs like green plants, algae, and some bacteria
• Cellular respiration occurs in all living organisms

Photosynthesis characteristics

- Requires energy (light) and is endothermic,
- Needs sunlight
- It is anabolic

Mitochondria vs Chloroplast

- Mitochondria break down organic molecules to produce ATP through cellular respiration
- Chloroplasts capture light energy and convert it into chemical energy through photosynthesis

Leaf and Chloroplast Structure

• The two structures are: thylakoid, grana, stroma

Pigments

• Pigments include the electromagnetic spectrum, chlorophylls, carotenoids, and photosystems

Electromagnetic Spectrum

• It is the full range of electromagnetic radiation, organized by frequency or wavelength
• Photons are fundamental particles and make up electromagnetic radiation, including light and radio waves
• The absorption spectrum decreases the intensity of radiation at specific wavelengths

Chlorophylls

• Chlorophylls are green pigments found in plants, algae, and cyanobacteria
• Chlorophyll A is the primary pigment responsible for photosynthesis
• Chlorophyll B is an accessory pigment, collecting light energy to pass it on to chlorophyll a

Carotenoids

• Carotenoids are pigments found in plants, algae, and photosynthetic bacteria
• Carotenoids produce vivid yellow, red, and orange colors in nature
• Phycobiliproteins are water-soluble proteins found in cyanobacteria

Stages of Photosynthesis

• Light-dependent reactions occur in thylakoid membranes
• There are two routes for electron flow: cyclic and noncyclic

Cyclic Photophosphorylation

• Photosystem I only creates ATP

Noncyclic Photophosphorylation

• Photosystem II, spanning from cyanobacteria to higher plants, uses light energy to initiate the transfer of electrons from plastocyanin to ferredoxin
• ATP and NADPH act as coenzymes to carry electrons in enzymatic reactions
• The Z diagram shows the Z scheme of light reactions in photosynthesis
• Photosynthetic electron transport generates chemical energy and reducing equivalents in phototrophic organisms
• Chemiosmosis in photosynthesis occurs in the thylakoid membrane of chloroplasts
• Then, protons (H⁺ ions) move across a membrane down their electrochemical gradient, generating ATP through ATP synthase

Light-Independent Reactions/The Calvin Cycle

• Reactions convert carbon dioxide and other compounds into glucose in the stroma of the chloroplast

Carbon Fixation

• Living organisms convert inorganic carbon, primarily carbon dioxide (CO2), into organic compounds
• Rubisco incorporates CO2 into plants during photosynthesis

Reduction

• Reduction occurs with NADPH

Regeneration

• Regeneration occurs with RuBP

Yield

• 3 turns of the cycle = 1 G3P, 2 G3P make glucose

Energy Cycle

• The chloroplast needs light energy, water (H2O), and carbon dioxide (CO2) as inputs
• It produces oxygen gas (O2) as a waste product, and energy-rich molecules such as ATP and NADPH
• Mitochondria need glucose, fatty acids, and pyruvate as inputs
• Mitochondria then produce ATP, and water (H2O)

Photorespiration

• Rubisco “undoes” carbon fixation, reduces yield
• The conditions favoring photorespiration are when Rubisco “undoes” carbon fixation, reducing yield

Types of Respiration

• C3 – only Calvin Cycle
• C4 – spatial separation of Calvin cycle reduces photorespiration
• CAM – temporal separation of Calvin cycle reduces photorespiration
• C4 and CAM examples