Chapter 7 // Pt1: Intro to Cellular Respiration
Chapter 7
Intro to Cellular Respiration
Metabolism is a characteristic of life
Early Cells
- First cells around 3.5 BYA
There was no oxygen in the atmosphere. Life had to be anaerobic.
Cellular Respiration
- Any pathway that uses an electron transfer chain to harvest energy from organic molecules to make ATP
- Breaking down glucose to produce ATP * Ex: electron transfer phosphorylation in light-dependent reactions of photosynthesis
- Photosynthesis v. cellular respiration * Electron phosphorylation in photosynthesis uses inorganic compounds * Ex: CO₂ * Cellular respiration uses organic compounds * Ex: glucose
- Opposite to photosynthesis (CO₂ to O₂), cellular respiration is O₂ to CO₂
✨Oxygen✨
Early photosynthetic organisms evolved from cyclic light reactions (no oxygen) to noncyclic light reactions (produces oxygen) ← how oxygen came to be on Earth
- Oxygen was toxic
- It polluted the air
- O₂ easily steals electrons = dangerous free radicals = dying cells
- Great Oxidation Event * Killed off most anaerobic life * Survivors = life that was away from O₂ * Deep water, muddy sediments, etc. * Caused by cyanobacteria 2.5 BYA * Triggered an ice age * Helped give rise to multicellularity * Explosion of minerals
Aerobic organisms started evolving
- Antioxidants - minimizes damages caused by O₂
- First aerobic organisms - could live in presence of oxygen
- Oxygen using metabolism evolved * Aerobic organism’s metabolism evolved to include oxygen * Aerobic respiration * Used oxidative properties of oxygen as part of their respiration
Aerobic Cell Respiration Happens in the Mitochondria
- Folded membrane makes ATP very efficiently
- Electron transfer chain in membrane * Similar to chloroplast in photosynthesis
- Hydrogen ions creates gradients to power ATP synthesis
- Oxygen molecules uses electrons at ends of chains
Free Radicals
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- O₂ usually finds hydrogens to bind with to make H₂O
- Sometimes oxygen atoms escape, missing an electron = free radical
- Enzymes clean up the mess, most of the time * The mitochondria can’t detoxify free radicals on it’s own * Must use antioxidant enzymes in cytoplasm * Neutralizes the free radical * Ex: one of these enzymes is catalase
Lots of foods have antioxidants too: Vitamins C and E, beta carotene
Oxygen causes oxidative stress
- If free radicals accumulate they stop the mitochondria from functioning 💀
- Then the cell stops functioning
- Causes tissue damage called oxidative stress
- Oxidative stress causes lots of problems * Aging, cancer, Parkinson’s, autism
- Oxidative stress damage can be inherited * It damages the mitochondria which can cause mitochondrial disorders * Congenital blindness, deafness, diabetes, seizures, strokes
Why is ATP so important?
- Used by nearly all cellular reactions as energy
- It stores energy from bonds
- Cells harvest energy from organic molecules by breaking carbon backbone
- This releases energy
- Energy capture by ATP molecules
Aerobic Respiration
Cellular respiration using oxygen
- Different than respiration (breathing) but breathing is a part of cell respiration
- Breathing bring O₂ to cells
- Photosynthesis and cellular respiration work together * Photosynthesis produces oxygen which is inhaled * Exhaled in CO₂ and water which are used for photosynthesis
- 4 stages of aerobic respiration: * Glycolysis * Acetyl CoA formation * Citric acid cycle * Electron transfer phosphorylation
- Aerobic cell respiration often paired with fermentation * Breaking down glucose to make ATP but no oxygen is used * Anaerobic respiration * Pro: no harmful oxygen * Con: doesn’t make a lot of ATP * Only some tiny unicellular organisms can sustain themselves with fermentation
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