Sec 8- Cellular Respiration Flashcards
Unit III- Energy Matters
What does every organism extract energy from?
Every organism extracts energy from food molecules manufactured by photosynthesis or obtained from the environment (eating plants, other organisms, etc.)
What are the different energy metabolism?
- Aerobic Metabolism
- Uses oxygen
- Aerobic/Cellular respiration
- Anaerobic Metabolism
- Uses no oxygen
- Anaerobic respiration
- Fermentation
What is cellular respiration?
Its purpose is to produce ATP.
Includes four steps:
1. Glycolysis
2. Acetyl-CoA formation
3. Krebs cycle (citric acid cycle)
4. Electron transport chain
Why do we breath?
If we don’t constantly take in oxygen and expire carbon dioxide, we die.
- Why?
Cellular respiration!
What happens to glucose and oxygen in Cellular Respiration?
- Energy gets relaeased by “falling” electrons.
- Oxygen “catches” the fallen electrons.
- Hydrogen follows electrons
How do cells release energy?
They release energy gradually.
What is the “Dance of The Electrons”?
- Energy can be transferred from one molecule to another by transferring electrons.
- Oxidation + reduction reactions = redoc reactions
Oxidation
- Loss of electrons
- “Electron donor”
- Loss of hydrogen
- Loss of energy
- Exothermic
Reduction
- Gain of electrons
- “Electron acceptor”
- Gain of hydrogen
- Gain of energy
- Endothermic
What is carbon in glycolysis?
In glycolysis, one six-carbon molecule of glucose is split into two three-carbon molecules of pyruvate.
What is energy in glycolysis?
The energy products of glycolysis are 2 net molecules of ATP and 2 NADH molecules.
What is NADH?
- It is a molecule that comes in two forms: NAD^+ and NADH
- It is a temporary electron (= energy) carrier
- It is a dinucleotide
Glycolysis Summary
Glucose, ADP +Pi, NAD^+ —> pyruvate, ATP, NADH
Acetyl-CoA Formation (Carbon and Energy)
- Pyruvate is transported into the mitochondria in eukaryotic cells
- One carbon is removed and leaves as CO2 and coenzyme A is added
- This leaves the two-carbon acetyl-CoA
- In the process NAD^+ is reduced to NADH
- Result oer glucose:
2 acetyl-CoA
2 CO2
2 NADH
Carbon in the Krebs Cycle (Citric Acid Cycle)
- Both carbons of acetyl-CoA are released as CO2 in the Krebs cycle
- For each original glucose, there are two rounds of the Krebs cycle
- Two turns of the Krebs cycle results in:
4 CO2
2 ATP
6 NADH
2 FADH2
Where does Acetyl-CoA formation and the Krebs cycle occur?
The matrix of the mitochondria.
The Electron Transport Chain
- In the last step of cellular respiration, the NADH and FADH2 produced earlier are traded in for ATP
- One NADH molecule results in ~3 ATP
- One FADH2 molecule results in ~2 ATP
- (At this point, the six carbons of glucose have all already left as CO2)
The last step, the electron transport chain, occurs across the inner mitochondrial membrane.
* NADH and FADH2 are oxidized
* Per glucose:
10 NADH
2 FADH2
* Electrons jump from one intermembrane protein to another, releasing energy
* This energy is used to pump hydrogen ions (protons) into the intermembrane space, thereby creating a concentration gradient
* At the “end of the line,” oxygen catches (is reduced) the spent electrons and turns into water
* The electron transport chain creates a proton (hydrogen ion) gradient
Why does the proton gradient matter?
- Protons move down their concentration gradient through the intermembrane protein/enzyme ATP synthase
- This rlease of potential energy causes the formation of ATP
What is chemiosmosis?
- The process of protons rushing through ATP synthase is called chemiosmosis.
- ~ 34 ATP are made per glucose during this step
Chemiosmosis in Bacteria-
- Bacteria don’r have mitochondria
- Instead of the inner mitochondrial membrane, they use the plasma membrane for chemiosmosis
Anerobic Respiration vs Fermentation
- Anerobic Respiration
1. Glycolysis
2. Acetyl-CoA formation
3. Krebs Cycle
4. Electron Transport Chain - O2 is not the final electron acceotir, but sulfate, for example, making H2S
- Fermentation
1. Glycolysis
2. Fermentation - The final electron acceptor is neither O2 nor sulfate, but an organic molecule
What is Lactic Acid Fermentation?
- When there is not enough oxygen reaching our muscle cells during heavy exercise, cells switch from cellular respiration to lactic acid fermentation to make ATP
- Lactic acid is associated with the “burn” of working out
- Lactic acid fermentation makes only 2 ATP per glucose versus 36 ATP!
- This is a “last ditch effort”
- Cells gain a net of 2 ATP per glucose through glycolysis
- 2 reduced NADh molecules need to be oxidized back to NAD^+ otherwise additional rounds of glycolysis would be impossible
- NADH reduces pyruvate, which turns into lactic acid
- Some bacteria do lactic acid fermentation; its what gives cheese, yogurt, pickles, etc. their sour flavor
What is alchoholic fermentation?
Alcoholic fermentation produces ethanol (alcohol) and CO2 gas
* Alchoholic fermentation is similar to lactic acid fermentation, but the 3-carbon pyruvate is first split into CO2 and a 2-carbon acetaldehyde
* There is still only a gain of 2 ATp per glucose
- yeast does alchohol fermentation
What are some alternative energy sources?
Monosaccharides glucosem fructose, and galactose go through cellular respiration.
Fats and proteins can also enter at various points of cellular respiration to make ATP.
What does insulin do?
Regulation: Insulin allows glucose to enter cells.
- Glucose enters cells through glucose transport proteins
- The hormone insulin, allows glucose to enter cells
- In diabetes no/low insulin is produces and the cells are starved for ATP because glucose can’t enter cells from the bloodstream
