Cell Respiration and Fermentation Flashcards
What is the overall purpose of aerobic cell respiration?
- Living systems require energy to do work (energy comes from breakdown of food molecules like glucose)
- In most living things, this breakdown requires oxygen (is aerobic) and releases carbon dioxide as a waste product
- Breath in O2, exhale CO2
- Ex: humans plants, fungi, protists, many bacteria
Objective of cellular respiration
- To maximize the potential energy retrieval stored inside the glucose/pyruvate molecules
- To harvest the energy stored in food and transfer to a molecule that we can use – ATP
- Energy stored in bonds in the form of high energy electrons
- Need to get these high energy electrons from food to ATP
What is the overall purpose of photosynthesis?
- Photosynthesis provides plant cells with sugar by using energy harvested from the sunlight
What are the overall balanced chemical reactions for cell respiration and photosynthesis?
Cell Respiration: C6H12O6 + 6O2 = 6CO2 + 6H2O + 38 ATP
Photosynthesis: 6CO2 + 6H2O + sunlight = C6H12O6 + 6O2
What is the relationship between cell respiration and photosynthesis?
-
How efficient is cell respiration at releasing and capturing the energy in glucose?
- About 40%
- 60% given off as heat
What are oxidation and reduction reactions? (OIL RIG)
- Oxidation: the loss of electrons from one substance
- Reduction: the addition of electrons to another substance
What is the role of FAD+ and NAD+ in cell respiration pathways?
- Electron taxis
-
NAD+ coenzyme derived from niacin, carries electrons in cell respiration — NADH carries electrons (reduced)
- NAD+ + H+ + 2e- ⇔ NADH
-
FAD a coenzyme derived from riboflavin, also carries electrons in cell respiration
- FAD + 2H+ + 2e- ⇔ FADH2
Aerobic cellular respiration
Glycolysis –> Krebs Cycle –> Oxidative Phosphorylation (ETC and Chemiosmosis)
Glycolysis
- Where does it happen?
- What happens? (what goes in and what comes out)
- Converts 6-carbon glucose to two 3-carbon pyruvate molecules
- Produces 2 ATP (net) and 2 NADH
- Occurs in the cytoplasm
- Does not require oxygen as reactant
- Prokaryotic cells (bacteria) and eukaryotic cells all perform glycolysis
- Most of energy from glucose goes to pyruvate
Pyruvate grooming
- Pyruvates transported to mitochondrian after glycolysis
- Carboxyl group (-COO-) removed from pyruvate and given off as CO2
- Two carbon compound remaining is oxidized while a molecule of NAD+ is reduced to NADH
- Coenzyme A joins with two carbon group to form Acetyl CoA
- Happens only when O2 is present in the cell becausee it requires NAD+ in the mitochondrial matrix to proceed
Krebs Cycle
- Where does it happen?
- What happens? (what goes in and what comes out)
- Occurs in the matrix of the mitochondria
- Involves a huge enzyme complex
- Goal: to finish completely oxidizing what’s left of glucose by transferring the electrons and H+ to NAD+ and FAD
-
Products: per Acetyl-CoA:
- 1 ATP (2 total)
- 2 CO2 as waste (4 total)
- 3 NADH (6 total)
- 1 FADH2 (2 total)
- Most of energy is in NADH and FADH2
Electron Transport Chain
- Where does it happen?
- What happens? (what goes in and what comes out)
- ETC is a series of electron transport/carrier proteins embedded in the inner mitochondrial membrane
- This protein chain passes down energy in the form of electrons which originate from NADH and FADH2
- During each of the electron transfers, the energy released is used to pump H+ ions against their concentration gradient, into the inner membrane space
- End result: high concentration of H+ ions in this space
- H+ diffuse
- Chemiosis
- Where does it happen?
- What happens? (what goes in and what comes out)
- When H+ diffuses back into the matrix through the protein ATP Synthase, it releases energy and this energy drives the production of ATP from ADP and Pi
- Coupling an energy process (H+ diffusing into the matrix) with an energy-consuming process (making ATP from ADP)
- O2 very electronegative combines with a pair of H+ in the matrix to form water
- What is ATP and how does it “store” energy?
- Found in all cells
- Made of adenine, a ribose sugar, and 3 phosphate groups (PO4-)
- A great deal of energy is stored in unstable bonds between the phosphates
- This energy can be transferred by attaching a phosphate to other molecules (phosphorylation)
How does phosphorylation allow the transfer of this energy?
-
What is substrate-level phosphorylation and when/where does it occur in cell respiration?
- An enzyme transfers a phosphate group from a substrate molecule directly to ADP, forming ATP
- Produces a small amount of ATP in glycolysis and Krebs cycle
Energy accounting
-
How many ATP, NADH and FADH are made at each step of cell respiration?
- For each NADH, how many ATP are made?
- For each FADH2 how many ATP are made?
- 1 NADH yields 3 ATP
- 1 FADH2 yields 2 ATP
- Enters the ETC at a lower energy level
Why is oxygen so important for aerobic cell respiration?
(It’s very electronegative – why is this significant?)
- Each oxygen atom accepts two electrons from the chain and picks up two H ions from the surrounding solution to form water
What is the purpose of the electron transport chain? Where are H+ ions pumped into?
-
What is the purpose of the H+ gradient across the inner mitochondrial membrane?
-
What is the role of ATP synthase in Chemiosmosis?
-
Poisons that act on oxidative phosphorylation?
How do they interrupt ATP production?
-
How is cellular respiration regulated by the cell?
- Inhibition of phosphofructokinase by Citrate and ATP, activation by AMP
What happens when no oxygen is available? (in certain cells/organisms)
-
Anaerobic Processes
Glycolysis –> Alcoholic Fermentation
OR
Glycolysis –> Lactic Acid Fermentation
What is the POINT of fermentation?
- When oxygen is not readily available to allow aerobic respiration to occur, pyruvate can follow a different chemical pathway after glycolysis
What are some problems with this alternate pathway?
- Efficiency bout 2-3% (19x less efficient than aerobic)
- This is because the waste products of fermentation still contain a lot of energy
- Potentially toxic byproducts
What kinds of cells/organisms carry out Alcoholic fermentation? Lactic Acid fermentation?
-
What is the relationship between catabolic molecular breakdown and anabolic biosynthesis?
-
Mitochondrian:
- Matrix
- Inter-membrane space
- Outer / inner membrane
- Matrix: where the Kreb cycle occurs
- Inter-membrane space: where the H+ will be pumped during next step of cell resp.
- Outer membrane: porous
- Inner membrane: very selective
Lactic acid fermentation
- Common in some bacteria (in yogurt-making), some fungi, and animal muscle cells
- Allows organism to still produce some ATP by simply replenishing supply of NAD+ needed for glycolysis to continue
- Lactic acid is produced in muscles during rapid exercise when there is not enough oxygen to carry out aerobic respiration
- The lack of oxygen that precedes this build up causes a drop in pH in muscle tissue – soreness
- Eventually lactic acid is flushed away from muscle tissue, taken to liver where converted back to pyruvic acid
Alcohol fermentation
- Commonly occurs in yeasts and some bacteria
- Allows organism to still produce some ATP by simply replenishing supply of NAD+ needed for glycolysis to continue
- Accepts 2 electrons and an H+ from each NADH made in glycolysis
- Glycolysis continues with NAD+ produced in fermentation
- Making bread, beer, wine
