topic 7 Flashcards
- Cellular work includes:
- Mechanical
- Chemical * Transport
- Organisms obtain energy by ingesting:
- Other animals
- Photosynthetic organisms
Energy flows and chemicals cycle
- Energy enters ecosystem as light
- Energy leaves as heat
- Chemical elements are recycled
- Ie) carbon and nitrogen cycles
Photosynthesis generates
O2 and organic molecules
* O2 and organic molecules are used in cellular respiration
* Cells use chemical energy stored in organic molecules to generate ATP, which powers work
Catabolic pathways:
Release stored energy by breaking down complex molecules (fuel)
* Breaking down complex molecules releases electrons
* Processes are central to cellular respiration
- The breakdown of organic molecules is
exergonic
* Releases potential energy in the bonds between atoms
* These molecules are known as fuels
- fermentation, aerobic respiration, anaerobic respiration
1) Fermentation:
- A partial degradation of sugars that occurs without O2
- Wine, cheese, beer, bread, etc
2) Aerobic respiration:
- Consumes organic molecules and O2, yielding ATP
- Performed by most eukaryotic cells and many prokaryotic cells
Organic Compounds + Oxygen > Carbon dioxide + Water + Energy
3) Anaerobic respiration:
- Similar to aerobic respiration, but consumes compounds other than O2 (ie: NO3- or SO42-)
Cellular respiration:
- Includes both aerobic and anaerobic respiration, but is often used to refer to aerobic respiration
- Carbohydrates, fats, and proteins are all consumed as fuel
In cellular respiration, electrons are transferred
- Transfer of electrons during chemical reactions releases energy stored in organic molecules
- This released energy is ultimately used to synthesize ATP
- Chemical reactions that transfer electrons between reactants are called oxidation- reduction reactions, or redox reactions
- Chemical reactions that transfer electrons between reactants are called
oxidation- reduction reactions, or redox reactions
- Oxidation:
- A substance loses electrons, or is oxidized
reduction
a substance gains e
Organic molecules with an abundance of H are excellent sources of
high-energy electrons
Energy is released as the electrons associated with
H ions are transferred to O, a lower energy state
* C in methane ‘loses’ electrons > spend more time around O than C
- During cellular respiration:
- fuel- glucose is oxidized
- oxygen reduced
- energy is released as the elecrons associated with hydrogen ions are transferred to a oxygen, a lower energy state
Stepwise Energy Harvest
- In cellular respiration, glucose and other organic molecules are broken down in a series of steps
- Step wise release of energy allows for better control of reaction
- Electrons from organic compounds are usually first transferred to
NAD+ a coenzyme
- nad+ is an electron acceptor, which is the oxidizing agent during cellular respiration
- Each NADH (the reduced form of NAD+) represents
stored energy that is tapped to syntesize atp
Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
- NADH passes the electrons to the electron transport chain (ETC)
- Unlike an uncontrolled reaction, the ETC passes electrons in a series of steps (instead of one explosive reaction)
- O2 pulls electrons down the chain in an energy- yielding tumble
- The energy yielded is used to regenerate ATP
The Steps of Cellular Respiration
Harvesting of energy from glucose has three stages
1. Glycolysis:
* Breaks down glucose into two molecules of
pyruvate
2. The citric acid cycle:
* Completes the breakdown of glucose
3. Oxidative phosphorylation:
* Accounts for most of the ATP synthesis (~90% of ATP production)
- OxidativePhosphorylation:
- Powered by redox reactions of the electron
transport chain - ~90% of ATP production
- Substrate-Level Phosphorylation:
- Enzyme transfers phosphate group from
substrate to ADP - Fewer ATP produced, via glycolysis and the citric
acid cycle - Foreachglucose,cellmakesupto32ATP molecules
Glycolysis – oxidizes glucose to pyruvate
- Sugar splitting
- Splits 1 glucose (1x6C) into 2 pyruvate
(2x3C) - Occurs in cytosol
- Occurs whether O2 is present or not
- Occurs in prokaryotic and eukaryotic cells
2 Major phases of Glycolysis
- Energy investment phase
- Cell expends energy (2 ATP)
- Energy payoff phase
- Cell produces 4 ATP via substrate level
phosphorylation
net production from 1 glucose in glycolsis
- 2 Pyruvate
- 2 ATP
- 2 H2O
- 2 NADH + 2H+
At the end of Glycolysis
- All of the C originally in glucose is found in the 2 molecules of pyruvate
- No C released as CO2 in glycolysis * Glycolysis occurs whether O2 is
present or not - In presence of O2, pyruvate enters a mitochondrion
Pyruvate Oxidation
- In the presence of O2, pyruvate enters a mitochondrion
- Where the oxidation of glucose is completed
- Before Citric Acid Cycle can begin: * Pyruvate needs to be converted to
Acetyl Coenzyme A (Acetyl CoA) - Links Glycolysis to Citric Acid Cycle
Pyruvate Oxidation: Converting Pyruvate to Acetyl
Carried out by a multi-enzyme complex that catalyzes three reactions
- Oxidation of pyruvate and release of CO2
2.Reduction of NAD+ to NADH
3.Combination of the remaining 2C fragment and coenzyme A to form acetyl CoA
* Has Sulfur group (S-CoA)
* Acetyl CoA: high potential energy
Acetyl CoA now ready to enter Citric Acid Cycle
The Citric Acid Cycle
- Also known as Krebs Cycle or tricarboxylic acid (TCA) cycle
Citric Acid Cycle (CAC): - Completes the breakdown of pyruvate to CO2
- Occurs in the mitochondrial matrix
The Citric Acid Cycle Output
- Oxidizes organic fuel derived from one acetyl CoA generating, per turn:
- 1ATP
- 3NADH
- 1 FADH2
- Each pyruvate becomes 3 CO2:
- One CO2 in pyruvate oxidation
- Two CO2 in CAC
- Each molecule of glucose produces 2 pyruvate, therefore output doubles per 1 glucose molecule
how many steps in citric acid cycle
8 each catalyzed by enzyme
The acetyl group of acetyl CoA joins the cycle by combining
combining with oxaloacetate, forming citrate
decompose the citrate back to oxaloacetate, making the process
a cycle
* Carbons from initial acetylCoA (red) become carbons in oxaloacetate (blue) in subsequent cycle
* Lost as CO2 in subsequent cycle
For each Acetyl CoA:
- 1 ATP
- 1 FADH2
- 3 NADH
- The NADH and FADH2 produced by the CAC relay electrons extracted from
food to the electron transport chain
Oxidizes organic fuel derived from one Acetyl CoA generating, per turn:
- 1ATP
- 3NADH *
1 FADH2
Each pyruvate becomes
3 CO2:
* One CO2 in pyruvate oxidation
* TwoCO2inCAC
Each molecule of glucose produces
2 pyruvate, therefore output doubles per 1 glucose molecule
Upon completion of glycolysis and the CAC
- NADH and FADH2 account for most of the energy extracted from food
- NADH and FADH2 are electron carriers that donate electrons to the electron transport chain
- Electron Transport Chain:
Powers ATP synthesis via oxidative phosphorylation
ETC is in the
inner membrane (cristae) of mitochondria
Most components are multi protein complexes in inner mitochondrial membrane
Electrons are transferred from NADH or FADH2 to the
ETC
* Carriers come from Glycolysis or CAC
* Electrons are passed through numerous proteins, ending with O2 (most electronegative)
Electrons drop in… as they go down the ETC
free energy as they go down the chain and are finally passed to O2, forming H2O
* Breaks the large free-energy drop from food to O2 into smaller steps
* Releases energy in manageable amounts
Electron carriers alternate between
reduced and oxidized states as they accept and donate electrons
Terminal electron acceptor:
- Oxygen, which is strongly electronegative,
then forms H2O - The ETC generates no ATP directly
If the ETC generates no ATP directly, how is ATP produced?
- The energy released as electrons are passed down the ETC:
- Pumps H+ from the mitochondrial matrix to the intermembrane space
- The ETC creates a higher [H+] in intermembrane space
- H+ then moves down its concentration gradient back across the membrane
- passes through the protein complex atp synthase
Chemiosmosis:
the use of energy in a H+ gradient to drive cellular work
* H+ moves into binding sites on the rotor of ATP synthase, causing it to spin and catalyze phosphorylation of ADP + inorganic Phosphate > ATP
5 steps of chemiosmosis
- H+ ions flow down concentration gradient
- H+ ions enter binding sites in rotor, changing shape of subunit so rotor spins within membrane
- Each H+ ion makes one spin before exiting via a channel into mitochondrial matrix
- Spinning of rotor causes internal rod to spin
- Spinning rod causes catalytic sites in the catalytic knob to produce ATP from ADP and Pi
- During cellular respiration, most energy flows in this sequence:
- Glucose → NADH or FADH2 → ETC → proton- motive force → ATP
- About 34% of the energy in a glucose molecule is transferred to ATP, making about 32 ATP
- The rest of the energy is lost as heat
total atp in cellular respiration
32
* Depends on the electron shuttle used to bring electrons from cytosolic NADH (glycolysis) across mitochondrial membrane
Anaerobic Respiration
- Some prokaryotic organisms
- Has an electron transport chain, but does not use oxygen as final electron acceptor
- Therefore,doesnotproducewateratend
- Other final electron acceptors are less electronegative than oxygen, and are less efficient at producing energy
- SO42- * NO3-
Fermentation
- After glycolysis, in presence of O2,
cells use aerobic respiration - Electronegative Oxygen pulls electrons down ETC
- In absence of O2, this ETC will not operate
- Instead, glycolysis couples with fermentation to produce ATP
fermentation uses
- Uses substrate-level phosphorylation instead
of an ETC to generate ATP - Consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis
two types of fermentation
- Alcohol fermentation
- Lactic acid fermentation
Alcohol Fermentation
- Pyruvate is converted to ethanol in two steps
- The first step releases CO2 from pyruvate
- The second step produces NAD+ and ethanol
- Alcohol fermentation by yeast is used in brewing, winemaking, and baking
Lactic Acid Fermentation
- Pyruvate is reduced by NADH, forming NAD+ and lactate as end products
- NoreleaseofCO2
- Lactic acid fermentation by some fungi and
bacteria is used to make cheese and yogurt - Lactic acid fermentation in human muscle cells:
- Generates ATP during strenuous exercise when O2 is scarce
- Cells switch from aerobic respiration to lactic acid fermentation
Comparing Fermentation with Anaerobic and Aerobic Respiration
- All use glycolysis to oxidize glucose and harvest the chemical energy of food
- Net ATP = 2
- In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis
- Different mechanisms for oxidizing NADH to NAD+:
fermentation an organic molecule acts as a final eletron acceptor
- in cellular respiration, electrons are transferred to the etc
Fermentation produces
cellular respiration produces
(ATP)
2 ATP per glucose molecule
32 atp per glucose molecule
Glycolysis during evolution
- Glycolysis is shared by prokaryotic and eukaryotic cells, regardless of oxygen presence
- This pathway occurs in the cytosol
- Doesnotrequirethemembrane-bound
organelles of eukaryotic cells - Early prokaryotes likely used glycolysis to produce ATP before O2 accumulated in the atmosphere
Energy from multiple sources
- Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration
- Carbohydrates
- Proteins
- Fats
