Topic 5:organotrophy Flashcards
Explain how energy is transferred when in redox reactions; given a reaction, identify which molecules are oxidized and which are reduced.
Oxidation is when an atom gives away electrons. when it gives away electrons, it loses some energy
Reduction is when an atom gets electrons. Its like saying, thanks ill take these electrons. when it gets an electron it gains some energy
here is a simple generic redox reaction for illustration:
A+B +→A+ +B
In this reaction, A is being oxidized because it loses an electron to become A+. B is being reduced because it gains an electron to go from B+ to B.
Let’s look at a specific example:
2Na +Cl2→2Na+ +2Cl
In this reaction:
-Sodium (Na) is oxidized as it loses electrons to form Na+.
-Chlorine (Cl2) is reduced because it gains electrons to form 2 Cl^-.
The Na is the reducing agent because it provides electrons to the Cl2, and the Cl2 is the oxidizing agent because it accepts electrons from Na.
The energy change in a redox reaction is often harnessed in biochemical processes—for example, in the electron transport chain of cellular respiration, where energy is methodically extracted from electrons as they are transferred through a series of proteins, ultimately being used to form ATP, the energy currency of the cell.
explain why glucose is an imporant source of energy and why it is oxidized in a series of reactions, rather than all at onc
Glucose is a critical source of energy for most organisms because it can be easily used in metabolic pathways to extract energy. It is a simple sugar, or monosaccharide, with the chemical formula C6H12O6, which means it contains a good balance of carbon, hydrogen, and oxygen atoms that can be broken down through cellular processes to release energy.
Here are a few reasons why glucose is such an important energy source:
Availability: Glucose is widely available as it is a primary product of photosynthesis, the process by which plants convert sunlight into chemical energy. It is also a major component of the diet of many organisms, either directly or through the consumption of plants or plant-eating organisms.
Solubility: Glucose is soluble in water, making it easy to transport through the bloodstream or within cells, where it can be readily accessed for metabolic processes.
Efficiency: The metabolism of glucose provides a high yield of ATP (adenosine triphosphate), which is the primary energy currency of the cell. Through glycolysis, the Krebs cycle, and oxidative phosphorylation, one glucose molecule can yield up to 36 or 38 ATP molecules (depending on the efficiency of the transport of electrons and protons in the mitochondria).
Versatility: Glucose can be metabolized both with and without oxygen (aerobic and anaerobic metabolism), making it a versatile source of energy that can be used in various cellular conditions.
Glucose is oxidized through a series of reactions rather than in one go because:
- Gradual breakdown allows efficient capture and use of energy in the form of ATP.
2.Controlled oxidation enables the cell to regulate energy release, preventing waste.
3.Intermediate compounds from glucose breakdown are useful for other metabolic pathways.
4.Slow oxidation reduces the risk of cellular damage from free radicals and reactive oxygen species.
Explain the role of glycolysis in energy transformation and the production of intermediates for further metabolic reactions.
- Energy transformation
Initial phase: Glycolysis starts by using energy, where two ATP molecules are consumed to activate glucose - Terminal phase: The latter half of glycolysis is energy-producing. Here
4ATP are produced,
leading to a net gain of 2ATP. Additionally, 2NADH, another energy-carrying molecule, is generated. These NADH molecules can be used in the electron transport chain to produce even more ATP.
describe the conserved pathways/ mechanisms for transforming/using energy within a cell/organism (ATP/reducing power/gradients)
Adenosine Triphosphate (ATP)
Role: ATP is often referred to as the “energy currency” of the cell. It captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes.
Production: ATP is produced in various metabolic pathways, notably glycolysis, the citric acid cycle, and oxidative phosphorylation.
Usage: When a cell needs energy, ATP is hydrolyzed to produce ADP (adenosine diphosphate) and inorganic phosphate (Pi), releasing energy in the process.
2.Reducing Power: NADH & FADH2
Role: These molecules act as electron carriers. They store energy in the form of high-energy electrons and protons, which can be transferred to other molecules or used in energy-producing reactions.
Production: Both NADH and FADH2 are produced in glycolysis, the citric acid cycle, and other metabolic pathways where they capture energy by accepting electrons (and protons).
Usage: NADH and FADH2 donate their electrons to the electron transport chain, located in the mitochondria. As electrons are transferred through this chain, energy is released and used to pump protons across the inner mitochondrial membrane, creating a gradient. This leads us to the next mechanism.
3.Proton Gradients (Chemiosmotic Potential)
Role: The electron transport chain generates a proton (H+) gradient across the inner mitochondrial membrane. This gradient represents a form of stored energy, known as the proton motive force (PMF).
Production: As electrons pass through the electron transport chain, protons are pumped from the mitochondrial matrix into the intermembrane space, creating a concentration gradient.
Usage: The enzyme ATP synthase utilizes this proton gradient. As protons flow back into the mitochondrial matrix through ATP synthase (following the gradient), energy is harnessed to synthesize ATP from ADP and Pi.
4.Phosphorylation
Role: Phosphorylation involves the addition of a phosphate group to a molecule, often resulting in a conformational change or activation of the molecule.
Types:
Substrate-level phosphorylation: Direct transfer of a phosphate group from a substrate to ADP, producing ATP. This occurs in glycolysis and the citric acid cycle.
Oxidative phosphorylation: ATP production linked with the transfer of electrons through the electron transport chain in mitochondria.
Photophosphorylation: ATP production using the energy of sunlight in photosynthesis.
describe the different types of chemical energy used by the cell to perform work (e.g ATP, proton motive force, NADH/NADPH/FADH2) and explain the role of electron carrier molecules In metabolic pathways
TYPES OF CHEMICAL ENERGY USED BY CELLS:
1. ATP
description: ATP consists of an adenine base, ribose sugar, and three phosphate groups. The high-energy bonds between the phosphate groups can be hydrolyzed to release energy
role: Often referred to as the “energy currency” of the cell, ATP provides the immediate source of energy for many cellular processes, including muscle contraction, synthesis of molecules, and transport of substances across membranes.
- PROTON MOTIVE FORCE:
description: a gradient of protons (H+ ions) across a membrane, typically the inner mitochondrial membrane or the thylakoid membrane in chloroplasts.
ROLE: the difference in proton concentration and the resulting difference is electrical potential across the membrane can be harnessed to produce ATP ( in mitochondria) or to drive the transport of molecules across the membranes.
THINK OF IT AS WATER BEHIND A DAM. WHEN THE WATER IS RELEASED, IT CAN DO WORK
- USED TO MAKE ATP OR MOVE STUFF AROUND THE CELL. - ELECTRON CARRIERS: NADH, NADPH, AND FADH2:
Description: these molecules can accept and donate electrons, acting as shuttle buses for electrons in the cell.
- used in processes that either produce energy (NADPH, FADH2) or build things (NADPH)
WHAT ELECTRON CARRIERS DO:
1. transfer energy: they pick up and give away energy in the form of electrons
2. Help make ATP: they play a part in a process that makes ATP
3. Support building and protecting; NADPH helps in building things in the cell and protecting it.
Describe the three pathways by which glucose is oxidized in aerobic respiration (glycolysis; citric acid (Krebs) cycle; electron transport chain and chemiosmosis) and be able to diagram the relationship among these three pathways
- glycolysis:
location: cytoplasm
process:
- one glucose (6 carbons) is split into two molecules of pyruvate ( 3 carbons each)
- this process produces a small amount of ATP directly and also creates high-energy molecules called NADH - Citric acid (Krebs) cycle:
location: mitochondrial matrix
process:
Before entering the cycle, each pyruvate from glycolysis is converted into acetyl-coA, producing NADH and releasing a carbon dioxide molecule
- the acetyl-coA enters the Krebs cycle, and as it gets processed, more high-energy molecules (NADPH AND FADH2) are produced.
- carbon dioxide is released as a waste product - Electron transport Chain and chemiosmosis:
location: inner mitochondrial membrane
process:
- NADH and FADH2 from the previous steps donate their electrons to proeins in the chain.
- as electrons move down the chain, they release energy which pumps protons (+H ions) across the inner mitochondrial membrane
- this creates a gradient or difference in concentration known as the proton motive force.
- at the end of the chain, electrons combine with oxygen (from the air we breathe) and protons to form water.
- the proton motive force drives protons back across the membrane through an enzyme called ATP synthase, creating ATP in the process. This mechanism is called chemiosmosis
For the three pathways, you do not need to memorize all the reactions, but you do need to know:
- What the starting molecules for these processes are;
- what molecules are produced.- How ATP is made in this step (by what process?)
- what is the main accomplishment of the pathway?
- where most of the energy that was originally present in glucose is at the end of each process
- where in eukaryotic and prokaryotic cells these pathways occur;
- how are the pathways similar in eukaryotic and prokaryotic cells, and how are they different?
- Glycolysis
starting molecule: GLUCOSE
Molecules produced: 2 pyruvate, 2 NADH, 4 ATP (Net gain of 2 ATP)
How ATP is made: Substrate level-phosphorylation (direct transfer of phosphate group to ADP)
main accomplishment: Splitting glucose into two molecules of pyruvate
energy from glucose: some energy from glucose is transferred to ATP and NADH; much remains in pyruvate
LOCATION:
eukaryotes : cytoplasm
Prokaryotes: cytoplasm
Similarities and differences: glycolysis is essentially the same in eukaryotic and prokaryotes. - Citric acid (Krebs) CYCLE:
starting molecule: ACETYL-coA (formed from pyruvate)
molecules produced: CO2, 3NADH, 1FADH2, 1ATP (per turn, and the cycle turned twice for each glucose molecule)
How ATP is made: substrate-level phosphorylation
Main accomplishment: Complete oxidation of the carbon acetyl-CoA to CO2
energy from glucose: stored in NADH and FADH2, which will be used to make ATP in the next step; CO2 released contains the oxidized carbon
LOCATION:
Eukaryotes: Mitochondrial Matrix
Prokaryotes: Cytoplasm
similarity and difference: The process is very similar in both types of cells. However, the location is different due to the presence or absence of mitochondria.
- Electron Transport Chain and Chemiosmosis:
Starting Molecule: NADH and FADH₂
Molecules Produced: Water, ATP
How ATP is made: Chemiosmosis (ATP synthase harnesses the proton motive force to synthesize ATP)
Main Accomplishment: Use of energy from NADH and FADH₂ to pump protons and drive ATP synthesis; electrons reduce oxygen to form water
Energy from Glucose: Mostly stored in ATP. The rest is released as heat or used for other cellular processes
Location:
Eukaryotes: Inner mitochondrial membrane
Prokaryotes: Plasma membrane
Similarity & Difference: Both cell types utilize an electron transport chain and proton gradient for ATP synthesis. However, the physical structures housing these processes differ (mitochondria in eukaryotes vs. plasma membrane in prokaryotes).
Explain how pyruvate oxidation allows for aerobic respiration to proceed in the presence of oxygen
- Conversion to Acetyl-CoA: After glycolysis occurs in the cytoplasm, pyruvate (a 3-carbon molecule) is transported into the mitochondria, undergoing oxidation. During this process, each pyruvate molecule is converted into an Acetyl-CoA (a 2-carbon molecule). This conversion is vital for feeding the citric acid cycle.
2.Release of Carbon Dioxide: One carbon atom from pyruvate is released as carbon dioxide (CO₂). This is the first step in glucose metabolism where CO₂ is released.
3.Reduction of NAD+: Another crucial event during pyruvate oxidation is the reduction of NAD+ to NADH. The electrons that are removed from pyruvate are transferred to NAD+ to produce NADH. This NADH will later donate its electrons to the electron transport chain, driving ATP production.
4.Presence of Oxygen: While pyruvate oxidation doesn’t directly use oxygen, the subsequent steps in aerobic respiration (namely the electron transport chain) do require oxygen. Oxygen acts as the final electron acceptor in the electron transport chain. If oxygen isn’t available, the electron transport chain would back up, and NADH would not be reconverted to NAD+. Without available NAD+, the citric acid cycle and pyruvate oxidation would halt. Thus, by oxidizing pyruvate and producing NADH, aerobic respiration is set to utilize oxygen in the later steps.
5.Continuation of Energy Extraction: The Acetyl-CoA produced from pyruvate enters the citric acid cycle, where it undergoes further oxidation. This cycle produces more NADH and FADH₂, which are electron carriers that will donate electrons to the electron transport chain, driving the production of ATP.
In summary, pyruvate oxidation ensures that the breakdown products of glucose from glycolysis are further processed in the presence of oxygen to extract maximum energy. This step prepares the molecules for the citric acid cycle and links glycolysis with the oxidative phases of aerobic respiration.
Explain the process of chemiosmosis: explain why electrons flow along the series of membrane
-bound complexes that make up the electron transport chain
- describe and be able to diagram how the flow of electrons along the ETC creates a proton motive force
- describe and be able to diagram how the proton force is used to produce ATP via ATP synthase - explain why oxygen is required for aerobic respiration
- given a scenario involving blockage or breakdown of electron flow along the ETC, be able to predict the effect on the overall process of respiration.
- explain the benefit obtained by organisms that can use aerobic respiration in terms of overall ATP production per unit of glucose
Chemiosmosis overview: chemiosmosis is the process by which ATP is produced in the mitochondria and chloroplasts of cells. It involves the flow of protons (H+) ACROSS A MEMBRANE driven by an electrochemical gradient.
2.Electron Flow in the Electron Transport Chain (ETC):
The ETC is a series of protein complexes embedded in the inner mitochondrial membrane.
Electrons are passed along this chain from one protein complex to another. These electrons come from NADH and FADH₂, which are produced in prior stages of cellular respiration.
The reason electrons flow is due to the differences in redox potential between the electron donors and acceptors in the chain.
3.Proton Motive Force Creation:
As electrons flow through the ETC, certain complexes actively pump protons from the mitochondrial matrix into the intermembrane space.
This creates a higher concentration of protons outside the matrix, resulting in an electrochemical gradient or proton motive force.
4.ATP Production via ATP Synthase:
ATP synthase is an enzyme located in the inner mitochondrial membrane.
The proton motive force drives protons back into the matrix, but they can only do so through ATP synthase.
As protons flow through ATP synthase, the energy released is used to convert ADP and inorganic phosphate into ATP.
5.Role of Oxygen in Aerobic Respiration:
Oxygen is the final electron acceptor in the ETC.
At the end of the chain, electrons combine with oxygen and protons to form water.
Without oxygen, electrons would accumulate, halting the flow through the ETC and stopping the entire process.
6.Blockage or Breakdown of the ETC:
If there’s a blockage or breakdown, electrons would back up, halting the ETC.
This means protons wouldn’t be pumped, the proton motive force wouldn’t form, and ATP production would stop.
This could be detrimental to the cell because ATP is required for many cellular processes.
- Benefits of Aerobic Respiration:
Aerobic respiration produces up to 36-38 ATP molecules per glucose molecule, which is much more than anaerobic processes.
It’s more efficient, allowing organisms to get more energy from the same amount of food.
