Energy and Respiration Flashcards
Where do living organisms gain their continuous supply of energy from?
- Absorption of light energy
2. Chemical potential energy (energy stored in nutrient molecules)
What does photosynthesis do and supply living organisms with?
- Transfers light energy into chemical potential energy
- An energy supply and usable carbon compounds
What do all biological macromolecules uses (e.g. carbohydrates, lipids and proteins) contain?
- Carbon
- All living organisms therefore need a source of carbon
What are autotrophs?
- An organism that can trap an inorganic carbon source (carbon dioxide) using energy from light or from chemical
- Organisms that can use an inorganic carbon source in the from of carbon dioxide
What are heterotrophs?
- An organism needing. supply of organic molecules as its carbon source
- Organisms needing a ready-made organic supply of carbon
What is an organic molecule?
- A compound including carbon and hydrogen
- The term originally meant a molecule derived from an organism, but now includes all compounds of carbon and hydrogen even if they do not occur naturally
How can organic molecules be used?
- Serve as ‘building blocks’ for making other organic molecules that are essential to the organism
- They can represent chemical potential energy that can be released by breaking down the molecules in respiration
- This energy can then be used for all forms of work
What is the relationship between heterotrophs and autotrophs?
Heterotrophs depend on autotrophs for both materials and energy
What does work in a living organism include?
- The synthesis of complex substances from simpler ones (anabolic reactions), such as the synthesis of polysaccharides from monosaccharides, lipids from glycerol; and fatty acids, polypeptides from amino acids and nucleic acids from nucleotides
- The active transport of substances against a diffusion gradient such as the activity of the sodium-potassium pump
- Mechanical work such as muscle contraction and other cellular movements; for example the movement of cilia and flagella, amoeboid movements and the movement of vesicles through cytoplasm
- In a few organisms, bioluminescence and electrical discharge
How do mammals and birds maintain a constant body temperature?
- Mammals and birds use thermal energy (heat) that is released from metabolic reactions to maintaining a constant body temperature
- Mammals and birds are endotherms releasing enrich thermal energy within their bodies to moaning them above the temperature of their surrounding when necessary
- They also maintain a constant body temperature through negative feedback loops
What are ectotherms?
- Most animals are ectotherms
- The thermal energy that warms them comes from outside their bodies
How can living organisms do work?
-Energy requiring reactions must be linked to those that yield energy
-In the complete oxidation of glucose (C6H12O6) in aerobic conditions, a large quantity of energy is made available
(Respiration equation and 2870kJ)
How do reactions in order to do work take place?
- Reaction such as this take place in a series of small steps, each releasing a small quantity of the total available energy
- Multi-step reactions allow precise control via feedback mechanisms
- Moreover the cell could not usefully harness the total available energy if all of it were made available at one instant
Why is the complete oxidation of glucose to carbon diode and water no happen very easily?
Despite its very high energy yield, glucose is quite stable because of the activation energy that has to be added before any reaction takes place
How is the activation energy overcome?
- In living organisms the activation energy is overcome by lowering it using enzymes
- Also by raising the energy level of the glucose by phosphorylation
How is energy harnessed at each step in respiration?
- Theoretically the energy released from each step of respiration could be harnessed directly to some form of work in the cell
- However a much more flexible system occurs in which energy-welding reaction in all organisms are used to make in intermediary molecule ATP
How is ATP broken apart?
- When a phosphate group is removed from ATP, adenosine diphosphate (ADP) is formed and 30.5 kJmol-1 of energy is released
- Removal of a second phosphate produce adenosine monophosphate (AMP) and 30.5 kJmol-1 of energy is again released
- Removal of the last phosphate leaving adenosine resale only 14.2kJmol-1
What are all of these reactions with ATP?
reversible
Which reaction is most important for providing energy for the cell?
-It is the interconversion of ATP and ADP that is all-important in providing energy for the cell
ATP + H2O (reversible arrow) ADP + H3PO4 ±30.5kJ
What is the rate of interconversion of ATP and ADP?
- The rate of interconversion or turnover is enormous
- It is estimated that a resting human uses about 40kg of ATP in 24 hours, but at any one time contains only about 5g of ATP
- During strenuous exercise, ATP breakdown may be as much as 0.5kg per minute
Describe ATP
- The cell’s energy-yielding reactions are linked to ATP synthesis
- The ATP is then used by the cell in all forms of work
- ATP is the universal intermediary molecules between energy-yielding and energy-requiring reactions used in a cell, whatever the type of cell
- In other words, ATP is the ‘energy currency’ of the cell
How is ATP suitable for its role?
- The cell ‘trades’ in ATP weather than making use of a number of different intermediates
- Suitable for role as readily hydrolysed to related energy and it is small and water soluble
- This allows it to be easily transported around the cell
What are energy transfers?
inefficient
Why are energy transfers inefficient?
- Some energy is converted to thermal energy whenever energy is transferred
- At the different stages in a multi-step reaction such as respiration, the energy made available may not perfectly correspond with the energy needed to synthesis ATP
- Any excess energy is converted to thermal energy
- Many energy-requiring reaction in cells also used less very that that realised by hydrolyses of ATP and ADP and any extra energy will be realised as thermal energy
What is an energy currency molecule?
An energy currency molecule acts as the immediate donor of energy to the cell’s energy required reactions
What is an energy storage molecule?
An energy storage molecule is a short term (glucose or sucrose) or long term (glycogen, starch or triglyceride) store of chemical potential energy
Where does energy for ATP synthesis come from?
- Respiration
2. Electrical potential energy
How does the energy for ATP synthesis come from respiration?
In respiration energy related by reorgansing chemical bonds (chemical potential energy) during glycolysis and the Krebs cycle is used to make some ATP
How does the energy for ATP synthesis come from electrical potential energy?
- Most ATP in cells is generated using electrical potential energy
- This energy is from the transfer of electron by electron carriers in mitochondria and chloroplasts
- It is stored as a difference in proton (hydrogen ion) concentration across some phospholipid membranes in mitochondria and chloroplasts which are essentially impermeable to protons
What happens to protons as a result of the concentration difference?
- Protons are then allowed to flow down they concentration gradient (by facilitated diffusion) through a protein that spans the phospholipid bilayer
- Part of this protein acts as an enzyme that synthesises ATP and is called ATP synthase
- The transfer of three protons allows the production of one ATP molecule provided that ADP and inorganic phosphate group (Pi) are available inside the organelle
- This process (chemisosmosis) occurs in both mitochondria and chloroplasts
Describe the structure of ATP synthase
- Three bidding sites and a part of the molecules (gamma) that rotates as hydrogen ions (H+) pass
- This produced structural changes in the binding sites and allows them to pass sequentially through three phases
1. Binding ADP and Pi
2. Forming tightly bound ATP
3. Releasing ATP
What is active transport?
- Active transport is the emolument of molecules or ions across a partially permeable membrane against a concentration gradient
- Energy is needs from ATP to counteract the tendency of these particles to move by diffusion down the gradient
What is the sodium potassium pump?
- All cells show difference in the concentration of ions in auricular sodium and potassium ions, inside the cell with respect to the surrounding solution
- Most cells seem to have sodium pumps in the cell surface membrane that pump sodium ions out of the cell
- This is usually coupled with the ability to pump potassium ions from the surrounding solution into he cell
Describe how the sodium potassium pump works
- The sodium potassium pump is a protein that spans the cell surface membrane
- It has binding sites for doom ions (Na+) and for ATP on the inner side, and for potassium ion (K+) on the outer side
- The proteins acts as an ATPase and catalyses the hydrolysis of ATP to ADP and inorganic phosphate related energy to drive the pump
- Changes in the shape of the protein move sodium and potassium ions across the membrane in opposite directions
What happens for each ATP used?
For each ATP used, two potassium ions move into the cell and three sodium ions move out of the cell
Why is a potential difference created?
- As only two potassium ions are added to the cell contents for every three sodium ions removed, a potential difference is created across the membrane that is negative inside with respect to the outside
- Both sodium and potassium ions leak back across the membrane, down their diffusion gradients
- However cell surface membranes are much less permeable to sodium ions than potassium ions so this diffusion actually increases the potential difference across the membrane
What is one of the specialisations of the nerve cell?
An exaggeration of the. potential difference across the cell surface membrane as a result of the activity of the sodium potassium pump
How important is active transport in ion movement into and out of cell?
Very important as about 50% of the ATP is used by a resting mammal is devoted to maintaining the ionic content of cells
What is respiration?
- Enzymatic release of energy from organic compounds in living cells
- Respiration is a process in which organic molecules act as a fuel
What happens to the organic molecules in respiration?
The organic molecules are broken down in a series of stages to release chemical potential energy, which is used to synthesise ATP
What is the main fuel for most cells?
- Carbohydrate, usually glucose
- Many cells can use inky glucose as their respiratory substrate but other break down fatty acids, glycerol and amino acids in respiration
What are the four stages of glucose breakdown?
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
What is glycolysis?
- Glycolysis is the splitting or lysis or glucose
- It is a multi-step process in which a glucose molecule with six carbon atoms is eventually split into two molecules of pyruvate, each with three carbon atoms
How is ATP related to glycolysis?
- Energy from ATP is needed in the first steps, but energy is released in the later steps, when it can be used to make ATP
- There is a net gain of two ATP molecules per molecule of glucose broken down
Where does glycolysis take place?
In the cytoplasm of a cell
What is and happens in the first stage of glycolysis?
- In the first stage, phosphorylation, glucose is phosphorylated using ATP
- Glucose is energy rich but does not react easily so to tap the bond energy of glucose, energy muscle first be sued to make the reaction easier
- Two ATP molecules are used for each molecule of glucose to make first glucose phosphate and then fructose phosphate and then fructose bisphosphate, which breaks down to produce two molecules of triose phosphate
What happens to the triose phosphate in glycolysis?
- Hydrogen is then removed from triose phosphate and transferred to the carrier molecule NAD (nicotinamide adenine dinucelotide)
- Two molecules of reduced NAD are produced for each molecule of glucose entering glycolysis
- The hydrogens carried by reduced NAD can easily be transferred to other molecules and are used in oxidative phosphorylation to generate ATP
Describe the end product of glycolysis
- The end product of glycolysis, pyruvate, still contains a great deal of chemical potential energy
- When free oxygen is available some of this energy can be released via the Krebs cycle and oxidative phosphorylation
- However the pyruvate first enters the link reaction which takes place in the mitochondria
What is the first stage of the link reaction?
Pyruvate passes by active transport from the cytoplasm, through the outer and inner membranes of a mitochondrion and into the mitochondrial matrix
What happens to the pyruvate in the mitochondrial matrix?
- It is decarboxylated (carbon dioxide is removed),
- Dehydrogenated (hydrogen is removed)
- Combined with coenzyme A (CoA) to give acetyl coenzyme A
- This is known as the link reaction
What is coenzyme A?
- Coenzyme A is a complex molecule composed of a nucleoside (adenine plus ribose) with a vitamin (pantothenic acid) and acts as a carrier of acetyl groups to the Krebs cycle
- The hydrogen removed from pyruvate is transferred to NAD
What else can be used to produce acetyl coenzyme A?
- Fatty acids from fat metabolism may also e side to reduce acetyl coenzyme A
- Fatty acids are broken down in the mitochondrion in a cycle of reactions in which each turn of the cycle shortens the fatty acid chain by a two-carbon acetyl unit
- Each of these can react with coenzyme A to produce acetyl coenzyme A, which, like that produced from pyruvate now enters the Krebs cycle
What is the Krebs cycle?
- A cycle of reactions in aerobic respiration in the matrix of the mitochondrion in which hydrogens pass to hydrogen carriers for subsequent ATP synthesis and some ATP is synthesised directly
- A closed pathway of enzyme controlled reactions
What is the Krebs cycle also known as?
- Citric acid cycle or tricarboxylic acid cycle
- Discovered in 1937 by Hans Krebs
What are the stages of the Krebs cycle?
- Acetyl coenzyme A combines with a four carbon compound (oxaloacetate) to form a six carbon compound citrate and the CoA is related back into the link reaction
- The citrate is decarboxylated and dehydrogenated in a series of steps to yield carbon dioxide which is given off as waste gas and hydrogens which are accepted by the carriers NADox and FADox to NADre and FADre
- Oxaloacetate is regenerated to combine with another acetyl coenzyme A
- No oxygen is sued - For each turn, two carbon dioxide molecules are produced, one FAD and three NAD molecules are reduced and one ATP molecule is generated
What happens for each turn of the Krebs cycle?
Two carbon dioxide molecules are produced, one FAD and three NAD molecules are reduced and one ATP molecule is generated via an intermediate compound
How is oxygen used in the Krebs cycle?
- Although part of aerobic respiration, the reactions of the Krebs cycle make no use of molecular oxygen
- However oxygen is necessary for the final stage of aerobic respiration which is called oxidative phosphorylation
What is the most important contribution of the Krebs cycle to the cell’s energetics?
The release of hydrogens which can be used in oxidative phosphorylation to provide energy to make ATP
What happens in the final stage of aerobic respiration?
In the final stage of aerobic respiration, oxidative phosphorylation the energy for the phosphorylation of ADP to ATP comes from the activity of the electrons transport chain
Where does oxidative phosphorylation take place?
The inner mitochondrial membrane
What is oxidative phosphorylation?
The synthesis of ATP from ADP and Pi using energy fro oxidation reactions in aerobic respiration
What is the electron transport chain?
Chain of adjacently arranged carrier molecules in the inner mitochondrial membrane along which electrons pass by redox reactions
What happens in oxidative phosphorylation?
- Reduced NAD and reduced FAD are passed to the electron transport chain
- Here the hydrogens are removed from the two hydrogen carriers and each is split into its constituent proton (H+) and electron (e-)
- The energetic electron is transferred to the first of a series of electron carriers and as an electron moves from one carrier at a higher energy level to one at a lower energy level energy is realised, of which some is used to move H+ from the matrix to the intermemebrane space creating a concentration gradient
- The higher concentration of H+ in the intermediate space and as the H+ move down they concentration gradient, through a channel associated with ATP synths, ATP is produced in chemisomosis
- Oxygen is the final electron acceptor as it accepts and electron and hydrogen ion reducing it to water
What are most of the carriers associated with?
Membrane proteins of which there are four types
What does a functional unit, called a respiratory complex consist of?
-Consists of one of each of these proteins arranged in such a way that electrons can be passed from one to another down an energy gradient
What happens as an electron moves from one carrier at a higher energy level to another one at a lower level?
- Energy is released
- Some of this energy is used to move protons from the matrix of mitochondrion into the space between the inner and outer membranes of mitochondrial envelope
- This produces a higher concentration of protons in the inter membrane space than in the matrix, setting up a concentration gradients
What happens as a result of the concentration gradient set up in oxidative phosphorylation?
- Protons mass back into he mitochondrial matrix through protein channels in the inner membrane, moving down they concentration gradient
- Associated with each channel is the enzyme ATP synthase
- As the protons pass through the channel their electrical potential energy is used to synthesise ATP in the process called chemiosmosis
What role does oxygen play in oxidative phosphorylation?
- Oxygen is the final electron acceptor
- In the mitochondrial matrix, an electron and a proton are transferred to oxygen reducing it to water
- The process of aerobic respiration is complete
What is the theoretical yield of ATP and why is it not achieved?
- Theoretically three molecules of ATP can be produced from each molecule of reduced NAD and two molecules of ATP from each molecule of reduced FAD
- However this tied cannot be achieved unless ADP and Pi are available inside the mitochondrion
What is the yield of ATP?
- About 25% of the total energy yield of electron transfer is used to transport ADP into the mitochondrion and ATP into the cytoplasm
- Hence, each reduced NAD molecule entering the chain produces on average two and a half molecules of ATP and each reduced FAD produce sone and a half molecules of ATP
Does the number of ATP molecules produce vary?
-The number of ATP molecules actually produced varies in different tissues and different circumstances, largely dependent on how much energy is used to move substances into and out of the mitochondria
What is NAD made of?
NAD is made of two linked nucleotides
What are the nucleotides in NAD?
- Both nucleotides contain ribose
- One nucleotide contains the nitrogenous base adenine
- The other has a nicotinamide ring, which can accept a hydrogen ions and two electrons, thereby becoming reduced
What is a slightly different form of NAD?
- A slightly different form of NAD has a phosphate group instead of the hydrogen on carbon 1 in one of the ribose rings
- This molecule is called NADP (nicotinamide adenine dinucleotide phosphate)
- And it is used as a hydrogen carrier molecule in photosynthesis
What is FAD?
Falvin adenine dinucleotide and is similar in function to NAD and is sued in respiration in the Krebs cycle
What is FAD made of?
FAD is made of one nucleotide contains ribose and adenine and one with an unusual structure involving a linear molecule, ribitol instead of ribose
What is the mitochondrion in eukaryotic organisms?
The site of the Krebs cycle and the electron transport chain
Describe mitochondria
- Rod-shaped or filamentous organelles about 0.5-1 mum in diameter
- Time-lapse photography shows that they are not rigid but can change their shape
What does the number of mitochondria in a cell depend on?
On its activity e.g. a highly active mammalian lover cells contain between 1000 and 2000 mitochondria, occupying 20% of the cell volume
What is the structure of mitochondria?
- Like chloroplasts, each mitochondrion is surrounded by an envelope of two phospholipid membranes
- The outer membrane is smooth, but the inner is much folded inwards to form cristae (singular crista)
What is the cristae?
- These cristae give the inner membrane a large total surface area
- Cristae in mitochondria from different types of cell show considerable variation, but in general mitochondria from a active cells have longer, more densely packed cristae than mitochondria from less active cell
Are the two membranes in mitochondria different?
- The two membranes have different compositions and properties
- The outer membrane is relatcielt permeable to small molecules, whereas the inner membrane is less permeable
What is the inner membrane?
- The inner membrane is studded with tiny spheres. about 9nm in diameter which are attached to the inner membrane by stalks
- The spheres are the enzyme ATP synthase
- The inner membrane is the site of electron transport chain and contains the proteins necessary for this
Describe the space between the membranes?
The space between the two membranes of the envelope usually has a lower pH than the matrix of the mitochondrion as a result of the protons that are released into the inter membrane space by the activity of the electron transport chain
Describe the matrix
- The matrix of the mitochondrion is the site of the link reaction and the Krebs cycle and contains the enzymes needed for these reactions
- It also contains small (70S) ribosomes and several identical copies of lopped mitochondrial DNA
Where is ATP formed?
- ATP is formed in the matrix by the activity of ATP synthase on the cristae
- The energy for the production of ATP comes from the proton gradient between the intermembrane space and the matrix
- The ATP can be used for all the very requiring reactions of the cell, both inside and outside the mitochondrion
What happens with respiration when free oxygen is not available?
- When free oxygen is not present, hydrogen cannot be disposed of by the combination with oxygen
- The electron transfer chain therefore stops working and no further ATP is formed by oxidative phosphorylation
- If a cell is to gain even the two ATP molecules for each glucose yielded by glycolysis, it is essential to pass on the hydrogens from the molecules of reduced NAD that are made in glycolysis
How made different anaerobic pathways are there?
- There are two different anaerobic pathways that solve the problem of ‘dumping’ this hydrogen
- Both pathways take place in the cytoplasm in the cell
What happens in yeast?
- In various microorganisms such as yeast and in some pant tissues, the hydrogen from reduced NAD is passed to ethanol (CH3CHO)
- This releases the NAD and allows glycolysis to continue
What happens in alcoholic fermentation?
- First pyruvate is decarboxylated to ethanal and the ethanol accepts the hydrogen then the ethanal is reduced to ethanol (C2H5PH) by the enzyme alcohol dehydrogenase
- The conversion of glucose to ethanol is referred to as alcoholic fermentation
When is pyruvate converted to lactate?
- In other microorganisms, and in mammalian muscles when deprived of oxygen, pyruvate acts as the hydrogen acceptor and is converted to lactate by the enzyme lactate dehydrogenase (named after the reverse reaction, which it also catalyses)
- Again the NAD is related and allows glycolysis to continue in anaerobic contusions
- This pathway is known as lactic fermentation
What is alcoholic fermentation?
Anaerobic respiration in which glucose is converted to ethanol
What is lactate?
- (or lactic acid)
- The end product of lactic fermentation often produced by muscles during exercise
What is lactic fermentation?
Respiration in which in the absence of oxygen, glucose is converted to lactic acid (lactate)
What does lactic and alcoholic fermentation do?
- These reactions ‘buy time’
- They allow the continued production of at least some ATP eventhough oxygen is not available as the hydrogen acceptor
- However, as the products of anaerobic reactions ethanol or lactate, are toxic, the reactions cannot continue indefinitely
Can these processes be reversed?
- The pathway leading to ethanol cannot be reversed, and the remains chemical potential energy of ethanol is wasted
- The lactate pathway can be reversed in amass and lactate is carried by the blood plasma to the liver and converted back to pyruvate
- The liver oxidises some (20%) of the incoming lactate carbon dioxide and water via aerobic respiration when oxygen is available again
- The remainder of the lactate is converted by the liver to glycogen
Describe a person’s exercise rate
- Standing still a person absorbs oxygen at a resting rate of 0.2 dm^3min-1 (this is a measure of a person’s metabolic rate)
- When exercise begins, more oxygen is needed support aerobic respiration in the person’s muscles, increasing the overall demand to 2.5dm^3min-1
- However it takes four minutes for the heart and lungs to meet this demand and during this time lactic fermentation occurs in the muscles
- Thus the person builds up an oxygen debt and for the next three minutes enough oxygen is supplied
What happens when exercise stops?
The person continues to breathe deeply and absorb oxygen at a higher rate than when at rest and this post exercise uptake of extra oxygen, which is ‘paying back’ the oxygen deficit, is called the oxygen debt
What is the oxygen needed for?
- Conversion of lactate to glycogen in the liver
- Reoxygenation of haemoglobin in the blood
- A high metabolic rate, as many organs are operating at above resting levels
Are there other respiratory substrates?
-Although glucose is the essential respiratory substrate for some cells such as neurones in the brain, red blood cells and lymphocytes other cells can oxidise lipids and amino acids
What happens when lipids are respired?
- Carbon atoms are removed in pairs as acetyl coenzyme A from the fatty acid chains and fed into the Krebs cycle
- The carbon hydrogen skeletons of amino acids are converted into pyruvate or into acetyl coenzyme A
Where does most of the energy liberated in aerobic reposition come from?
- The oxidation of hydrogen to water when reduced NAD and reduced FAD are passed tot he electron transport chain
- Hence the greater number of hydrogens in the structure of the substrate molecule, the greater the energy value
Where does most of the energy liberated in aerobic reposition come from?
- The oxidation of hydrogen to water when reduced NAD and reduced FAD are passed tot he electron transport chain
- Hence the greater number of hydrogens in the structure of the substrate molecule, the greater the energy value
- Fatty acids have more hydrogens per molecule than carbohydrates do and so lipids have a greater energy value per unit mass of energy density than carbohydrates or proteins
How do you determine the energy value of a substrate?
- By burning a known mass of the substance in oxygen in a calorimeter
- The energy liberated by oxidising the substage can be determined from the rise in temp of a known mass of water in the calorimeter
What is a calorimeter?
The apparatus in which the energy value of a compound can be measured by burning it in oxygen
What is the ratio of oxygen taken in and carbon dioxide released?
1:1
What happens to the ratio when other substrates are respired?
- When other substrates are respired the ratio of the volume of oxygen used and carbo dioxide given off differ
- It follows that measuring this ratio called the respiratory quotient (RQ) shows what substrate is being used in respiration
- It can also show whether or not anaerobic respiration is occurring
How do you calculate the respiratory quotient?
RQ = volume of carbon dioxide given out in unit time / volume of oxygen taken in in unit time RQ= moles or molecules of carbon dioxide given out / moles or molecules of oxygen taken in
What is the respiratory quotient?
The ratio of the volume of carbon dioxide given out in respiration to that of oxygen used
When can no RQ be calculated?
- No RQ can be calculated for muscle cells using the lactate pathway as no carbon dioxide is produced
- glucose (C6H12O6) –> 2 lactic acid (C3H6O3) + energy
How is rice grown and why?
- Although rice can grow in dry conditions, it is often grown in ‘paddies’ - fields where the ground is intentionally flooded
- Rice can tolerate growing in water whereas most of the weeds that might compete with it are not able to do so
Why can most plants not grow in deep water? Why is this bad?
- Because their roots do not get enough oxygen
- Oxygen is required for aerobic respiration which provides ATP as an energy source for active transport and other energy-consuming processes such as cell division
What is another issue other than oxygen that most plants cannot grow in deep water?
- Nor, if the leaves are submerged, can photosynthesis take place, because there is not enough carbon dioxide available
- This happens because gases diffuse much more slowly in water than they do in air
- Moreover the concentrations of dissolved oxygen and dissolved carbon dioxide in water are much less than they are in air
- This is especially true in rice paddies where the rich mud in which the rice roots are planted contains large populations of micro-organisms, many of which are aerobic and take oxygen from the water
How do rice respond to flooding?
- Some varieties of rice respond to flooding by growing taller
- As the water rises around them, they keep growing upwards so that the top parts of their leaves and flower spikes are always held above the water
- This allows oxygen and carbon dioxide to be exchanged through the stomata on the leaves
How are the stems of the rice plants organised?
- The stems of the rice plant contain loosely packed cells forming a tissue known as aerenchyma
- Gases are able to diffuse through the aerenchyma to other parts of the plant including those under the water
- This is supplemented by air that is trapped in between the ridges of the underwater leaves
- These leaves have a hydrophobic corrugated surface that holds a thin layer of air in contact with the leaf surface
Is there any alcoholic fermentation in rice? What is the effect?
- Nevertheless, the cells in the submerged roots do still have to use alcoholic fermentation at least some of the time
- Ethanol can therefore build up in the tissues
- Ethanol is toxic, but the cells in the rice roots can tolerate much higher levels than most plants
- They also produce more alcohol dehydrogenase, which breaks down ethanol
- This allows the plants to grow actively even when oxygen is scarce, using ATP produced by alcoholic fermentation
What is aerenchyma?
Plant tissue containing air spaces
Why is ATP the universal energy currency of cells?
- It is used in all cells
- In all different organisms
- Used in many metabolic reactions that require energy
- Links anabolic and catabolic reactions
What re three roles of ATP in plant cells?
- Light independent reaction to reduce GP to TP
- In glycolysis
- Growth e.g. synthesis of polymers from monomers
- Active transport
Where does glycolysis happen?
Cytoplasm (systole)
Where does the link reaction happen?
Mitochondrial matrix
Where does the Krebs cycle happen?
Mitochondrial matrix
Where does oxidative phosphorylation happen?
Inner mitochondrial membrane
Why is anaerobic respiration produce much less ATP than aerobic respiration?
- There is no oxygen so no final hydrogen acceptor form the electron transport chain in oxidative phosphorylation
- As a result no ATP is formed (and hence the potential energy remains in the repdocut (lactic acid) ) no reoxidation of the coenzyme and the Krebs cycle stops
Why does a faster use of ATP require a greater rate of oxygen consumption?
- ATP made in electron transport chain / by oxidative phosphorylation
- Oxygen final electron acceptor
- Inner mitochondrial matrix
- Transfer of electrons between electrons carriers provides energy
- Energy used to pump hydrogen ions into intermembrane space
- Creates a proton gradient
- Diffusion of hydrogen ions down their electrochemical gradient causes ATP to be synthesised
- Chemsiosmosis
- If less oxygen consumed then fewer electrons transferred along the chain
Outline the princess of glycolysis in a mammalian cell
- Glucose is phosphorylated by ATP
- Forms hexose/fructose bisphosphate
- Lowers activation energy of reaction
- Breaks down to two TP so 6C goes to 2 x 3C
- Hydrogen atoms removed
- 2 reduced MAD framed
- 4 ATP produces and a net gain of 2 ATP
- Pyruvate produced
Why is ATP ideal as energy currency in living organisms?
- Loss of phosphate/hydrolysis leads to energy relases
- Small packets of energy
- Small/water soluble, so can move around cell
- Immediate energy donor
- Link between energy yielding and energy requiring reaction
- High turnover
What are products of oxidative phosphorylation?
- NAD
- FAD
- Water/H2O
Why do lipids have a higher energy value than carbohydrate?
- More C-H bonds (more hydrogen)
- Produces more reduced NAD
- Produces more ATP per unit mass
- More aerobic respiration/oxidative phosphorylation
- Fats only broken down aerobically
What is the typical RQ of carbo or lipid?
- Carb: 1.0
- Lipid: 0.7
What happen when respiration in yeast become anaerobic?
RQ becomes greater than 1
What is the function of DNA and ribosomes in a mitochondrion?
- DNA for transcription / codes for mRNA
- Ribosomes for translation
- Synthesis of respiratory enzymes
How does an animal produce ATP in no oxygen environment?
- Anaerobic respiration
- Substrate level phosphorylation in glycolysis
- At triose phosphate to pyruvate step
- Pyruvate reduced/gains hydrogens
- Forming lactate
- NAD regenerated
- This allows glycolysis to continue
