Respiration Flashcards
Describe glycolysis (overview)
-occurs in the cytoplasm
-anaerobic process
glucose is split into two, three-carbon pyruvate molecules
-ATP and reduced NAD is also formed
What are the main steps in glycolysis?
1) phosphorylation
2)Lysis
3)Phosphorylation
4) Dehydrogenation and formation of ATP
Describe the first step of glycolysis?
phosphorylation- two phosphates released from two ATP molecules are attached to a glucose molecule forming hexose bisphosphate
What occurs in glycolysis after the formation of hexose bisphosphate?
lysis- molecule destabilises, splitting into two triose phosphate molecules
What occurs in glycolysis after lysis?
phosphorylation- another phosphate group is added to each triose phosphate forming triose bisphosphate molecules. These phosphate groups come from free inorganic phosphate ions present in the cytoplasm
What occurs in glycolysis after the formation of triose bisphosphate?
Dehydrogenation and formation of ATP- two triode bisphosphate molecules are then oxidised by the removal of hydrogen atoms (dehydrogenation) to form two pyruvate molecules. NAD coenzymes accept the removed hydrogens- they are reduced, forming two reduced NAD molecules
what is substrate level phosphorylation?
Formation of ATP without the involvement of an electron transport chain. In glycolysis, ATP is formed by the transfer of a phosphate group from a phosphorylated intermediate (triose bisphosphate) to ADP
What is the overall net ATP yield in glycolysis?
2 as 2 ATP molecules are used in the beginning and 4 ATP molecules are produced
function of outer mitochondrial membrane?
separates contents of mitochondrion from the rest of the cell (compartmentalisation), creating ideal conditions for anaerobic conditions
Function of inner mitochondrial membrane?
contains electron transport chains and ATP synthase
Function of cristae?
projections of inner membrane which increase surface area available for oxidative phosphorylation
Function of the matrix?
contains enzymes for the kerbs cycle and link reaction, also contains mitochondrial DNA
Function of inter membrane space?
Proteins are pumped into this space by the electron transport chain. The space is small so the concentration builds up quickly
Describe oxidative decarboxylation?
-first step in aerobic respiration
-referred as the link reaction as it links anaerobic glycolysis (in the cytoplasm) to the aerobic steps of respiration (occurring in the mitochondria)
In eukaryotic cells, how does pyruvate enter the mitochondrial matrix?
by active transport via specific carrier proteins
How does pyruvate undergo oxidative decarboxylation?
-carbon dioxide is removed (decarboxylation) along with hydrogen (oxidation)
-hydrogen atoms are accepted by NAD forming reduced NAD
-therefore pyruvate converts to acetate (2C)
-acetate combines with coenzyme A to form acetyl coenzyme A (2C)
-Coenzyme A delivers acetyl coA to the next stage of aerobic respiration, known as the kerbs cycle
-The reduced NAD is used in oxidative phosphorylation to synthesise ATP
What will happen with the remaining carbon dioxide formed in decarboxylation?
-carbon dioxide will diffuse away or be removed as metabolic waste
-in autotrophic organisms, it maybe used in photosynthesis
Describe the kerbs cycle (overview)?
-occurs in the mitochondrial matrix
-breakdown of acetyl group
What occurs in the kerbs cycle?
1) two carbon acetyl group combines with four carbon oxaloacetate to form six carbon citrate
2) Citrate molecule undergoes deoxycarboxylation and dehydrogenation producing one reduced NAD and carbon dioxide. A five carbon compound is formed.
3) The five carbon compound under goes further decarboxylation and dehydrogenation reactions, eventually regenerating oxalocetate.
When oxaloacetate is being regenerated from citrate how does substrate level phosphorylation occur?
The hydrogen atoms released are picked up by the coenzymes NAD and flavin adenine dinucleotide (FAD)
What reactions occur in the kerbs cycle are what are the products?
-decarboxylation: carbon dioxide formed
-dehydrogenation
-substrate level phosphorylation: ATP formed
-two more reduced NADs and one reduced FAD is formed
Function of coenzymes in respiration?
-transfer protons, electrons and functional groups between many of these enzyme-catalysed reactions
What are the similarities of the coenzymes FAD and NAD?
both accept protons and electrons
What is the difference between the coenzyme FAD and NAD?
-NAD takes part in all stages of cellular respiration but FAD only accepts hydrogens in the kerbs cycle
-NAD accepts one hydrogen and FAD accepts two hydrogens
-reduced NAD is oxidised at the start of the electron transport chain releasing protons and electrons while reduced FAD is oxidised further along the chain
-reduced NAD results in the synthesis of three ATP molecules but FAD results in the synthesis of two ATP molecules
coenzymes are devoured from?
vitamins
what is chemiosmosis?
net movement of protons down an electrochemical gradient through ATP synthase by diffusion
How are high energy electrons released during oxidative phosphorylation?
-hydrogen atoms are released from coenzymes NAD and FAD to electron transport chain present in the membranes of the cristae
-hydrogen atoms dissociate into hydrogen ion and electrons
-high energy electrons are used in the synthesis of ATP by chemiosmosis
How is ATP synthesised from the diffusion of protons through ATP synthase during oxidative phosphorylation?
-energy is released during redox reactions as the electrons reduce and oxidise electron carriers as they flow through the electron transport chain
-energy is used to create a proton gradient as protons move from the matrix to the intermembrane space by active transport.
-this causes the diffusion of protons through ATP synthase resulting in the synthesis of ATP.
What occurs at the end of the electron transport chain during oxidative phosphorylation?
electrons combine with hydrogen ions and oxygen to form water. Oxygen is the final electron acceptor and the electron chain cannot operate unless oxygen is present.
how is oxidative phosphorylation exothermic?
hydrogens released from NAD and FAD combine directly with oxygen, releasing energy from the formation of bonds during the production of water- heat is released
what is substrate level phosphorylation?
the production of ATP involving the transfer of a phosphate group from a short lived, highly reactive intermediate such as creatine phosphate.
what’s the difference between aerobic and anaerobic respiration
in anaerobic respiration, less ATP is produced
what are the different categories organisms fall into depending on their dependence on oxygen?
-obligate anaerobes
-facultative anaerobes
-obligate aerobes
Describe obligate anaerobes?
-cannot survive in the presence of oxygen (prokaryotes and some fungi)
describe facultative anaerobes?
synthesise ATP by aerobic respiration if oxygen is present but can switch to anaerobic respiration in the absence of oxygen (e.g yeast)
describe obligate aerobes?
-can only synthesise ATP in the presence of oxygen (e.g mammals)
-individual cells (e.g muscle cells) can be described as facultative anaerobes. However this is only for short periods and oxygen is eventually needed to break down anaerobic products.
What is fermentation?
a form of anaerobic respiration- process by which complex organic compounds are broken down into simpler inorganic compounds without oxygen or an electron transport chain.
How much ATP is produced in fermentation?
much less ATP than anaerobic respiration as organic compounds (glucose) are not fully broken down. ATP is synthesised by substrate-level phosphorylation alone.
where does alcoholic fermentation occur?
in yeast and some plant root cells
what are the products of alcohol fermentation?
ethanol (alcohol) and carbon dioxide
where does lactate fermentation occur?
animal cells
what are the products of lactate fermentation?
lactate
what occurs when there is a lack of oxygen in aerobic respiration?
-no oxygen to act as final electron acceptor at the end of the electron transport chain in oxidative phosphorylation
-flow of electrons stop and synthesis of ATP by chemiosmosis stops.
-reduced NAD and FAD cannot be oxidised and regenerated
-decarboxylation and oxidation of pyruvate and the kerbs cycle halts as there are no coenzymes to accept hydrogens removed
-glycolysis halts due to the lack of NAD
Describe lactate fermentation in mammals?
-pyruvate acts as the hydrogen acceptor taking hydrogen from reduced NAD, catalysed by the enzyme lactate dehydrogenase.
-pyruvate is converted to lactate (lactic acid) and NAD is regenerated, keeping glycolysis going so small quantity of ATP is synthesised
-not a reversible process
how is lactic acid converted back to glucose?
converted in the liver and oxygen is needed to complete process (oxygen debt)
why can lactate fermentation not occur indefinitely?
-reduced quantity of ATP cannot maintain vital processes for a long time
-accumulation of lactic acid, decreases pH leading to proteins to denature. Respiratory enzymes and muscle filaments made form proteins will not function at low pH
why can lactate fermentation not occur indefinitely?
-reduced quantity of ATP cannot maintain vital processes for a long time
-accumulation of lactic acid, decreases pH leading to proteins to denature. Respiratory enzymes and muscle filaments made form proteins will not function at low pH
Explain the process of alcoholic fermentation in yeast (and many plants)
-it is not a reversible process
-pyruvate is first converted to ethanal, catalysed by enzyme pyruvate decarboxylase.
-ethanal can then accept a hydrogen atom from reduced NAD, becoming ethanol.
-The regenerated NAD can then continue to act as a coenzyme and glycolysis can continue.
-can occur indefinitely in the absence of oxygen.
Describe ethanol as a waste product in alcoholic fermentation?
ethanol is toxic to yeast cells and they are unable to survive if ethanol accumulates above 15 percent. This occurs during the production of alcohol in brewing.
how do you investigate the respiration rates in yeast? (experiment)
-sealed flask with capillary tube
-as the yeast respires, carbon dioxide is released, increasing the volume of gas in the flask, increasing pressure.
-increased pressure causes coloured liquid to move along the capillary tube
-the distance moved by the liquid together with the diameter of the tube can be used to calculate the increase in volume of carbon dioxide in the flask over a period of time.
why is respiration not 100 percent efficient?
energy is lost as heat
how can the heat produced from respiration be measured?
using a data logger
how do bacteria adapt to live in low oxygen enviroments?
-evolved to use nitrate and sulphate ions and carbon dioxide as a final electron acceptor in anaerobic respiration.
how do mammals adapt to live in low oxygen enviroments?
1) Biochemical adaptations including greater concentrations of haemoglobin and myoglobin and higher tolerance to lactic acid and carbon dioxide
2) Physiological adaptation including modified circulatory system e.g slowing the heart reducing energy demand and modified gas exchange system e.g higher exchange of air in lungs
3) physical adaptations including streamlined body, reducing energy demand
what is a respiratory substance?
organic molecule broken down to release energy for the synthesis of ATP
What are the different respiratory substances?
-glucose (main)
-carbohydrates
-proteins
-tryglcerides
-alcohol
how are tryglycerides respiratory substrates?
-tryglycerides are hydrolysed into 3 fatty acids, which enter the kerbs cycle via acetyl CoA and glycerol
-glycerol formed is converted to pyruvate before undergoing oxidative decarboxylation, producing an acetyl group which is picked up by coenzyme A, forming acetyl CoA
how is the net energy release arranged in respiratory substrates?
lipid (most energy release), alcohols, proteins, carbohydrates (least energy release)
three fatty acids can form how many acetyl CoA and ATP?
by beta oxidation, 50 acetyl- CoA can be made which can form 500 ATP molecules
How are proteins respiratory substrates?
-proteins are hydrolysed to amino acids
-amino acids are deaminated to form pyruvate. This process requires ATP, reducing the net ATP production
how is the respiratory quotient (RQ0 of a substance calculated?
by dividing the volume of carbon dioxide released by the volume of oxygen taken in during respiration of that particular substrate.
what apparatus is used to measure respiratory quotient?
respirometer
what is the respiratory quotient of glucose?
-it takes six molecules of oxygen to respire one molecule of glucose which forms six molecules of carbon dioxide.
-RQ is 1.0
what is the respiratory quotient of carbohydrates, proteins and lipids?
carbohydrates: 1.0
protein: 0.9
lipids: 0.7
what is the respiratory quotient during aerobic and anaerobic respiration?
aerobic respiration: 0.8-0.9
anaerobic respiration: 1.0
