respiration Flashcards
what occurs during cellular respiration
the formation of ATP from the break down of glucose takes place during the process of cellular respiration
what are the 2 different cellular respiration
aerobic respiration
anaerobic respiration
what is aerobic respiration
require oxygen and produces carbon dioxide, water and much ATP
what is anaerobic respiration
this takes place in the absence of oxygen and produces lactate (in animals) or ethanol and carbon dioxide (in plants and fungi ) but only a little ATP in both cases
what are the four stages of aerobic respiration
- glycolysis
- link reaction
- krebs cycle
- oxidative phosphorylation
what occurs in glycolysis
the splitting of the 6 carbon glucose molecule into two 3- carbon pyruvate
what occurs in the link reaction
3 carbon pryvate molecules enter into a series of reactions which lead to the formation of acetylcoenzyme A a 2- carbon molecule
what occurs in the krebs cycle
the intro of acetylcoenzyme A into a cycle of oxidation reduction reaction that yield some ATP and a large quantity of reduced NAD and FAD
what occurs in oxidative phosphorylation
the use of the electrons, associated with reduced NAD and FAD, released from the krebs cycle to sythesise ATP with produced as a by- product
what is glycolysis
glycolysis is the initial stage of both aerobic and anaerobic respiration
where does glycolysis occurs
glycolysis occurs in the cytoplasm of all living cells and is the process which a hexose sugar - usually glucose- is split into two molecules of 3 - carbon molecule pyravate
what is the end product of glycolysis
pyravate
what are the four stages of glycolysis
- phosphorylation of glucose to glucose phosphate
- splitting of the phosphorylated glucose
- oxidation of triose phosphate
- the production of ATP
what occurs in the first stage of glycolysis
before it can be split into two, glucose must first be made reactive by the addition of two phosphate molecules (phosphorylation)
The phosphate molecules come from the hydrolysis of two ATP molecules to ADP. This provides energy to activate glucose and lowers the activation energy for the enzyme controlled reaction that follows
what occurs in the second stage of glycolysis
each glucose molecule is split into two 3- carbon molecules known as triose phosphate
what occurs in the third stage of glycolysis
hydrogen is removed from each of the triose phosphate molecules and transferred to a hydrogen - carrier molecule known as NAD to form reduced NAD
what occurs in the fourth stage of glycolysis
enzyme - controlled reaction convert each triose phosphate into another 3 - carbon molecule called pyravate
In the process, two molecules of ATP are regenerated from ADP
what is the energy yield from glycolysis
2 molecules of ATP
(four molecules of ATP are produced by two were used up in the initial phosphorylation of glucose and so the net increase is tow molecules)
2 molecueles of reduced NAD
2 molecules of pyravate
what does the reduced NAD produced in glycolysis have the potential to do
they have the potential to provide energy to produce more ATP
why does glycolysis provide indirect evidence for evolution
glycolysis provides indirect evidence for evolution
Enzymes for the glycolysis pathway are found in the cytoplasm of cells and so glycolysis does not require any organelle or membrane for it to take place
why can glycolysis occur without oxygen
no oxygen is needed so it can take place whether or not it is present
what happens to the pyravate in the absence of oxygen
in the absence of O2, the pyruvate produced by glycolysis can be converted into either lactate/ethanol during anaerobic respiration
This is necessary in order to re-oxidise NAD so that glycolysis can be continue
what happens to the pyravate in the krebs cycle
the pyravate molecules produced during glycolysis process has potential energy that can only be released in a process called the krebs cycle
before they can enter the krebs cycle they must be oxidised in a process known as the link reaction
what must happen to the pyruvate before it enters the krebs cycle
before they can enter the krebs cycle, these pyruvate molecules must first be oxidised in a procedure known as the link reaction
where does the krebs and links cycle occur
they both occur in the mitochondria
what are the stages of the link reaction
- pyruvate molecule produced in the cytoplasm during glycolysis are actively transported into the matrix of mitochondria
- pyruvate undergoes a series of reactions:
- the pyravate is oxidised to acetate
- In this reaction, the 3- carbon pyruvate loses a CO2 molecule and two hydrogens. These hydrogens are accepted by NADP to form reduced NAD which is later used to produce ATP
The 2 carbon acetate combines with a molecule called coenzyme A (CoA) to produce a compound called acetylcoenzyme A
what is the overall equation of the link reaction
the overall equation can be summarised as:
-pyruvate + NAD + CoA - acetylCoA + reduced NAD + CO2
what are the steps of the krebs cycle
involves a series of oxidation - reduction reactions that take place in the matrix of mitochondria
It follows:
- 2 carbon acetylcoenzyme A from the link reaction combines with a 4 carbon molecule to produce a 6 - carbon molecule
In a series of reaction this 6- carbon molecule loses carbon dioxide and hydrogen to give a 4 - carbon molecule and a single molecule of ATP as a result of substrate - level phosphorylation
The 4 - carbon molecule can now combine with a new molecule of acetylcoenzyme A to begin the cycle again
what is the yield for in the krebs and link cycle
for each molecule pyruvate, the link reaction and the krebs cycle produce:
-reduced coenzyme e.g. NAD and FAD which have the potential to provide energy to produce ATP molecules by oxidative phosphorylation and therefore the important products of krebs cycle
- 1 molecule of ATP
- three molecules of CO2
(as two molecules are produced for each original glucose molecules, the yield from a single glucose molecule is double the quantities above)
what are coenzymes
coenzymes are not enzymes
These are molecules that some enzymes require in order to function
what do coenzymes do
coenzymes carry hydrogen atoms from one molecuke to another
what are the different coenzymes
NAD - important throughout respiration
FAD - important in the Krebs cycle
NADP - important in photosynthesis
what is the most important coenzyme
NAD is the most important in respiration
It works with dehydrogenase enzymes that catalyse the removal of hydrogen atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation
why is the krebs cycle important
the krebs cycle performs an important role in the cells of organisms for four reasons:
- it breaks down macromolecules into smaller ones - pyruvate is broken into CO2
- it produces hydrogen atoms that are carried by NAD to the electron transfer chain abd provide energy for oxidative phosphorylation. This leads to the production of ATP that provides for the cell
- it regenerates the 4 - carbon molecule that combines the acetylcoenzyme A, which otherwise accumulate
- It is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll
what are mitochondria
mitochondria are organelle that are found in eukaryotic cells bounded by a smooth outer membrane and an inner one folded into extensions called cristae
these are the sites of oxidative phosphorylation
what does the inner space ( the matrix) contain
it contains proteins,lipids and traces of DNA
what are in the cristae
enzymes and other proteins involved in oxidative phosphorylation and therefore ATP synthesis
what is the electron transfer chain
the sythesis of ATP by oxidative phosphorylation involves the transfer of electrons down a series of electron carrier molecules which together form the electron transfer chain
what are the stages of oxidative phosphorylation
- hydrogen atoms produced during glycolysis and the Krebs cycle combine with the coenzyme NAD and FAD
- The reduced NAD and FAD donate the electrons of the hydrogen atoms they are carrying to the first molecule in the electron transfer chain
- the electrons pass along a chain of electron transfer carrier molecules in a series of oxidation-reduction reactions. As the electrons flow along the chain, the energy they release causes the active transport of protons across the inner mitochondrial membrane and into inter-membrane space. The concentration of protons is higher in the intermembrane space than the inner mitochondrial membrane and so an electrochemical gradient is formed
- the protons accumulate in the inter-membranal space before they diffuse back into the mitochondrial matrix through ATP synthase channels embedded in the inner membrane. This movement provides the energy for the synthesis of ATP from ADP and inorganic phosphate Pi. ( this is called the chemiosmosis and hence the chemiosmotic theory)
- At the end of the chain, the electrons combine with these protons and oxygen to form water
oxygen is, therefore, the final acceptor of electrons in the electron transfer chain
why is oxygen important in respiration
it acts as the final acceptor of the hydrogen atoms produced in glycolosis and the krebs cycle
what would happen if oxygen did not act as the final acceptor
without its role in removing hydrogen atoms at the end of the chain the hydrogen ions (protons) and the electrons would “back up” along the chain and the process of respiration would come to a halt
what happens when there is a large amount of energy being released in a single step
the greater the energy that is released in a single step, the more of it is released as heat and the less there is available for more useful purposes
why is it better for a little energy to be released at a time for an organism
when energy is released a little at a time, more of it can be harvested for the benefit of the organism
For this reason, the electrons carried by NAD and FAD are not transferred in one explosive step, instead they are passed along a series of electron transfer carrier molecule, each of which us at a slightly lower energy level - the electrons therefore move down an energy gradient
what are the alternate respiratory substrate
both lipids and proteins may in certain circumstances be used as respiratory substances, without first being converted to a carbohydrate
respiration of lipids
before being respired, lipids are first hydrolysed to glycerol and fatty acids
glycerol is then phosphorylated and converted to triose phosphate which enters the glycolisis pathway and enter the krebs cycle
The fatty acid component is broken down into 2- carbon fragments which are converted to acetyl coenzyme A
This then enters the krebs cycle
what does the oxidation of lipids produce
the oxidation of lipids produces 2 carbon fragments of carbohydrate and many hydrogen atoms
The hydrogen atoms are used to produce ATP during oxidative phosphorylation
For this reason, lipids release more than double the energy of the same mass of carbohydrate
respiration of protein
protein is another potential source of energy
It is first hydrolysed to its constituent amino acids
These have their amino group removed (deamination) before entering the respiratory pathway at different parts depending on the number of carbon atoms they contain
what are the products of the respiration of protein
3 carbon compounds are converted to pyruvate while 4 and 5 compounds are converted to the immediates in the krebs cycle
what happens when oxygen is not present
in the absence of oxygen, neither the krebs cycle nor the electron transfer chain can continue because soon all FAD and NAD will be reduced
Therefore, no FAD/NAD will be available to take up the H+ produced dueing the krebs cycle and so the enzymes stop working
why must anaerobic respiration occur
for glycolysis to continue its products of pyruvate and hydrogen must be removed
In particular, the hydrogen must be released from the reduced NAD in order to regenerate NAD
Without this, the already tiny supply of NAD in cells will be entirely converted to reduced NAD leaving no NAD to take up the hydrogen newly produced in glycolysis
glycolysis will then grind to a halt
how is NAD replenished
the replishment of NAD is achieved by the pyravate molecule from glycolysis accepting the hydrogen from reduced NAD
The oxidised NAD produced can then be used in further glycolysis
what are the 2 types of anaerobic respiration in eukaryotic cells
in plants and in microorganisms e.g. yeast, the pyravte is converted to ethanol and CO2
in animals, the pyruvate is converted to lactate
explain the production of ethanol in plants and some microorganisms
- occurs in certain bacteria e.g. yeast and some cells of higher plants e,g, roots cells under waterlogged conditions
the pyravate molecule formed at the end of glycolysis loses a molecule of CO2 and accepts hydrogen from NAD to produce ethanol:
pyruvate + reduced NAD - ethanol + carbon dioxide + oxidised NAD
what is the benefits of this form of anaerobic respiration in plants
this form of anaerobic respiration in yeast has been exploited by humans for thousands of years in the brewing industry
In brewing ethanol is the important product. Yeast is grown in anaerobic conditions which it ferments natural carbohydrates in plant products, such as grapes (wine production) or barley seeds (beer productions) into ethanol
explain the production of lactate in animals
overcomes a temporary shortage of oxygen
lactate production occurs most commonly in muscles as a result of extraneous exercise. In these conditions O2 may be used up more rapidly than it can be supplied and therefore an oxygen debt occurs
it is important that muscles continue to work despite the shortage of oxygen
what happens when there is a shortage of oxygen in animals
the NAD from glycolysis can accumulate and must be removed
describe anaerobic respiration in animals
pyravate molecule produced takes up the two hydrogen atoms from the reduced NAD produced in glycolysis to form lactate
at some point, the lactate produced is oxidised back to pyravate
This can then be either further oxidised to release energy or converted into glycogen
This happens when when oxygen is once again available
what will lactate cause
- cramp
- muscle fatigue
if the lactate accumulates in the muscle tissue
lactate is an acid and so it causes a ph change which affects enzymes
muscles have a tolerate to lactate but it is nevertheless important that it is removed by the blood and taken to the liver to be converted to glycogen
required practical 9: aerobic respiration
- put a known volume and concentration of substrate solution (e.g. glucose) in a test tube.
Add a known volume of buffer solution to keep the pH constant (Choose the optimum pH for the yeast you’re testing - usually 4.6) - Place the test tube in a water bath st to one of the temperatures being investigated. Leave it there for 10 minutes to allow the temperature of the substrate to stabilise
- Add a known mass of dried yeast to the test tube and stir for 2 minutes
- after the yeast has dissolved into the solution, put as bung with a tube attached to a gas syringe in the top of the test tube. The gas syringe should be set to zero
- start a stopwatch as soon as the bung has been put in the test tube
- as the yeast respire, the CO2 formed will travel up the tube and into the gas string, which is used to measure the volume of CO2 released
- At regular time intervals (e.g. every minute), record the volume of CO2 that is present in the gas syringe. Do this for a set amount of time (e.g. 10 minutes)
- a negative control experiment should also be set also set up at each temperature, where no yeast is present. No CO2 should be formed without the year
- Repeat the experiment three times at each temp you are investigating. Use our data to calculate the mean rate of CO2 production at each temperature
required practical 9: anaerobic respiration
- set up the apparatus according to steps 1 and 3 of the previous card
- After the yeast has dissolved into the substance solution, trickle some liquid paraffin down the inside of the test tube so that it settles on and completely covers the surface of the solution.
This stips oxygen getting in, which will force the yeast to respire aerobically - Put a bung, with a tube attached to the gas syringe, in the top of the test tube. The gas syringe should be set to zero
- repeat steps 5-9 from the method in the previous card
how do we use a respirometer to measure oxygen consumption
- the apparatus should be partially submerged in a water bath at 15C to provide optimum temperature for the woodlice and therefore, the optimum temperature for the enzymes involved in their respiration
- the control tube is set up exactly the same way as the woodlice tube, except that the woodlice are substituted with glass beads of the same mass
- for ten minutes, the tao is left open and the string is removed to allow the apparatus to equilibrate (accounting for any expansion that might cause the pressure to change inside) and the respiration rate of the woodlice to stabilise in their new environment
- when the ten minutes is up, the tap is closed and the syringe is attached
- the syringe is used to reset the manometer so that the ends of the fluid are at the same level on either side of the U and the reading from the volume scale on the syringe (usually in cm3) is recorded
- as respiration occurs, the volume of air in the test tube containing woodlice will decrease, due to the oxygen consumed during respiration, (all the CO2 is being produced is absorbed by the potassium hydroxide)
- The decrease in the volume of the air will reduce the pressure in the test tube, causing the coloured fluid in the capillary tube of the manometer to move towards it
- after leaving the apparatus to run for a set period of time, the syringe is used to reset the manometer and the reading on the syringe volume is recorded again. The difference between this figure and the figure taken at the start of the experiment is the oxygen consumption for this time period. You can use this to calculate the rate of respiration
- to check the precision of the results, the experiments is repeated and a mean volume of O2 is calculated
