5.7- Respiration Flashcards
Describe the need for organisms to respire
- Respiration- process that occurs in living cells- releases he energy stored in organic molecules e.g. glucose
- The energy is immediately used to synthesise molecules of ATP from ADP and inorganic phosphate (Pi)
- ATP in cells can be hydrolysed to release energy needed to drive biological processes
- Microorganisms (eukaryotic and prokaryotic), plants, animals, fungi and Protoctists all respire to obtain energy
Describe why living organisms need energy
- Energy is the capacity to do work
- Potential energy- The energy that is stored in complex organic molecules- e.g. fats, carbohydrates and proteins
- This is also chemical energy converted from light energy during photosynthesis
- When this energy is released from organic molecules via respiration, it can be used to make ATP to drive biological processes
List biological processes that are driven by ATP
- Active transport
- Endocytosis
- Exocytosis
- DNA replication
- Cell division
- Movement- e.g. of bacterial flagella, eukaryotic cilia, undulipodia, motor proteins
- Activation of chemicals- glucose is phosphorylated at the beginning of respiration so that it becomes more reactive and able to be broken down to release more energy
Describe 2 different types of metabolic reactions
- Anabolic- large molecules synthesised from smaller molecules
- Catabolic- hydrolysis of large molecules to smaller ones
What type of energy do atoms and ions have (in living cells)
Kinetic energy
Describe kinetic energy in ions/atoms
Kinetic energy allows them to move e.g. when molecules diffuse down a concentration gradient, moving from one place to another- use their kinetic energy
Energy transfer between and within living organisms diagram
Describe the role of ATP
- Standard intermediary between energy-releasing and energy-consuming metabolic reactions in both eukaryotic and prokaryotic cells
- energy currency- can be hydrolysed to ADP- releases phosphate- releases 30KJ of energy- used in metabolic reactions
Describe the structure of ATP
- Phosphorylated nucleotide
- Each molecule consists of:
- adenosine (nitrogenous base adenine + the 5-carbon sugar ribose)
- 3 phosphate (phosphoryl) groups
- Phosphodiester bond between sugar and phosphate
- Glycosidic bond between sugar and nitrogenous base
- Phosphoanhydride bond between phosphates
Full names of ATP, ADP and AMP
ATP- adenosine triphosphate
ADP- adenosine diphosphate
AMP- adenosine monophosphate
Describe the stability and movement of ATP
- ATP is relatively stable (doesn’t break don into ADP and Pi) when in solution in cells
- However, it is readily hydrolysed by enzyme catalysis
- Whilst in solution, it can easily be moved from place to place within a cell
- Each cell requires the structures associated with respiration as it cannot cross the plasma membrane
Describe the reactions associated with ATP
- Hydrolysis of ATP into ADP and Pi releases energy (requires water, catalysed by enzymes called ATPases)
- This reaction is coupled with an energy-consuming metabolic reaction- Condensation- ADP and P- releases water
- ATP is the immediate energy source for a metabolic reaction
Is ATP advantageous over direct energy transfer from glucose, why
- yes
- When ATP is hydrolysed to ADP and P, a small quantity of energy is released for use in the cells - Cells can therefore obtain the energy they need for a process in small manageable amounts that will not cause damage or be wasteful
- ATP is referred to as the universal energy currency- occurs in all living cells and is a source of energy that can be used by cells in small amounts
What is released in respiration and ATP hydrolysis, describe this
- Heat
- Not wasteful- helps keep living organisms ‘warm’ and enables their enzyme-catalysed reactions to proceed at or near their optimum rate
Describe the amount of energy released through each hydrolysis reaction of ATP
- ATP –> ADP = 30.5 kJmol-1
- ADP –> AMP = 30.5 kJmol-1
- AMP –> Adenosine = 13.8 kJmol-1
- Total = 74.8
List the 4 main processes involved in aerobic respiraton
- Glycolysis
- Link reaction
- Krebs Cycle
- Oxidative Phosphorylation
Last three only take place under aerobic conditions- the pyruvate molecules from glycolysis are actively transported into the mitochondria for the link reaction
List the main processes involved with anaerobic respiration
- glycolysis
- Pyruvate is converted, in the cytoplasm, to lactate or ethanol
- In the process, the reduced NAMD molecules are reoxidised so that glycolysis can continue to run, generating 2 molecules of ATP for every glucose molecule metabolised
Stages of respiration diagram
Describe the use of enzymes in respiration
- Each stage is catalysed by a specific enzyme
- Reactions in respiration are examples of oxidation and reduction reactions
o Oxidation: loss of electrons (loss of hydrogen).
o Reduction: gain of electrons (gain of hydrogen).
Describe the use of Coenzymes in respiration
Coenzymes are needed to assist other enzymes in a reduction or oxidation reaction (because they can pick up and lose hydrogen atoms)
Co-enzymes used in respiration:
- NAD- Nicotinamide Adenine Dinucleotide
- CoA- Coenzyme A
- FAD - Flavine Adenine Dinucleotide
Co-enzymes that have been reduced are used in the final stage of respiration (oxidative phosphorylation) which produces ATP
Outline glycolysis
- biochemical pathway that occurs in the cytoplasm of all living organisms that respire (incl. many prokaryotes)
- involves sequnece of 10 reactions each catalysed by different enzyme
- some involve help of coenzyme NAD
- doesn’t require oxygen
- energy investment and energy pay off stage
- occurs in cytoplasm
Describe NAD
- Nicotinamide adenine dinucleotide
- non-protein molecule
- helps dehydrogenase enzymes carry out oxidation reactions
- oxidised substrate molecules during glycolysis, the link reaction and the Krebs cycle
Describe the synthesis/structure of NAD
Synthesised in living cells from:
- nicotinamide (vitamin B3)
- Ribose (5-carbon sugar)
- 2 x phosphoryl groups
Describe the working of NAD
- the nicotinamide ring can accept 2 hydrogen atoms, becoming reduced NAD
- Reduced NAD carries the protons and electrons to the cristae of mitochondria and delivers them to be sed in oxidative phosphorylation for the generation of ATP from ADP and Pi
- When reduced NAD gives up the portions and electrons that it accepted during one of the first 3 stages of respiration, it becomes oxidised and can be reused to oxidise more substrate- in the process becoming reduced again
Outline the 3 main stages of glycolysis
1- Phosphorylation of glucose to hexose bisphosphate
2- Splitting each hexose bisphosphate molecule into 2 triose phosphate molecules
3- Oxidation of triose phosphate to pyruvate
Describe the first stage of glycolysis
Phosphorylation of glucose to hexose bisphosphate:
- glucose = hexose sugar (contains 6 carbon atoms)
- molecules are stable- need to be activated before they can split into two 3-carbon compounds
1) One molecule of ATP is hydrolysed (to ADP and Pi), the released phosphoryl group is added to glucose to make hexose monophosphate (fructose 1 phosphate)
2) Another molecule of ATP is hydrolysed (to ADP and Pi), the phosphoryl group is added to the hexose phosphate to form molecule of hexose bisphosphate
Products- one molecule of hexose bisphosphate that has 2 phosphate groups (one at C1 and other at C6)
The energy from the hydrolysed ATP molecules activates the hexose sugar, prevents it from being transported outside of the cell
Describe the second stage of Glycolysis
Splitting each hexose bisphosphate:
- Each molecule of hexose bisphosphate is split into two 3-carbon molecules- triose phosphate
- each still has phosphate group attached
Describe part 1 of the 3rd stage of glycolysis
Before oxidation- Second phosphate (from cytoplasm) gets added to each triose phosphate to form triose bisphosphate
Oxidation of triose phosphate:
- Dehydrogenase enzymes, aided by coenzyme NAD, remove hydrogen from each triose phosphate (oxidation of substrate as it is losing hydrogen atoms)
- 2 molecules of NAD accept the hydrogen atoms (protons and electrons)- become reduced
- 2 molecules of NAD are reduced for every molecule of glucose undergoing this process
Describe part 2 of the 3rd stage of glycolysis
Removal of phosphate group:
- subtsrate level phosphorylation
- 4 molecules of ATP are made for every 2 triose bisphosphate molecules undergoing oxidation
- Each phosphoryl group from the two triose phosphates is used to make 2 molecules of ATP- 4 total
- phosphorylation of ADP is condensation reaction- endogonic- energy transferred from substrate to ATP molecule
- products- 2 x pyruvate molecules
Describe the products of glycolysis
- 2 Molecules of ATP (4 were made in second part of stage three, but 2 were used for phosphorylation in stage 1- [4-2=2 net total])
- 2 molecules of reduced NAD
- 2 molecules of pyruvate (a 3-carbon sugar)
Why do we only have a low amount of ATP in our body at any one time
- only have around 5g at any time
- however, may used between 36 and 50kg each day
- possibly because the ATP molecules are continually being hydrolysed and then resynthesised
- at rest, a person consumes and continually generates ATP at the rate of 1.5kg per hour (increases when active)
Describe what happens to the pyruvates after being produced in glycolysis
- transported across the outer and inner mitochondrial membranes via a specific pyruvate H= symport- transport protein that transports two ions/molecules in same direction into the matrix
- Pyruvate then converted into 2C acetyl group (link reaction), acetyl group oxidised In Krebs cycle
Describe the link reaction
1) Carboxyl group is removed- decarboxylated (this is the origin of some of the carbon dioxide produced during respiration)
2) It is also dehydrogenated- hydrogen removed from pyruvate
3) Decarboxylation of pyruvate together with dehydrogenation produces an acetyl group
4) The acetyl group combined with coenzyme A (coA) to become acetyl CoA
5) The coenzyme NAD becomes reduced (accepts hydrogen from dehydrogenation)
Link reaction equation
2 pyruvate + 2NAD + 2CoA –> 2CO2 + 2 reduced NAD + 2 acetyl CoA
What happens after the link reaction
Coenzyme A accepts the acetyl group and, in the form of acetyl CoA, carries the acetyl group onto the Krebs cycle
Briefly outline the Krebs cycle
- Series of enzyme-catalysed reactions that oxidise the acetate from the link reaction to 2 molecules of carbon dioxide
- Conserves energy by reducing coenzymes NAD and FAD (Flaine adenine dinucleotide)
- Reduced coenzymes then carry the hydrogen atoms to the electron transport chain on the cristae
- Aerobic- not directly used in link/Krebs, but will not occur in absence of oxygen
Stages of the Krebs cycle with diagram
1:
- The acetyl group (released from acetyl CoA) combine with a 4C compound oxaloacetate
- Forms 6C compound citrate
2:
- Citrate is decarboxylated and dehydrogenated
- Produces:
* 5C compound
* One molecule of carbon dioxide
* One molecule of reduced NAD
3:
- This 5 C compound is further decarboxylated and dehydrogenated
- Produces:
* 4C compound
* One molecule of carbon dioxide
* One molecule of reduced NAD
4:
- 4C compound combined temporarily with, and is then released from, coenzyme A
- Substrate level phosphorylation takes place
- produces 1 molecule of ATP
5:
- The 4C compound is dehydrogenated
- Produces:
* Different 4C compound
* Molecule of reduced FAD
6:
- Rearrangement of the atoms in the 4C molecule- catalysed by an isomerase enzyme
- Followed by further dehydrogenation
- Regenerates a molecule of oxaloacetate so the cycle can continue
NB- For every molecule of glucose there are 2 turns of the Krebs cycle
Glycolysis- location, number of reduced NAD, Reduced FAD, Carbon dioxide and ATP (per glucose)
Location- Cytoplasm
NAD- 2
FAD- 0
CO2- 0
ATP- 2
The link recation- location, number of reduced NAD, Reduced FAD, Carbon dioxide and ATP (per glucose)
Location- Mitochondrial matrix
NAD- 2
FAD- 0
CO2- 2
ATP- 0
The Krebs cycle- location, number of reduced NAD, Reduced FAD, Carbon dioxide and ATP (per glucose)
Location- Mitochondrial matrix
NAD- 6
FAD- 2
CO2- 4
ATP- 2