Respiration Flashcards
Where does respiration occur?
Respiration occurs in living cells to release the energy stored in organic molecules such as glucose.
What is the energy produced by respiration used for?
The energy is used to synthesise molecules of ATP, from ADP and inorganic phosphate (Pᵢ), which can be hydrolysed in cells to release the energy needed to drive biological processes.
What respires to gain energy?
Protoctists, fungi, plants and animals all respire to obtain energy.
Draw a cycle to represent the energy transfer between and within living organisms.
The potential chemical energy stored in complex organic molecules such as proteins, carbohydrates and fats is released via respiration in order to make ATP to drive which biological processes?
Energy is the capacity to do work;
- Transport of molecules
- Synthesis of molecules
- Cell division
- Activation of chemicals.
What are all the chemical reactions that take place within living cells are known collectively as?
All the chemical reactions that take place within living cells are known collectively as metabolism or metabolic reactions:
What are two types of metabolic reaction?
Anabolic reactions are metabolic reactions where large molecules are synthesised from smaller molecules
Catabolic reactions are metabolic reactions where large molecules are hydrolysed into smaller molecules
Draw a molecule of ATP.
What is ATP?
ATP is a phosphorylated nucleotide consisting of:
- Adenosine
- Three phosphate groups.
Why is ATP the standard intermediary between energy-releasing and energy-consuming metabolic reactions?
ATP is the standard intermediary between energy-releasing and energy-consuming metabolic reactions in both eukaryotic and prokaryotic cells as it is relatively stable is solution in cells, but is readily hydrolysed by enzyme catalysis.
The energy-releasing hydrolysis of ATP is coupled with an energy-consuming metabolic reaction, what is released at this stage?
ATP is the immediate energy source for this metabolic reaction.
When ATP is hydrolysed to ADP and Pᵢ, a small quantity of energy is released for use in the cells so they can obtain the energy they need in small manageable amounts that will not cause damage or be wasteful.
What other forms of energy is released from the hydolysis of ATP?
Some of the energy released from the hydrolysis of ATP is as thermal energy: this may seem inefficient but the heat actually helps the organism keep warm so their enzyme-catalysed reactions can proceed around their optimum rate.
How much ATP do you have in your body at any one time?
In your body you have, at any one time, around 5 g of ATP: however, you may use 36 – 50 kg each day. This is possible because the ATP molecules are continually being hydrolysed then resynthesised.
At rest, a person consumes and continually regenerates ATP at the rate of 1.5 kg per hour.
What are the four stages of respiration?
Respiration of glucose has four stages:
- Glycolysis
- The link reaction
- The Krebs cycle
- Oxidative phosphorylation.
What stages of respiration require areobic conditions?
The last three stages only take place under aerobic conditions where the pyruvate molecules from glycolysis are actively transported into the mitochondria for the link reaction.
How does the process of respiration change for anerobic conditions?
In anaerobic conditions, pyruvate is converted to lactate or ethanol, in the cytoplasm, where reduced NAD molecules are reoxidised so that glycolysis can continue generating two molecules of ATP for every glucose molecule metabolised.
What is glycolysis?
- Glycolysis is a biochemical pathway that occurs in the cytoplasm of all living organisms that respire, including many prokaryotes.
- The pathway involves a sequence of 10 reactions, each catalysed by a different enzyme, some with the help of coenzyme, NAD.
What are the three main stages of glycolysis?
The three main stages are:
- Phosphorylation of glucose to hexose bisphosphate
- Cleavage of each hexose bisphosphate into two triose phosphate molecules
- Oxidation of triose phosphate to pyruvate.
What is the respiritory pathway in anerobic and areobic conditions?
What is the purpose of NAD?
Enzymes that catalyse redox reactions need the help of coenzymes as they accept the hydrogen atoms removed during oxidation.
NAD (nicotinamide adenine dinucleotide) is a non-protein molecule that helps dehydrogenase enzymes to carry out oxidation reactions as it oxidises substrate molecules by accepting two hydrogen atoms in the nicotinamide ring during glycolysis, the link reaction and the Krebs cycle.
How is NAD synthesised?
NAD is synthesised in living cells from nicotinamide (vitamin B₃), ribose, adenine and two phosphate groups.
How does NADH complete its cycle and be reused?
- Reduce NAD (NADH) carries the protons and electrons to the cristae of the mitochrondria to be used in oxidative phosphorylation for the generation of ATP from ADP and Pᵢ.
- When NADH donates the protons and electrons that accepted during glycolysis, link or Krebs, its oxidised to be reused to oxidise more substrate.
Draw the molecular structure of NAD.
What are the three main stages of glycolysis?
- Phosphorylation
- Cleavage
- Oxidation
Describe the process of phosphorylation in glycolysis.
Glucose molecules are stable so they need to be activated before they can be split into two three-carbon compounds.
- One molecule of ATP is hydrolysed where the released Pᵢ group is added to glucose making hexose monophosphate.
- Another molecule of ATP is hydrolysed where the released Pᵢ group is added to the hexose monophosphate making hexose bisphosphate.
- The energy from the hydrolysed ATP molecules activates the hexose sugar and prevents it from being transported out of the cell.
Describe the process of cleavage in glycolysis.
The hexose bisphosphate is split into two three-carbon molecules called triose phosphate which each have a phosphate group attached.
Describe the process of oxidation in glycolysis.
- Dehydrogenase enzymes, aided by NAD, remove two hydrogen atoms from each triose phosphate to become pyruvate.
- The two NAD molecules accept the two hydrogen atom each to become reduced.
- Four molecules of ATP are made for every molecule of glucose (two molecules of triose phosphate).
What are the products of glycolysis?
Net gain
- ATP = 2
- NADH = 2
- Pyruvate = 2
What deficiency disease is related to NAD?
Pellagra is a dietary deficiency disease that has symptoms of diarrhoea, dermatitis and dementia, caused by the lack of nicotinamide.
Humans can synthesis nicotinamide from the amino acid tryptophan.
Describe the discovery of the mitrochondrion.
Mitochondria are organelles that are present in all types of eukaryotic cells which were first identified in animal cells in 1840 and in plant cells in 1900. However, their ultrastructure was not worked out until the 1950s after extensive studies using electron microscopes.
What shape are mitrochondria?
Mitochondria can be rod-shaped, threadlike or spherical with diameters of 0.5–1.0 µm and lengths of 2–5 µm, but occasionally up to 10 µm.
What features does the mitrochondria which enable it to function?
- A nuclear envelope made of an inner and an outer phospholipid membrane
- An intermembrane space between the membranes
- The outer membrane is smooth and the inner membrane is folded into cristae giving it a large surface area
- Proteins that transport electrons embedded in the inner membrane are proteins that transport electrons and protein channels associated with ATP synthase enzyme that allows protons to diffuse through them
- A matrix, enclosed by the inner membrane, which is semi-rigid and gel-like; it contains mitochondrial ribosomes, lopped mitochondrial DNA, enzymes for the link reaction and Krebs cycle.
How does the mitrochondrial marix allow it to carry out its function?
The matrix is where the link reaction and the Krebs cycle take place so it contains:
- Enzymes that catalyse the stages of these reactions
- Molecules of the coenzymes NAD and FAD
- The four-carbon compound, oxaloacetate, that accepts the acetyl group from the link reaction
Mitochondrial DNA which closes for mitochondrial enzymes and other proteins
How does the outer membrane enable the mitrocondria to correctly carry out its function?
- Phospholipid bilayer
- Contains protein channels and carries that allow the passage of molecules such as pyruvate into the mitochondria
How does the inner membrane enable the mitrocondria to correctly carry out its function?
- Phospholipid bilayer
- Less permeable to small ions such as hydrogen ions than the outer membrane
- The cristae gives it a large surface area for the electron carriers and ATP synthase enzymes embedded in them
The electron carriers are arranged in electron transport chains
How does the intermembrane space enable the mitrocondria to correctly carry out its function?
The inner membrane is in close contact with the matrix so the molecules of NADH and FADH₂ can easily deliver hydrogens to the electron transport chain
In the electron transport chain what are electron carrier proteins?
Electron carrier proteins are oxido-reductase enzymes which contain a cofactor, a non-protein haem group, which contains an iron ion, Fe³ᐩ.
How does the passing of charge along an electron transport chain electron create a proton gradient?
- The enzymes also have a coenzyme that, using energy released from the electrons, pumps protons from the matrix to the intermembrane space.
- The protons accumulate in the intermembrane space causing a proton gradient to form across the inner membrane.
Describe ATP synthase enzymes.
ATP synthase enzymes are large proteins, which protons can pass through, that protrude from the inner membrane into the matrix.
State the stages of the link reaction.
- Pyruvate is carboxylate and dehydrogenated to produce an acetyl group
- The acetyl group combines with coenzyme A (CoA) to become acetyl CoA to carry the acetyl group onto the Krebs cycle
- The coenzyme NAD becomes reduced.
(2pyruvate + 2NAD + 2CoA → 2C)
What is the first stage of the krebs cycle?
- The acetyl group released from acetyl CoA combines with a four-carbon compound, oxaloacetate, to form a six-carbon compound, citrate.
What is the second stage of the krebs cycle?
Citrate is decarboxylated and dehydrogenated, producing a five-carbon compound, one molecule of carbon dioxide and one molecule of NADH.
What is the third stage of the krebs cycle, producing a four carbon compound?
The five-carbon compound is further decarboxylated and dehydrogenated, producing a four-carbon compound, one molecule of carbon dioxide and one molecule of NADH.
Describe the 4th and 5th steps of the krebs cycle, where substrate-level phosphorylation is used.
- The four-carbon compound combines temporarily with CoA to produce one molecule of ATP in substrate-level phosphorylation.
- The four-carbon compound is dehydrogenated, producing a different four-carbon compound and one molecule of FADH₂.
In the krebs cycle how does the four carbon compound regenerate?
The atoms of the four-carbon compound are rearranged, catalysed by an isomerase enzyme, following by further dehydrogenation producing one molecule of NADH and regeneration of oxaloacetate so the cycle can continue.
How does oxidative phosporylation begin?
- NADH and FADH₂ are reoxidised by delivering their hydrogen atoms to the electron transport chain.
- The hydrogen atoms released from the reduced coenzymes split into protons and electrons.
- The protons go into solution in the mitochondrial matrix.
How is ethanol produced from ethanal in the ethanol respiration pathway?
- The ethanal accepts hydrogen atoms from NADH, becoming reduced to ethanol, catalysed by the enzyme ethanol dehydrogenase.
- In the process, NADH is reoxidised becoming available to accept more hydrogen atoms from glycolysis, thus allowing glycolysis to continue.
State the stages of lactate fermentation.
- Pyruvate, produced during glycolysis, accepts hydrogen atoms from the NADH, also made during glycolysis, catalysed by the enzyme lactate dehydrogenase.
- Pyruvate is reduced to lactate and NAD is reoxidised.
- The reoxidised NAD can now accept more hydrogen atoms from triose phosphate during glycolysis, and glycolysis can continue to produce ATP to sustain muscle contraction for a short period of time.
