aerobic respiration Flashcards
describe respiration
- a catabolic process involving a series of enzyme-catalysed reactions in cells
- energy-rich substrates are hydrolysed to release energy
- some energy is trapped as chemical energy in ATP and some is released as heat energy
how is ATP produced from respiration?
during respiration, high energy C-C, C-H and C-OH bonds are broken by enzymes in a series of small steps
define aerobic respiration
the release of large quantities of ATP energy from glucose or another organic substrate in the presence of oxygen
- carbon dioxide is produced
define anaerobic respiration
takes place in the absence of oxygen and produces lactate in animal cells and carbon dioxide and ethanol in yeast cells
- produces a small yield of ATP energy
name 3 substrates that can be used to release energy in respiration
- glucose
- amino acids
- fatty acids + glycerol
most of the energy released during respiration is used to synthesise ATP. how is the rest of the energy released?
heat
give similarities and differences between aerobic and anaerobic respiration
SIMILARITIES:
- both produce ATP
- both produce carbon dioxide
DIFFERENCES:
- anaerobic doesn’t require oxygen, aerobic does
- yield of energy lower for anaerobic
what does ATP stand for?
adenosine triphosphate
name 6 roles of ATP
- protein synthesis
- active transport
- secretion/exocytosis
- nerve transmission
- muscle contraction
- DNA replication
describe the formation of ATP
- the enzyme ATP synthase combines ADP (adenine diphosphate) and Pi (inorganic phosphate) in a condensation reaction.
- this requires an input of energy (30.6kJ mole-1) in an ENDERGONIC reaction
what is phosphorylation?
the addition of inorganic phosphate to ADP
describe the hydrolysis of ATP
- the enzyme ATPase hydrolyses the terminal phosphate bond releasing a small packet of energy (30.6kJ mol-1) in an EXERGONIC reaction.
- this forms ADP and Pi
how are the properties, structure and formation of ATP linked to its role in cells?
- the hydrolysis of ATP to ADP releases immediate energy. the hydrolysis of glucose takes much longer and involves many intermediate reactions
- only one enzyme is needed to release energy from ATP, whereas many are needed in the case of glucose
- ATP releases energy in small packets when and where it is needed
- ATP is the universal energy in many reactions in all living organisms
- ATP is easily transported across membranes
what are the stages of respiration?
where do they occur?
- glycolysis - cytoplasm
- link reaction - mitochondrial matrix
- krebs cycle - mitochondrial matrix
- electron transport chain - inner mitochondrial matrix
what is an example of redox reactions in respiration?
- NAD is reduced to form reduced NAD (NAD/H+)
- FAD is reduced to form reduced FAD (FADH2)
define oxidation and reduction
oxidation - loss of electrons / hydrogen
reduction - gain of electrons / hydrogen
describe redox reactions in respiration
hydrogen atoms are removed from intermediate compounds and split into protons and electrons
how does glucose enter the cytoplasm?
- active transport
- facilitated diffusion
in glycolysis, per glucose molecule how much:
- reduced NAD produced?
- gross ATP produced?
- used ATP?
- net total ATP produced?
reduced NAD produced - 2
gross ATP produced - 4
used ATP - 2
net total ATP produced - 2
what is glycolysis?
initial biochemical pathway in both aerobic and anaerobic respiration
describe the process of glycolysis
- glucose is phosphorylated to form hexose phosphate. this requires the addition of 2 ATP molecules
- hexose phosphate splits into two triose phosphate molecules
- each triose phosphate molecule is oxidised to pyruvate. this means that hydrogen is removed by a dehydrogenase enzyme in a dehydrogenation reaction. the hydrogen is accepted by NAD forming reduced NAD
- the production of pyruvate from triose phosphate also results in the phosphorylation of 2 ADP molecules to produce 2 ATP - this is substrate level phosphorylation
glycolysis results in a small yield of chemical energy in the form of ATP. What other form of energy is also released?
heat / thermal energy
why is pyruvate provided as a respiratory substance for mitochondria and not glucose?
glucose can only be hydrolysed in the cytoplasm during glycolysis.
- pyruvate can enter by facilitated diffusion into the mitochondria for the link reaction
describe the link reaction
in the presence of oxygen, pyruvate diffuses from the cytoplasm into the mitochondrial matrix where the link reaction takes place:
- pyruvate is decarboxylated by a decarboxylase enzyme which removes one molecule of CO2.
- pyruvate is also oxidised to acetate : dehydrogenase enzymes remove hydrogen which is accepted by NAD to form reduced NAD ; acetate is produced
- acetate combines with coenzyme A to form acetyl coenzyme A which enters krebs cycle
overall in the link reaction, 2 molecules of CO2, 2 molecules of reduced NAD and 2 molecules of acetyl coenzyme A are produced per glucose molecule
six molecules of glucose enter glycolysis and are oxidised. how many acetate molecules would be produced at the end of a link reaction?
12
why is it an advantage to have pyruvate as an intermediate compound in respiration?
3C compound easily diffuses into the mitochondrion
- there are no carrier proteins for glucose on the membrane of a mitochondrion
describe the role of coenzyme A
transports 2C acetate to the krebs cycle
in krebs cycle, per glucose molecule how many:
- reduced NAD produced?
- carbon dioxide produced?
- reduced FAD produced?
- ATP produced by substrate level phosphorylation?
- reduced NAD produced = 6
- carbon dioxide produced = 4
- reduced FAD produced = 2
- ATP produced by substrate level phosphorylation = 2
what is krebs cycle also known as?
citric acid cycle`
what happens to the coenzyme A after it has delivered acetate to krebs cycle?
coenzyme A is regenerated and returns to link reaction to collect more acetate
what is the fate of the reduced NAD and FAD produced in Krebs cycle?
delivers hydrogen to the etc for synthesis of ATP by chemiosmosis
describe the process of the Krebs cycle
- krebs cycle liberates energy from carbon-carbon bonds to make ATP, reduced NAD and reduced FAD. carbon dioxide is also produced as a waste product
- the acetate from acetyl coenzyme A combines with a 4C compound to form a 6C compound.
- a series of enzyme controlled reactions then takes place ; there are 2 decarboxylation reactions and 4 dehydrogenation reactions per turn of the cycle
- the acetate which enters Krebs cycle is completely broken down to CO2 and water and the 4C compound is regenerated via 6C and 5C intermediates.
name the molecule required for hydrolysis reactions to occur
water
define decarboxylation
any chemical reaction in which a carboxyl group (-COOH) is split off from a compound as CO2. catalysed by decarboxylase enzymes
define dehydrogenation
a chemical reaction that involves the elimination of hydrogen.
it is catalysed by dehydrogenase enzymes.
give examples of dehydrogenation and decarboxylation reactions from aerobic respiration
decarboxylation :
- link : pyruvate to acetate
- krebs : 6C –> 5C –> 4C#
dehydrogenation:
- triose phosphate to pyruvate
- link pyruvate to acetate
- krebs : 6C –> 5C –> 4C –> 4C
describe the process of dehydrogenation
- 4C substrate and NAD+ collide with dehydrogenase enzyme
- the substrate is oxidised (loses hydrogen)
- NAD+ accepts the hydrogen and is therefore reduced
- products are released. active site is unchanged and available for re-use
why is it an advantage for the inner mitochondrial membrane to be folded into cristae?
increased surface area for stalked particles so more ATP can be synthesises
suggest 2 functions for mitochondrial DNA
- codes for its own replication
- codes for enzymes (proteins) involved in aerobic respiration
describe the process of the electron transport chain
- reduced NAD and reduced FAD deliver their pairs of hydrogen atoms to the electron transport chain at the inner mitochondrial membrane
- the hydrogen atoms split into protons (H+) and electrons (e-)
- the high energy electrons are transferred along carriers in the inner mitochondrial membrane along the electron transport chain, moving from high energy levels to lower energy levels
- the energy released during electron transport fuels the proton pumps
- protons are pumped through channel proteins from the matrix to the intermembrane space
- the build up of protons in the intermembrane space forms an electrochemical gradient
- stalked particles lining the cristae contain the enzyme ATP synthase
- protons flow down their concentration gradient through an ion channel in ATP synthase (permeable to H+)
- the flow of protons releases enough energy for the synthesis of ATP from ADP and Pi
- the production of an electrochemical gradient which results in the diffusion of protons through a proton channel in ATP synthase, fuelling the synthesis of ATP, is known as chemiosmosis
state the number of ATP molecules generated at the ETC for each molecule of:
- reduced NAD
- reduced FAD
reduced NAD : 3 (carrier system involving NAD has 3 proton pumps)
reduced FAD : 2 (carrier system involving FAD has 2 proton pumps)
how many ATP molecules of ATP are produced from substrate level phophorylation?
4
how many ATP molecules are produced from aerobic respiration
38
how many ATP molecules are produced from oxidative phosphorylation?
34
suggest why cells may not actually produce 38 ATP molecules from one glucose molecule
in the absence of oxygen, only glycolysis will occur producing a net gain of 2 ATP molecules (anaerobic respiration uses glycolysis)
- some of the intermediate compounds of respiration may be used in biosynthetic pathways within cells
glucose catabolism during aerobic respiration is spread out over many reactions, suggest an advantage of this
ATP is released in small pockets rather than all at once which could release too much thermal energy, denaturing enzymes
how is ATP used in protein synthesis?
required for amino acid activation in the cytoplasm
how is ATP used in active transport?
changes the shape of transport proteins to move molecules against a concentration gradient
how is ATP used in secretion / exocytosis?
packaging and transport of secretory products, like enzymes in vesicles
how is ATP used in nerve transmission?
sodium/potassium pumps actively transport ions across the axon membrane
how is ATP used in muscle contraction?
energy is required for contraction of muscle fibres
how is ATP used in DNA replication?
synthesis of DNA from nucleotides during DNA replication at interphase
