Respiration Flashcards
Define tissue/ cell respiration
This is a process by which organic food materials are broken down in a cell to release energy in the form of ATP.
Describe the structure of ATP
ATP is a molecule made up of a nitrogen base; adenine, a ribose sugar and three phosphate groups.
Adenine is attached to carbon 1 of ribose sugar while the chain of phosphate groups is attached to carbon 5 of ribose.
True or false;
More energy is obtained from the hydrolysis of ATP to ADP and ADP to AMP than from hydrolysis of AMP.
True
This explains why hydrolysis of AMP to release energy isn’t feasible.
By what process is ATP formed;
Phosphorylation; in which a phosphate is added to ADP.
Explain the three types of phosphorylation
i. Substrate level phosphorylation:
This involves the transfer of phosphate group directly from a high energy compound to ADP to form ATP.
Examples of high energy compounds include 1, 3- bisphosphoglycerate
ii. Oxidative phosphorylation:
This is the process of ATP synthesis using energy from oxidation of compounds such as NADH and FADH2
iii. Photophosphorylation:
This is the process by which ATP synthesis takes place in a cell using energy from light.
E.g. during photosynthesis.
Why is ATP is preferred to other high energy compounds to provide energy for cell metabolism?
- Provides the right amount of energy for cellular needs when hydrolyzed
- ATP can be moved to any place when need arises
- Is easily hydrolyzed to provide energy at the right time.
State uses of ATP
- Provides phosphates for phosphorylation
- Stores energy
Give the uses of energy from ATP in cells
- Enables loading and unloading of sugars in plants
- Enables translocation of organic food materials in phloem of plants
- Enables movement of cilia and flagella
- Enables contraction of muscles
- Enables active transport of molecules across cell membrane
- Used for synthesis of compounds and structures e.g. DNA and protein synthesis
- For activation of chemical compounds, to make them more reactive. E.g. phosphorylation of glucose during glycolysis
- For Contraction of microfilaments during cell division
- Powers movement of a sperm cell toward the secondary oocyte
- Transmission of nerve impulses
- For secretion of substances such as hormones that are formed in cells
Where does respiration occur in prokaryotic cells?
- Cytoplasm, mesosome
Where does respiration occur in eukaryotic cells?
- Cytoplasm, mitochondrion
What are the three stages of cellular respiration, their sites of occurrence and their conditions?
- Glycolysis
Occurs in the cytoplasm
Anaerobic conditions - Krebs cycle/ tricarboxylic acid cycle
Occurs in the mitochondrial matrix
Aerobic conditions - Electron transport chain
Occurs in the cristae of the mitochondrion
Aerobic conditions
Define glycolysis
- This is a series of enzyme controlled reactions that involve the splitting of a single glucose molecule to form two molecules of pyruvate with release of two ATP molecules
Describe the process of glycolysis
- Glucose; phosphorylated to form glucose-6-phosphate to raise its energy level and prevent it from leaving the cell. Reaction is catalyzed by the a kinase enzyme.
- The glucose-6-phosphate; isomerized to form fructose-6-phosphate. Reaction catalyzed by isomerase enzyme.
- Fructose-6-phosphate; phosphorylated to form fructose-1, 6- bisphophate. Reaction catalyzed by enzyme kinase.
- The fructose-1, 6-bisphosphate is unstable and splits to form two 3 carbon compounds which are isomers; dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. Reaction is catalyzed by enzyme aldolase.
- Dihydroxyacetone phosphate; isomerized to glyceraldehyde-3- phosphate. The reaction is catalyzed by enzyme isomerase.
- Thus, each glucose molecule is cleaved to form 2 molecules of three carbon compound glyceraldehyde-3-phosphate.
- Each of the glyceraldehyde-3-phosphate is oxidized by oxidized Nicotinamide adenine dinucleotide (NAD+) and then phosphorylated to to form 1,3-bisphosphoglycerate. Reaction catalyzed by kinase enzyme.
- Two molecules of reduced nicotinamide adenine dinucleotide (NADH+H+) are formed. Reaction is catalyzed by dehydrogenase enzyme
- Each molecule of 1, 3-bisphosphoglycerate is used to from an ATP molecule during substrate level phosphorylation of ADP.
- Two molecules of 3-phosphoglycerate (PGA) are formed. Reaction is catalyzed by phosphoglycerokinase enzyme.
- Each of the PGA molecules isomerizes to form 2-phosphoglycerate.
- The molecules now lose a water molecule under catalysis of enzyme enolase to form 2 molecules of phosphoenolpyruvate (PEP)
- A phosphate group is transferred from each of the PEP molecules to ADP, forming 2 molecules of ATP, during substrate level phosphorylation.
- Two molecules of pyruvate are formed. Reaction is catalyzed by pyruvate kinase enzyme.
What is the significance of glycolysis?
- Formation of ATP used to power cell activities
- Formation of (NADH+H+) from which more energy is extracted during the electron transport system
- Formation of pyruvate from which more energy can be extracted either in aerobic conditions or anaerobic conditions during Krebs cycle.
Describe the Krebs Cycle
•During aerobic conditions, pyruvic acid is transported across the mitochondrial membrane into the matrix where it is decarboxylated.
• First, the pyruvate is decarboxylated and then oxidized to form acetate, carbon dioxide and (NADH+H+).
• The acetate combines with coenzyme A to form acetyl coenzyme A, making the acetyl group very reactive.
• Acetyl coenzyme A now joins the Krebs cycle where it is further oxidized to release more energy.
• In the Krebs cycle, acetyl CoA reacts with oxaloacetate a 4C compound to form citrate, a 6C compound.
• Coenzyme A is reformed and may be used to combine with another acetate molecule from pyruvate.
• Citrate isomerises to form isocitrate, a more reactive molecule by addition and removal of a water molecule.
• The isocitrate is oxidized by (NAD+) to (NADH+H+) and then decarboxylated by loss of carbon dioxide to form α-ketoglutarate
• The α-ketoglutarate loses a carbon dioxide molecule and oxidized by (NAD+), the remaining product reacts with coenzyme A to form a 4C compound, succinyl CoA, which is unstable.
• The CoA is displaced, ATP is formed and a more stable 4C compound, succinate forms.
• The succinate is oxidized by removal of two hydrogen atoms by (Flavine adenine dinucleotide) FAD, to form FADH2. Fumarate is formed.
• Addition of a water molecule to the fumarate results into formation of malate, a 4C compound.
• Malate is oxidized by NAD+ to regenerate oxaloacetate. (NADH+H+) is also formed
How many NADH molecules are formed from the Krebs Cycle per pyruvate molecule?
3
How many FADH2 molecules are formed from the Krebs Cycle per pyruvate molecule?
1
How many ATP molecules are made in the Krebs cycle?
2
What is the role of coenzyme A?
• Activates acetate so that more energy can be obtained from it
• Transfers the acetyl group formed from pyruvate to combine with 4C compound oxaloacetate, forming 6C compound citrate. This reaction is catalysed by the enzyme citrate synthatase.
• Provides a pathway by which fatty acids and proteins can be used as respiratory substrates via a central link of acetyl coenzyme A
State the importance of the Krebs cycle
- Brings about degradation of macromolecules; 3 carbon pyruvate is broken down to carbon dioxide
- It is a source of hydrogen atoms which are transferred to the electron transport system so that more energy can be harnessed from them
- It is a valuable source of intermediate compounds used in the manufacture of other substances e.g. fatty acids, amino acids and chlorophyll
State similarities between glycolysis and Krebs cycle
- In both, NADH+H+ is formed
- In both, ATP is formed
- Both involve reduction in number of carbon atoms of initial substrate
- Both are enzyme catalysed
- Both occur in living cells
Give differences between glycolysis and Krebs cycle
GLYCOLYSIS
- Electron acceptor FAD not involved
- Carbon dioxide not formed
- Occurs in the cytoplasm of the cell
- Doesn’t require oxygen availability to occur
- Does not involve CoA
KREBS CYCLE
- Electron acceptor FAD involved
- Carbon dioxide formed
- Occurs in mitochondrial matrix
- Requires oxygen to occur
- Involves coenzyme A
Where does the electron transport chain occur?
Inner membrane of the mitochondria
Describe the electron transport system
- Two hydrogen atoms are removed from an intermediate compound and taken up by a hydrogen carrier NAD which is thereby reduced
- The hydrogen atoms then pass to a second carrier FAD which in turn is reduced and NAD is re-oxidized
- Sufficient energy in this transfer is released for synthesis of an ATP molecule
- The oxidation-reduction process is repeated with cytochrome and cytochrome oxidase
- The chain of reactions yields three molecules of ATP
Account for the number of ATPs formed per glucose molecule
GLYCOLYSIS
2 NADH x 3 = 6 ATP
2 ATP
TOTAL: 8 ATP
KREBS CYCLE
2 FADH x 2 = 4 ATP
6 NADH x 3 = 18 ATP
2 ATP
TOTAL: 24 ATP
PYRUVATE DECARBOXYLASE (link reaction)
2 NADH x 3 = 6 ATP
TOTAL
38 ATP
Explain why the actual yield of ATP is less than 38
i. The inner mitochondrial membrane allows some protons to re-enter the matrix without passing through ATP-generating channels.
Define anaerobic respiration
This is a process by which organic materials such as sugars are broken down to release ATP without oxygen.
Why is the yield of ATP in anaerobic respiration significantly lower than that in aerobic respiration?
The ATPS are formed exclusively by substrate level phosphorylation during glycolysis, for which only 2 ATPs are formed per glucose molecule as compared to the 38 ATPs expected in aerobic conditions.
What are the two types of fermentation?
a) Lactic acid fermentation.
b) Alcohol fermentation (plant & fungi cells)
What occurs during lactic acid fermentation?
- In anaerobic conditions, the pyruvate formed from glycolysis is reduced directly by NADH to form lactic acid (lactate).
- No carbon dioxide is formed.
- The NAD+ formed enables continuation of glycolysis.
True or false;
Carbon dioxide is formed in both lactic acid fermentation and alcohol fermentation
False
No carbon dioxide is formed in lactic acid fermentation.
(Lactic acid and pyruvate are both 3C compounds while Ethanol is a 2C compound hence carbon dioxide is only formed in alcohol fermentation)
What happens to excess lactate after strenuous exercise.
It is transported gradually to the liver where in presence of oxygen, it can be converted back to pyruvate in liver cells.
What is the significance of lactic acid fermentation?
- Enables rapid formation of ATP for muscle contraction in skeletal muscles when oxygen is scarce
- Lactic acid fermentation in certain fungi and bacteria used in dairy industry to make cheese and yoghurt.
What are the two steps of forming ethanol in alcohol fermentation?
i. Pyruvate is decarboxylated to give ethanal (acetaldehyde) [toxic] and carbon dioxide. Reaction is catalysed by pyruvate decarboxylase.
ii. The acetaldehyde formed is then reduced by NADH to form ethanol and NAD+. Reaction catalysed by alcohol dehydrogenase.
- The NAD+ that is regenerated is essential for the continuation of glycolysis.
What is the significance of alcohol fermentation?
- Enables brewing of alcohol using yeast cells
- Carbon dioxide produced by baker’s yeast allows dough/bread to rise
What are the industrial applications of fermentation?
- In brewing industry, fermentation of sugars results into formation of alcoholic drinks like wines and spirits
- In baking industry, yeast fermentation results into production of carbon dioxide which rises the dough
- Industrial lactic acid fermentation results into formation of yoghurt and cheese
- Anaerobes such as bacteria are used in sewage treatment plants to break down solid and semi-solid waste.
State similarities between aerobic respiration and fermentation in cells
- ATP is produced in both
- In both, glycolysis results into formation of pyruvate
- In both NAD+ oxidizes glucose to form pyruvate
- Both involve phosphorylation of glucose to raise its energy level
State differences between aerobic respiration and fermentation in cells
AEROBIC RESPIRATION
- Requires oxygen for ATP formation
- Occurs in cytoplasm and mitochondria
- Glycolysis, Krebs cycle and ETS involved
- Water formed
- Acetyl CoA formed as an intermediate product
- Net production of 38 ATPs per glucose molecule
FERMENTATION
- Does not require oxygen for ATP formation
- Occurs in cytoplasm
- Glycolysis only involved
- Water not formed
- Acetyl CoA not formed as an intermediate product
- Net production of 2 ATPs per glucose molecule
How is cellular respiration regulated?
- Negative feedback inhibition mechanism. During this mechanism, the end product of a metabolic pathway becomes an allosteric inhibitor to an enzyme that catalyses an early step in the series of metabolic reactions.
- Negative feedback inhibition mechanism prevents cells from wasting energy and vital intermediates (metabolites).
What external factors affect the rate of respiration?
a) Temperature
- Low temperature results into increase in respiration rate. To provide much needed heat to ensure optimum temperature for enzyme activity. Extremely low temperature will result into decrease in respiration rate
- High temperature generally results into low respiration rate. But beyond high critical temperature of an organism, further increase in temperature results into increased metabolic rate (respiration rate).
b) Body size
- Smaller organisms with a larger surface area to volume ratio lose heat faster than larger organisms thus have a higher respiration rate.
c) Level of activity
- More active organisms have a higher respiration rate to enable supply of much needed ATP as compared to less active ones.
d) Growth
- Organisms or parts of organisms that are actively undergoing growth have a higher respiration rate as compared to dormant organisms or those in senescence.
Define respiratory quotient
This is a measure of the ratio of carbon dioxide evolved to the oxygen consumed by an organism at the same time period during respiration.
Why do fats have an RQ value of less than 1?
Fats have a lower proportion of oxygen to carbon thus require more oxygen for complete oxidation during respiration.
Why don’t proteins have a uniform RQ value?
Due to variation in composition of proteins.
What does an infinite RQ value or one greater than 1 imply?
Anaerobic respiration occured
