Metabolism and Survival, KA 1-4 Flashcards
What are metabolic pathways?
Metabolic pathways are integrated and controlled pathways of enzyme-catalysed reactions within a cell.
Metabolic pathways can have reversible steps, irreversible steps and alternative routes.
Anabolic and catabolic reactions
Reactions within metabolic pathways can be anabolic or catabolic.
Anabolic reactions build up large molecules from small molecules and require energy.
Catabolic reactions break down large molecules into smaller molecules and release energy.
What are embedded in membranes?
Protein pores, pumps and enzymes are embedded in membranes.
What are metabolic pathways controlled by?
Metabolic pathways are controlled by the presence or absence of particular enzymes and the regulation of the rate of reaction of key enzymes.
Induced fit
Induced fit occurs when the active site changes shape to better fit the substrate after the substrate binds.
Affinity (chemical attraction)
The substrate molecule(s) have a high affinity for the active site and the subsequent products have a low affinity, allowing them to leave the active site.
What drives a sequence of reactions in a particular direction?
Some metabolic reactions are reversible and the presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction.
Activation energy
The activation energy is the energy needed to break chemical bonds in the reactant chemicals.
The presence of an enzyme lowers the activation energy.
What is an inhibitor?
An inhibitor is a substance that decreases the rate of an enzyme controlled reaction.
There are three types of inhibition: competitive, non-competitive and feedback.
Competitive inhibition
Competitive inhibitors bind at the active site preventing the substrate from binding.
Competitive inhibition can be reversed by increasing substrate concentration.
Non-competitive inhibition
Non-competitive inhibitors bind away from the active site but change the shape of the active site preventing the substrate from binding.
Non-competitive inhibition cannot be reversed by increasing substrate concentration.
Feedback inhibition
Feedback inhibition occurs when the end-product in the metabolic pathway reaches a critical concentration. The end-product then inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end-product.
Stages in aerobic respiration
- Glycolysis - occurs in the cytoplasm.
- Citric acid cycle - occurs in the matrix of the mitochondria.
- Electron transport chain - occurs on the inner mitochondrial membrane.
What is glycolysis?
Glycolysis is the breakdown of glucose to pyruvate in the cytoplasm.
Energy investment phase
This is the first phase of glycolysis.
ATP is required for the phosphorylation of glucose and intermediates in this stage.
Energy pay-off phase
This is the second phase of glycolysis.
The phosphorylation of glucose and intermediates during the first stage of glycolysis leads to the generation of more ATP during this stage and results in a net gain of ATP.
What happens to the pyruvate if oxygen is present?
In aerobic conditions, pyruvate is broken down to an acetyl group that combines with coenzyme A forming acetyl coenzyme A.
Citric acid cycle
In the citric acid cycle the acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate.
During a series of enzyme-controlled steps, citrate is gradually converted back into oxaloacetate which results in the generation of ATP and release of carbon dioxide.
What occurs in both glycolysis and the citric acid cycle?
Dehydrogenase enzymes remove hydrogen ions and electrons and pass them to the coenzyme NAD, forming NADH.
The hydrogen ions and electrons from NADH are passed to the electron transport chain on the inner mitochondrial membrane.
What is the electron transport chain?
The electron transport chain is a series of carrier proteins attached to the inner mitochondrial membrane.
ATP synthesis
Electrons are passed along the electron transport chain releasing energy.
This energy allows hydrogen ions to be pumped across the inner mitochondrial membrane.
The flow of these ions back through the membrane protein ATP synthase results in the production of ATP.
Finally, hydrogen ions and electrons combine with oxygen to form water.
Fermentation
In the absence of oxygen, fermentation takes place in the cytoplasm.
In animal cells, pyruvate is converted to lactate in a reversible reaction.
In plants and yeast, ethanol and CO2 are produced in an irreversible reaction.
Fermentation results in much less ATP being produced than in aerobic respiration.
What is the role of ATP in the transfer of energy?
ATP is used to transfer energy to cellular processes which require energy.
How can metabolic rate be measured?
Metabolic rate can be measured using respirometers, oxygen probes, carbon dioxide probes and calorimeters.
How do we compare metabolic rates?
Measurement of oxygen consumption, carbon dioxide and heat production allow us to compare metabolic rates.
Metabolic rate in different groups of animals
Birds and mammals have higher metabolic rates than reptiles and amphibians, which in turn have higher metabolic rates than fish.
What do organisms with high metabolic rates require?
Organisms with high metabolic rates require more efficient delivery of oxygen to cells.
Complete double circulatory system
Birds and mammals have a complete double circulatory system.
The heart consists of two atria and two ventricles.
There is no mixing of oxygenated and deoxygenated blood.
Incomplete double circulatory system
Amphibians and most reptiles have an incomplete double circulatory system.
The heart consists of two atria and one ventricle.
The oxygenated and deoxygenated blood mix in the ventricle.
Single circulatory system
Fish have a single circulatory system.
The heart consists of one atrium and one ventricle.
Which circulatory system is most efficient and why?
Complete double circulatory systems enable higher metabolic rates to be maintained.
There is no mixing of oxygenated and deoxygenated blood and the oxygenated blood can be pumped out at a higher pressure.
This enables more efficient oxygen delivery to cells.
What affects the ability of an organism to maintain its metabolic rate?
The ability of an organism to maintain its metabolic rate is affected by external abiotic factors.
What are abiotic factors?
Non-living factors such as pH, salinity and temperature.
Conformers
Conformers’ internal environment is dependent upon external environment.
They have low metabolic costs and a narrow range of ecological niches.
Conformers use behavioural responses to allow them to tolerate variation in their external environment to maintain optimum metabolic rate.
Regulators
Regulators maintain their internal environment regardless of external environment.
Regulators use metabolism to control their internal environment, which increases the range of possible ecological niches.
This regulation requires energy to achieve homeostasis.
This increases their metabolic costs.
What is the hypothalamus and where is it located?
The hypothalamus is the temperature monitoring centre and it is located in the brain.
Thermoregulation by negative feedback
Information is communicated by electrical impulses through nerves to the effectors, which bring about corrective responses to return temperature to normal.
Corrective responses to an increase in body temperature
Sweating: body heat used to evaporate water in the sweat, cooling the skin.
Vasodilation of blood vessels: increased blood flow to the skin increases heat loss.
Decreased metabolic rate: less heat produced.
Corrective responses to a decrease in body temperature
Shivering: muscle contraction generates heat.
Vasoconstriction of blood vessels: decreased blood flow to skin decreases heat loss.
Hair erector muscles contract: traps layer of insulating air.
Increased metabolic rate: more heat produced.
Why is thermoregulation important?
Regulating temperature is important for optimal enzyme activity and high diffusion rates to maintain metabolism.
