Flashcards in MAB 1 Deck (23):
What are enzymes and why are they important?
Enzymes are highly specific biological catalysts that allow essential chemical reactions to occur by providing an alternate path with a lower activation energy, which allows the reactants to react more readily. Without enzymes, reactions would occur too slowly to sustain life.
Describe the chemical composition of enzymes
Enzymes are made of proteins. Proteins are long chains of amino acids made of the elements carbon, hydrogen, oxygen and nitrogen, and are joined together by peptide bonds to form polypeptide chains.
Compare and contrast the lock and key model and the induced fit model
The lock and key model suggests that the active site of enzymes are rigid and substrate molecules are reciprocally shaped and perfectly fits into the active site. However, the induced fit model suggests that the binding of a substrate to the active site of an enzyme induces the enzyme to alter its shape slightly, to fit more tightly around the substrate. Both models simplify a biological process that cannot be observed easily.
Explain why, at high temperatures, enzyme activity completely drops to zero, while at low temperatures, enzyme activity is still present.
In more organisms, the optimal temperature for enzyme activity is around 40 degrees. However, at high temperatures e.g. over 60 degrees, enzyme activity completely drops to zero as the heat breaks the hydrogen bonds that keep the enzyme in its shape. Once broke, the active site of the enzyme changes shape and will no longer be able to fit the substrate, ie the enzyme denatures. This is irreversible. However, at low temperatures, enzyme activity is still present, just at a slower rate. The enzyme becomes rigid and the rate of reaction slows down heavily. Substrate molecules have less energy, and move into the active site more slowly. This is not a permanent change.
Whats the Lock and Key Model?
A lock and key model for enzyme specificity shows that a certain enzyme can only react with a certain substrate because of the shape of its active site which correlates to the shape of the substrate. Neither chemical will change to fit the other.
Whats the Induced-Fit Model?
The shape of the active site and the substrate molecules will both modify slightly, so the enzyme can react with more substrates. These enzymes have a lower specificity.
Why is the maintenance of a constant internal environment important for optimal metabolic efficiency?
Enzymes control all metabolic processes in the body.
Enzymes work optimally in an environment where their optimum temperature and pH conditions are met. At temperatures and pH values other than the optimum, the enzymes fail to work efficiently and kept as stable as possible.
The process by which an organism maintains a relatively stable internal environment, despite changing external environmental conditions
What are the two stages of homeostasis?
1. Detecting changes from the stable state
2. Counteracting changes from the stable state
How are changes from the stable state detected?
Receptors (sensory cells or organ) detect any changes e.g. thermoreceptors can detect changes in temperature
How are changes from the stable state counteracted?
Effectors (eg muscles move, gland secrete chemicals) bring about responses to stimuli and returns the body back to homeostasis.
What is the role of the nervous system in detecting and responding to environmental changes?
The nervous system works to regulate and maintain an animal’s internal environment and respond to the external environment by sending messages to the brain and back to the sensory organs.
Develop a model of a feedback mechanism.
Stimulus: increased body temperature e.g. when exercising or in hot surrounds
Receptor: Hypothalamus detects change and activates cooling mechanisms
Reponse: Sweat glands activated, increased evaporative cooling
Stimulus: decreased body temperature e.g. when in cold surrounds
Receptor: Hypothalamus detects change and activates warming mechanisms
Response: Skeletal muscles activated, shivering generates heat
What is the range of temperatures over which life is found and what are the limits?
Temperatures on earth can range from -70 degrees to above 50 degrees. Organisms must be able to survive in a range of temperature to allow cells to function. Most species can only tolerate a narrow range of temperature in their local environment due to enzyme specificity
Compare endotherms and ectotherms
Endotherms are organisms whose body metabolism generates heat and maintains a constant internal temperature. Examples include birds and mammals. Ectotherms are organisms that are dependent on energy from the environment to regulate body temperature. Endotherms require more food and energy , whereas ecotherms require less energy. Both endothermic and ectothermic organisms maintain homeostasis.
Explain the relationship between metabolic rate and temperature regulation in birds and mammals.
Birds and mammals are endotherms, which means that their body metabolism generates more heat and maintains a constant body temperature. Endotherms tend to have high body temperatures as a result of their high metabolism. When surrounding temperatures are cold, endotherms increase metabolic heat production to keep their body temperature constant. Thus, the act of regulating body temperature increases metabolic rate.
Describe the advantage to ectotherms of allowing their body temperature to fluctuate with the ambient temperature, especially at low temperatures.
Ectotherms are able to live in a larger range of temepratures, as a result of not having to constantly adjust interal body temperatures and expending energy. Homeostasis can be maintained through behaviour which is much less energetically expensive than endothermic homeostasis.
What are some adaptations and response that a named endotherm has for temperature change?
Temp increases: it licks its forearms as its form of evaporative cooling. Evaporation of saliva promotes heat loss from blood.
Temp decreases: it shivers, and this increases muscle activity, which increases metabolic activity which gains heat.
Temp increases: it sleeps in its burrow where temperature is constantly 10 degrees.
Temp decreases: it curls up to conserve heat, and hairs may become raised to trap a layer of warm air surrounding the body.
What are some adaptations and response that a named ectotherm has for temperature change?
Temp increases: retreats to shade to stay cool
Temp decreases: basks in the sun in the morning to stay warm after a cold night
Temp increases: Raises its frills and flaps it to create a cooling sensation
Temp decrease: Raises its thin frill and holds it to the sun (it is well supplied with blood vessels) to absorb heat. Also basks in the sun
What are some responses of plants to temperature change?
The Beech tree drops its leaves when it gets cold to conserve water and energy.
Eucalypt leaves hand vertiaclly downwards when it gets hot to reduce the surface area exposed to the sun. When the sun is hottest at midday, less of the leaf is exposed to it due to its vertical nature.
Describe an experiment you performed to show the effect of temperature of a named enzyme. In your answer include:
- a list of the equipment used
- safety precautions
- a general description of your results
Equipment: 6 test tubes, 3 beakers, pipette, ice, tap water, boiled + warm water, milk, rennin (enzyme), timer, measuring cylinder, safety glasses, thermometer
• Controlled: Amount of milk, amount of enzyme, size of equipment
• Independent: Temperature
• Dependent: Rate of enzyme activity
Safety precautions: Hot water can spill and cause burns, and so beakers were handled carefully and it was ensured they didn't spill. High temperatures can cause beakers to break, and broken glass can injure or cut skin. Safety glasses were worn and it was ensured that beakers weren't heated up to extreme temperatures.
1. We filled each test tube with 10mL of milk using a measuring cylinder
2. Each beaker was filled half-way with water of different temperatures
a. Beaker #1: Hot water
b. Beaker #2 Warm water
c. Beaker #3: Ice + tap water
3. A thermometer was placed in each beaker to get the temperature to 70°C, 40°C, and 10°C respectively.
4. Once the optimum temperature was reached, 1mL of the enzyme rennin was placed in the 3 test tubes using a pipette
5. A test tube containing milk and rennin, and a test tube containing only milk was then placed in each beaker, with the timer started as soon as the test tube came into contact with the water
6. The test tubes containing rennin were then occasionally tilted or turned to check for milk clotting
7. Once the milk had started to solidify, the time was recorded
Results: It was found that the fastest time as at 40°C. The rate increased steaily until 40°C then dramatically dropped. The milk at at 70°C did not clot.
Describe an experiment you performed to show the effect of pH of a named enzyme. In your answer include:
- a list of the equipment used
- safety precautions
- a general description of your results
Equipment: : Beaker, hot water, enzyme (rennin), milk, 4 test tubes, pipette, thermometer, measuring cylinder, timer, hydrochloric acid (HCl), sodium hydroxide (NaOH), distilled water, universal indicator
• Controlled: Amount of water in each test tube, amount of enzyme
• Independent: The pH of milk
• Dependent: Rate of the reaction
Safety Precautions: HCl is corrosive and was avoided contact with skin and eyes. Similarly, NaOH is corrosive and can cause severe burns. Care was taken when handling these chemicals.
1. We filled a beaker with hot water, and with 4 test tubes filled with 10mL of milk and each one containing substances with differing pH, they were placed into the beaker until a temperature of 40°C was reached
2. Once the test tubes were at 40°C, add 1mL of the enzyme rennin using a pipette
3. The test tubes were timed until the milk started to curd
Results: At a pH of I, the enzyme’s activity occurred the fastest. At a pH of 14, the enzyme is assumed to have already denatured.