Enzymes
Which of the following is true of enzymes?
I. They increase the rate of reaction by stabilizing the transition state
II. They raise activation energy to shift the equilibrium to favor the products
III. They lower activation energy by altering the products of a reaction
I only
Define energy, give at least two examples.
Energy- Ability to promote, change, or do work
-Kinetic energy (Associated with movement)
- Potential energy ( Due to structure or location)
- Chemical energy (The energy in molecular bonds, form of potential energy)
O2 is a reactant in cellular respiration, what is the role of O2 in cellular respiration?
O2 acts as the final electron acceptor in the electron transport chain (ETC)
Chloroplasts
- Grana/Thylakoids (Light Dependent)
- Stroma (Light Independent)
What step of cellular respiration yields the most ATP and how much?
Electron transport chain (ETC)
34-36 ATP
What are the factors that affect enzyme activity?
- Temperature
- Salt Concentrations
- pH
What are the first two laws of thermodynamics?
1. "Law of conservation of energy". Energy cannot be created or destroyed, but can be transformed from one type to another.
2. Transfer of energy from one form to another increases the entropy (degree of disorder) of a system. As entropy increases, less energy is available for organisms to promote change.
Give the steps of cellular respiration and where each step occurs at:
1. Glycolysis- In cytoplasm
2. Transition step- To matrix
3. Krebs Cycle- Matrix of mitochondria
4. Electron transport chain (ETC)- Inner membrane of the mitochondria
Why do plants absorb mostly red and blue wavelengths of light while reflecting green light?
Plants absorb mostly red and blue wavelengths of light because chlorophyll pigments absorb these wavelengths more efficiently than green light.
Where is the mitochondrial matrix?
Inner most space of the mitochondria, between the inner membrane.
Describe the difference between lock and key and induced fit models of enzyme conformation
Lock and Key: Only the right key (substrate) will fit in the lock (enzyme). More specific
Induced Fit: Interaction also involves conformation changes
What is the difference between oxidation and reduction?
Oxidation: The loss of electrons from an atom or molecule; these reactions release energy
Reduction: The gain of electrons (and whatever energy contained in the electrons) by an atom or molecule. These reactions require energy.
If in doubt remember OIL RIG
Explain what happens when the cell is depleted of O2, and why the related process is necessary:
- Glycolysis occurs, but instead of going to the Krebs Cycle, electrons from NADH reduce pyruvate and fermentation occurs.
- Fermentation is important because it is able to generate ATP even if O2 is not present
Compare and contrast Photosynthesis and Respiration
Photosynthesis Respiration
Food Produced Consumed
Energy Stored as glu Released from glu
Light Required Not required
H2O Consumed Released
CO2 Consumed Released
O2 Released Consumed
Describe the two main types of metabolic pathways:
Catabolic Pathways
- Breakdown cellular components
- Exergonic
Anabolic Pathways
- Synthesis cellular components
- Endergonic
- Must be coupled to exergonic reaction
What may be some other requirements of enzymes?
Prosthetic Groups- Small molecules permanently attached to the enzyme
Cofactor- Usually inorganic ion that temporarily binds to enzyme
Coenzyme- Organic molecule that participates in reaction but is left unchanged afterward
1. Substrate-level phosphorylation: Enzyme directly transfers phosphate from one molecule to another molecule
2. Chemiosmosis: Energy stored in an electrochemical gradient is used to make ATP from ADP and Pi
What is the purpose of each step of cellular respiration?
-Glycolysis: Rearranges the glucose molecule (to pyruvate) and extracts some energy
- Transition step: Moving carbon molecules from the cytoplasm to the matrix, extracts some energy
- Krebs Cycle: Complete breakdown of glucose, most energy that was released is in NADH and FADH2 molecules
- ETC: Converts energy to molecules of ATP through chemiosmosmotic phosphorylation
Compare and contrast C3, C4, and CAM plants.
C3: Occurs during the day, has no way to avoid photorespiration, works best in a cool and moist environment (most plant species are C3 ~95%), downfall is photorespiration.
C4: Occurs during the day, avoids photorespiration by having light reactions and carbon reactions occurring in separate cells. Works best in a hot and dry environment, downfall is there is a high ATP cost. Very few plants C4 (~1%)
CAM: Occurs during the night and day, avoids photorespiration by absorbing CO2 at night then light reactions and carbon reactions occur during the day, thrives in a hot and dry environment. Downfall is reduced carbon availability at night. Few plants are CAM (~3-4%)
How do enzymes lower activation energy?
1. Straining bonds in reactants: to make it easier to achieve transition state
2. Positioning reactants together: to facilitate bonding
3. Changing local environment: direct participation through very temporary bonding
In the first step of glycolysis, hexokinase produces glucose-6-phosphate. G-6-P itself can also bind to hexokinase at the active site, blocking access to ATP. This is an example of:
Feedback Inhibition
Draw a coupled reaction
Show me :)
Write the net reactions for every step:
Glycolysis:
C6H12O6 + 2NAD+ + 2H+ + 4e- + 2ADP + 2P -> 2 pyruvate + 2NADH + 2ATP
Transition step:
2 pyruvate + 2NAD+ + 2H+ + 4e--> 2 CO2 + 2 acetyl-CoA + 2NADH
Krebs Cycle:
2 acetyl-CoA + 2 ADP + 2P + 6NAD+ + 6H+ + 12e- + 2FAD + 4H+ + 4e- -> 4 CO2 + 2ATP + 6NADH + 2FADH2
ETC:
1/2 O2 + 2H+ + 2e- +NADH + FADH2 + ADP + P -> H2O + NAD+ + H+ + 2e- + FAD + H+ + 2e- + ATP
A plant is placed in complete darkness for 24 hours but continues receiving water and carbon dioxide. Explain what happens to its ATP production, NADPH availability, carbon fixation, and stored carbohydrates.
- ATP production occurs in mito. through cellular respiration instead of light-dependent reactions
- Photosystem I requires light to give electrons to NADPH so no NADPH will be made for photosynthesis
- Carbon fixation wont occur bc calvin cycle requires atp and nadph from light dependent reactions
- Stored carbs like starch are broken down to sugar to be used in cellular respiration
What rotary machinery lead atp? List the precurouser of atp for this machinery? What is this process called?
Atp synthase; ADP+Pi=ATP
oxidative phosphorylation