Grade 12 AP Bio - Metabolic Processes Unit Test Review

How do enzymes increase the rate of a reaction?

• Providing correct orientation (they orient atoms of substrates so they are able to create the desired product)

• Putting stress on bonds (they stretch and bend bonds between molecules to expose charged areas so they can interact with other reactants and form new bonds)

Describe the effect of temperature and pH on enzyme activity

Temperature:

• Increase in temperatures increase the reaction rate, until the optimal temperature is reached and the enzyme denatures, which reduces the enzyme’s activity

pH:

• Changes in pH cause the enzyme to denature, reducing its activity

Compare competitive and non-competitive enzyme inhibitors. What is the effect of increasing the substrate concentration for each?

Competitive inhibitors:

• Inhibitors resemble normal substrate

• They bind and block the active site so the substrate can’t bind

• Increasing the substrate concentration reduces the effect of inhibition

Non-competitive inhibitors:

• Inhibitors bind to an alternate site on the enzyme, changing the shape of the active site so the substrate can’t bind

• Increasing the substrate concentration has no effect

Describe feedback inhibition. Why is it beneficial for a product of a pathway to inhibit an enzyme at the beginning of that pathway?

• Feedback inhibition is a mechanism where the end product regulates the metabolic pathway by inhibiting an enzyme at the pathway’s start.

• It is beneficial for a product of a pathway to inhibit an enzyme at the beginning of that pathway because it prevents excess product accumulation by shutting down the pathway when enough product is made

• Low concentration of product results in more active enzymes that will make more product

• High concentration of product results in more inactive enzymes that will make less product

Briefly describe the light-dependent and light-independent reactions of photosynthesis

Light-dependent:

• Occur in the thylakoid membrane

• Requires photons (light energy), and water

• Produces ATP, NADPH, and releases O2

• Linear pathway (green plants), cyclic pathway (bacteria, or plants when NADP+ is low)

Light-independent:

• Occurs in stroma of chloroplasts

• Uses products of light-dependent reactions (ATP and NADPH) to convert CO2 to G3P

• NADPH is oxidized, donating its electrons to reduce CO2 to sugar

• ATP is hydrolyzed, releasing energy that drives the endergonic reactions of the cycle

• 1. carbon fixation, 2. reduction, 3. regeneration

What is the source of the carbon that makes up organic molecules such as G3P?

• CO2 fixed in the Calvin cycle

Describe the role of water in photosynthesis

• Water splits by the water splitting complex into oxygen, hydrogen ions, and electrons

• The electrons are released and replace the lost electrons of photosystem 2

• O2 that is released as a byproduct in light-dependent reactions comes from the water

• Electron and proton donor

Describe the role of light energy in photosnthesis

• Light energy excites electrons in the chlorophyll, initiating electron transport and enabling ATP and NADPH production

• Energy source for converting ADP to ATP, and NADP+ to NADPH

What is the final electron acceptor of the light dependent electron transport chain?

• NADP+, which becomes NADPH after accepting electrons

Explain the purpose of the H+ concentration gradient created during the electron transport chain of the light dependent reactions

• The H+ gradient across the thylakoid membrane drives ATP synthase, which generates ATP

• As electrons move down the electron transport chain in the thylakoid membrane, energy from these electrons is used to pump H+ ions from the stroma into the thylakoid lumen

• This creases a high concentration of H+ ions in the thylakoid membrane and a low concentration of H+ ions in the stroma, forming a H+ gradient

• H+ ions flow back to the stroma through ATP synthase, a protein that acts as an enzyme and a channel for protons

• The flow of H+ ions through ATP synthase releases energy, which ATP synthase uses to convert ADP + Pi to ATP

• Process of ATP generation driven by a proton gradient is called chemiosmosis

Describe the relationship between the light-dependent reactions and the Calvin cycle (light-independent reactions)

• Light-dependent reactions produce ATP and NADPH, which the Calvin cycle uses to fix carbon into G3P

• Light-dependent reactions require energy, Calvin cycle releases energy

What is photorespiration? Under what conditions does it become a problem for plants?

• Photorespiration occurs when the enzyme rubisco binds to O2 instead of CO2 during the Calvin cycle

• Net effect is lose 3 fixed C atoms, which reduces the efficiency of photosynthesis by diverting energy and carbon away from the production of glucose

• Photorespiration becomes a problem for plants in hot, dry conditions

• In these environments, plants close their stomata to conserve water, which limits the intake of CO2 and causes a buildup of O2 in the leaf

• With less CO2 available and more O2 present, rubisco is more likely to bind to O2, increasing photorespiration and reducing the plant’s ability to produce sugars efficiently

Briefly describe the C4 photosynthetic pathway

• C4 photosynthetic pathway is an adaption in certain plants to reduce photorespiration and improve photosynthesis efficiency in hot, dry environments

• CO2 is fixed into a 4 carbon compound in mesophyll cells

• The 4 carbon compound is transported to bundle sheath cells, where Co2 is released for use in the Calvin cycle

• By concentrating CO2 in the bundle sheath cells, the C4 pathway keeps rubisco from encountering high levels of oxygen, which reduces photorespiration

Briefly describe the stages of cellular respiration: glycolysis, pyruvate oxidation, citric acid cycle, and oxidative phosphorylation

Glycolysis:

• Occurs in cytosol

• Splits glucose into 2 pyruvate, producing 2ATP and 2 NADH

Pyruvate oxidation:

• Occurs in the mitochondrial matrix

• Each pyruvate releases a CO2 and binds to a coenzyme forming acetyl-CoA

• 2 NAD+ are reduced to NADH

Citric acid cycle:

• Occurs in mitochondrial matrix

• Acetyl-CoA combines with a 4 carbon molecule and goes through a cycle of reactions, releasing 2 CO2 to regenerate the 4 carbon starting molecule

• 2 ATP are made by substrate level phosphorylation

• 6 NAD+ are reduced to NADH

• 2 FAD are reduced to FADH2

• Breaks down acetyl-CoA, producing CO2, ATP, NADH, and FADH2

Oxidative phosphorylation:

• Occurs on mitochondrial inner membrane

• NADH and FADH2 are oxidized back to NAD+ and FAD

• The electrons are put into an electron transport chain - oxygen is the final electron acceptor, it combines with protons to form water. - as electrons are passed along the electron transport chain, the energy released pumps protons out of the mitochondrial matrix to form a gradient

• Protons flow back into the matric through ATP synthase, making ATP

• Uses electrons from NADH and FADH2 to generate a large amount of ATP via the electron transport chain

How many net ATP are produced in glycolysis?

• 2 ATP

Compare the pathways and ATP production of NADH and FADH2

NADH:

• Enters the electron transport chain earlier, producing 3 ATP per molecule of glucose

FADH2:

• Enters the electron transport chain later, yielding 2 ATP per molecule of glucose

Compare aerobic cellular respiration and fermentation. Which stage is common to both?

Aerobic cellular respiration:

• Requires oxygen

• Fully oxidizes glucose in a series of steps (glycolysis, pyruvate oxidation, citric acid cycle, and oxidative phosphorylation)

• Many ATP are made (38 ATP)

• Byproducts are CO2 and H2O

Fermentation:

• Occurs without oxygen

• Only includes glycolysis

• Produces less ATP (2 ATP)

• Lactic acid fermentation (in animals) produces lactate as byproduct

• Alcoholic fermentation (in yeast and some bacteria) produces ethanol and CO2 as a byproduct

Glycolysis is common to both aerobic cellular respiration and fermentation

What is the purpose of fermentation?

• The purpose of fermentation is to regenerate NAD⁺ from NADH without the citric acid cycle or the electron transport chain, allowing glycolysis to continue producing ATP in the absence of oxygen.