BIO QUIZ 12

I CAN account for the ATP produced in all parts of aerobic cellular respiration (see diagram on page 140 of your textbook) and compare the amount to the total ATP produced in fermentation.

Aerobic - 36-38 ATP Glycolysis: 2 ATP Krebs Cycle: 2 ATP Electron Transport Chain (Oxidative Phosphoylation): 32-34 ATP Anaerobic (Fermentation) - 2 ATP Glycolysis: 2 ATP Fermentation: 0 ATP

I CAN compare alcoholic and lactic acid fermentation and list the types of organisms that generally use each of those processes.

Alcoholic - In this process, NADH donates its electrons to a derivative of pyruvate, producing ethanol. Yeast use this process. This is a two step process, in the first step, a carboxyl group is removed from pyruvate and released in as carbon dioxide, producing a two-carbon molecule called acetaldehyde. In the second step NADH passes its electrons to acetaldehyde, regenerating NAD+ and forming ethanol. Lactic Acid - NADH transfers its electrons directly to pyruvate, generating lactate as a byproduct. Bacteria that make yogurt and red blood cells perform lactic acid fermentation.

I CAN explain why the glycolysis biochemical pathway is typically divided into an energy investment phase and an energy payout phase.

Because in the first phase, a phosphate group is being added to glucose in order to make it unstable, allowing it to split in half and form two phosphate-bearing three-carbon sugars, and energy is being used to complete the process (2 ATP). Where as in the second phase, in which each three-carbon sugar is converted into another three-carbon molecule, pyruvate, through a series of reactions, energy is being made (4 ATP and 2 NADH).

I CAN state the model for aerobic cellular respiration in the form of a simple chemical equation.

C6H12O6 + 6O2 -------> 6CO2 + 6H2O + ATP

I CAN identify the redox reactions that occur during all forms (aerobic and anaerobic) of cellular respiration.

Cellular respiration involves many reactions in which electrons are passed from one molecule to another. Reactions involving electron transfers are known as oxidation-reduction reactions (or redox reactions). Oxygen gains electrons through reduction while carbon dioxide loses those electrons through oxidation.

I CAN describe how fermentation allows glycolysis to continue even when oxygen is not present.

Fermentation allows glycolysis to continue without oxygen because it replenishes the NAD+ using the NADH + H+ that has already been produced by glycolysis. Fermentation is used to regenerate the electron carrier NAD+ from the NADH produced in glycolysis. The extra reactions accomplish this by letting NADH drop its electrons off with an organic molecule (such as pyruvate, the end product of glycolysis). This drop-off allows glycolysis to keep running by ensuring a NAD+.

I CAN explain why glycolysis is considered to be an anaerobic process.

Glycolysis is an anaerobic process because none of its steps involve the use of oxygen.

I CAN describe in detail the biochemical process that occurs in the light dependent reactions.

In the light-dependent reactions, which take place at the thylakoid membrane, chlorophyll absorbs energy from sunlight and then converts it into chemical energy with the use of water. The light-dependent reactions release oxygen as a byproduct as water is broken apart. The light dependent reactions happen on the thylakoid membrane of the chloroplast. Step 1 (Photolysis): Light strikes chlorophyll in photosystem II, causing the electrons to become excited (gain energy). These electrons then leave photsystem II and travel down the proteins of the electron transport chain. Step 2 (Photolysis): Water is plit to replace the electrons lost in photosystem II, thic process also creates hydrogen ions (H+) and oxygen. As the excited electrons continue down the chain, their energy is used to pump hydrogen ions across the membrane and into the thylakoid space from the stroma. The hydrogen ions are then difused back into the stroma by ATP synthase. This causes ATP synthase to rotate, allowing it to produce ATP. Electrons continue to photosystem I, where thay are struck by light and excited again. These electrons then travel down a second electron transport chain, where they are used to reduce NADP+ to form NADPH (an electron carrier). The ATP and NADPH are moved to the stroma where they are used in the Calvin cycle.

I CAN describe in detail the biochemical process that occurs in the light independent reactions.

Phase 1: Carbon Fixation - CO2 is attached to RuBP by the enzyme RUBISCO, this forms 2 molecules of 3-phosphogylcerate for each CO2 added. Phase 2: Reduction - Each molecule of 3-phosphoglycerate is reduced to the form G3P, this requires energy from ATP, and electrons from NADPH. G3P is the final product of the light dependent reactions. Phase 3: Regeneration of RuBP - 1 molecule of G3P will leave the cycle, and the other 5 that are produced are used to regenerate RuBP so that the calvin cycle can continue, to regenrate RuBP ATP is required.

I CAN describe two adaptations that allow plants to avoid photorespiration.

Photorespiration - A respiratory process in many higher plants by which they take up oxygen in the light and give out some carbon dioxide, contrary to the general pattern of photosynthesis. Photorespiration is a wasteful pathway that occurs when the Calvin cycle enzyme rubisco acts on oxygen rather than carbon dioxide. 1. C4 plants minimize photorespiration by separating initial CO2 fixation and the Calvin cycle in space, performing these steps in different cell types. 2. Crassulacean acid metabolism (CAM) plants minimize photorespiration and save water by separating these steps in time, between night and day.

I CAN describe the biochemical process of glycolysis including the reactants needed and the products that are generated throughout the biochemical pathway.

Reactant - Glucose + 2 ATP Product - 2 Pyruvates + 2 ATP + 2 NADH Glycolysis takes place in the cytoplasm of a cell, and it can be broken down into two main phases: the energy-requiring phase, and the energy-releasing phase. Energy requiring phase - The starting molecule of glucose gets rearranged, and two phosphate groups are attached to it. The phosphate groups make the modified sugar unstable, allowing it to split in half and form two phosphate-bearing three-carbon sugars. Because the phosphates used in these steps come from ATP, two ATP is used in the process. Energy releasing phase - In this phase, each three-carbon sugar is converted into another three-carbon molecule, pyruvate, through a series of reactions. In these reactions, two ATP molecules and one NADH molecule are made. Because this phase takes place twice, once for each of the two three-carbon sugars, it makes four ATP and two NADH molecules overall. Overall, glycolysis converts one six-carbon molecule of glucose into two three-carbon molecules of pyruvate. The net products of this process are two molecules of ATP and two molcules of NADH.

I CAN describe biochemical process of the Krebs (citric acid cycle) including the reactants needed and the products that are generated throughout the biochemical pathway.

Reactants - Acetyl-CoA Products - 2CO2 + 1 ATP + 3 NADH + 1 FADH2 (x2 because there will be 2 turns per one glucose molecule) Step 1 - Aceytl-CoA joins with a 4 carbon molecule oxaloacetate, releasing the CoA group and forming a 6 carbon molecule called citrate. Step 2 - Citrate is converted into isocitrate. Step 3 - Isocitrate is oxidized, causing it to release a molecule of CO2, leaving behind a 5 carbon molecule known as ketoglutarate. In this step NAD+ is also reduced to from NADH. Step 4 - Ketoglutarate is oxodized in this step, leaving behind a 4 carbon molecule, which then picks up coenzyme A, forming an unstable compound known as succynl CoA. In this step NAD+ is also reduced to from NADH. Step 5 - The CoA in succynl CoA is replaced with a phosphate group which is then transferred to ADP to make ATP. Leaving behind a 4 carbon molecule known as succinate. Step 6 - Succinate is oxidized, forming another 4 carbon molecule known as fumarate. Two hydrogen atoms, with their electrons, are transferred to FAD to produce FADH2. Step 7 - Water is added, changing fumarate into another 4 carbon molecule known as malate. Step 8 - Oxaloacetate (the beginning 4 carbon compound) is regenerated by oxidizing malate. Another molecule of NAD+ is reduced to NADH during this process.

I CAN explain how the limitations and "flaws" in the enzyme rubisco can affect the efficiency of photosynthesis.

The limitations of rubisco are that firstly, it is very slow for an enzyme that is used as a catalyst, and secondly, it is not very good at distinguishing between CO2 and O2. Because it often (around 25-30% of the time) latches onto oxygen instead of carbon dioxide, it causes the the carbon-fixation reactions spit out a compound called glycolate that is toxic and must be removed. The reaction cycle by which it is removed, called photorespiration, is long, complicated and a major drain on the efficiency of the plant. Additionally, when the enzyme distinguishes well between oxygen and carbon dioxide, then it tends to be slow, and if it works really fast, then it isn't as selective.

Reduction

The process of gaining electrons (hydrogen atoms).

Oxidation

The process of losing electrons (hydrogen atoms).