Biochemistry: Enzymes and Cellular Respiration

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Questions and Answers

What is the primary characteristic of cofactors in enzymatic reactions?

They are required for proper enzyme activity. (correct)

They are produced by the enzyme during the reaction.

They enhance enzyme specificity.

They are always proteins.

What happens during oxidation in a redox reaction?

Gain of electrons lowers energy

Loss of electrons increases energy

Gain of electrons increases energy

Loss of electrons lowers energy (correct)

Which of the following best describes competitive inhibitors?

They chemically resemble the substrate and bind to the active site. (correct)

They can only inhibit enzymes without cofactors.

They bind to an allosteric site.

They cause irreversible changes to the enzyme.

What is a consequence of allosteric regulation in enzymes?

It can stabilize either the active or inactive form of the enzyme. Signup and view all the answers

Which molecule acts as an electron acceptor in cellular respiration?

NAD+ Signup and view all the answers

During cellular respiration, glucose is primarily converted into which of the following?

Carbon dioxide Signup and view all the answers

What type of reaction allows energy stored in food to be transferred to ATP?

Catabolic reaction Signup and view all the answers

Which statement best describes the nature of energy flow in biological systems?

Energy enters as sunlight and leaves as heat. Signup and view all the answers

What is one of the primary roles of the electron transport chain in respiration?

To extract energy from electrons Signup and view all the answers

Which process is responsible for the synthesis of ATP from ADP?

Cellular Respiration Signup and view all the answers

Which stage of cellular respiration occurs in the cytosol?

Glycolysis Signup and view all the answers

What is produced as a result of the Krebs Cycle?

NADH and ATP Signup and view all the answers

How do inorganic cofactors differ from organic cofactors?

Organic cofactors can be vitamins, while inorganic cofactors are usually metal ions. Signup and view all the answers

What mechanism allows a molecule to perform work following phosphorylation?

It undergoes a conformational change. Signup and view all the answers

What is the function of dehydrogenases in cellular respiration?

To remove hydrogen atoms from substrates Signup and view all the answers

What is the total maximum ATP yield from the complete oxidation of one glucose molecule during cellular respiration?

38 ATP Signup and view all the answers

What is produced during one complete turn of the Krebs cycle per glucose molecule?

2 ATP, 6 NADH, and 2 FADH2 Signup and view all the answers

What is the primary role of the electron transport chain?

To generate a proton gradient across the membrane Signup and view all the answers

Which of the following best describes the function of ATP synthase?

To phosphorylate ADP into ATP using the H+ gradient Signup and view all the answers

What is the ultimate electron acceptor in the electron transport chain?

Oxygen (1/2 O2) Signup and view all the answers

What role does the proton motive force play in cellular respiration?

It helps in the synthesis of ATP via oxidative phosphorylation Signup and view all the answers

What happens to the electrons from FADH2 in the electron transport chain compared to those from NADH?

They are processed later and produce less ATP Signup and view all the answers

What is a consequence of cyanide as a respiratory poison?

Blocks electron flow to oxygen Signup and view all the answers

Which statement accurately reflects the nature of the electron transport chain components?

Most components are proteins with cofactors alternating states Signup and view all the answers

What is the primary effect of Dinitrophenol (DNP) when used in a cellular context?

Makes the lipid bilayer permeable to H+ Signup and view all the answers

In which type of respiration do strict anaerobes engage when oxygen is not present?

Fermentation Signup and view all the answers

How many ATP are generated during glycolysis in cellular respiration?

2 ATP (net) Signup and view all the answers

What is the main purpose of the steps after glycolysis in fermentation?

To recycle NAD+ Signup and view all the answers

Which of the following statements about ATP production efficiency is true?

Eukaryotic cells are about 40-60% efficient Signup and view all the answers

What enzyme is known to be inhibited by both citrate and ATP during the regulation of the Krebs cycle?

Phosphofructokinase Signup and view all the answers

Which products result from alcoholic fermentation in yeast?

2 ethanols + 2 CO2 Signup and view all the answers

Which macromolecule is broken down into glycerol and fatty acids during catabolism?

Lipids Signup and view all the answers

What is the main product generated in the Calvin Cycle?

G3P Signup and view all the answers

Which of these components is primarily used in the Calvin Cycle to reduce carbon dioxide?

NADPH Signup and view all the answers

How many CO2 molecules must enter the Calvin Cycle to produce one G3P sugar?

3 Signup and view all the answers

What role does Rubisco play in the Calvin Cycle?

It catalyzes the reaction between CO2 and RuBP Signup and view all the answers

What molecule is primarily produced when cyclic photophosphorylation occurs?

ATP Signup and view all the answers

What happens during photrespiration that negatively affects photosynthesis?

Increased oxygen concentration Signup and view all the answers

During each cycle of the Calvin Cycle, how many RuBP molecules are regenerated for use?

3 Signup and view all the answers

What is the energy storage form used by plants?

Starch Signup and view all the answers

What is the main product of the light reactions in photosynthesis?

ATP and NADPH Signup and view all the answers

Where do the light independent reactions occur in the plant cell?

Stroma fluid Signup and view all the answers

What is the function of accessory pigments in photosynthesis?

To absorb light and transfer energy to chlorophyll a Signup and view all the answers

What occurs when chlorophyll absorbs a photon of light energy?

The chlorophyll undergoes photooxidation Signup and view all the answers

Which statement best describes the process of carbon fixation in photosynthesis?

CO2 is converted into sugar using ATP and NADPH Signup and view all the answers

Which pigment is considered the main pigment found in chloroplasts?

Chlorophyll a Signup and view all the answers

What happens to an electron in chlorophyll once it is boosted to an excited state?

It returns to the ground state and releases energy as heat Signup and view all the answers

What role do the thylakoid membranes play in photosynthesis?

Location of light reactions where energy conversion occurs Signup and view all the answers

Study Notes

Cell Energetics

Photosynthesis is a process that uses water, carbon dioxide, and sunlight energy to produce glucose (sugar) and oxygen.
Chloroplasts are the organelles where photosynthesis occurs.
Cellular respiration uses glucose and oxygen to produce carbon dioxide, water, and energy (ATP).
Mitochondria are the organelles where cellular respiration takes place.

Metabolism

Metabolism encompasses all chemical processes in an organism.
Metabolic pathways are a series of enzyme-catalyzed reactions.
Catabolic pathways release energy by breaking down complex molecules (e.g., cellular respiration).
Anabolic pathways consume energy to build complex molecules (e.g., protein synthesis).

Energy Basics

Energy is the ability to do work, moving matter against opposing forces like gravity.
Cells cannot create or recycle energy.
The ultimate energy source for cells is the Sun.
Kinetic energy is energy of motion, and potential energy is stored energy based on position or arrangement (e.g., chemical energy).
Energy can be converted from one form to another.
The first law of thermodynamics states that energy can be transformed but not created or destroyed. -The second law of thermodynamics states that every energy transformation increases the entropy (disorder) of the universe.

Free Energy

Free energy is the amount of energy available to do work for cells.
It determines whether a reaction will occur spontaneously.
Cells perform mechanical, transport, and chemical work. (Examples of work are muscle movement, pumping substances across membranes and exergonic vs endergonic reactions)

ATP

Adenosine triphosphate (ATP) is the immediate source of energy for cellular work.
ATP is made of adenine, ribose sugar, and three phosphate groups.
ATP(and other molecules can be phosphorylated, the addition of a phosphate group, to change shapes to perform work.

Activation Energy

Activation energy is the amount of energy needed for a chemical reaction to start.
Different reactions need different amounts of activation energy.
By increasing temperature, reactant concentration, or pressure , or adding a catalyst, activation energy can be reduced and the reaction speeds up.

Catalysts and Enzymes

Catalysts accelerate chemical reactions without being permanently changed in the process.
Enzymes are biological catalysts, all proteins.
They lower the activation energy needed for reactions to occur.
Enzymes are highly specific to a substrate due to the shape of their active sites, using the lock-and-key or induced-fit models.
Cofactors are small molecules required for enzyme function that are not proteins (inorganic or organic).
Enzyme inhibitors (Competitive and Noncompetitive) can slow or stop enzyme activity.

Allosteric Regulation

Allosteric regulation occurs when a site other than the active site on an enzyme binds to a molecule (activator or inhibitor) that changes the enzyme's shape. This alters the enzyme's ability to bind to the substrate.
Allosteric enzymes have more than one polypeptide chain and have both active and inactive conformations.
Enzymes have varying numbers of active and inactive conformations.

Cellular Respiration Overview

Aerobic respiration is a process that uses oxygen to extract energy from glucose via glycolysis, the Krebs cycle, and the electron transport chain.
Respiration is an oxidation-reduction process that involves the transfer of electrons from glucose to oxygen.
Glucose is partially oxidized during glycolysis and completely oxidized during the Krebs cycle.
Energy is released in small amounts in a series of reactions.
In the electron transport chain (ETC) electrons are moved down the chain until they reach oxygen and water is formed.
Chemiosmosis is the process that uses the generated H+ gradient to make ATP indirectly via ATP synthase.

Glycolysis

Glycolysis is the first stage of cellular respiration.
It happens in the cytoplasm.
It splits glucose in to two 3-C molecules and releases energy in two phases (investment and energy yielding).
Two ATPs are used in the investment phase and four ATPs are made in the energy yielding phase.

Pyruvate Shuttle (Between Glycolysis and Krebs Cycle)

Pyruvate is transported to the mitochondrial matrix
One carbon is removed as CO2.
NADH is produced.
The remaining two-carbon molecule combines with coenzyme A to form acetyl CoA.

Krebs Cycle (Citric Acid Cycle)

The Krebs cycle occurs in the mitochondrial matrix.
It completes the oxidation of organic fuel from acetyl COA and produces CO2 and electron-carrying molecules (e.g. NADH, FADH2).
It regenerates the starting material to run the cycle again.

Electron Transport Chain and Oxidative Phosphorylation

The electron transport chain (ETC) occurs in the inner membrane of mitochondria.
Electron carriers (proteins) transfer electrons from NADH and FADH2 to oxygen, releasing energy in the process.
The energy released is used to pump protons (H+) from the matrix to the intermembrane space to create a gradient.
Chemiosmosis uses the H+ gradient to produce ATP.

ATP production

Substrate level phosphorylation occurs directly when a phosphate group is transferred to ADP from a substrate. This produces a small amount of ATP.
Oxidative phosphorylation (via chemiosmosis) occurs indirectly when the H+ gradient that is created is used to power ATP synthase.

Oxygen Requirements

Organisms can be strict aerobes (need oxygen), strict anaerobes (cannot tolerate oxygen), or facultative anaerobes(can survive with or without oxygen).

Fermentation

Fermentation is an anaerobic process that occurs when oxygen is not available.
It starts with glycolysis but does not produce any additional ATP (ATP created in glycolysis is the only ATP net).

Catabolism of Other Molecules

Other molecules are broken down and converted into molecules that can be used in glycolysis or the Krebs cycle.

Control of Respiration

Feedback inhibition is a control mechanism that helps maintain a stable metabolic rate.
Enzymes are often regulated allosterically by molecules like ATP, ADP, citrate.

Photosynthesis Overview

Photosynthesis converts light energy into chemical energy stored in sugars.
Carbon dioxide, water, and light energy are required.
Photosynthesis takes place in Chloroplasts (Thylakoid membranes and Stroma).
Oxygen is released as a byproduct.

Chloroplasts Parts

Chloroplasts are surrounded by an outer and inner membrane.
Thylakoids are membrane pouches within chloroplasts containing chlorophyll and are often stacked in stacks called grana.
Stroma is the solution surrounding the thylakoids.

Photosynthetic Prokaryotes

Photosynthetic prokaryotes (like cyanobacteria) do not have chloroplasts.
Photosynthetic pigments in these organisms are found embedded in their plasma membranes.

Photosystems

A photosystem has an antenna complex and a reaction center.
Photosystem I absorbs far-red light best (700 nm). Cyclic electron flow
Pigments channel energy to the P700 reaction center in Photosystem I.
Electrons are passed along an ETC until they return to their original stage in P700, thus cycling back.

Non-Cyclic electron flow

Involves both photosystem I and photosystem II.
Electrons are passed to NADP+ with H+ from water producing NADPH (high energy electron).
Water is split to replace electrons lost from photosystem II to keep the cycle going.

Calvin Cycle

The Calvin cycle is a carbon-fixation process that converts carbon dioxide into carbohydrates using ATP and NADPH produced in the light reactions.
RuBP carbon fixation is cyclic (RuBP is the starting and ending molecule).
The products of the Calvin cycle (e.g. G3P molecules) can be used to synthesize sugars, starch, and cellulose.

Photorespiration:

Reduces sugar yield in photosynthesis during hot, dry days.
Oxygen competes with carbon dioxide at the active site of the enzyme Rubisco, creating a 2-C molecule that is oxidized.

C4 and CAM Plants

C4 plants minimize photorespiration by concentrating CO, in cells where the enzyme PEP (not Rubisco) fixes CO2 first. This fixes organic acids (4-carbon molecules) in mesophyll cells that release CO2 and pass it to cells with Rubisco in close proximity, helping keep CO2 concentrations high.
CAM plants separate the carbon fixation and Calvin cycles by performing them during different times of the day (stomata open at night, to minimize water loss). These plants fix CO2 at night when it is cool and store organic acids (4-carbon molecules) and then release CO2 for photosynthesis in the day, keeping stomata close to prevent excess water loss.

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Description

Test your knowledge on the characteristics of cofactors, the processes of cellular respiration, and the roles of enzymes. This quiz covers key concepts including oxidation, energy flow, and ATP synthesis. Perfect for students studying biochemistry topics in detail.