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Questions and Answers
What is the primary function of metabolism in cells?
What is the primary function of metabolism in cells?
Which term describes the process of building larger molecules from smaller ones?
Which term describes the process of building larger molecules from smaller ones?
What characterizes catabolic reactions?
What characterizes catabolic reactions?
How do enzymes function in metabolic reactions?
How do enzymes function in metabolic reactions?
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What is the role of substrates in enzymatic reactions?
What is the role of substrates in enzymatic reactions?
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What differentiates simple enzymes from conjugated enzymes?
What differentiates simple enzymes from conjugated enzymes?
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What happens to enzymes when they denature?
What happens to enzymes when they denature?
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Which of the following best describes an exergonic reaction?
Which of the following best describes an exergonic reaction?
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What is the name of the protein portion of a conjugated enzyme?
What is the name of the protein portion of a conjugated enzyme?
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Which type of cofactor is classified as organic?
Which type of cofactor is classified as organic?
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What mechanism do enzymes follow when catalyzing reactions?
What mechanism do enzymes follow when catalyzing reactions?
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Which class of enzymes is responsible for cleaving bonds on molecules with the addition of water?
Which class of enzymes is responsible for cleaving bonds on molecules with the addition of water?
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What distinguishes exoenzymes from endoenzymes?
What distinguishes exoenzymes from endoenzymes?
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Which example describes a constitutive enzyme?
Which example describes a constitutive enzyme?
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Which enzyme class is not involved in transferring functional groups?
Which enzyme class is not involved in transferring functional groups?
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What is the role of metallic cofactors in enzyme activity?
What is the role of metallic cofactors in enzyme activity?
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What is the maximum yield of ATP from anaerobic respiration?
What is the maximum yield of ATP from anaerobic respiration?
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Which process exclusively utilizes glycolysis for ATP production?
Which process exclusively utilizes glycolysis for ATP production?
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What compound is pyruvic acid converted to before entering the Krebs cycle?
What compound is pyruvic acid converted to before entering the Krebs cycle?
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What is the primary role of the electron transport system in ATP synthesis?
What is the primary role of the electron transport system in ATP synthesis?
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Which of the following is an end product of alcoholic fermentation?
Which of the following is an end product of alcoholic fermentation?
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What is the primary role of NAD in metabolic reactions?
What is the primary role of NAD in metabolic reactions?
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What causes the release of energy when ATP is converted to ADP?
What causes the release of energy when ATP is converted to ADP?
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Which of the following is NOT one of the basic catabolic pathways?
Which of the following is NOT one of the basic catabolic pathways?
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What is the primary purpose of substrate-level phosphorylation?
What is the primary purpose of substrate-level phosphorylation?
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Which process uses sunlight-driven reactions to form ATP?
Which process uses sunlight-driven reactions to form ATP?
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What occurs during enzyme repression?
What occurs during enzyme repression?
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What distinguishes competitive inhibition from noncompetitive inhibition?
What distinguishes competitive inhibition from noncompetitive inhibition?
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How do exergonic and endergonic reactions interact?
How do exergonic and endergonic reactions interact?
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Which statement about oxidation and reduction is correct?
Which statement about oxidation and reduction is correct?
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What role does phosphorylation play in cellular energy transfer?
What role does phosphorylation play in cellular energy transfer?
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What triggers the induction of enzymes?
What triggers the induction of enzymes?
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In the process of noncompetitive inhibition, what happens to the enzyme?
In the process of noncompetitive inhibition, what happens to the enzyme?
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Generally, what is the effect of substrate concentration on enzyme activity?
Generally, what is the effect of substrate concentration on enzyme activity?
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Study Notes
Metabolism
- All the chemical reactions and workings of a cell
- Accomplishes processes through anabolism and catabolism
- Conserves energy in the form of ATP or heat
- Electrons are critical to metabolic processes
Anabolism
- Making smaller molecules into larger molecules
- Also known as biosynthesis, the synthesis of cell structures
- Requires the input of energy
Catabolism
- The opposite of anabolism
- Breaking down larger molecules to release energy
- Related to exergonic reactions, which release energy
Enzymes
- Catalysts that speed up the rate of a chemical reaction without becoming part of the products or being consumed in the reaction
- Speed up reactions by about 1000x million times compared to a reaction without enzymes
- Bind to substrates and participate directly in changes to the substrate, but do not become part of the product, are not used up in the reaction, and can function repeatedly until they denature or are shut off.
- Substrates are the reaction molecules with which the enzymes interact
The Structure of Enzymes
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Enzymes can be simple or conjugated
- Simple enzymes consist of the protein alone.
- Conjugated enzymes, also known as holoenzymes, contain a protein and some other non protein molecule.
- The protein portion of the conjugated (holoenzyme) is called the apoenzyme. This is where the substrate binds, and is also called the active site or the catalytic site.
- The nonprotein portion of the holoenzymes is called a cofactor.
- Organic cofactors are called coenzymes; Inorganic cofactors are metallic cofactors.
- Organic cofactors (coenzymes) work with the apoenzyme to alter the substrate. They remove a chemical group from one substrate and add it to another substrate. They can carry and transfer hydrogen atoms, electrons, carbon dioxide, and amino groups.
- Metallic (non-organic) cofactors such as iron, copper, magnesium, zinc, cobalt, selenium, etc. assist with precise functions between enzyme and substrate. They help bring the substrate and active site to each other and participate directly in chemical reactions.
- Organic cofactors are called coenzymes; Inorganic cofactors are metallic cofactors.
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Enzymes have their own primary structure, variations in folding, and a unique active site specific to the substrate.
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Enzymes follow a lock & key mechanism.
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Enzyme processes take place very quickly, up to 1 million times per second!
Six Classes of Enzymes
- Oxidoreductases: transfer electrons from one substance to another OR
- Dehydrogenases: transfer a hydrogen from one compound to another
- Transferases: transfer functional groups from one substrate to another
- Hydrolases: cleave bonds on molecules with the addition of water
- Lyases: add groups or remove groups from double-bonded substrates
- Isomerases: change a substrate to its isomeric form (same formula, different atomic arrangements)
- Ligases: catalyze the formation of bonds with the input of ATP and the removal of water
Location of Enzymes: Exoenzymes and Endoenzymes
- Exoenzymes are more harmful to host cells. They are transported extracellularly and break down large food molecules or harmful chemicals. They are made within the cell and transported out of the cell.
- Endoenzymes are made within the cell and function within the cell. Most enzymes of metabolic pathways are endoenzymes.
Enzyme Regulation
- Enzymes can either be constitutive enzymes or regulated enzymes.
- Constitutive enzymes are present in relatively consistent amounts, regardless of the cell’s environment. An example would be enzymes used for glucose, because glucose is an extremely constant molecule utilized by cells.
- Regulated enzymes can either be induced or repressed in response to changed in concentration of the SUBSTRATES.
- Enzyme repression stops further synthesis of an enzyme somewhere along its pathway.
- Types of inhibition/repression of enzymes
- Competitive inhibition is when a molecule resembles the substrate and occupies the active site, preventing the substrate from binding. Because of this, the enzyme cannot get rid of the inhibitor and shuts down.
- Noncompetitive inhibition: an enzyme may have different binding sites, a binding site and a regulatory site. When the regulatory molecule binds to the enzyme, it chemically changes the active site. This process is caused by when a certain concentration of a product is reached and the enzyme is not needed.
- Types of inhibition/repression of enzymes
- Enzyme induction
- Enzymes are only induced/appear when a suitable substrate is present; this is the inverse of enzyme repression.
- Enzyme repression stops further synthesis of an enzyme somewhere along its pathway.
Energy in Cells
- Exergonic reactions: release energy as they go forward; energy is available for doing cellular work.
- Endergonic reactions: require the addition of energy to move forward.
- Both exergonic and endergonic reactions are coupled together. The released energy from exergonic reactions are immediately used for endergonic reactions.
Biological Oxidation and Reduction
- Oxidation: loss of electrons; the compound that loves the electron is oxidized (broken down)
- Reduction: gain of electrons; the compound that receives the electron is reduced
- Generally, a reduced molecule has more energy than the oxidized molecule.
Phosphorylation
- The energy captured in the electron carrier is used to phosphorylate (add inorganic phosphate) to ADP or another compound.
- Stores energy in a high energy molecule such as ATP.
Electron Carriers
- Different electron carriers exist, with the most common being NAD (nicotinamide adenine dinucleotide).
- NAD carries hydrogens and electrons from dehydrogenation reactions.
- Dehydrogenation reactions occur during a redox reaction when hydrogens are removed from a compound.
- Reduced NAD looks like this: NADH H+ or NADH.
- The NADH can now transfer the H+ ion to pave the way for another metabolic reaction. In other words, NAD is an electron carrier.
ATP: universal currency for energy!
- Made up of adenine (nitrogenous base) + ribose (5-carbon sugar), and three phosphate groups binded to the ribose
- The phosphate group is bulky, with a negative charge. Their repelling electrostatic charges imposes a strain between the last two phosphate groups, and the breaking of the phosphates releases a lot of energy.
- ATP replenishment is an ongoing cycle; when it is used in a chemical reaction, it must be replaced immediately.
Metabolic Roles of ATP
- Substrate-level phosphorylation: the generation of ATP through a transfer of a phosphate group from a phosphorylated compound directly to ADP.
- Oxidative phosphorylation: a series of redox reactions occurring during the final phase of the respiratory pathway.
- Photophosphorylation: ATP formed through a series of sunlight-driven reactions in phototrophs.
Three Basic Catabolic Pathways
- Aerobic respiration
- Anaerobic Respiration
- Fermentation
Glycolysis: most commonly used to breakdown glucose!
- Aerobic respiration converts glucose to CO2 and allows the cell to recover significant amounts of energy.
- Uses: glycolysis, Krebs cycle, and ETC
- Yields: 36-38 ATPs
- Aerobic respiration: energy yielding scheme for aerobic heterotrophs.
Anaerobic Respiration
- Utilizes glycolysis, Krebs Cycle, and the ETC; however, yields 2-36 ATPs; final electron acceptor can be NO3-, SO4 2-, CO3 2- or other OXIDIZED compounds.
Fermentation
- Only uses glycolysis; oxygen is NOT required.
Glycolysis
- Glucose is enzymatically converted to pyruvic acid; synthesizes a small amount of ATP
- Pyruvic acid allows strict aerobes and some anaerobes to send it to the Krebs cycle for processing and energy release; facultative anaerobes utilize it for acids or other products.
The Krebs Cycle
- Pyruvic acid is converted to acetyl CoA before entering the cycle, then is converted to citric acid. NADH is formed is moved to the ETC to produce ATP; all reactions in the Krebs Cycle occurs twice.
- The Krebs cycle yields: 4 CO2, 6 NADH, 2 FADH2, and 2 ATP (reduced NADH and FADH2 and 2 ATP through substrate-level phosphorylation).
The Electron Transport System
- Receives the electrons from NADH and FADH2; ATP synthase synthesizes ATP from H+ ions that allow it to go through the cell membrane and bind with ADP to form ATP.
- The proton motive force is the concentration gradient of hydrogen ions through the membrane; in prokaryotic cells, this happens in the cytoplasmic membrane; in eukaryotic cells it occurs in the mitochondrial membranes.
- Yields 34 ATP
Fermentation
- The incomplete oxidation of glucose or other carbohydrates in the absence of oxygen
- Uses organic compounds as the terminal electron acceptors
- Only yields 2 ATP
- End products of alcoholic fermentation are ethanol and CO2; occurs in yeast or bacterial species.
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Description
Explore the intricacies of metabolism, including the processes of anabolism and catabolism. Learn how enzymes function as catalysts to accelerate chemical reactions and their roles in energy conservation. This quiz covers essential concepts of cellular chemistry and energy transformation.
