Metabolism and The Role of Enzymes
Metabolism: Pertains to all chemical reactions and physical workings of the cell
Anabolism:
Any process that results in the synthesis of cell molecules and structures
A building process that forms larger macromolecules from smaller ones
Requires the input of energy
Catabolism:
Breaks the bones of larger molecules into smaller molecules
Releases energy
Metabolism performs these functions:
Assembles smaller molecules into larger macromolecules - ATP (energy) is utilized to form bonds (anabolism)
Degrades macromolecules into smaller molecules, a process that yields energy (catabolism)
Stores energy in the form of ATP (adenosine triphosphate)
Enzymes: Catalyzing the Chemical Reactions of Life
Enzymes
Chemical reactions of life cannot proceed without them
Are catalysts that increase the rate of chemical reactions without becoming part of the products or being consumed in the reactions
Concept Check - 1
Anabolism and catabolism constitute the sum of reactions in the cell known as _____.
A. Binary fission
B. Metabolism
C. Energy balance
D. Mutation
How Do Enzymes Work?
Reactants are converted into products by bond formation or bond breakage
Substrate: Reactant molecules acted on by an enzyme
Speed up the rate of reactions without increasing the temperature
Much larger than substrates
Have a unique active site on the enzyme that fits only the substrate
Checklist of Enzyme Characteristics
Most composed of protein; may require cofactors
Act as organic catalysts to speed up the rate of cellular reactions
Have unique characteristics such as shape, specificity, and function
Enable metabolic reactions to proceed at a speed compatible with life
Have an active site for target molecules called substrates
Are much larger than their substrates
Associate closely with substrates but do not become integrated into the reaction products
Are not used up or permanently changed by the reaction
Can be recycled, thus functioning in extremely low concentrations
Are greatly affected by temperature and pH
Can be regulated by feedback and genetic mechanism
Conjugated Enzyme Structure
Metallic cofactor
Coenzyme
Coenzyme and Metallic cofactor
All of them made apoenzymes
Cofactors: Supporting the Work of Enzymes
The need of microorganisms for trace elements arises from their roles as cofactors for enzymes
Iron, copper, magnesium, manganese, zinc, cobalt, selenium, etc.
Participate in precise functions between the enzyme and substrate
Help bring the active site and substrate close together
Coenzymes
Organic compounds that work in conjunction with an apoenzyme
The general function is to remove a chemical group from one substrate molecule and add it to another substrate molecule
Carry and transfer hydrogen atoms, electrons, carbon dioxide, and amino groups
Many derive from vitamins
Enzyme-Substrate Interactions
A temporary enzyme-substrate union must occur at the active site
Fit is so specific that it is described as a “lock-and-key” fit
The bond formed between the substrate and enzyme are weak adn easily reversible
Products are formed
Enzyme is free to interact with another substrate
Concept Check - 2
What is true about enzymes? They _________
A. are proteins
B. speed up reactions
C. are specific to substrates
D. are not consumers in reactions
E. all
Concept Check - 3
Micronutrients such as Cu, Fe, Mn, and Zn, are essential for microbes because they function as ________
A. coenzymes
B. cofactors
C. active site
D. apoenzymes
Concept Check - 4
Apoenzymes are _______ part of a conjugated enzyme
A. protein
B. protein + inorganic adjuncts
C. protein + organic adjuncts
D. Substrates
E. all
Metabolic Pathways
Often occur in a multistep series or pathway, with each step catalyzed by an enzyme
Products of one reaction are often the reactant (substrate) for the next, forming a linear chain or reaction
Many pathways have branches that provide alternate methods for nutrient processing
Others have a cyclic form, in which the starting molecule is regenerates to initiate another turn of the cycle
Do not stand alone; interconnected and merge at many sites
ATP: Metabolic Money
Three-part molecule
Nitrogen base (adenine)
5-carbon sugar (ribose)
Chain of three phosphate groups bonded to ribose
Phosphate groups are bulky and carry negative charges, causing a strain between the last two phosphates
The removal of the terminal phosphate releases energy
The Metabolic Role of ATP
ATP utilization and replenishment is an ongoing cycle
Energy released during ATP hydrolysis powers biosynthesis
Activates individual subunits before they are enzymatically linked together
Used to prepare molecules for catabolism
When ATP is utilized, the terminal phosphate is removed to release energy, and ADP is formed
Input of energy is required to replenish ATP
In heterotrophs, catabolic pathways provide the energy infusion that generates the high-energy phosphate to form ATP from ADP
Getting Materials and Energy
Nutrient processing in bacteria is extremely varied, but in most cases the nutrient is glucose
Aerobic respiration
Conversions of glucose CO2 with the production of energy (ATP)
Utilizes glycosis, the Kerbs cycle, and the electron transport chain (ETC)
Relies on free oxygen as the final electron and hydrogen acceptor
Characteristics of many bacteria, fungi, protozoa/animals
Anaerobic respiration
Used by strictly anaerobic organisms and those who are unable to metabolize without oxygen
Involves glycolysis, the Kerbs cycle, and the electron transport chain
Uses NO 3-, SO4 2-, CO3 3-, and other oxidized compounds as final electron acceptors
Fermentation
Incomplete oxidation of glucose
Oxygen is not required
Organic compounds are final electron acceptors
Concept Check - 5
The energy molecule ATP is made up of
A. Proteins
B. Adenine
C. Ribose + Adenine + 3P
D. Adenine + 3P
E. All
Concept Check - 6
Aerobic & Anaerobic - both types of cellular respiration - involve
A. Glycolysis
B. Krebs Cycle
C. Electron Transport System
D. All above
E. Only B, C
Glycolysis
Turns glucose into pyruvate, which yields energy in the pathways
The Krebs Cycle: A Carbon and Energy Wheel
Takes place in the cytoplasm of bacteria and in the mitochondrial matrix of eukaryotes
A cyclical metabolic pathway begins with acetyl CoA
Transfer the energy stored in acetyl CoA to NAD+ and FAD by reducing them
NADH and FADH2 carry electrons to the electron transport chain
2 ATPs are produced for each molecule of glucose through phosphorylation
Concept Check - 7
Glycolysis is the first step in catabolism that generates
A. Pyruvate
B. ATP
C. NADH
D. All above
E. Only B, C
Concept Check - 8
The Krebs Cycle starts with converting ______ into ______ that runs the wheel of releasing energy molecules.
A. Pyruvate, Acetyl CoA
B. ATP, NADH
C. NADH, Pyruvate
D. Acetyl, CoA, Pyruvate
The Respiratory Chain: Electron Transport
A chain of special redox carriers that receives reduced carriers (NADH, FADH2) generated by glycolysis and the Krebs cycle
Passes them in a sequential and orderly fashion from one to the next
Highly energetic
Allows the transport of hydrogen ions outside of the membrane
In the final step of the process, oxygen accepts electrons and hydrogen, forming water.
Primary