Biochemistry and the environment

Question 1

What are Xenobiotics?

Answer 1

• Foreign chemical compounds that enter an organism and interfere with biological processes, compound usually not found there
• Can have negligible or severe effects on metabolic processes
• Xenobiotics come from pollutants that are disposed of in waste or landfills
• Foreign compounds: plastics, pesticides, pharmaceutical compounds, chemical solvents

Question 2

What is antibiotic waste? How is it harmful to the environment?

Answer 2

• Antibiotics are used to treat bacterial infections, expired or unused antibiotics can contaminate environment, antibiotic resistance
• Animals injected with antibiotics to prevent and control infections can also release them
• Excreted animal waste may contain antibiotic-resistant bacteria and flow into wastewater system or soil
• Antibiotics in bodies of water or soil can kill ‘good’ bacteria and allow ‘bad’ bacteria to grow
• To remove antibiotics, activated sludge process can be used (bacteria metabolise the compound, remove it from water), some are resistant to metabolism

Question 3

What is biomagnification? How is it harmful to the environment?

Answer 3

• It is the increase in concentration of a substance as it moves up through the food chain, concentration increases with each level
• When one organism eats another that has stored xenobiotics, concentration increases
• Non-polar and water-insoluble tend to accumulate, cannot easily dissolve in bloodstream, accumulate in liver or fatty tissues

Question 4

What are pesticides? How is it harmful to the environment?

Answer 4

• A DDT is a pesticide that is colourless, tasteless, nearly odourless, ideal for adding to crops (cannot be detected by consumer)
• Insects began to develop a resistance to DDT, decreasing the effectiveness of the compound
• DDT accumulated in insects, moving up the food chain, became toxic to larger animals, hence banned in 2004

Question 5

What are heavy metals? How is it harmful to the environment? Give an example.

Answer 5

• Heavy metals accumulate in organisms, results in biomagnification
• Cannot easily be broken down by metabolic processes because some have a high affinity for tissues and become stored and not excreted
• Mercury in the form of methylmercury is formed by aquatic microbes
• The presence of methyl group makes compound non-polar with poor water solubility, can easily cross fat layer, causes toxic neutral effects, interferes with functions of proteins

Question 6

What are properties of plastic and why are they harmful for the environment?

Answer 6

• Made from addition polymers formed from alkenes, long chain of hydrocarbons
• Make plastic rigid or flexible, higher or lower density, durability
• Very difficult to break down over time, high levels of plastic waste, requires high temp or sunlight to break down
• When breaking down, produce harmful compounds
• Plastic waste in landfill sites not exposed to sunlight, lack of decomposition and can travel to natural habitats (ingested, entangled, chemicals)

Question 7

What is photodegradation?

Answer 7

• When sunlight breaks the covalent bonds in the plastic to break
• Polymer breaks into shorter sections, still harmful and ingested by aquatic animals

Question 8

What are biodegradable plastics?

Answer 8

• Substances that can be broken down by the process of biodegradation, involving bacteria, they can be natural bioplastics or synthetic (PET)
• When bacteria or other living organisms break down waste over time by consuming or digesting
• A bacteria can break down a plastic called PET, used in beverage bottles. Enzyme PETase can digest the polymer into individual monomers
• Bacteria uses these monomers to metabolise for energy

Question 9

What are bioplastics?

Answer 9

• Most plastics are petroleum-based, criticised for their inability to break down, not renewable
• Biodegradable plastics however can easily be digested by bacteria into harmless carbon dioxide and water
• Bioplastics: substances developed from renewable plant-based materials, made of starches, cellulose or biopolymers

Question 10

What role does starch play in biodegradable plastics?

Answer 10

• Starch is present in half of all bioplastics, they are completely biodegradable, durable and perform like traditional petroleum-based plastics
• Starch-based bioplastics made from renewable plant-based sources (corn, grasses), suitable for storing foods without any unwanted chemicals
• Ordinary bacteria can digest starch on landfills

Question 11

What is bioremediation?

Answer 11

• Process of using microorganisms, bacteria, to clean up waste by metabolising the harmful or toxic compounds into smaller products
• The bacteria may use enzymes that can help in the degradation of plastic waste

Question 12

What is host-guest chemistry?

Answer 12

• Formation of supramolecular complex formed between two or more molecules or ions held together by non-covalent bonds e.g. intermolecular forces, ionic, hydrogen
• These weaker bonds allow allow large molecules to bind specifically to form supramolecular complex

Question 13

How does host-guest chemistry work?

Answer 13

• Larger compound ‘host’ and smaller compound ‘guest’ form the complex
• Hosts are enzymes, guest toxins/pollutants
• The host mimic some of the actions performed by enzymes, synthetically produced (bind to specific guest)
• Type of interactions: hydrogen, dipole-dipole, ionic bonds
• Binding follows specific lock-and-key model, allows specific targeting and removal or toxins

Question 14

How are enzymes applied in the removal or toxins?

Answer 14

• Enzymes (host) used to clean up waste (guest) from chemical spills
• Oil spils are difficult to clean up, especially when in bodies of water
• Oil is non-polar and sticks to plants and wildlife, forms a coat that is difficult to remove
• Enzymes metabolise the oil, converts them into CO2 and H2O through diodegradation
• More of the oil can be targeted, oil is converted chemically into harmless products
• Enzymes allow the reaction to occur multiple times
• Enzymes also used to clean up other wastes, sewage and treatment facilities

Question 15

Give three examples of enzymes, which compounds they target and their industrial application.

Answer 15

• Protease: proteins used in food, leather and pharmaceutical
• Cellulase: cellulose used in textile, pulp & paper
• Lipase: lipids used in food cosmetic, pulp & paper

Question 16

How are enzymes used in biological detergents?

Answer 16

• Detergents are water-soluble, sued to dissolve impurities, effective cleansing agents
• Detergents are amphiphilic, have polar and non-polar froups, allow to attract polar and non-polar impurities
• They form a micelle around impurities, allow them to become more soluble in water
• Enzymes digest impurities, make more soluble and easier to wash away
• Uses multiple enzymes: lipase, protease, amylase

Question 17

What are advantages of biological detergents?

Answer 17

• Washing at lower temperatures, reducing energy requirements
• Require less detergent
• More effective stain removal for a variety of stains
• Less pre-treating of stains required with other products

Question 18

What is green chemistry?

Answer 18

• Aims to reduce waste and energy to produce safer compounds, also limit the use and production of harmful compounds in the process into the environment

Question 19

What are the 7 principles of green chemistry?

Answer 19

1. Prevention of waste
2. Atom economy
3. Less hazardous chemical design and synthesis
4. Safer and restricted use of solvents
5. Energy efficiency
6. Design for degradation
7. Catalysis

Question 20

Explain the first three principles of green chemistry.

Answer 20

1. Prevention of waste: prevent waste, rather than cleaning up waste
2. Atom economy: synthesis of a compound, all materials used should be incorporated into the final product, avoid leftover materials (byproducts)
3. Less hazardous chemical design and synthesis: Compound with little or no toxicity should be developed

Question 21

Explain the last four principles of green chemistry.

Answer 21

4. Safer and restricted solvents: safer solvents used, recycled when possible, use of no solvents preferred
5. Energy efficiency: Amount of energy used to make compounds should be kept to a minimum
6. Design for degradation: Compounds generated, designed to break down into harmless compounds, not remain in environment
7. Catalysis: selective catalytic reagents should be used when possible, reduce waste generated

Question 22

How can enzymes be considered ‘green’?

Answer 22

• Enzymes provide more efficient reaction
• They are regenerated following a reaction (used over again), hence less material waste is generated
• Enzymes secreted by microorganisms can also be used to treat waste, safer for disposal

Question 23

How can the choice of a solvent be considered ‘green’?

Answer 23

• Solvent in aqueous medium, easier disposal
• Use bufffers to maintain a limited pH range
• Good choice of buffer agents ensures that the chemical waste produced is safe for disposal

Question 24

What is energy efficiency, how may high temperatures be disadvantageous?

Answer 24

• Biochemical reactions must be performed at same temperature the organism operates
• Many experiments performed at higher temps to increase rate of reaction, may lead to denaturation of biomolecules

Question 25

How can waste production be made safer?

Answer 25

• Waste generated can be infectious, may end up in water supply
• Treating living organisms (yeast) with bleach, can destroy them, can end in water supply
• Avoid further growth of organism and avoid contamination
• For robust pathogens, sterilisation with chemical agents often not enough
• Autoclaving method that uses heat and steam to sterilise waste and equipment

Question 26

How are substance classified as ‘green’?

Answer 26

• Several factors must be examined before a substance can be accepted as ‘green’.
• Uses Green chemistry metrics, system used to measure the ‘greenness’ of a substance

Question 27

How is the yield accessed to determine whether a substance is green? What are its challenges?

Answer 27

• Reactions with a percentage yield approaching 100%, there would be very little waste leftover
• The process would be efficient in terms of waste production, but it may be at the cost of other green chemistry principles
• Might require more energy, reducing overall greenness of the process or might produce large quantities of an undesirable byproduct

Question 28

How is the atom economy used to determine whether a substance is green?

Answer 28

• This encourages using all materials involved in the reaction to make the final product, restricting production of leftover compounds
• It takes the mass of reactants including catalysts into consideration
• The solvent used, is ignored in the final product
• Encourages the reduction of waste
• A high atom economy (near 100%) is valued as a green principle

Question 29

What is the challenge with atom economy?

Answer 29

• Many biochemical reaction involve use of enzymes, which are regenerated and not consumed in the reaction
• Hence the catalysts does not fulfill the catalysis principle, hence atom economy not always appropriate for all reactions assessing greenness
• Catalysts promote a pathway requiring less energy, not factored into atom economy measurement, but is important principle of green chemistry
• Hence a reaction without a catalyst might have a higher calculated atom economy but greater energy requirement, less green