Biology - Enzymes (sem 2)

Metabolism

• Reactions that occur inside of cells and organisms

• Products of these reactions are important for cellular functioning

• There two general types of metabolic reactions - ana, cata

• All metabolic reactions are regulated by enzymes

Anabolic Reactions

• Building reactions

• When two simple form a complex

• Photosynthesis is a common example

• eg, CO2 + H2O → C6H12O6

Catabolic

• Breaking down reactions

• When a complex becomes multiple simple products

• Cellular respiration is a common example

• eg, C6H12O6 + O2 → CO2 + H2O

What is an enzyme?

• Enzymes are specialised proteins that act as biological catalysts. They reduce the activation energyrequired for the reaction to take place, enabling them to occur at a more efficient rate.

Enzyme anatomy

• enzymes have a unique shape that ensure they interact w/ specific molecules (substrates)

• The key area is the active site. This is where substrates bind to allow metabolism

• They are sensitive to environmental conditions. The rate of reaction changes if conditions change (tolerance ranges)

• Enzymes are not consumed and are able to rebind after the reaction

• Enzymes = proteins

What are the two models that explain enzyme activity?

• Lock and key

• Induced fit

Exergonic reactions

• These reactions release energy

• Referred to as downhill reactions

• Always catabolic reactions

• eg, When molecular bonds are broken down, energy is realeased

Endergonic reactions

• Happens when molecular bonds are formed

• Referred to as uphill reaction

• eg, photosynthesis

Enzyme binding

• For enzymes to be able to complete their reaction on a substrate they must bind with it.

• The active site is where the substrate will bind and be metabolised

• Enzymes are specific with which substrate they interact with and to explain this behaviour, two models exist.

Lock and Key Model

• The lock and key model states that the enzymes active site has a specific shape and will only interact with substrates that fit the exact shape

• This model limits the number of substrates enzymes can interact with

• With enzymes being this specific it results in biochemical pathways and metabolic reactions requiring many enzymes

Lock and Key Diagram

Induced Fit Model

• The enzyme active site is more flexible and results in the enzyme being able to interact with many substrates

• The enzyme can therefore be involved in many reactions due to the variety of substrates it can interact with.

Induced Fit Diagram

Environmental Influence on Enzyme

• Enzymes are sensitive to environmental conditions. This sensitivity stems from the organisms evolution and tolerance ranges.

• Sensitivity impacts the reaction rate (impacting metabolism and impacting survivability of the organism)

What are the main environmental factors?

1. Temp

2. pH

3. a) Substrate concentration

   b) Enzyme concentration

4. Inhibitors

   • Competitive

   • Non competitive

Environmental influence - 1. Temperature

• Enzymes have optimal temperatures where the reaction rate is at its highest

• Temp can impact enzyme activity by increasing or decreasing it. As temp reduces (lowers), the kinetic energy of the objects (enzyme and substrate) decrease, reducing collisions and reducing the enzyme reaction.

• So, as temp increases, the kinetic energy increase, therefore increasing reaction rate. If temp increases beyond the optimum, the enzyme is at risk of denaturing.

Denaturing

• This is the irreversible change to an enzymes functional shape preventing the binding of substrates to enzymes active sites.

Temp - In Relation to the 4 Levels of Structure.

1. Primary structure

   • Not affected by theat as petife chains are strong and usually stay intact

2. Second structure

   • Broken down by heat, this is due to disrupting hydrogen bonds

3. Tertiary structure

   • Disrupted by heat

4. Quaternary structure

   • Disrupted as heat breaks non-covalent interactions holding subunits together.

Environmental influence - 2. pH

• The solution surrounding an enzyme and substrate can have differing levels of acidity or alkalinity

• This impact an enzymes shape as deviations impacts the bonding that occurs within an enzyme and can lead to denaturing

• Most enzymes have an optimum pH at or close to neutral, however, theure are some unique cases such as pepsin in the stomach which has an optimum of 1, and amylase in saliva has an optimum of 7.

• Deviations in pH can impact substrate shape and prevent binding to required enzymes, therefore lowering r.r.

Environmental influence - 3. Substrate and Enzyme concentration

• Amount of substrate and enzyme limits how much product is produced in a reaction

• More substrate leads to more product until all enzymes are working at full capacity

• Increasing enzyme concentration causes product levels to rise exponentially until the substrate is all used up or products starts to inhibit the enzyme

• The reaction rate is proportional to enzyme concentration as long as there is excess substrate

• Enzyme concentrations are regulated by cells based on needs. This happens through

  • controlling enzyme production

  • breaking down enzymes

  • activating enzymes in response to stimuli

Cofactors and Coenzymes

• Some enzymes are inactive until they bind with other molecules or ions that change their shape

• This changes the active sites shape and charge, allowing it to better bind substrates and catalyse reactions

• Two types of substances can help activate enzymes

  • Cofactors

    • small inorganic substances

  • Coenzymes

    • small, non protein molecules

    • required for enzyme activity

    • act as carriers to and from reactions

    • often made from dietary vitamins

Environmental influence - 4. Inhibitors

• Inhibitors are molecules that reduce reaction rate by preventing enzymes from interacting with substrates

• Two types exist

  • Competitive

  • Non Competitive

Competitive Inhibitor

• The competitive inhibitor will bind to the enzymes active site, it then blocks the substrate from binding and reduces the reaction by preventing the formation of the enzyme - substrate complex.

Competitive Inhibitor - Diagram

Non Competitive Inhibitor

• Is a molecule that binds with the enzyme, away from the active site, but sue to the formation of new bonds, the enzyme active site changes shape

• As the active site shape changes the substrate will no longer be able to bind, therefore an overall reaction rate

Non Competitive Inhibitor - Diagram

Common Inhibiotors

1. Penicillin

2. Aspirin

3. Mercury

Penicillin - Competitive

• Target enzyme - Transpeptidase

• Mechanism:

  • Penicillin mimics the substrate and binds the the active site

  • Forms a covalent bond, permanently deactivating it

• Effect:

  • Weakens bacterial cell walls leading to cell lysis

Aspirin - Competitive

• Target enzyme - Cyclooxygenase

• Mechanism:

  • Blocks prostaglandin synthesis (causing pain)

• Effect:

  • Reduces pain, fever, and inflammation

Mercury - Non competitive

• Target enzyme - Any enzyme with sulfhydryl

• Mechanism:

  • Mercury binds tightly to sulfhydryl groups, causing enzymes to denature or lose function

• Effect:

  • Disrupts cellular metabolism, especially in nervous tissue

  • Causes symptoms of mercury poison

Why would enzyme action be inhibited?

• Medications inhibit enzymes to block unwanted processes

Common Enzymes

1. Cellulase

2. Amylase

3. Protease

4. Lipase

Cellulase

• Some cellulase can be found in small amounts in the gut, from gut micro bacteria

• The role of cellulase is to break down cellulose into simple sugars like glucose or cellobiose

• In humans most cellulose passes through undigested acting as dietary fibre

Amylase

• Amylase is an enzyme produced in the salivary glands to produce salivary amylase (ptyalin). It is also produced by the pancreas to produce pancreatic amylase

• Amylase breaks down starch (polysaccharide) into simpler sugars like maltose (disaccharide), and eventually glucose (monosaccharide).

Protease

• Protease is produced by and formed in the stomach → pepsin, the pancreas → trypsin + chymotrypsin, and small intestine lining.

• Protease breaks down proteins into smaller peptides and amino acids, which the body can absorb and use to build own proteins

Lipase

• Lipase is produced by and found in the pancreas → pancreatic lipase, the mouth → small amounts of lingual lipase, and the stomach to form → gastric lipase.

• The role of lipase is to break down lipids (fats and oils) into glycerol and fatty acids