Chapter 3- Human Biology

Enzymes, Cellular respiration etc..

What is an enzyme?

globular protein which acts as biological catalyst by speeding up the rate of chemical reaction.

• enzymes not changed or consumed by reactions, they catalyse, thus can’t be re-used

• Typically names after the molecules they react with (substrate), end with suffix-ase

What is a substrate?

Molecules that the enzyme reacts with

What is an active site?

region on the surface of the enzyme which binds the substrate

What is an enzyme-substrate complex?

structure produced during a reaction when the enzyme and substrate become joined together for a short period of time.

Only a specific substrate is capable of binding to a particular enzyme’s active site (Restricted by size, shape and chemical properties)

What is the lock and key model?

• folding of an enzyme formed a fixed groove, or a pocket-shaped active site

• Groove can accomodate one or more particular substrate molecules

• Active site highly specific for particular substrate

• Substrate must be of a comparable shape for binding to occur

What is the indices fit model?

• More accepted than lock-and-key

• Substrate molecule entered enzyme’s active site, forming weak bonds that cause the enzyme molecule to change its shape so the two molecules fit tgt more closely

• as result blind within substrate are strained and lowers the activation energy required to kick-start reaction

• TOXIC RELATIONSHIP!!!

What does the indices fit model explain?

• Explains how enzymes may exhibit broad specificity (lipase can bind to a variety of lipids)

• Explains how catalysis may occur (conformational change stresses binds in the substrate, increasing reactivity)

Factors affecting reactions and enzymes

1- Concentration of enzymes

2- Substrate concentration

3- Products must be continually removed

4- temperature

5- pH

6- Cofactors and Coenzymes

7- Inhibitors

How does the concentration of enzymes affect reactions?

• Enzyme concentration regulated in response to the needs of the cell

• Achieved by controlling production of protein, breaking down enzyme or by activating the enzyme in response to stimulus.

• Higher the concentration of enzyme = faster rate of reaction because there are more enzymes to influence the reactants

How does Substrate concentration affect reactions?

• higher concentration of substrate (reactant) = faster reaction rate because there are more molecules to interact with each other and the enzymes

• Increasing substrate to a certain concentration will cease to have an effect because active sites in enzyme molecules will be fully occupied

How does removing products affect reactions?

• rate of reaction will slow because it becomes more difficult for the substrate molecules to make contact with the enzyme molecules (if not removed)

• If products are continually removed, the reactions will stop once equilibrium is reached

How does Temperature affect reactions?

• enzymes have an optimal temperature range in which they operate, which will align with the environment they are found in

• Enzymes can’t work if the temp is too high, they die

• ~37 perfect, too high will denature

What is denaturation?

• when structure of enzyme has been permanently compromised by changes in environment, resulting in active site no longer being compatible with its substrate

• If enzyme structure is affected, enzyme not work efficiently

How does pH affect reactions?

• each enzyme has optimum pH

• Some work in broad range, others sensitive and only work in narrow range

• Relates to environment they are found in

How do Cofactors and Coenzymes affect reactions?

• some enzymes inactive until they bind with cofactors or coenzymes that change their conformation (shape) thus changing active site to more efficiently capture substrate molecules

• Cofactors are small inorganic substances

• Coenzymes are non-protein in organic substances

How do inhibitors affect reactions?

• competitive inhibitors are molecules that can bind to the active site, locking the substrate from binding and thus preventing the reaction

• Non-competitive inhibitors, bind to secondary site on enzyme, changing enzyme shape and making it incompatible to the intended substrate, thus slowing the rate of reaction

What is cellular respiration?

• process in which organisms take molecules broken down food and release the chemical energy stored in chemical binds of those molecules

• Food NOT direct source of energy

What is the chemical formula of cellular respiration?

What is the energy used for from cellular respiration?

• in complete break down of Glucose, CO2, Water ~60% of energy released as heat

• Remaining energy is used for a compound called adenosine triphosphate (ATP)

What is ATP?

• Adenosine triphosphate (ATP) is the energy-carrying molecule used in cells because it can release energy very quickly

• Made of 3 phosphate groups

How is energy from ATP released and what does it become?

• energy is released when end phosphate removed

• Once ATP has released energy, becomes ADP (adenosine diphosphate), which is a low energy molecule

How can ADP be recharged back into ATP??

• by adding phosphate

• Requires energy

• Adding energy to adenosine + 2 phosphate groups = ATP

• Molecules can be recycled so constant stream of energy-rich ATP is available for all metabolic pathways in cell

• Almost alll cellular processes need ATP to give reaction its required energy

What will ATP be used for?

• releases energy for cellular metabolic processes

• Active transport of molecules across cell membrane

• Protein synthesis

• Muscle contractions

Aerobic vs Anaerobic respiration

• overall, cellular respiration is AEROBIC

• Aerobic: requires presence of oxygen

• Aerobic: do not require presence of oxygen

Where does cellular respiration occur?

• mitochondria and cytoplasm of the cell

What are the 3 major steps of Cellular respiration?

1. Glycolysis (anaerobic)

2. Kerbs Cycle (aerobic)

3. Electron Transport Chain (aerobic)

What is Glycolysis?

• process of breaking down glucose into 2 molecules of pyruvate

• Occurs in cytoplasm

• ANAEROBIC

• 2 ATP

• 2 NADH produced

What happens after glycolysis?

How does glycolysis turn into the Krebs cycle?

Through a link reaction (Acetyl-CoA)

• b4 pyruvic acid enters the Krebs cycle, combines with an enzyme called Conenzyme A (CoA)

• Reaction produces molecule Acetyl CoA

• ^ produced by almost all nutrients b4 entering Krebs cycle

What is the Krebs Cycle?

reactants: Acetyl CoA

Produces: CO2, NADH, FADH

Makes 2 ATP (1 EVERY CYCLE, 2 CYCLE TOTAL)

Location: Mitochondria

AEROBIC

What is The Electron Transport Chain

Reactants: NADH, FADH, O2

Products: H20

Makes ~26-34

Location: Mitochondria

What is the process of an Anaerobic Pathway?

• Anaerobic respiration (glycolysis)

• Fermentation

If there is no oxygen available, pyruvate produced in glycolysis is the converted to lactic acid by fermentation

Anaerobic respiration- fermentation

• production of lactic acid from Glucose is called anaerobic respiration

• Allows cells to produce some energy in the absence of oxygen

• Important during vigorous physical activity

• Pyruvate converted to lactic acid