Biology CHEMICAL REACTIONS AND ENZYME ACTION

### KEY TOPICS

star Types of Changes
star Enzymes increase rate of reaction

### TYPES OF CHANGES

● Chemical compounds undergo color{brown}("two types") of changes.

● A physical change simply refers to a change in shape without color{violet}("breaking of bonds").

● This is a color{brown}("physical process.")

● Another physical process is a change in state of matter: when ice melts into water, or when water becomes a color{violet}("vapour.")

● These are color{brown}("physical processes.")

● However, when color{violet}("bonds") are broken and new bonds are formed color{violet}("during transformation"), this will be called a color{brown}("chemical reaction.")

● For example : Ba(OH)_2 + H_2SO_4 →BaSO_4 + 2H_2O

● It is an color{brown}("inorganic") chemical reaction.

● Similarly, color{violet}("hydrolysis of starch") into glucose is an color{brown}("organic") chemical reaction.

● color{violet}("Rate of a physical or chemical process") refers to the amount of product formed per unit time.

It can be expressed as:

"rate" = (deltaP)/(delta t)

● Rate can also be called color{brown}("velocity") if the direction is specified.

● color{violet}("Rates of physical and chemical processes") are influenced by color{brown}("temperature") among other factors.

● A general rule of thumb is that rate doubles or decreases by half for every color{brown}("10°C change") in either direction.

### ENZYMES INCREASE RATES OF REACTION

● color{violet}("Catalysed reactions") proceed at rates vastly higher than that of color{violet}("uncatalysed ones.")

● When color{violet}("enzyme catalyzed reactions") are observed, the rate would be vastly higher than the same but color{violet}("uncatalysed reaction.")

● For example

underset("carbondioxide ")(CO_2) + underset("water")(H_2O) overset("carbonic anhydrase")→ underset(" carbonic acid
")(H_2CO_3)

● In the absence of any color{violet}("enzyme this reaction") is color{brown}("very slow,") with about 200 molecules of H_2CO_3 being formed in an hour.

● However, by using the color{violet}("enzyme") present within the cytoplasm called color{brown}("carbonic anhydrase"), the reaction speeds dramatically with about color{violet}("600,000 molecules") being formed every second.

● The color{violet}("enzyme") has accelerated the reaction rate by about color{violet}("10 million times.")

● There are thousands of types of enzymes each color{violet}("catalysing a unique chemical") or color{violet}("metabolic reaction.")

● A color{violet}("multistep chemical reaction"), when each of the steps is catalysed by the same color{violet}("enzyme complex") or different enzymes, is called a color{brown}("metabolic pathway.")

● For example, color{violet}("Glucose →2 Pyruvic acid")

● color{violet}(C_6H_(12)O_6 + O_2 →2C_3H_4 O_3 + 2H_2O) is actually a color{violet}("metabolic pathway") in which glucose becomes color{violet}("pyruvic acid") through ten different enzyme catalysed color{violet}("metabolic reactions").

● At this stage you should know that this very color{violet}("metabolic pathway") with one or two additional reactions gives rise to a variety of color{violet}("metabolic end products.")

● In our skeletal muscle, under anaerobic conditions, color{brown}("lactic acid") is formed.

● Under normal aerobic conditions, color{brown}("pyruvic acid") is formed.

● In yeast, during color{brown}("fermentation,") the same pathway leads to the color{violet}("production of ethanol (alcohol).")

● Hence, in different conditions different products are possible.