ENERGY

What is energy??

Energy is generally described as the amount of work that can be done.

Types/forms of energy: ????

What do we use energy for in our body? Movement of muscles Maintain body temperature Making new chemicals Break down food Repair tissue damage

HOW DO WE GET ENERGY??

FOOD! Since we are unable to make our own

food, we need to get food and energy from other sources.

Autotrophs are organisms that can make their own food. Plants are autotrophs that use the energy from the sun to make sugars (carbohydrates).

We are heterotrophs; organisms who can not make their own food. We get our energy (food) from other sources that can make their own food.

 

Energy is studied through systems. A system involves an input, transformation, and output of energy. The transformation of energy occurs in the cell.

  Energy is different than matter. Energy does

not cycle between autotrophs and heterotrophs. However, we have the continuous addition of energy from the sun to prevent a system from running out of energy.

REMEMBER LAWS OF THERMODYNAMICS:

There are two laws that govern energy conversion:

  First Law: Energy cannot be created nor

destroyed, but only change form.   An electrical company does not create

energy they just convert it to a convenient useable form.

Second Law: Energy conversions are accomplished by an increase in disorder, or randomness. Energy systems have a tendency to increase their disorder than to decrease it. Think about your bedroom……

  The amount of disorder in a system is called

entropy. The greater the disorder in the system the greater the entropy.

 

Heat is one form of disorder. The more heat generated during energy conversions, the more the entropy of the system. For example, when you exercise, your body gives off heat. Heat is a waste energy. Not of the energy is used for muscle contraction; some will be wasted as heat.

WHAT ABOUT CELLS?

A cell creates ordered structures all the time; amino acids. An increase in order is a decrease in entropy. An increase in order in the system causes an increase in disorder in the surroundings.

Examples in nature:An owl will eat a mouse. However, not all the chemical energy will be converted into useful energy. Heat will escape from the mouse and the owl. Remember the energy is NOT destroyed. The energy may go to the mouse or to the owl.

METABOLIC REACTIONS

Two types of metabolic reactions: 1) Exothermic Reactions

These are reactions that release energy. There is a net loss of energy because the products of the reaction have LESS energy than the reactants.

Example: burning of wood 

2) Endothermic ReactionsThese reactions require an addition of energy. The products have more energy than the reactants

Remember: energy is NOT created, therefore, the energy require must come from an external source.

Example: Photosynthesis

The sum of endothermic and exothermic reactions is called cellular metabolism

So what is responsible for powering all of these reactions in our body??

Energy is stored in the form of adenosine triphosphate (ATP). ATP is composed of:

a five carbon molecule (ribose) adenine (a nitrogen base) three phosphate groups

ATP!!

The energy of ATP is found in the phosphate bonds. Think of ATP a wallet full of money. A wallet carries money which you can spend. ATP carries chemical energy that cells can use.

There are covalent bonds between the phosphate groups of ATP. The bond between the second and third phosphate is very unstable and is easily broken through hydrolysis. When the covalent bond is broken there is a net release of energy.

ATP + water --> Energy + ADP + P

When the third phosphate group is removed ATP becomes ADP. The hydrolysis of ATP is an exothermic reaction. Within the cell, a protein molecule can acquire the free phosphate and gain energy; enabling it to do work. The transfer of a phosphate to a molecule is called phosphorylation.

The formation of ATP is an ENDOTHERMIC reaction.

  Energy + ADP + P ATP + water  ATP is formed via dehydration synthesis.

This cycle of ATP occurs continuously in the cell. The cell uses energy coupling to drive reactions. The energy released from an exothermic reaction is used to generate an endothermic reaction.

REACTIONS AND REACTION RATES

Activation Energy (EA)

The energy required to initiate a reaction. With the case of ATP, the activation energy is

the amount of energy needed to break the bond between the second and third phosphate. Without the requirement of activation energy, ATP would spontaneously break down.

 

http://www.youtube.com/watch?v=VbIaK6PLrRM&feature=related

Chemical reactions that occur in the cell need to occur quickly, accurately and precisely. There are four factors that affect the rate of a chemical reaction:

1) TemperatureUsually an increase in temperature will increase the reaction rate.

2) Concentration of the reactantsAn increase in the concentration of reactants will cause an increase in the reaction rate.

  3) State

The state in which the reactants are in will determine the rate of the reaction. Molecules in a solid state move slower than molecules in a gaseous state.

4) Enzymes and Catalysts A catalyst is a chemical that controls the rate of

the reaction. A catalyst DOES NOT alter or change the

products of the reaction. The catalyst remains unchanged after the

reaction. A catalyst does not add energy to the reaction; it

lowers the EA barrier.

Enzymes are protein catalysts that serve in biological reactions

HOW DO ENZYMES WORK?

Enzymes have distinct three-dimensional shapes. It is this shape that determines which reaction the enzyme will catalyze.

A substrate is the substance that the enzyme acts on. It is the reactant. Each enzyme recognizes a specific substrate.

 

Catalyzing a Reaction: 1) The enzyme will bind to the substrate(s) 2) The substrate binds to the active site of the enzyme. The

active site is a groove or pocket on the enzyme. The active site only fits one type of substrate.

3) When the substrate attaches to the active site, the active site slightly changes so that the site is tightly wrapped around the substrate.

4) Once the substrate is in the proper position, the enzyme can catalyze the reaction.

5) While attached to the active site, the reaction occurs; the substrate turns into the product(s).

6) After the completion of the reaction, the enzyme releases the product(s).

This model is called the induced fit model because of the slight change in the active site once the substrate binds.

 

An enzyme can act on thousands or millions of substrate molecules per second.

http://www.youtube.com/watch?v=V4OPO6JQLOE&feature=related

WHAT AFFECTS THE ACTIVITY OF ENZYMES? 

Temperature High temperatures denature enzymes.

pH Most enzymes work best at a neutral pH (6-8).

However, stomach enzymes will only function at the pH of the stomach.

Concentration of substrate The greater the number of substrate molecules,

the greater the number of collisions, and therefore the greater the rate of the reaction.

Co-factors Some enzymes will not work unless they have a

co-factor. A co-factor is generally an inorganic molecule (i.e. zinc or iron, or copper). If a co-factor is an organic molecule, then it is called a coenzyme. Majority of coenzymes are vitamins or made from vitamins.

ENZYME INHIBITORS

Anything that blocks the activity of an enzyme is called an enzyme inhibitor. There are two types of inhibitors:

1) Competitive InhibitorResembles the enzyme’s normal substrate so it competes with the regular substrate to attach to the active site. If the inhibitor binds to the active site, the enzyme will not be able to act.

2) Non-competitive InhibitorThis inhibitor will not bind to the active site. However, it binds to the enzyme on another site. This binding causes the enzyme to change shape so that the substrate can no longer bind to the active site.

Some inhibition is reversible, while others are not. The reversibility depends on the strength of the bond formed between the inhibitor and the enzyme.

Inhibition can be good for cell metabolism. If the inhibition is reversible, then it can aid in regulation.

NEGATIVE FEEDBACK INHIBITION

ATP acts as a noncompetitive inhibitor for itself.

ALLOSTERIC ACTIVITY

Feedback inhibition is an example of allosteric activity. The final product of the pathway binds to the regulatory site of the enzyme. This binding causes a change in the active site, and will inhibit further reactions.

SOME INTERESTING INFORMATION ABOUT ENZYMES

Some pesticides are harmful to insects because they bind to important enzymes irreversibly in their nervous system. If the nerve cells are prevented from transmitting signals then the insect dies.

One type of pesticide, malathion, is poisonous to insects, animals, and humans. However, the dose that kills insects is not strong enough to kill humans.

 

Antibiotics Some antibiotics work by binding to the

enzymes that are essential to the bacteria. Penicillin inhibits the enzyme that is essential for the bacteria to make cell walls.

Siamese CatsSiamese cats have a heat sensitive

enzyme called tyrosinase. Tyrosinase converts tyrosine to melanine (black pigment). The enzyme will denature at normal body temperature. The black pigment is only present at the cooler parts of the body. You can test this by looking at Siamese cats that have been left outside all winter, they will be all black. Siamese cats that have been outside in hot climates will be all white.

 

Hydrogen cyanideHydrogen cyanide will bind

permanently to the active site of cytochrome c oxidase, which is essential in cellular respiration. The cell can not function properly and dies from lack of energy.

 

Alcohol BreakdownThe enzyme alcohol dehydrogenase

aids in the breakdown of alcohol that would otherwise be toxic. Young women do not express the enzyme as well as men. This is one reason why men can out-drink, or hold their alcohol better. The activity of the enzyme and expression is also different in regions of the world. It has been found that Europeans have higher activity than Asian or American countries.

ENZYMES IN THE BODY:

In the mouth amylase breaks down carbohydrates In the stomach there is the production of pepsin

which breaks down proteins. Gastric lipase breaks down lipids. Gastric amylase breaks down starch.

In the small intestine trypsin and chymotrypsin cleave proteins into amino acids. There are also enzymes that will break down disaccharides into monosaccharides such as sucrase, maltase, and lactase.

Enzymes: http://www.youtube.com/watch?v=E90D4BmaVJM   Digestion and enzymes http://www.youtube.com/watch?v=AFbPHlhI13g