Chapter 5-7, 10

Read P. 75-82, 91-100, 107-117

and 173-185

Introduction to Metabolism and Enzymes

Catabolic reactions (also called “catabolism”) break down larger, more complex molecules into smaller molecules and release energy in the process. The smaller end products of a catabolic reaction may be released as waste or they may be fed into other reactions.

Metabolic pathways are catabolic (break-down molecules)

or anabolic (synthesize or combine molecules) and result

in molecular products which can be used by the cell

immediately, used to initiate another chemical reaction, or stored in the cell. Uses energy.

Requirements for Metabolism

Enzymes

https://www.youtube.com/watch?v=qgVFkRn8f10Enzyme video

Enzyme Structure

How Do Enzymes Function?

Factors Affecting Enzyme FunctionLike living organisms, enzymes function within an optimum range that is specific to the organism.

Outside their range enzymes become denatured, which means, the active sites lose their shape

and therefore are unable to fit the reactants. Not being able to bring the reactants together means

that the activation energy will not be able to be lowered. This has a drastic affect on the

metabolism and the overall well-being of the organism. Without the enzymes, the necessary metabolic reactions may slow down or possibly not occur at all resulting in death.

2 Factors:

1. pH

2. Temperature

1.

2.Temperature: Enzymes will also work at optimum

temperatures depending on the environment and species.

Thermophilic bacteria, for example will have enzymes that

function best for their metabolic reactions at very high

temperatures (70°C). Outside this range they are not

operational. Humans have an internal temperature range of

about 37°C. Obviously thermophilic bacterial enzymes would not operate in our bodies or vice versa.

ATP – The reaction of ATP (energy)

The reactions that occur are as

follows:

1. Catabolically (breaking of large

into small, breaking bonds,

releasing energy):

A-P-P-P -----------> A-P-P + P

2. Anabolically (forming large from small, building

bonds, storing energy):

A-P-P + P -------------> A-P-P-P

When these reactions occur what happens to the P and

the energy (stored or released)? The answers explain how ATP drives cellular work.

Energy and Phosphate Transfer

ATP, as a molecule, is a form of stored energy.

In order for cells to perform work this energy must be released. Like a shelled nut, the energy is within and to obtain this energy, the shell must be broken.

Likewise, ATP must catabolically break into ADP and P. In this chemical reaction energy is released and a P (phosphate) is made available.

As the Laws of Thermodynamics state: energy is never lost but transferred. Therefore, the energy and the P from this reaction must be transferred somewhere.

The energy can go into forming new bonds between different reactants,

for an example. This would be an anabolic reaction where energy is

required and stored to build new bonds. This energy would come from

the breaking apart of ATP. The P is typically transferred to a protein.

As stated in previous units, proteins are unique to their function and

enzymes unique to their reactions. Transferring a P to a protein allows a

unique shape required for some metabolic reactions.

When the P is removed from the protein, the original shape is retained and the reaction stops, permitting the original reaction to start again.

ATP Cycle ATP is continuously being used by cells, which means the catabolic

breakdown of ATP is occurring always.

However, ATP is also a renewable resource, which means that the opposite reaction, the anabolic formation of ATP is also always occurring. Because these two can occur in both directions it is called an equilibrium and is known as the ATP cycle.

4. Examples of Cellular Metabolic

Reactions……1. Protein DigestionProteins are a polymer composed of amino acids (aa) as monomers joined together by peptide bonds in a chain. Important in the cell, they are also a nutrient often acquired through the diet. These proteins are too large to be used by cells and therefore must be digested or broken down.

How would this look in the form of an equation (it is after all a metabolic chemical reaction).

This reaction shows a protein of 3 amino acids in length,

catabolically being broken into its individual monomers. The

individual monomers are now small enough to be transported

into and used by the cell. As a result of this catabolic reaction,

energy is released.

This energy can now be transferred and stored in the following reaction:

2. Protein Synthesis

Protein Synthesis is usually achieved in a two-step process of transcription and translation.

Transcription occurs in the nucleus of the cell and involves DNA giving the initial code for the particular protein that is needed to be built. DNA, as a transcript, delivers the protein code in the form of a mRNA (m=messenger).

In translation, this mRNA moves out of the nucleus and finds its way to a ribosome. The ribosome is able to interpret the mRNA's message and thus the DNA's code. It is the nitrogen bases (A,U,C,G) of the mRNA that is read and the message is read in groups of threes, known as a codon. Because the entire message is so long it is easier for the message to be read in groups of threes, after each reading the particular amino acid found and brought to the ribosome site. It is the tRNA (t=transfer) that will match the read codon with its opposite bases known as an anticodon. With the anticodon the specific amino acid is also transferred by the tRNA to the ribosome. The building of protein has now begun.

3. Photosynthesis

Photosynthesis is a metabolic pathway that most autotrophs, such as green plants, perform.

The chloroplast is the organelle required; therefore it can be assumed that any cell containing chloroplasts will perform photosynthesis (the taking of inorganic carbon dioxide and water to form organic glucose and oxygen).

It is a very complicated process, much more complicated than the intent of this course. It involves several reactions, both anabolic and catabolic, and also involves ATP.

There are two steps involved in the process of photosynthesis:

Light Reactions and Dark Reactions (AKA – Calvin Cycle)

The light reactions involve taking water (H2O) and catabolically breaking it apart into oxygen (O2). This reaction involves light and produces ATP. It occurs in the stroma or fluid portion of the chloroplasts.

Step 1 (catabolic): H2O -------> O2 + energy

Step 2 (anabolic): ADP + P + energy -------> ATP

The dark reactions however are not dependent on light because the ATP produced in the previous step will now be the energy source to anabolically produce glucose (C6H12O6) from carbon dioxide (CO2).

This step occurs in the thylkoid sacs of the chloroplasts:

Step 3 (catabolic): ATP -------> ADP + P + energy

Step 4 (anabolic): energy + CO2 ---------> C6H12O6

Combining these 4 steps produce the overall equation:

Overall: CO2 + H2O + light energy ---------------> C6H12O6 + O2

4. Aerobic Cellular Respiration

Like photosynthesis, aerobic cellular respiration is a complicated metabolic pathway that involves several reactions, both anabolic and catabolic.

The difference is that cellular respiration occurs in all cells as it is a characteristic of living organisms. Also, it is commonly described as an overall catabolic process.

The reaction that we will observe will be aerobic cellular respiration which involves O2, and occurs in the mitochondria.

The entire process involves three steps: Glycolysis, Kreb's Cycle and Electron Transport chain. These steps are much more complicated than the steps in photosynthesis. There are also many more molecules involved in the process.

What we will outline here will be in its simplest form. It will leave out a number of reactions that in reality occur and are extremely important to the process. First, let's see the overall reaction:

C6H12O6 + O2 --------------> CO2 + H2O + energy

As you probably observed, the reaction is the reverse of photosynthesis.

Students make the mistake of thinking that the primary function of respiration is to break down glucose. This occurs but the reason why all cells do some form of respiration is for the production of energy.

Aerobic and anaerobic respiration connections between cellular respiration and other

pathways fermentation is another anaerobic (non oxygen requiring) pathway for breaking

down glucose, fermentation doesn't require oxygen either; The difference is whether or not

an electron transport chain is present.

Difference between Anaerobic Respiration and Fermentation - YouTube

https://www.youtube.com/watch?v=KqoHQWz2Mxk

Fermentation

When the pyruvate is not oxidized, it undergoes the process of fermentation. It is then converted into thewaste products lactate or lactic acid (lactic acid fermentation) and ethanol (ethanolor alcoholic fermentation).

During strenuous exercise, fermentation occurs in the muscles because of limited oxygen supply, creatinglactic acid which also causes muscle cramps. Sugars are very important in fermentation and so is yeast. Ithelps in the production of ethanol in alcoholic drinks and carbon dioxide.

Differentiate between cellular respiration and fermentation (aerobic and anaerobic respiration)

Assignment #5