What are Inhibitors?
Some molecules are capable of lowering the activity of enzymes by binding with them; such molecules are known as Enzyme Inhibitors. Inhibitors can be used as poisons as well as medicines. Two major types of inhibitors are Competitive and Non-Competitive.

Competitive Inhibition
In competitive inhibition the inhibitor and the substrate compete for placement in the active site of the enzyme. These inhibitors are said to have the same shape to that of the substrate and prevents the enzyme/substrate complex from forming. This is done when the inhibitor enters the active site thus preventing the substrate from entering. Therefore the rate of reaction is decreased due to less substrate molecules binding to the active site. This type of inhibition can be overcome by increasing the substrate concentration.

Competitive Inhibition

Non-Competitive Inhibition
In this form of inhibition the inhibitor does not compete with substrate for a place in the active site but however does reduces enzyme activity by binding to another site on the enzyme known as the Allosteric site. Unlike the competitive inhibition, non-competitive inhibition prevents the formation of products from substrates (enzyme/product complex). Another thing to note about these inhibitors is that they are unaffected by substrate concentration thus most of them are permanent.

Non-competitive Inhibition

Examples of inhibition:
The inhibitor poison malonate can prevent respiration by binding to the enzyme Succinate Dehydrogenase thus preventing succinate from entering the active site by competing with it.

What are Enzymes?


Enzymes are molecules which catalyze chemical reactions. Enzyme molecules are large and globular and possess catalytic properties. Before modern discoveries all enzymes where thought to be proteins, but that belief was dismissed when some where proved to be made of RNA, however most enzymes are proteins. The configuration of an enzyme molecule is as a result of bonding such as hydrogen bonding, ionic bonding, disulphide bridges and hydrophobic interactions.

A Catalyst can alter the rate of a reaction without having itself undergo any permanent change. This therefore means that they can be used more than once.

Enzyme Function


In previous lessons we learned that the activation energy is the minimum energy required for a reaction to take place. Therefore reactions need to exceed their activation energy in order for them to take place. Enzymes reduce this need for activation energy thus allowing reactions to take place more readily.

It also reduces the temperature at which reactions take place thus allowing them to take place at temperatures lower than normal.

The lock and key mechanism refers to the way the substrate molds itself to fit into the active site of the enzyme in the same way a key fits a lock.

Terms you should know: 

Active site: - This is the part on the molecule of an enzyme into which the substrate fits.
Activation energy: - Minimum energy required for a reaction to take place.
Substrate: - The molecule at the beginning of a reaction that is later converted into products.
Specificity: - Enzymes are specific to reactions they catalyze and the substrates involved.

Enzyme Catalyzed Reaction

Metabolism


Chemical reactions are constantly taking place within living organisms this is known as metabolism.
Metabolism can be divided into two groups these are:

1. Anabolism
2. Catabolism

Anabolism Vs Catabolism


Anabolism is simply a phase of metabolism which results in the buildup of simple chemicals into more complex ones while Catabolism is the reverse; it involves the breakdown of complex chemicals into simpler ones.

In spontaneous chemical reactions the products will have a higher entropy that the reactants meaning they will have less free energy. However for chemical reactions to take place an initial input of energy is needed, this initial input of energy is known as the activation energy.

All chemical reactions are said to be reversible; simply put their direction is determined by their conditions. An example of this would be pH, high and low pH can cause reactions to proceed in opposite directions respectively.

Reactions are capable of releasing energy, in biology these are known as exergonic while some can absorb free energy these are known as endergonic.

What is Moments?

By definition Moments, also known as torque, is the turning effect of a force. Moments can either be in a clockwise or anti-clockwise direction. The unit of moments is the Newton Meter (Nm).

Formula for Moments of a force:

      Moments (torque) = Force × Perpendicular distance from the pivot

How to calculate Moments?

Example 1
Find the total moments of the system below:

Diagram Showing Moments

Step 1

Identify which force in the system is moving in the clockwise direction and which is moving in an anticlockwise direction. The 50N force is the one moving in the clockwise direction (the same direction a clock’s pointer would move) while the 80N is moving in the opposite direction (anti-clockwise direction).

Showing Clockwise and Anti-clockwise Moments

Step 2

Use the formula given above to calculate the clockwise and anti-clockwise moments separately.

          Moments = Force × Perpendicular distance

          Clockwise Moments = Force × Perpendicular Distance
                                          = 50N × 6m
                                          = 300Nm

          Anti-Clockwise Moments = Force × Perpendicular Distance
                                                  = 80N × 4m
                                                  = 320Nm

Step 3

Now that you have calculated both clockwise and anti-clockwise moments you can now find the total moments of the system. This is found by subtracting the smaller moments from the larger, in this case the smaller of the two is the clockwise while the larger is the anti-clockwise.

         Total Moments = 320Nm – 300Nm
                                 = 20Nm in the anti-clockwise direction

 Note: Anti-clockwise direction is written at the end because it is larger.

What is Co-ordinate Bonding?

You may have learned about covalent bonding which involves both atoms sharing a pair of electrons; however this is not the case for coordinate bonding. By definition coordinate bonding is a form of covalent bonding in which only one of the atoms share the pair of electrons while the other doesn’t.

Examples of coordinate bonding:

• In the reaction between ammonia and hydrogen chloride a coordinate bond takes place forming solid ammonium chloride. 

                        NH₃ + HCl  ----->  NH₄ Cl

In this reaction the hydrogen ion from the hydrogen chloride leaves its electrons and gets transferred to the lone pair of electrons on the ammonia molecule forming ammonium ions(NH4 +). This is known as a coordinate bonding. Seeing that the hydrogen has left its electrons the chloride will therefore have a negative charge while the ammonium will have a positive charge. The diagram below shows the reaction:

Coordinate bonds are usually represented by using a diagram similar to the one below, the arrow usually points from the atom donating the lone pair to the atom accepting it.

 

• Another example would be the reaction between ammonia and boron trifluoride. Boron trifluoride is said to be electron deficient meaning it has 3 pairs of electrons at its bonding level but it is capable of having four pairs. In this reaction the ammonia is used to supply this extra lone pair. A coordinate bond is formed where the lone pair from the nitrogen moves toward the boron. The end containing the nitrogen will therefore become more positive while the boron end will become more negative because it has received electrons.

 

Resources:

Read more on coordinate bonding at chemguide

Osmosis is a kind of diffusion in which water molecules move through a partially permeable membrane from a more dilute solution to a more concentrated solution.

Isotonic Solutions
Isotonic means the concentration of the solute is the same as that of the cell. In these solutions no change occurs to the cell. The diagram below shows the effect of isotonic solutions on cells.

Hypotonic/Weak Solutions
A Hypotonic solution is one in which the concentration of the solute in the solution is less than that of the cell. Examples of these include dilute sugar solutions or water. In these solutions the plant cell will absorb water by osmosis to become turgid (stiff), the cytoplasm and vacuole will also increase in volume and the cell wall will stretch. The diagram below shows a plant cell in a hypotonic solution.

Hypertonic/Strong Solutions
A Hypertonic solution is one in which the concentration of the solute in solution is greater than the concentration in the cell. Here the cells have a higher water potential than the solute. The plant cell loses water by osmosis to become flaccid, its vacuole decreases in volume and the plasma membrane shrinks from the cell wall. The diagram below shows this effect:

Other Resources:

To perform a lab/experiment involving plant cells immersed in different solutions click here

Substances can enter or leave the plant cell through two known processes these are active and passive transport. Active processes involve the use of energy while passive processes do not involve the use of energy but depends mainly on the permeability of the membrane. Active processes deal with the transfer of molecules and particles whereas passive processes involve diffusion, facilitated diffusion and osmosis.

What is Diffusion?
Diffusion can be defined as the movement of particles from an area where they are at a high concentration to areas where they are at a lower concentration. This will continue until the particles' concentration is uniformed throughout.

What is facilitated Diffusion?
This involves the movement of specific molecules down a concentration gradient (difference in concentration). This is done using a carrier protein, which binds to the molecule allowing it to pass through the membrane. Examples of these include amino acids and glucose.

What is Osmosis?
This is the movement of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential. Having a partially permeable membrane means it only allows for some molecules to pass through but not all usually it does not allow for larger solute molecules to pass through.

Active Transport
This is the movement of molecules against a concentration gradient (from lower to higher concentration) with the use of energy. The energy supplied comes from ATP of the mitochondria.

The table below shows examples where the processes mentioned above are operative:

Process	Cases where process is taking place
Diffusion	Gas exchanges in photosynthesis: ·         More carbon dioxide is outside the leaf than inside so carbon dioxide will diffuse into the leaf while the opposite happens for oxygen.
Facilitated Diffusion	Glucose is too large to pass through pores of the membrane therefore it has to bind to a specific carrier protein in order to pass through.
Osmosis	In the roots of plants water is absorbed from the soil.
Active Transport	Re-absorption of salts in the proximal convoluted tubule.

Other Resources:

   Click here to see a PDF containing a more detailed explanation.

   Read Exocytosis | Endocytosis

What is Friction?

Friction can be defined as a resistance force formed from the rubbing between two surfaces. Friction is a form of force that slows down motion and dampens energy. There are two types of friction:

• Static Friction.
• Sliding/Dynamic(moving) Friction.

Static Friction


Static friction is the friction caused between objects that are not moving relative to each other.
Limiting Friction is the maximum value of static friction just before the object begins moving. Therefore it can also be concluded that the value of the required force to just begin moving the object is equal to the Limiting Friction.

Sliding (Dynamic) Friction


Sliding friction is the friction formed between objects that are moving relative to each other. It is important to note that static friction is always greater than sliding/dynamic friction.

Laws of Friction

1. The frictional force between two surfaces opposes their relative or attempted motion in other words friction is a resistance force.
2. Frictional forces are independent of the area of contact of the surfaces.
3. For two surfaces which have no relative motion the limiting frictional force is directly proportional to the normal reaction force.

Formula:

What is Impulse?
Impulse can be defined as the force per unit time or change in momentum. Momentum is changed whenever a force is applied to a body. From these definitions one can already see what formulas are in relation to impulse.

Formulas associated with Impulse:

                  Impulse = Force x Time

                                 Or

                  Impulse = Change in momentum = mV – mU

Where ‘m’ is Mass and V, U is final and initial velocity respectively.

Below are some calculations involving impulse. Here you’ll be using the formulas above to find the missing variable.

Example 1.
A force of 100 N is applied for 8 seconds. What is the impulse?

Answer:
Right away you can easily solve for impulse using the first formula above because all other variables are given.

       Therefore Impulse = Force x Time
                                   = 100N x 8sec
                                   = 800Ns

Example 2.
An impulse of 250Ns is applied for 10 seconds. What is the applied force?

Answer:
Again you can see that you have to use the first formula above, but in this case they gave values for impulse and time, therefore all you have to do is transpose the formula to make Force the subject and then solve for Force.

Example 3.

A body of 4kg is moving at 5m/s when it is given an impulse of 8Ns in the direction of the motion.

a) What is the Velocity of the body immediately after the impulse?
b) If the impulse acts for 0.02 seconds. What is the average value of the force exerted?

Answers:
a) Here they gave you mass (4kg), initial velocity (5m/s) and impulse (8Ns). Therefore all you need to do is transpose the second formula, which relates impulse to momentum, to make the final velocity(V) the subject of the formula and then solve.

b)All you need to do is transpose for force and then solve. When done transposing you should get:

These are cellular organelles found in animals they have many functions including breaking down waste materials as well as cellular debris using acid hydrolase enzymes. The digestive enzymes of a lysosome works around a pH of 4.5, it is the membrane surrounding this organelle that allows for these enzymes to work at this pH. Lysosomes contains a variety of enzymes namely, protease, amylase, phosphoric acid and lipase.

Below are some common functions of lysosomes:

• Lysosomes as stated above, contains numerous amounts of enzymes, some of these enzymes are capable of digesting a wide variety of substances.
• They are capable of digesting membranes and organelles, this function is of great importance because it allows cells to remodel or replace old organelles.
• They are often called “suicide bags” because of their ability to rapidly digest an entire old cell.
• Digesting foreign bacteria and other waste substances.
• Digesting macromolecules.

The Golgi apparatus is a composition of parallel membranes enclosing the cisternae, which is a flattened fluid-like space. The cisternae are slightly curved causing the entire structure to appear concave. Unlike others the Golgi is not a stationary cell organelle it disappears at the early stages of mitosis and re-appears during the late stages. The Golgi’s main function is to process proteins that are synthesized in the Endoplasmic Reticulum. It also has other functions these are listed below.


Functions of the Golgi apparatus:

• Carries out its function of transporting and storing lipids.
• Manufactures Glycoproteins, these are required in secretions.
• The production of secretary enzymes.
• Helps in the formation of Lysosomes.

Golgi Apparatus 

(image taken from here)

Endoplasmic Reticulum

What is the Endoplasmic Reticulum?


In its simplest form these are membranes forming channels within the cytoplasm, they are continuous with the nuclear membrane and enclose the Cisternae (cellular spaces).


Types of Endoplasmic Reticulum(ER):

• Rough Endoplasmic Reticulum(RER)
• Smooth Endoplasmic Reticulum(SER)

Rough Endoplasmic Reticulum


RER is covered with ribosomes; these are tiny granules which help in the synthesis of proteins. It is because of these ribosomes why the RER has its name. Rough endoplasmic reticulum is found mainly in cells that are growing rapidly or that secrete proteins, some are also found in the pancreas which secretes insulin.

Smooth Endoplasmic Reticulum


SER has its name because it contains no ribosomes. Unlike RER it is mainly found in cells that secrete Steroids and lipid substances and serves its functions in many metabolic processes.

Functions of the Endoplasmic Reticulum:

• It manufactures proteins and enzymes.
• It manufactures Steroids as well as lipids.
• It has a large surface area which allows for biological and chemical reactions to take place.
• Collects and stores synthesized materials.
• The cell carries out many processes including the transport and exchange of materials; therefore it is the ER which acts as a pathway for these transport and exchanges.
• Maintenance of cellular shape by forming a structural skeleton.

Spontaneous Fission is a form of radioactive decay in which the original nucleus divides or splits into smaller nuclei. This usually involves the ejection of one or more electrons. Spontaneous fission is said to be a very slow process for lighter isotopes. It is a characteristic of very heavy isotopes.

An example of spontaneous fission is shown below:

(Note for more detailed explanation please visit here)

Radioactivity can be defined as the spontaneous emission of radiation from an atom having unstable nuclei or as a result of a nuclear reaction.

There are three types of radiation that are covered in this topic:

1. Alpha Decay(α)
2. Beta Decay(β)
3. Gamma Decay(γ)


Alpha Decay


An Alpha particle has the same mass number and atomic number as Helium and is said to be the same as the Helium-4 nucleus. Usually most heavy elements emit alpha particles. When an atom undergoes this form of decay its mass number will decrease by 4 while its atomic number decreases by 2.

For example:

Beta Decay

• Electron Emission: - As the term suggests, this is when an electron gets emitted from the nucleus, this usually results in the charge in the nucleus increasing by one.

An example of how to calculate Beta Decay is given below:

Gamma Decay


This usually occurs after alpha decay has taken place. This is as a result of the excess energy produced by the alpha particle; this energy is released when the gamma-ray is emitted from the nucleus. Usually no chemical change occurs when an atom emits gamma-ray because it has neither charge nor mass. Gamma-rays are also delayed, short-lived and metastable (m).

Example:

The atom comprises protons, neutrons and electrons. The protons and neutrons are enclosed in a central nucleus that is at the center of the atom, together they are collectively known as nucleons. All of the mass of an atom is said to be in the nucleus because electrons weigh little.

The table below shows some comparisons between protons, neutrons and electrons:

Sub-atomic particle	Relative Mass	Relative Charge
Proton	1	+1
Neutron	1	0
Electron	1/1836	-1

Calculations:


Finding protons, neutrons or mass number:-
Given the values of two of these variables one can transpose the following formula to find the third variable.

     Mass # (A) = # of protons (z) + # of neutrons

Note: The names may vary for e.g. number of protons can sometimes be called atomic number and mass number can be called nucleon number.

For example calculate the number of neutrons in this atom:

If you look at the diagram closely you will see that they have given you two value the mass number and the number of protons (in this example the term atomic number is used instead). Right away one can see that all is needed is to transpose the previous formula to find number of neutrons.

    Mass number = number of protons or atomic number + number of neutrons
                                                    
             19          =         9     +      N


When done transposing this formula for N you should get:

                      19 – 9 = 9 – 9 + N
                      19 – 9 = 0 + N
                            10 = N
                         =>N = 10

Finding the number of electrons:-


It is relatively easy to find the number of electrons because no calculation is needed. Atoms are neutral the positive charges from the protons will balance the negative charges of the electrons. Therefore the electrons would have to be the same number as that of the protons.
     Number of protons = Number of electrons.

Isotopes:
These are atoms of the same element with the same atomic number but different mass numbers. This is due to a difference in the amount of neutrons present in each atom; the protons however do not change. For example there are three isotopes of carbon namely: Carbon-12, Carbon-13 and carbon-14(the numbers represent mass) their protons remain the same being 6 but the neutrons vary being 6, 7 and 8 respectively.

Relative Atomic Mass:
The relative atomic mass of an element can be defined as the ratio of the mass of an atom of the element to one twelfth the mass of carbon-12.

The relative atomic mass can be found using the following formula:

     R.A.M = Mass of one atom of the element   × 12
                     Mass of one atom of Carbon-12