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The Working Cell

Enzymes are essential proteins in cellular processes, acting as biological catalysts that speed up chemical reactions by lowering the activation energy required for these reactions to begin.

The Working Cell

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The Working Cell

Enzymes

How enzymes work
Inhibitors are chemical that inhibit enzyme's activity.
Enzyme Inhibitors
2- Regulate enzyme activity in a cell.
1- Block enzyme action.

2- non-competitive inhibitors.

Change the shape of enzymes active site.

1- competitive inhibitor.

Compete for the active site. Block substrate from entering the active site.

Some enzymes require non-proteins helper
Coenzymes are organic molecules and are often vitamins.
Cofactors are inorganic, e.g. Zinc, Iron, Cooper.
For optimum activity, enzymes require certain environmental condition.
Enzymes also require a pH around neutrality (7pH) for best results.
High temperature will denature human enzymes.
Temperature is very important and optimally, human enzymes function best at 37 C.
Each cellular reaction catalyzed by a specific enzyme.
The enzyme has an active site where the enzyme interact with the enzyme's substrate.
Enzymes have three-dimensional shapes.
Each enzyme has a particular target molecule called the substrate.
Heating a cell will speed up all chemical reactions, not just the necessary ones, and too much heat will kill the cell.
Most of the complex molecule of your cells are rich of potential energy.
The energy barrier of activation energy protect the highly ordered molecules of your cell from spontaneously breaking down.
High-energy systems tend to change toward a more stable state of low energy.
Almost all enzymes are proteins.
Activation energy barrier reduced by enzyme.
Enzymes increasing the rate of a reaction without being consumed by the reaction.
Enzymes speed up a reaction by lowering the activation energy needed for a reaction to begin.
activation energy is the energy barrier that must be overcome before a chemical reaction can begin.
Enzymes function is speed up the cell's chemical reaction.
Enzymes are molecules that function as biological catalysts.

Cell's Energy

ATP
ATP, Adenosine Triphosphate, is the energy currency of cells.

Energy released by hydrolysis reaction.

ATP = ADP + Phosphate group + Energy

Composed of:

3- Three phosphate group.

2- Ribose sugar ( Five-carbon sugar ).

1- Adenine ( nitrogenous base ).

ATP, is the immediate source of energy. that power most forms of cellular work.

ATP (1)shuttles chemical energy and (2)drives cellular work.
Energy transformation
Metabolism, is a series of chemical reactions that either

2- Anabolism: build up a complex molecule.

1- Catabolism: break down a complex molecule.

Cellular respiration, the chemical energy stored in organic molecules is converted to a form that cell can use to perform work.

Glucose + Oxygen >> Cellular Respiration >> Carbon dioxide + water.

The other 66% generates heat.

Cells convert about 38% of the chemical energy in their fuel to energy for cellular work.

The second law of thermodynamics

- During every energy transformation, some energy is lost as heat.

- Energy conversions increase the entropy (disorder) of the universe.

The first law of thermodynamics (Low of energy conservation)

- Plant cells convert light energy to chemical energy.

- State that the energy in the universe is constant and energy can be transferred and transformed, but cannot be created or destroyed.

Thermodynamics, is the study of energy transformation that occur in a collection of matter.
Forms of energy
Energy: the capacity to cause change or to perform work.

Potential energy, is energy that matter possess as a result of its location or structure.

Chemical energy is the most important type of energy for living organisms; it is the energy that can be transformed to power the work of the cell.

Chemical energy, is the potential energy available for release in a chemical reaction

Molecules possess potential energy because of the arrangement of electrons in the bonds between their atoms.

Example: Water behind a dam.

Kinetic energy, is the energy of motion.

Light energy, another type of kinetic energy, can be harnessed to power photosynthesis.

Thermal energy (Heat), is a kinetic energy associated with random movement of atom or molecules.

Cell's Membrane

Membrane Transportation
Endocytosis and Exocytosis

Endocytosis

There are three kinds of endocytosis :-

The 3 types of endocytosis

Receptor-mediated endocytosis.

Pinocytosis or "cellular drinking"

It takes in any and all solutes dissolved in the droplets. not specific

Process: The cell gulps droplets of fluid into tiny vesicle.

Phagocytosis or "cellular eating"

Example: an amoeba takes in a food particle via phagocytosis.

2- The vacuole then fuses with a lysosome, whose hydrolytic enzymes digest the contents of the vacuole.

1- The cell engulfs a particle by packaging it within a membrane-enclosed sac, large enough to called vacuole.

A cell use Endocytosis process to import large molecule.

A cell membrane fold inward enclosing materials from the out side

Exsocytosis

Exocytosis Process :-

The vesicle fuses with the plasma membrane, and the vesicle's contents spill out of the cell.

A transport vesicle filled with macromolecule buds from Golgi apparatus and moves to the plasma membrane.

A cell use Exocytosis process to export bulky materials.

such as Proteins and polysaccharides.

Active Transport

Active Transport Process :-

Figure 4.5 - Page 56

The phosphate group detaches, and the transport protein returns to its original shape.

The protein change shape in such a way that the solute is released on the other side of the membrane.

Thet ATP transfers a phosphate group to the transport protein.

A solute molecules (in the cytoplasm) attach to specific binding site on the transport protein.

ATP molecule supplies the energy for most active transport.

Active Transport: the transport that requires energy to move a solute against its concentration gradient.

Passive Transport

Facilitated Diffusion is a type of passive transport. Because it does not require energy.

Transport protein, provides a hydrophilic channel that some molecules or ions use as a tunnel through the membrane.

e.g. Aquaporins, protein channel allows the entry or exit of water molecules. (3 billion molecule per second)

Polar or charged substances can move across a membrane with the help of specific transporter protein in a process called facilitated diffusion.

Oxygen enter the cell. Carbon dioxide passes out of the cell. Both are essential for metabolic. Both are Small, nonpolar. (cross easily).

The molecules diffuses down its concentration gradient.

Passive Transport: diffusion across a membrane with no energy investment.

Diffusion and Osmosis

a solute is a substance that dissolve in a liquid solvent, producing a solution.

Equilibrium, Molecules still move back and forth, but there is no net change in concentration. (when the concentration is the same.)

Concentration gradient means from high concentration to low concentration.

Osmosis is the diffusion of water across a membrane.

Solvent Molecules move from lower concentration of solute to higher concentration of solute.

Water cross a membrane by passive transport.

Diffusion, the tendency for particles of any kind to spread out evenly in an available space.

Molecules move from lower concentration of solute to higher concentration of solute.

Much of the traffic across cell membranes occurs by diffusion.

Molecules vibrate and move randomly as a result of a type of energy called thermal energy (heat). . One result of this motion is diffusion.

Membrane stucture
An important figure in page 54 to understand.
Selective Permeability: allow sme substance to cross more easily than others.

- Polar molecules do not cross easily. (Require transport protein).

e.g. Glucose.

- Non-polar molecules cross easily.

e.g. Carbon dioxide - Oxygen.

Many ions and molecules require transport protein to enter or leave the cell.

Six major functions performed by membrane proteins

6- Transport of substance across the membrane.

5- Intercellular junctions: a protein attach adjacent cells.

4- Cell-Cell recognition: their attached carbohydrates function as identification tags that are recognized by membrane proteins of other cells.

- recognition allows cells to reject foreign cells.

3- Enzymatic activity: enzymes grouped in a membrane to carry out sequential steps of a metabolic pathway.

2- Signal transduction: Receptor for chemical messengers (signaling molecules).

1- Help maintain cell shape and coordinate changes.

Different types of cells have different membrane proteins.
The steroid cholesterol helps stabilize the membrane temperature.
Composed of

2- Embedded and attached proteins.

1- Bilayer of phospholipids.

The plasma membrane is the boundary that enclose a living cell.