The cell

The cell
The cell is the smallest unit capable of performing life’s function. They form the building blocks of an organism. They possess many organelles of various structure and function:
 Nucleus
 Cytoplasm
 Endoplasmic reticulum
 Golgi apparatus
 Ribosomes
 Chloroplast
 Lysosomes
 Mitochondria
 Cytoskeleton
 Proteasome
 Cell wall
 Cell membrane

Animals and plant cells organelles have some variation, example: animals have no cell wall or chloroplast but plants do.
Cell size is limited because of surface to volume ratio, which decreases as cell size increases. Thus cells cannot get too large or too small because there might be enough DNA to support life, with the exception being viruses.

Prokaryotes are single celled organisms with no true nucleus, example: bacteria
Eukaryotes are multi or single celled organisms. They possess a true nucleus. Example: Protista, animals and plants.
These also have many similarities and differences in terms of structure.

By AmethystAP


From these videos you will learn that:
Enzymes are biological catalysts that speed up the rates of reactions by providing an alternative pathway of lower activation energy. Most enzymes are globular proteins and have a tertiary structure which is maintained by electrostatic bonds, hydrogen bonds, disulphide bonds and most importantly hydrophobic forces. Denaturation as a result of heat, chemicals, metal ions and strong acids or bases can disrupt these bonds that give protein their three dimensional shape. This in turn affects their optical activity. Various factors affect enzyme catalysed reactions such as temperature, substrate concentration, enzyme concentration and pH.
Enzymes have amazing catalytic ability. Without these biomolecules life as we know it would not exist since enzymes ensures that the many biological reactions that occur within us, which are necessary for life, happen at a sustainable rate. Imagine if our body didn’t have enzymes?
However catalysts are not only biological there are inorganic as well but their catalytic ability are inferior to enzymes.
There are six major classes of enzymes:
1. Oxidoreductases
2. Transferases
3. Hydrolases
4. Lyases
5. Isomerases
6. Ligases
These classes represent the first digit of the four digit EC number of enzymes. This classification allows one to identify enzymes accurately according to their major class, sub-class, sub sub-class and individual entry.
Some enzyme require a cofactor to work: apoenzyme + cofactor  holoenzyme
Enzymes are specific but this can vary for each:
• relative,
• moderate,
• absolute,
• optical or stereo-specific and
• dual specificity
The active site of an enzyme is the region to which a substrate binds. Two hypothesis, lock and key and induced fit are explored to explain this. The specificity of enzymes becomes important.
Inhibitors are molecules that can bind to the enzyme affecting product formation. There are four types of reversible inhibitors:
 Competitive
 Non competitive
 Uncompetitive
 Mixed
The Michaelis-Menten equation and curve along with the Lineweaver Burk plot illustrates each effect of the inhibitors.
Allosteric enzymes are also discussed.

By AmethystAP