4.2 Eukaryotic

The phrase "form fits function" means an object's design should serve its purpose.
- Example: In architecture, buildings are constructed to facilitate their intended activities.

Eukaryotic cells possess a plasma membrane similar to prokaryotes.
It is defined as:
- A phospholipid bilayer embedded with proteins.
- Function: To separate the cell from its environment.
Main functions include:
- Regulating the movement of organic molecules, ions, water, and oxygen (O) into and out of the cell.
- Allowing waste products such as carbon dioxide (CO2) and ammonia (NH3) to exit the cell.

The nucleus houses the cell's DNA and directs the synthesis of ribosomes and proteins.
Structure:
- The nuclear envelope is a double-membrane structure that forms the nucleus’s outermost layer.
- Nuclear pores regulate the movement of ions, molecules, and RNA between the nucleoplasm (the semisolid fluid that contains chromatin and nucleolus) and the cytoplasm.

Contains chromosomes, which are linear DNA-protein structures, having a specific number per eukaryotic species.
Chromatin exists in:
- Condensed form (during cell division).
- Decondensed form (non-dividing).
The nucleolus is a specific area within the nucleus responsible for the assembly and export of ribosomal subunits to the cytoplasm, utilizing sections of DNA that encode for ribosomal RNA.

Ribosomes are cellular organelles vital for protein synthesis.
Locations: Ribosomes can be attached to:
- Plasma membrane.
- Endoplasmic reticulum.
- Nuclear envelope membranes.
Their location correlates with the intended destination of the proteins synthesized.

Ribosomes are large protein-RNA complexes consisting of:
- Two subunits.
The mRNA from the nucleus provides the code that ribosomes translate into specific protein sequences.
Cells that synthesize high quantities of proteins, such as those producing pancreatic enzymes, contain a high number of ribosomes.

Mitochondria function as the cell's powerhouses, producing ATP, which is the primary energy currency, through the process of cellular respiration that utilizes chemical energy found in molecules like glucose.
Structure:
- Composed of double membranes with inner folds (named cristae), a matrix, and their own ribosomes and DNA for specialized energy production.
Example of function: Muscle cells are rich in mitochondria due to their high energy demands; in cases of oxygen deficiency, lactic acid is produced instead of ATP.

Peroxisomes are described as single-membrane organelles that execute oxidation reactions and detoxification processes.
They serve to:
- Break down fatty acids, amino acids, and hydrogen peroxide (H2O2) through oxidation.
- Detoxify alcohol in liver cells.
- Participate in metabolism, defense, and response to stress in plants.
- Specialized forms called glyoxysomes facilitate the conversion of fats to sugars.

Vesicles and vacuoles are membrane-bound sacs utilized for storage and transport.
Key differences:
- Vacuoles are typically larger than vesicles.
- Vesicles can fuse with other membranes to release contents, while vacuoles remain separate.
In plants, vacuoles contain enzymes that degrade macromolecules.

Differences in Structure:
- Animal cells have centrosomes and lysosomes, which are absent in plant cells.
- Plant cells contain a cell wall, chloroplasts, additional plastids, and a large central vacuole, all of which are not found in animal cells.
Both types of cells share common structures such as the plasma membrane, cytoplasm, nucleus, ribosomes, mitochondria, peroxisomes, and microtubule-organizing centers (MTOCs).

The centrosome acts as a microtubule-organizing center located near the nuclei of animal cells.
Function:
- Contains centrioles organized in microtubule triplets, crucial for organizing microtubules and assisting in the separation of chromosomes during cell division.
However, centrosomes are non-essential for cell division since cells devoid of them, as well as plant cells, can still divide.