MICROBIOLOGY

All cells are surrounded by a selective barrier known as the plasma membrane.
The plasma membrane serves as a selective barrier facilitating the passage of oxygen, nutrients, and waste, helping service the entire cell.
Inside every cell lies a semifluid substance called cytosol, which suspends subcellular components (organelle).
The cytoplasm refers to the internal content of all cells, which mainly consists of cytosol.
All cells contain chromosomes that carry genes in the form of DNA.
All cells possess ribosomes, responsible for protein synthesis according to genetic instructions.

In eukaryotic cells:
- DNA is housed within the nucleus, which is encased by a double membrane known as the nuclear membrane.
In prokaryotic cells:
- DNA is concentrated in a region termed the nucleoid, which is not enclosed by a membrane.
The cytoplasm in eukaryotes refers to the space between the nucleus and the plasma membrane, containing various membrane-bound organelles, unlike prokaryotic cells which lack them.
Size: Eukaryotic cells are typically larger than prokaryotic cells.

Characterized by a simple cell structure, lacking internal membrane systems and organelles.
Typical structures include:
- Flagella: Used for locomotion.
- Pili: Hair-like structures for attachment.
- Nucleoid: Contains genetic material.
- Ribosomes: Sites for protein synthesis.
- Cell wall: Provides structural integrity.
- Capsule: Offers additional protection.

Cocci (spheres): e.g., diplococci (in pairs), streptococci (in chains), staphylococci (clusters).
Bacilli (rods): Can have shapes like coccobacilli (short and wide) and vibrios (comma-shaped).
Spirilla (rigid spiral) and spirochetes (flexible spirals) indicate diverse bacterial forms.

Bacterial cell sizes can range from small bacteria (~0.3 μm) to larger forms like E. coli (~1.1 to 1.5 μm wide by 2 to 6 μm long) and Epulopiscium fishelsoni (up to 600 by 80 μm).
There exists a high surface area-to-volume ratio (S/V ratio), which enhances nutrient uptake and molecular diffusion efficiency.

Plasma membrane: A selectively permeable barrier that mediates transport processes.
Cell wall: Maintains cell shape and protects from osmotic stress.
Capsules and slime layers: Offer protection and aid in adherence.
Fimbriae and pili: Assist in surface attachment and Bacterial conjugation.
Flagella: Facilitate movement through a rigid cylinder of flagellin protein.

Passive transport includes diffusion and facilitated diffusion.
Active transport (using energy): Moves substances against their concentration gradient. For instance, the Na⁺/K⁺ pump actively maintains ion concentration differences across plasma membranes.

The diffusion of water across a selectively permeable membrane.
Isotonic solutions: No net movement of water, maintaining cell shape.
Hypertonic solutions: Cells lose water and become shriveled (plasmolysis).
Hypotonic solutions: Cells swell as water enters faster than it leaves, potentially bursting (lysis).

Membranes are composed of lipid bilayers interspersed with proteins.
- Integral Proteins: Amphipathic proteins embedded within the membrane.
- Peripheral Proteins: Loosely attached to membrane surfaces.
Functions include:
- Transport mechanisms (channels and carriers).
- Enzymatic activity.
- Signal transduction and cell-cell recognition.
- Intercellular joining and attachment to the cytoskeleton.

Consists of:
- Microtubules: Maintain cell shape and facilitate movement.
- Microfilaments: Involved in motility and maintaining cell structure.
- Intermediate Filaments: Ensure stability and maintain organelle positions.
Plays a crucial role in vesicle transport and cell division.

Understanding the structure and function of both prokaryotic and eukaryotic cells sheds light on biological processes critical for all living organisms. The mechanisms governing cellular transport, structure integrity, and metabolic processes highlight the intricate workings of life at the cellular level.