Biology Chapter: Cell Structure and Types

Study Notes

Cell Definition

The smallest unit that exhibits the characteristics of life.
Organelles are structures within cells that perform specialized metabolic functions, such as building, modifying, and storing substances.

Simple Animal Cell

Contains cytoplasm, DNA, a nucleus, a nucleoid, and a cell membrane.

Types of Cells

Eukaryotic Cells:
- Cells with a nucleus and internal compartments.
Prokaryotic Cells:
- Small, simple cells lacking a nucleus.

Modern Microscopes

Light microscopes:
- Use visible light to illuminate and magnify samples.
- Types include:
  - Phase-contrast microscopes: Enhance contrast in transparent specimens.
  - Reflected light microscopes: Used to examine opaque surfaces.
  - Fluorescence microscopes: Illuminate specific molecules with fluorescent dyes.
Electron microscopes:
- Utilize a beam of electrons for higher magnification and resolution.
- Types include:
  - Transmission electron microscope (TEM): Provides thin slices of samples for detailed internal structures.
  - Scanning electron microscope (SEM): Provides three-dimensional external views of samples.

Prokaryotes

Prokaryotes are single-celled organisms.
They include bacteria and archaea.
They are the smallest and most metabolically diverse forms of life.

Biofilm

A community of single-celled organisms embedded in a self-produced matrix of polysaccharides and glycoproteins.
Includes bacteria, algae, fungi, protists, and archaeans.

Eukaryotic Cells

They include protists, fungi, plants, and animals.
Contain a nucleus that houses their DNA.
Have various organelles, including:
- Cell wall: Provides structural support, found in plants, fungi, and some protists.
- Vacuole: Storage compartment, large in plant cells.
- Plasma membrane: Regulates the passage of molecules in and out of the cell.
- Mitochondrion: Powerhouse of the cell, generates ATP through cellular respiration.
- Nucleus: Contains the cell's genetic material (DNA) and is responsible for controlling cell functions.
- Central vacuole: Large storage compartment in plant cells, filled with water and dissolved substances.
- Chloroplast: Site of photosynthesis in plants, contains chlorophyll.
- Cytoskeleton: Network of protein fibers that provides structural support, facilitates movement, and transports materials.
  - Microtubules: Largest cytoskeletal fibers, involved in cell division, organelle movement, and structure.
  - Microfilaments: Thinner cytoskeletal fibers, involved in muscle contraction, cell division, and maintaining cell shape.
  - Intermediate filaments: Intermediate-sized cytoskeletal fibers, provide structural support for the cell.
- Plasmodesma: Channel connecting the cytoplasm of neighboring plant cells.
- Plasma Membrane: Controls movement of molecules into and out of the cell.
- Ribosomes: Sites of protein synthesis, found free in the cytoplasm or attached to the endoplasmic reticulum.
- Rough ER: Network of membranes studded with ribosomes, modifies proteins synthesized by ribosomes.
- Smooth ER: Network of membranes without ribosomes, synthesizes lipids, breaks down carbohydrates and fats, and detoxifies harmful substances.
- Golgi Body: Processes and packages lipids, enzymes, and proteins for distribution within the cell or export.
- Lysosome-Like Vesicle: Contains digestive enzymes to break down cellular waste and foreign substances.

Human White Blood Cell

Contains numerous organelles, including:
- Rough ER: Modifies proteins made by ribosomes attached to it.
- Smooth ER: Synthesizes lipids, breaks down carbohydrates and fats, and inactivates toxins.
- Golgi Body: Finishes, sorts, and ships lipids, enzymes, and proteins.
- Lysosome: Digests and recycles materials within the cell.
- Nuclear pore: Regulates the movement of molecules between the nucleus and the cytoplasm.

Structure of the Nucleon Envelope

The nuclear envelope is a double lipid bilayer.
Proteins embedded in the envelope control molecule transport between the nucleus and cytoplasm.

Structure of the Nucleus

Nucleoplasm: The viscous fluid within the nuclear envelope, similar to cytoplasm.
Nucleolus: A dense region within the nucleus where ribosome subunits are assembled from proteins and RNA.