Biology Chapter: Cells and Cell Theory

Cells are the basic structural unit of life.
Cell theory proposes:
- All living organisms are made of cells.
- A cell is the basic unit of life.
- All cells arise from pre-existing cells.

Contains a nucleus and membrane-bound organelles.
Can be unicellular or multicellular, measuring 10 to 100 micrometers in diameter.
Examples include animals, plants, fungi, and protists from Domain Eukarya.
Term "eukaryote" is derived from Greek words meaning "true nuclei."

Cell Membrane: Semi-permeable membrane regulating entry and exit of substances; consists of a bilipid layer of phospholipids; present in both prokaryotic and eukaryotic cells.
Cytoplasm: Gel-like fluid filling the cell’s interior where cellular processes occur; found in both prokaryotic and eukaryotic cells.
Endoplasmic Reticulum (ER): Network of sacs (cisternae); involved in protein and lipid synthesis; only in eukaryotic cells.
- Rough ER: Contains ribosomes for protein synthesis.
- Smooth ER: Lacks ribosomes, involved in lipid synthesis.
Golgi Apparatus: Sorts, modifies, packages, and transports molecules; found only in eukaryotic cells.
Lysosome: Acts as the cell's digestive system using hydrolytic enzymes; present only in eukaryotic cells.
Mitochondria: Known as the "powerhouse" of the cell, generates energy in the form of ATP (Adenosine Triphosphate), the "energy currency" of living organisms.
Nucleus: Control center of eukaryotic cells.
- Nucleolus: Site of RNA synthesis.
- Nucleoplasm: Fluid within the nucleus.
- Nuclear Membrane: Surrounds the nucleus, separating it from the cytoplasm.
Nucleoid: Control center of prokaryotic cells.
Ribosomes: Site of protein synthesis.
Peroxisome: Oxidizes and detoxifies harmful substances.

Cell Wall: Rigid outer layer providing strength and protection; found in prokaryotes and eukaryotes, but not present in plant cells.
Plastids:
- Chloroplast: Responsible for photosynthesis, contains chlorophyll (green pigment).
- Chromoplast: Assists in propagation and reproduction.
- Amyloplast: Stores starch and sugars.

Describes the flow of genetic information from DNA to RNA to protein, proposed by Francis Crick.
Replication: Process of duplicating DNA.
Transcription: Process of copying DNA information into RNA.
- mRNA (Messenger RNA): Product of transcription carrying coding information (codons); includes start codon (AUG) and stop codons (UAA, UGA, UAG).
- tRNA (Transport RNA): Carries anticodons correlating with mRNA for amino acid delivery.
- rRNA (Ribosomal RNA): Does not contain codons or anticodons but is essential in ribosomes for protein synthesis.