Bio 9-25

Definition: Prokaryotic cells are characterized as cells that do not have a nucleus and exhibit a simpler structure compared to eukaryotic cells.
Key Features:
- No nucleus: Instead of a nucleus, prokaryotic cells contain a nucleoid region where genetic material is located.
- Lack of membrane-bound organelles: Prokaryotic cells do not contain complex organelles like endoplasmic reticulum or mitochondria.
- Presence of ribosomes: Prokaryotes contain ribosomes, which are responsible for synthesizing proteins.
- Cell wall: Prokaryotic cells are equipped with a rigid cell wall that provides structural support and protection.
Ribosomes: The primary function of ribosomes in prokaryotic cells is to synthesize proteins essential for cell function.

Definition: Eukaryotic cells are defined as cells that possess a true nucleus and membrane-bound organelles, making them more complex compared to prokaryotic cells.
Organelles in Eukaryotic Cells:
- Endoplasmic Reticulum (ER): There are two types of ER:
- Rough ER: Studded with ribosomes, plays a key role in protein synthesis and processing.
- Smooth ER: Lacks ribosomes, functions in lipid synthesis and detoxification processes.
- Golgi Apparatus: Involved in modifying, sorting, and packaging proteins for secretion or use within the cell. It also creates new membranes.
Need for Membranes: Eukaryotic cells require additional membranes to accommodate their complex organelles and functions, facilitating cellular compartmentalization which is vital for various cellular processes.

Definition of Karyo: From the Greek word 'karyon', meaning nucleus, denoting a true nucleus present in eukaryotic cells.
- Presence of Nucleus: Unlike prokaryotic cells, which lack a nucleus, eukaryotic cells contain one or more nuclei where genetic material is housed.

Bacteria: Prokaryotic organisms typically classified separately from eukaryotic kingdoms (animal, plant, fungi) due to structural differences.
Unicellular vs. Multicellular:
- Unicellular: Most bacteria are unicellular (single-celled).
- Multicellular: Some prokaryotes may exhibit multicellularity but are still classified as prokaryotic due to their lack of a nucleus.

Composition: The bacterial cell wall is primarily composed of peptidoglycan, a polymer consisting of sugars and amino acids.
- Function: The cell wall protects the cell, helps retain moisture, and allows for cellular activities. Damage to the cell wall can be lethal to the organism.
Types of Cell Walls:
- Gram Positive: Characterized by a thick peptidoglycan layer, which appears blue when stained.
- Gram Negative: Has a thinner peptidoglycan layer and often appears red after staining.
- Staining Techniques: Different stains (e.g., crystal violet for Gram positive, safranin for Gram negative) help identify the type of bacteria based on their cell wall composition.

Shapes of Bacteria:
- Cocci: Circular-shaped bacteria.
- Bacilli: Rod-shaped bacteria.
- Spirilla: Spiral-shaped bacteria.
- Naming Convention: Bacteria are often named based on their shape (e.g., streptococci, which refers to circular cells in chains).

Four Biological Molecules:
- Carbohydrates: Organic compounds composed of carbon, hydrogen, and oxygen that provide energy.
- Lipids: Fats and oils, consisting of hydrocarbons.
- Nucleic Acids: DNA and RNA, important for genetic information and protein synthesis.
- Proteins: Composed of amino acids, essential for a variety of functions in living organisms.
Carbon as a Central Element: Carbon atoms form the backbone of biological molecules. A molecule not containing carbon is not classified as organic.

Characteristics of Water:
- Composed of hydrogen and oxygen (H2O).
- Does not contain carbon, hence not classified as a biological molecule despite its essential role in life processes.
Biological Significance: Water is crucial for life, participating in biochemical reactions but does not fit the criteria for being a biological molecule due to the absence of carbon.