Cells

Cells are the smallest unit of life.

To be a cell, you need:

• Ability to replicate.
• Organized molecular components.
• Self-contained metabolic systems.
• Response to environmental stimuli.

Cell Types

Prokaryotes

Is the older and simpler of the two types.

Streamlined design for efficiency.

• Everything happens in one main compartment.

• DNA is jumbled in nucleoid region, floating freely (jumbled core of dna in cytoplasm).

Fast reproduction and adaptation.

• Lower energy/nutrient requirements.

More commonly make up unicellular organisms, though not always.

Most prokaryotes have cell walls.
This means we can target their cell walls with antibiotics w/o them affecting our cells.

Eukaryotes

Newer and more complicated of the two types.

Specialized compartments for different functions.

• More complex processes possible.

• Has the DNA in a nucleus.

Slower, but can achieve greater complexity.

More commonly make up multicellular organisms, though not always.

These evolved from prokaryotes combining.
Larger prokaryote absorbs smaller (mitochondria/chloroplast) prokaryote - becomes an organelle.

All human cells are eukaryotes.
Human cells do not have cell walls.

Examples

Stem Cells

Maintain regenerative capacity.

Intestinal Cells

Maximize surface area for absorption of nutrients.

Blood Cells

Optimized for transport.

Muscle Cells

Packed with contractile proteins.

Liver Cells

Rich in detoxification enzymes.

Nerve Cells

Extended for long-distance communication.

Cell Theory

To be considered a cell:

• All organisms are composed of one or more cells.
  • Either unicellular organisms or multi-cellular organisms.
• All cells arise from pre-existing cells.
  • No spontaneous generation, only replication.
• Cells are structural and functional units of all living things.
  • Smallest independently functioning living things.
• All cells contain hereditary information.
  • DNA is passed from cell to cell during cellular division.
• All cells have similar metabolic process (ATP).
  • Energy flow (metabolism and biochemistry) occurs within cells.
• All cells are fundamentally similar.
  • These have a similar chemical composition.

Universal Cellular Features

Part of a cells chemical similarity. You can't be a cell without these things:

DNA Nucleic Acids

Genetic info that is passed to cellular offspring and is how the cell knows what to do.

Ribosomes Proteins

These are proteins that make RNA and Amino Acids meet to synthesize new proteins.

Cytoplasm Water-Based Gel

Water-based gel that fills the inside of the cell, containing enzymes/ions/molecules.

Acts as a medium/provides all components for biochemical reactions / metabolic processes.

Facilitates movements within the cell.

Keeps things suspended.

Cell Membrane Phospholipids

Selectively semi-permeable.

Maintains shape and integrity.

Made of a phospholipid bi-layer (2-tails).

Controls molecular traffic into and out of the cell.

Handles intercellular communication and recognition.

Has proteins/carbs/lipids embedded in the membrane.

• These act as messengers/receptors/enzymes with surrounding cells/molecules.

Cell Structures

Structure relates to function. Each prokaryotic cell has different structures depending on their environment.

Organelles

Little compartmentalized/specialized structures within the eukaryotic cells.

Internal Structures

Storage Inclusions

Dense core where bacteria stores materials for later use.

Gas Vesicles

Gas filled structures used for buoyancy.

Endospores

Extremely tough, usually dormant, structures used for extreme environmental protection.

Boundary Structures

Cell Walls

Tough carbohydrate-protein structure that protects the cell.

External Structures

Surface Layers

Capsule

A sticky outer coating made of carbs that protects the cell and helps it not dry out.

Appendages

Prokaryotic cells use these to absorb things and facilitate movement.

Flagella

Tail used for movement.

Found often in pathogenic bacteria.

Pili

Hair-like structures stick to surfaces and provide movement.

Found often in pathogenic bacteria.