Cell Types: Prokaryotic vs. Eukaryotic Cells

• The cell is the basic unit of biological organization
• Basic cell composition includes protoplasm, cell membrane and organelles
• There are two types of cells: eukaryotic and prokaryotic

Prokaryotic Cells

• These are small and simple cells
• Prokaryotic cells are 0.1 to 5.0 µm in size
• They are unicellular
• In prokaryotic cells, a nucleus is absent
• Contain circular DNA
• They contain a single haploid (n) chromosome
• Prokaryotic cells lack membrane-bound organelles
• These cells reproduce both sexually and asexually
• They divide by binary fission
• Bacteria and archaea cells are examples

Eukaryotic Cells

• These are large and complex cells
• Eukaryotic cells are 10 to 100 µm in size
• Unicellular or multicellular
• A nucleus is present
• Eukaryotic cells contain linear DNA
• They have a paired diploid (2n) chromosome
• These cells have membrane-bound organelles
• They mostly reproduce sexually
• Eukaryotic cells divide by mitosis
• Examples are plant and animal cells, including humans

Similarities between Prokaryotic and Eukaryotic Cells

• Have a cell or plasma membrane
• They have cytoplasm
• Contain ribosomes
• Have DNA

History of the Cell Theory

• Proposed in the 1830s by Schleiden and Schwann
• Modern cell theory states that cells are the smallest complete living things
• All organisms are composed of one or more cells
• Modern cell theory states that cells arise only from other cells
• All existing cells are descendants of the first cells

Cell Membrane

• A double phospholipid layer with embedded proteins
• Membrane transport includes osmosis, protein channels and active transport
• The cell membrane also uses a fluid mosaic model

Cytoplasm of the Cell

• Mostly water with chemical compounds in solution or colloid
• Colloids are individual or clumped atoms or ions distributed in a medium
• Polar compounds go into solution
• Nonpolar compounds go into colloidal suspension

Nucleus

• The control center of the cell
• The nuclear membrane has pores to allow the passage of substances
• Chromatin genetic material is inside the nucleoplasm
• Nucleolus is the site of ribosome formation

Mitochondria

• The powerhouses of the cell
• Cristae are inner folds where cellular respiration occurs
• The energy requirements of a cell determine cristae number

Lysosomes

• Digestive enzyme packages
• These digest stored food
• They handle maintenance and repair of organelles
• Lysosomes are suicide agents for old or weak cells
• Contain hydrolytic enzymes like proteases, lipases, nucleases, and glycosidases

Endoplasmic Reticulum

• A system of membranes that makes up channels
• Connects with outer nuclear and cell membranes
• Cisternae are sac-like or channel-like cavities
• Rough ER is for protein synthesis
• Rough ER has attached ribosomes
• Smooth ER is for fat transport and sex hormone synthesis

Golgi Apparatus

• A collection of flat saclike cisternae
• The area for concentration and collection of cellular compounds
• Storage warehouses of the cell
• The carbohydrate synthesis site

Ribosomes

• Distributed throughout the cytoplasm
• Attached to the rough endoplasmic reticulum
• Ribosomes have no membrane covering
• The site of protein synthesis
• Protein functions include structure, enzymes or catalysts, and immune response
• DNA contains the code for a particular protein
• DNA is found in the nucleus

Transcription

• Messenger RNA copies DNA code and leaves the nucleus

Translation

• Transfer RNA picks up amino acids
• Ribosomes link amino acids together

Centrioles

• A centrosome contains two centrioles at right angles to each other
• Composed of nine sets of triplet fibers
• Form spindle fibers during cell division
• Guide duplicated chromosomes to daughter cells

Cilia and Flagella

• Hairlike protrusions from the cell membrane
• Nine double fibrils around two single central fibrils
• Cilia move materials across the cell surface
• A flagellum propels the cell through a medium

Plastids of Plant Cells

• Chloroplasts are the most common plastid
• Photosynthesis is the conversion of light into chemical energy
• Granum is made of thylakoids and connected by lamella
• Chromoplasts contain carotenoid pigments
• Leucoplasts store food
• The cell membrane is surrounded by a cell wall
• The cell wall is composed of cellulose
• Cellulose is dietary fiber and is synthesized by Golgi bodies
• Animal cells do not have cell walls