Cell Biology Basics

Life Processes

• Seven essential life processes: homeostasis, metabolism, nutrition, excretion, growth, response to stimuli, and reproduction

Atypical Cells in Eukaryotes

• Atypical cells in eukaryotes: red blood cells, phloem sieve tube elements, skeletal muscle cells, and aseptate fungal hyphae
• Red blood cells are enucleated, lacking a nucleus, allowing them to be smaller and more flexible
• Phloem sieve tube elements have large pores for sap to pass through, and their nucleus and most cell contents break down during development
• Skeletal muscle cells are multinucleated, with long cylindrical fibers formed from the fusion of individual cells
• Aseptate fungal hyphae lack septa and cell membranes between cells, resulting in a large multinucleate structure

Cell Specialization

• In multicellular organisms, cells become specialized to form different cell types
• Each cell does a small number of functions extremely efficiently
• Different cell types interact to achieve complex functions

Differentiation

• Every cell in a multicellular organism is a clone of an original parent cell (except gametes)
• All cells that come from this will have identical DNA
• Certain cells will express specific genes, while others will express other genes

Stem Cells

• Stem cells are unspecialized cells with two key properties: self-renewal and potency
• When a stem cell differentiates and becomes specialized, it cannot change again
• Stem cells are limited in availability

Types of Stem Cells

• Three types of stem cells: totipotent, pluripotent, and multipotent
• Totipotent stem cells can form any cell type and divide into new organisms
• Pluripotent stem cells can form any cell type
• Multipotent stem cells can form a number of closely related cell types

Cell Membranes

• Cell membranes enclose the cellular contents, separating them from the external environment
• Cell membranes have two properties: semi-permeability and selectivity
• Cell membranes have two major components: phospholipids and proteins

Phospholipids

• Phospholipids have a polar head (glycerol and phosphate) and two nonpolar tails (fatty acids)
• The head is hydrophilic, and the tails are hydrophobic, making phospholipids amphipathic molecules
• Phospholipids spontaneously form bilayers in water, with tails forming the center and heads on the outside

Membrane Proteins

• The phospholipid bilayer is embedded with proteins, forming a mosaic
• Membrane proteins can be integral (permanently attached to the bilayer) or peripheral (attaching to the membrane surface)
• Membrane proteins serve a variety of functions: junctions, enzymes, transport, recognition, anchorage, and transduction

Glycosylation

• Phospholipids and proteins can have carbohydrate chains added to them, forming glycolipids and glycoproteins
• The carbohydrate extends to the extracellular side of the membrane and can function for adhesion and recognition

Membrane Transport

• Simple diffusion occurs in cells for particles that can pass between the phospholipids
• Osmosis is the movement of water into and out of cells, which is possible through aquaporins, water channel proteins
• Facilitated diffusion occurs through channel proteins for large, charged, or polar molecules
• Active transport requires energy (ATP) and moves particles from low to high concentrations

Cell Compartmentalization

• Eukaryotic cells are compartmentalized, with discrete organelles that are specialized to carry out specific tasks
• Each organelle is separated from the rest of the cell, allowing for greater efficiency and organization