Cellular Structure and Function

Cell theory

Cell theory

1. All organisms are composed of one or more cells

2. The cell is the most basic unit of life

3. All cells come from other pre-existing cells

*We don’t know what LUCA (last universal common ancestor) is or when it was

Prokaryote

• Bacteria and archaea

• Lack of a nucleus and membrane-bound organelles

Eucaryote

• All forms of life besides bacteria and archaea

• Contain a nucleus and membrane-bound organelles

Endosymbiotic theory

• Mitochondria and chloroplasts have DNA, so it is thought that they used to be prokaryotes

• Chloroplasts did photosynthesis, mitochondria performed cellular respiration

• Mitochondria and chloroplasts may have combined with larger prokaryotes and worked together, creating ancestral eucaryotes

Cell differentiation

The acquisition of a cell’s specific structural and functional features. (Every cell in the body has the same DNA, but there are specific genes that are turned on and off for different cell types)

Phospholipid bilayer

• Composed of phospholipid heads and tails

• Hydrophilic heads face extracellular fluid and the cytoplasm

• Hydrophobic tails line the inside of the bilayer

Fluid mosaic model

• Mosaic of proteins and carbohydrates in fluid consisting of the lipid bilayer

• Integral proteins embedded to lipid bilayer, peripheral proteins attached to surface

Plasma membrane functions

Transport, enzymatic activity, signal transduction, intercellular joining, cell-cell recognition, attachment to the cytoskeleton and extracellular matrix

Hypertonic

Concentration of solute is greater outside of the cell than inside

Plasmolysis

Cells can shrink from the exit of water (like a wilting leaf)

Isotonic

Concentration of solute is equal outside of the cell and inside (dynamic equilibrium)

Hypotonic

Concentration of solute is less outside of the cell than inside

Cytolysis

Cells can expand to the point of bursting from influx of water

Simple diffusion

• Through the phospholipid bilayer

• Small, non-polar molecules and small, uncharged polar molecules

Osmosis

• The phospholipid bilayer

• H2O

Facilitated diffusion

• Integrated protein channels

• Large, uncharged polar molecules and ions

Active transport

• Located in carrier proteins in the phospholipid bilayer

• Ions and molecules move from low to high concentration using energy (ATP)

Endocytosis

• Cell takes in macromolecules by forming vesicles from the plasma membrane

• Ex: phagocytosis (cellular eating), pinocytosis (cellular drinking), receptor mediated endocytosis

Exocytosis

Cell secretes macromolecules when vesicles fuse within the plasma membrane

Concentration gradient

• Difference in concentration from inside and outside of a cell

• Substances move the concentration gradient from high to low

Turgor pressure

Force directed against the cell wall in a plant cell from influx of water in hypotonic extracellular fluid

Cell size issues

• If too large, cannot move nutrients in and waste out efficiently

• When cell grows larger so does the demand placed on DNA

• 37 trillion cells in average adult human

Universal organelles (plants and animals)

Nucleus, ribosomes, endoplasmic reticulum, golgi apparatus, mitochondria, peroxisomes, microfilaments, and microtubules

Animal-only organelles

Centrioles (for mitosis), locomotion organelles (flagellum like on sperm and cilia like little hairs)

Plant-only organelles

Plastids/chloroplasts, cell wall, central vacuole, plasmodesmata