Prokaryotes & Eukaryotes By Diana L. Duckworth Rustburg High School Campbell County

Features in common All cells are surrounded by a plasma membrane Inside membrane is semifluid substance called cytosol (cytoplasm) All cells contain chromosomes carrying genes in form of DNA All cells contain ribosomes (site of protein manufacture)

Prokaryotic Cells DNA found in region called nucleoid No membrane isolates DNA from cytosol No specialized organelles in cytosol May have cilia or flagella for locomotion Cell wall – rigid structure outside membrane May have a capsule around cell wall

Streptococcus

Eukaryotic Cell DNA combines with histones to form chromosomes Inside a nuclear membrane (DNA isolated from cytoplasm) Well defined nucleus Numerous specialized organelles in cytoplasm Many internal membranes Much larger than prokaryotes

Plant Cell Animal Cell chloroplast vacuole Cell wall

Why be small? Cells must obtain nutrients & expel wastes across cell membranes As size decreases, surface area increases. Amount of surface area/volume increases. Cell functions more efficiently.

Cell or Plasma Membranes Phospholipid Bilayer Hydrophobic lipid tails orient away from water in cytoplasm & outside cell Hydrophyllic heads contain phosphate groups Lipid tails either saturated or unsaturated

Electron Micrograph of Cell Membranes 8 nm thick Cell membranes

Membrane Proteins Ends of proteins are hydrophyllic Center is hydrophobic Integral proteins go through membrane Peripheral proteins are only on surface Proteins have many functions (later)

Other Components of Membranes Carbohydrate chains attached to proteins (glycoproteins) or lipids (glycolipids) –(blood types) In animal cells cholesterol molecules are embedded in membrane –Keeps membrane fluid at low temps (homeostasis) Membranes are fluid Phospholipids move 10 million times/second Some proteins move; others don’t

Membranes are “sided” Selective permeability –Allow some things in and not others Vacuoles expell some waste & proteins to outside Vacuole membrane must merge with cell membrane –Inside of vacuole is same as outside of cell