T HE N UCLEUS, C YTOPLASM, And Eukaryotic vs. Prokaryotic Cells

T HE N UCLEUS Enclosed by a phospholipid bilayer (membrane) The nuclear membrane is impermeable to most molecules The membrane contains pores that allow specific proteins and nucleotides to exit Contains the genetic material for the cell in the form of DNA Keeping the DNA separate from the rest of the cell increases the cells control of gene expression

N UCLEUS

C YTOPLASM Makes up around 70% of the cells contents Contains the free floating ions, molecules and other nutrients The “juice” that fills space inside the cell Where many cell processes occur

T WO CATEGORIES OF CELLS :

E UKARYOTIC C ELLS Do have a nucleus Genetic material is held within a nucleus. They are internally complex, with organelles and a nucleus to house DNA. Many single-celled organisms are eukaryotes, and ALL multi-cellular organisms are eukaryotes.

P ROKARYOTIC C ELLS Small and structurally simple. They lack a nucleus Their DNA is in direct contact (floats freely) with cytoplasm and is coiled into a nucleoid region. All bacteria are prokaryotic cells.

P ROKARYOTES VS E UKARYOTES Similarities Both have a cell membrane Both have DNA for genetic material Both are made from the same basic chemicals: carbohydrates, proteins, nucleic acid, minerals, fats Both require an energy supply

P ROKARYOTES VS E UKARYOTES Differences Age First prokaryotes appeared 3.5 billion years ago First Eukaryotes appeared 1.5 billion years ago Nucleus Eukaryotes must have a nucleus, Prokaryotes must not have a nucleus Organelles Eukaryotes have many organelles Prokaryotes have very few or no organelles Size Eukaryotic cells are, on average, ten times larger than prokaryotic cells.