CELL STRUCTURE CELL STRUCTURE Enormous variety in the

CELL STRUCTURE

CELL STRUCTURE � Enormous variety in the size and shape of different cells � Smallest cells belong to group of organisms Mycoplasma � Only about 0. 2 µm in diameter � So small that often beyond the limit of resolution of light microscopes

CELL STRUCTURE � Large cells (giant amoeba) Chaos chaos � About 1000 µm in diameter

� Larger cells yolks of bird eggs � Single cells containing stored food for the developing bird � for the most part, cells are between 5 & 50 µm in diameter

CELL STRUCTURE � certain structures are common to most cells � plants, animals, and related organisms have 3 basic structures: � cell membrane-outer boundary � nucleus-control center � cytoplasm-material between the cell membrane and nucleus

CELL MEMBRANE � all cells are separated from their surroundings by a cell membrane � regulates what enters and leaves the cell � aids in the protection and support of the cell � similar to cell walls that surround a house

CELL MEMBRANE � it must communicate with other cells, take in food, and water and eliminate wastes � composed of several kinds of molecules � lipids, proteins, cho’s

LIPIDS • double layer of lipid molecules, known as a ‘bilayer’ forms the basic unit from which cell membranes are constructed

PROTEIN �some proteins stick to the surface of the lipid bilayer, others are free to move around within the bilayer � some act as channels through which molecules can pass � others act like small pumps, actively pushing molecules from one side of the membrane to the other

CARBOHYDRATES �cho’s are attached to proteins or lipids at the membrane surface � many act like chemical id cards, allowing cells to recognize and interact with each other

CELL WALL � in organism such as plants, algae, and some bacteria, the cell membrane is surrounded by a cell wall � helps to protect and support the cell � very porous water, oxygen, carbon dioxide, and other substances can pass through easily � made up of two or more layers � layers form in a series of steps

PRIMARY CELL WALL � 1 st layer to form develops where two plant cells meet � Contains a gluey substance called pectin, that helps hold the cells together �Each of these cells then forms a primary cell wall on its side of this gluey layer � Made up of cellulose (a fibrous material) � Make the cell wall elastic stretch as it grows

SECONDARY CELL WALL �Plants that have woody stems, another layer secondary cell wall, develops � Composed of cellulose and lignin � Lignin makes cellulose more rigid � Wood consists mainly of secondary cell walls

NUCLEUS � Nucleus-info � Seen center of the cell in many cells as a large dark structure � 1 st described by Robert Brown � Not all cells have nuclei � Small unicellular organism bacteria and several other kinds of organisms, do not have nuclei

PROKARYOTES / EUKARYOTES � The absence or presence of a nucleus can be used to divide organisms into two categories: � Prokaryotes-lack nuclei � Eukaryotes-contain nuclei � Karyon=nucleus � Pro=before � Eu=true

PROKARYOTES � Prokaryotic � Bacteria organism and their relatives � Usually small and unicellular

EUKARYOTES � Eukaryotic � Both organisms unicellular and multicellular

NUCLEUS � Nucleus is the information center of the cell � Contains DNA=instructions for making thousands of different molecules � Directs all the activities that occur in a living cell

NUCLEUS � Nuclear envelope � Composed of two membranes that form boundary around nucleus � Inside dozens of nuclear pores � Molecules move in and out of nucleus through nuclear pores

NUCLEUS � Nucleolus � Most nuclei contain a small region called nucleolus � Made up of RNA and proteins � Where ribosomes are made

NUCLEUS � Chromosomes � The DNA in the nucleus of eukaryotic cells is attached to special proteins and forms large structures called chromosomes � Contain genetic information that must be passed to each new generation of cells

CYTOPLASM � Cytoplasm � Area between the nucleus and the cell membrane � Contains important structures

TOMORROW � We will discuss the organelles found within the cytoplasm!!!!!!