CHAPTER 6 A TOUR OF THE CELL

Cytology: science/study of cells Light microscopy resolving power~ measure of clarity Electron microscopy TEM ~ electron beam to study cell ultrastructure SEM ~ electron beam to study cell surfaces Cell fractionation ~ cell separation; organelle study Ultracentrifuge ~ cell fractionation; 130,000rpm

A cell is a living unit greater than the sum of its parts While the cell has many structures that have specific functions, they must work together.

Prokaryote bacteria cells Eukaryote animal cells Types of cells - no organelles - organelles Eukaryote animal cells Eukaryote plant cells

Cell Types: Prokaryotic Nucleoid: DNA concentration No organelles with membranes Ribosomes:protein synthesis Plasma membrane: (all cells); semi-permeable Cytoplasm/cytosol(all cells)

Cell types: Eukaryotic Nucleus:membrane enclosed organelle containing chromosomes Membrane bound organelles of specialized form and function Generally larger than prokaryotic cells

Cell Size As cell size increases, the surface area to volume ratio decreases Rates of chemical exchange may then be inadequate for cell size Cell size, therefore, remains small

Why organelles? mitochondria chloroplast Golgi ER Specialized structures specialized functions cilia or flagella for locomotion Containers partition cell into compartments create different local environments separate pH, or concentration of materials distinct & incompatible functions lysosome & its digestive enzymes Membranes as sites for chemical reactions unique combinations of lipids & proteins embedded enzymes & reaction centers chloroplasts & mitochondria chloroplast Golgi Why organelles? There are several reasons why cells evolved organelles. First, organelles can perform specialized functions. Second, membrane bound organelles can act as containers, separating parts of the cell from other parts of the cell. Third, the membranes of organelles can act as sites for chemical reactions. Organelles as specialized structures An example of the first type of organelle is cilia, these short filaments act as "paddles" to help some cells move. Organelles as Containers Nothing ever invented by man is as complex as a living cell. At any one time hundreds of incompatible chemical reactions may be occurring in a cell. If the cell contained a uniform mixture of all the chemicals it would not be able to survive. Organelles surrounded by membranes act as individual compartments for these chemical reactions. An example of the second type of organelle is the lysosome. This structure contains digestive enzymes, these enzymes if allowed to float free in the cell would kill it. Organelle membranes as sites for chemical reactions An example of the third type of organelle is the chloroplast. The molecules that conduct the light reactions of photosynthesis are found embedded in the membranes of the chloroplast. ER

Cells gotta work to live! What jobs do cells have to do? make proteins proteins control every cell function make energy for daily life for growth make more cells growth repair renewal

Proteins do all the work! cells DNA Repeat after me… Proteins do all the work! organism

Cells functions Building proteins read DNA instructions build proteins process proteins folding modifying removing amino acids adding other molecules e.g, making glycoproteins for cell membrane address & transport proteins

Building Proteins Organelles involved nucleus ribosomes endoplasmic reticulum (ER) Golgi apparatus vesicles The Protein Assembly Line Golgi apparatus nucleus ribosome ER vesicles

What kind of molecules need to pass through? histone protein chromosome DNA Nucleus Function protects DNA Structure nuclear envelope double membrane membrane fused in spots to create pores allows large macromolecules to pass through nuclear pores pore nuclear envelope nucleolus What kind of molecules need to pass through?

Nucleolus Function ribosome production build ribosome subunits from rRNA & proteins exit through nuclear pores to cytoplasm & combine to form functional ribosomes small subunit large subunit ribosome rRNA & proteins nucleolus

Ribosomes Function Structure protein production rRNA & protein small subunit large Ribosomes Function protein production Structure rRNA & protein 2 subunits combine 0.08mm Ribosomes Rough ER Smooth The genes for rRNA have the greatest commonality among all living things. There is very little difference in the DNA sequence of the rRNA genes in a humans vs. a bacteria. Means that this function (building of a ribosome) is so integral to life that every cell does it almost exactly the same way. Change a base and this changes the structure of the RNA which causes it to not function.

Types of Ribosomes Free ribosomes Bound ribosomes suspended in cytosol synthesize proteins that function in cytosol Bound ribosomes attached to endoplasmic reticulum synthesize proteins for export or for membranes membrane proteins

Endoplasmic Reticulum Function processes proteins manufactures membranes synthesis & hydrolysis of many compounds Structure membrane connected to nuclear envelope & extends throughout cell accounts for 50% membranes in eukaryotic cell

Types of ER rough smooth

Smooth ER function Membrane production Many metabolic processes synthesis synthesize lipids oils, phospholipids, steroids & sex hormones hydrolysis hydrolyze glycogen into glucose in liver detoxify drugs & poisons ex. alcohol & barbiturates

Membrane Factory Build new membrane synthesize phospholipids builds membranes ER membrane expands bud off & transfer to other parts of cell that need membranes

Which cells have lot of rough ER? Rough ER function Produce proteins for export out of cell protein secreting cells packaged into transport vesicles for export Which cells have lot of rough ER? Which cells have a lot of ER? protein production cells like pancreas = production of digestive enzymes (rough endoplasmic reticulum from a cell of exocrine pancreas (88000X))

Golgi Apparatus

Vesicle transport vesicle budding from rough ER fusion of vesicle with Golgi apparatus migrating transport protein ribosome

Any Questions!! 2007-2008