AP BIOLOGY Cell Structure INTRO Chapter 6 Slide shows combined and modified from: http://gbs.glenbrook.k12.il.us/Academics/gbssci/bio/apbio/Lecture/lecture.htm; http://www.explorebiology.com/ http://home.att.net/~tljackson/neville.html

CELL THEORY All organisms are made of one or more cells. Cells are the basic unit of structure and function in living things Cells arise only by division of a pre- existing cell.

Anton van Leeuwenhoek 1st to see 1665- Robert Hooke saw “little boxes” in cork and called them cells 1673- Anton van Leeuwenhoek 1st to see living cells Microscope image: http://www.answers.com/topic/microscope Cork image: http://www.cortex.de/img_kork/cork_cells_big.jpg Hooke image: http://www.metaweb.com/wiki/upload/5/5c/Hookeyoungmtwb.jpg Microscope/Leeuwenhoek image: http://www.answers.com/topic/microscope Animation from: http://web.jjay.cuny.edu/~acarpi/NSC/13-cells.htm

1838- Matthias Schleiden concluded that ALL PLANTS are made of cells 1839- Theodor Schwann concluded that ALL ANIMALS are made of cells Plant image: http://www.epa.gov/maia/images/classification.gif Schleiden image: http://web.visionlearning.com/events/Schleiden_Apr5_2005.htm Schwann image: http://home.tiscalinet.ch/biografien/biografien/schwann.htm Animals image: http://animaldiversity.ummz.umich.edu/index.htm

Rudolph Virchow saw dividing cells in the microscope and reasoned that 1855- Rudolph Virchow saw dividing cells in the microscope and reasoned that cells come from other cells Virchow: http://www.parlament-berlin.de/Galeriecopy.nsf/0/8ABC720262898739C1256A480037F869?OpenDocument Mitosis: http://biology.dbs.umt.edu/biol101/labs/lab_6_images/sect01and06/Rebecca,%20tanner,%20and%20liam%20mitosis%20root%20tip.jpg

How do we study cells? Microscopes Light microscopes Electron microscopes Transmission (TEM) Scanning electron microscope (SEM)

LIGHT MICROSCOPES 0.2 µm resolution (10-6 m) ~ size of bacterium Visible light passes through specimen Can be used to study LIVE cells http://www.global-b2b-network.com/b2b/51/1046/54022/sell_biological_microscope.html

TRANSMISSION ELECTRON MICROSCOPY (TEM) Aims an electron beam through thin sections of specimens Used mainly to study internal structure of cells Uses heavy metals to stain Image called a “micrograph”

SCANNING ELECTRON MICROSCOPE (SEM) Used to study surface structures Sample covered with thin film of gold Beam excites electrons on surface Great depth of field ~ appears 3D

Differential centrifugation Cell Fractionation Tissue cells Homogenization Homogenate 1000 g (1000 times the force of gravity) 10 min Differential centrifugation Supernatant poured into next tube 20,000 g 20 min Pellet rich in nuclei and cellular debris mitochondria (and chloro- plasts if cells are from a plant) “microsomes” (pieces of plasma mem- branes and cells’ internal membranes) ribosomes 150,000 g 3 hr 80,000 g 60 min ULTRACENTRIFUGE used to separate organelles from cell Variable density of organelles

EXAMPLE: RIBOSOMES PROKARYOTIC vs EUKARYOTIC S = Svedberg unit Measure of sedimentation rate (how fast it settles) http://www.mun.ca/biology/scarr/MGA2-03-33.jpg

Cell Size As size increases, volume increases much more rapidly than surface area.

PROKARYOTES EUKARYOTES DNA in nucleoid Chromosomes in region, without a nucleus nuclear membrane surrounded by a nuclear membrane

Nucleus Nucleolus – ribosome sub-units are made here; Repository for genetic material Directs activities of the cell Usually single, some cells several, RBC none Nucleolus – ribosome sub-units are made here; Surface of nucleus bound by two phospholipid bilayer membranes nuclear membrane (envelope) Nuclear pores – protein gatekeepers Usually proteins going in and RNA going out

Chromosomes DNA of eukaryotes is divided into linear chromosomes. exist as strands of chromatin, except during cell division associated with packaging histones, packaging proteins Nucleosomes- beadlike unit of DNA packaging (histones help)