C HAPTER 6 A Tour of the Cell

Y OU M UST K NOW Three differences between prokaryotic and eukaryotic cells. The structure and function of organelles common to plant and animal cells. The structure and function of organelles found only in plant cells or only in animal cells.

H OW W E S TUDY C ELLS Biologists use microscopes and the tools of biochemistry to study cells

Size range of cells Note that light microscopes can not magnify as well as electron microscopes

Light Microscopy (LM) vs. Electron Microscopy (EM)

C OMPARISONS OF S COPES Visible light passes through specimen Refracts light so specimen is magnified Magnify up to 1000X Specimen can be alive/moving Color Focuses a beam of electrons through/onto specimen Magnify up to 1,000,000 times Specimen non-living and in vacuum Black and white Light Electron

E LECTRON M ICROSCOPY 2-D Creates a flat image with extreme detail Can enhance contrast by staining atoms with heavy metal dyes 3-D Used for detailed study of surface of specimen Gives great field of depth Transmission (TEM) Scanning (SEM)

Studying cell structure & function 1.Cell fractionation - take apart cells, separate major organelles 2.Ultracentrifuge - applies force 1 million times the force of gravity to separate further the cell organelles with the most dense at the bottom

2 T YPES OF C ELLS : 1. Prokaryotes : Domain Bacteria & Archaea 2. Eukaryotes (Domain Eukarya): Protists, Fungi, Plants, Animals

A P ROKARYOTIC C ELL ( BACTERIA )

P ROKARYOTE V S. E UKARYOTE “before” “kernel” No nucleus DNA in a nucleoid Cytosol No organelles other than ribosomes Small size Primitive i.e. Bacteria & Archaea “true” “kernel” Has nucleus and nuclear envelope Cytosol Membrane-bound organelles with specialized structure/function Much larger in size More complex i.e. plant/animal cell

C ELL S IZE AND S CALE Scale of the Universe: rse_2012

surface area to volume ratio Cells must be small to maintain a large surface area to volume ratio Large S.A. allows  rates of chemical exchange between cell and environment

A NIMAL S URFACE A REA E XAMPLE (A NIMAL ): Small Intestine: highly folded surface to increase absorption of nutrients Villi Villi: finger-like projections on SI wall Microvilli Microvilli: projections on each cell

F OLDS  V ILLI  M ICROVILLI

P LANT S URFACE A REA E XAMPLE (P LANT ): Root hairs Root hairs : extensions of root epidermal cells; increase surface area for absorbing water and minerals

N UCLEUS Function: control center of cell Contains DNA Surrounded by double membrane ( nuclear envelope ) Continuous with the rough ER Nuclear pores : control what enters/leaves nucleus Chromatin : complex of DNA + proteins; makes up chromosomes Nucleolus : region where ribosomal subunits are formed

N UCLEUS Contains DNA Function: control center of cell Surrounded by double membrane ( nuclear envelope ) Continuous with the rough ER Nuclear pores : control what enters/leaves nucleus Chromatin : complex of DNA + proteins; makes up chromosomes Nucleolus : region where ribosomal subunits are formed

R IBOSOMES Function: protein synthesis Composed of rRNA + protein Large subunit + small subunit Types: 1. Free ribosomes : float in cytosol, produce proteins used within cell 2. Bound ribosomes : attached to ER, make proteins for export from cell

E NDOMEMBRANE S YSTEM : Regulates protein traffic & performs metabolic functions

E NDOPLASMIC R ETICULUM (ER) Network of membranes and sacs Types: 1. Rough ER : ribosomes on surface Function: package proteins for secretion, send transport vesicles to Golgi, make replacement membrane 2. Smooth ER : no ribosomes on surface Function: synthesize lipids, metabolize carbs, detox drugs & poisons, store Ca 2+

E NDOPLASMIC R ETICULUM (ER)

G OLGI A PPARATUS Function: synthesis & packaging of materials (small molecules) for transport (in vesicles); produce lysosomes Series of flattened membrane sacs (cisternae) Cis face : receives vesicles Trans face : ships vesicles

L YSOSOMES Function: intracellular digestion; recycle cell’s materials; programmed cell death (apoptosis) Contains hydrolytic enzymes

V ACUOLES Function: storage of materials (food, water, minerals, pigments, poisons) Membrane-bound vesicles Eg. food vacuoles, contractile vacuoles Plants: large central vacuole -- stores water, ions

Parts of plant & animal cell p

M ITOCHONDRIA Function: site of cellular respiration Double membrane: outer and inner membrane Cristae : folds of inner membrane; contains enzymes for ATP production; increased surface area to  ATP made Matrix : fluid-filled inner compartment

C HLOROPLASTS Function: site of photosynthesis Double membrane Thylakoid disks in stacks (grana); stroma (fluid) Contains chlorophylls (pigments) for capturing sunlight energy

E NDOSYMBIONT THEORY Mitochondria & chloroplasts share similar origin Prokaryotic cells engulfed by ancestors of eukaryotic cells Evidence: Double-membrane structure Have own ribosomes & DNA Reproduce independently within cell

P EROXISOMES Functions: break down fatty acids; detox alcohol Involves production of hydrogen peroxide (H 2 O 2 )

C YTOSKELETON : NETWORK OF PROTEIN FIBERS Function: support, motility, regulate biochemical activities

MicrotubulesMicrofilaments Intermediate Filaments Protein = tubulin Largest fibers Shape/support cell Track for organelle movement Forms spindle for mitosis/meiosis Component of cilia/flagella Protein = actin Smallest fibers Support cell on smaller scale Cell movement Eg. ameboid movement, cytoplasmic streaming, muscle cell contraction Intermediate size Permanent fixtures Maintain shape of cell Fix position of organelles 3 T YPES OF C YTOSKELETON F IBERS :

MicrotubulesMicrofilaments Intermediate Filaments 3 T YPES OF C YTOSKELETON F IBERS :

Centrosomes : region from which microtubules grow Also called microtubule organizing center Animal cells contain centrioles

C ILIA & F LAGELLA Flagella: long and few; propel through water Cilia: short and numerous; locomotion or move fluids Have “9+2 pattern” of microtubules

E XTRACELLULAR M ATRIX (ECM) Outside plasma membrane Composed of glycoproteins (ex. collagen) Function: Strengthens tissues and transmits external signals to cell

I NTERCELLULAR J UNCTIONS (A NIMAL CELLS ) Tight junctions : 2 cells are fused to form watertight seal Desmosomes : “rivets” that fasten cells into strong sheets Gap junctions : channels through which ions, sugar, small molecules can pass

P LANT C ELLS Cell wall: protect plant, maintain shape Composed of cellulose Plasmodesmata : channels between cells to allow passage of molecules

Plant Cells OnlyAnimals Cells Only Central vacuolesLysosomes ChloroplastsCentrioles Cell wall of celluloseFlagella, cilia Plasmodesmata Desmosomes, tight and gap junctions Extracellular matrix (ECM)

H ARVARD CELL VIDEO