1The CellOrganelles

Eukaryotic cell

z Enclosed by plasma membranez Subdivided into membrane bound compartments

- organelles z One of the organelles is membrane bound nucleus

z Cytoplasm contains supporting matrix called cytoskeleton

Plasma membrane: a cells boundary

z Separates two compartmentsz Defines the perimeter of the cell z Place of communication with the environment

and other cellsz Channelsz Receptorsz Markersz Adhesion to each other and extracellular matrix

The plasma membrane separates the cell from the environment

z Life is a watery process z Needs boundaries

Plasma membrane

z Plasma membrane is a lipid bilayer with various proteins that are embedded in it

z Plasma membrane = lipid bilayer

The plasma membrane

z The fundamental structure of all cell membranes is lipid bilayer

z Lipid bilayer is similar in every organism and every part of the cellz Lipid bilayer just isolates two spaces

z Membrane proteins that are present in the cell membranes give each membrane a specific function (markers, channels, receptors)

2The nucleus: control center of the cell

z Largest organellez First described by Robert Brown in 1831z Contains hereditary apparatus (chromosomes)

submerged in nucleoplasmz Enveloped by double membrane called nuclear

envelope (double membrane does NOT mean bilayer, it means TWO bilayers!!!)

Nuclear envelope

z Double membrane bag that surrounds nucleusz Outer membrane z Inner membrane

z Contains nuclear poresz Nuclear pores are place

of selective transport between cytoplasm and inside of nucleus (proteins, mRNA)

Nuclear envelope

z Outer membrane is continuous with the rough endoplasmic reticulum (ER) and has ribosomes attached

z The space between the outer and inner membranes is continuous with rough endoplasmic reticulum space

Nuclear pores

z Formed at sites where inner and outer membranes membranes are pinched together

z Chromatin is organized so that a "pathway" is created to the nuclear pore

z Filled with filamentous material

Structure of the nuclear pore

z Nuclear pore is a selectivity filter

z A ring of 8 subunits z Each subunit projects a

spoke-like unit into the center so that the pore looks like a wheel with 8 spokes from the top

z Inside is a central "plug

SEM photo of nuclear pores

3Inside of the nucleus

z Interior contains nucleoplasm z Chromatine arranged in chromosomes is

submerged in nucleoplasmz Chromatin exists in extended and condensed forms

Nucleolus

z A highly visible region in nucleus consisting of aggregation of rRNA and ribosomal proteins -place of ribosomes assembly

z Nucleolus is not a structure!!! Just a visible region

Endoplasmic reticulum (ER): walls within the cell

z Little netz Network of interconnected,

closed membrane vesiclesz Single membranez Divides a cell into

compartmentsz Place of protein and

phospholipid synthesisz Connected with the nuclear

envelope!

Smooth ER

z No attached ribosomesz Anchoring place for enzymesz Site of fatty acid and phospholipid synthesisz Ca2+ storage (intracellular Ca2+ stores)

Rough ER

z ER with ribosomes attached to it (not permanently!)

z Place of the synthesis proteins that will be later inserted into the cell membranes and proteins that will be secreted from the cell

z + everything that smooth ER does

Golgi complex - delivery system of the cell

z Contains several to several hundred flattened compartments & vesicles that: z Process z Packagez Distribute molecules synthesized

in the cellz Single membrane

4Golgi complex

z Three defined regionsz Cis - fusion with ER (entry)z Medial z Trans - place of budding

secretory vesicles (exit)z Each region contains different

set of modifying enzymes

Lysosomes: recycling centers of the cell

z Digestive organellesz Responsible for degradingz Certain cell components z Material internalized from the

extracellular environment

Lysosomes

z Single membrane organellez Acidic organelles - low pH due to proton

pump (pH=5) in the membranez Contain many degradative enzymes such as

acid hydrolases

Lysosomes

z Primary lysosome inactivez Proton pump is not working

z Secondary lysosome activez Proton pump is o and pH drops to 5.0 or less

z Without constant energy lysosomes pour into cytoplasm and digest the cell

Tay-Sachs disease is a genetic defect in one of specific lysosomal hydrolases Peroxisomes

z Responsible for oxidation of fatty acids z No ATP production, just heat

z Protect the cell from hydrogen peroxide (contain peroxidase)

z Containz Single membrane z Oxidases and catalase

z Single membrane organelles

5Mitochondrion: the cells chemical furnace

z Place of oxidative metabolism and ATP production

z Tubular sausage-shaped organelles enveloped by double membrane

z Contains its own DNA and ribosomes

Mitochondria

z Two membranes of different composition and propertiesz Outer membranez Inner membrane z Intermembrane space

z Matrixz All enzymes for Krebs

cyclez mtDNA and ribosomes

Mitochondrial DNAs (nongenomic)

z Mitochondria contain multiple mtDNA moleculesz Genes in mtDNA exhibit cytoplasmic (maternal)

inheritance and encode rRNAs, tRNAs, and some mitochondrial proteins

z The size and coding capacity of mtDNA varies considerably in different organisms

Human mitochondrial DNA

z Circular moleculez Encodes mitochondrial rRNAs and 22 tRNAsz Contains no introns and no long noncoding

sequencesz The products of mitochondrial genes are not

exported

Human mitochondrial DNA Origins of double membrane

z Mitochondria (and chloroplasts) are thought to have originated as symbiotic, aerobic bacteria swallowed by the cell

6Cytoskeleton: interior framework of the cell

z A network of protein filaments which lend support to the cell as well as effect cell movement

z Dynamic system - constant assembly and disassembly

Three different types of cytoskeletal fibers

z Cytoskeleton consists of three different kinds of filaments each composed a different type of protein z Microfilaments z Intermediate filaments z Microtubules

z All are protein polymers

Three different types of cytoskeletal fibers Cytosol (cytoplasm)

z The portion of the cell enclosed by the cell membrane but not part of any organelle

z Divided into compartments through complicated array of internal membranes

z Containsz All organellesz Cytoskeletonz Ribosomesz Metabolic enzymes