Cells

Prokaryotic and Eukaryotic

Prokaryotes

• Prokaryotic cells have no “true” nucleus but rather a nuclear “region”

• Typical prokaryotic components are:– Capsule– Cell wall– Plasma membrane– Cytoplasm (alt. cytosol)– Pili (fimbriae)– Flagella– Ribosomes– Nucleoid (nuclear region)

Prokaryotic Cell

Escherichia coli (E. coli)

Result of Binary Fission

Eukaryotic Cells• More “evolved” cells

• Composed of:– Nucleus– Nucleolus– Chromatin– Nuclear Envelope– Plasma Membrane– Golgi Apparatus– Lysosome

- Peroxisome- Mitochondria- Endoplasmic Reticulum- Ribosomes- Microvilli- Cytoskeleton- Centrosome

Eukaryotic Cells

Organelle Structure & Function• Nucleus

– Contains the genetic information of the cell

– Surrounded by the nuclear envelope– Nuclear pores lined with pore

complex protein– Nuclear lamina maintains shape of

envelope– Chromosomes contain chromatin;

DNA mixed with proteins– Nucleolus synthesizes rRNA

• Proteins and rRNA make subunits of ribosomes

• May function in cell division

Structure & Function• Ribosomes

– Complex of rRNA and protein– Present abundantly in cells active in protein synthesis

(i.e., pancreas, muscle, etc.)– Sight of polypeptide assemblage – Free and bound– 70S and 80S ribosomes

• 70S in prokaryotes• 80S in eukaryotes

– Mitochondria/Chloroplast 70S

Endoplasmic Reticulum

• Approximately ½ of total membrane in eukaryotic cells

• Composed of cisternae or lumen

• Both smooth and rough endoplasmic reticulum

Smooth Endoplasmic Reticulum• Functions include

– Synthesis of lipids• Oils, phospholipds and steriods

– Cells that secrete sex hormones are rich in smooth ER (ovaries and testicles)

– Metabolism of carbohydrates– Detoxification of drugs and

poisons• Liver cells add hydroxyl group for

water solubility• Proliferation occurs with consistent

exposure– Calcium storage in muscle

tissue

Rough Endoplasmic Reticulum

• Studded with Ribosomes– Pancreatic cells synthesize

insulin on the ER– Polypeptide chains enter lumen

of ER• Bound to carbohydrates to form

glycoproteins• Considered “Secretory Proteins”• Secretory Proteins separated from

cytosol via transport vessicles

Golgi Apparatus• Receiving center for vesicles from ER• Plentiful in cells specialized for

secretion• Cis face and trans face to “stack” due to

polarity difference– Cis is receiving side of Golgi; trans is

shipping side• ER products are enzymatically modified

between cis and trans sides– Glycoproteins– Monomers are removed and substituted

for large variety of carbs– Membrane phospholipids also altered in

Golgi• Polysaccharides (pectin and other cell

wall materials) synthesized directly by the Golgi

• Targeting of products takes place between cis and trans face via molecular tags

Lysosome• Sack of hydrolytic enzymes

– Enzymes made at Rough ER and refined at Golgi• Lysosomes form from trans face of Golgi

Apparatus• Engage in phagocytosis• Lysosomes merge with food vacuoles in cells

and digest food– Products then passed onto the cytosol

• Autophagy– Damaged organelle surrounded by double membrane– Lysosome fuses with membrane and digests

organelles– Recycles raw materials back into cytosol

Vacuoles

• Food, contractile and central vacuoles

• Certain plants have vacuoles that act as disposal sites for “toxic” metabolic byproducts

• Others hold pigments that determine the petal color of flowers

• Defense mechanism to make plant unpalatable to animals

Mitochondria

• Site of cellular respiration• Found in nearly all eukaryotic cells: plants, animals, fungi

and most protists– Human parasites have organelles that may have evolved from

mitochondria

• Number of mitochondria correlates to level of metabolic acitivty

• Mitochondria move, alter shape and divide• Double phospholipid bilayer encases mitochondria

– Outside smooth; inside convoluted and forms “cristae”– More folds create more efficiency

• Mitochondrial matrix is inside inner membrane– Enzymes, mitochondrial DNA and ribosomes present here

• Some enzymes aid in cellular respiration

Chloroplasts

• Member of the plastid family– Amyloplasts

• Contain chlorophyll and photosynthetic enzymes

• Double membrane bound• Three major components

– Thylakoids– Granum– Stroma (DNA and ribosomes)

Peroxisome

• Single membrane• Transfers hydrogen to various molecules

to create H2O2 (some conversions are for mitochondria)– Enzymes within lysosome convert H202 to

water for expulsion from cell

• Glyoxysomes found in plant seed fat tissue– Converts fatty acids to sugar

Cytoskeleton

• Mechanical support and maintenance of shape

• “Monorail” theory for movement within cell

• Three components of cytoskeleton– Microtubles – Micorfilaments– Intermediate filaments

Microtubules

• Hollow tube 25 nm in diameter• Composed of tubulin protein

– Dimer: composed of two subunits• Growth occurs by adding tubulin dimers

• “Plus end” is the more active of two microtubule ends

• Functions include– Guiding secretory vesicles from Golgi– “Beating” of cilia and flagella– Separate chromosomes during cell division

• Form from centrosome (near nucleus)– Centrioles located here

Microfilaments

• Composed of actin (globular protein)– Twisted chain with branching ability

• Function in specialized cells that pull materials across plasma membrane (microvilli)

• Play a major role in cell motility (think muscle cells and clevage furrows)

Intermediate Fibers

• Form the “permanent” framework for the cell

• Much more of a structural molecule than microtubules and microfilaments– Nuclear lamina– Nucleus– Nerve cell strength