comparing prokaryotic and eukaryotic cells

prokaryotic cells

• domains bacteria and archea

• no nucleus-DNA concentrated in region called the nucleotide

• no membrane- enclosed organelles

• 1-10 um in diameter

eukaryotic cells

• domain eukarya

• true nucleus encoded by a double membrane

• numerous organelles suspended in cytosol

• 10-100 um in diameter

why cells are so small

• cell surface to volume ratio

  • volume increases at faster rate than surface area

• plasma membrane surrounding cell must provide sufficient surface area for exchange of oxygen, nutrients, and wastes relative to the volume of the cell

exploring eukaryotic cells

• membranes compartmentalize the eukaryotic cell

  • provide local environment for specific metabolic functions

the nucleus

• surrounded by nuclear envelope

  • double membrane w/pores regulates movement of materials between nucleus and cytoplasm

• most of the cells DNA is located in the nucleus

  • organized into chromosomes

    • made of chromatin (DNA+proteins)

• each eukaryotic species has a specific number of chromosomes

  • visible only when condensed in a dividing cell

nucleolus

• dense structure visible in the non-dividing nucleus

  • synthesizes ribosomal RNA (rRNA)

  • combines it with protein to assemble ribosomal subunits

• ribosomal subunits then pass through nuclear pores to the cytoplasm for protein synthesis

ribosomes- protein factories

• composed of protein and rRNA

• free ribosomes

  • produce proteins to be used within the cytosol

• bound ribosomes

  • attached to endoplasmic reticulum or nuclear envelope

  • make proteins that will be included within membranes, packaged into organelles, or exported from the cell

endomembrane system

• consists of:

  • nuclear envelope

  • ER

  • Golgi apparatus

  • lysosomes

  • vesicles

  • vacuoles

  • plasma membrane

• all these membranes are related wither through direct contact or by the transfer of membrane segments by membrane bound sacs called vesicles

• as membranes move from the ER to the Golgi apparatus and then to other organelles, their compositions, functions, and contents are modified

endoplasmic reticulum (ER)

• membranous system that is continuous with the nuclear envelope

• smooth ER- diverse function (depends on cell type)

  • lacks ribosomes on outside surface

  • its enzymes involved in phospholipid and steroid synthesis, carbohydrate metabolism, and detoxification of drugs

    • barbiturates, alcohol, and other drugs increase liver cells production of smooth ER

      • leads to increased tolerance/reduced effectiveness

  • also functions in storage and release of calcium ions during muscle contractions

• rough ER-

  • manufactures proteins intended for secretion

    • many covalently bonded to small carbohydrates

    • transported in membrane bond organelles called vesicles

  • rough ER also manufactures membranes

    • enzymes assemble phospholipids

Golgi apparatus- shipping and receiving

• consists of a stack of flattened sacs

• vesicles that bud from the ER join the cis face of the golgi

  • adding their contents and membrane for processing

• Golgi products are sorted into vesicles, which pinch off from trans face

  • surface molecules direct pinched vesicles to plasma membrane of other organelles

lysosomes- digestive compartment

• in animal cells only

• membrane- enclosed sacs containing hydrolytic enzymes that digest macromolecules

  • acidic pH for hyrdrolytic digestion

• carry out intracellular digestion and recycle organic materials

  • digest food and pass products into cytosol (phagocytosis)

    • amino acids/monosaccharides (simple sugars)

  • damaged organelles fuse to lysosome, enzymes dismantle the membrane bound material, organic monomers are returned to cytosol for reuse (autophagy)

vacuole- maintenance compartment

• large vesicles- diverse functions depending on cell type

• food vacuole- formed as a result of phagocytosis

• contractile vacuole- pump excess water out of freshwater protists

• storage vacuole- in plants

  • store organic compounds and inorganic ions for the cell

  • may contain dangerous metabolic by products

  • poisonous or unpalatable compounds for protection from predators

• large central vacuole- in plants

  • encloses a solution called cell sap

  • a plant increases in size as a vacuole absorbs water and expands

    • can fill 80 percent or more of a cell

mitochondria and chloroplasts

• change energy from one form to another

• cellular respiration- metabolic process of fuels to produce ATP

  • occurs in the mitochondria of eukaryotic cells

• photosynthesis- production of sugars from CO2 and water by absorbing solar energy

  • occurs in the chloroplasts of plants and photosynthetic protists

evolutionary origin of mitochondria and chloroplasts

• endosymbiont theory- mitochondria and chloroplasts originated as prokaryotic cells engulfed by an ancestral eukaryotic cell

  • evidence- both organelles _____

    • surrounded by double membrane

    • grow and reproduce independently within a cell

    • contain a small amount of DNA and ribosomes

    • synthesize some of their own proteins

mitochondria- chemical energy conversion

• powerhouse of the cell- provides ATP for the cell

  • number of mitochondria is proportional to cells metabolic activity

• double membrane- each a phospholipid bilayer

  • narrow inner membrane space exists between the two layers

• smooth outer membrane

• inner membrane is folded to for cristae

  • folding increases surface area for enzymatic reactions

  • respiratory enzymes embedded in membrane

• mitochondrial matrix- inside inner membrane

  • contains respiratory enzymes, mitochondrial DNA, and ribosomes

chloroplasts- capture light energy

• two membranes separated by a thin inner membrane space

• thylakoids- inside inner membrane

  • membranous system of flattened sacs

    • stacks of thylakoids called grana

  • photosynthetic enzymes embedded

• stroma- fluid surrounding thylakoids

  • contain chloroplast DNA, ribosomes and enzymes

• other plastids- family of plant organelles that contain pigment or food

  • amyloplasts- store starch

  • chromoplasts- contain pigments for fruits and flowers

peroxisomes- oxidation

• oxidative organelles that perform different functions

  • break down fatty acids for energy

  • detoxification of alcohol and other poisons

• all produce hydrogen peroxide as a toxic by product of these oxidative reactions

  • contains enzymes for break down of hydrogen peroxide

• in plant glyoxysomes contain enzymes that convert fatty acids to sugars for emerging seedlings

cytoskeleton- support and mobility

• network of protein fibers that give mechanical support

  • literally means “skeleton of the cell”

  • 3 types of protein fibers

    • microtubules

    • microfilaments

    • intermediate filaments

• also function in cell movement (motility)

  • both internal structures and cell as a whole

  • special proteins called motor proteins produce cellular movements

microtubules

• hollow rods constructed of globular proteins called tubules

• change length through the addition and subtraction of tubulin dimers

• provide supporting framework for cell

• separate chromosomes during cell division

• serve as tracks for movement of organelles by motor proteins

motor proteins- cellular movement

• powered by ATP hydrolysis

• critical for cell function

  • transports organelles along cytoskeleton to appropriate parts of the cel

  • responsible for muscle contraction

  • responsible for cell division

cilia and flagella

• locomotor extensions

  • nearly universal structure (evolutionary significance)

• cilia are numbers and short

• flagella - 1 or 2 to a cell

• may be used to move through aqueous media

• stationary cels use to move fluid past the cell

cell wall of plants

• protects the cell from damage and maintains cells shape

• some cells add a secondary cell wall between the plasma membrane and primary wall for more protection and support; such as wood

extracellular matrix (ECM)

• animal cells secrete an extracellular matrix (outside cell)

  • composed of glycoproteins and carbohydrate molecules

    • collagen is main structural protein of ECM of most tissues

• cells attached to the ECM by fibronectins and integrins

  • communication occurs between ECM and cytoplasm

    • mechanical signaling pathway between fibronectins/integrins of ECM and microfilaments of cytoplasm

cell junctions

• plant junction- plasmodesmata

  • channel in plant cell wall that connects plasma membrane of bordering cells

    • water, small solutes, some proteins, and RNA can move cell to cell

• animal cell junctions

  • tight junction- hold adjacent cell membranes tightly together

  • desmosomes- anchoring junctions hold cells in strong sheets

  • gap junctions- communicating junctions for exchange of ions and small molecules between cells