Cell Biology Chapter 6

Student learning outcomes:

• Distinguish between prokaryotic and eukaryotic cells• Explain how organelles and cells fit in biological hierarchy• Describe structures, functions of cytoplasmic membrane

• List the steps and structures for making proteins• Describe the structures and functions of various

eukaryotic organelles • Describe structure of prokaryotic (bacterial) cell and

explain how it differs from eukaryotic cell

Prokaryotes and eukaryotes All cells have:• Outer cell membrane: separates internal contents from environment• Contain cytoplasm: liquid with dissolved substances• Contain DNA, genetic information

• some have cell walls

• Prokaryotes: no nucleus single-celled

DNA is amorphous nucleoid (Fig. 6.9).

Domain Bacteria; Domain Archaea• Eukaryotes: true nucleus (membrane bound);

other organelles (membrane bound) (Fig. 6.6). Domain Eukarya: Unicellular protists and yeasts;

Multicellular fungi, animals, plants

Organelles and cells

• Organelles: subcellular structures carry out specific functions: ex. Mitochondrion, nucleus

• Cells: Microorganisms are mostly unicellular• Population of microbes: localized group of one species (colony on plate)

• Community: single-celled and multicellular organisms in an ecosystem (ex. Pondwater, intestines)

Cytoplasmic membrane = plasma membranePhysical partition between cell contents and outside

Composed mostly of phospholipid molecules:• Phosphate group at one end (P and O; PO4) (hydrophilic)• 2 long fatty acid tails (mostly C and H) (hydrophobic)

• Also specific proteins: channels, carriers (Fig. 6.3**)

Cytoplasmic membrane = plasma membrane

• Phospholipid bilayer : 2 layers of molecules: Fatty acid tails inside; phosphates outside

• Selectively permeable: selective about what materials pass through

• Fluid mosaic model: membrane is dynamic; molecules can move sideways

Movement through membrane:

• Diffusion – passive processMolecules move from concentrated to less concentrated• Osmosis – special diffusion of water through selectively

permeable membrane (Fig. 6.5)• Solution = homogeneous mixture:• Solute – material that is dissolved; ex. sugar• Solvent – liquid into which solute is dissolved; ex. water

Movement through membrane:• Active transport – cell uses energy to bring nutrients

from outside into cell, through channels, carriers• Phagocytosis – cell ‘eats’ other cell; ex. White blood

cell (macrophages) eat bacteria

Ribosomes and protein synthesisRibosomes are assembly line - join amino acid subunits in

chains to form proteins• rRNA (ribosomal RNA) forms proteins• Instructions come from DNA as mRNA (messenger RNA)• Little tRNA (transfer RNA) carry amino acids to be joined

** Prokaryotic and eukaryotic ribosomes differ in size, composition.Many antibiotics inhibit prokaryotic ribosomes and kill bacteria;

ex. Streptomycin, chloramphenicol

Cell organelles of Eukaryotes

Animal Cell

Plant Cell

Cell organelles of Eukaryotes (Fig. 6.6)

• Cytoplasm – inside of cell; cytosol is liquid part.• Nucleus – chromosomes enclosed in nuclear envelope• Endoplasmic reticulum (ER)

Network of tubes, channels – for communication; transport of proteins

• Rough ER; ribosomes synthesize proteins for transport• Smooth ER makes lipids• Golgi apparatus- processing, packaging, shipping proteins

Packages vesicles that go outside cell or to organelles

Cell organelles of Eukaryotes

Mitochondrion- power station • Energy from food -> ATP (adenosine triphosphate), • Mitochondria have DNA (related to bacteria)

Chloroplast- photosynthesis in plants• Energy from sun -> ATP , make sugars from CO2, H2O• Chloroplasts have DNA (related to bacteria)

Cell organelles of Eukaryotes• Lysosome – recycling centerDigestive enzymes break down damaged organelles, invading bacteria• Cytoskeleton – internal scaffold

• Cell movement – short cilia, long flagella• Cell wall – present in plants (cellulose), fungi (chitin, other polymers)

Prokaryotic

cells

• Single-cell factories: – no organelles;• ribosomes• DNA (amorphous nucleoid)• Cytoplasmic membrane

• [Archaeal cells have very different cell wall, cell membrane from Bacteria]

Prokaryotic cells• Cell wall of Bacteria – peptidoglycan (Fig. 6.10) carbohydrate , short protein chains• Gram-positive cells have very thick wall• Gram-negative cells have thin wall, outer membrane layer• Mycoplasma do not have cell walls• Mycobacterium (tuberculosis) has waxy walls

Prokaryotic cellsGram was scientist who discovered differential staining

technique for the two kinds of bacteria(reflects cell wall structures).

• Gram + are purple; Gram- are pink (with counterstain)

*Note penicillins interfere with synthesis of peptidoglycan, are most effective against Gram+ bacteria ex. Streptococcus

Prokaryotic cells• Glycocalyx –polysaccharide layer outside wall:

Capsule if firm; slime layer if soft; protect bacteria from phagocytosis

• Flagella (flagellum), fimbriae (fimbria), pili (pilus): extend from wall; help with locomotion, transfer between bacteria

Prokaryotic cellsEndospores are survival –• form inside some bacterial cells; • regenerate and cause disease:

Clostridium botulinum = botulism Bacillus anthracis = anthrax Clostridium tetani = tetanus

Review questions• 1. Draw a prokaryotic and eukaryotic cell

(Explain the basic differences)

• 2. Diagram and describe the organization of the cytoplasmic membrane

• 3. How can we use structural differences between prokaryotic and eukaryotic cells to help treat disease?

• 4. Diagram the structures and functions of different eukaryotic organelles