2 Types of Cells

• Prokaryotes: Domain Bacteria & Archaea

  • No nucleus

  • DNA in a nucleoid

  • Cytosol

  • No organelles other than ribosomes

  • Small size

  • Primitive

  • i.e. Bacteria & Archaea

• Eukaryotes (Domain Eukarya): Protists, Fungi, Plants, Animals

  • Has nucleus and nuclear envelope

  • Cytosol

  • Membrane-bound organelles with specialized structure/function

  • Much larger in size

  • More complex

  • i.e. plant/animal cell

Cell Size and Scale

• Cells must be small to maintain a large surface area to volume ratio

• Large surface area allows increased rates of chemical exchange between cell and environment

• The diffusion rate increases as the area to volume ratio increases.

  • The two are directly proportional.

Nucleus

• Nucleus 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

Ribosomes

• Ribosomes 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

Endoplasmic Reticulum

• Endoplasmic Reticulum: network of membranes and sacs

• Types:

  1. Rough ER: ribosomes on surface

     • Rough ER Function: package proteins for secretion, send transport vesicles to Golgi, make replacement membrane

  2. Smooth ER: no ribosomes on surface

     • Smooth ER Function: synthesize lipids, metabolize carbs, detox drugs & poisons, store Ca2+

Golgi Apparatus

• Golgi Apparatus 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

Lysosomes

• Lysosomes Function: intracellular digestion; recycle cell’s materials; programmed cell death (apoptosis)

• Contains hydrolytic enzymes

Vacuoles

• Vacuoles Function: storage of materials (food, water, minerals, pigments, poisons)

• Membrane-bound vesicles

• Eg. food vacuoles, contractile vacuoles

• Plants: large central vacuole -- stores water, ions

Mitochondria

• Mitochondria 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

Chloroplasts

• Chloroplasts Function: site of photosynthesis

• Double membrane

• Thylakoid disks in stacks (grana); stroma (fluid)

• Contains chlorophylls (pigments) for capturing sunlight energy

Endosymbiont 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

Peroxisomes

• Peroxisomes Functions: break down fatty acids; detox alcohol

• Involves production of hydrogen peroxide (H2O2)

Cytoskeleton

• Cytoskeleton: network of protein fibers

• Cytoskeleton Function: support, motility, regulate biochemical activities

Intracellular Junctions

• 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

Plant Cells

• Cell wall: protect plant, maintain shape

  • Composed of cellulose

• Plasmodesmata: channels between cells to allow passage of molecules