The Cell

The Cell Theory Cells are the basic building blocks of life All cells come from pre-existing cells Cells are the basic functional unit of life Cells are the basic structural unit of life

Essential Tasks Obtain food and energy – metabolism Convert energy into a form that is useable to the organism – cellular respiration Construct and maintain the molecules that make up parts of the cell – growth & repair Carry out chemical reactions - metabolism Eliminate wastes - excretion Reproduce – mitosis/meiosis Keep instructions on how to build structures - DNA

Prokaryotes vs. Eukaryotes Two basic cell types: Prokaryotes Eukaryotes “single celled” Lack a nucleus, DNA in nucleoid instead Lack most organelles e.g – Most Bacteria “multi celled” Have DNA concentrated in a nucleus Have organelles e.g – Plants, Animals

Cell Wall + Cell Membrane Cell Membrane Cytoplasm Cytoplasm Cell Wall Cell Membrane Nucleus Nucleus Centriole Vacuole Vacuole Chloroplast Green Plant Cell Animal Cell Outside Covering Cell Wall + Cell Membrane Cell Membrane Vacuoles Large Central Vacuole Small random vacuole Chloroplasts Present Absent Centrioles

The Cell Membrane

Cell Membrane Function 1) Transportation of Materials - Transport raw materials into the cell from the surrounding Extra Cellular Fluid (ECF) e.g – O2,H2O,glucose,aa - Transport manufactured products and wastes out of the cell into the ECF e.g. – hormones, enzymes, CO2

Cell Membrane Functions 2) Gatekeeper for the Cell - Prevent entry of unwanted matter into the cell e.g. – bacteria, poisons - Prevents the escape of matter needed within the cell to perform cellular functions e.g. – keep cell parts, needed enzymes, nutrients inside cell

Composition of the Cell Membrane CM is composed of 1) Lipids 2) Proteins 3) Carbohydrates

Phospholipids CM is essentially a double layer (bilayer) of phospholipids Phospholipids resemble triglycerides in structure, except that one of the 3 fatty acids has been replaced with a polar phosphate/nitrogen chain

Polar Head P/N group Glycerol Backbone Glycerol Backbone Fatty Acid Chain Fatty Acid Chain Fatty Acid Chain Fatty Acid Chain Fatty Acid Chain

Polar Head - hydrophilic - P/N chain Non polar Tail - hydrophobic - FA chains

The dual nature of the phospholipid molecule, the cell membrane is formed of a double later of these molecules, arranged “tail-to-tail” = phospholipid bilayer Head Tails Head

The polar head of the phospholipid is attracted to water (which is also polar) Soluble in water This part of the molecule is said to be hydrophilic (water-loving) The non-polar tail of the phospholipid is not attracted to water Not soluble in water This part of the molecule is said to be hydrophobic (water-hating) and will avoid contact with water at all costs

Hydrophobic tails face inward to form the interior of the membrane (avoid contact with water) Hydrophilic heads face outward to form the inner and outer surface of the membrane (wanted contact with water) This phospholipid bilayer forms the backbone of the cell membrane, throughout which other macromolecules are scattered

Proteins Various shapes and sizes, depending on function in the membrane 2 main kinds: 1) Peripheral Proteins – on the surface 2) Integral Proteins – through the membrane

Peripheral Proteins Hydrophilic (water-loving) Are attached to inner and outer surface of membrane In contact wit hydrophilic heads of phospholipids and watery interior/exterior of cell

Integral Proteins Have both hydrophilic and hydrophobic areas Penetrate completely through or partially into the phospholipid bilayer Hydrophobic areas contact watery interior & exterior of cell Hydrophobic areas are embedded inside the bilayer to avoid contact with water

Carbohydrates Polar – hydrophilic Found attached to outer surface of membrane only Carbohydrate + protein = glycoprotein Carbohydrate + lipid = glycolipid

Cholesterol Allows the cell membrane to remain more rigid at high temperatures Makes the membrane more fluid at low temperatures Ensures that the membrane is less permeable to biological molecules Only present in animal cells, plants have a different molecule that achieves the same functionality