The Cell is basic structural and functional unit of the body • can perform all basic life functions

Principal Parts of the Cell:

1. Cell Membrane / Plasma Membrane / Plasmalemma • Composed of: a) phospholipid bilayer • phosphate head group (hydrophilic) • FA tails (hydrophobic) • separates ICF + ECF: i) Intracellular fluid (ICF) = inside cell ii) Extracellular fluid (ECF) = outside cell b) cholesterol • scattered throughout membrane • adds stability to the cell membrane c) Membrane Proteins • 2 types: i) integral proteins • within the membrane ∴ have a hydrophobic region • some extend across entire membrane = transmembrane ii) peripheral proteins • attached to extracellular or intracellular region of integral proteins i.e. on the periphery of the cell membrane

• Functions of Membrane Proteins: i) enzymes ii) transporters iii) channels iv) receptors v) anchors vi) identity markers (for immune system) d) membrane carbohydrates • only on outer surface • bound to proteins (glycoproteins) or lipids (glycolipids) • Functions: • cell recognition e.g. egg and sperm • anchor cells together e) microvilli • small projections of cell membrane to increase surface area • best seen on cells of the small intestine and kidney Fluid mosaic model of the cell membrane: • fluid – membrane constituents can move around (phospholipids and some proteins) • mosaic – proteins dot surface like tiles in a mosaic 2) Cytoplasm • AREA between the inside of the cell membrane and the outside of the nucleus • 2 divisions:

• a) cytosol = gel-like intracellular fluid • contains water and a suspension of carbohydrates, b) Organelles 3) Non-membranous organelles a) Ribosomes proteins, and lipids • may contain inclusions e.g. melanin (pigment), glycogen (stored glucose) • structures that perform a specific function and are essential for life i) non-membranous • in direct contact with cytosol ii) membranous • surrounded by membrane that isolates them from the cytosol • sites for protein synthesis • contain ribosomal RNA (rRNA) + proteins • May be: b) Centrosome i) free in cytosol - make proteins destined for cytosol, mitochondria, nucleus ii) attached to endoplasmic reticulum (ER) - make proteins destined for all other sites • dense area of cytoplasm, usually contains 2 centrioles (function uncertain - some cells lack them) • organizes microtubules of cytoskeleton & spindle apparatus (for cell division) c) Cytoskeleton • ALL types support cell shape and are formed from proteins

• important in cell movement, cell division, movement/anchoring of organelles + proteins (e.g. receptors, enzymes) • 3 types: i) Microfilaments made of actin • Functions: • muscle contraction (with myosin) • maintenance of cell shape and projections (e.g. microvilli) • cytokinesis ii) intermediate filaments • composition is tissue specific e.g. keratin • Function: • support the cytoplasm (scaffolding for the cell) iii) microtubules • hollow tubes made of tubulin • Function: • form: • 1) centrioles • 2) spindle apparatus • 3) cilia (short) • 4) flagella (long) • structural • move or secure organelles in place

4. Membranous organelles a) mitochondria • site of ATP synthesis • contains own DNA, RNA, + proteins • have a double membrane b) Endoplasmic Reticulum (ER) • membranous network throughout cytoplasm 2 types: i. Rough ER (RER) • ribosomes attached - synthesis of secretory, lysosomal and membrane proteins ii. Smooth ER (SER) • lacks attached ribosomes • continuous with RER • synthesizes lipids + steroid hormones c) Golgi Apparatus/Complex • stacks of membrane discs • modifies (e.g. trims or adds CHO groups), sorts, packages, and delivers proteins/lipids to cell membrane, lysosomes, or for secretion (cellular post office) d) lysosomes • filled with digestive enzymes • digest bacteria, viruses, worn-out organelles (clean up function)

5. Nucleus • largest membranous organelle • cell control centre • cells may have 1 or more nuclei • Parts: a) nuclear envelope → double membrane with nuclear pores → connected to ER b) nucleolus → non-membranous → dense (less light gets through) region of DNA, RNA, + proteins where ribosomes are made and assembled c) chromosomes/chromatids → made of DNA + histone proteins → can be: i) dispersed = Chromatin DNA uncoiled + not individually visible in this form MOST of the time (when cell is not dividing) ii) condensed + chromosomes individually visible → found in dividing cells (during mitosis/meiosis)