Eukaryotic cell Organelles Nucleus- most obvious It is enclosed in a double membrane with pores Contains chromosomes made up of deoxyribonucleic acid (DNA) In humans, autosomes- 22 pairs sex chromosomes – male XY, female XX Chromatin (complex of DNA and proteins) determines the charact eristics of the organism Storehouse of genetic information (genes) Directs the activities of the rest of the cell - Dense collection of granules called nucleolus which produces rib osomes (packets of RNA)

2. Endoplasmic reticulum- A network of vesicles and tubules throughout the cell Smooth endoplasmic reticulum (SER) - Different functions depending on the cell type e.g. synthesis of lipid and steroid hormones, release of calcium in muscle contraction Rough endoplasmic reticulum (RER)- Ribosomes which synthesise proteins are found on the surface of the vesicles

3. Golgi complex (apparatus)- A stack of vesicles responsible for storing, concentrating and packaging cell secretions and transferring to cell surface for release e.g. hormones, neurotransmitters 4. Lysosomes- Vesicles packed with granules which are hydrolytic enzymes (an intracellular digestive system) 5. Ribosomes- Synthesise the required proteins 6. Peroxisomes- Contain oxidative enzymes which produce H2O2 as a by product. Other enzymes break down H2O2 preventing damage caused by it

5. Mitochondria- - Power house where final oxidation of body fuels to provide energy takes place - Primary energy source is ATP - Provide energy to move, divide, produce secretions 6. Cytoskeleton- - A system of fibers consisting of microtubules, intermediate filaments and microfilaments - Helps to maintain shape, motility, internal movement of organelles, contraction, etc 7. Centrosome- made up of centrioles from which microtubul es grow out

Cell membrane * A boundary between the inside and outside of the cell * Point of contact with agents capable of influencing the cell * A vital and dynamic structure responsible for guarding the contents of the cell compared to the outside i.e. controlling the intracellular composition

Cell membrane- structure Made up of lipids and proteins * Lipids - A double layer of phospholipids (lipid bilayer) Lipid molecules have a hydrophilic (soluble in water), polar head towards the outside and a hydr ophobic (insoluble in water), nonpolar tail towards th e inside Therefore serves as a protective barrier for unc ontrolled flow of water - Cholesterol

* Proteins - Transmembrane proteins span the width of the membrane (integral proteins) channel proteins carrier proteins - Peripheral proteins are mainly attached to the surface * Extracellular coating of carbohydrates (glycocalyx)

Lipid of the cell membrane

Cell membrane- functions * A selectively permeable barrier to ions (Ion channels and transport proteins also vary permeability) * A receiver and transducer of information * Membrane proteins vary from cell to cell enzymes transport proteins ion channels pumps receptors for hormones and antigenic determinants neurotransmitters

Membrane permeability Differences in composition of ICF and ECF are mainly due to properties of the cell membrane Lipid bilayer is permeable to water Permeability to other substances depends on size, lipid solubility and charge * Impermeable to intracellular protein and other anions * O2 and N2 molecules are hydrophobic, dissolve in the lipid bilayer and cross with ease * CO2 is a small, hydrophilic molecule and crosses with ease * Glucose is a large, uncharged, hydrophilic molecule and crosses slowly

Donnan equilibrium When there is a non-diffusible ion on one side of a membrane, at equilibrium the diffusible ions distribute themselves so that the concentration ratios are equal e.g. Cell membrane is not permeable to intracellular proteins Gibbs –Donnan equation [K+ out] * [Cl – out] = [ K+ in ] * [Cl – in]

Types of transport proteins Transport proteins facilitate the selective movement of a few substances across the membrane e.g. urea, ions, glucose, small molecules Types of transport proteins * Simple ion channels - - continuously open- e.g. K+ channels - gated e.g ligand- hormone, voltage- Na+ * Carriers- bind ions and move them along chemical or electrical gradients. No energy is required and the process is termed facilitated diffusion. e.g. Na-glucose transporter. Can get saturated * Other carriers requiring energy e.g. Na-K ATPase - transport ions against chemical or electrical gradients. Energy is required and the process is termed active transport 15

Transport through the cell membrane Passive transport (energy not required) 1. Diffusion (simple)- movement from areas of high concentration to areas of low concentration 2. Facilitated diffusion (carrier-mediated diffusion) 1 and 2 depend on concentration and electrical gradients, permeability of the membrane, etc 3. Osmosis- movement of solvent (water) into a region with a high concentration of solute (substance) through a membrane which is impermeable to the particular solute 19

Active transport (requires energy) Primary- uses ATP energy to move ions and molecules across a concentration gradient e.g. Na/K pump – pumps 3 Na out and 2K in Secondary – uses the energy stored from ion gradients. Active transport of one substance is coupled to transport of another substance e.g. Na/ glucose transport (symport- same direction co-transport) Uses energy derived from the Na/K pump Na/ H exchanger (antiport- opposite directions counter-transport)

Primary active transport: Sodium-potassium ATPase pump

Secondary active transport of : - glucose and sodium - hydrogen and sodium

Vesicular transport Exocytosis- Secretory vesicles from Golgi apparatus move to the cell membrane, their membrane fuses with the cell membrane and the area of fusion breaks down e.g. hormones, neurotransmitters (macromolecules). The contents are moved to the outside Endocytosis- Reverse of exocytosis e.g. bacteria (phagocytosis), some substances (pinocytosis)

Endocytosis and exocytosis

Connections between cells Tight junctions- Junctions that fasten cells to one another and to surrounding tissues Give strength and stability to tissues Gap junctions- Junctions by which molecules are transferred from one cell to another. Rapid propagation of electrical activity from cell to cell and exchange of chemical messengers is possible