1 . CELL PHYSIOLOGY. STRUCTURE AND FUNCTIONS OF THE CELL. PROPERTIES OF THE CELL MEMBRANE; CELL JUNCTIONS.INTERCELLULAR SIGNALLING. TRANSPORT THROUGH THE CELL MEMBRANE

sections

• define cell

• structure and function of cell

• function of organelles

• properties of cell membrane

• cell junctions

• intercellular signalling

• transport mechanism of transport through cell

define cell

• a cell is the simplest structural functional unit

structure and function of cell

• has nucleus, plasma membrane, cytoplasm (composed of five substances: water, ions, proteins, lipids and carbohydrates)

• cell contains genetic code

• cell arises from division (mitosis and meiosis - growth and reproduction)

• cells acquire and utilize energy - ATP

• chemical reactions, catabolism, anabolism and metabolism

• mechanical activities, hormone responses

• regulate activities: DNA synthesis

function of organelles

1. Nucleus - contains chromosomes, used for protein synthesis, contain DNA, makes ribosomes

2. Ribosomes - site of protein synthesis, DNA as loop

3. RER - transport protein, fold and process protein that were made at ribosome

4. SER - synthesis of lipids and steroids

5. Mitochondria - site of later stages of aerobic respiration, ATP production

6. Centrioles - hollow cylinders involved in spindle formation and cellular transport

7. Lysosomes - digestive enzymes, destroy cellular waste

8. Vesicle - fluid-filled sac, transport substances in and out of cell via cell membrane and between organelles, endocytosis (entering) exocytosis (exiting)

9. Peroxisomes - contains oxidases with catalase it can detoxify substances, oxidative organelles

properties of cell membrane

• Cell membrane = outer layer

• Primary functions:

  • encloses (protects)

  • fluid mosaic model components - has lipid membrane so lipophilic so impermeable, has channels

  • polar - can induce electric potential difference permeable to diff ions, diffusion potential that develops depends on concentration inside and outside of membrane

  • channels that are open in membrane

cell junctions

• structural multiprotein complexes

• provide contact between neighbouring cells or between cell and extracellular matrix

• Function:

  • tight junction - prevent passage of molecules and ions through space between cells

    • Material must enter by diffusion or active transport

    • block movement of integral membrane proteins

  • adhere junction - joins actin filaments of cells together. Cadherins and catenin used for adhesion

  • Desmosomes - hold two cells tightly together, found in epithelia

  • Gap junction - intercellular channels allow passage between cells of ions and small molecules

intercellular signalling

• coordinates cell actions

• Synaptic way - neuronal signals are transmitted electrically along nerve cell axon

• Paracrine way - signal released by cells into extracellular fluid and act locally

• Endocrine way - hormones produced in endocrine glands are secreted into bloodstream and distributed widely throughout the body

• Contact- dependent - cell surface bound signal molecule binds to a receptor protein on an adjacent cell

transport mechanism of transport through cell

1. Simple diffusion

2. Facilitated diffusion:

3. Active transport: Depends on Permeability Passive transport of molecules

   • Diffusion: eg pulmonary capillaries.

   • Osmosis: isotonic, hypotonic, hypertonic

Filtration: in the capillaries, adapted - thin diffusion easily takes place through them, pressure dependent. Large molecules filtered ou