BIOH111. o Cell Biology Module o Tissue Module o Integumentary system o Skeletal system o Muscle system o Nervous system o Endocrine system

Transcription

1 BIOH111 o Cell Biology Module o Tissue Module o Integumentary system o Skeletal system o Muscle system o Nervous system o Endocrine system Endeavour College of Natural Health endeavour.edu.au 1

2 Textbook and required/recommended readings o Principles of anatomy and physiology. Tortora et al; 14 th edition: Chapter 3 Endeavour College of Natural Health endeavour.edu.au 2

3 BIOH111 Cell Module o Session 1 (Lectures 1): Homeostasis and Cell organisation and function of specific organelles o Session 2 (Lectures 2 and 3): Central Dogma and plasma membrane organisation and function o Session 3 (Lectures 4): Cell communication (vesicular transport) and extracellular matrix o Session 4 (Lectures 5 and 6): Cell communication (signalling) and Cell division Endeavour College of Natural Health endeavour.edu.au 3

4 BIOH111 Session 2: Lectures 2 and 3 Central Dogma and plasma membrane organisation and function Department of Bioscience endeavour.edu.au

5 Preparation for this session o Complete any missing concepts and linking words from Session 1 o Make a model of plasma membrane (see Session 2 tutorial) o Complete osmosis experiment and bring your observations to next class (see Session 2 tutorial) Endeavour College of Natural Health endeavour.edu.au 5

6 Objectives Lecture 2: Central Dogma Define central dogma Describe transcription and translation and relate product of these processes to their function Lecture 3: The plasma membrane Define structure of the plasma membrane and relate it to its functions Describe types of membrane proteins and define their structure and function Define types of transport Describe passive and active transports Endeavour College of Natural Health endeavour.edu.au 6

7 Animal cell Plasma membrane Nucleus Cytoplasm Organelles Endeavour College of Natural Health endeavour.edu.au 7

8 Central Dogma: NUCLEUS - function transcription translation DNA RNA protein Base triplet Codon + anticodon amino acid - double-stranded - nucleus - single-stranded - nucleus & cytoplasm - amino acid sequence determines the structure - anywhere in the cell Endeavour College of Natural Health endeavour.edu.au 8

9 DNA RNA Transcription Base triplet Codon Gene promoter + exons + introns Definition: Process by which genetic information encoded in DNA is copied onto a strand of RNA called messenger RNA (mrna). o o o Initiation: Promoter region initiates transcription by RNA Polymerase binding to a START base triplet ATG Elongation: RNAP reads a base triplet at a time and makes a complementary (antisense) RNA strand (mrna) from both intron and exon sequences; DNA only unwrapped at the site of transcription Termination: RNAP stops transcribing when it reaches a STOP base triplet (TAA; TAG; TGA) NOTE: trna and rrna are synthesised in the same way. For detailed process: session 18 BIOB111 Endeavour College of Natural Health endeavour.edu.au 9

10 For interest only Post-Transcription Processing o Involves the formation of mature mrna. o Both, exons & introns, are copied onto the mrna transcript during Transcription. Splicing o The process of editing of the RNA transcript, when the introns are removed to produce the mature mrna molecule. Stoker 2014, Figure p811

11 RNA Codon & Anticodon amino acid Genetic code: 1 codon = 1 amino acid Translation Definition: The process of reading the mrna nucleotide sequence to determine the amino acid sequence of the protein o o o Initiation: mrna with a START codon (AUG) is first read by the ribosome with the antisense trna anticodon (TAC) that caries amino acid methionine) Elongation: mrna is now a template for ribosome to keep translating codons into anticodons on trna which carry specific amino acid; this process in the ribosome builds a polypeptide chain that will become proteins Termination: once ribosome encounters a STOP codon on mrna, a corresponding trna signals release of polypeptide chain from the ribosome Stoker 2014, Figure p823 For detailed process: session 18 BIOB111 Endeavour College of Natural Health endeavour.edu.au 11

12 Codon table Endeavour College of Natural Health endeavour.edu.au 12

13 Tertiary Structure of a Protein Stoker 2014, Figure p719 schoolworkhelper.net NOTE: what happens with a protein once it is made will be covered in detail in BIOB111

14 beautifulproteins.blogspot.com

15 Objectives Lecture 2: Central Dogma Define central dogma Describe transcription and translation and relate product of these processes to their function Lecture 3: The plasma membrane Define structure of the plasma membrane and relate it to its functions Describe types of membrane proteins and define their structure and function Define types of transport Describe passive and active transports Endeavour College of Natural Health endeavour.edu.au 17

16 Animal cell Plasma membrane Nucleus Cytoplasm Organelles Endeavour College of Natural Health endeavour.edu.au 18

17 THE PLASMA MEMBRANE o Function: flexible but sturdy barrier that surrounds the cell o Fluid mosaic model o Structure: 1. Lipids 75% phospholipids, 20%cholesterols and 5% glycolipids. 2. Proteins integral and peripheral membrane proteins with various functions Endeavour College of Natural Health endeavour.edu.au 19

18 THE LIPID BILAYER o Amphipathic Polar head and non- polar tails o Cholesterol molecules are weakly amphipathic and are interspersed among other lipids. o Glycolipids only present in the outer membrane leaflet. Endeavour College of Natural Health endeavour.edu.au 20

19 o Comprises 75% of plasma membrane lipids Phospholipids o Phospholipid bi-layer = 2 parallel layers of molecules o Each molecule is amphipathic (has both polar & non-polar region) polar parts (heads) are hydrophilic and face a watery environment both inside and outside of the cell nonpolar parts (tails) are hydrophobic and line up next to each other in the interior of the bilayer Endeavour College of Natural Health endeavour.edu.au 21

20 o Comprises 20% of cell membrane lipids Cholesterol o Interspersed among the other lipids in both layers o Stiff steroid rings & hydrocarbon tail are nonpolar and reside within the bi-layer spartapoint.com o Lipid rafts cell membrane platforms of high cholesterol and protein levels Endeavour College of Natural Health endeavour.edu.au 22

21 o Comprise 5% of the lipids of the cell membrane Glycolipids o Lipid with a carbohydrate group attached to its polar head o Carbohydrate groups form a polar head only on the outside membrane leaflet (facing the extracellular fluid) o Function: recognition from the outside Endeavour College of Natural Health endeavour.edu.au 23

22 PHYSICAL PROPERTIES OF PLASMA MEMBRANE FLUIDITY o Ensures free rotation and movement of proteins and lipids within the bilayer, helps in formation of cell junctions and allows the lipid bi-layer to self seal if it is torn or punctured. o Depends on the number of double bonds in the fatty acid tails of the lipids that make up the bi-layer and amount of cholesterol present. MEMBRANE MEMBRANE PERMEABILITY o Selectively semi-permeable - permeable to small, nonpolar, uncharged molecules and water but impermeable to ions and charged or polar molecules. o Ensures tight control of the cellular homeostasis e.g. if cell needs to adapt its concentration of intracellular ion levels it can do this by free movement of water across the membrane and control the transport of that ion thus establishing gradients o Integral proteins and vesicular transporttransport of large molecules is tightly controlled Endeavour College of Natural Health endeavour.edu.au 24

23 GRADIENTS ACROSS MEMBRANE o Concentration gradient is the difference in the concentration of a molecule between two sides of the plasma membrane. e.g. oxygen and sodium ions are more concentrated outside the cell with carbon dioxide and potassium ions more concentrated inside the cell o An electrical gradient is the difference in the electrical charges across the bilayer. Inner surface of plasma membrane is more negatively charged and outer surface is more positively charged this is called membrane potential. The combined concentration and electrical gradients are called the electrochemical gradient. Endeavour College of Natural Health endeavour.edu.au 25

24 MEMBRANE PROTEINS o Integral proteins extend into and across the entire lipid bi-layer among the fatty acid tails of the phospholipid molecules. The transmembrane domain is always a-helical. o Peripheral proteins are found at the inner or outer surface of the membrane and can be stripped away from the membrane without disturbing membrane integrity. o Many membrane proteins are Glycoproteins. a-helix. Also see session 14 BIOB111 Endeavour College of Natural Health endeavour.edu.au 26

25 FUNCTIONS OF MEMBRANE PROTEINS Integral o Ion channel o Carrier/Transport protein o Receptor o Cell identity o Linker o Enzyme Peripheral o Cell identity o Linker o Enzyme Endeavour College of Natural Health endeavour.edu.au 27

26 FUNCTIONS OF MEMBRANE o Ion Channel allow specific ion to pass through a water-filled pore e.g. Na 2+, K +, Cl - channels PROTEINS o Transporter bind a specific substance, change their shape & move it across membrane e.g. amino acid (glutamate) and glucose transporters Endeavour College of Natural Health endeavour.edu.au 28

27 FUNCTIONS OF MEMBRANE o Receptor Protein recognises specific extracellular ligand and alters cell s function e.g. hormone receptors PROTEINS o Cell identity marker allows for recognition of self e.g. MHC proteins Endeavour College of Natural Health endeavour.edu.au 29

28 o Linker FUNCTIONS OF MEMBRANE anchors intracellular and extracellular filaments to the cell membrane and allow cell movement, cell shape & structure e.g. E-cadherin PROTEINS o Enzyme catalyses reactions inside or outside the cell e.g. lactase Endeavour College of Natural Health endeavour.edu.au 30

29 Objectives Lecture 2: Central Dogma Define central dogma Describe transcription and translation and relate product of these processes to their function Lecture 3: The plasma membrane Define structure of the plasma membrane and relate it to its functions Describe types of membrane proteins and define their structure and function Define types of transport Describe passive and active transports Endeavour College of Natural Health endeavour.edu.au 31

30 Transport across the plasma membrane is essential for maintaining cellular homeostasis Types of transport: Passive transport o Simple diffusion o Facilitated diffusion (channel & carrier) o Osmosis Active transport o Primary o Secondary Covered in next session Vesicular transport o Endocytosis o Exocytosis - Small polar and non-polar molecules - Amino acids - Water - Macromolecules - Organisms Endeavour College of Natural Health endeavour.edu.au 32

31 Transport across the plasma membrane is essential for maintaining cellular homeostasis Types of transport: Passive transport o Simple diffusion o Facilitated diffusion (channel & carrier) o Osmosis - Small polar and non-polar molecules - Amino acids - Water Endeavour College of Natural Health endeavour.edu.au 33

32 PRINCIPLES OF DIFFUSION Definition: Diffusion is the random mixing of particles (solute) that occurs in a solution (solvent) as a result of the kinetic energy of the particles. Molecules of solute and solution diffuse from high to low concentration. Diffusion rate across plasma membranes is influenced by: Steepness of the concentration gradient Temperature Size or mass of the diffusing substance Surface area Diffusion distance Endeavour College of Natural Health endeavour.edu.au 34

33 SIMPLE DIFFUSION o Definition: passive process in which solute move freely through the lipid bilayer of the plasma membrane of the cells without the help of membrane transport proteins. o e.g. nonpolar, hydrophobic molecules (respiratory gases, some lipids, small alcohols, ammonia) and some polar molecules (water, urea, small alcohols) o Important for: gas exchange, absorption of some nutrients (e.g. vitamins soluble in lipid (A,D,E,K)) and lipid-soluble hormones, and excretion of waste Endeavour College of Natural Health endeavour.edu.au 35

34 FACILITATED DIFFUSION Definition: spontaneous passive process of solute movement across a biological membrane via specific transmembrane integral proteins (two types). o Rate of movement depends on: steepness of concentration gradient number of transporter proteins (transport maximum) o This type of diffusion exhibits saturation o e.g. glucose, urea, fructose, galactose and some vitamins. Transport maximum/ saturation Endeavour College of Natural Health endeavour.edu.au 36

35 FACILITATED DIFFUSION 1. Channel-mediated a solute moves down its concentration gradient across the lipid bilayer through a membrane channel. o Most channels are ion channels, allowing passage of small, inorganic ions which are hydrophilic (e.g. K +, Na 2+, Ca 2+, Cl - ) o Ion channels are selective and specific on the ion s shape and charge and may be gated (e.g. K + channel) or open all the time. Endeavour College of Natural Health endeavour.edu.au 37

36 2. Carrier-mediated FACILITATED DIFFUSION a carrier is used to move a solute down its concentration gradient across the plasma membrane. o The molecule binds to a carrier on one side of the plasma membrane which causes the carrier to undergo a change in shape so that molecule can be released on the other side. o Solute binds more often on the side of membrane with higher concentration so this process depends on the steepness of concentration gradient across the membrane. Endeavour College of Natural Health endeavour.edu.au 38

37 E.g. facilitated diffusion of glucose o Glucose binds to transport protein o Transport protein changes shape o Glucose moves across cell membrane (but only down the concentration gradient) o Kinase enzyme reduces glucose concentration inside the cell by transforming glucose into glucose-6-phosphate Endeavour College of Natural Health endeavour.edu.au 39

38 OSMOSIS Definition: osmosis is the net movement of a solvent through a selectively permeable membrane, or in living systems, the movement of water (the solvent) from an area of higher concentration to an area of lower concentration across the membrane. Water molecules penetrate the membrane by simple diffusion through the lipid bilayer or through aquaporins, transmembrane proteins that function as water channels. Water moves from an area of lower solute concentration to an area of higher solute concentration. Osmosis occurs only when the membrane is permeable to water but not to certain solutes. Endeavour College of Natural Health endeavour.edu.au 40

39 o Osmotic pressure of a solution is proportional to the concentration of the solute particles that cannot cross the membrane. Osmotic pressure helps to maintain cell volume and prevents diffusion of water molecules. o Hydrostatic pressure pressure exerted by the liquid, promotes diffusion of water form high to low concentration. o Osmotic pressure force exerted by the impermeable solutes in the solution (number of molecules) Endeavour College of Natural Health endeavour.edu.au 41

40 TONICITY Definition: Tonicity is a measure of a solution s ability to change the volume of cells by altering their water concentration. There are important medical uses of isotonic, hypotonic, and hypertonic solutions. Endeavour College of Natural Health endeavour.edu.au 42

41 ACTIVE TRANSPORT Definition: an energy-requiring process that moves solutes such as ions, amino acids, and monosaccharides against a concentration gradient. Endeavour College of Natural Health endeavour.edu.au 43

42 PRIMARY ACTIVE TRANSPORT Definition: energy derived from ATP changes the shape of a transporter protein, which pumps a substance across a plasma membrane against its concentration gradient. e.g. Na+/K+ pump (also called Na+/K+ ATPase why?): requires 40% of cellular ATP Ubiquitously and highly expressed maintains low concentration of Na+ and a high concentration of K+ in the cytosol Cystic fibrosis Endeavour College of Natural Health endeavour.edu.au 44

43 SECONDARY ACTIVE TRANSPORT o In secondary active transport, the energy stored in the form of a sodium or hydrogen ion concentration gradient is used to drive other substances against their own concentration gradients. o Plasma membranes contain several antiporters and symporters powered by the sodium ion gradient. o Symporters move two substances in same direction o Antiporters move two substances in the opposite directions across the membrane Endeavour College of Natural Health endeavour.edu.au 45

44 e.g. Na + /glucose symporter Endeavour College of Natural Health endeavour.edu.au 46

45 e.g. Na + /Ca 2+ antiporter 1. Primary active transport via Na + /K + ATPase (3 Na + out/ 2 K + in) drives increase of Na + outside the cell. 2. Transport of Na+ ions back into the cell via Na + /Ca +2 antiporter (does not need energy for function) allows transport of Ca +2 out of the cell (net effect: 3 Na + in/ 1 Ca +2 out) Endeavour College of Natural Health endeavour.edu.au 47

46 Relevance Digitalis Using the diagram above, explain what is the outcome of the use of digitalis (inhibits Na + /K + ATPase) on intracellular calcium levels in cardiac muscle cells and ultimately heartbeat. What type of patients may benefit from this treatment? Endeavour College of Natural Health endeavour.edu.au 48

47 Recap of Session 2 o Nucleus contains DNA which is used as a template for producing proteins in a process called central dogma (transcription and translation) o Plasma membrane structure contains proteins and lipids each are responsible for different plasma membrane functions: Fluid Mosaic Model Membrane transport proteins o Plasma membrane function of transport depends on the size and charge of the particle being transported Endeavour College of Natural Health endeavour.edu.au 49

48 Recap of plasma membrane structure Endeavour College of Natural Health endeavour.edu.au 50

49 Preparation for next session o Complete any missing concepts and linking words from Session 2 o Bring the model of plasma membrane to Session 3 o Revise the plasma membrane structure and function for easier understanding of vesicular transport Endeavour College of Natural Health endeavour.edu.au 51