Cell Membrane. A level Biology Module 2

Transcription

1 Cell Membrane A level Biology Module 2 CRD 2015

2 Contents 1. The Structure and Function 2. Factors affecting membrane structure 3. Diffusion 4. Active transport 5. Osmosis

3 The Structure and Function of Membranes 5.1 CRD 2015

4 5.1 Learning Objectives Outline the roles of membranes within cells and at the surface of cells. Describe the fluid mosaic model of membrane structure. Describe the roles of the components of the cell membrane, including phospholipids, cholesterol, glycolipids, proteins and glycoproteins.

5 Role of Membranes The role of membranes include: Separating cell contents from the outside environment. Separating cell components from cytoplasm. Cell signalling and recognition. Holding the components of some metabolic pathways in place. Regulating the transport of materials into and out of the cell.

6 Phospholipid

7 Phospholipid

8 Phospholipid bilayer

9 Fluid Mosaic Model

10

11 Membrane Proteins Intrinsic proteins (integral proteins) transmembrane proteins that are embedded through both layers of the membrane. Extrinsic proteins (peripheral proteins) are present in one side of the bilayer.

12 Intrinsic Proteins Passive movement of polar molecules and ions down a concentration gradient. Involved in both active and passive transport.

13 Glycoproteins and Glycolipids Involved in cell adhesion and as receptors (eg. neurotransmitters and peptide hormone receptors) Antigens

14 Cholesterol Increases membrane stability and fluidity. Hydrophilic end interacts with heads of phospholipid bilayer and hydrophobic end with the tails.

15 Specialised membranes Membranes are specialised according to their function

16 Other components The number and function of other components differ between cells.

17 Sites of chemical reactions Proteins in membranes of organelles need to be in the correct position for the chemical reactions to take place.

18 Communication and Cell Signalling Communication between cells in multicellular organisms is very complex. In order to detect signals cells have cell surface receptors. Receptors are generally proteins. Receptors work because they have a complementary shape to the substance that binds to it.

19 Hormone receptors Hormones are chemical messengers. The are produced by specific cells then released into the organisms. Cells with a receptor for the hormone are target cells. The hormone binds with the receptor on a target cell.

20 Insulin example of a hormone Insulin is released by β-cells in the islets of Langherhans in the pancreas. Released due to increased blood sugar levels. Insulin is a protein molecule.

21 Insulin receptor Insulin attaches to insulin receptors on the plasma membrane of target cells. When insulin is attached it triggers internal responses in the cell that lead to more glucose channels being present in the plasma membrane.

22 Medicinal drugs Some developed that are complementary to the shape of receptors. Intended to block receptors. eg. β-blockers prevent heart muscle from increasing the heart rate. Some drugs mimic a neurotransmitter. eg. Drugs used to treat schitzophrenia.

23 Hijacking receptors Viruses enter cells by binding with receptors on the cells plasma membrane that normally bind to the host s signalling molecules. Some poisons binds with receptors. HIV virus Toxin extracted from bacterium Clostridium botulinum.

24 Factors affecting Membrane Structure 5.2 CRD 2015

25 5.2 Learning Objectives Describe and explain the effect of temperature and solvents on membrane structure and permeability. Describe how practical investigations on membrane permeability can be carried out.

26 Membrane structure Membranes control the substances that go in and out of the cell. If structure is disrupted, they can lose control of this.

27 Temperature With an increase in temperature: Increase kinetic energy (phospholipids) Increase in permeability. Channel and carrier proteins denatured.

28 Solvents - water Water, a polar solvent, is essential in the formation of the bilayer.

29 Solvents - organic Many organic solvents are less polar / nonpolar. Eg. Alcohol (less polar) Dissolves membranes, disrupting cells. Benzene (non polar)

30 Alcohol and cell membranes Strong alcohol solutions are toxic as it destroys cells in the body. Less concentrated solutions do not dissolve membranes but still disrupt them. Increased fluid and permeable.

31 Alcohol and nerves Nerves need intact cell membranes to function. When disrupted unable to transmit impulses as normal. When it occurs in the brain normal behaviour is affected.

32 Investigating membrane permeability Beetroot contains betalain.

33 Crossing the Membrane - Diffusion 5.3 CRD 2015

34 5.3 Learning Objectives Understand and explain the concept of water potential. Explain diffusion. Be able to perform and interpret practical investigations into the factors affecting diffusion.

35 Diffusion

36 Diffusion Each molecule diffuses down its own concentration gradient.

37 Rate of diffusion Rate of diffusion is affected by: Temperature Concentration gradient Stirring / moving Distance / thickness Size of molecule

38

39 Types of diffusion Simple diffusion Facilitated diffusion using a protein channel Facilitated diffusion using a carrier protein

40 Crossing the Membrane - Active 5.4 CRD 2015

41 5.4 Learning Objectives Describe and explain what is meant by active transport, endocytosis and exocytosis.

42 Active Transport

43 Active Transport

44 Coupled transport Uses concentration of ion as an energy source.

45 Types of coupled transport

46 Animation

47 Endocytosis and exocytosis

48 Endocytosis Phagocytosis - food Pinocytosis - liquids

49 Endocytosis

50 Exocytosis

51 Use of ATP in endocytosis and exocytosis Energy in the form of ATP is used to: Move vesicles along cytoskeleton Change the shape of the cell Fusion of cell membrane with vesicle.

52 Animation

53 Osmosis 5.5 CRD 2015

54 5.5 Learning Objectives Explain what is meant by osmosis, in terms of water potential. Recognise and explain the effects of solutions of different water potentials on plant and animal cells.

55 Osmosis Osmosis is the diffusion of water.

56 Water Potential ( ) Water Potential ( ) is: A measure of the potential energy of water relative to pure water Water s interaction with other particles, gravity and air pressure results in its potential energy

57 Water Potential ( ) The Greek symbol for Water Potential, Ψ W, is the letter psi (pronounced sigh ). Several forces act on water to alter its ability or potential to do work. These forces are pressure, concentration, electrical and gravity; added together they make up the Water Potential. So essentially, Water Potential = Pressure + Concentration + Electrical + Gravity but only the first two of these are important

58 Water Potential ( ) Simplified Definition of Ψ w : Y w = Ψ P + Ψ S Where, Ψ P = pressure potential - represents the pressure in addition to atmospheric pressure Ψ S = osmotic or solute potential - represents the effect of dissolved solutes on water potential; addition of solutes will always lower the water potential

59 Water Potential ( ) Water potential is a combined measure of solute concentration and pressure (psi) measured in MPa (megapascals) 1 MPa 10 atmospheres Pure water in an open container: = 0 Mpa Solutes decreases Pressure increases Negative pressure (tension) decreases

60 Water Potential (Ψ) The water potential of pure water is zero. Addition of solutes decreases the water potential makes is more negative.

61 Water Potential ( ) In a cell the cytoplasm always contains salts and sugars results in is -ve

62 Water Potential ( ) If a cell loses water to the environment it becomes flaccid and then plasmolysed. If a cell gains water from the environment it becomes turgid. Have a look at: molysis.htm

63

64 Cells in solution