Topic 2 - Cells and membranes

1. Topic 2 - Cells and membranes

2. Prokaryote cells • The general size of a prokaryotic cell is about 1-2 um. • Note the absence of membrane bound organelles • There is no true nucleus with a nuclear membrane • The ribosome's are smaller than eukaryotic cells • The slime capsule is used as a means of attachment to a surface • Only flagellate bacteria have the flagellum • Plasmids are very small circular pieces of DNA that maybe transferred from one bacteria to another.

3. Cell Wall: Made of a murein (not cellulose). Provides structure to the cell, prevents explosion by osmotic pressure. Plasma membrane: Controls the entry and exit of substances, pumping some of them in by active transport. Cytoplasm: Contains all the enzymes needed for all metabolic reactions, since there are no organelles. Ribosome: The smaller (70 S) type are all free in the cytoplasm, not attached to membranes (like RER). They are used in protein synthesis which is part of gene expression. Nucleoid:Is the region of the cytoplasm that contains DNA. It is not surrounded by a nuclear membrane. DNA is always a closed loop (i.e. a circular), and not associated with any proteins to form chromatin. Flagella: These long thread like attachments are generally considered to be for movement. They have an internal protein structure that allows the flagella to be actively moved as a form of propulsion. Pilli: These thread like projections are usually more numerous than the flagella. They are associated with different types of attachment. In some cases they are involved in the transfer of DNA in a process called conjugation or alternatively as a means of preventing phagocytosis. Slime Capsule: A thick polysaccharide layer outside of the cell wall. Used for sticking cells together, as a food reserve, as protection against drying out and chemicals, and as protection against phagocytosis. In some species the capsules of many cells in a colony fuse together forming a mass of sticky cells called a biofilm. Dental plaque is an example of a biofilm. Plasmids: Extra-nucleoidDNA of up to 400 kilobase pairs. Plasmids can self-replicate particularly before binary fission. They are associated with conjunction which is horizontal gene transfer. It is normal to find at least one anti-biotic resistance gene within a plasmid. This should not be confused with medical phenomena but rather is an ecological response to other antibacterial compounds produced by other microbes. Commonly fungi will produce anti-bacterial compounds which will prevent the bacteria replicating and competing with the bacteria for a resource.

4. Prokaryotic cells divide by binary fission. This is an asexual method of reproduction in which a 'parental' cell divides into two smaller but equally sized cells. The cells are genetically identical and form the basis of a reproductive clone. • 1. Note the double membrane of this E. coli. • 2. There is some evidence in the image of pilli which are the surrounding light grey masses. • 3. In the cytoplasm of the bacterium there are no visible organelles which is consistent with how we expect a prokaryote cell to appear. • 4. The nucleoid region is not seen well in this particular image but is clearer in the next image. This is an electron-micrograph of a bacteria E.coli

5. Eukaryote cells - Animal http://kirewyyhyv.blogspot.com/2011/05/animal-cell-labeled-with-functions.html

6. Eukaryote cells - Plant http://www.lacs-ny.org/webpages/nmatuszczak/files/plant%20cell%20labeled.gif

7. Nucleus: This is the largest of the organelles. The nucleus contains the chromosomes which during interphase are to be found the nucleolus. The nucleus has a double membrane with pores. The nucleus controls the cells functions through the expression of genes. Some cells are multi nucleated such as the muscle fibre. Plasma membrane: controls which substances can enter and exit a cell. It is a fluid structure that can radically change shape. The membrane is a double layer of water repellant molecules. Receptors in the outer surface detect signals to the cell and relay these to the interior. The membrane has pores that run through the water repellant layer called channel proteins. Mitochondria: location of aerobic respiration. It is a Double membrane organelle. Inner membrane has folds called cristae. This is the site of oxidative phosphorylation. Centre of the structure is called the matrix and is the location of the Krebs cycle. Oxygen is consumed in the synthesis of ATP on the inner membrane The more active a cell the greater the number of mitochondria. Rough endoplasmic reticulum (rER): protein synthesis and packaging into vesicles. rERform a network of tubules with a maze like structure. In general these run away from the nucleus The 'rough' on the reticulum is caused by the presence of ribosomes. Proteins made here are secreted out of the cell. Ribosomes: the free ribosome produces proteins for internal use within the cell. Golgi apparatus: modification of proteins prior to secretion.  Modified proteins are then packaged in membrane sacs (vesicles) so they can be excreted through the plasma membrane. Lysozyme: Formed on the golgi apparatus. Are membranes sacs containing hydrolytic (breaking things up using water) enzymes. Functions include the digestion of old organelles, engulfed bacteria and viruses and large molecules. Hydrolytic enzymes are retained within the vesicle membrane (sac) to prevent autodigestion of the cell.

8. Comparison of animal and plant cells

9. Comparison of Pro- and Eukaryotes

10. 2 Roles of extra-cellular components Plant cell wall. • Composed of celluloseand Found around all plant cells. Maintains the shape of the cell. • Provides structural support against the force of gravity. Prevents excessive uptake of water by the cell • Bone Interstitial matrix: • Bone has a matrix between its cells which includes collagen with a calcium phosphate. • Other tissues are surrounded by a matrix composed of a kind of gel that provides support for the tissue.

11. Membrane structure Hydrophilic end – loves water ----------------------- Hydrophobic end – hates water http://www.takdangaralin.com/wp-content/uploads/2009/10/image42.png

13. Movement through a membrane http://kentsimmons.uwinnipeg.ca/cm1504/membranefunction.htm

14. Diffusion • Diffusion is the movement of molecules from a high concentration to a low concentration. It is a Passive movement of molecules (requires no energy). Diffusion animation-> http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

15. Osmosis • Osmosis is the passage of water from a region of high water concentrationthrough a semi-permeable membrane to a region of low water concentration. • or because “high water concentration” is the same as “dilute solution:” • Osmosis is the passage of water from a dilute solution through a semi-permeable membrane to a more concentrated solution • for example the movement of water from the soil to the roots. Osmosis animation -> http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

16. Consequences of Osmosis • Semi permeable = Cell membranes will allow small molecules like Oxygen, water, Carbon Dioxide, Ammonia, Glucose, amino-acids, etc. to pass through. Cell membranes will not allow larger molecules like Sucrose, Starch, protein, etc. to pass through. • Isotonic – same concentration both sides of a membrane. • Hypertonic – the more concentrated solution • Hypotonic – the less concentrated solution

18. Facilitated diffusion Facilitated diffusion involves the use of a protein to facilitate the movement of molecules across the membrane. In some cases, molecules pass through channels within the protein. Animation ->http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html • Active Transport. Active Transport is a type of transport where substances move against a concentration gradient, in the opposite direction to diffusion. (From an area of lower concentration to an area of higher concentration.) Active transport needs energy and a protein pump (found in a membrane) to work. Animation -> http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

19. What happens to big food particles that won’t fit through the membrane? http://www.biosulf.org/1/images/endocytosis.gif