1、Department of Health and Human Sciences BI 101 ACell BiologyLECTURE NOTES2004BI101 Cell BiologyWeek No. TitlePage No.1 Cell Theory 22 Plasma membrane - Composition and Structure 73 - Functions and Functioning 114 Cell Compartments and Cell Junctions 165 Protein Biosynthesis 206 Energy Transduction -
2、 Principles 247 - Central Pathways 298 - Photosynthesis 3719 Nucleus, Cell Cycle and Mitosis 4010 Meiosis and Mendelian Genetics (I) 4311 Mendelian Genetics (II) 4912 Cell Shape, Movement and Extracellular Matrix 532Week 1 CELL THEORYLearning objectivesBy the end of this week you should be able to:
3、understand the meaning and significance of Cell Theory review the development of cell biology distinguish the major cell types within the context of biological diversity appreciate the hierarchical organisation of biological systems explore the limits of cell size.Cell TheoryTowards the middle of th
4、e 19th century, nearly 200 years after cells were first observed using primitive microscopes, Matthias Schleiden and Theodore Schwann developed the original Cell Theory. This recognised the cellular organisation of all plant and animal tissues. Modern Cell Theory, which also incorporates the later w
5、ork of Rudolf Virchow on cell division, states: i) the cell is the fundamental structural and functional unit of life ii) the cell is the simplest unit capable of independent existenceiii) all cells arise only from pre-existing cellsiv) all living organisms are made of cells and cellular secretions.
6、A living organism is defined as any structure displaying the attributes or properties of life. The major attributes of life are metabolism, growth, irritability and self-reproduction. Other attributesof lifeare specific organisation, movement, adaptation, and homeostasis.Living organisms may be unic
7、ellular or multicellular. A unicellular organism must be capable of carrying out all the major life attributes. In a multicellular organism groups of cells may be differentiated (specialised) to carry out one particular function, such as secretion of the hormone insulin by pancreatic cells; here the
8、 multicellular organism as a whole displays the life attributes.Forms that do not have a cellular organisation and therefore do not display all the major life attributes are termed acellular (non-cellular). Viruses, viroids and prions are acellular forms. They are technically non-living because they
9、 do not contain metabolic machinery and cannot reproduce in the absence of living cells. Exceptionally, as obligate parasites capable of redirecting a host cells activities, viruses may be viewed as microorganisms at the interface of non-living and living.The significance of Cell Theory is that it i
10、dentifies and stresses the cellular basis of all life. It follows that an understanding of cell structure and functioning is an essential prerequisite for the study of more complex biological systems. 3Development of Cell BiologyCell biology has developed through 3 main themes:i) the realisation tha
11、t the cell is the fundamental unit of biological organisationii) a progressive understanding of the structure of different cell typesiii) increasing knowledge of cellular functioning.This development began with microscopic anatomy and continues to be expanded by cell physiology, biochemistry, molecu
12、lar biology and genetics. Nowadays, with respect to the plasma membrane, a microscopist may use labelled antibodies to reveal the presence of particular membrane components. A biochemist may identify the component molecules of a membrane signal transduction process and investigate their properties a
13、nd relationships. Physiologists may study the overall signal transduction process in a particular tissue by monitoring the effect of stimulating its component cells. The molecular biologist and geneticist may help explain membrane function by identifying relevant mutants and comparing their gene pro
14、ducts with those of normal cells. The invention and progressive improvement of analytical techniques has been crucial. For example, cells were discovered and named by Robert Hooke in 1665 using a compound microscope that he had made himself. This instrument had a magnification of x30. His drawings s
15、how the cell walls in the dead cork tissue he observed. In 1674 Anthon van Leeuwenhoek described living cells using his simple microscopes which had superior magnification (x275). In the 19th century improved microscope lenses facilitated the observations of Matthias Schleiden and Theodore Schwann w
16、hich lead to Cell Theory. Other workers used improved staining techniques to observe structures like chromosomes. Today, a modern light microscope can achieve a magnification of x1,000 and a resolution of 0.2m whilst the transmission electron microscope typically achieves magnifications of x10,000 5
17、0,000 and can resolve details 1nm apart. The ultracentrifuge, developed in the 1920s by Theodor Svedberg, provides another example of how knowledge of cell biology has expanded with the use of new technology. Early machines permitted isolation of the relatively heavy mitochondria from other cell com
18、ponents. By the 1940s aerobic respiration had been localised to this mitochondrial cell fraction. As differential and density gradient ultracentrifugation techniques improved, the roles of the lighter organelles, such as lysosomes, were elucidated. Modern ultracentrifuges can achieve centrifugal for
19、ces 500,000x that of the earths gravitational field and are used to sediment macromolecules as well as organelles. The sedimentation constant, usually expressed in Svedberg units (S), is calculated from the rate at which a component sediments divided by the force applied. Proteins, organelles and vi
20、ruses may have sedimentation constants around 10S, 100S and 200S respectively. Generally, the larger structures have higher S values although sedimentation rate is also affected by other factors such as shape.Milestones in the development of cell biology can be further explored in the interactive ti
21、meline as well as in the later lectures.(interactive activity 1A)4Major Cell TypesIn 1937 Chatton proposed the terms prokaryotic (before the nucleus) and eukaryotic (true nucleus) to distinguish the two major groups of cells.The protoplasm of prokaryotic cells lacks a membrane bound nucleus but cont
22、ains a single circular chromosome of double-stranded DNA in the nucleoid region. Generally there are no membrane-bound compartments (other than elaborations of the cell membrane). However, cyanobacteria have thylakoid membranes that function in photosynthesis. Ribosomes are small (70S) and endocytos
23、is is limited. In colonial prokaryotes the cells are generally identical. Cells generally reproduce asexually by binary fission. Nearly all prokaryotes have a cell wall. Adherent pili or capsules may be present. Plasmids may also be found. A flagellum, if present, is simple. Cell diameter is typical
24、ly 1-5m. Within the prokaryotic group the Archaea (Archaebacteria) and the Bacteria (Eubacteria) are distinguished by DNA sequence data and cell wall structure.The protoplasm of eukaryotic cells consists of a membrane-bound nucleus surrounded by cytoplasm. The nucleus contains linear chromosomes and
25、 at least one nucleolus. The cytoplasm consists of the cytosol and numerous organelle compartments. Ribosomes are large (80S) and endocytosis is not rare. Multicellular eukaryotes may show differentiation of cell structure and function. Mitosis and meiosis occurs; therefore both diploid and haploid
26、cells are found, the latter during sexual reproduction. A flagellum, if present, contains microtubules. Cell diameter is typically 10-30m. Eukaryotes encompass the Protista (which includes protozoa and eukaryotic algae), Plantae, Fungi and Animalia. Plant cells may be distinguished from animal cells
27、 by the presence of a cell wall, chloroplasts, starch granules and a cell vacuole. Fungal cells lack chloroplasts, vacuoles and motile elements but have a cell wall. Protists show an enormous variety of cell structure, size and shape; many are large, motile, unicellular organisms.(interactive activi
28、ty 1B)(interactive activity 1C)(interactive activity 1D)(interactive activity 1E)Hierarchical OrganisationBiologists break living systems up into a number of hierarchical levels (summarised below) in order to organise the bank of knowledge in a manageable way and to recognise that all life is depend
29、ent on its component parts.CellsElements monomers polymers macromolecular assemblies and organelles cellsComplex multicellular organismsSpecialised cells tissues organs organ systems organismsBiosphere5Organisms populations communities ecosystems biosphereMan has 200 different cell types which make
30、up the 4 animal tissue types (epithelial, connective, nervous and muscular tissues). Plant cells fall into 5 categories (parenchyma, collenchyma, sclerenchyma, xylem and phloem) which make up the 3 plant tissue systems (dermal, vascular and ground tissues). Organs are compound tissues which function
31、 within organ systems.So, we can see the place of any cell type within the multicellular organism, or the relationship of chemical building blocks to the cell as a whole:Carbon,hydrogen,oxygen glucose cellulose cell wall plant cellCardiac muscle cells cardiac muscle heart cardiovascular system manCe
32、ll SizeThe volume of eukaryotic cells, reflecting their greater complexity, is at least 1000x that of most prokaryotic cells. Despite their differences, eukaryotic and prokaryotic cells are considered to be equally successful. The extra energy and nutrient cost of eukaryotic compartmentalisation mus
33、t be offset by the advantages provided by specialist organelles and a cytoskeleton. Although most cells have a diameter of 1-30m, some cells, like the mycoplasma below, are smaller than the largest viruses whilst some neurones, egg cells and protists, are considerably larger.The table below compares
34、 approximate cell sizes: cell diameter (m) volume(m3) relative volume (PPLO* = 1)Prokaryotic cellsPPLO 0.1 0.001 1Streptococcus sp. 1 1 103Eukaryotic cellsSaccharomyces sp. 10 1,000 106Rat liver cell 20 8,000 8 x 106Human egg cell 125 1,953,125 2 x109*PPLO = pleuro-pneumonia-like organism, a mycopla
35、sma and one of the smallest cells which can only be seen with an electron microscope.(interactive activity 1F)6The lower size limit depends on the minimum number of molecules necessary to maintain a self-reproducing unit. Calculations based on the volume occupied by around 100-200 enzymes and associ
36、ated membranes gives a cell size in agreement with that of the smallest cells.The upper size limit is restricted (in the absence of transport mechanisms) by the diffusion coefficients of essential metabolites. Schack Krogh calculated that diffusion alone could provide sufficient oxygen to support ae
37、robic respiration in a cell or organism up to 1mm in diameter. This is in agreement with the size of the larger protists.Week 2 THE PLASMA MEMBRANE - COMPOSITION AND STRUCTURELearning objectivesBy the end of this week you should be able to: describe the structure of membranes present the evidence su
38、pporting our understanding of membrane structure show an understanding of the chemical composition of membranes relate the properties of the major components of membranes to their link-barrier roles.Membrane: a thin flexible solid sheet or film; a thin sheet-like structure (The Chambers Dictionary,
39、1998).Membranes are important components of cells. The protoplasm of each cell is surrounded by a plasma membrane and many cell organelles are surrounded by a membrane which is generally similar to the plasma membrane. Membranes act as links and barriers. The plasma membrane separates the protoplasm
40、 from the external environment, and organelle membranes isolate their contents from the cytoplasm.The plasma membraneThe membrane that surrounds the cell is called the plasma membrane. It serves to separate the cell cytoplasm from the extracellular environment. It acts as a barrier between the cell
41、contents and its surroundings. By preventing the passage of some molecules whilst allowing that of others the internal environment of the cell can be maintained, and in some respects it can be very different from the external environment.Evidence for the plasma membrane7When cells are viewed under t
42、he light microscope they are seen to possess a distinct boundary. Unless they are damaged the contents remain within the cell. Red blood cells can conveniently be used for studies on membranes. These cells occur naturally as distinct entities in suspension in blood plasma. They contain the red pigme
43、nt haemoglobin so that individual cells can be readily observed. When red blood cells are suspended in an isotonic solution water movement through the membrane into and out of the cell is balanced and the cells retain their appearance. However if they are suspended in water then water enters the cel
44、ls because of osmosis. This causes the cells to swell until they eventually burst, just as a balloon increases in size until it bursts when it is inflated. When the red blood cell bursts the contents are liberated and the ruptured plasma membrane can be distinguished. The empty membranes are called
45、red cell ghosts. (interactive activity 2 fig 1)The lipid nature of membranesWhen red blood cells are treated with an apolar solvent the haemoglobin leaks out.(interactive activity 2 fig 2)Apolar solvents dissolve lipids and so we conclude that lipids are a major constituent of the plasma membrane. F
46、urthermore apolar solutes that are lipid soluble can be readily absorbed by cells, a finding consistent with the plasma membrane having a lipid nature.Polar molecules can also be taken up by cells. Smaller polar molecules are able to enter more rapidly than larger molecules, suggesting that there ar
47、e pores in the plasma membrane through which polar molecules can pass.The structure of membranesThe bimolecular leaflet (Gortner and Grendel 1925).These workers extracted the lipid from red blood cell membranes and measured its surface area. They worked out the surface area of the average red blood
48、cell and found that the surface area of lipid was exactly twice the surface area of a red blood cell. They concluded that the plasma membrane consists of two layers of lipid ie it is a bimolecular leaflet.The Gortner and Grendel experiment.1. Red blood cells were prepared from a sample of blood and
49、their numbers were estimated. 2. The cells were lysed by suspension in water and the plasma membranes were collected.3. Lipid was extracted from the membranes.4. The area of lipid was determined by spreading it in a layer one molecule thick on the 8surface of water.5. The average size of red blood cells was determined and from this their surface area was calculated.6. It was found that the total surface area of lipid was exactly twice that of the red blood cells.We now know that Gortner and Grendel obtained the right answer, but their e
