Introduction to Cells and the Cell Membrane (1) PDF

 Welcome to Module 006283 Cellular and Molecular Biology Summary of Aims Introduce basic concepts of cell biology, including cell structure, biological macromolecules, molecular biology, cell communication and genetics provide laboratory experience to develop skil...

 Welcome to Module 006283 Cellular and Molecular Biology Summary of Aims Introduce basic concepts of cell biology, including cell structure, biological macromolecules, molecular biology, cell communication and genetics provide laboratory experience to develop skills in acquiring and presenting experimental data, with due regard to ethics, risks and health and safety aspects To provide sufficient background to complement other current modules and enable students to continue with more specialised courses in subsequent years Learning outcomes At the end of this module you should: have acquired an understanding of the key concepts in cell and molecular biology be able to design, perform and analyse simple experiments Some preliminary comments about working with lectures… A key method of introducing topics and providing new information at University is through lectures The intention of lectures is to present material in a way that helps you to learn facts to some extent, but more importantly to help you to understand the subject A key skill which you need to develop is the ability to take the material delivered to you in the lecture and "process it" in a way that helps you to understand it You should actively make notes during the lectures Passively listening to what is being said is a poor way of capturing understanding We aim to make these lectures both informative and accessible, but understand there are many different learning styles Your feedback is always welcome  Assessment information- important dates Two assessment elements (MOD006283) 010 In-class test (4th December 2023) 011 Lab report (Canvas submission by 2pm on 24th November 2023) The Iceberg Illusion: Success Textbooks…recommended for the module …..delivers comprehensive, clearly written, and richly illustrated content to today’s students, all in a user-friendly format. Textbooks…..another good one …”designed to provide the fundamentals of cell biology required by anyone to understand both the biomedical and the broader biological issues that affect our lives” a clear account of the essentials Another one….aimed at the advanced reader A thick book aimed at the more advanced (enthusiastic) reader Distils some latest research and goes into more detail than ‘Essential Cell Biology’  Brief overview of module- major topics Cells (Cell theory) and cell membranes Subcellular organelles and endosymbiotic theory Membrane transport Biological macromolecules DNA structure and replication of DNA Transcription & Translation Cell cycle & cell division Cell death (programmed cell death) Signal transduction – how cells ‘talk’ to each other  Question How would you define ‘life’ What is a cell ? Fundamental units of life….all life ! exist alone as unicellular organisms (eg bacteria, yeasts, protozoa, and unicellular plants) or as communities of cells as in multicellular organisms (animals, plants and fungi) Not all cells are alike – vary enormously in appearance and function (eg typical bacterial cell is a few micrometers but a frog egg is approx. 1 millimetre) An idea of cell size…  Cells come in a variety of shapes and sizes Cocci = spherical Spirilli = spiral-shaped Bacilli = rod-shaped A brief history of cell biology…… Before the 17th century no one new cells existed ! Discovery of cells (around 1665) Robert Hooke looked at thin slices of cork and observed a ‘honeycomb’ structure (row of empty boxes), he coined the word ‘cell’ (latin= cella) Anton van Leeuwenhoek (1632-1723) Dutch draper, contemporary of Robert Hooke. Best known for his work on the improvement of the microscope Known as the ‘Father of Microbiology’, first to observe and describe single-cell organisms – animalcules (microorganisms) Observed - Muscle fibres - Bacteria - Spermatozoa - Blood flow in capillaries The Cell Theory Fundamental theory of biology Early part of 19th century, biologists suggested that all living things were made up of cells But the definitive statement that cells were the building blocks of life not put forward until 1839 ▪ (1839) Theodor Schwann & Matthias Schleiden - All living organisms are composed of one or more cells - The cell is the most basic unit of life ▪ (1855) Rudolf Virchow extended the theory to include the third tenet - All cells arise only from pre-existing cells (Latin: Omnis cellula e cellula) Collective observations of these three scientists form the Cell Theory ! Principles of Cell Theory All living things are made of cells Smallest living unit of structure and function of all organisms is the cell All cells arise from preexisting cells (this principle discarded the idea of spontaneous generation) All living things are constructed from cells Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company All cells have a similar chemistry and work by same basic principles All cells are composed of the same sort of molecules that participate in similar types of reactions All living things store ‘genetic instructions’ (genes) in DNA molecules – using the same code and translated by the same molecular machinery Protein molecules are the read-out of these instructions (sometimes referred to as the ‘activators’) – proteins perform a wide variety of functions in the cell – more on this later Fundamental cell activities Maintain their integrity; keeping inside in and outside out Store information required to build and reproduce themselves Convert this info into activators (primarily proteins) Capture (transform) energy to fuel their own activities Transport substances in and out of the cell and between different parts of the cell (intracellular transport) Divide to produce new cells Transmit, receive and respond to signals from their environment Characteristics of All Cells A surrounding membrane (Cell membrane) Cytoplasm – all of the cell interior (enclosed by cell membrane) except cell nucleus Organelles – structures inside the cell for cell function, each organelle has specific function – (eg mitochondria) Intracellular DNA (either inside a membrane bound nucleus or not) Membrane-bound DNA or not….. Defines two fundamental cell types (also a fundamental classification of living things) Prokaryotic: organisms have cells that do not have a membrane-bound nucleus (free-floating DNA !) Eukaryotic: organisms have cells whose DNA is enclosed in a membrane-bound nucleus Prokaryotic Cells Probably the first cell type on earth Includes Bacteria and Archaea (two domains of prokaryotes)- unicellular No membrane bound nucleus Nucleoid = region of DNA concentration Organelles not bound by membranes (but essentially no organelles !)  Eukaryotic Cells DNA bound by a nuclear membrane. The DNA is organized into linear chromosomes that store genetic info. By definition, all eukaryotic cells have a nucleus Possess many membrane-bound organelles (membranes define compartments !) In general are larger than prokaryotic cells all of the more complex multicellular organisms (plants, animals and fungi) are formed from eukaryotic cells Differences between eukaryotic and prokaryotic cells Eukaryotes Prokaryotes Membrane-bound nucleus - Two or more linear chromosomes, DNA bound to One circular chromosome proteins (histones) Introns, repetitive DNA not transcribed Introns found in archaebacteria Larger ribosomes (80S/18S) – outside the nucleus 70S/16S Cytoskeleton (actin/tubulin filaments) for support and motility Internal membrane systems (organelles) 2-1000 microns(typically 10-100 microns) Typically about 1 micron (0.5-50 microns) Representative Eukaryotic Cell Microscopy – a basic tool of cell biology Brightfield microscopy Simplest form of light microscopy Sample illuminated from below White light is transmitted through sample Generally low contrast Explore other advantages/disadvantages Fluorescence Microscopy Fluorescent dyes (fluorochromes) used for staining cells Like ordinary light microscopy except that illuminating light is passed through two filters The first only passes light of wavelengths that excite the fluorescent dye Limits of light microscopy Light microscopes have a fundamental limitation based on the wavelength of light (visible light 380-750 nm) Light microscopes limited to a useful magnification of approx. 2000X, beyond this no further detail can be detected Resolving power of an optical microscope is defined as the shortest distance between two points on a specimen that can still be distinguished by the instrument as separate entities (not the same as saying the smallest size of object that can be observed with microscope !) – an instrumental property ! The minimal resolvable spacing depends on wavelength of illuminating wavelength of light All other optical/specimen parameters optimal, then shorter wavelengths producing higher degrees of resolution. Visible light has a minimum wavelngth  Electron microscopy Electron microscopy (EM) is a technique for obtaining high resolution images of biological and non-biological specimens The high resolution of EM images results from the use of high energy electrons (which have shorter wavelengths) as the source of illuminating radiation Electron microscopy is used in conjunction with a variety of ancillary techniques (e.g. thin sectioning, immuno-labeling, negative staining) to answer specific questions EM images provide key information on the structural basis of cell function and of cell disease Transmission and Scanning Electron Microscopes (TEM and SEM) There are two main types of electron microscope – the transmission EM (TEM) and the scanning EM (SEM) TEM is analogous in many ways to the conventional (compound) light microscope In TEM electrons can pass through the specimen (placed in a vacuum) to generate an image Contrast is provided by staining specimen with electron-dense material that absorbs or scatters electrons, thus removing them from the beam as it passes through the specimen TEM can produce useful magnification of 500000 X with best possible resolution of 0.5nm (cf light microscope best possible resolution of approx. 200nm) used to visualize exterior of cells Scanning Electron Microscope (SEM) termed scanning electron microscope because the image is formed by scanning a focused electron beam onto the surface of the specimen in a specific pattern specimen is coated with very thin film of a heavy metal quantity of electrons scattered or emitted (secondary electrons) as the beam bombards successive points on the surface of specimen is measured by a detector get images of 3D objects, fine detail of internal structure, maximum useful magnification approx. 100000 X and can resolve details to between 3-20 nm Transmission EM Scanning EM Fundamental cell activities Maintain their integrity; keeping inside in and outside out Store information required to build and reproduce themselves Convert this info into activators (primarily proteins) Capture (transform) energy to fuel their own activities Transport substances in and out of the cell and between different parts of the cell (intracellular transport) Divide to produce new cells Transmit, receive and respond to signals from their environment The Cell Membrane A cell is essentially a discrete mass of cytoplasm separated from the environment by a membrane (plasma membrane) Defines the boundary of the cell – essential components of living cells as few cellular activities would occur in their absence Biological cell membranes are made up of lipid and protein – different cells have a different proportions of lipid to proteins Membrane lipids All membrane lipids share one important feature – they are amphipathic Amphipathic means that it has a polar part (hydrophilic head group) and a pair of nonpolar hydrophobic tails Membrane lipids form a bilayer structure Tails point inwards and the heads outwards Able to separate two aqueous environments Membrane lipids Most abundant membrane lipids have glycerol as part of their structure and are called glycerophospholipids Glycerophospholipids are based on the structure of glycerol-3- phosphate Structure of membrane phospholipids Long chain fatty acids are esterified to two of the –OH groups (primary and secondary carbons) to form phosphatidic acid A polar molecule (X) can be attached to the phosphoryl group to form the phosphatidyl group X is usually highly polar (charged) and this forms the polar head group Examples of polar groups (X) choline, serine, ethanolamine and inositol forming phosphatidycholine, phosphatidylserine, phosphatidylethanolamine and phosphatidylinositol, respectively !  O O H2C O C R2 R1 C O CH O H2C O P O X O− glycerophospholipid In most glycerophospholipids (phosphoglycerides), Pi is in turn esterified to OH of a polar head group (X): e.g., serine, choline, ethanolamine, glycerol, or inositol. The 2 fatty acids tend to be non-identical. They may differ in length and/or the presence/absence of double bonds. Example of membrane lipid structure: phosphatidylcholine Other major membrane phospholipids (50% of lipid) Fatty acid components of membrane lipids Fatty acyl tails vary in length, can range from C14 to C24 Almost always an even number of carbon atoms in the chain The fatty acyl tails may be the same or different on the two carbons When different, fatty acid attached to C1 is saturated and that on C2 is unsaturated Degree of unsaturation determine membrane fluidity; double bound is in the cis configuration and introduces a kink in it Straight saturated chains pack together but kinked ones cannot Fatty acid configurations