2.1.1 Cell Theory•All living things Since the microscope are made of was introduced biologists cells. have examined the•Cells are the structure of living things. basic units of In most cases they have life. been found to be compose of cells. There•Cells come only are however some from other cells strange exceptions to the general cell pattern.
Muscle Cells: very large with many nuclei •Muscle Cells called fibers can be very long (300mm). •They are surrounded by a single plasma membrane but they are multi- nucleated.(many nuclei). •This does not conform to the standard view of a small single nuclei within a cell
Fungal Hyphae: again very large withmany nuclei and a continuous cytoplasm •The tubular system of hyphae form dense networks called mycelium. •Like muscle cells they are multi- nucleated •They have cell walls composed of chitin •The cytoplasm is continuous along the hyphae with no end cell wall or membrane
Protoctista:a cell capable of all necessary functionsProtoctista•Single celled organisms haveone region of cytoplasmsurrounded by a cellmembrane.•They can perform all thefunctions of a differentiatedMulticellular organism.•This is an image of an amoeba. A single cell protoctista capable of all essential functions. What cell organelles can you see?
Acetabularia an extra ordinary large cell! •This is an example of an algae •The cells are some 7 cm long! •This seems to contradict theory about cell size. We would expect a large surface area to volume ratio which facilitates a rapid rate of diffusion.
Bone: so much extra cellular material the basic cell structure seems lost •There are some cells that secrete material outside of the cell membrane •The secretions solidify and dominate the structure •In this example the bone cell has secreted concentric layers of bone largely calcium phosphates. •The living cell is difficult to distinguish.
A virus is a non-cellular structure •Composed of a protein coat and containing either the nucleic acid DNA or RNA •Viruses are the smallest and simplest of the microbes. •They are a-cellular (not made of cells) and, since they cannot reproduce (or do any of the seven characteristics of life) on their own, they are considered non-living.
•They are in fact more like complex chemicals than simple living organisms.•Viruses are obligate parasites that can only reproduce inside host cells which get damaged in the process, leading to disease.•Viruses are thought to have arisen from lengths of DNA that became separated from their cells.
•This is a picture ofBacteriophage viruses .•These are viruses that infectbacterial rather thaneukaryotic cells•They are an important tool ingenetic engineering•Remember this is a proteinstructure not a cell
Advantages of using a light microscope •Light microscopy has a resolution of about 200 nm, which is good enough to see cells, but not the details of cell organelles. •Specimens can be seen in color (unlike the monochrome electron micrographs) which includes staining and natural colors. •There is a wide field of view to observe the tissue structure (2mm) •Living specimens can be observed and therefore their movement can be studied
Advantages of the Electron Microscope The electron microscope has greater resolution (detail) and magnification than the light microscope. •Resolution approx = 0.25 nm •Magnifications = x 500,000Rather than shinning light through the specimen the EM takes advantage of the short wavelength of the electron.
Rather than shinning light through thespecimen the EM takes advantage of theshort wavelength of the electron. •A beam of electrons is fired from a hot metal wire and focused on the specimen by a series of electromagnets. •The image is produced by the same principles as a TV screen. Photographs are then produced (electron micrographs) •The Electron Microscope allows the study of the organelles of cell structure.
There are two kinds of electron microscope. •The transmission electron microscope (TEM) works much like a light microscope, transmitting a beam of electrons through a thin specimen and then focusing the electrons to form an image on a screen or on film. This is the most common form of electron microscope and has the best resolution. •The scanning electron microscope (SEM) scans a fine beam of electron onto a specimen and collects the electrons scattered by the surface. This has poorer resolution, but gives excellent 3-dimensional images of surfaces.
Disadvantages of the Electron Microscope : •Specimens are dead due to preparation technique such as staining, dehydration and placement in a vacuum •Artifacts (not natural/artificial feature)can be produced in the specimens by the preparation techniques •No movement can be studies as specimens are dead •Field of view is very small
Light ElectronCheap to purchase Expensive to buy(100 –500) (over 1,000,000)Cheap to operate Expensive to produce electron beamsSmall and portable Large and requires special roomsSimple and easy preparations Lengthy and complex preparationsMaterial rarely distorted by Preparation distorts materialpreparationVacuum is not required Vacuum is requiredNatural color maintained All images in black and whiteMagnifies objects only up to Magnifies over 500,000 times2000 times
Comparison of Size•In cell Biology it is most important to be able to provide details of the size of structure observed. SI units are used at all times to provide this information.•The following diagram provides an approximation of the sizes of different structures
MagnificationOn an image of a specimen it is useful to show how muchlarger/smaller the image is than the real specimen. This iscalled magnification.To calculate magnification• using a ruler measure the size of a large clear feature on the image•measure the same length on the specimen•convert to the same units of measurementMagnification = length on the image /length on the specimenLength of the actual specimen = length on the image/Magnification
example•In this example the image of a Rose leaf the magnification is X 0.83•This tells us the image is smaller than the real specimen.•The length of the real specimen = picture length/ 0.83 or 4.2cm/0.82 = 5.0 cm
Scale Bars •A scale bar is a line added to a drawing, diagram or photograph to show the actual size of the structures. •The scale bar in the picture allows you quickly to determine the approximate size of a feature. •The main feature in the micrograph is a nucleus with a dark region called the nucleolus. •Using the picture estimate the size of the nucleus and its nucleolus.
Surface area : Volume ratio and cell size• All organisms need to exchange substances such as food, waste, gases and heat with their surroundings. These substances must be exchanged between the organism and its surroundings.• As the size of a structure increases the surface area to volume ratio decreases.• Therefore the rate of exchange (diffusion/radiation) decreases.• This is true for organelles,cells, tissues, organs and organisms.
• The rate of exchange of substances therefore depends on the organisms surface area that is in contact with the surroundings.• The exchange depends on the volume of the organism, so the ability to meet the requirements depends on , which is known as the surface area : volume ratio•As organisms get bigger their volume and surface area both get bigger, but not by the same amount.This can be seen by performing some simple calculations concerning different-sized organisms.
Assume we have 3 cubes: With sizes: 3 2 1 1 cm 10 cm 100 cmWhat will happen to ratio between V and S.A. as theirsize increases?
Ratio of V:S.A.Cube Side Volume S.A. (6x2) Ratio Length (x3) (S.A./V)1 1 cm 1 cm3 6 cm2 62 10 cm 1 000 cm3 600 cm2 0.63 100 cm 1 000 000 60 000 cm2 0.06 cm3
Example 2Conclusions:•As the organism gets bigger its surface area : volume ratio decreases
Unicellular Organisms• A unicellular organism is asingle cell that can carryout all those functions oflife that are necessary tosurvive separately fromother cells. They can relyon large SA:Vol ratios forExchange.• The cell is specializedinternally to obtain nutrition; carry out respirationand to reproduce.• As has been already noted some biologists regardsuch organisms as acellular. Such biologist regardcells as inter dependant units and not independent asthese specialized unicellular organisms
All organisms must carry out functions of life.MOVEMENT – Intracellular and/or extracellularRESPIRATION – Gas exchange. Not always O2 and CO2NUTRITION – Need raw materials, i.e.- food, water, mineralsEXCRETION – Get rid of waste materialsREPRODUCTION – Ability to produce like organismsIRRATIBILITY – Respond to external stimuliGROWTH – Cells grow larger . . . and don’t forget . . .‘Mr. Smullen’ also carries out the functions of life!
Multi-cellular Organisms• Multi-cellular organisms are large and have to specialize parts of their structure to complete the various functions that are characteristic of life.• Cells within a multi cellular organism specialize their function.• Specialized cells have switched on particular genes (expressed) that correlate to these specialist functions.• These specific gene expressions produce particular shapes, functions and adaptations within a cell.• Therefore a muscle cell will express muscle genes but not those genes which are for nerve cells.
Tissues, Organs and Organ Systems Cell differentiation leads to higher levels of organization: During the process of cell specialization A process called differentiation occurs. In the cells of the tissue some genes are expressed and others are suppressed. 1.) A tissue is a group of similar cells performing a particular function. Simple tissues are composed of one type of cell, while compound tissues are composed of more than one type of cell. Some examples of animal tissues are:
2.) An organ is a group of physically-linked different tissues working together as a functional unit. For example the stomach is an organ composed of epithelium, muscle, glandular and blood tissues.3.) A system is a group of organs working together to carry out a specific complex function. Humans have seven main systems: the circulatory, digestive, nervous, respiratory, reproductive, urinary and muscular-skeletal systems.
Evolution: The Blind Watchmaker • What do the components of the watch do individually? • What do they do when they are put together in the right way? • This is an example of emergent properties: the whole is more than the sum of its parts. • One analogy used for evolution is that of the blind watchmaker. • Given millions of years and infinite mutations and combinations, it is inevitable that even complex structures will emerge. • There is no purpose or design to evolution beneficial mutations in a particular environment will allow the organism to survive and reproduce.
Stem Cells Retain the Capacity to divide• Totipotent: Can become any cell type• Pluripotent: can become any type except embryonic membrane• Multipotent: can become a number of different cell types• Unipotent: Can only become one cell type• Nullpotent: Cannot divide (red blood cells)• Differentiation depends on the activation of genes in sequence, often triggered by environmental changes.• Once a stem cell had differentiated, it can only make more stem cells or the differentiated cell type.
Cell Differentiation: the result of gene expression
Cell Differentiation• All cells in the body carry the same genes in their nuclei.• What makes a cell diffeent is which genes are expressed which are turned on or off• This is triggered by changes and the environment around the cell.
Uses for Stem Cells• In the treatment for lymphoma, bone marrow is destroyed in chemo or radio therapy. Before this aggressive treatment takes place, stem cells are harvested from the bone marrow and stored.• These harvested cells can be used to replace damaged bone marrow, producing healthy blood cells in the recovering patient.
Therapeutic Cloning of Stem Cells• Therapeutic cloning involves the in-vitro culturing of tissues using patient or donor stem cells. It can be used to replace tissues lost in disease, burned skin or even nerve cells.
Topic 2.2Prokaryotic Cells
Prokaryotic Cell: general structure The structural difference between the Prokaryotes and the Eukaryotes are so significant that some biologist think that these two groups merit the status of Super Kingdoms. The main distinguishing feature between the Prokaryotes and Eukaryotes is the lack of a true nucleus in the former.
•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 ribosomes 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.
Function of Prokaryotic Cell StructuresStructure Function Cell Wall Made of murein (not cellulose), which is a glycoprotein or peptidoglycan (i.e. a protein/carbohydrate complex).Pili A hair-like structure found on the surface of the membrane. These structures are used to connect bacteria to each other. They may provide a means of transporting materials from one another and maybe involved in reproduction.
Structure Function Plasma membrane •Controls the entry and exit of substances, pumping some of them in by active transport. Mesosome •A tightly-folded region of the cell membrane containing all the membrane-bound proteins required for respiration and photosynthesis. •Can also be associated with the nucleoid. •This is now thought to be an artifact of the electron microscope and not a real structure.
Structure Function Cytoplasm •Contains all the enzymes needed for all metabolic reactions, since there are no organelles Ribosomes •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.Naked DNA •Nucleoid is the region of the cytoplasm that contains DNA. It is not surrounded by a nuclear membrane. DNA is always circular (i.e. a closed loop), and not associated with any proteins to form chromatin. Sometimes confusingly referred to as the bacterial chromosome
Structure Function Slime Capsule •A thick polysaccharide layer outside of the cell wall, like the glycocalyx of eukaryotes. Used for sticking cells together, as a food reserve, as protection against desiccation 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.
Electron Micrograph structure of the prokaryote • 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.
Prokaryotic MetabolismBacteria have a large range of differentmetabolic reactions at their disposal, far morethan in the eukaryotes, who are confined tojust respiration or photosynthesis. 1. Fermentation: Fermentation•sometimes these bacteria oxidize organic molecules like glucose. In many instances they metabolize as far as lactic acid or alcohol molecules making them useful to fermentation industry
2. Photosynthesis • Many bacteria are photosynthetic and use the same process of photosynthesis as plants. These phototrophic bacteria were some of the earliest forms of life on the planet, and their metabolic reactions increased the oxygen content of the atmosphere from 1% to 20%. 3. Nitrogen Fixing•obtain their energy by oxidizing inorganic compounds like ammonia, nitrite, methane or hydrogen sulphide. These bacteria use a variety of unusual metabolic reactions and many are able to synthesise carbohydrates from carbon dioxide – the chemosynthetic bacteria.
2.2.4 Binary Fission • Prokaryotic cells divide by binary fission. • This is an asexual method of reproduction in which a cell divides into two same sized cells. • The cells are genetically identical and form the basis of a reproductive clone.
(a) Reproduction signa l: The cell receives a signal, to initiates the cell division.(b) Replication of DNA : bacterial cells have a single condensed loop of DNA. This is copied by a process known as semi-conservative replication to produce two copies of the DNA molecule one for each of the daughter cells(c) Segregation of DNA: One DNA loop will be provided for each of the daughter cells.(d) Cytokinesis: Cell separation.
Topic 2.3Eukaryotic cells
The Nucleus• The nucleus is generally a very conspicuous membrane-bound organelle. It contains most of the genes that control the entire cell.• It averages ~ 5 um in diameter• It is enclosed by a nuclear envelope• It contains chromosomes/chromatin
Mitochondria •Mitochondria is the site of aerobic respiration. •The matrix is the site of the Krebs cycle •Oxidative phosphorylation occurs on the cristae membrane •Very active cells usually have a lot of mitochondria e.g. muscle cel
Plasma membrane• Controls what enters and leaves the cell.Function & structure are covered in more detail in section
Rough Endoplasmic Reticulum •A complex interconnected network of membrane tubes. •The surface is covered in ribosomes where proteins are made for secretion •Unattached ribosomes make proteins for internal use.
Ribosome•Ribosome size measured in Svedberg (S) units; derived from sedimentation in ultracentrifuge•Ribosomes made of 40S and 60S subunits, assemble into 80S ribosome•Contains many enzymes for general metabolism•Compartment in which foodstuffs enter and from which wastes leave cell
Golgi apparatus•Modification of proteins for secretion
Chloroplast Structure1. Intermembrane Space- separates the two membranes.2. Thylakoids- Are flattened sacs inside the chloroplast. They segregate the interior of the chloroplast into 2 compartments: – Thylakoid space – stroma
Thylakoids• Chlorophyll is located in the thylakoid membrane.• They are stacked together (grana).
Chloroplast StructureStroma- photosynthetic rxns that convert chemical energy into sugars. The stroma is a viscous fluid outside the thylakoids CO 2 + H 2 O + light C 6 H 12 O 6 + O 2
Vacuole •The vacuole is a storage area in plants for amino acids and sugars (sap). •The tonoplast is a membrane like the plasma membrane it controls what enters and leaves the vacuole
Cell Wall•The cell wall supports plant tissue•Composed of a fully permeable wall of cellulose•Important structure in establishing turgidity Extracellular component
Prokaryotic vs Eukaryotic cells
Comparison of Plant and Animal Cells
Topic 2.4.1:Cell Membrane
2.4.1 Fluid mosaic model•Fluid because it can change shape but also because the phospholipids can change position in the same plane•Mosaic as the membrane has protein molecules embedded and attached to its surface•This model accounts for the behavior observed in cell membranes. Like a any good model it also predicts some characteristics.
2.4.2 Phospholipid Properties • The heads have large phosphate group, thus they are hydrophilic and (attract water) or polar. •The fatty acid tails are non- charged, hydrophobic and (repel water). This creates a barrier between the internal and external water environments of the cell. The tails effectively create a barrier to the movement of charged molecules
2.4.2 Phospholipid PropertiesHydrophilic‘ loves water’ •The individual phospholipids are attracted through their charges and this gives some stability. They can however move around in this plane •The stability of the phospholipid can be increased by the presence of cholesterol molecules. Hydrophobic ‘ afraid of water’
Integral Proteins•Usually span from one side of the phospholipid bilayer to the other.•Proteins that span the membrane are usually involved in transporting substances across the membrane
Peripheral Proteins•These proteins sit on one of the surfaces (peripheral proteins). They can slide around the membrane very quickly and collide with each other, but can never flip from one side to the other.•Proteins on the inside surface of plasma membrane are often involved in maintaining the cells shape, or in cell motility.•They may also be enzymes, catalysing reactions in the cytoplasm
Glycoproteins• Usually involved in cell recognition which is part of the immune system. They can also acts as receptors in cell signaling such as with hormones. These are extracellular components Cholesterol •Binds together lipid in the plasma membrane reducing its fluidity as conferring structural stability
2.4.3 Membrane Protein Functions Channel proteins • These proteins span the membrane from one side to another. They allow the movement of large molecules across the plasma membrane. Included within this are the passive and active membrane pumps
Receptor proteins• These proteins (B in diagram) may detect hormones arriving at cells to signal changes in function. They may also be involved in other cell and substance recognition as in the immune system.
Enzymes• Integral in the membrane they may be enzymes e.g. ATP Synthetase, Maltase
Electron Carries • Help catalyze chemical reaction an important role in photosynthesis and cell respiration.
Diffusion and Osmosis•The movement of particles is caused by the kinetic energy possessed by the particle•The direction of movement is random•Observing groups of particles they appear to move from regions of high concentration to regions of low concentration•However, most biological diffusion takes place through membranes and involves sources, sinks and diffusion gradients T2 T3 T1
MembranesDiffusion is the passive movement of particles from a region of high concentration to a region of low concentration (down a concentration gradient), until there is an equal distribution.Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration (high water concentration) to a region of higher solute concentration (low water concentration).
Diffusion moves down the concentration gradient just like a ball rolling down a hill. It cannot roll uphill without energy. High LowConcentration Concentration
Passive transport across membranes in terms of diffusion. • Requires no energy • Moves from down the concentration gradient • Some molecules pass through the membrane • Some molecules use channels for facilitated diffusion
Effects of osmosis on cells:The examples illustrate the problems that organisms will have ifthey live in: •concentrated solutions (hypertonic) •dilute solutions (hypotonic)Most organism have a mechanism to deal with these difficulties.These are studied through out the course. How do you maintainisotonic conditions for your tissues?
Animal Cells and Osmotic Pressure• All cells have thin delicate membranes – animal cells have only plasma membrane• They respond to differences in external solute concentration and osmotic pressure• If isotonic (usually 0.9% w/vol NaCl), no change in shape• If hypertonic (high salt) then shrinks• If hypotonic (low salt) then expands and destroy the cell membrane
Plant Cells and Osmotic Pressure • In plants, hypotonic solutions produce osmotic pressure that produces turgor pressure – Turgor means “tight or stiff owing to being very full” – Keeps plant upright; in hypertonic conditions plants wiltVacuole fills Vacuole shrinks Hypotonic solution Hypertonic Hypertonic
Active transport across membranes. • Requires energy, in the form of ATP, or adenosine triphosphate • Molecules are ‘pumped’ across the membrane UP the concentration gradient • Pumps fit specific molecules • The pump changes shape when ATP activates it, this moves the molecule across the membrane
Vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane. The fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis.
Exocytosis the mass movement OUT of the cellby the fusion of a vacuole and the membrane
Endocytosis the mass movement INTO thecell by the membrane ‘pinching’ into a vacuole
Topic 2.5Cell Division
Mitosis• Cellular division in eukaryotic cells.• Chromatin is arranged into chromosomes.• Chromosomes double.• Cell grows in size.• Cells divide.• Is cellular cloning.
Phases of the Cell Cycle the ‘life cycle’ of a cell.There are 2 phases: 1. Interphase 2. M phase (mitotic phase) a. Prophase b. Metaphase c. Anaphase d. Telophase & cytokinesis
Figure 12.4 The cell cycle
1. Interphase• The non-dividing phase in a cell• Lasts about ~ 90% of the cell cycle.• The cell grows and replicates DNA preparing for Mitosis.• There are three periods:
3 periods of Interphase1. Go – a cell functioning as normal2. G1 phase – first growth phase3. S phase- synthesis of DNA4. G2 phase- 2nd growth phaseMitosis is a reliable process. Only one error occursPer 100,000 cell divisions.
2. Mitosis: Prophase• The nucleolus disappears.• Chromatin condenses into visible chromosomes.• There are two sister chromatids held together by a centromere.• The mitotic spindle forms in the cytoplasm.
Figure 12.3 Chromosome duplication and distribution during mitosis
“Pro”metaphase• The nuclear envelope disappears.• Spindle fibers extend from each pole to the cell’s equator.• Spindle fibers attach to the centromeres.
Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase
Metaphase• Chromosomes are lined up in the equator (middle) of the cell.• This is called the metaphase plate.
Figure 12.6 The mitotic spindle at metaphase
Anaphase• Characterized by movement. It begins when pairs of sister chromatids pull apart.• Sister chromatids move to opposite poles of the cell.• Chromosomes look like a “V” as they are pulled.• At the end of anaphase, the two poles have identical number and types of chromosomes.
Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis.
Telophase and Cytokinesis• Microtubules elongate the cell.• Daughter nuclei begin to form at the two poles.• Nuclear envelopes re-form.• Nucleolus reappears.• Chromatin uncoils.• Cells split their cytoplasm.• It is basically the opposite of prophase.
Figure 12.5x Mitosis
Figure 12.8 Cytokinesis in animal and plant cells
Figure 12-09x Mitosis in an onion root
Role of Mitosis•Growth: Multicellular organisms increase their size through growth. This growth involves increasing the number of cells through mitosis. These cells will differentiate and specialize their function. •Tissue Repair: As tissues are damaged they can recover through replacing damaged or dead cells. This is easily observed in a skin wound. More complex organ regeneration can occur in some species of amphibian. •Asexual Reproduction : This the production of offspring from a single parent using mitosis. The offspring are therefore genetically identical to each other and to their “parent”- in other words they are clones. Asexual reproduction is very common in nature, and in addition we humans have developed some new, artificial methods
TumorsThe cancer cells are a mass of cells produced from uncontrolled cell divisionand can occur in an tissue. These cells disrupt biological order and function. Ifleft unchecked, to bring the whole complex, life sustaining edifice that is thehuman body crashing down This mass is called a tumor.There are two major types of tumor:1. Benign Tumors this is a mass of cancerous cells that do not invade other areas of the body. These are not as dangerous to health but may still require removing to prevent effects on neighboring tissue
2. Malignant Tumors is a mass of cancer cells that may invade surrounding tissues or spread to distant areas of the body. Cancer cells replace normal functioning cells in distant sites:e.g. replacing blood forming cells in the bone marrow, replacing bones leading to increased calcium levels in the blood, or in the heart muscles so that the heart 1. Image is a normal CT. Images 2, 3 & 4 fails. PET scans, Light green/blue areas Are show cancer cells