3 By the end of this lesson, you should be able to: Outline the Cell TheoryBe able to compare relative sizes of cells and cellular componentsBe able to calculate linear magnification of drawingsUnderstand gene selectivityUnderstand the importance of stem cells
4 What level of complexity is necessary for life? Aristotle (384 – 322BC)
5 History of the Cell Hooke, 1665 Looked through compound microscope at cork samples and coined the term “cells”
6 History of the Cell Leeuwenhoek, 1675 Discovers unicellular organisms in pond water
7 History of the Cell Matthias Schleiden & Theodor Schwann, 1838-1839 Suggested that plants and animals; respectively, are composed of cells“The cell is the basic unit of living tissue”Rudolf Virchow (1858) noted that: “all cells come from pre-existing cells”
8 Main Ideas of Cell Theory Those early scientists did experiments on living things and developed CELL THEORYMain Ideas of Cell TheoryAll living things are made of one or more cells1)Cells are the basic units of structure & function of living things; “The smallest unit of life”2)All cells come from existing cells3)
10 Cell: “The smallest Unit of Life” Leeuwenhoek’s unicellular organisms show all the signs of lifeMetabolismResponse to stimuliGrowthReproductionHomeostasisNutrition
11 2.1 Cell Theory2.1.3State that unicellular organisms carry out all the functions of life. (1)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 . . .
12 What level of complexity is necessary for life? Xavier Bichat ( ): An organ is composed of different tissues and several organs can be grouped together as an organ system (e.g. the digestive system)An idea of hierarchy of structure developed:OrganismOrgan-systemOrganTissueCell
13 2.1 Cell Theory2.1.1 Discuss the theory that living organisms are composed of cells. (3) Skeletal muscle and some fungal hyphae are not divided into cells but have a multinucleate cytoplasm. Some biologists consider unicellular organisms to be acellular.
14 2.1 Cell Theory2.1.2State that a virus is a non-cellular structure consisting of DNA or RNA surrounded by a protein coat. (1)
16 2.1 Cell Theory2.1.3 State that all cells are formed from other cells. (1) x ref Mitosis, 8.1- Meiosis
17 2.1 Cell Theory2.1.4Explain three advantages of using light microscopes. (3)Advantages include:colour images instead of monochrome,a larger field of view,easily prepared sample material,the possibility of examining living material and observing movement.
18 2.1 Cell Theory2.1.5 Outline the advantages of using electron microscopes.(2) Greater: Resolution – the ability to distinguish between two points on an image. Like pixels in a digital camera. Magnification – how much bigger a sample appears to be under the microscope than it is in real life.
19 3.1 Cell TheoryTransmission electron microscopes pass a beam of electrons through the specimen. The electrons that pass through the specimen are detected on a fluorescent screen on which the image is displayed.Thin sections of specimen are needed for transmission electron microscopy as the electrons have to pass through the specimen for the image to be produced.
20 2.1 Cell TheoryScanning electron microscopes pass a beam of electrons over the surface of the specimen in the form of a ‘scanning’ beam.Electrons are reflected off the surface of the specimen as it has been previously coated in heavy metals.It is these reflected electron beams that are focused on the fluorescent screen in order to make up the image.Larger, thicker structures can thus be seen under the scanning electron microscope as the electrons do not have to pass through the sample in order to form the image.However the resolution of the scanning electron microscope is lower than that of the transmission electron microscope.
21 2.1 Cell Theory Light Electron Cheap to purchase (£100 – 500) Expensive to buy (over £1,000,000)Cheap to operateExpensive to produce electron beamsSmall and portableLarge and requires special roomsSimple and easy preparationsLengthy and complex preparationsMaterial rarely distorted by preparationPreparation distorts materialVacuum is not requiredVacuum is requiredNatural color maintainedAll images in black and whiteMagnifies objects only up to 2000 timesMagnifies over 500,000 times
22 2.1 Cell Theory 2.1.4 Define organelle. (1) Literally ‘little organ’ An organelle is a discrete structure within a cell, and has a specific function.i.e. – nucleus, cell membrane, mitochondria
23 2.1 Cell Theory molecules (1 nm), 2.1.4Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using appropriate SI units Appreciation of relative size is required (2)molecules (1 nm),thickness of membranes (10 nm), xref. 1.4viruses (100 nm),bacteria (1 µm), xref. 1.33organelles (up to 10 µm), xref , 7.1.3, 7.2.1most cells (up to 100 µm).Don’t forget: all of these structures are in 3D space
25 2.1 Cell Theory2.1.5 Calculate linear magnification of drawings. (2) Drawings should show cells and cell ultra-structure with scale bars Magnification could also be stated, eg x250.
26 Bacteria (prokaryote) How Big are Cells?Eukaryotic CellUp to 100 μmOrganellesUp to 10 μmBacteria (prokaryote)1 μmLarge Virus (HIV)100 nmCell Membrane10 nmMolecules1 nmAdenovirus1 micrometer (μm) is 1 millionth of a meter (10-6)1 nanometer (nm) is 1billionth (1 thousand milllionth) of a meter (10-9)E. coliWeem et al., 2007
27 Why so small? If cell was larger…. Diffusion distance becomes too far to be energy efficientSurface to volume ratio becomes too small to allow the necessary exchange
28 Why so small?The production rate of cellular heat/waste and consumption of resources is directly proportional to its volumeSince everything goes via the cell membrane, the rate of uptake/removal is proportional to the cell surface areaHowever
29 2.1 Cell Theory2.1.5 Explain the importance of the surface area to volume ratio as a factor limiting cell size. (3) The rate of metabolism of a cell is a function of its mass:volume ratio, Whereas the rate of exchange of materials and energy (heat) is a function of its surface area. Simple mathematical models involving cubes and the changes in the ratio that occur as the sides increase by one unit could be compared.
30 Volume and surface to area ratios 110110Length of side = 1 cmSurface area = 6 cm2 (6 * 1 * 1)Volume = 1 cm3Surface area:Volume ratio = 6:1This means every 1 cm3 of cell has 6 cm2 of surface areaLength of side = 10 cmSurface area = 600 cm2 (6 * 10 * 10)Volume = 1000 cm3Surface area:Volume ratio = 0.6:1This means that every 1 cm3 of cell has 0.6 cm2 of surface area; 10 times less
31 Ratio of V:S.A. Cube Side Length Volume (x3) S.A. (6x2) Ratio (S.A./V) 11 cm210 cm3100 cm1 cm36 cm261 000 cm3600 cm20.6cm3cm20.06
32 Ways cells adapt to help this problem ProtrusionsFlattening cell
33 Multicellular organisms have same problem LungsAlveoli help to increase surface area to allow greater diffusionIntestinesVilli help to increase surface area to allow greater absorptionCirculatory systemReduces diffusion distance
34 2.1 Cell Theory2.1.7 Define: (1) Tissue – A group of cells working together to perform a common function Organ – A group of tissues working together to perform a common function Organ System – A group of organs working together to perform a common function
35 The cells specialize (differentiate) 2.1.8 More is different!As a multicellular organism grows and develops it follows a structured planThe cells specialize (differentiate)A developing multicellular organism shows emergent propertiesThe whole is more than the sum of its parts
36 Cells interact to acquire properties that, alone, they do not possess 2.1.7 Emergent propertiesCells interact to acquire properties that, alone, they do not possessExample: The human brainIndividual neurons not capable of thought but the cooperation and communication among the individuals enables us to think
37 Specialized cellsIn multicellular organisms, cells differentiate to become specialized for their functionOnly a small portion of the genes are necessaryEach human cell has 40,000 potential genesTo avoid waste, cell activates only those genes necessary to carry out its function
38 Stem Cells Unspecialized, “immortal” cells Have not silenced their genes yet, therefore, can potentially become any cellTotipotent – Can become any type of cellEmbryonic cellsPluripotent – Partly differentiated, are restricted to certain cell types (ex. Blood cells)Most of your stem cells in your bone marrow are pluripotentZygotic cellsMultipotent – More differentiated but can still differentiate into a limited number of cell types
39 What can stem cells do for you? Cell therapyThe totipotent potential of stem cells permits their use to replenish damaged/missing cells of our own body
40 Cell Therapy Leukemia (cancer of the blood) Skin grafts A bone marrow transplant can replenish blood cells lost to leukemia/chemotherapySkin graftsStem cells can re-grow skin damaged by burns/accidentsCorneal replacementRe-grow cells of the eye for vision restorationParkinson’s/Alzheimer’sStem cells possess the ability to re-grow brain cellsDiabetesPancreas cells responsible for insulin production could be re-grown for type I diabetes
41 Where do stem cells come from? Umbilical cordEmbryosUnused from in-vitro fertilizationAbortedYour own bone marrowAlthough not totipotent, investigation is determining whether they can be converted to be totipotentRequires embryonic investigation
45 Electron micrograph of E.coli Escherichia coliElectron micrograph of E.coliDamon, et al Standard Level Biology, 2009
46 Flagella (not in all cells) 2.2.3 Prokaryotic CellsSize 5-10µmCytoplasmcontains enzymes that catalyse the chemical reactions of meabolism and DNA in a region call the nucleoidPili (not in all cells)Hairlike growth on the outside of cell membraneUsed for attachmentMain function is to join bacterial cells in preparation for DNA exchangeFlagella (not in all cells)longer than piliUsed for motility
47 ribosomes 70s Nucleoid (naked DNA) synthesize proteins by translating messenger RNA. Some proteins stay in the cell and others are secretedNucleoid (naked DNA)stores the genetic information that controls the cell and is passed on to daughter cellsSingle, long, continuous (circular)Bacteria may contain plasmidssmall, circular DNA fragments that replicate independently of the bacterial chromosome
48 2.2.4 Bacterial Replication Reproduce by binary fissionNo exchange of genetic materialTakes 20 min in good conditions
49 Eukaryotic Cells Size 50-150 µm Contains a nucleus and distinct organellesDNA is enclosed in a nuclear envelopeCell division by mitosis
51 Eukaryotic Cells Ribosomes 80s – protein synthesis Rough endoplasmic reticulum (rER) – synthesis of proteins to be secretedLysosome – holds digestive enzymesGolgi apparatus – for processing of proteinsMitochondrion – for aerobic respirationNucleus – holds the chromosomes
53 2.3.5 State three differences between plant and animal cells. StructurePlant CellsCannot produce its own foodXChloroplastCan produce its own food.Flexible, can easily change shape.XCell WallRigid, cannot easily change shape.Does not store large amounts of liquid. Smaller size of cell.XCentral VacuoleStores large amounts of liquid (juice). Larger size of cell.Carbohydrates stored as glycogen.Carbohydrates stored as starch.
55 2.3.6 Extracellular components The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the whole plant up against the force of gravity.Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support, adhesion and movement.
57 2.4 Membranes Go to the boardwork!!!! 2.4.1Draw a diagram to show the fluid mosaic model of a biological membrane.The diagram should show the phospholipid bilayer, cholesterol, glycoproteins and integral and peripheral proteins.Integral proteins are embedded in the phospholipid of the membrane whereas peripheral proteins are attached to its surface.
58 2.4 Membranes2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes. (3) Hydrophobic – ‘afraid of water’ Hydrophilic – ‘loves water’
66 Facillitated diffusion Passive TransportSimple diffusionDiffusionFacillitated diffusionOsmosisRequires no energyMoves from down the concentration gradientSome molecules pass through the membraneSome molecules use channels for facilitated diffusion
67 Diffusion2.4.4 Define diffusion Diffusion 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. Define osmosis 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).
68 Do not mix diffusion with osmosis!!! Diffusion moves down the concentration gradient just like a ball rolling down a hill. It cannot roll uphill without energy.High ConcentrationLow Concentration
70 Active Transport Transporters (proteins) Transport through vesicles Bind ATP directly and use the energy of its hydrolysis to drive active transportDirectly use of energyTransporters (proteins)Use of the energy already stored in the gradient of a directly-pumped ionIndirectly use of energyEndocytosisTransport through vesiclesExocytosisRequires energy (ATP) or adenosine triphosphateMovement of molecules or ions against concentration gradientPumps fit specific moleculesThe pump changes shape when ATP activates it, this moves the molecule across the membrane
71 Indirectly use of energy EXAMPLESDirectly use of energyNa+/K+ ATPaseIt uses the energy from the hydrolysis of ATP toactively transport 3 Na+ ions out of the cellfor each 2 K+ ions pumped into the cell.Indirectly use of energyThe picture is in Cell Resp ppt!!ATP SynthaseChemiosmosis:Electron transport provides energy for the synthesis of ATP, but only indirectly. When electron transport chains pump H+ across the membrane, the protons become more concentrated on one side of the membrane than on the other. Such a concentration gradient stores potential energy. ATP is generated by a molecule called ATP synthase.ATP synthase is a combination of proteins that act as both an ion channel and an enzyme. As an ion channel in the membrane of the mitochondria or thylakoids, it allows H+ to diffuse through it (facilitated diffusion). This actionspins a component of the ATP synthase. This rotation activates the active sites in the enzyme that attach phosphate groups to ADP molecules to generate ATP.
74 Transport through vesicles 2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane Describe how the fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis. THIS ITEM IS IN MEMBRANE´S BOARDWORK!!!!!
76 2.4 Membranes2.4.8Endocytosis – the mass movement INTO the cell by the membrane ‘pinching’ into a vacuole Exocytosis – the mass movement OUT of the cell by the fusion of a vacuole and the membrane This is possible because the of the fluid properties of the membrane (able to break and reform easily, phospholipids not attached just attracted)