Cell Theory

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Large Cells! ostrich egg

Assessment Statements (objectives) 2.1.1 Outline the cell theory 2.1.2 Discuss the evidence for the cell theory 2.1.3 State that unicellular organisms carry out all the functions of life. 2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit 2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification 2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size. 2.1.7 State that multicellular organisms show emergent properties. 2.1.8 Explain that cells in multicellular organisms differentiate to carry our specialized functions by expressing some of their genes but not others. 2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways. 2.1.10 Outline one therapeutic use of stem cells.

Cell Theory All organisms are composed of one or more cells. Cells are the smallest units of life. All cells come from pre-existing cells.

Cell Theory Cont. Theory: A hypothesis that has been extensively tested over time and that explains a broad range of scientific facts with a high degree of reliability Scientific question → Hypothesis → Data → Theory Cell theory has taken several hundred years to formulate Many scientists contributed to its development Microscope has given the theory credibility

Scientists and Cell Theory Robert Hooke 1st described cells in 1665 looking at cork with a homemade microscope

Scientists and Cell Theory Leeuwenhoek Observed first living cells a few years later and called them “animalcules” Meaning little animals

Scientists and Cell Theory Matthias Schleiden In 1838, stated plants are made of “independent, separate beings” called cells Theodor Schwann Made same statement about animal cells

Cell Theory Cont. We have not been able to find any living entity that is not made of at least one cell. Louis Pasteur Sterilized chicken broth by boiling, and showed that living organisms would not “spontaneously” reappear. Pre-existing cells were needed to re-establish life

Pasteurization Heat food at specific temperature for a certain length of time and then cooling it immediately Reduces the number of pathogens and bacteria in food

Life is Everywhere!

Functions of Life All organisms exist in either a unicellular or multicellular form. All organisms carry out all the functions of life. Functions of life: Metabolism Growth/development Reproduction Response Homeostasis Nutrition Order Adaptation Unicellular Multicellular

Function of life Metabolism: Growth and development: All chemical reactions that occur within an organism Growth and development: Heritable programs in the form of DNA direct the pattern of growth and development Produces an organism that is characteristic of its species

Function of life Reproduction: Response to environment: Involves hereditary molecules that can be passed to offspring Organisms reproduce their own kind Life comes only from life Response to environment: Imperative to survival Plants growing towards sunlight

Function of life Homeostasis: Nutrition: Maintaining a constant internal environment (e.g. temperature, acid base levels) even though external environment may fluctuate Nutrition: Organisms take in energy and transform it to do many kinds of work Providing source of compounds with many chemical bonds which can be broken down to provide energy and nutrients necessary to maintain life

Function of life Order: Adaptation: Characteristics of life emerge from organisms highly ordered structure Adaptation: Life evolves as a result of interaction between organisms and their environments Adaptation of organisms to their environment

Cells and Sizes Cells are made up of a number of different subunits Subunits are microscopically small Most cases, microscopes are needed to see cells and their subunits

Microscopes Magnification Resolution Enlarging the physical appearance or image of something Resolution The closest proximity of two objects that can be seen as two distinct regions of the image (like pixels) Refers to the clarity of viewed object

Light Microscopes Use light to pass through the living or dead specimen to form an image Stains may be used to improve viewing

Electron Microscopes Provide greatest magnification (over 100,000x) and resolution Electrons pass through a specimen to form an image Pollen

1 micrometer = 1µm = 1 x 10-6 1 nanometer = 1nm = 1 x 10-9 Relative Size Cells (up to 100µm) are relatively large, and then in decreasing size order are: Organelles (up to 10µm) Bacteria (up to 1µm) Viruses (up to 100nm) Membranes (up to 10nm) Molecules (near 1nm)

Scale Bars 100nm Mitochondria 0.5µm

Calculating Specimen Size In order to calculate actual specimen size: Magnification may be stated (x400, x10) or Scale bars may be used to first calculate magnification and then specimen size This is considered the image size. Size from magnification Specimen size is its true size in nature. Usually too small to be seen without aid.

Calculating Specimen Size given Magnification Specimen Size = (Image Size) / (Magnification) Ex: Onion cells under 400x magnification Step 1 Measure image of one onion cell (pay attention to length vs. height) Step 2 (not to actual scale it’s for example purpose) Calculate (10 cm) / (400) Specimen size = 0.025 cm Image Size ( 10 cm)

Calculating Specimen Size given Scale Bar Specimen Size = (Image Size) / (Magnification) Ex: Onion cells with scale bar Step 1 (not to actual scale it’s for example purpose) Measure length of scale bar (scale bar image size) with ruler Step 2 Convert scale bar image size to µm (1.5cm) x (1m/100cm) x (1µm/(1x10-6m) = 1.5 x 104 µm Calculate magnification= (Image size)/(specimen size) (1.5 x 104 µm)/ (10 µm)= 1.5 x 105 Step 3 Calculate specimen size of cell using magnification Measure cell and divide by magnification (units matter!) (9.5cm)=(9.5x104µm)/(1.5x105) = 0.63 µm 10 µm Image Size ( 1.5 cm)

All cells have at least on feature in common… they are small in one or more dimensions Why do cells stay so small? and Why don’t they grow to a larger size?

Limiting Cell Size There is a factor called the surface area to volume ratio that effectively limits the size of cells. Surface area: total area of given surface Ex. rectangular prism Surface area = (height x width) + (height x width) + … of each side (six total) Volume: the amount of space an object takes up Height x width x length

Cell Volume The following are functions of (depend on) cell volume: Rate of heat and waste production Rate of resource consumption Most chemical reactions occur inside the cell, so its size affects the rate of these reactions.

Cell Surface Area On the surface of the cell, the membrane controls what materials move in and out of it All raw materials, energy, and waste can enter or leave the cell only by crossing the plasma membrane Microvilli

Surface Area to Volume Ratio Cells with more surface area per unit volume are able to move more materials in and out As width of cell increases, surface area also increases, but to a much slower rate than volume Therefore, a large cell has less surface area to bring in needed materials and to rid the cell of waste Cells are limited to a size they can carry out the functions of life

Large animals do not have larger cells, they have more cells

Cell Reproduction and Differentiation Cells retain the ability to reproduce themselves In multicellular organisms: this allows the possibility of growth and the replacement of damaged or dead cells Live cells fluoresce green Dead cells fluoresce red

Multicellular Organisms Show Emergent Properties Emergent properties arise from the interaction of component parts: the whole is greater than the sum of its parts MacromoleculeOrganelleCellTissueOrgan SystemOrganism When units of biological material are put together, the properties of the new material are not always additive, or equal to the sum of the properties of the components. Instead, at each level, new properties and rules emerge that cannot be predicted by observations and full knowledge of the lower levels. Such properties are called emergent properties (Novikoff, 1945). As an example of why the reductionist approach fails, consider the function of one cell within a multicellular organism. Even if we understand the cell's function, that does not mean we fully understand the organism's physiology. After all, the activity of each cell is affected by the activity of other cells in the tissues, organs, and organ systems within the organism. The cell is thus no longer in isolation, and its integration into a system provides that system with emergent properties (Novikoff, 1945).

Multicellular Organisms Start out as a single cell after sexual reproduction This single cell has the ability to reproduce at a rapid rate Resulting cells go through a differentiation process to produce all the required cell types for the well-being of the organism (staggered)

All of the cells in your adult body originated from a single cell (fertilized egg)… And all of those cells (except those destine to become sperm or eggs) have exactly the same set of DNA, Then why is your body composed of lots of different kinds of specialized cells? If all your cells have the exact same set of genes, why don’t all your cells stay identical?

Differentiation A cell becomes different from its parent or sister cell At various developmental stages of life, cells differentiate because they begin to express different genes.

Cell Differentiation Each cell contains all the genetic information for the production of the complete organism However, each cell becomes a specific type of cell dependent on which DNA segment becomes active Some cells have a greatly, or even completely, diminished ability to reproduce once they become specialized. Nerve and muscle cells are prime examples of this type of cell. Other cells, like epithelial cells like skin, retain the ability to rapidly reproduce throughout their life. The offspring of these rapidly reproducing cells then differentiate into the same cell type as the parent.

Stem Cells Populations of cells within organisms that retain their ability to divide and differentiate into various cell types

Stem Cells Stem cells may be pluripotent or multipotent. Pluripotent stem cells can give rise to any type of cell in the body except those needed to support and develop a fetus in the womb. Can be isolated from human embryos Stem cells that can give rise only to a small number of different cell types are called multipotent.

Stem Cells Plants contain stem cells in meristematic tissue Occur near root and stem tips Composed of rapidly reproducing cells that produce new cells capable of becoming various types of tissue Gardeners take advantage of this by taking cuttings from stems or roots to produce new plants

Embryotic Stem Cells (ESC) Ultimate stem cell is fertilized egg All specialized cells of body originate from it First 8 cells of human embryo are also stem cells b/c haven’t differentiated

Embryonic Stem Cells In early 1800s, scientist found embryonic stem cells in mice These cells retain the ability to: Form any type of cell in an organism Form a complete organism “immortal” Why researchers use them: Easier to work with than adult cells b/c don’t adhere as tightly Don’t usually provoke tissue rejection Easier to administer to a patient Can still become a specialized cell

ESC Research Use stem cells to replace differentiated cells lost due to injury or disease: Parkinson’s disease Alzheimer’s disease Both caused by loss of brain cells Implanted stem cells could replace them Diabetes Help restore pancreas of essential cells that are depleted Paralyzed victims Nerve Muscle

Other Stem Cell Research Tissue specific stem cells Ex. Blood cells to replace damaged bone marrow in leukemia patients New research harvesting umbilical cord blood at birth Keep vs. donate?? Induce Pluripotent Stem Cells (iPSC) http://www.teachersdomain.org/asset/nsn08_vid_stemcell2/

Therapeutic use of stem cells. A retrovirus that has been rendered harmless is used to introduce a gene into a bone marrow stem cell of a patient that lacks it. The cell and its descendants will possess the gene. Fig. 20.16

Is Stem Cell Research Ethical? Cells that come from embryos involves the death of the embryo Does this represent the taking of a human life? Others argue That this research could result in the significant reduction of human suffering.