2.1 Cell theory * 2. Cells
2.1 cell theory
Dec 07, 2014
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2.1 Cell theory
*2. Cells
*Introduction: class activity
*Each will receive a section of text. Read it and study it for a few minutes.
*Find other students with different sections of text and get together in groups
*Explain your section to the other members of the group to learn and understand the main concepts.
*As a group prepare an oral presentation of the topic. You will be randomly chosen.
*2.1 Cell theory
*The cell theory has 3 basic principles:
*ALL LIVING THINGS ARE MADE FROM CELLS
*CELLS ARE THE SMALLEST UNITS OF LIFE
*CELLS COME ONLY FROM OTHER CELLS
*Exceptions? Muscle cells, fungal cells, protoctista, virus
*Evidence for the cell theory
*Robert Hooke (1635 – 1703)
*Pioneer microscopist, optics enthusiast, coiner of the term “cell”
*Famous drawings of cork section in a microscope
*Antonie van Leeuwenhoek (1632 – 1723)
*“Father of microbiology”
*Master lens-maker
*He discovered ‘animalcules’ in water and became known as the discoverer of many cells
*Microscopes
*Early microscopes
*Light microscopes
*Transmission Electron Microscope
*Scanning Electron Microscope
*Evidence for the cell theory*“All living things consist of cells”
*Since Hooke and van Leeuwenhoek, huge numbers of tissue samples from many different organisms have been examined using microscopes and have been found to be made of cells.
*“Cells are the smallest unit of life”
*Based on the idea that nothing smaller than a cell can survive independently
*Experiments can be done to separate the cell’s subunits, and these do not survive by themselves.
*A cell is the smallest unit that can show all the characteristics of living processes.
*Evidence for the cell theory
Pasteur’s Experiment for spontaneous generation
*“Cells come from pre-existing cells”
*Spontaneous generation: by preventing entry of airborne particles to a nutrient broth, Pasteur stopped the growth of the culture.
*Robert Remak discovered cellular division
*Magnification and size*Magnification = size of image actual size of specimen
•Often calculations are needed to convert from the size of the image to the real size of the specimen
• It is important to use the same metric prefixes: micrometers or millimeters for all
• Scale bars are often used on drawings and pictures
*Relative sizes
*1. molecules (1nm). 2. cell membrane thickness (10nm).3. virus (100nm).4. bacteria (1um).5. organelles (less 10um).6. cells (<100 um).7. generally plant cells are larger than animal cells.
*Calculate magnification *A. Calculate magnification
Magnification= measured length scale bar label
B. Actual size
Actual size = measured length magnification
Remember: To answer questions “calculate the magnification” the image is irrelevant as long as you have the scale bar.
*Examples*A student looks at an image of a cell magnified 350
times. The image is 250mm long. Calculate the actual length of the sample in the image
*Examples
*A sperm cell has a tail 50μm long. A student draws it 75mm long. What is the magnification?
*Surface area to volume ratio*Why are most cells so small?
*Because of the surface area-to-volume ratio.
*Doubling the diameter of a cell increases its volume by 8 times, but increases the its surface area only by 4 times.
*The significance of this relationship is that the volume of a cell determines the chemical activity that can take place within it, whereas the surface area determines the amount of substances that can be exchanged between the inside and the outside of the cell.
*Surface area to volume ratio
*The rate of heat production, the rate of waste production and the rate of resource consumption of a cell are functions of its volume
*The rate of exchange of materials and energy (heat) is a function of its surface area.
*A large SA:vol ratio benefits by:
*Diffusion pathways are shorter, therefore more efficient
*Concentration gradients are easier to generate (it takes less solute to make a 10% solution in a beaker than in a bucket!)
*Surface area to volume ratio
*Cells are small because: (oxygen example)
*A big cell needs more oxygen to diffuse across the membrane
*A big cell has a relatively small surface area compared to its volume
*The rate of diffusion across the membrane limits the amount of oxygen that enters the cell.
*Two cells are more efficient than one large cell.
*This also leads to cell differentiation, specialized functions and more complex multicellular life.
*Surface area to volume ratio
Emergent properties*Emergent properties arise from the interaction of
component parts: the whole is greater than the sum of its parts.
*TOK: The concept of emergent properties has many implications in biology. Life itself can be viewed as an emergent property, and the nature of life could be discussed in the light of this, including differences between living and non-living things and problems about defining death in medical decisions.
*Emergent properties*As a model consider the electric light bulb. The bulb is
the system and is composed of a filament made of tungsten, a metal cup, and a glass container. We can study the parts individually how they function and the properties they posses. These would be the properties of :
*Tungsten
*Metal cup
*Glass container.
*When studied individually they do not allow the prediction of the properties of the light bulb. Only when we combine them to form the bulb can these properties be determined. There is nothing supernatural about the emergent properties rather it is simply the combination of the parts that results in new properties emerging.
*Emergence is the occurrence of unexpected characteristics or properties in a complex system. These properties emerge from the interaction of the ‘parts’ of the system. Remember that biology insists on a population thinking so that we know the interacting ‘parts’ vary in themselves and therefore their ‘emerging’ properties can only be generalised. On a biological scale consider the current debate about the nature of human consciousness or the origin of life itself.*Mayr, E (2004) What Makes Biology Unique? Cambridge University
Press: Cambridge
*A relatively new field in biology, Systems Biology, looks at the way different parts of a whole organism interact with each other to give emergent properties.
*Think about the human brain, for example.
*Emergent properties
*Differentiation in multicellular organisms
*Remember: When we studied genes and DNA we saw how cells acquire a specific function: differentiation.
*As a general principle then we find that the larger a multicellular organisms become the more diversity and differentiated specialisms there are within the organism.
*Rather than all cells carrying out all functions, tissues and organs specialise to particular functions. These organs and systems are then integrated to give the whole organism (with its emergent properties).
*Specialised 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.
*What is the benefit of differentiation and specialisation of tissues rather than all tissues carrying out all functions?
*Differentiation in multicellular organisms
*STEM CELL THERAPY*Embryonic stem cells
*Potential: promising source for treating many diseases
*Considerations: Needs drugs to suppress immune system
*Ethically: When isolating hES (human) in the lab, embryos are destroyed
Genetic Science Learning Center (1969, December 31) Stem Cell Quick Reference. Learn.Genetics. Retrieved February 26, 2012, from http://learn.genetics.utah.edu/content/tech/stemcells/quickref/
*STEM CELL THERAPY*Somatic stem cells
*Potential: Routinely used for blood-related diseases, but not for producing an unrelated cell type.
*Considerations: Most types of somatic stem cells are present in low abundance and are difficult to isolate and grow in culture.
*Ethically: Not controversial
*STEM CELL THERAPY
*Induced pluripotent stem cells
*Potential: Mouse iPS cells can become any cell in the body. Although more analysis is needed, the same appears to be true for human iPS cells.
*Considerations: much less expensive to create than ES cells generated through therapeutic cloning
*Ethically: subject to the same ethical considerations that apply to all medical procedures.
*STEM CELL THERAPY
*Therapeutic cloning
*Potential: can, in theory, generate ES cells with the potential to become any type of cell in the body.
*Considerations: made from a patient's own DNA, there is no danger of rejection by the immune system. the cloning process has been time consuming, inefficient, and expensive
*Ethically: involves creating a clone of a human being and destroying the cloned embryo, and it requires a human egg donor.
*Amazing cells
*Learn Genetics web page: http://learn.genetics.utah.edu
*Membranes
*Inside the cell
*Transport inside the cell
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