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• Cells were discovered and studied by using microscopes • cell theory = all living cells are formed by division of existing cells and inherit their characteristics from them • cell theory is the basis of all biology • our understanding of how cells behave gives us clues to the past - evolution Plant root tip Kidney ducts Tissue = cells surrounded by extracellular matrix 1M=1000mm=1,000,000μm (micron) .2μm=200nm Brightfield Phase contrast Differtial-interference A living cell seen under a light microscope .2nm=2Å Yeast eucaryote by light microscope Eucaryotes have intracellular membrane organalles like nuclei Procaryotes do not = bacteria (eubacteria and archaebacteria) Nuclius -DNA as chromatin Chromosomes in a cell about to divide - DNA condensed Mitochondria by light microscope Mitochondria by electron microscope Theory of the origin of mitochondria Chloroplasts - photosynthesis Leaf cells by light microscopy Electron micrograph of a chloroplast Theory of the origin of chloroplasts Endoplasmic reticulum golgi endocytosis exocytosis Cytoskeleton - A.actin filaments (thinnest - rapid,muscles), B microtubules (thickest - hollow tubes - spindle/ mitosis, movement of organelles), C intermediate filaments (mechanical stability) Gives cells mechanical strength, controls shape, drives and guides intracellular and cell movements Microtubules (spindle) in a dividing cell Cells vary enormously in appearance and function Protozoan neuron Plant stem bacterium Paramecium dendrite flagella Cell body axon cilia The larger a cell is the more surface area is required for all the transactions needed taking in nutrients, getting rid of wastes. Intracellular membranes add to the surface area and allow the volume or size of the cell to be greater. Therefore eucaryotic cells are larger than procaryotic cells Neutrophil (white blood cell) engulfing a red blood cell Cells are enormously diverse chemically also. Some need oxygen, for some oxygen is poison. Some make hormones, some are “engines” like muscles. But all living cells have a similar basic chemistry. • All living cells are similar – grow, reproduce, convert energy from one form into another, etc. – chemistry - DNA stores genetic instructions using the same chemical code (nucleotides), this code is duplicated, transcribed and translated in the same way in all cells. – DNA codes for the construction of protein molecules which in large part determine the behavior of the cell – The same 20 different amino acids are the building blocks for proteins in all cells. • DNA duplicates before a cell reproduces (divides). • Daughter cells receive a set of the DNA and therefore resemble parent. But not exactly. • Mutations (changes in the DNA) can lead to a change that is bad - less able to survive and reproduce, a change that is neutral - makes no difference in survival, or a change that is for the better - better able to survive - evolution. • In general, the struggle for survival (food etc) eliminates the bad, favors the good, and tolerates the neutral changes -natural selection. • Sexual reproduction also leads to different combinations of genetic material - evolution. • Evolution = changes in the DNA (evolving) and selection of the organisms that are better able to survive over thousands of millions of cell generations. • Present day cells may be fundamentally similar because they all inherited their genetic instructions from a common ancestor. • Cells are ultimately made of inorganic chemicals, oxygen, carbon, etc. So cells obey the laws of physics thermodynamics and chemistry. Cannot create energy etc. • The larger a cell is the more surface area is required for all the transactions needed - taking in nutrients, getting rid of wastes. Intracellular membranes add to the surface area and allow the volume or size of the cell to be greater. Therefore eucaryotic cells are larger than procaryotic cells Bacteria are small, diverse, and reproduce quickly, so they evolve quickly. They outnumber other organisms. Their chemistry is very diverse, virtually any organic material can be used for food. Two kingdoms eubacteria and archaebacteria. Archaebacteria are unique - found in hostile environments. Biologists have chosen a small number of organisms as a focus for intense investigations. Because of the underlying similarity in all cells, we have learned much about our own cells from the bacteria Escherichia coli Some bacteria are photosynthetic. Bacteria not only use organic material, they can also live on inorganic substances, getting CO2, nitrogen, hydrogen, sulfur, etc from the air. Even plants can not capture nitrogen from the atmosphere. Escherichia coli (electron micrograph) have been studied extensively. Lives in the guts of humans and other vertebrates and grown easily in broth culture. Contains a single molecule of DNA which codes for about 4000 proteins Evolutionary scientists think that giardia may be an intermediate stage in evolution. Has 2 nuclei but no other intracellular organelles. Analysis of it’s DNA demonstrates a close relationship to bacteria and eucaryotes. Brewer’s yeast has been studied extensively as a minimal eucaryote model. It is small, single-celled fungus with a rigid cell wall. Has about 2.5 times the DNA of E coli • Protozoans are large, complex, singlecelled organisms. Feed on sugar, secrete alcohol, and carbon dioxide. Can be photosynthetic or carnivorous, motile or sedentary. Have complex structures like cilia, stinging darts, mouth parts. Didinium “eating” another Didinium Arabidopsis is a model flowering plant studied extensively Has only 3 or 4 times as much DNA as yeast • Model animals studied include • Drosophila melanogaster, a fly (the majority of animals are insects) – genetics of embryonic and larval development – from a single fertilized egg to a multicellular organism • Caenorhabditis elegans, a nemotode worm smaller and simpler than Drosophila - also genetics of embryonic development • Mice - are inbred so we know their genetics and genes can be mutated or introduced. • Humans - cannot be studied like mice, but human cells can be studied in culture and much has been learned by studying families with genetic diseases. • Model animals studied include • Drosophila melanogaster, a fly (the majority of animals are insects) – genetics of embryonic and larval development – from a single fertilized egg to a multicellular organism • Caenorhabditis elegans, a nemotode worm smaller and simpler than Drosophila - also genetics of embryonic development • Mice - are inbred so we know their genetics and genes can be mutated or introduced. • Humans - cannot be studied like mice, but human cells can be studied in culture and much has been learned by studying families with genetic diseases. Both have defects in the same gene (kit), required for the development and maintenance of pigment cells. We have learned so much. Mammalian genes have close counterparts in Drosophila and C elegans. But we have much to learn • The cells of an individual animal or plant are extraordinarily varied. Yet all these differentiated cell types are generated during embryonic development from a single fertilized egg cell and all contain identical DNA. • Amazingly different, incredibly the same • Different cells express different genes, depending on the cues.
