lecture 6 for BGYA01

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Biological Sciences
Clare Hasenkampf

Lecture 6 BGYA01 September 27, 2007 All right so far we have talked about the macromolecules that make up the cell, and we have lloked at the process by which cells make their DNA, RNA and proteins. The carbohydrates and lipids are made in biochemical pathways that are controlled by the enzymes. Now I would like to look at how the proteins , carbohydrates and lipids are organized into cells and cellular structures, and where the DNA and RNA are found and organized. THE MAJOR GROUPS OF ORGANISMS Scientists have studied organisms, living and extinct, and have placed them into groups of related organisms. The kinds of properties they consider when classifying organisms are: - the structure of the cells - the organization of cells into an organism - the methods of acquiring their building materials and energy - the method of reproduction. Current classification schemes group the living and extinct species into three domains. The three domains are Bacteria, Archaea, and Eukarya. Figure 1.11 page 12. The tree diagram of figure 1.11 illustrates the idea that the first type of organism diverged into two types of organisms. One type gave rise to the domain known as Bacteria, and the second type was the ancestor of both the Archaea and the Eukarya. Available evidence suggests that the Archaea and Eukarya share a common ancestor, not shared with the Bacteria. At a later point in time this second type of organism diverged into the separate domains of Archaea and Eukarya. It is estimated that organisms within a domain have been evolving separately from organisms in the other domains for at least a billion years. Lets look at some key characteristics of the three domains. (Well discuss these characteristics in more detail later). Bacteria (1) Have cells that lack double membrane bound organelles (2) Are single celled organisms (3) Have either no cell walls OR a cell wall containing peptidoglycan (4) Most have a single circular double stranded DNA as its hereditary material 1 www.notesolution.comArchaea (1) Have cells that LACK double membrane bound organelles (2) Are single celled organisms (3) Have some members with cell walls but the walls do NOT contain peptidoglycan (4) Most have a single circular double stranded DNA as its hereditary material Eukarya (1) Have cells that DO have double membrane bound organelles (2) Have some single celled members, and many multi-cellular members. (3) Have some members with cell walls, but the walls do NOT contain peptidoglycan (4) All have several linear double stranded DNAs as its hereditary material The two most ancient domains, Bacteria are both in the important category we call prokaryotes. All of the other branches of the Tree of Life are called eukaryotes. The distinction between prokaryote or eukaryote is based on the degree of structural organization within the cell. The prokaryotes (both Bacteria and the Archea) are single celled organisms WITHOUT internal membrane-bound, compartments. They have relatively simple, internal cell structure. Most prokaryotes have one circular, double stranded, DNA molecule as their hereditary material. All eukaryotes have internal membrane-bound, compartments, and a true nucleus. All eukaryotes have several, linear DNA stranded molecules as their hereditary material. The differences between pro- and eukaryotes will be more clear to you later as we study cell structure. Clicker questions An organism as a circular DNA molecule, and a cell wall with no peptidoglycan. It is a member of a) Eukarya b) Bacteria c) Archaea ** is the correct answer d) Gram negative bacteria e) Gram positive bacteria 2 www.notesolution.com
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