Chem 2223b Inter. 2008: Cellular Structure & Function

Transcription

1 Department of Chemistry, The University of Western Ontario Chem 2223b Inter. 2008: Cellular Structure & Function This section provides a very brief introduction to cellular structure and the function of some of the cellular components. After studying this section, students will be expected to be able to: o Describe the fundamental structures of prokaryotic and eukaryotic cells, and explain their similarities and differences. o Identify cellular components and their chemical composition o Identify the location of certain metabolic processes inside a cell, and, if applicable, the organelles responsible for the metabolic processes o Be familiar with the function of some of the components covered After completing this section, attempt: o 2008 Midterm: 6 and 7

2 A. Introduction Cellular Structure and Function 2 While there are millions and millions of different cells, which contribute to the biological diversity of our planet, they all share common, fundamental properties. For example, all cells have a lipid-based plasma membrane to hold the cell contents. All cells carry genetic information via DNA, which can be used to make proteins via transcription and translation. Moreover, despite small differences between cell types, the fundamental metabolic concepts (chemical reactions) have been retained during 4 billion years of evolution.

3 B. Eukaroytes (plants, animals, fungi, and protists) Cellular Structure and Function 3 The distinctive feature of eukaryotic cells is the presence of membrane-bound compartments known as organelles. Each organelle has a specific function. Animal cell

4 Plant cell Cellular Structure and Function 4

5 Cellular Structure and Function 5 Major differences of plant cells from animal cells: o Cell wall, predominantly cellulose, plus other carbohydrates and protein. This thick, inflexible wall is used for structural and mechanical support. Animal cells, which do not have a cell wall, are flexible. o Chloroplasts, made of lipid membranes, contain chlorophyll and other pigments for photosynthesis (conversion of CO 2 to carbohydrates). o Large vacuole (up to 90% of cell volume), a lipid-membrane vesicle, with a primary purpose of controlling turgor pressure. Secondary purpose of storage. Animal cells may have vacuoles, but they are very small. o No centrioles or lysosomes

6 Cellular Structure and Function 6 Both animal and plant cells have an internal membrane (endomembrane) system

7 Cellular Structure and Function 7 Mitochondria are used for aerobic respiration and energy generation. They have their own DNA and can self-replicate, and most likely originated as prokaryotes. In the cristae, pyruvate (formed by glycolysis) is oxidized to CO 2. The reduction products NADH and FADH 2 are used by the electron transport chain to make ATP, using O 2, hence the term aerobic respiration (oxidative phosphorylaton).

8 C. Prokaryotes (most bacteria) Cellular Structure and Function 8 Prokaryotic organisms are almost always unicellular. These cells are simpler and are not compartmentalized. Most chemical reactions take place in either the cytoplasm or across the cell membrane.

9 Cellular Structure and Function 9 The cell wall, found in bacteria, is comprised mainly of peptidoglycan, a carbohydrate polymer cross-linked with short peptides. Type depends on species. Carbohydrates used are N-acetylglucosamine and N-acetylmuramic acid.

10 Cellular Structure and Function 10 Gram-negative bacteria also have an outer membrane, made of lipopolysaccharide, between the capsule and the peptidoglycan. (Not shown in diagram on page 8). The Gram stain uses the triarylmethane dye crystal violet. Gram-( ) bacteria are not stained, as the outer membrane prevents the dye from reaching the peptidoglycan. Gram-(+) bacteria, which do not have the membrane, are stained purple.