1. Overview of the cell structure Overview of the cell structure

2. Readings and Objectives Reading – Russell: 2.5a, 21.2, 22 – Cooper: Chapter 1 Objectives – Cell Theory – Basic properties of cells – Cell size – Cell diversity – Prokaryotic vs eukaryotic cells Diversity Structure

3. Properties of Cells Basic properties of cells Order and complexity – surrounded by a semi-permeable membrane, similar in composition and function – Similar chemical composition: similarity of structural patterns of macromolecules and their functions – Similar biochemical and regulatory processes – hierarchal complexity from molecules to supramolecular structures Self replication by division: all cells come from existing cells by division, process of division share similarities among cells

4. Properties of Cells Basic properties of cells Cells are small (see module 3)see module 3 – Varied between ~0.5 to a few 100 um (eg E.coli ~0.6 um, RBC 8 um, skin epithelial cells ~30 nm and ameoba ~500 um) – Why cells are generally small? – Limiting factor: Surface to volume ratio (S/V) – Surface is the portal of supply for the volume of cell

5. Properties of Cells Basic properties of cells Cells are small (see module 3)see module 3 – S/V vs X in nonlinear – S/V exponentially reduced as X increases Surface (size of cell) reaches a limit that cannot support the cell’s need (volume) Eukaryotes: have increased the S/V by extending internal membrane surfaces

6. Properties of Cells Properties… Interaction with the environment All have transmittable genetic program – DNA: similar structure and function, being inherited – Genes: units of genetic function, basic similarity – Evolution: plasticity of genetic information, functional divergence in response to environmental cues Energy biogenesis Similarity of metabolic pathways, eg. glycolytic pathway, Krebs cycle, adaptive variations on a general theme Use of ATP as the universal cellular energy currency  Chemical and mechanical activity Similar enzymes carry out metabolic reactions → energy Use of energy to do mechanical work

7. Cell theory Early observations Robert Hooke (1665): first to observe unit structures in cork, called them “cells” Antone Van Leeuwenhoek: discovers microbial single “cells” Matthias Schleiden and Theodor Schwann (1839): Independently concurred that all living organisms, –All living organisms consist of unit structures called Cells (The Cell theory) Rudolf Virchow (1855): expanded the cell theory, –Each cell is the result of division of previous cells Modern cell biology addresses the question “how cells work” To understand the molecular basis of cellular processes

8. Cell diversity Domains of life: cells are organized in three domains Procaryotes- Eubacteria and Arhaebacteria Eucaryotes- Protista, Fungi, Plants and Animals Similarities:Similarities: Procaryotes and eucaryotes –Cell membrane – energy metabolism –Genetic code Differences:Differences: –Procaryotes are unicellular –Except for many members of protista the rest of eukaryotes are multicellular –Size: procaryotes 0.5-5 um, eucaryotes 5-500 um –Membrane bound organelles present in eucaryotes but not procaryotes –Reproduction: cell fission in procaryotes vs mitosis in eukarotes

9. Procaryotes: Structure Bacterial cytoplasm is surrounded by a cell membrane, a cell wall, and for some with a polysaccharide capsule Cell wall: used for protection, shape, rigidity Composed of peptidoglycan, a polysaccharide of alternating acetlylated muramic acid and glucoseamine β1  4 glycosidic bond btw sugars cross-linked by a short oligopeptide Two types of bacteria based on cell wall structure – Gram positive: multiple layers of peptidoglycan – Gram negative: few layers of peoptidoglycan G- bacteria G+ bacteria

10. Procaryotes: Structure Plasma membrane – Beneath the cell wall is the plasma membrane, a phospholipid bilayer with associated proteins – Steroid like molecules instead of cholesterol

11. Procaryotes: Structure Cytoplasm: lacks membrane bound organelles Ribosomes – 70S; 3 rRNA + 55 proteins (in 2 subunits 50S and 30S) – Protein synthesis Chromosome: single supercoiled chromosome that resides in a region called nucleoid (not membrane bound)

12. Procaryotes: Structure Bacteria have appendages with specific functions – Flagella, composed of flagellin helps bacteria move – Fimbriae are small bristlelike fibers that allow bacteria to attach themselves to surfaces – Sex pili (F pilus) used for conjugation to transfer DNA from one bacterium to another Genes coding for F-pilus are on F plasmid

13. Procaryotes: reproduction Reproduction Fission instead of mitosis Chromosomal DNA replicationCytokinesis formation of divisome (several proteins that tag the centre of cell) Cell wall peptidoglycan deposited Chromosomes separated

14. Eucaryotic cells Diversity Protista: free-living marine unicellular, some photosynthetic e.g. Giardia lamblia, dinoflagellates, Paramecium, Plasmodium Multicellular organisms – Fungi, Plants, Animals – Differentiation – Model organisms (a) Saccharomyces cerevisiae (yeast) (b) Arabidopsis thaliana (c) Caenorhabditis elegans (d) Drosophila melanogaster (e) Mus musculus

15. Eucaryotic cells Structure Characteristics: Typically 10-30 um Separation of DNA and cytoplasm by nuclear envelope Presence of membrane-bound compartments with specialized functions: Mitochondria, chloroplasts, ER, Golgi complex Highly specialized motor proteins Nuclear envelope and internal membranes – Originated from cell membrane – differentiated and acquired special functions

16. Eucaryotic cells organelles can be divided into four categories – The nucleus and ribosomes – endomembrane system – energy-related organelles – cytoskeleton

17. Can you meet these objectives? Describe the cell theory Describe the basic properties of cells Outline the major advances leading to modern cell biology Describe the properties of procaryotic cells Contrast and compare prokaryotes and eukaryotes Discuss the cellular structure of prokaryotes