Exploring Cells: The Fundamental Units of Life

1. Chapter 6 A Tour of the Cell

2. Cells: The Fundamental Units of Life • first cell observed – Robert Hooke in 1665 • thin slices of bottle cork • saw a network of “cells” that a monk would live in • first living cell (Spirogyra) observed by Anton van Leeuwenhoek in 1674 • also described bacteria he found in his mouth (1676) Anton van Leeuwenhoek

3. Cells: The Fundamental Units of Life • the cell is the simplest collection of matter that can be alive • the Cell Theory: • 1. all organisms are made of at least one type of cell • 2. all cells come from pre-existing cells by this cell dividing in two • 3. the cell is the basic, fundamental unit of life • attributed to: Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow

4. Concept: Eukaryotic cells have internal membranes that compartmentalize their functions • the basic structural and functional unit of every organism is the cell • two types of cells: prokaryotic or eukaryotic • protists, fungi, animals, and plants all consist of eukaryotic cells

5. Cells • Basic features of all cells • Plasma membrane • Semifluid substance called cytoplasm • organized DNA in the form of Chromosomes(carry genes) • Ribosomes (make proteins)

6. Comparing Prokaryotic and Eukaryotic Cells • Prokaryotic cells: • no nucleus • DNA in a region of the cytoplasm called the nucleoid • no membrane-bound organelles • a Cytoplasm bound by the plasma membrane • smaller ribosomes • Eukaryotic cells • membrane – bound nucleus containing DNA • membrane-bound organelles • a Cytoplasm in the region between the plasma membrane and nucleus • larger ribosomes

7. The Eukaryotic Cell • 1. Plasma membrane • 2. Nucleus • 3. Cytoplasm • a. cytosol • b. cytoskeleton • 4. Cytoplasmic organelles • membrane-bound • non-membrane bound Plants and fungus have a Cell Wall outside of the plasma membrane – not the same composition

8. (a) TEM of a plasmamembrane Outside of cell The Plasma Membrane • the plasma membrane is a semi-permeable barrier • allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell • the general structure of a biological membrane is a double layer of phospholipids • known as a phospholipid bilayer • membrane proteins embedded within it or found attached to one layer Inside of cell 0.1 m Carbohydrate side chains Hydrophilicregion Hydrophobicregion Hydrophilicregion Phospholipid Proteins (b) Structure of the plasma membrane

9. The Cytoplasm • Comprised of • 1. The cytosol • 2. The cytoplasm • Cytoskeleton = a“skeleton” of protein filaments found prokaryotic and eukaryotic cells • Cytosol = intracellular fluid of the prokaryotic or eukaryotic cell

10. The Cytosol • also known as the intracellular fluid or ICF • about 55% of the cell’s volume • about 70-90% water PLUS • ions • dissolved nutrients – e.g. glucose • soluble and insoluble proteins • waste products • macromolecules and their components - amino acids, fatty acids • ATP • unique composition with respect to extracellular fluid (ECF) • fluid found outside of a cell

11. Nucleus Nucleolus The Eukaryotic Nucleus: Information Central Chromatin Nuclear envelope: • the nucleus contains most of the eukaryotic cell’s genes and is usually the most conspicuous organelle • the nuclear envelope encloses the nucleus, separating it from the cytoplasm • not found in prokaryotic cells – so NO nucleus in prokaryotic cells • the nuclear envelope is comprised of two phospholipid bilayers • the nucleolusis located within the nucleus and is the site of ribosomal synthesis • a prominent dark region inside the nucleus • nuclear pores exist for import and export Inner membrane Outer membrane Nuclear pore Rough ER Porecomplex Ribosome Close-upof nuclearenvelope Chromatin

12. histone Eukaryotic DNA: Chromatin & Chromosomes DNA helix nucleosome • organized form of DNA in the nucleus = chromatin • described as “beads on a string” model • DNA helix is wrapped around complexes of proteins called histones • the histone-DNA complex is called a nucleosome • described by Roger Kornberg – Nobel Prize 2006

13. Eukaryotic DNA: Chromatin & Chromosomes • eukaryotic DNA needs to be condensed when the cell divides • done just after the cell “copies” its DNA before mitosis • cell “compacts” its chromatin into a duplicated chromosome • histones play an important role

14. Membranous Organelles • surrounded by one or two phospholipid bilayers that are similar to the plasma membrane • major functions of the membranous organelles • 1. protein synthesis – ER and Golgi • 2. energy production – mitochondria • 3. waste management – lysosomes & peroxisomes

15. Endoplasmic reticulum (ER) = multiple membrane-bound compartments called cisterna (plural = cisternae) -often attached to the nucleus -responsible for: • protein synthesis • lipid & phospholipid synthesis • calcium storage -two types: Rough ER vs. Smooth ER -Rough ER (RER) – ribosomes “docked” onto their surface  protein synthesis -Smooth ER (SER) – no ribosomes: lipid synthesis & calcium storage

16. 2. Golgi Apparatus = multiple stacks of cisternae next to the ER -described by Camillo Golgi in 1897 -responsible for: 1. protein modifications – sugar addition, trimming 2. protein sorting and targeting

17. 3. Mitochondria • -singular = mitochondrion • -surrounded by a two phospholipid bilayers • an outer mitochondrial membrane • an inner mitochondrial membrane • a fluid-filled space = matrix -the inner membrane is folded into folds calledcristae -these increase the membrane surface area for the enzymes of ATP synthesis (via Oxidative phosphorylation)

18. 4. Lysosomes= “garbage disposals” -dismantle debris, eat foreign invaders/viruses internalized by the cell -cell biologists not really sure exactly how the lysosome forms -contain powerful enzymes to breakdown substances into their component parts -these enzymes are collectively known as acid hydrolases e.g. nucleases = breakdown RNA & DNA into nucleotides e.g. proteases = breakdown proteins into amino acids

19. 5. Peroxisomes: found in all cells but abundant in liver and kidney cells -only identified in 1954 -major function is breakdown of fatty acids • butthis reaction generates hydrogen peroxide (H2O2) • so peroxidases contain an enzyme (called catalase) that catalyzes the breakdown of the H2O2 into H2O and O2

20. Non-membranous Organelles A. Centrioles:short cylinders of a protein called tubulin - 9 microtubule triplets called a 9+0 array (9 peripheral triplets, 0 in the center) -found in cells capable of division (in an area of the cell called the centrosome) -has a rolein mitosis - spindle and chromosome alignment -duplicate just prior to the onset of mitosis -migrate to opposite ends of the replicating cell -mitoticspindle grows in between centriole spindle

21. B. Cilia & Flagella • cilia = projections off of the plasma membrane of eukaryotic cells • flagella = larger cilia • made of hollow “straws” of tubulin called microtubules • beat rhythmically to transport material – power & recovery strokes • found in linings of several major organs covered with mucus where they function in cleaning • e.g. trachea, lungs Trachea Tubulin in a microtubule

22. B. Cilia & Flagella • cilia and flagella = 9+2 array  9 doublets around the periphery + 2 singlets in the center of the cilia

23. C. Ribosomes: Protein Factories • Ribosomes are particles made of ribosomal RNA (rRNA) and protein • comprised of two subunits • large • small • ribosomes carry out protein synthesis 0.25 m Free ribosomes in cytosol Endoplasmic reticulum (ER) Ribosomes bound to ER Largesubunit Smallsubunit TEM showing ER andribosomes Diagram of a ribosome