Cells

Scientists

• Hooke-saw cork cells under a microscope• Van Leeuweenhoek – saw living bacteria• Pasteur – studied bacteria and developed the

germ theory that said that ‘germs’ cause disease. He also developed the first vaccines.

• Koch – rules to test if a germ is the cause of a specific disease

• Margulis – tested DNA in mitochondria and found it was the same as bacteria DNA

Cell Theory

• All living organisms are composed of one or more living cells

• Cells are the basic units of life

• All cells come from preexisting cells

Microscopes

• Compound Light Microscope – series of glass lens that can be no better than 1000X, but can be used to view living cells

• Electron microscopes – aims a beam of electrons at thin slices of cells (dead)– Transmission electron microscope (TEM)– Scanning electron microscope (SEM)

Microscopes

Cell size

• As cell size increases, the surface area to volume ratio decreases

• Rates of chemical exchange may then be inadequate for cell size

• Cell size, therefore, remains small

Cell Size

Cell Size

Basic Cell Types

• Prokaryotes – cells without a nucleus or other membrane bound organelles– Example: most unicellular organisms, e.g.,

bacteria

• Eukaryotes – cells with a nucleus and other membrane bound organelles (ER, mitochondria, Golgi apparatus, chloroplast, lysosome)

Plasma Membrane

The Lipid Bilayer

• Lipids of the bilayer– fluid or liquid-crystalline state

• Proteins move within the membrane

Fig. 5-2b, p. 108

Integral(transmembrane)

protein

(b) Fluid mosaic model. According to this model, a cellmembrane is a fluid lipid bilayer with a constantly changing“mosaic pattern“ of associated proteins.

Phospholipidbilayer

Peripheralprotein

Hydrophilicregion of protein

Hydrophobicregion of protein

Cytoplasm

• Environment inside cell membrane

• Cytoskeleton – supporting network of long, protein fibers that form a network and anchor for the cell organelles

Membrane structure

• Phospholipids~ membrane fluidity• Cholesterol~ membrane

stabilization• “Mosaic” Structure~ proteins• Membrane carbohydrates ~ cell

to cell recognition;

Nucleus

• Genetic material...•chromatin•chromosomes

• Nucleolus:; ribosome synthesis• Double membrane envelope

with pores• Protein synthesis

Ribosomes

• Protein manufacture

Endomembrane system, I

• Endoplasmic reticulum (ER)• Smooth ER

•no ribosomes; •synthesis of lipids

• Rough ER•with ribosomes;

•synthesis of proteins

Endomembrane system, II

• Golgi apparatus– •ER products are modified, stored, and then shipped

Endomembrane system, III

• Lysosomes •sac of hydrolytic enzymes; digestion of macromolecules

• Tay-Sachs disease~ lipid-digestion disorder

Other membranous organelles, I

• Mitochondria • quantity in cell correlated with metabolic activity;

•cellular respiration •contain own

DNA

Other membranous organelles, II

• Chloroplast (doubled membranous plastid) •photosynthesis •own DNA

Peroxisomes

• Metabolism of fatty acids; detoxification of alcohol (liver)

Cellular Transport

• Passive Transport – does not require energy– Diffusion– Across a membrane

• Osmosis• Facilitated diffusion

• Active Transport – requires energy– Sodium/Potassium pump– Transport of Large Particles

• Endocytosis• Exocytosis

Diffusion

Osmosis

Water balance

• Osmoregulation~ control of water balance

• Hypertonic~ higher concentration of solutes

• Hypotonic~ lower concentration of solutes

• Isotonic~ equal concentrations of solutes

• Cells with Walls:• Turgid (very firm)

• Flaccid (limp)

• Plasmolysis~ plasma membrane pulls away from cell wall

Turgor and Plasmolysis

Facilitated Diffusion

Types of Active Transport

• Sodium-potassium pump• Exocytosis~ secretion of

macromolecules by the fusion of vesicles with the plasma membrane

• Endocytosis~ import of macromolecules by forming new vesicles with the plasma

membrane

•phagocytosis•pinocytosis

Fig. 5-17b, p. 121

1. Three Na+ bindto transport protein.

2. Phosphate group istransferred from ATPto transport protein.

3. Phosphorylationcauses carrier proteinto change shape, releasing3 Na+ outside cell.

4. Two K+ bind totransport protein.

5. Phosphate is released.6. Phosphate release causescarrier protein to returnto its original shape. TwoK+ ions are released insidecell.

Phagocytosis

Large particles enter cell