1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany CONCEPTS IN BIOLOGY TWELFTH EDITION Enger Ross Bailey CHAPTER 4

2 4.1 The cell theory All living things are made of cells. A cell – The basic unit of all living things. Robert Hook’s Compound microscope

3 The historical context of the cell theory (I) Robert Hooke coined the term “cell”. – Look at cork cells under a simple microscope. Anton van Leeuwenhoek – Made better microscopes – Used them to look at a variety of substances and identified animalcules (i.e., little animals). Replica of van Leewenhoek microscope

Modern compound microscope

Electron microscope

6 The historical context of the cell theory (II) Mathias Jakob Schleiden (1838, German) – Concluded that all plants were made of cells Theodor Schwann (1839, German) – Concluded that all animals were made of cells

Initial observations of cells Cell wall – Outer non-living part of plant cells Protoplasm – Interior living portion of the cell – Nucleus Contains the genetic information of the cell – Cytoplasm Fluid part of the protoplasm – Organelles “Little organs” within the protoplasm

8 Different kinds of cells Prokaryotic – Structurally simple cells – Lack a nucleus – Lack most other organelles – Bacteria Eukaryotic cells – More complex – Have a nucleus – Have a variety of organelles – Plants, animals, fungi, protozoa and algae (See p. 69 & Next slide of Fig. 4.4)

Major cell types

4.2 Cell size Prokaryotic cells – 1-2 micrometers in diameter Eukaryotic cells – micrometers in diameter

Surface area to volume ratio Cell size is limited. – Cells must get all of their nutrients from their environment through their cell membranes. – Volume increases more quickly than surface area. – Surface area-to-volume ratio must remain small (because metabolic and nutrition requirements). A few exceptions, please see page 72.

The structure of cell membranes Cell membranes – Thin sheets composed of phospholipids and proteins Fluid-mosaic model – Two layers of phospholipids Fluid – Has an oily consistency – Things can move laterally within the bilayer. Mosaic – Proteins embedded within the phospholipid bilayer

13 The phospholipid bilayer Phospholipid structure – Hydrophobic tails – Hydrophilic heads Bilayer – Hydrophobic tails of each layer associate with each other. – Hydrophilic heads on the surface of the bilayer Cholesterol – Hydrophobic – Found within the hydrophobic tails – Keeps the membrane flexible

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15 Membrane proteins Some are on the surface. Some are partially embedded. – Protrude from one side Some are completely embedded. – Protrude from both sides Functions (See p ) – Transport molecules across the membrane – Attachment points for other cells – Identity tags for cells

Organelles composed of membranes Plasma membrane (cell membrane) Endoplasmic reticulum Golgi apparatus Lysosomes Peroxisomes Vacuoles and vesicles Nuclear membrane

17 The plasma membrane Composed of a single phospholipid bilayer Separates the contents of the cell from the external environment Important features – Metabolic activities (See p. 73) – Moving molecules across the membrane (p. 73) – Structurally different inside and outside (p. 73) – Identification: Self vs. nonself (p ) – Attachment sites (p. 74) – Signal transduction (p. 75)

The endoplasmic reticulum A set of folded membranes and tubes throughout the cell. Provides a large surface area for important chemical reactions. – Because it is folded, it fits into a small space. Two types of ER – Rough Has ribosomes on its surface – Sites of protein synthesis (Protein- manufacturing machine, e.g. pancreas cell, p. 75) – Smooth Lacks ribosomes Metabolizes fats Detoxifies damaging chemicals e.g. Human liver (p. 75)

Figure 4.9

20 The Golgi apparatus Stacks of flattened membrane sacs. Functions – Modifies molecules that were made in other places. – Manufactures some polysaccharides and lipids. – Packages and ships molecules.

21 Traffic through the Golgi – Vesicles bring molecules from the ER that contain proteins. – Vesicles fuse with the Golgi apparatus. – The Golgi finishes the molecules and ships them out in other vesicles. Some are transported to other membrane structures. Some are transported to the plasma membrane. Some vesicles become lysosomes. (p. 77)

22 Lysosomes Vesicles containing enzymes that digest macromolecules. – Carbohydrates – Proteins – Lipids – Nucleic acids Interior contains low pH – These enzymes only work at pH=5. – The cytoplasm is pH=7. If the lysosome breaks open, these enzymes will inactivate and will not damage the cell.

Functions of lysosomes Digestion – of food taken into the cell Destruction – Disease-causing organisms (p. 77) – Old organelles

24 Peroxisomes Contain the enzyme catalase – Breaks down hydrogen peroxide (H 2 O 2 ) – Breaks down long-chain fatty acids – Synthesizes cholesterol and bile salts – Synthesizes some lipids Different from lysosomes not formed by Golgi apparatus and they contain different enzymes

25 Vacuoles and vesicles Membrane-enclosed sacs Vacuoles – Larger sacs – Contractile vacuoles Forcefully expel excess water from the cytoplasm Vesicles – Smaller vesicles

26 The nuclear membrane Separates the genetic material from the rest of the cell Filled with nucleoplasm Composed of two bilayers Contains holes called nuclear pore complexes – Allow large molecules like RNA to pass through the membrane into the cytoplasm

27 Interconversion of membranes Membranes are converted from one membranous organelle to another.

28 Energy converting organelles Mitochondrion(See p.80, Fig. 14 a) – A small bag with a large bag stuffed inside. – Larger internal bag is folded into cristae. Cristae contain proteins for aerobic cellular respiration. – Releases the energy from food – Requires oxygen – Uses the energy to make ATP (See Ch.6)

29 Energy converting organelles Chloroplasts (See p. 80, Fig b) – Saclike organelle – Contain chlorophyll – Perform photosynthesis Uses the energy in light to make sugar – Contain folded membranes called thylakoids Thylakoids stacked into grana Thylakoids contain chlorophyll and other photosynthetic proteins. – Thylakoids surrounded by stroma (See p. ch.7)

30 Nonmembranous organelles Ribosomes Cytoskeleton Centrioles Cilia flagella Inclusions

31 Ribosomes Made of RNA and proteins (p.79) Composed of two subunits – Large – Small (p.79-80) Are the sites of protein production (p.80) Found in two places – Free floating in the cytoplasm (p.80) – Attached to endoplasmic reticulum (p.80)

Cytoskeleton Provides shape, support and movement Made up of – Microtubules (p.81) – Microfilaments (p.81) – Intermediate filaments (p.81)

33 Centrioles Two sets of microtubules arranged at right angles to each other. Located in a region called the centrosome. – Microtubule-organizing center near nucleus. Organize microtubules into spindles used in cell division.

34 Cilia and Flagella (See p.82) Hair-like projections extending from the cell. Flagella – Long and few in number – Move the cell through its environment Cilia – Small and numerous – Move the environment past the cell arrangement of microtubules

35 Inclusions Collections of miscellaneous materials – Can be called granules (p. 82) Temporary sites for the storage of nutrients and waste (p. 82)

36 Nuclear components (p ) Contains chromatin – DNA + proteins – Becomes condensed during cell division into chromosomes. Surrounded by nuclear membrane Contains one or more nucleoli – Site of ribosome synthesis Contains nucleoplasm – Water, nucleic acids, etc.

37 Getting through membranes (p. 84) Diffusion Osmosis Facilitated diffusion Active transport Endocytosis Exocytosis

38 Diffusion Molecules are in constant, random motion. Molecules move from where they are most concentrated to where they are less concentrated. – This is called diffusion. – Involves a concentration gradient (diffusion gradient) No concentration gradient=dynamic equilibrium

39 The rate of diffusion Depends on – The size of the molecule Smaller molecules diffuse faster. – The size of the concentration gradient The greater the concentration difference, the faster the diffusion.

40 Diffusion across membranes Diffusion can only happen if there is no barrier to the movement of molecules. Can only happen across a membrane if the membrane is permeable to the molecule – Membranes are semi-permeable; they only allow certain molecules through. – Membrane permeability depends on the molecules size, charge and solubility.

41 The direction of diffusion Determined solely by the concentration gradient. Diffusion is passive that does not require energy input. Example: – Oxygen diffusion (p. 85)

42 Osmosis The diffusion of water through a selectively- permeable membrane. Occurs when there is a difference in water concentration on opposite sides of the membrane. Water will move to the side where there is less water – Or more solute

43 Hypertonic vs. hypotonic (p. 86) If a cell has less water (more solute) than its environment – It is hypertonic to its surroundings. If a cell has more water (less solute) than its environment – It is hypotonic to its surroundings. If a cell has equal amounts of water (and solute) as its environment – It is isotonic to its surroundings.

44 Physiological relevance of osmosis

45 Osmosis in animal and plant cells

46 Facilitated diffusion Some molecules have to be carried across the membrane. – Accomplished by carrier proteins Still involves diffusion – Follows a concentration gradient – Is passive transport – Example (glucose, p.88)

Active transport Opposite of diffusion Moves molecules across a membrane UP their concentration gradient Uses transport proteins in the membrane – Specific proteins pump specific molecules Requires the input of energy Example (Na and K ion, p. 88)

48 Endocytosis Moves large molecules or sets of molecules into the cell – Phagocytosis Cell eating Food engulfed by the membrane Material enters the cell in a vacuole. – Pinocytosis Cell drinking Just brings fluid into the cell – Receptor-mediated endocytosis Molecules entering the cell bind to receptor proteins first

49 Exocytosis Moves large molecules or sets of molecules out of the cell. Vesicles containing the molecules to be secreted fuse with the plasma membrane. – Contents are dumped outside the cell.

50 Endocytosis and exocytosis

51 Prokaryotic cells Two different types of prokaryotes – Domain eubacteria Contains bacteria – Domain archaea Contains prokaryotes that live in extreme environments

52 Prokaryotic cell structure Contain DNA and enzymes – Able to reproduce – Engage in metabolism Surrounded by a plasma membrane – Plasma membrane surrounded by a cell wall Maintains the shape of the cell – Cell wall surrounded by a capsule Helps them adhere to hosts Protects them from destruction Contain ribosomes (Example p. 90 of Antibiotics) May contain flagella – Facilitates movement

53 Different types of eukaryotic cells

54 Summary of cell organelles and their functions