Chapter 7 CELLS

Section 1 Section 2 Section 3 Section 4 Cell Theory Microscopes Cell Types - Prokaryote and Eukaryote Section 2 Plasma Membrane – Structure and Function Section 3 Structures and Organelles (see pg 199) Section 4 Cellular Transport

Section 1 Principles of Cell Theory 1. All living things are composed of cells. 2. In organisms, the cell is the basic unit of structure and function. 3. Cells come from pre-existing cells.

Why are cells small? Many substances must move in/out of cells. (Ex: CO2 , O2) Small cell = efficient! Less distance to travel! More cell membrane to enter and exit! The size of cells is limited by surface area to volume ratio.

SA: Vol 6:1 is better than 24:8 (3:1) Small cells have more surface area for their volume of cytoplasm than large cells. Substances can move in and out of the cell more efficiently! SA: Vol 6:1 is better than 24:8 (3:1)

Low SA:V ratios High SA:V ratios

Relative sizes of cells.

Microscopes 1665: Robert Hooke used a simple microscope to observe cork cells. 1683: Anton van Leeuwenhoek observed tiny organism known today a protozoans. 1830’s: Scientists proposed that plant and animals are made of cells.

Types of Microscopes Dissection or Stereoscope Light illuminated. 3 dimensional image 2x to 30x Best for larger objects

10X 40X

Compound Light microscope: series of glass lenses produce a magnified image. 2 dimensional image. Can observe cells and live organisms. Up to 2000x magnification

Scanning electron microscope (SEM) Electron illuminated (beam of electrons) 3 D image Object is coated in gold and electrons bounce off gold, creating image. Up to 200,000X Water must be removed so no live specimens.

Pollen Butterfly tongue Flower petal

Transmission electron microscope (TEM) Electron illuminated (beam) Electrons pass through the object. 2 D image, very thin slice. 500,000x

Herpes virus assembled in the nucleus. (Courtesy of Dr Herpes virus assembled in the nucleus. (Courtesy of Dr. Duncan Wilson) http://www.aecom.yu.edu/aif/gallery/TEM/tem.htm

High-contrast direct DNA image, TEM                                                                                                                                                                                                        High-contrast direct DNA image, TEM C015/1926 Rights Managed This image is part of the sequence science and technology: first-ever DNA images Credit: PROFESSOR ENZO DI FABRIZIO, IIT/SCIENCE PHOTO LIBRARY Caption: High-contrast direct DNA image. Transmission electron micrograph (TEM) of the first high-contrast direct image of a bundle (fibre) of strands of DNA (deoxyribonucleic acid). This bundle is six DNA strands wrapped around a seventh. The inset at lower right shows the helical structure, with the red arrows pointing to the edges of the helix. The width of a DNA strand is 20 angstroms (2 nanometres), and the scale bar (bottom left) is 20 nanometres long. This image was obtained by a team led by Enzo di Fabrizio from the Department of Nanostructure, at the Italian Institute of Technology (IIT) in Genoa. The results were published in November 2012 in the journal Nanoletters, and in Nature in January 2013.

2 Basic Cell Types 1. Prokaryotic Cells: Cells without a nucleus ( circular DNA) Most are unicellular organisms (bacteria) May be similar to the first organisms on earth. Endosymbiont Theory: prokaryotic cells may be the precursor to organelles in eukaryotic cells.

Photo credit: http://learn.genetics.utah.edu/content/cells/organelles/

2. Eukaryotic Cells Contain a nucleus and other organelles Nucleus: contains genetic material, DNA Organelles: enable cell functions to take place in different parts of the cell at the same time.

Section 2 The Plasma Membrane (aka cell membrane) Function: to help maintain homeostasis How? It controls the movement of substances into and out of the cell.

TEM: Transmission electron microscopy

Key Property: Selective Permeability It only lets certain substances in or out.

Structure of the Plasma Membrane Phospholipid Bilayer: 2 layers of phospholipids arranged tail to tail Polar head is outside (hydrophilic or water loving). Non-polar tail is inside (hydrophobic or water repelling).

How do substances get across? Movement of substances across the membrane: 1. Water and other polar molecules move freely. 2. Water-soluble substances don’t move through the membrane. They are stopped by the nonpolar middle. How do substances get across? Transport proteins: assist in movement of substances in and out of cell. There are several types!

We will talk about these in Section 4! Channel Protein - Passive Transport Carrier Protein - Active Transport We will talk about these in Section 4!

Fluid Mosaic Model Other components of the plasma membrane: The components of the membrane can move around, creating a shifting pattern or mosaic. Other components of the plasma membrane: Cholesterol (helps make the membrane flexible) Proteins (receptors, anchors the membrane, tunnel for transport of materials) Carbohydrates (helps cells identify chemical signals – what’s good or bad)

There are many substances in and around the plasma membrane! Carbohydrates help identify Unknown substances.