4.1 The Plasma Membrane (p. 76; Figs. 4.3, 4.4, 4.5, 4.6, 4.7)

A. All cells are surrounded by a plasma membrane composed of a bilayer of phospholipids, according to the fluid mosaic model.

B. The polar ends of these phospholipids interact with the fluid interior and exterior environments of the cell, while the nonpolar fatty acid chains form the interior of the membrane.

C. The phospholipids are arranged in a bilayer, with nonpolar tails extending to the inside.

D. Proteins Within the Membrane

1. Floating within the lipid bilayer are a variety of membrane proteins that function either to transport materials across the membrane (transmembrane proteins) or to serve as identification markers in cell communication (cell surface proteins).

Transport Across Cell Membranes (p. 92)

4.2 Diffusion and Osmosis (p. 92; Figs. 4.26, 4.27, 4.28)

A. Materials must move in and out of the cell in order for the cell to survive.

B. Movement across the cell membrane occurs in three ways:

1. Water diffuses through the membrane.

2. Particles and liquids are engulfed by the membrane folding around them.

3. Proteins in the membrane allow the passage of certain molecules.

C. Diffusion

1. The random motion of molecules tends to make them disperse from areas in which they are more concentrated to areas of lesser concentration until a uniform distribution is attained.

2. Simple diffusion is based on the random motion of molecules and is the way that small molecules, like gases, enter and exit cells.

D. Osmosis

1. Movement of water across a membrane is a special case of diffusion called osmosis.

2. When water moves into a cell, there is greater pressure, called osmotic pressure.

3. Water moves from areas with less solute and proportionately more free water, to areas with more solute and less free water.

4.3 Selective Permeability (p. 95; Fig. 4.31)

A. Cells use an attribute called selective permeability to regulate the passage of specific molecules into or out of the cell.

B. Selective Diffusion

1. Cells can carefully control what enters and exits their membranes by using channel proteins.

C. Facilitated Diffusion

1. Facilitated diffusion is a special case of diffusion that involves passage in either direction through a carrier protein.

2. Carrier proteins are limited in number and can become saturated when there is an excess of the transported substance.

4.4 Active Transport (p. 96; Figs. 4.32, 4.33, 4.34)

A. Active transport is a process that requires both a transport protein and energy to move molecules from an area of lesser concentration to one of greater concentration.

B. Almost all of the active transport is carried out by the sodium-potassium pump and the proton pump.

Genetic Engineering (p. 212)

9.1 A Scientific Revolution (p. 212; Fig. 9.1)

A. Transferring genes from one organism to another falls into the realm of genetic engineering.

B. Genetic engineering is having a major impact on medicine and agriculture.

9.2 Restriction Enzymes (p. 213; Fig. 9.2)

A. The first step of genetic engineering is to cleave the DNA that the geneticist wishes to transfer.

B. This process involves the use of restriction enzymes that bind specific sequences of nucleotides and split the DNA in that position.

C. Since DNA is made up of complementary bases, both strands do not split at the same position.

9.3 The Four Stages of a Genetic Engineering Experiment (p. 214; Figs. 9.3, 9.4, 9.5, 9.6)

A. Transferring genes from one organism to the next involves four stages.

B. Stage 1: Cleaving DNA

1. Cleaving DNA makes use of various restriction enzymes, each cleaving at a different nucleotide sequence.

C. Stage 2: Producing Recombinant DNA

1. Recombining DNA often makes use of a bacterial plasmid, a small circular piece of DNA separate from the normal bacterial DNA.

D. Stage 3: Cloning

1. Cloning involves getting thousands of bacterial colonies to grow, which together make up a clone library.

E. Stage 4: Screening

1. The screening part of genetic engineering is often the most time-intensive, and investigators must first eliminate any clones that do not contain vectors.

2. Secondly, investigators use a probe of ribosomal RNA to detect the presence of source genes.

9.4 Other Genetic Techniques (p. 218; Figs. 9.7, 9.8, 9.9)

A. PCR Amplification

1. Alternative to using bacterial plasmids to produce clones of source genes, geneticists use the polymerase chain reaction (PCR) to produce many copies of the source gene.

2. This procedure involves locating short sequences of nucleotides, called primers, on either side of the desired gene.

3. Heat is applied to a solution of DNA, the primers, nucleotides, and DNA polymerase, which disrupts the hydrogen bonds of DNA and produces single strands.

4. When cool, the primers are bound to their complementary sequences near the desired gene.

5. The enzyme, DNA polymerase, then begins at a primer and replicates the single-stranded DNA.

6. Many copies of the desired gene can be made in this manner.

B. DNA Fingerprinting

1. DNA can be analyzed for its unique restriction endonuclease patterns, yielding information that can be used to identify suspects from crimes.

Advances in Medicine (p. 220)

9.5 Genetic Engineering and Medicine (p. 220; Fig. 9.10; Tables 9.1, 9.2)

A. Making “Magic Bullets”

1. Medical advances have also been made since the advent of genetic engineering.

2. Bacteria now mass-produce human insulin, the hormone that is underproduced in diabetics.

3. Other products, such as anticoagulants to dissolve blood clots and factor VIII to promote clotting, are now safely produced by bacteria, which eliminates the possibility of transferring diseases from a human donor.

B. Piggyback Vaccines

1. Vaccines have been used for years to trigger immunity to a wide variety of diseases.

2. Vaccines can now be made more safely by inserting the gene for a pathogen's surface protein into the DNA of a harmless virus.

3. Such piggyback vaccines are being developed for malaria and other diseases.

C. Human Gene Therapy

1. Gene therapy, inserting normal genes into people who have inherited defective genes, is now possible with the advent of genetic engineering.

Transforming Agriculture (p. 222)

9.6 Genetic Engineering of Crop Plants (p. 222; Figs. 9.11, 9.12, 9.13)

A. Pest Resistance

1. Certain crops, like cotton, have been engineered to be resistant to insect pests, which means these crops will not require pesticides.

2. Bacterial genes that produce enzymes toxic to certain plant pests have been inserted into tomatoes and other crops so that when the insect bites into a plant, it is killed by the now plant-produced enzymes.

B. Herbicide Resistance

1. Agriculture has benefited from the genetic engineering of herbicide-resistant crops.

2. The active ingredient in Roundup, called glyphosate, is easily broken down in the environment and is thus a comparatively safe herbicide.

3. Making crops resistant to glyphosate means less tilling is needed, thus soils are saved from erosion and less fuel and expense are needed to raise the crop.

C. More Nutritious Crops

1. Rice can be modified to contain more minerals, such as iron, and vitamins.

2. “Golden” rice has been genetically engineered to contain vitamin A, a vitamin that is normally insufficient in diets worldwide.

D. How Do We Measure the Potential Risks of Genetically Modified Crops?

1. Consumers worry that eating genetically-modified food might be dangerous or that GM crops are harmful to the environment.

2. Other than allergic reactions to modified proteins, dangers to the consumer appear to be slight.

3. Whether GM products are potentially harmful to the environment is not yet clear.

9.7 Genetic Engineering of Farm Animals (p. 225; Figs. 9.14, 9.15)

A. Yet another agricultural advance has been the mass production by bacteria of bovine somatotropin, which when fed to dairy cows, greatly enhances milk production.

B. Similar growth hormones enhance the size of pigs and cattle.

9.8 Ethics and Regulation (p. 228)

A. Much controversy surrounds the issue of human cloning and use of embryos.

B. It is important to carefully weigh the ethical considerations before proceeding.

LEARNING OBJECTIVES

· Recognize that the ability to manipulate genes and move them from one organism to another has led to great advances in medicine and agriculture.

· .Discuss the uses and accuracy of DNA fingerprinting.

· Give examples of how inserting human genes into bacteria has produced many medical advances.

· Describe piggyback vaccines.

· Be aware of public sentiment and fears concerning genetic engineering and cloning.