Chapter 6Genes and Gene Technology

Genes need to do 2 things

1) Supply instructions for cell processes and for building cell structures

2) Must be able to be copied so that each cell contains an identical set of genes.

Nucleotides – the subunits of DNA

• DNA is made of only four subunits

• Each subunit is identical except for the base.

sugar + phosphate + base

• Possible bases are

1) adenine

2) thymine

3) guanine

4) cytosine

Adenine Guanine Thymine Cytosine

Chargaff’s Rule

In 1950, he found that the amount of adenine in DNA always equaled the amount of thymine and that the amount of guanine always equaled the amount of cytosine.

# adenine = # thymine

# guanine = # cytosine

Watson and Crick

* Discovered the

structure of DNA

* Concluded that it resembles

a twisted ladder called a

double helix

DNA

Double Helix

DNA Structure

• The two sides of the ladder are made of alternating sugar and phosphate molecules.

• The rungs of the ladder are composed of a pair of nucleotide bases.– Adenine always pairs with

Thymine– Guanine always pairs with

Cytosine

Making Copies of DNA

• Because adenine always bonds with thymine and guanine always bonds with cytosine, one side of a DNA molecule is complementary to the other side.

• ACCGT will always bind with TGGCA

• In order to copy itself the DNA must first partially unwind.

Exceptions to Mendel’s Rules

• In higher level organisms, like humans, Heredity is much more complicated and harder to predict than Mendel’s peas.

1) Incomplete Dominance

2) Codominance

3) One gene influencing many traits

4) Many genes influencing a single trait

The importance of environment

• Many things in your environment also influence how you grow and develop.

• Diet, exercise, exposure to dangerous chemicals or radiation.

• Genetic Predisposition – a higher than normal probability that a particular trait will appear. Expression of the gene is influenced by the environment. Something in the environment turns the gene on (the ?)

DNA unites all organisms

• DNA functions in the same way for all organisms from bacteria to mosquitoes to whales to humans. All life as we know it is governed by DNA.

• At the same time it is what causes each of us to be unique.

How DNA Works• The order of the

bases on the DNA determines the order of amino acids on the proteins which are assembled based upon the instructions coded in the genes.

Each group of 3 bases codes for one amino acid

Why Proteins

Proteins exist in an almost limitless variety.

The human body contains about 50,000 different proteins.Proteins are the reason for the multitude of different shapes, sizes, colors, and textures found in living things, such as antlers, claws, hair, and skin.

How the Protein is Made

1) A copy of the section of the DNA containing the gene for a particular protein is made.

2) Copier enzymes copy this by utilizing the complementary code.

3) A mRNA (messenger RNA) than carries this genetic info from the nucleus out into the cytoplasm.

How the Protein is Made continued

4) The copied DNA is fed through the ribosome (acting like a factory) reading three bases at a time & constructing the protein.

5) Transfer molecules (tRNA) carry around a specific amino acid in the cytoplasm. As the DNA copy is fed through the ribosome, the appropriate tRNA links up with the bases on the DNA. This causes the tRNA to drop off the amino acid it is carrying, such that a chain of amino acids is formed in concert.

Changes in Genes

Mutation – a substitution, deletion, or an insertion of an extra base into the code. Caused by random errors and mutagens.

Most mistakes are corrected by repair enzymes but sometimes the code is not corrected.

3 possible outcomes of mutations

1) An improvement

2) No change

3) Harmful change

If the mutation occurs in the sex cells then it can be passed on from

generation to generation

How can DNA be damaged

Mutagen – physical or chemical agent that can cause a mutation.

high energy radiationasbestoscigarette smoke

Sickle Cell Anemia

One 3 base sequence (GAA) that codes for the amino acid glutamic acid if changed to (GTA) ends up coding for valine instead resulting in a human blood cell being sickle shaped instead of the normal biconcave - resulting in substantial reduction in oxygen carrying capacity.

Genetic Counseling

Carriers?

Why counsel?

What is a Pedigree diagram?

Sickle Cell Pedigree Chart

Designer Genetics

Genetic Engineering – manipulation of individual genes to improve an organism or to repair a problem.

Selective genetics – organisms with desirable characteristics are mated to produce a new breed or a super organism.

Ethical, Beneficial or Not?

Cloning?

Genetic Engineering of Foods?

Gene Therapy for Diseases?

Genetic Choice for babies?

Creating super animals?

Creating super humans? ?