Chapter 6 Section 2

Explain the relationship between DNA, genes, and proteins

Outline the basic steps in making a protein

Describe 3 types of mutations, and provide an example of a gene mutation

Describe 2 examples of uses of genetic knowledge

Almost every body cell contains about 2 meters of DNA!

How does it all fit into a small cell?

How does this DNA hold a code for certain traits?

DNA is wound around proteins and coiled and bundled into strands

DNA and proteins are bundled into chromosomes in the nucleus

This structure allows DNA to hold information

The order of the bases on one side of the molecule is a code that carries information

Gene: a string of nucleotides that give the cell information about how to make a specific trait

http://campus.udayton.edu/~hume/DNA/DNA.ht26.gif http://www.drtummy.com/images/stories/dna/dna_to_chromosome.jpg

1. DNA in nucleus codes for proteins that determine traits

2. DNA is part of chromatin. Long strands of chromatin are bundled in the nucleus

3. A single strand of chromatin is made up of a long strand of DNA that is coiled around proteins

4. Each strand of DNA contains 2 halves (double helix)

5. When a cell divides it packages the chromatin into chromatids. 2 chromatids make a chromosome

Groups of 3 bases are the codes for specific amino acids• Ex. CCA codes for proline• Ex. AGC codes for serine

A long string of amino acids forms a protein

Each gene is a set of instructions for making a protein

Proteins act as chemical triggers & messengers for processes in cells

Proteins help to determine traits (hair color, height, etc.)

We have 1000’s of genes that code for 1000’s of proteins

RNA: another type of molecule that helps make proteins (ribonucleic acid)

Similar to DNA

Provides a temporary copy of a DNA sequence

There are several forms of RNA that do the work of changing code into proteins

1. Make a copy of 1 side of DNA

2. A mirror-like copy of DNA is made out of RNA (messenger RNA - mRNA)

3. Each group of 3 bases on mRNA codes for 1 amino acid

4. mRNA is fed through the ribosome (“factory”)

5. Molecules of transfer RNA (tRNA) deliver amino acids to the ribosome

6. Amino acids are dropped off at the ribosome

7. Amino acids are joined to make a protein

8. One protein is produced for each gene

http://www.odec.ca/projects/2004/mcgo4s0/public_html/t3/mRNA%20to%20protein.gif

Mutations: changes that happen accidentally in DNA

Changes can be in the number, type, or order of the bases on a piece of DNA

If a base is left out: deletion If a base is added: insertion If a wrong base is used: substitution

3 possible consequences to changes in DNA:• An improved trait• No change• A harmful trait

There are some cells that can detect an error

Some mistakes don’t get fixed; sex cell errors get passed along

Random errors get copied

Damage to DNA can also happen

Harmful chemical or physical agents: mutagens• Ex. High-energy radiation (x-ray, UV rays),

asbestos, chemicals in cigarette smoke

May cause a gene to produce the wrong protein

Example: GAA sequence incorrectly copied as GTA

A simple change in an amino acid can cause sickle cell anemia

http://access.mmhs.ca/docs/Science/MMHS%20Web%20Folder/Kamla/substitution.gif

Genetic Engineering • Scientists can manipulate individual genes within

organisms• Ex. Genetically engineered plants; new drugs,

foods, fabrics Genetic Identification

• DNA Fingerprinting – identifies unique patterns in an individual’s DNA

• May be used to solve crimes or identify family relations

• Clones: a new organism with an exact copy of DNA

Holt Science and Technology: Life Science. Austin: Holt Rinehart & Winston, 2007. Print.