how dna works ch 6.2 7th
DESCRIPTION
Notes for 7th grade obtained from Holt Science and Technology: Life Science. Austin: Holt Rinehart & Winston, 2007. Print.TRANSCRIPT
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.