Download - How DNA Works Ch 6.2 7th
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Chapter 6 Section 2
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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
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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?
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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
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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
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http://campus.udayton.edu/~hume/DNA/DNA.ht26.gif http://www.drtummy.com/images/stories/dna/dna_to_chromosome.jpg
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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
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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
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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
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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
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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”)
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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
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http://www.odec.ca/projects/2004/mcgo4s0/public_html/t3/mRNA%20to%20protein.gif
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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
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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
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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
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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
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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
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Holt Science and Technology: Life Science. Austin: Holt Rinehart & Winston, 2007. Print.