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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
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 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.
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.