Download - DNA (4.3)
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Section 4.3 DNA
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C I DA
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C I DA
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-OBIRYXOED
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Discovering DNA
• When did we first know that there was a nucleus in cells that contained large molecules called nucleic acids?
• mid-1800s
• By the 1950s we still were not sure how the nucleic acids and DNA were arranged.
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Rosalind Franklin discovered that DNA is 2 chains of molecules in a spiral form.
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Watson and Crick further studied the DNA model.
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Watson and Crick discovered that each side of the ladder is make of a sugar-phosphate molecule.
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What does DNA look
like
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Each side of the ladder is make up of sugar-phosphate molecules.
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Each molecule consists of a sugar called deoxyribose and a phosphate group.
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The rungs of the ladder are made up of other molecules called nitrogen bases.
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DNA has 4 kinds of nitrogen bases - adenine, guanine, cytosine, and thymine.
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The nitrogen bases are represented by the letters A, G, C, and T.
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Adenine always pairs with thymine, and guanine always pairs with cytosine.
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Before Mitosis or Meiosis, DNA needs to be copied.
How does the double stranded DNA copy its information?
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Copying DNA to prepare for Mitosis or Meiosis
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Copying DNA to prepare for Mitosis or Meiosis
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Copying DNA to prepare for Mitosis or Meiosis
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Copying DNA to prepare for Mitosis or Meiosis
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Copying DNA to prepare for Mitosis or Meiosis
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• Most of your characteristics, such as the colour of your hair, your height, and how things taste to you, depend on the kinds of proteins your cells make.
• DNA in your cells stores the instructions for making these proteins.
• Proteins build cells and tissues or work as enzymes.
• The instructions for making a specific protein are found in a gene.
GEnes
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GEnes
• A gene is a section of DNA on a chromosome.
• A chromosome contains 100’s of genes.
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GEnes
• Proteins are made of amino acids linking together.
• The code for making a protein is found...
• .......in a gene.
• The gene determines the order of the hundreds or thousand of amino acids that link together.
• If you change the order, you make a different protein or nothing at all.
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• Genes are found in the nucleus, but proteins are made on ribosomes in the cytoplasm.
• How does the code for a protein make it out of the nucleus to a ribosome?
• The codes for making proteins are carried from the nucleus to the ribosome by another type of nucleic acid called ribonucleic acid, RNA.
GEnes
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RNA - Ribonucleic Acid
RNA is made in the nucleus on a DNA pattern but is different from DNA. If DNA is like a ladder, RNA is like a ladder that has all its rungs cut in half.
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nitrogenbases sugar shape
DNA A G C T deoxyribose ladder
RNA A G C U* ribose ladder cut in half
*U - uracil
DNA vs RNA
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1. An enzyme splits a DNA molecule, so that a gene can be copied. The gene is the instructions for how to make a protein.
1
Transcriptioncopying a DNA to make RNA
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2. The free floating nitrogen bases in the nucleus match with a nitrogen base on the split DNA. The partnering is the same as when DNA is copied except that Adenine matches with Uracil.
2
Transcriptioncopying a DNA to make RNA
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3. The nitrogen bases pair up on the split DNA temporarily until a complete gene is copied.
3
Transcriptioncopying a DNA to make RNA
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4. The newly made mRNA will now detach from the DNA and leave the nucleus. 4
Transcriptioncopying a DNA to make RNA
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mRNA rRNA tRNA
messenger ribosomal transfer
travel out of nucleus to ribosome
make up ribosomes bring amino acids to ribosomes
3 types of RNA
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Translation - RNA to Protein
• Protein production begins when mRNA moves into the cytoplasm. There, ribosomes attach to it.
• Ribosomes are made of rRNA.
• Transfer RNA molecules in the cytoplasm bring amino acids to these ribosomes.
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• Inside the ribosomes, 3 nitrogen bases on the mRNA temporarily match with 3 nitrogen bases on the tRNA.
• The same thing happens for the mRNA and another tRNA molecules.
• The amino acids that are attached to the two tRNA molecules bond.
• This is the beginning of a protein.
Translation - RNA to Protein
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• The code carried on the mRNA directs the order in which the amino acids bond.
• After a tRNA molecule has lost its amino acid, it can move about the cytoplasm and pick up another amino acids just like the first one.
• The ribosome moves along the mRNA. • New tRNA molecules with amino acids match up and add
amino acids to the protein molecule.
Translation - RNA to Protein
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3 nitrogen bases on mRNA temporarily match to 3 bases on the tRNA.
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Another tRNA bonds.
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The amino acids that are attached to the tRNA bond, beginning to form the protein.
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Controlling Genes
• In many-celled organisms, each cell uses only some of the thousands of genes that it has to make proteins.
• Genes that code for muscle proteins will not be used in nerve cells.
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Controlling Genes
• Cells must be able to control the genes by turning some off and some on.
• This is done in different ways:
• DNA is twisted so tightly that no RNA can be made.
• Chemicals bind to the DNA so that it cannot be used.
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Mutations
• If DNA is not copied correctly the proteins might not be made correctly.
• Mutations - any permanent change in the DNA sequence of a gene or chromosome of a cell
• Examples: • cells receive an extra or are missing a
chromosome• outside factors: X rays, sunlight, some chemicals
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Results of Mutations
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REsults of Mutations
• A mutation might or might not be life threatening.
• If the mutation occurs in the sex cell then all the cells of the new organism will contain the mutation.
• Most mutations are very harmful, but some can be beneficial.
• Beneficial?
• A plant with a mutation might cause it to produce a chemical that certain insects avoid, insects will not eat the plant.