DNA

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DNA

• Chapter 4 Section 3

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What is DNA?

• Deoxyribonucleic acid

• Hereditary material of a cell.
• Chemical that stores information for the growth
  and function of an organism.
• Stores this info in the form of a code.
• Copied and passed on to new cells each time a
  cell divides.

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What is DNA?

• Discovering DNA

• Mid-1800s
• Scientists knew that the nuclei of cells
  contained large molecules called nucleic acids.
• 1950
• Scientists knew what the nucleic acid DNA was
  made of but didnt understand its structure

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What is DNA?

• DNAs Structure

• 1952
• Rosalind Franklin discovered DNA is two chains of
  molecules in a spiral form, similar to a twisted
  ladder.
• 1953
• James Watson and Francis Crick made a model of
  DNA.

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What is DNA?

• A DNA Model

• Each side of the ladder is made up of a sugar
  (deoxyribose) and a phosphate molecule.

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What is DNA?

• A DNA Model

• Rungs of the ladder are made of 4 different
  nitrogen bases
• Adenine (A), Guanine (G), Cytosine (C), and
  Thymine (T)
• Bases always occur in pairs
• Guanine will only pair with cytosine
• Adenine will only pair with thymine
• So,
• Amount of cytosine in the cell always equals the
  amount of guanine.
• The amount of adenine in the cell always equals
  the amount of thymine.

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What is DNA?

• Copying DNA

1. The two sides of the DNA molecule unwind and
   separate.
2. The nucleotides on each side pair with free
   nucleotides to form two new DNA strands.

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Genes

• Gene

• A section of DNA on a chromosome.
• Contains instructions for making a specific
  protein.
• Proteins determine most of your characteristics
  (by building tissues and cells and controlling
  chemical reactions (enzymes).
• Each protein is made from multiple amino acids.
• Genes control the order of the amino acids used
  to make the protein.

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Genes

• Making Proteins

• Genes are located in the nucleus.
• Proteins are made on ribosomes in the cytoplasm.
• So, codes for making the proteins have to be
  carried from the nucleus to the ribosomes by RNA.

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Genes

• Ribonucleic Acid

• Made in the nucleus from the pattern of the DNA.
• Can be thought of as half of a DNA molecule.
• Has one side made of a sugar (ribose) and a
  phosphate group.
• Contains 4 bases
• Adenine, Guanine, Cytosine, and Uracil (U)
• 3 types
• Messenger RNA (mRNA)
• Ribosomal RNA (rRNA)
• Transfer RNA (tRNA)

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Genes

• Making Proteins

1. mRNA is made in the nucleus from the DNA pattern
   and than sent to the cytoplasm.
2. In the cytoplasm, a ribosome made from rRNA
   attaches to the mRNA.
3. tRNA brings amino acids to the ribosome.
4. Each tRNA molecule will only bind with a specific
   amino acid.

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Genes

• Making Proteins

1. Inside the ribosome, the three nitrogen bases on
   the tRNA molecule bind with matching bases on the
   mRNA.
2. The ribosome slides down the mRNA chain to the
   next set of bases.
3. A new tRNA molecule carrying a second amino acid
   pairs with the new bases.

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Genes

• Making Proteins

1. The two amino acids that are now adjacent to each
   other form a bond.
2. The first tRNA releases its amino acid and moves
   back to the cytoplasm to get a new amino acid.
3. Amino acids continue to be assembled in this
   manner until the protein is complete and released
   from the mRNA.

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Genes

• Controlling Genes

• Codes contained in the mRNA determine the order
  that amino acids are assembled.
• Different orders of amino acids make different
  proteins.
• If amino acids are assembled in the wrong order,
  the protein wont function properly.

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Genes

• Controlling Genes

• Each cell uses only some of the thousands of
  genes that it has to make proteins.
• Each cell only makes the proteins that it needs.
• So, cells have to control genes by turning some
  genes on and some genes off.
• Cells can turn genes on and off in many ways,
  including
• Twisting so tightly that no RNA can be made.
• Binding to chemicals so the DNA cannot be used

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Mutations

• Mutation

• Any permanent change in the DNA sequence of a
  gene or a chromosome of a cell.
• Occur when DNA is not copied properly.
• Results in the production of the wrong proteins,
  malfunctioning proteins, etc.
• Mutations can be caused by extra or missing
  chromosomes or by outside factors such as X rays,
  sunlight, or chemicals.

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Mutations

• Results of a mutation

• Can
• be harmful (most) or beneficial
• change the traits of the organism
• be fatal
• have no effect
• If in a body cell
• mutation only affects those cells made from the
  body cell.
• If in a sex cell
• mutation is passed on to all cells in the
  organism produced from the body cell.