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13.3 DNA. Mr. Perez. Important vocabulary. DNA RNA Heredity Chromosome Gene Mutation. What is dna ?. DNA ( d eoxyribo n ucleic a cid) Contains information for an organism’s growth and function Stored in a cell’s nucleus in hereditary material (chromosomes)

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13 3 dna

13.3 DNA

Mr. Perez

Important vocabulary
Important vocabulary

  • DNA

  • RNA

  • Heredity

  • Chromosome

  • Gene

  • Mutation

What is dna
What is dna?

  • DNA (deoxyribonucleic acid)

    • Contains information for an organism’s growth and function

    • Stored in a cell’s nucleus in hereditary material (chromosomes)

  • When a cell divides, it must first duplicate its DNA to pass it on to the new cells

    • Remember, MITOSIS: one cell creates two identical daughter cells

    • Every cell in your body has DNA


  • Discovering dna
    Discovering DNA

    • Mid 1800s: scientists know that the nuclei of cells contains large molecules called “nucleic acids”

    • 1950s: chemists know what the nucleic acid of DNA was made of, but they didn’t know how it was arranged

    Structure of dna
    Structure of DNA

    • Rosalind Franklin (1952)

      • Scientist who discovered that DNA is two chains of a molecule in spiral form

      • Used X-ray technique

  • James Watson & Francis Crick (1953)

    • Used Dr. Franklin’s work and others

    • Made first model of DNA

  • A dna model
    A DNA Model

    • DNA looks like a twisted ladder

      • Each side of the ladder is made of a sugar-phosphate molecule

      • The sugar molecule is called: deoxyribose

      • The rungs (or steps) of the ladder, are made of 4 nitrogen bases

        • Adenine

        • Thymine

        • Cytosine

        • Guanine

    A dna model1
    A dna model

    • Because the amount of A always equaled the amount of T and the amount of C always equaled the amount of G, scientists hypothesized that

      • Adenine (A) always matches with Thymine (T)

      • Cytosine (C) always matches with Guanine (G)


  • The following DNA strand is missing its partner, find what its partner DNA strand would look like.

    Strand 1: AACTGAC

    Strand 2: ???????

  • Copying dna
    Copying DNA

    • When chromosomes are duplicated before mitosis or meiosis, the amount of DNA in the nucleus is doubled

    • Watson and Crick’s model shows how DNA is copied in the nucleus:

      • The two sides of DNA unwind and separate

      • Each side becomes a pattern on which a new side forms

      • New DNA has bases exactly like the original and in the same order


    • Most of the characteristics (or traits) such as your hair color and height depend on the proteins your cells make

      • DNA stores the instructions for making proteins

  • Proteins

    • Help build cells and tissues in your body

    • Work as enzymes

    • Made from 20 amino acids arranged in chains that contain hundreds or thousands of them

  • Genes1

    • Genes: section of DNA on a chromosome that carry instructions for making a specific protein

      • Each chromosome can contain hundreds of genes

      • A gene determines the order of amino acids in protein

        • Changing the order would make a different protein

    Making proteins
    Making proteins

    • Genes are on chromosomes in the nucleus, but proteins are made on ribosomes in the cytoplasm

    • RNA (ribonucleic acid): nucleic acid that carries the code for making proteins from the nucleus to the ribosomes

    Ribonucleic acid
    Ribonucleic acid

    • RNA is made in the nucleus on a DNA pattern

    • RNA is like a ladder that has had all of its rungs sawed in half

    • Instead of Thymine (T), RNA has Uracil (U)

    • The sugar-phosphate is ribose instead of deoxyribose

    • There are three types of RNA:

      • mRNA (messenger)

      • rRNA (ribosomal)

      • tRNA (transfer)

      • Try This:

        DNA: ACTGGTA

        RNA: ? ?????

    Ribonucleic acid1
    Ribonucleic acid

    • Steps in making a protein:

      • mRNA moves into cytoplasm from nucleus and ribosomes attach

      • rRNA make ribosomes in the cytoplasm

      • tRNA bring the ribosomes amino acids

      • Inside the ribosomes, three tRNA nitrogen bases switch with three mRNA nitrogen bases

      • The amino acids attached to the tRNA molecules bond

      • Protein formation begins


    Controlling genes
    Controlling Genes

    • Just because every cell in your body has the same DNA doesn’t mean that all cells make the same protein.

    • Each cell only uses SOME of its genes to make proteins.

      • Just as an actor only uses his/her lines in the script

      • For example, muscle cells make muscle proteins

  • Gene activity is determined by the mRNA made from DNA

    • But, a gene can be turned on or off by the production of a certain protein or if the new protein is changed in any way

  • Mutations

    • Mutations- mistakes made in DNA when copied incorrectly

      • Permanent changes in the DNA sequence of a gene or chromosome of a cell

  • Some mutations include adding a chromosome, others include the removal of a chromosome

  • Xrays, sunlight, and some chemicals have been known to cause mutations

  • Results of mutations
    Results of mutations

    • A mutation can change the traits of an organism, causing it to not grow, maintain or repair its cells properly

    • Body cell mutations may or not be life-threatening.

    • Sex cell mutations will cause all the cells formed from that cell to have the mutation

    • Mutations can be both good and bad. An advantageous mutation can allow an organism to be better adapted to an environment, hence carrying the mutation down to future offspring (Variation in natural selection)


    • Florida Science Grade 8

    • Glencoe Science & McGraw Hill Publishing

    • Google Images