Chapter 12 dna and rna
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Chapter 12: DNA and RNA. Wheatley-Heckman Honors Biology/Chemistry. DNA. DNA is a long molecule made up of units called nucleotides . Each nucleotide is made up of 3 basic components: 5-carbon sugar (deoxyribose) Phosphate group Nitrogenous base.

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Chapter 12: DNA and RNA

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Chapter 12 dna and rna

Chapter 12: DNA and RNA

Wheatley-Heckman

Honors Biology/Chemistry


Chapter 12 dna and rna

DNA

  • DNA is a long molecule made up of units called nucleotides.

  • Each nucleotide is made up of 3 basic components:

    • 5-carbon sugar (deoxyribose)

    • Phosphate group

    • Nitrogenous base


Chapter 12 dna and rna

  • There are 4 kinds of nitrogenous bases in DNA:

    • Adenine

    • Thymine

    • Cytosine

    • Guanine


Chapter 12 dna and rna

  • Two scientists named Watson and Crick concluded that the shape of the DNA molecule was a double helix, in which two strands of DNA were wound around each other.


Chapter 12 dna and rna

  • The backbones of the double helix are formed by the sugar and phosphate groups of each nucleotide.

  • The nitrogenous bases stick out sideways from each strand.


Chapter 12 dna and rna

  • Years before the double helix was discovered, a scientist named Edwin Chargaff discovered that:

    • The percentages of guanine (G) and cytosine (C) are almost equal in any sample of DNA.

    • The percentages of adenine (A) and thymine (T) are almost equal in any sample of DNA.

  • This became known as Chargaff’s Rules


Chapter 12 dna and rna

  • Using Chargaff’s rule, Watson and Crick determined that hydrogen bonds could form only between certain bases, and provide just enough force to hold the 2 strands of the double helix together.


Chapter 12 dna and rna

  • The base-pairing rules became:

    • For every A (adenine) on one strand, there is a T (thymine) on the other strand.

    • For every C (cytosine) on one strand, there is a G (guanine) on the other strand.

The two strands are said to be “complementary”.


Practice

Practice!

  • Following the base-pairing rules, write the complementary strand of DNA for the given sequence of nucleotides:

  • AAGCCAGATAGT


Building a dna molecule

Building a DNA Molecule

  • Black pentagons: Deoxyribose sugar

  • White tubes: Phosphate groups

  • Colored tubes: Nucleotides

    • Orange: Adenine

    • Green: Thymine

    • Blue: Guanine

    • Yellow: Cytosine


Chapter 12 dna and rna

  • Build a single nucleotide containing the nitrogenous base adenine (orange).

  • Now build a second nucleotide, but containing cytosine (yellow).

  • Connect it’s phosphate group to the sugar of your first nucleotide. This is forming a sugar-phosphate backbone.


Chapter 12 dna and rna

  • Continue adding nucleotides until you have completed a strand following the code below:

    A C T G G A T C T

  • Once that single strand is completed, build a complementary strand.

  • Connect the two strands with hydrogen bonds (white solid pegs).

  • Twist the two strands to make a double helix.


Dna replication

DNA Replication

  • During DNA replication, the DNA molecule separates into two strands, and then produces two new complementary strands following the rules of base pairing.

  • Each strand of the double helix serves as a template, or model for the new strand.


Chapter 12 dna and rna

  • Step 1: An enzyme called helicase “unzips” the double helix by breaking the hydrogen bonds between bases.

  • The region where the two strands are splitting is called the replication fork.


Chapter 12 dna and rna

  • Step 2: A second enzyme, DNA polymerase, adds complementary nucleotides to each of the original separated strands.

  • As DNA polymerase adds new nucleotides, it also “proofreads” to avoid any errors in base-pairing.


Chapter 12 dna and rna

  • Each strand of DNA has a 5’ end and a 3’ end, referring to the orientation of the 5-carbon sugar.

  • The strands run anti-parallel to each other.

  • DNA polymerase can only add to the 3’ end of a DNA strand.


Chapter 12 dna and rna

  • Leading strand: strand that reads 5’-3’

    • Replicated continuously.

  • Lagging strand = strand that reads 3’-5’

    • Creates fragments called “Okazaki Fragments” that are later connected by the enzyme ligase


  • Chapter 12 dna and rna

    • This process continues until the entire double helix has been replicated.

    • The process is considered to be semi-conservative because each of the 2 new double helices contains one original strand and one newly synthesized strand.

    Review Animation


    Rna and protein synthesis

    RNA and Protein Synthesis

    • Genes are coded DNA instructions that control the production of proteins.

    • These genetic messages must first be copied from DNA to RNA.

    • The RNA is then used to make proteins.


    Structure of rna

    Structure of RNA

    • There are 3 main differences between DNA and RNA:

      • The sugar in RNA is ribose instead of deoxyribose.

      • RNA is generally single-stranded.

      • RNA contains uracil in place of thymine.


    Types of rna

    Types of RNA

    • There are three main types of RNA:

      • messenger RNA (mRNA)

      • ribosomal RNA (rRNA)

      • transfer RNA (tRNA)


    Chapter 12 dna and rna

    • Messenger RNA (mRNA)carries copies of instructions for assembling amino acids into proteins.


    Chapter 12 dna and rna

    Ribosomes are made up of proteins and ribosomal RNA (rRNA).


    Chapter 12 dna and rna

    • During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome.


    Protein synthesis

    Protein Synthesis

    • The process of making proteins has two steps:

      • Transcription

      • Translation

    DNA strand

    (template)

    TRANSCRIPTION

    mRNA

    TRANSLATION

    Protein


    Transcription

    Transcription

    • Helicase separates the DNA double helix, and an enzyme called RNA polymerase uses one strand of DNA as a template to make a single strand of mRNA.

    • Regions called promoters determine which segment of DNA (which gene) the RNA polymerase will copy, or transcribe.


    Chapter 12 dna and rna

    • RNA is formed using the same base-pairing rules discussed before, except that uracil has replaced thymine.

    • “Transcribe” the following DNA strands into mRNA:

      • AACTGACTTC

      • GGATCCATCG


    Rna editing

    RNA Editing

    • Some DNA within a gene is not needed to produce a protein. These areas are called introns.

    • The DNA sequences that code for proteins are called exons.


    Chapter 12 dna and rna

    • As the mRNA leaves the nucleus, the introns are cut out of RNA molecules.

    • The exons are the spliced together to form mRNA.


    The genetic code

    The Genetic Code

    • Proteins are made by joining amino acids into long chains.

    • There are 20 different amino acids, and it is the unique combination of amino acids in your proteins that determine your genes.

    • Amino acids are coded for by mRNA.


    Chapter 12 dna and rna

    • A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.


    Chapter 12 dna and rna

    • There are 64 different 3-letter codons that only code for 20 amino acids.

    • This means that more than one codon can code for the same amino acid.

    • Some codons serve as a “stop” signal, and do not code for actual amino acids.


    Chapter 12 dna and rna

    • Transcribe the following DNA strands into mRNA, and then translate the codons into amino acids using the wheel:

    • DNA Strand 1: TAC GGC AGT

    • DNA Strand 2: GAC TTT CCA


    Translation

    Translation

    • Translation is the decoding of an mRNA message into a polypeptide chain (protein).

    • Translation takes place on ribosomes.

    • During translation, the cell uses information from messenger RNA to produce proteins


    Chapter 12 dna and rna

    • The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA.

    • Each tRNA molecule holds an anticodon that is complementary to a codon.


    Chapter 12 dna and rna

    • As tRNA brings amino acids to the ribosome, the ribosome will form peptide bonds between the amino acids, forming a chain.


    Chapter 12 dna and rna

    • This chain will grow until the ribosome reaches a stop codon, which triggers the release of the polypeptide chain.


    Chapter 12 dna and rna

    • The completed polypeptide chain (protein) will be sent to the golgi body, where it will be packaged and shipped to its final destination.


    Chapter 12 dna and rna

    DNA

    mRNA

    Protein


    Summary of protein synthesis

    Summary of Protein Synthesis

    • Transcription

    • Process by which genetic information encoded in DNA is copied onto messenger RNA

    • Occurs in the nucleus

    • DNA  mRNA

    • Translation

    • Process by which information encoded in mRNA is used to assemble a protein at a ribosome

    • Occurs on a Ribosome

    • mRNA  protein


    Types of mutations

    Types of Mutations

    • Mutations are changes in the genetic material.

    • Gene mutations: involve changes in one or a few nucleotides, known as point mutations.

      • Substitutions

      • Insertions

      • Deletions


    Chapter 12 dna and rna

    • Substitutions usually affect no more than a single amino acid.


    Chapter 12 dna and rna

    • The effects of insertions or deletions are more dramatic.

    • The addition or deletion of a nucleotide causes a shift in the grouping of codons.

    • Changes like these are called frameshift mutations.


    Chapter 12 dna and rna

    In an insertion, an extra base is inserted into a base sequence.


    Chapter 12 dna and rna

    In a deletion, the loss of a single base is deleted and the reading frame is shifted.


    Chapter 12 dna and rna

    • Chromosomal mutations involve changes in the number or structure of chromosomes.

    • Chromosomal mutations include deletions, duplications, inversions, and translocations.


    Chapter 12 dna and rna

    • Deletions involve the loss of all or part of a chromosome.

    • Duplications produce extra copies of parts of a chromosome.


    Chapter 12 dna and rna

    • Inversions reverse the direction of parts of chromosomes.

    • Translocations occur when part of one chromosome breaks off and attaches to another.


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