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Chapter 12 How Genes Work. Cooperative Activity. 1. What do you know about DNA? 2. What do you want to know about DNA?. DNA & Today. 1988: DNA profiling was used in Britain, murder of 2 girls 1994: OJ Simpson murder trial Crime shows Cold Cases. Review: What is DNA?.

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Chapter 12 how genes work

Chapter 12 How Genes Work

Cooperative activity
Cooperative Activity

1. What do you know about DNA?

2. What do you want to know about DNA?

Dna today
DNA & Today

  • 1988: DNA profiling was used in Britain, murder of 2 girls

  • 1994: OJ Simpson murder trial

  • Crime shows

  • Cold Cases

Review what is dna
Review: What is DNA?

  • DNA stores our genetic information

  • Where is DNA found?

    • Nucleus of cell

What is a gene
What is a gene?

  • Section of DNA that codes for a trait

  • Where are genes found?

    • Chromosomes

What is a chromosome
What is a chromosome?

  • Bundles of DNA

  • Where are chromosomes found?

    • Nucleus of cell


  • Humans are made up of:

    • 20,000 – 30,000 genes

    • 23 pairs of chromosomes

    • 3 billion nitrogen bases

Human genome
Human Genome

  • Genetic map of the human body

  • Includes chromosomes and genes

Human genome cont
Human Genome (cont.)

  • You inherit 2 copies of every gene

    • one from mom & one from dad

Human Genome (cont.)

  • Only 1% of your DNA codes for genes

Why are genes important
Why are genes important?

  • Genes contain the instructions to make proteins

Structure of dna
Structure of DNA

  • Made up of parts: nucleotides

    • Chemical building blocks

Parts of a nucleotide
Parts of a Nucleotide

  • Nitrogen-containing Base (A, T, C, G)

  • Sugar (Deoxyribose)

  • Phosphate


Base pairing
Base Pairing

  • Adenine (A) & Thymine (T)

  • Cytosine (C) & Guanine (G)

    • Hydrogen bonds hold bases together

Dna basic structure
DNA – Basic Structure

  • Backbone: Alternating Sugar & Phosphate

  • Inside: Nitrogen Bases

  • Shape: Double Helix

Making copies of dna
Making Copies of DNA

  • Every time our body makes new cells, we need more DNA

  • This process is called: DNA Replication

Dna replication step 1
DNA Replication – Step 1

Helicase (enzyme)

  • unwinds chains

  • separates nucleotides by breaking bonds

DNA Replication – Step 2

2. DNA polymerase assembles new chains

  • Complementary to one another

DNA Replication – Step 3

3. DNA ligase links the two sections

Dna replication end result
DNA Replication – End Result

Two identical strands of DNA (Two daughterDNA)

Reading the genetic code
Reading the Genetic Code

  • Genes have the instructions to make proteins

  • Occurs in two steps

    • Transcription

    • Translation

Review protein synthesis
Review: Protein Synthesis

  • Q: Which organelle helps make proteins?

  • Ans: Ribosomes


  • Process of copying genetic information from DNA to mRNA (messenger)

    • Takes place in nucleus

Why do we need mrna
Why do we need mRNA?

Carries copied info from nucleus to ribosomes

DNA cannot leave the nucleus

Protect the code

Transcription steps
Transcription Steps

RNA Polymerase

1. Unwinds DNA double helix

2. Adds RNA nucleotides to build mRNA chain

Transcription steps cont
Transcription Steps (cont.)

3. mRNA moves out of nucleus


  • Process of assembling amino acids into proteins on ribosomes

  • Order of amino acid determines protein

Translation steps
Translation Steps

1.) 3 letter code on tRNA anticodonmatches up with mRNA codon

  • tRNA (transfer)

Translation steps cont
Translation Steps (cont)

2.)tRNA interprets the mRNA code sequence

3.)Code is read 3 letters at a time

Translation steps cont1
Translation Steps (cont)

4.)Amino acids bond together to form proteins


  • A change in the copying of the genetic message

  • Can occur during DNA replication or transcription

  • Rare - occur in 1 out of 1 billion bases

Factors that affect the rate of mutations
Factors that affect the rate of mutations

  • Mutagens

    • Radiation / UV light

    • Chemicals

Translating the code
Translating The Code


  • tRNA anticodon: AAA

  • mRNA codon: UUU

  • UUU codes for amino acid phenylalanine

  • Translation1



    Venn diagram rna dna


    ribonucleic acid


    A – U (Uracil)

    C – G

    Single stranded


    deoxyribo- nucleic acid


    A – T

    C – G

    Double stranded

    Venn Diagram: RNA & DNA

    Mcas questions
    MCAS Questions

    Which of the following statements best describes

    why the change in only one DNA base of the

    hemoglobin gene results in a different protein

    product of the gene?

    A. The change prevents mRNA from being made. 

    B. The change alters the amino acid sequence of the protein. 

    C. The change causes the blood cells to divide in an uncontrolled way. 

    D. The change creates a second strand of mRNA for each RNA molecule.

    Mcas questions1
    MCAS Questions

    In a eukaryotic cell, which of the

    following processes directly

    involves DNA?

    A. translation 

    B. cellular respiration 

    C. active transport of ions

    D. replication of chromosomes

    Mcas questions2
    MCAS Questions

    In a molecule of double-stranded

    DNA, the amount of adenine

    present is always equal to the

    amount of

    A. cytosine.  C. thymine.

    B. guanine.   D. uracil.

    Mcas questions3
    MCAS Questions

    During DNA replication, the wrong

    nucleotide was inserted in the DNA

    sequence. Which of the following

    terms describes this situation?

    A. mutation  C. transcription

    B. regeneration   D. translation

    Mcas questions4
    MCAS Questions

    A portion of one strand of a DNA molecule

    has the sequence shown below. ACCTGAAGG

    Assuming there are no mutations in this

    portion of the DNA, what is the corresponding

    sequence on the complementary DNA




    Mcas questions5
    MCAS Questions

    Fireflies produce light inside their bodies. The enzyme

    luciferase is involved in the reaction that produces the light.

    Scientists have isolated the luciferase gene.

    A scientist inserts the luciferase gene into the DNA of cells

    from another organism. If these cells produce light, the

    scientist knows that which of the following occurred?

    A. The luciferase gene mutated inside the cells. 

    B. The luciferase gene was transcribed and translated. 

    C. The luciferase gene destroyed the original genes of the cells. 

    D. The luciferase gene moved from the nucleus to the endoplasmic reticulum.

    Mcas questions6
    MCAS Questions

    Individuals with one form of lactose

    intolerance do not produce the enzyme

    lactase because the gene coding for

    the production of lactase is shut off in

    their cells. This means that which of the

    following processes does not occur for

    the gene?

    A. Hydrogenation C. replication

    B.mutation  D. transcription

    Mcas questions7
    MCAS Questions

    Which of the following statements best describes a DNA molecule?

    A. It is a double helix. 

    B. It contains the sugar ribose. 

    C. It is composed of amino acids. 

    D. It contains the nitrogenous base uracil.