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Chapter 12: DNA- The Molecule of Heredity

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Title: Chapter 12: DNA- The Molecule of Heredity


1
Chapter 12 DNA- The Molecule of Heredity
2
  • DNA determines the structure of proteins
  • All living things contain proteins
  • Provide complete instructions for making proteins
  • Made up of nucleotides

3
History of DNA
  • Griffith (1928)
  • Tried to figure out how bacteria causes pneumonia
  • Experiment
  • 1st injected mice with disease-causing bacteria
    (all died) and again with harmless bacteria (no
    sickness)
  • He heated the disease-causing bacteria to kill
    them and injected it into mice (mice lived)
  • 2nd mixed heat-killed bacteria with live,
    harmless bacteria and injected into mice (all
    died)

4
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5
  • Conclusion transformation ? 1 strain changed
    into another
  • Genes control changes to organisms

6
History of DNA
  • Avery (1944)
  • Repeated Griffiths work
  • Experiment Made an extract from heat-killed
    bacteria and treated it with enzymes (destroyed
    organic compounds)
  • Transformation still occurred
  • Repeated using enzymes to break down DNA
  • Transformation did not occur
  • Conclusion DNA stores and transmits genetic info

7
  • Hershey and Chase (1952)
  • Did experiments using radioactive viruses to
    infect bacteria (bacteriophages)
  • Used radioactive markers to determine what
    actually entered a bacterial cell
  • Conclusion Discovered DNA was the genetic
    material of all living things

8
  • Franklin and Wilkins (1950s)
  • Experiment Used X-ray diffraction on DNA
  • Conclusion strands in DNA are twisted around
    each other (helix)

9
  • Watson and Crick (1953)
  • No experiment
  • Conclusion Discovered the structure of DNA
  • Made up of 2 chains of nucleotides held together
    by nitrogen bases
  • Double helix (twisted ladder)

10
Chapter 12 Scientist Review
  • Match the scientist with the description of his
    or their conclusions
  • Griffith Avery Hershey Chase
  • _____ concluded that the genetic material of a
    bacteriophage is DNA
  • _____ concluded that DNA was the factor that
    caused one bacterium to transform into another
  • _____ concluded that bacteria could be
    transformed from harmless to disease-causing by
    an unknown factor

11
DNA in Cells
  • Located in the nucleus of cells as chromosomes
  • Packed tightly
  • Consists of more than 30 million base pairs
  • Complimentary DNA strands
  • Can use 1 strand to make a copy of the other
    strand using base pairing

12
Nucleotides
  • Make up DNA
  • 3 parts to a nucleotide
  • A simple sugar called Deoxyribose
  • A phosphate group
  • A nitrogen base

13
Nitrogen Bases
  • 4 possible nitrogen bases
  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Thymine (T)

14
Adenine (A) and Guanine (G)
  • Double-ringed nitrogen bases
  • Called purines

15
Thymine (T) and Cytosine (C)
  • Single-ringed nitrogen bases
  • Called pyrimidines

16
Chargaff
  • of Guanine and Cytosine are equal
  • of Adenine and Thymine are equal

17
  • Nucleotides join together to form long chains of
    complimentary base pairs
  • Adenine always pairs with Thymine (A-T or T-A)
  • Guanine always pairs with Cytosine (G-C or C-G)

18
Structure of DNA
  • Nitrogen bases of the nucleotides hold 2 strands
    of DNA together with weak hydrogen bonds
  • Twisted DNA ? double helix

19
  • Sides of the ladder
  • alternating phosphate groups and sugar molecules
  • Rungs of the ladder
  • pairs of nitrogen bases
  • joined by weak hydrogen bonds

20
DNA Replication
  • Making a copy of DNA
  • DNA is copied before cell division
  • Takes 6 hours in humans
  • During the S phase of interphase
  • DNA will separate into 2 strands
  • Carried out by the enzyme DNA polymerase
  • Unzips DNA by breaking hydrogen bonds to unwind
    the double helix
  • Each strand acts as a template or model to make
    new DNA strands
  • Makes new complimentary strands through
    base-pairing

21
  • Example
  • TACGTT Old DNA strand
  • ATGCAA New DNA strand
  • After DNA is replicated, DNA will have 1 old
    strand and 1 new strand

22
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23
Chapter 12 Bell Ringer 1
  1. The structure of a DNA molecule can be described
    as a _____.
  2. During DNA replication, the DNA molecule ______
    into two strands.
  3. DNA looks like a twisted ladder. Which parts of a
    twisted ladder represent the hydrogen bonds and
    the sugar-phosphate backbones?

24
The Genetic Code
  • DNA controls protein synthesis
  • Proteins have chains of amino acids
  • A code is needed to convert messenger RNA (mRNA)
    into a protein
  • 20 amino acids
  • Codon a group of 3 Nitrogen bases that code for
    a specific amino acid
  • 64 possible combinations of codons
  • Some code for amino acids
  • Some code for making proteins
  • More than 1 codon can code for the same amino acid

25
  • There is 1 start codon (amino acid methionine)
  • DNA ? TAC
  • RNA ? AUG
  • There are 3 stop codons
  • Code for no amino acids

26
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27
  • The sequence of nucleotides (N-bases) is the code
    for what controls the production of all proteins

28
Transcription
  • Occurs in the nucleus
  • Making an RNA copy of a part of DNA
  • Makes messenger RNA (mRNA)
  • Requires RNA polymerase
  • Binds to and separates DNA
  • Strands of DNA used as a template
  • Binds to DNA regions called promoters

29
  • 4 Steps
  • RNA polymerase unzips the DNA
  • Free RNA nucleotides floating in the cytoplasm
    base pair with nucleotides on DNA strand (makes
    mRNA)
  • mRNA strand breaks away and DNA strands go back
    together
  • mRNA leaves nucleus and goes out to the cytoplasm
  • Result of transcription formation of 1
    single-stranded RNA molecule

30
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31
Example DNA mRNA
A G C T G A C T G
32
Example DNA mRNA
Name of amino acid
A G C T G A C T G
U C G A C U G A C
33
Two Types of Nucleic Acids RNA and DNA
34
DNA RNA (3 types)
Sugar Deoxyribose Ribose
Bases G, C, A, T G, C, A, U (uracil)
Structure Double-stranded Single-stranded
Location in a Cell Only in the nucleus In nucleus and cytoplasm
Base Pairing C-G and A-T C-G and A-U
35
Messenger RNA (mRNA)
  • Brings instructions from DNA out of the nucleus
    and into the cytoplasm
  • Moves toward the ribosomes

36
Ribosomal RNA (rRNA)
  • Makes up ribosomes
  • Binds to messenger RNA
  • Uses the instructions from DNA to put amino acids
    in the correct order

37
Transfer RNA (tRNA)
  • Delivers the amino acids to the ribosomes to be
    made into a protein

38
RNA Editing
  • DNA has introns (sequences of nucleotides)
  • Edited out before they become functional
  • Not involved in coding for proteins
  • Exons code for proteins
  • Remaining pieces of DNA ? put together with cap
    and tail final RNA molecule

39
DNA Controls Protein Synthesis
  • What are proteins?
  • Long chains of amino acids (polypeptides)
  • Key structures and regulators of cell functions
  • Help with structural parts
  • Enzymes ? chemical reactions
  • Help in transport through cell membrane

40
Making Proteins
  • Protein production is similar to building car
  • DNA provides workers with instructions for making
    proteins
  • Workers build proteins (RNA)
  • Other workers bring parts (amino acids) to the
    assembly line

41
Translation
  • Process of building proteins from mRNA
  • Takes place in the ribosomes
  • Transfer RNA (tRNA) brings amino acids to the
    ribosomes
  • Attaches to only 1 type of amino acid
  • Amino acid will become bonded to 1 side of the
    tRNA
  • The other side of the tRNA has 3 nitrogen bases
    called an anticodon
  • Pairs up with mRNA codon

42
  • Amino acids are joined by peptide bonds
  • Anticodon bind to the codon of mRNA through base
    pairing
  • Example Codon CGA
  • Anticodon GCU
  • A chain of amino acids form until a stop codon is
    reached
  • Translation will end
  • Amino acid strand is released from the ribosome
    to become proteins

43
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44
Chapter 12 Bell Ringer 2
  • The 3 main types of RNA are ___, ___, ___.
  • 2. Copying part of a nucleotide sequence of DNA
    into a complementary sequence in RNA is called
    ____.
  • 3. During the process of _____, the information
    carried by mRNA is used to produce proteins.
  • 4. Each tRNA molecule contains 3 unpaired bases,
    called the _____, which ensure that amino acids
    are added in the correct sequence.

45
Mutations
  • Any change in the sequence of DNA
  • Can be caused by errors in
  • DNA replication
  • Transcription
  • Cell division
  • External agents

46
Mutations in Reproductive Cells Birth Defects
  • Within the egg or sperm cells
  • Can produce new traits
  • Can result in proteins that do not work (can kill
    organism)
  • Could have positive effects
  • Faster
  • Stronger
  • Important in the evolution of a species

47
Mutations in Body Cells
  • Not passed on to offspring
  • May impair cell function
  • Can affect genes that control cell division
    (cancer)

48
Point Mutation (substitution)
  • Change in 1 N-base in DNA
  • Example CGATTACGC (normal DNA) CGATTTCGC
  • (mutated DNA)
  • Albinism
  • Inability to produce pigments
  • Lethal to plants

49
Frameshift Mutation
  • 1 N-base is added or deleted
  • Changes all codons from that point on
  • Example CGATTACGC CGAATTACGC (N-base added)
  • Example CGATTACGC CGTTACGC (N-base deleted)
  • May cause no problems or can be severe
  • More dangerous than point mutations

50
Chromosomal Mutations
  • Involve many genes
  • Usually very bad
  • Can change location of genes or number of copies
  • Involve changes in number or structure of
    chromosomes

51
  • 4 types
  • Deletions ? taking away
  • Insertions ? adding
  • Inversions ? switching parts (ex ab? ba)
  • Translocations ? breaking off
  • Many occur from improper separation during
    meiosis

52
Causes of Mutations
  • Spontaneous or random mutations
  • Mutagens (things that cause mutations)
  • Radiation, X-Rays, UV light, chemicals
  • Carcinogens
  • Source of genetic variation

53
Gene Regulation
  • Certain DNA sequences serve as promoters (binding
    sites for RNA polymerase)
  • Ex E. coli
  • Group of 3 genes that are turned on and off
    together (called an operon)
  • E. coli uses lactose as food
  • Genes must be expressed ? called lac operon

54
  • Lac genes turned off by repressors (binds to
    operator)
  • Prevents transcription of its genes
  • Lac genes turned on by presence of lactose
  • Binds to repressor, allowing RNA polymerase to
    transcribe genes
  • Operons generally not found in eukaryotic cells

55
  • Eukaryotic cells (more complex)
  • Has short region of DNA (TATA box)
  • 30 base pairs long
  • Helps RNA polymerase position itself
  • Hox genes
  • Series of genes that controls organs and tissues
    that develop in embryos
  • Determine basic body plan
  • Mutations can change organs
  • Ex fruit fly
  • Expressed genes are transcribed into RNA
  • Genes are expressed with help from DNA-binding
    proteins

56
Chapter 12 Bell Ringer 3
  • Genetic information is altered when changes in
    the DNA sequence, called ____ occur.
  • 2. Changes in the DNA sequence of a single gene
    are called _____.
  • 3. What causes the lac genes in E. Coli to turn
    off?
  • 4. What causes the Lac genes in E. Coli to turn
    on?
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