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Chapter 12: DNA- The Molecule of Heredity

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Presentation on theme: "Chapter 12: DNA- The Molecule of Heredity"— Presentation transcript:

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)


5 Conclusion: transformation  1 strain changed into another
Genes control changes to organisms

6 History of DNA Avery (1944) Repeated Griffith’s 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 (1950’s)
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


23 Chapter 12 Bell Ringer #1: The structure of a DNA molecule can be described as a _____. During DNA replication, the DNA molecule ______ into two strands. 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


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


31 Example: DNA mRNA A G C T

32 Example: DNA mRNA Name of amino acid: A G C T U C G A

33 Two Types of Nucleic Acids: RNA and DNA

34 In nucleus and cytoplasm
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


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 Source of genetic variation
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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