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DNA Module B: Bio . B.1.

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Presentation on theme: "DNA Module B: Bio . B.1."— Presentation transcript:

1 DNA Module B: Bio . B.1

2 Describe the sculpture
Ask students to describe the sculpture shown (ex: circular, twisted, colorful) Point out that this sculpture models the structure of DNA, a molecule that carries genetic information in living things. Explain that the structure of DNA was not determined until the 1950s. An understanding of DNA’s function gave some clues to its structure. Observations and experiments by many scientists also provided clues into DNA’s structure. Some things to think about as we cover this chapter…What is the structure of DNA and how does it function in genetic inheritance?

3 Bio. B.1.2: Explain how genetic information is inherited
Bio.B Describe how the process of DNA replication results in the transmission and/or conservation of genetic material.

4 Before we get started… What is genetics? What is the genetic material?

5 The Role of DNA: What is the role of DNA in heredity?
DNA must be capable of: 1. Storing information 2. Copying information 3. Transmitting information

6 DNA stores information
In what ways is DNA like a “how-to” book? (it stores instructions) How does DNA store information (in its molecular structure) Why is it important that DNA can be accurately copied? (so each daughter cell receives a complete and correct copy of the genetic material during cell division)

7 DNA copies and transmits information
Why is it important that DNA can be accurately copied? (so each daughter cell receives a complete and correct copy of the genetic material during cell division)

8 DNA is made of nucleotides
Nucleotides are the building blocks of DNA Nucleotides composed of: 1. Phosphate 2. Sugar (deoxyribose) 3. Nitrogen Base Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

9 Nucleotides link together

10 STRUCTURE of DNA Chargaff:
Chargaff’s Rule: percentages of A (adenine) and T(thymine) were equal in many sample of DNA percentages of C (Cytosine) and G (Guanine) were also equal

11 STRUCTURE of DNA Chargaff’s Data
If a species has 35% adenine in its DNA, what is the percentage of the other three bases? Can you figure it out?

12 STRUCTURE of DNA Rosalind Franklin
X-ray picture of DNA DNA had two strands that twisted around each other like a coil

13 STRUCTURE of DNA Watson and Crick
James Watson and Francis Crick built a three dimensional model of DNA Shape of the DNA = double helix. Strands run in opposite direction (anti-parallel) Base pairing rules (A pairs with T; C pairs with G) Strands held together by hydrogen bonds Watson TED talk

14 Antiparallel DNA Strands:

15

16 What happens to the DNA structure during S phase?
DNA replicates (duplicates, is copied, etc.) Watson and Crick’s 3D model immediately proposed a replication mechanism animation

17 DNA Replication: DNA gets copied during interphase
Ensures that each resulting cell has the same complete set of DNA Each strand has all the information needed to construct the other strand

18 Process of DNA Replication:
1. DNA is “unzipped” or separated Enzyme = helicase Breaks hydrogen bonds that hold the two strands of DNA together

19 Process of DNA Replication:
New strands are built Enzyme = DNA polymerase Joins individual nucleotides together to produce a new strand of DNA that is complementary to the other Proofreads each new strand

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21 How is replication different in prokaryotes?
In eukaryotes, replication begins at many different locations and proceeds in both directions until each chromosome is completely copied In prokaryotes, replication begins at one point and proceeds in two directions until the entire chromosome Is copied

22 Prokaryotes Vs eukaryotes
DNA Replication Prokaryotes Vs eukaryotes

23 Quick Check 1. A nucleotide does not contain A 5-carbon sugar
An amino acid A nitrogen base A phosphate group

24 Quick Check 2. According to Chargaff’s rule of base pairing which of the following is true about DNA? A=T and C=G A=C and T=G A=G and T=C A=T=G=C

25 Quick Check 3. The bonds that hold the two strands of DNA together come from The attraction of phosphate groups for each other Strong bonds between nitrogenous bases and the sugar-phosphate backbone Weak hydrogen bonds between bases Carbon-to-carbon bonds in the sugar portion of the nucleotides

26 Quick Check 4. In prokaryotes, DNA molecules are located in the
Nucleus Ribosomes Cytoplasm histones

27 Quick Check 5. In eukaryotes, nearly all the DNA is found in the
Nucleus Ribosomes Cytoplasm histones

28 Quick Check 6. The main enzyme involved in linking individual nucleotides into DNA molecules is DNA protease Ribose Carbohydrate DNA polymerase

29 PREC-CLASS… All of the parts of a cell are controlled by the information in DNA, yet DNA does not leave the nucleus. How do you think the information in DNA might get from the nucleus to the rest of the cell?

30 Central Dogma of Molecular Biology
Describes flow of information from DNA to protein transcription translation RNA DNA Protein RNA is the link between DNA and proteins.

31 Analogy for central dogma
The master plan has all the information needed to construct a building.

32 Analogy for central dogma
But builders never bring a valuable master plan to the building site where is might be damaged or lost.

33 Analogy for central dogma
Instead, builders work from blueprints, inexpensive disposable copies of the master plan.

34 Analogy for central dogma
Master plan = DNA Building site = ribosomes (in cytoplasm) Blueprint copies = RNA

35 DNA vs RNA RNA DNA Single stranded Made of nucleotides Sugar = ribose
Bases = U instead of T Double stranded Made of nucleotides Sugar = deoxyribose Bases = C,G, A, T

36 Different types of RNA Messenger RNA – carries the instructions from DNA to cytoplasm on how to make the protein Ribosomal RNA – form ribosomes in cytoplasm to help build the protein Transfer RNA – delivers the amino acids needed to build the protein

37 Transcription (RNA synthesis)
DNA  RNA Occurs in the nucleus Requires RNA polymerase Builds RNA strand Uses one strand of DNA as template Involves single gene Produces MANY RNA copies

38 RNAi Video

39 Replication vs Transcription
Replication copies the entire DNA Transcription only copies one gene Replication only makes one copy Transcription makes many copies BOTH involve complex enzymes BOTH follow complementary base pairing BOTH occur in the nucleus

40 If you were given the sequence of a DNA strand, could you figure out the sequence of the mRNA strand? Remember, U instead of T in RNA!!! For example: DNA T A C G C C C T A T T G A T mRNA ?? A U G C G G G A UA AC U A

41 Central Dogma of Molecular Biology
Describes flow of information from DNA to protein transcription translation RNA DNA Protein

42 Translation (protein synthesis)
RNA  protein Occurs in the cytoplasm Involves ribosome, mRNA, tRNA and amino acids RNA is “translated” into amino acid sequence

43 The language of protein synthesis
Language of RNA = nucleotides Language of protein = amino acids Triplet code: three mRNA bases (codon) code for one amino acid

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45 Genetic Code: Codon = a group of three nucleotide bases in the mRNA that codes for a particular amino acid RNA contains 4 bases Bases form a language with just four letters in the alphabet RNA is translated three “letters” at a time so that each “word” is three bases long and corresponds to one amino acid Each three letter “word” = codon

46 Genetic Code: (mRNA codon to amino acid)
RNA contains 4 bases Bases form a language with just four letters in the alphabet RNA is translated three “letters” at a time so that each “word” is three bases long and corresponds to one amino acid Each three letter “word” = codon

47 Genetic Code START codon signals the start of translation
AUG also codes for methionine STOP codons signal stop of translation UGA, UAA, UAG Do not code for any amino acid

48 Genetic Code = common language
UNIVERSAL – shared by all organisms REDUNDANT – more than one codon may code for the same amino acid Allows flexibility if mistakes are made

49 Quick Check A certain gene has the following base sequence:
GACAAGTCCAATC Write the sequence of the mRNA molecule transcribed from this gene Divide you mRNA sequence into codons How many codons? What amino acid does each codon code for? How many amino acids?

50 QUICK CHECK… Remember, U instead of T in RNA!!!
For example: DNA T A C G C C C T A T T G A T A mRNA ?? Amino acids

51 The role of ribosomes in translation
Ribosomes act as the machinery Ribosomes use the sequence of codons in mRNA to assemble amino acids into protein chains

52 The role of tRNA in translation
Each tRNA molecule carries one kind of amino acid Anticodon on tRNA recognizes complementary codon on mRNA For example, tRNA for methionine has the anticodon UAC which pairs with the methionine codon (AUG)

53 Process of Translation
Ribosome binds to mRNA mRNA codons attract complementary tRNA anticodons peptide bond forms between amino acids then breaks bond holding the amino acid to the tRNA Empty tRNA leaves; the ribosome pulls the mRNA exposing the next codon

54 QUICK CHECK… Remember, U instead of T in RNA!!!
For example: DNA T A C G C C C T A T T G A T A mRNA ?? Amino acids tRNA

55 Central Dogma of Molecular Biology
Describes flow of information from DNA to protein transcription translation RNA DNA Protein

56 Mutations are changes in the DNA
Gene mutations (single gene) Chromosomal mutations (multiple genes involved) mutated base

57 1. Gene Mutations Also known as point mutations because they occur at a single point in the DNA sequence Occur during replication Different types Substitutions Insertions and deletions

58 A. Substitutions One base is changed to a different base
Only affect one amino acid Sometimes have no effect (silent) EX: changing mRNA codon from CCC to CCA Codon still specifies proline; SILENT EX: changing mRNA codon from CCC to ACC Replaces proline with threonine

59 B. Insertions and Deletions
Frameshift mutations – “shift” the reading frame Effects are dramatic Can change every amino acid after the mutation

60 Frameshift Mutations

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62 2. Chromosome mutations Changes in number or structure of chromosomes
Occur during meiosis Four types Deletion (loss of all or part of a chromosome) Duplication (extra copy) Inversion (reverse in the direction of a chromosome) Translocation (one chromosome attaches to another)

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64 Mutagens Chemical or physical agents in the environment that can cause mutations in DNA Include Pesticides, tobacco, environmental pollutants, UV light, X-rays

65 Harmful and Helpful Mutations
Mutations can be harmful if… They cause drastic changes in the protein that is produced Defective proteins can disrupt normal function Ex: sickle cell anemia, some cancer The effects of mutations on genes vary widely. Some have little or no effect; and some produce beneficial variations. Some negatively disrupt gene function.

66 Harmful and Helpful Mutations
Beneficial effects Variation produced by mutations can be highly advantageous to organisms in different or changing environments Responsible for evolution EX: pesticide resistance (bad news for humans but good news for mosquitoes) EX: human resistance to HIV The effects of mutations on genes vary widely. Some have little or no effect; and some produce beneficial variations. Some negatively disrupt gene function.


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