How can something so small cause problems so large?

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2 How can something so small cause problems so large?

3 Objectives Identify the structural components of DNA and relate to its function Create and ask questions about a model of DNA

4 DNA is made of genes. Gene - a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color..etc) Genes control the inherited characteristics of living things

5 1953: James Watson & Francis Crick discovered structure of DNA molecule (with the help from Franklin s X-rays) Double Helix- two strands of nucleotides wound around a central axis Looks like a twisted ladder or spiral staircase

6 DNA is a long molecule made up of units called nucleotides 5 carbon sugar (deoxyribose) Phosphate group Nitrogen base Adenine Thymine Guanine Cytosine

7 Sides of the DNA helix are made of sugar (deoxyribose) and phosphates Bases are in the middle & are held together by Hydrogen bonds strong enough to hold bases together, but weak enough to be broken during replication *The rungs of the ladder can occur in any order (as long as the base-pair rule is followed)

8 Nucleotides (also called Bases) Adenine, Thymine,, Guanine, Cytosine or A, T, G, C Nucleotides pair in a specific way - called the Base-Pair Rule Adenine pairs to Thymine Guainine pairs to Cytosine base pairs said to be complementary Also called Chargaff s Rule

9 Those 4 bases have endless combinations just like the letters of the alphabet can combine to make different words. Endless combinations result in different traits, appearances, and functions of the organism For example: compare these stretches of DNA for a fictional organism A A A T T A T T T = curly tails A A A T T A G G G = straight tails A A A T T A C C C = no tails

10 e.com/watch?v=5m QdXjRPHmQ 5mins

11 DNA is often compared to a ladder or a spiral staircase. Look at Figure 4 (pg. 296) and answer the following questions. 1. How is the structure of DNA similar to that of a ladder or spiral staircase? 2. How is it different from that of a ladder or spiral staircase?

12 DNA is copied for Cell Division. Objectives: Explain how DNA s structure relates to DNA replication

13 In eukaryotes: Replication occurs at multiple points called replication forks DNA located in a cell s nucleus on multiple chromosomes Remember DNA condenses to form chromosomes Before a cell divides, DNA is copied in a process called replication - ensures each resulting cell will have a complete set of DNA molecules

14 DNA replication involves several enzymes & regulatory molecules Principle enzyme of DNA replication is DNA polymerase- it polymerizes (puts together) individual nucleotides to produce DNA Also proofreads each new DNA strand to maximize the odds that each new molecule is a perfect copy of the original DNA

15 The enzyme DNA helicase unzip a molecule of DNA by breaking the Hydrogen bonds between the base pairs This causes the 2 strands of DNA to unwind Each strand serves as a template for attachment of complimentary bases (A-T & G-C) For example: TACGTT would match up with ATGCAA

16 Prokaryotes: Only one chromosome in a circular loop Prokaryotes: DNA replication a single point and proceeds in two directions until entire chromosome is replicated DNA floats freely in the cytoplasm (because they have no nucleus) DNA is contained on one circular chromosome that holds the cell s genetic information DNA REPLICAION

17 1. What does DNA stand for? 2. What is the shape of DNA? 3. Who established the structure of DNA? 4. Adenine always pairs with? 5. The sides of the DNA ladder of deoxyribose and?

18 6. Guanine always pairs with. 7. What is the complementary sequence of CATTAG? 8. the two sides of DNA are held together by a bond. 9. DNA is composed of repeating subunits called. 10. What are the 4 bases that make up the rungs of the DNA ladder?

19 Objectives: Describe structural differences between DNA and RNA. Describe the different types of RNA Explain the role of RNA in helping to make proteins (protein synthesis)

20 Protein synthesis -making of proteins Genes are coded DNA instructions that control the production of proteins within the cell The first step in decoding these genetic messages is to copy part of the nucleotide sequence from DNA into RNA (ribonucleic acid) which carry out the process of making proteins

21 3 main differences between DNA & RNA: 1. Sugar of RNA is ribose DNA s sugar is deoxyribose 2. RNA is a single strand of nucleotides DNA is a double strand of nucleotides 3. RNA s nitrogen bases are: Uracil, Adenine, Guanine & Cytosine DNA has Thymine, Adenine, Guanine & Cytosine

22 RNA is a disposable copy of a segment of DNA and is a working copy of a single gene The ability to copy a single DNA sequence into RNA makes it possible for a single gene to produce hundreds or thousands of RNA molecules

23 Assembly of amino acids into proteins is controlled by RNA 3 main types of RNA: 1. messenger RNA (mrna): carries copies of instructions for assembling amino acids into proteins by serving as messengers from DNA to rest of the cell

24 2. ribosomal RNA (rrna): makes up ribosome (site of protein assembly) & helps form peptide bonds that hold amino acids together in a protein 3. transfer RNA (trna): transfers each amino acid to ribosome for protein assembly

25 Your body is made of trillions of cells, of all different kinds: muscle cells, brain cells, blood cells, and more. Inside those cells are proteins allowing your body to do what it does: break down food to power your muscles, send signals through your brain, and transport nutrients through your blood. Proteins are made of subunits called amino acids

26 1. Transcription RNA is made from DNA 2. Translation Proteins are made from mrna

27 Transcription: RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complimentary strand of mrna (DNA mrna) RNA polymerase binds to DNA & separates the DNA strands so that one strand of the DNA nucleotides can serve as a template from which nucleotides are assembled into a strand of mrna

28 RNA polymerase will bind only to regions of DNA called promoters Promoters have specific base sequences and act as signals in DNA to indicate to the enzyme where to bind to make RNA Similar signals in DNA cause transcription to stop when the new RNA molecule is completed

29 Proteins are made by joining amino acids into long chains called polypeptides; each of which contains any or all of the 20 different amino acids Properties of proteins are determined by the order in which the amino acids are joined together Bases of DNA and RNA must be translated into a particular order of amino acids to form polypeptides

30 The language of mrna instructions is called the genetic code Written in 4 bases: (A)Adenine, (U) Uracil, (C) Cytosine, and (G) Guanine Read 3 letters at a time: codon- 3 consecutive nucleotides that specify a single amino acid

31 4 different bases; allows for 64 different codons in the genetic code Some amino acids can be specified by more than one codon AUG is the start codon; signals the initiation of protein synthesis as well as coding for the amino acid methionine 3 stop codons; UAA, UAG, UGA signal the end of a polypeptide

32 To decipher the genetic code: UCGCACGGU Break down into codons: UCG CAC GGU Serine -Histidine -Glycine

33 The decoding of an mrna message into a protein is known as translation (mrna amino acid sequence) The cell uses information from messenger RNA to produce proteins

34 1. mrna is transcribed in nucleus & released into cytoplasm

35 Each trna molecule has an amino acid attached to one end & a region of 3 unpaired bases on the other The 3 bases on the trna molecule are called an anticodon and are complimentary to one of the mrna codons trna anticodon

36 2. mrna attaches to a ribosome. As codons move through the ribosome, the proper amino acid is brought to the ribosome (via trna) and attached to the growing polypeptide chain.

37 3. Ribosome will form a peptide bond between the 1 st & 2 nd amino acids. The ribosome then moves to each consecutive codon.

38 4. The polypeptide chain continues to grow until the ribosome reaches a stop codon on the mrna. It then releases the newly formed polypeptide & the mrna molecule & completes the process of translation

39 Every once in a while, cells make mistakes in copying their own DNA An incorrect base can be inserted or sometimes a base is skipped as the new DNA is being assembled Mutation : changes in DNA sequence that affect genetic information

40 Mutation : changes in DNA sequence that affect genetic information Gene mutations: result from changes in a single gene Chromosomal mutations: involve changes in whole chromosome

41 Point mutation: affect one nucleotide Occur at a single point in the DNA sequence Often one nucleotide is substituted for another Generally change just one amino acid Usually not lethal

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43 Frameshift mutation- results from the insertion or deletion of a nucleotide Since genetic code is read in groups of three, adding or deleting a nucleotide shifts all resulting amino acids This mutation can alter a protein so much that it is unable to perform its normal functions Most likely lethal

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45 Chromosomal mutations involves changes in the number or structure of chromosomes May change the locations of genes on chromosomes & even the number of copies of some genes

46 Deletion: Involves the loss of all or part of a chromosome Duplication: A segment of a chromosome is repeated

47 Inversion: Part of a chromosome becomes oriented in the reverse of its usual direction Translocation: Part of one chromosome breaks off and attaches to another chromosome

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49 The nucleus of a human cell contains more than 1 meter of DNA: must be folded to fit into the tiny space of a cell s nucleus chromatin- DNA & proteins (histones) tightly packed together DNA & histone molecules form beadlike structure called a nucleosome

50 Nucleosomes pack with one another to form a thick fiber which is shortened by a system of loops & coils This makes chromosomes visible & may aid in their separation during mitosis Important because a mistake in DNA folding could harm a cell s ability to reproduce Nucleosomes may also play a role in how genes are read to make proteins

51 Nucleosomes pack with one another to form a thick fiber which is shortened by a system of loops & coils This makes chromosomes visible & may aid in their separation during mitosis Important because a mistake in DNA folding could harm a cell s ability to reproduce Nucleosomes may also play a role in how genes are read to make proteins

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