Understanding the Importance of DNA in Life

1. DNA Dr. Bill Stafford 2018 "What could be more important than the study of life, to any intelligent being who has the good fortune to be alive?" Isaac Asimov 

2. DNA – Chapter 8 • Deoxyribonucleic acid • DNA holds the instructions for life • DNA holds the code or blueprint for a cell’s proteins • Proteins determine an organism’s traits and chemical reactions (metabolism) through enzymes • DNA is passed from parents to offspring and is what makes two dogs produce only dogs and two humans produce only humans • The DNA of an individual is unique to that individual – no one else has ever had the same exact DNA except identical twins

3. DNA – Chapter 8 • There are 23 pairs of chromosomes in each human cell for a total of 46 chromosomes • The DNA in each human cell has 3,000,000,000 (billion) base pairs and would be over 6 feet long if it is stretched out • There are 73,000,000,000,000 (trillion) cells in our bodies and if all the DNA was stretched out it would reach to the moon and back 100 times • If the bases were written out, they would fill 5,000 books

4. DNA – Chapter 8 • Scientists • 1928 – Frederick Griffith • “transforming principle” – what made a R-type nondisease causing bacteria become disease-causing when mixed with heat-killed pathogenic S-type bacteria • The transforming principle was later determined to be DNA

5. Frederick Griffith • 1928

6. DNA – Chapter 8 • Scientists (continued) • 1944 – Oswald Avery determined that the “transforming principle” was DNA • DNA has phosphate and nitrogen

7. Oswald Avery • 1944

8. DNA – Chapter 8 • Scientists • 1952 – Alfred Hershey and Martha Chase – gave conclusive evidence that the “transforming principle” was DNA • Used bacteriophages (viruses that attack bacteria) • DNA contains phosphorous • Proteins contain sulfur • Radioactively identified sulfur and phosphorous http://www.dnai.org/timeline/index.html

9. DNA –Chapter 8.2 • Structure of DNA • The monomer of DNA is a nucleotide which has three parts – four different nucleotides based on which nitrogen base is used • A simple sugar – deoxyribose – same in all DNA nucleotides • A phosphate group – same in all DNA nucleotides • A nitrogen base – four different ones • Adenine – A • Guanine – G • Cytosine – C • Thymine - T

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11. DNA – Chapter 8.2 • Structure of DNA (cont.) • Nucleotides join together to form long chains - DNA • The phosphate group of one nucleotide is bonded to the deoxyribose of an adjacent nucleotide • One of the four nitrogen bases join to each deoxyribose sugar • The phosphate group – deoxyribose chain forms the backbone (sides of the ladder) of the DNA molecule • The nitrogen base of one nucleotide weakly bonds (hydrogen bonds) to a nitrogen base of another nucleotide to form the steps of the ladder • Adenine (A) always bonds with thymine (T) and cytosine (C) always bonds with guanine (G) – they are complementary with each other

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13. DNA –Chapter 8.2 • Structure of DNA (cont.) • Two of the four nitrogen bases have one ring and are called pyrimidines – they are the bases thymine (T) and Cytosine (C) • The other two bases have two rings and are called purines – they are the bases adenine (A) and guanine (G) • A purine A always binds to a pyrimidine T and the purine G always binds with the pyrimidine C • It has to always be a purine to a pyrimidine to make the double helix the correct thickness. http://learn.genetics.utah.edu/content/begin/dna/

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15. DNA – Chapter 8.2 • Structure of DNA (cont.) • The structure of the DNA molecule was discovered by James Watson and Francis Crick in 1953 • They determined that the DNA molecule is a double strand with the phosphate group – deoxyribose forming the sides of the ladder • The nitrogen bases form the steps of the ladder and always pair complementarily with A-T and C-G • They called the structure a double helix

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17. DNA – Chapter 8.2 • The special message in DNA is carried by the unique sequence of nucleotide bases. • This sequence is what makes a deer a deer, a dog a dog, or a human a human. • This special sequence of nucleotide bases is what makes each organism unique and is why we all look different. • Identical twins have identical DNA and therefore look alike. • The more similar the sequence of nucleotide bases, the more similar two individuals are.

18. DNA Replication – Chap. 8.3 • Definition – process in which DNA is copied to prepare the cell for mitosis or meiosis • Happens during the S phase of interphase • Occurs completely in the nucleus of eukaryotic cells. • Each strand of the double helix serves as a template to form two identical double strands of DNA – semi-conservative replication • The key to this process is complementary bonding of the nucleotide bases – always A-T and C-G

19. DNA Replication – Chapter 8.3 • The steps in which DNA replication occurs: • The parent DNA double strand “unzips” by the action of an enzyme called helicase that breaks the weak bonds holding the nitrogen bases together. • Then free nucleotides floating in the nucleus bond to the exposed nitrogen base on each of the two single strands of the parent DNA. • This continues until the whole parent strand is unzipped and replicated. • The result is two new identical strands of DNA

20. DNA and RNA – Chap. 8.4 • RNA • A nucleic acid – ribonucleic acid • Structure is like DNA except for three differences: • RNA is always single stranded – DNA is double stranded • The sugar in RNA is ribose – not deoxyribose • The nitrogen bases are the same except instead of thymine (T) RNA uses uracil (U)

21. DNA and RNA – Chap. 8.4 • Transcription – the process of making RNA from DNA • Happens in the nucleus in eukaryotic cells because that is where the DNA is. • RNA polymerase is the primary “enzyme” involved.

22. DNA and RNA – Chap. 8.4 • Transcription – (continued) • Need RNA to carry the message from DNA out into the cytoplasm to direct the making of a protein • Central dogma of Biology • DNA  RNA  protein

23. RNA – Chapter 8.4 • RNA serves as the workers for protein synthesis – they carry the message for making a protein from the DNA in the nucleus to the ribosome in the cytoplasm. • RNA comes in three different types: • Messenger RNA (mRNA) – made from DNA in the nucleus and serves as the blueprint for making a protein- the process of making mRNA is called transcription • Ribosomal RNA (rRNA) – made in the nucleus from DNA and makes up a large part of the ribosome which is made in the nucleolus

24. RNA –Chapter 8.4 • Three types of RNA (cont.) • Transfer RNA (tRNA) – made from DNA in the nucleus. • Moves out of the nucleus into the cytoplasm • Its role in protein synthesis is to carry a particular amino acid to the mRNA-ribosome structure to form the polypeptide chain that makes up the particular protein • The three types of RNA work together with the ribosome in the cytoplasm to assemble a protein • The particular order of amino acids in the protein is determined by the special sequence of nucleotides in the mRNA which is determined by the DNA it is made from.

25. Genes and Proteins • Genes are a segment of a strand of DNA that determines the special sequence of the amino acids found in a particular protein • What a protein does in the body is determined by the sequence of amino acids that make it up • 20 different amino acids

26. Proteins – Chapter 8 • Proteins are made from amino acids and the process is directed by DNA and performed by RNA and ribosomes • Roles of proteins in our body • Structure of cells and our bodies – muscles are proteins • Cell transport – controls most of what enters or leaves the cell through the plasma membrane • Enzymes – control all the chemical reactions (metabolism) of the cells • Important in fighting infection and cancer • Important in communication between cells and in the cell

27. Proteins – Chap. 8.4 • Each cell makes 2,000 cells/second and 173 million/day • We have 73 trillion cells in our body, so we make 1.28 x 1021 proteins per day in our bodies • Each protein lasts a day or two and is destroyed – this allows for dynamic equilibrium • ½ of our proteins are devoted to communication within the cell and with all the other cells in our bodies

28. Transcription – Chap. 8.4 • Definition – making a RNA copy (mRNA) of a segment of DNA (gene) • Happens in the nucleus • Happens much like DNA replication • The DNA molecule “unzips” as it did during DNA replication • Then free RNA nucleotides in the nucleus bond to the exposed nitrogen bases of the DNA molecule – C bonds with G and since there is no thymine RNA nucleotide U bonds with A • The DNA molecule reassembles to its original form • Produces a single strand of RNA

29. Coding Strand 5’ ATGGGCATCGGCCCC 3’ 3’ TACCCGTAGCCGGGG 5’ Template Strand Displaced Coding Strand 5’ ATGGGCATCGGCCCC 3’ C Nascent mRNA (growing from 5’ to 3’) 5’ AUGGG 3’ 3’ TACCCGTAGCCGGGG 5’ Template Strand 5’ ATGGGCATCGGCCCC 3’ 5’ AUGGGCAUCGGCCCC 3’ Completed mRNA 3’ TACCCGTAGCCGGGG 5’ Transport to cytoplasm 5’ AUGGGCAUCGGCCCC 3’ 5’ ATGGGCATCGGCCCC 3’ 3’ TACCCGTAGCCGGGG 5’ Unaltered DNA Met

30. Genetic Code – Chap.8.5 • The message for assembling the amino acids into proteins is transcribed (carried by) mRNA into the cytoplasm for protein assembly • Since there are only four nucleotides and 20 amino acids, it is obvious that it takes a group of three nucleotides to specify each of the 20 amino acids • This group of three nucleotides is called a codon • Each codon codes for a particular amino acid

31. Genetic Code – Chap. 8.5 • There are 64 total codons and only 20 amino acids • Some codons do not specify an amino acid but give directions for assembling proteins such as a stop codon and a start codon • Some amino acids have more than one codon • All organisms use the same 20 amino acids and the same codon for each amino acid – the genetic code is universal • Proteins vary in size from 20 amino acids to 400 amino acids and their structure and function is determined by their unique order of amino acids which is determined by the sequence of nucleotides in the mRNA  DNA

32. Translation Chap. 8.5 • Definition – The process of converting the information in a sequence of nucleotides in mRNA into a sequence of amino acids that make up a protein • Takes place at the ribosome in the cytoplasm • Involves five things • Ribosomes – combination of rRNA and proteins • mRNA • tRNA • Amino acids • Enzymes

33. Translation – Chap. 8.5 • Role of tRNA – carry a specific amino acid to the ribosomes for protein assembly • Each tRNA has an anticodon that matches up with a particular codon on the mRNA strand • The tRNA anticodon matches up to the mRNA strand by base pairing – A-U and C-G • Example: mRNA codon of U-G-U and the corresponding anticodon on the tRNA would be A-C-A

34. TRANSLATION – Chap. 8.5 • The process • The process begins with a start codon on the mRNA – AUG which also codes for the amino acid methionine • The ribosome slides down the mRNA to the next codon on mRNA and the tRNA with the complementary anticodon comes in and attaches to the mRNA • The ribosome slides down to the next codon and continues this process till it reaches a stop codon • A peptide bond forms between each amino acid to build a polypeptide chain that becomes the desired protein.

35. Translation – Chapter 8.5 • Once the polypeptide chain is completed, it is released from the ribosome • The polypeptide chain then folds itself into a particular shape and once it is in its proper shape and form it is ready to do its particular job in the cell or body • We have 30-40,000 genes and produce maybe as many as 100,000 proteins

36. Genetic Changes – Chap. 8.7 • Mutations – a change in the DNA sequence from what it should be – results in different sequences of amino acids in the proteins produced and therefore a protein that cannot do the job it is supposed to do • Can occur during DNA replication • Mutations in reproductive cells – sperm or egg cells • These mutations will become part of every cell’s DNA in the offspring if that mutated egg or sperm are involved in fertilization • Usually results in death of the offspring • Sometimes will be positive and make the offspring better able to survive

37. Genetic Changes – Chap. 8.7 • Mutations (cont.) • Mutations in body (somatic) cells • Can be caused by mutagens such as radiation or sunlight • Will not be passed on to offspring • Usually results in death of a cell • Can result in a cancer cell • Every cell that results from the mutated cell by mitosis will have the same mutation – mitosis results in two new cells with identical DNA to the parent DNA

38. Genetic Changes – Chap. 8.7 • Types of mutations • Point mutations – a change in a single base pair in DNA • Only changes one amino acid in the resulting protein – might not be a big deal – could be as this is what causes sickle cell anemia • Frameshift mutations – a mutation where a single base is inserted (addition) or a single base deleted (deletion) • Changes every amino acid codon from the mutation to the end of the protein • Much more damaging than point mutations • Usually results in the death of the cell

39. Genetic Changes – Chap. 8.7 • Chromosomal mutations – a mutation that happens to a chromosome • Usually occurs during mitosis or meiosis • Deletions – part of chromosome breaks off and is lost • Insertions – a part breaks off and attaches to the homologous chromosome • Inversions – a part breaks off and reattaches backwards • Translocations – part of one chromosome breaks off and attaches to a nonhomologous chromosome • Usually results in the death of the cell

40. Genetic Changes – Chap. 8.7 • A mutagen is anything that causes a mutation • Can be several things such as: • High energy radiation • Chemicals • High temperatures • A mutagen can be a carcinogen if the mutation results in cancer

41. Genetic Changes – Chap. 8.7 • Repairing DNA • Enzymes proofread the DNA molecule as it is replicated and usually catches and repairs all mutations • The more exposure there is to mutagens, the more likely a mutation will be missed by the cell’s correction methods

42. Genetic Changes