Molecular Inheritance

1. Molecular Inheritance Biology Module B

2. Big Ideas-DNA Structure • What is the shape and composition of a DNA molecule? • How is information organized in a DNA molecule? • How is prokaryotic DNA different than eukaryotic DNA?

3. DNA Structure • http://www.youtube.com/watch?v=VegLVn_1oCE • One of the characteristics of life is genetic material in the form of the molecule deoxyribonucleic acid, or DNA. This genetic material is inherited from parents and exists in a predictable, simple form. • A molecule of DNA is made up of many smaller units called genes, which are the individual instructions for traits. • When all genes are condensed and organized they are known as chromosomes.

4. DNA, gene, chromosome organization

5. DNA Structure • DNA is a nucleic acidmacromolecule made up of nucleotide monomers. • A nucleotide is made up of three parts: a phosphate group, a sugar group, and a nitrogen-containing base. • The phosphate groups and the sugar molecules of different nucleotides link together to form a “backbone” for the DNA strand. • The sugar in DNA is called deoxyribose, from which DNA gets its full name, deoxyribonucleic acid.

6. DNA Structure

7. DNA Structure • In 1953 Watson and Crick proposed that DNA is a double helix(a twisted ladder) with two phosphate/sugar backbones and runged nucleotides that pair in the middle with hydrogen bonds

8. Visual Concept: Double Helix Click above to play the video.

9. DNA Structure • Once the molecular structure of DNA was verified, we discovered that each organism has a unique pattern to the order of the nitrogenous bases-this tells us that it is the order of these bases that contains our genetic information. • In DNA, each nucleotide has the same deoxyribose and phosphate group, but each nucleotide can have one of four nitrogenous bases. • The four kinds of bases are adenine (A), guanine (G), thymine (T), and cytosine (C).

10. DNA Structure • The bases have very specific rules, known as Chargaff’s Rules, in how they pair across the DNA molecule with hydrogen bonds: • adenine always pairs with thymine (A with T) • guanine always pairs with cytosine (G with C) • Hydrogen bonds between bases keep the two strands of DNA together.

11. DNA Structure • Paired bases are said to be complementary because they fit together like puzzle pieces. • Because of base-pairing rules, if the sequence of bases is known for one strand of DNA, then the sequence of bases for the complementary strand can be quickly identified.

12. DNA Base-Pairing Rules Practice • A _____ • T _____ • G _____ • C _____ • T _____ • G _____ • A _____ • C _____ Rules A T T A G C C G

13. DNA Structure • Remember that eukaryotic cells have a nucleus that contains the X-shaped chromosomes-typically eukaryotes have multiple sets of chromosomes, i.e. humans have 23 pairs. • Prokaryotes (bacteria) are simpler organisms and therefore have less DNA, so they typically only have 1 circular chromosome. • Despite this difference, all cells have the same DNA structure at the molecular level.

14. Big Ideas-DNA Replication • How does DNA replicate? • What are the roles of proteins in DNA replication?

15. DNA Replication • Organisms constantly need new cells to replace old & dying ones. In order to efficiently make these new cells, organisms need a molecular process to copy the DNA in chromosomes so that the new cells have the genetic information needed to survive. The process of making a copy of DNA is called DNA replication. • Because DNA is made of two strands of complementary base pairs, if the strands are separated then each strand can serve as a pattern to make a new complementary strand.

16. DNA Replication Process • DNA replication begins with 1 double stand of DNA-either in the nucleus of eukaryotes or cytoplasm of prokaryotes. • The enzyme DNA helicase untwists and unzips the DNA molecule. • The exposed DNA molecule now is 2 single strands in a Y-shape called the replication fork. • At the replication fork, the enzyme DNA polymerase adds new nucleotides from the cytoplasm to each side and new base pairs are formed according to Chargaff’s rules. • The end result is 2 identical strands of DNA.

17. DNA Replication • The replication of DNA involves 2 major proteins. Each protein has a specific function. • Proteins called DNA helicases unwind the DNA double helix during DNA replication. These proteins wedge themselves between the two strands of the double helix and break the hydrogen bonds between the base pairs. • Proteins called DNA polymerases move along each strand and add nucleotides that pair with each base.

18. DNA Replication • DNA polymerases also have a “proofreading” function. • During DNA replication, errors sometime occur and the wrong nucleotide is added to the new strand. • If a mismatch occurs, the DNA polymerase can backtrack, remove the incorrect nucleotide, and replace it with the correct one.

19. DNA Replication • After replication is complete, each double-stranded DNA helix is made of one new strand of DNA and one original strand of DNA-so the original DNA is semi-conserved.

20. DNA Replication

21. Big Ideas-RNA & Protein Synthesis • What role does RNA play in gene expression? • How are proteins made during the molecular process of protein synthesis?

22. RNA & Protein Synthesis • DNA is a molecule that contains instructions on how to make proteins, and it is these proteins that are expressed as our traits like eye and hair color. • However, DNA is too important to directly do the work of making proteins and risk getting damaged. So another molecule called ribonucleic acid, or RNA, takes the information from DNA and physically makes proteins. • Gene expression is how what is in your genes becomes your specific traits.

23. RNA & Protein Synthesis • RNA is a very important nucleic acid that is involved in all of the steps in gene expression-so without RNA we wouldn’t survive. • Like DNA, RNA is made of nucleotides linked together. However, RNA differs from DNA in three ways.

24. RNA & Protein Synthesis • RNA usually is composed of one strand (single helix) of nucleotides rather than two strands. • RNA nucleotides contain the sugar ribose rather than the sugar deoxyribose. • RNA nucleotides have a nitrogenous base called uracil (U) instead of the base thymine (T). • Uracil (U) is complementary to adenine (A) whenever RNA pairs with another nucleic acid.

25. RNA Base-Pairing Rules Practice DNA RNA RNA • A_____ _____ • T _____ _____ • G _____ _____ • C _____ _____ • T _____ _____ • G _____ _____ • A _____ _____ • C _____ _____ Rules A U T A G C C G U A

26. RNA vs. DNA Visual

27. RNA & Protein Synthesis • There are three types of RNA which play a role in gene expression. • Messenger RNA(mRNA) is produced when DNA is transcribed (copied) into RNA. • The mRNA carries instructions for making a protein from the DNA in the nucleus and delivers the instructions to the site where proteins are made, the ribosomes in the cytoplasm.

28. RNA & Protein Synthesis • At the ribosome, transfer RNA(tRNA) “reads” the instructions carried by the mRNA, then translates the mRNA sequence into protein pieces called amino acids. tRNA is like a taxi driver and amino acids are like the passengers. • Ribosomal RNA(rRNA) is an RNA molecule that makes up the actual ribosomes.

29. RNA & Protein Synthesis • Gene expression produces proteins during a process called protein synthesis, which has two steps- transcription and translation.

30. RNA & Protein Synthesis • The first stage of gene expression is called transcription and happens in the nucleus. Transcription is the process of making mRNA from the information in DNA. • Transcription is similar to copying (transcribing) notes from the board (DNA) to a notebook (RNA). • Transcription is not the same process as replication. • In transcription, a new molecule of RNA is made from the DNA. In DNA replication, a new molecule of DNA is made from the DNA.

31. RNA & Protein Synthesis • All cells contain the entire set an entire set of DNA, called the genome. However, cells are specialized and only express the genes necessary to their jobs, i.e. muscle cells turn on (express) muscle genes. • Every gene has three regions. The first is the promoter, which turns the gene on and off (like a light switch). The second region is the coding, which encodes the information for which protein to produce. The third region is the terminator, which signals the end of the gene.

32. RNA & Protein Synthesis • Transcription Steps • RNA polymerase, an enzyme inside the nucleus, binds to the DNA at the promoter region of the gene that needs to be turned into protein. • The RNA polymerase then unwinds the DNA and attaches to a single strand to read the bases. • The RNA polymerase moves along the DNA single strand along the coding region of the gene, copying the base sequence using nucleotides from the cytoplasm. This strand it is building is the mRNA. • RNA polymerase continues making the mRNA until it reaches the terminator, where it breaks off. • The mRNA leaves through a nuclear pore and travels to a ribosome. • The DNA folds back together.

33. Transcription Visual

34. RNA & Protein Synthesis • The second stage of gene expression is called translation. Translation uses the information in mRNA to make a specific protein. • Translation is similar to translating a sentence in one language (RNA, the nucleic acid “language”) to another language (protein, the amino acid “language”).

35. RNA & Protein Synthesis • Translation reads mRNA in codons-which are three nucleotide sequences (3 letters at a time). Each codon corresponds to 1 of 20 amino acids. • This system of matching codons and amino acids is called the genetic code. The genetic code is based on mRNA codons that each represent a specific amino acid.

36. Codons in mRNA-the genetic code is considered redundant b/c even though there are 20 amino acids, there are 64 ways to code for them.

37. RNA & Protein Synthesis • Translation Steps: • The mRNA made during transcription travels to a ribosome. • The mRNA feeds into the ribosome until a start codon, AUG, is found. • The ribosome reads the codons in mRNA, attaching the appropriate anti-codons of a tRNA molecule. • Each tRNA molecule has an amino acid attached to it. As the anti-codon of tRNA matches to the codon of mRNA, the amino acid is dropped off at the ribosome to build the protein.

38. RNA & Protein Synthesis • Translation Steps Continued: • This process of reading mRNA, bringing in tRNA, and dropping off amino acids continues until a stop codon is reached in the mRNA. • The ribosome then stops translation and the protein folds up and continues being assembled by the ER. • The ER sends the protein to the Golgi to get packaged and shipped from the cell.

39. Translation Visual

40. Protein Synthesis Video

41. Central Dogma of Biology-big idea for all of biology that explains how we express our genes. It also shows that flow of information is one-directional.

42. Big Ideas-Mutations • How can mutations affect whole chromosomes and individual genes?

43. Mutations • Mutations occur when DNA is altered. • There are 2 types of mutations: • Chromosomal mutations occur when an entire chromosome is altered; these mutations tend to be lethal • Point mutations occur when individual bases in a gene are altered; these mutations are less lethal but cause many diseases

44. Mutations-Chromosomal

45. Mutations-Point (5 types) • Missense Mutation-in a missense mutation, the new base alters a codon resulting in a different amino acid being incorporated into the protein chain Example : sickle-cell disease OriginalMutated Wrong Amino Acid, now protein won’t make sense

46. Mutations-Point (5 types) 2. Nonsense Mutation-with a nonsense mutation, the new nucleotide changes a codon that specified an amino acid to one of the STOP codons (TAA, TAG, or TGA). Therefore, translation of the messenger RNA transcribed from this mutant gene will stop early. OriginalMutated Now the protein will stop prematurely

47. Mutations-Point (5 types) • Silent Mutations-most amino acids are encoded by several different codon. For example, if the third base in the TCT codon for serene is changed to any one of the other three bases, serine will still be encoded. Such mutations are said to be silent because they cause no change in their product and can’t be detected without sequencing the gene (or its mRNA). OriginalMutated Even though there’s a mutation it doesn‘t change the protein

48. Mutations-Point (5 types) • Insertions-Extra base pairs may be added from the DNA of a gene. The number can range from one to thousands. Insertions of one or two bases or multiples of one or two cause frame shifts. These can have devastating effects because the mRNA is translated in new groups of three nucleotides and the protein being produced may be useless. OriginalMutated Wrong protein made

49. Mutations-Point (5 types) • Deletions-extra base pairs may be or removed from the DNA of a gene. The number can range from one to thousands. deletions of one or two bases or multiples of one or two cause frame shifts. These can have devastating effects because the mRNA is translated in new groups of three nucleotides and the protein being produced may be useless. OriginalMutated Not enough letters