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CHAPTER 12

CHAPTER 12 . MOLECULAR GENETICS. Ch. 12.1 – DNA: The Genetic Material You will be doing this section in small groups. Each group will read Section 12.1. You will divide up the section so that everyone is reading equal amounts.

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CHAPTER 12

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  1. CHAPTER 12 MOLECULAR GENETICS

  2. Ch. 12.1 – DNA: The Genetic Material • You will be doing this section in small groups. • Each group will read Section 12.1. • You will divide up the section so that everyone is reading equal amounts. • As you read your section you will put down some important information, such as: • Year for the discovery • Person(s) who did the discovery • What was discovered &/or how they made discovery • Next, you will put together all of your information into a timeline for the discoveries

  3. Ch. 12.1 – DNA – THE GENETIC MATERIAL • Key points from Section 1 • Nucleotides • Nucleotides are subunits of the macromolecule group of nucleic acid • Composed of 5 carbon sugar, a phosphate group, and a nitrogenous base • Nucleic acid • 2 different types: • DNA • Nucleotide is composed of deoxyribose sugar, a phosphate group and a nitrogenous base • Nitrogenous bases are: • Adenine (A), Guanine (G), Cytosine (C), or Thymine (T) • RNA • Nucleotide is composed of ribose sugar, a phosphate group and a nitrogenous base • Nitrogenous bases are: • Adenine (A), Guanine (G), Cytosine (C), or Uracil (U)

  4. Section 12.1 Key Points Continued • Purines are double ringed bases such as: • Guanine and Adenine • Pyrimidine are single ringed bases such as: • Thymine, cytosine, and uracil • Chargaff’s Rule: • C = G • T = A • Watson (IU graduate) & Crick built the double helix model for DNA • Unique feature of the DNA molecule is the direction the 2 strands run which is opposite of each other or antiparallel.

  5. Section 12.1 Key Points Continued • Chromosome Structure • A human chromosome length ranges from 51 million to 245 million base pairs long. • A DNA strand that is 140 million nucleotides long would measure approximately 5 cm. long (2 in.) • To fit all of this into the nucleus of the cell the DNA tightly coils around a beadlike protein called a histone • The histone & the DNA together creates a nucleosome. • The nucleosomes group together into chromatin fibers, which supercoil to create the DNA structure called a chromosome. biology.kenyon.edu

  6. SECTION 12.2 – REPLICATION OF DNA • MAIN IDEA – DNA replicates by making a strand that is complementary to each original strand. • REVIEW: • What nitrogen bases pair together? • What is contained in the nucleotide for DNA? • What nitrogen bases would you find in DNA? • What is contained in the nucleotide for RNA? • What bases would you find in RNA?

  7. SEMICONSERVATIVE REPLICATION • Semiconservative replication is where parental strands of DNA separate and serve as the template to produce DNA molecules that have one strand of parental DNA and one strand of new DNA. csls-text2.c.u-tokyo.ac.jp • Where does DNA replication take place? • During what phase does DNA replication take place? • Will DNA replication take place in mitosis, meiosis, or both?

  8. UNWINDING AND BASE PAIRING • DNA helicase, an enzyme, will unwinding & unzip the double helix leaving single strands of DNA. • DNA polymerase, an enzyme, helps in adding the correct nucleotides to the new DNA strand. • Adenine (A) pairs with thymine (T) • Guanine (G) pairs with cytosine (C) • Base pairing: • Template: A T C C A G G T G • DNA copy: • Produces identical copies to the original double stranded DNA • DNA replication will begin at many places along the chromosome

  9. SECTION 12.3 – DNA, RNA, AND PROTEIN • MAIN IDEA – DNA codes for RNA, which guides protein synthesis. • QUESTION: How does DNA replication relate to mitosis? • How does DNA replication relate to meiosis? • How does DNA replication relate to reproduction?

  10. CENTRAL DOGMA • Remember – proteins function as structural building blocks for the cells and as enzymes. • Central Dogma of biology: DNA codes for RNA, which controls the synthesis of proteins. • DNA → RNA → PROTEIN • RNA is a nucleic acid that is similar to DNA, except: • RNA contains the sugar ribose, uracil replaces thymine, and is single stranded.

  11. TRANSCRIPTION • Transcription is the step in the central dogma – synthesis of the mRNA from the DNA • Transcription= DNA → RNA • Transfers the DNA code to mRNA in the nucleus. • mRNA takes the code into the cytoplasm for protein synthesis • To create mRNA the DNA is unzipped in the nucleus and RNA polymerase binds to a specific section and creates the mRNA • The strand of DNA that is read by the RNA polymerase is called the template strand. • The strand of DNA not read by is called the nontemplate strand. • Uracil is used instead of thymine in mRNA • New mRNA strand leaves the nucleus through the nuclear pores into the cytoplasm

  12. CENTRAL DOGMA CONTINUED • 3 main types of RNA: • Messenger RNA (mRNA) • Long strands of RNA nucleotides that are formed complementary to one strand of DNA • Leave the nucleus and go to the ribosomes to direct the synthesis of a specific protein • Ribosomal RNA (rRNA) faculty.southwest.tn.edu • Type of RNA that combine with proteins to form ribosomes in the cytoplasm. legacy.hopkinsville.edu • Transfer RNA (tRNA) • Small segments of RNA nucleotides that transport amino acids to the ribosome.

  13. RNA PROCESSING • Scientists noticed that mRNA was shorter than the coding region of DNA • Found that the DNA is interrupted by sequences, called INTRONS, that are not in the final mRNA • Coding sequences that remain to make up the mRNA are called EXONS. • Before mRNA leaves the nucleus the INTRONS are removed

  14. TRANSCRIPION CONTINUED • Remember: Base pairs in RNA • Cytosine Guanine GuanineCytosine • AdenineUracil Uracil  Adenine • Thymine (from DNA)Adenine • DNA Strand: A T G C T A A G C RNA Strand: ________

  15. THE CODE • There are 20 amino acids that are used to make proteins. • DNA code is read as a 3 base code. • In DNA or mRNA the 3 base code is called a CODON • The codon that will start the reading of the mRNA is the codon AUG, which codes for the amino acid methionine

  16. GENETIC CODE:emc.maricopa.edu

  17. CIRCLE GENETIC CODE: krishnascience.info

  18. The Genetic Code • Proteins are made by joining amino acids into long chains called polypeptides • amino acids are like puzzle pieces • Proteins would be like the whole puzzle

  19. TRANSLATION • Translation = RNA → protein • Once the mRNA is made and the introns are removed and exons are left mRNA leaves the nucleus and goes and attaches to a ribosome in the cytoplasm • This is where the mRNA is read and translated to make a protein through a process called translation. • Translation involves: • tRNA that acts as the interpreters of the mRNA codon sequence. • tRNA has a cloverleaf shape that has a 3 base coding sequence called the anticodon. • Anticodons are complementary to a codon on the mRNA.

  20. ROLE OF THE RIBOSOME • Ribosomes consists of 2 subunits. • When mRNA leaves the nucleus the 2 subunits of the ribosome come together and attach to the mRNA. • Now the tRNA will bring in the correct amino acid and attach to the mRNA. • This continues until a stop codon is reached and it is the end of the protein synthesis. • Protein is now released.

  21. TRANSLATION: ajinomoto-eurolysine.com

  22. SECTION 12.4 – GENE REGULATION AND MUTATION • MAIN IDEA – Gene mutation is regulated by the cell, and mutations can affect this expression. • QUESTION: What words and images come to mind when you hear the words mutation or mutant?

  23. HOX GENES • Gene regulation is crucial during development. • Eukaryotes develop from a single cell called a zygote. • Zygote produces all the different kinds of cells needs by the organism by mitosis. • Hox genes helps control how the body of an organism develops. • Mutations in the Hox genes can cause a fruit fly to develop a leg where its antennae should be.

  24. HOX GENE MUTATION: palaeos.com

  25. MUTATIONS • Mutation is a permanent change in a cell’s DNA. • Types of gene mutations: • Point mutation is a chemical change in one base pair and could cause a genetic disorder. • Types of point mutations: • Substitution (missense) – one base is exchanged for another • EX: C is replaced with G (now codes for the wrong amino acid) • Substitution (nonsense) – changes the codon for an amino acid to a stop codon causing translation to end early resulting in a protein that cannot function normally.

  26. MUTATIONS – CONTINUED • Types of gene mutations continued: • Frameshift: Insertion – adds a nucleotide to the DNA sequence shifting the reading frame • EX: original strand: A C C G G C C A A amino acids: _________________________________ mutated strand:AC C C G G C C A A amino acids: _________________________________ • Frameshift: Deletion – deletes a nucleotide from the DNA sequence shifting the reading frame • EX: original strnad: A C C G G C C A A mutated strand: A C G G C C A A

  27. CHROMOSOMAL MUTATIONS • Deletions • Part of chromosome is deleted/gonecompletely • Original: A B C D Deleted: A C D • Duplications • Part of chromosome is duplicated/repeated • Original: A B C D Duplicated: A A B C D • Inversions • Part of code is read in a different direction (reverses the directions of the parts of the chromosome) • Original: A B C D, Inverted: A C D B • Translocations • Entire sections of chromosome are shifted (when part of one chromosome breaks off and attaches itself to another chromosome) http://staff.tuhsd.k12.az.us/gfoster/standard/bmut.htm

  28. CAUSES OF MUTATIONS: • Some mutations, like point mutations, occur spontaneously. • Cells proofread so it happens rarely • Mutagens are some types of chemicals and/or radiation

  29. BODY CELL VS. SEX CELL MUTATION • Body cell: • Mutation in a body cell (somatic cell) is in that one cell and the future daughter cells that this cell makes. • If these mutations do not cause problems for the cell it is called a neutral mutation. • If these mutation cause problems in the cell the cell could become cancerous or the cell may die. • These mutations are not passed down to offspring • Sex cell: • If the mutations occurs in the sex cells it will be passed down to the offspring and will be present in every cell of the offspring. • The mutation may or may not affect the offspring.

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