- Slides: 25
DNA & Genes Chapter 11 DNA, RNA, & Protein Synthesis
I. DNA Molecule of Heredity A. Structure • DNA (polymer) is a long molecule made up of Nucleotides (monomers) • A Nucleotide consists of: – Deoxyribose (a 5 -carbon sugar) – a phosphate group – One of 4 Nitrogenous bases (contain nitrogen) • Adenine (A) PURINES • Guanine (G) • Cytosine (C) PYRIMIDINES • Thymine (T) • The nitrogenous bases of DNA (purines – double ring / pyrimidines single ring)
Structure of DNA (cont. ) • DNA is like a twisted ladder: – Rungs: complementary base pairs (A=T, G=C) – Uprights: deoxyribose and phosphate groups • Your Turn: Match this DNA base sequence with its correct complementary DNA bases: • T-C-G-A-A-C-T • A-G-C-T-T-G-A
B. History 1. CHARGAFF (1949): discovered that the % of Cytosine and Guanine were about the same in DNA; the same was true about Adenine and Thymine – This suggests BASE PAIRING………. . that C bonds with G and A bonds with T! Source of DNA A T G C Streptococcus 29. 8 31. 6 20. 5 18. 0 Yeast 31. 3 32. 9 18. 7 17. 1 Herring 27. 8 27. 5 22. 2 22. 6 Human 30. 9 29. 4 19. 9 19. 8
History (cont. ) 2. Wilkins and Franklin(1952): took X -Ray photographs of DNA which suggested a twisted, helical structure, 2 strands, and bases in the center 3. Watson and Crick (1953): using all the research to date, discovered the structure for DNA: A DOUBLE HELIX (with sugar-phosphate backbones and bases on the inside held together by H bonds)
C. DNA Replication: making more DNA during the S Phase of the Cell Cycle (in the nucleus) 1. The enzyme helicase unwinds DNA double helix (breaks hydrogen bonds btwn. bases) & a replication fork is created. (Each old DNA strand will act as a template for 2 new strands to be added on) 2. Enzyme called DNA Polymerase binds to replication fork and adds free nucleotides to each old strand of DNA 3. DNA Polymerase remains attached until 2 new DNA strands are created; it “proofreads” the strands to minimize error in the process.
DNA Replication (cont. ) • Diagram of DNA Replication:
II. DNA Protein RNA: Ribonucleic Acid Used to make proteins Single-stranded polymer made up of nucleotides. RNA Monomer (Nucleotide) is made of Ribose (5 C sugar) + Phosphate group + N Base Cytosine (C) Guanine (G) Adenine (A) Uracil (U) – NO THYMINE in RNA!
Types of RNA – 3 types of RNA: 1. messenger RNA (m. RNA) – single stranded transmits info from DNA to protein syn. 2. transfer RNA (t. RNA) - single stranded/ 20 or more varieties ea. w/ ability to bond to only 1 specific AA 3. ribosomal RNA (r. RNA) – globular / major component of ribosome
Protein Synthesis (overview) • 2 Stages in making proteins: 1) Transcription – using DNA template to make m. RNA strand 2) Translation – using m. RNA strand to create polypeptides DNA Transcription RNA Translation Protein
1. Transcription • The Goal of Transcription is to produce a singlestranded m. RNA helix that contains information from DNA to make proteins • How it’s done: (This happens in the Nucleus!) 1. DNA strand unwinds/unzips complementary DNA strands 2. Enzyme called RNA Polymerase binds to DNA “promoter” regions and “plugs in” complementary RNA nucleotides to the DNA template. – Example = DNA Template: ATTGGCAGT new RNA Strand: UAACCGUCA
Transcription (cont. )
Transcription (cont. ) 3. Once produced, this pre-m. RNA strand breaks away when RNA polymerase reaches a sequence of bases on DNA that act as a stop sign. • The finished product (m. RNA) moves out of the Nucleus through a nuclear pore into the cytoplasm. 4. 2 DNA complementary strands rejoin
2. The Genetic Code • How do we get proteins from m. RNA strands? • The m. RNA strand must be read in groups of 3 nucleotides, called a CODON. • Different Codons translate for different Amino acids.
Codons in m. RNA
Codons in m. RNA • “Start” codon = AUG (Methionine) • “Stop” codons = UAA, UAG, and UGA • Example: • m. RNA Strand: • U-C-A-U-G-G-G-C-A-U-G-C-U-U-G-A-G methionine glycine threonine cysteine phenylalanine STOP
3. Translation • The Goal of Translation is to “translate” these m. RNA codons into their amino acids to form a polypeptide. • How it’s done: 1. m. RNA strand attaches to a ribosome (r. RNA) 2. Each m. RNA codon passes through ribosome 3. Free-floating Amino Acids from cytosol are brought to ribosome by t. RNA 4. Each t. RNA has an anticodon to match up to m. RNA codons 5. Amino Acids are joined as t. RNA keeps bringing them 6. Polypeptide chain grows until “stop” codon is reached
Translation (cont. ) • Translation
III. Genetic Changes: Mutations A. Types of Mutations 1. Gene Mutations: changes in nucleotides – Point Mutations or Frameshift Mutations 2. Chromosome Mutations: changes in # or structure of chromosome – Deletion – Insertion/Duplication – Inversion – Translocation
1. Gene Mutations a. Point Mutation: the substitution, addition or removal of a single nucleotide b. Frameshift Mutations: types of point mutations that shift the “reading frame” of the genetic message
B. Chromosome Mutations 1. Deletion……………… 2. Insertion/Duplication………… 3. Inversion…………… 4. Translocation………….
Reproductive vs. Body Cell Mutations • Reproductive Cells – Mutations when multiplied become the genetic makeup of the new offspring. • Body Cells – Ultraviolet Radiation, affects the cell of the individual. Not passed on, but can cause harm to individual. (Mutagens)
Are all mutations bad? • No! • Positive Mutations are often called adaptations. • These adaptations are beneficial to the species if they become a predominant part of the gene pool.
Homework • In your book page. 306 Mini-Lab 11 -2 • Complete the procedure and answer questions 1 -3. Quiz Thursday on DNA, Replication, Protein Synthesis, and Mutations
Gene Regulation in Prokaryotes The lac operon enables the production of lactose-processing enzymes in E. coli, but only when needed. • In the presence of lactose, the • In the absence of lactose, the repressor is inhibited from repressor protein binds to the binding with the operator; this operator on DNA and inhibits all ows transcription to take transcription of lactoseplace to produce lactoseprocessing enzymes.