DNA & Genes Chapter 12

DNA & GenesChapter 12 DNA, RNA, & Protein Synthesis

DNA Molecule of HeredityA. 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) • Guanine (G) • Cytosine (C) • Thymine (T) PURINES PYRIMIDINES • The nitrogenous bases of DNA (purines – double ring / pyrimidines single ring)

DNA • Deoxyribonucleic acid • Deoxyribose is sugar • Nitrogenous bases: Adenine binds with Thymine Cytosine binds with Guanine One nucleotide of DNA

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

DNA….who cares Is used to catch criminals Is used to determine the paternity of Children on shows such as: Is used to make genetically modified food Is used to compare similarities between species Is used to make antibiotics and vaccines

History: Griffith and Transformation • Year: 1928 • Examined 2 strains of pneumonia bacteria • Rough • Smooth • Injected mice with bacteria to see if they would develop pneumonia • Discovered transformation • Took the heat killed bacteria and combined it with the harmless bacteria, and mice developed pneumonia

History: Avery & DNA • 1944 • Used Griffith’s experiment. He wanted to know which molecule in the heat-killed bacteria was important in transformation • Avery used enzymes to discover that DNA was the molecule that allowed transformation to happen

History: Hershey-Chase • 1952 • The Hershey-Chase experiment used viruses known as bacteriophages. • Question: Wanted to know which part of the virus, protein or DNA, entered the infected core of bacterium. Preformed the experiment by using radioactive markers • Concluded, that the genetic material was DNA

B. History . 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! Purines Pyrimidines Phosphate group Deoxyribose

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)

More DNA info • DNA contains information that determines an organism’s function and appearance • Some DNA codes for proteins • DNA is located within genes (sections of a chromosome) inside of the nucleus of every cell

Wait a minute… Does that shape remind you of any other shape you may have seen before? How about this portion of an apple?

DNA Flo Rider Featuring – T-Pain-less Shawty got them apple bottom genes with the DNA (NA) Nucleotides twisted that way They start to fold (they start to fold) Next thing you know Shawty got chro mo so o o o o omes The A’s bond with the T’s and the C’s bond with the G’s (with the G’s) Hydrogen bonds in the double helix They start to fold (they start to fold) Next thing you know Shawty got chro mo so o o o o omes

DNA Replication • DNA opens up and makes a complete copy of itself – necessary during mitosis and meiosis • New nucleotides float in and pair in a complementary fashion – A to T, C to G and vice versa…

Figure 16.7 A model for DNA replication: the basic concept (Layer 1)

Figure 16.7 A model for DNA replication: the basic concept (Layer 4) Semi-conservative process…

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.

Chromosome Structure Nucleosome Chromosome DNA double helix Coils Supercoils Histones DNA Animation Go to Section:

DNA Replication (cont.) • Diagram of DNA Replication:

DNA  ProteinA. RNA • RNA: Ribonucleic Acid; used to make proteins / Single-stranded -RNA (polymer) made of nucleotides (monomer): -Ribose = 5 C sugar + Phosphate group + N Base 4 bases: • Cytosine (C) • Guanine (G) • Adenine (A) • Uracil (U) – NO THYMINE in RNA! • 3 types of RNA: 1. messenger RNA (mRNA) – single stranded transmits info from DNA to protein syn. 2. transfer RNA (tRNA) - single stranded/ 20 or more varieties ea. w/ ability to bond to only 1 specific AA 3. ribosomal RNA (rRNA) – globular / major component of ribosome

B. Protein Synthesis (overview) • 2 Stages in making proteins: • Transcription – using DNA template to make mRNA strand • Translation – using mRNA strand to create polypeptides DNA RNA Protein Transcription Translation

1. Transcription • The Goal of Transcription is to produce a single-stranded mRNA 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-mRNA strand breaks away when RNA polymerase reaches a sequence of bases on DNA that act as a stop sign. • The finished product (mRNA) 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 mRNA strands? • The mRNA strand must be read in groups of 3 nucleotides, called a CODON. • Different Codons translate for different Amino acids.

Codons in mRNA

Codons in mRNA • “Start” codon = AUG (Methionine) • “Stop” codons = UAA, UAG, and UGA • Example: • mRNA Strand: • U-C-A-U-G-G-G-C-A-C-A-U-G-C-U-U-U-U-G-A-G methionine glycine threonine cysteine phenylalanine STOP

3. Translation • The Goal of Translation is to “translate” these mRNA codons into their amino acids to form a polypeptide. • How it’s done: 1. mRNA strand attaches to a ribosome (rRNA) 2. Each mRNA codon passes through ribosome 3. Free-floating Amino Acids from cytosol are brought to ribosome by tRNA 4. Each tRNA has an anticodon to match up to mRNA codons 5. Amino Acids are joined as tRNA keeps bringing them 6. Polypeptide chain grows until “stop” codon is reached

Translation (cont.) • Translation 1st. mRNA strand attaches to a ribosome (rRNA)

Translation (cont.) • Translation • 2nd, Each mRNA codon passes through ribosome

Translation (cont.) • 3rd, Free-floating Amino Acids from cytosol are brought to ribosome • by tRNA • Translation

Translation (cont.) • Translation • 4th, Each tRNA has an anticodon to match up to mRNA codons

Translation (cont.) • Translation 5th, Amino Acids are joined as tRNA keeps bringing them

Translation (cont.) • Translation . Polypeptide chain grows until “stop” codon is reached

Genetic Changes: MutationsA. Types of Mutations 1. Gene Mutations: changes in nucleotides • Point Mutations • 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

Example of Point Mutation Induced Point mutation in growth hormone gene causes semi-dominant dwarfism & obesity *image borrowed from www.science.ngfn.de/6_164.htm

B. Chromosome Mutations 1. Deletion…………………………… 2. Insertion/Duplication………… 3. Inversion………………………… 4. Translocation…………………….

A chromosomal mutation involves changes in the number or structure of chromosomes. Chromosomal mutations may change the locations of genes on chromosomes and even the number of copies of some genes. • Deletion involves the loss of all or part of a chromosome. • The opposite of a deletion is a • Duplication, in which a segment of a chromosome is repeated. • When part of a chromosome becomes oriented in the reverse of its usual direction, the result is an Inversion. • A Translocation occurs when part of one chromosome breaks off and attaches to another, non-homologous, chromosome. In most cases, nonhomologous chromosomes exchange segments so that two translocations occur at the same time.

In the absence of lactose, the repressor protein binds to the operator on DNA and inhibits transcription of lactose-processing enzymes. In the presence of lactose, the repressor is inhibited from binding with the operator; this all ows transcription to take place to produce lactose-processing enzymes. Gene Regulation in Prokaryotes The lac operon enables the production of lactose-processing enzymes in E. coli, but only when needed.

DNA & Genes Chapter 12