DNA Chapter 12
DNA: The Genetic Material The Secret of Life
Think Back… • Gregor Mendel and inheritance… • Factors that determine traits are passed down from generation to generation, they come from both mom and dad • But where did this information come from, and where was it stored? • Scientists knew there were both proteins and nucleic acids (DNA) in the nucleus of cells • Left scientists wondering what molecule was involved in inheritance – DNA or proteins?
Discovery • Griffith: found that one strain of bacteria could be transformed into another • Created the search for the transforming substance. • Avery: identified the transforming molecule • Scientists were still skeptical • Hershey & Chase: experiments provided definitive evidence that DNA was the transforming factor • After these discoveries, scientists were more confident that DNA was the transforming factor
The Scandal Rosalind Franklin X-Ray Diffraction: Rosalind Franklin used this method to discover the double helix structure Other scientists stole this work, and used it to take credit for themselves, this later won them a Nobel Prize
WAIT! • Remaining questions – • How do nucleotides come together to form DNA? • How does DNA communicate information? • How does DNA store information? • How does DNA duplicate itself?
So we found it, but… WHAT IS IT!? Genetic material! Blueprint for living organisms! Passed from generation to generation! DNA: Deoxyribonucleic Acid Classified as a nucleic acid, made up of millions of tiny subunits called nucleotides
Nucleotides • NUCLEOTIDES • Made of a • sugar (deoxyribose) • a phosphate • a nitrogenous base
REMEMBER! • A nucleotide is made of • Sugar • Phosphate • Base
Double Helix • The phosphate of one group bonds to the sugar of another • The phosphate and sugar form the backbone of the DNA molecule • Like the “sides” of a ladder • The bases form the “rungs” • 4 types of bases
Bases • Guanine (G) • Adenine (A) • Cytosine (C) • Thymine (T) • Each base will only bond with 1 other specific base • A – T • C – G • Complementary base pairing • the order of the bases in one strand determines the order of the bases in the other strand
Hydrogen Bonds • Each pair is held together with a hydrogen bond • A – T: two hydrogen bonds • C – G: three hydrogen bonds
1) A Sugar Phosphate Backbone 2) FourBases (Attached in Pairs)
DNA • In prokaryotic cells, DNA is a loop in the cytoplasm • Eukaryotic DNA is organized into individual chromosomes in the nucleus • The length of a chromosome can be 51 million to 245 million base pairs! • And remember, each of your cells has a copy of ALL that DNA!!!! • DNA makes up GENES which make up CHROMOSOMES found in the NUCLEUS of the CELL
K’NEX NUCLEOTIDE PHOSPHATE SUGAR ADENINE DOUBLE HYDROGEN CYTOSINE TRIPLE HYDROGEN GUANINE THYMINE Following the directions on your handout, build your model Complete labeling sheet and crossword if not done DUE tomorrow
DNA Replication 12.2
DNA Replication • Remember – every cell in your body has a copy of your DNA • But, that DNA in the cell must be copied first so that the new cells (remember you get 2 new daughter cells from one parent in mitosis) get a copy of the old DNA. • How does it get there? • DNA replicates during interphase of mitosis and meiosis
DNA Replication • The double helix structure helps explain how DNA copies itself • DNA replicates by making a strand that is complementary to the original strand • The double helix separates, acts as a template, and creates a new strand • Unwinding • Base pairing • Joining
DNA Replication The “parent strand” has two complementary strands Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.
Unzip The first step is to “unwind” the parent strand DNA helicase: enzyme responsible for unwinding and unzipping the double helix. Hydrogen bonds are broken and there are two single strands
Template Free Floating nucleotides (in the nucleus) match up to the parent strands of DNA DNA polymerase adds new nucleotides to the single strands and proofreads before creating two new identical strands
DNA • DNA is a code • The nitrogen bases spell out a message that creates proteins • Proteins then make up the organism!
The Code • It’s like A, T, C, and G are the only letters in the alphabet - • You can use them as many times as you’d like and in any order to make “words” • These combine to make “sentences” • The “sentences” combine to make “paragraphs” • The paragraphs give instructions to the nucleus to make a living organism and all its unique traits
The Central Dogma How does DNA act as a code for protein synthesis? Amino acids make up proteins and proteins act as building blocks for cells and enzymes Central Dogma: DNA is TRANSCRIBED into RNA RNA is TRANSLATED into proteins
Ribonucleic Acid • Nucleic acid, single strand • Contains sugar ribose • Has Uracil instead of Thymine • A – U • C – G • Messenger protein (mRNA), carries the DNA to ribosomes • Translates DNA • Think of DNA as written in French, the RNA must translate it into English so the body can use it
The Code • DNA is a 3 base (nitrogen) code • 3 nitrogen bases in a strand of DNA code for 1 amino acid • For example, UCU codes for serine • This unique 3 base sequence is called a CODON • A start codon is where a specific gene starts, and a stop codon is where the gene ends • A codon of DNA is transcribed into RNA • 1st step of central dogma!
The Code • Once the RNA is synthesized and processed, it moves to the ribosome • Remember, ribosomes are the cell organelle that make proteins • The ribosome reads and translates the RNA in order to make a protein • 2nd step of central dogma
Mutations Sometimes errors occur when chromosomes are copied Sometimes, there is little to no effect because the cell has some repair mechanisms Mutation: a permanent change in a cell’s DNA
Mutations If a trait that hasn’t been present in either family suddenly appears, we can guess a mutation took place A mutation causes a change in a child’s trait only when it takes place in the parents’ sex cells Mutations in the autosomal cells do not get passed on Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.
Types of Mutations • Point Mutation: chemical change in just 1 base pair • Substitution: one base is exchanged for another • Missense: DNA will code for wrong amino acid • Nonsense: change codon to stop codon, causes translation to stop early • Frameshift Mutation: the gain or loss of a nucleotide • Insertion: addition of a nucleotide to the DNA sequence • Deletion: removal of a nucleotide to the DNA sequence • These all disrupt normal protein production and can sometimes cause genetic disorders
Causes of Mutations • Some are spontaneous • Some are caused from things outside of the cell • Radiation • Mutagens • Various chemicals - nicotine, pesticides
Genetic Engineering • Genetic Engineering: manipulating the DNA of one organism in order to insert the DNA of another organism • Jellyfish fluorescence added to mosquito DNA • Has applications in human health and agriculture • Can be used to increase or decrease the expression of specific traits • Biotechnology: The use of genetic engineering to solve problems
Genetic Engineering Glow in the dark cats - researchers took skin cells from Turkish Angora female cats and used a virus to insert genetic instructions for making red fluorescent protein Venomous cabbage - Scientists have recently taken the gene that programs poison in scorpion tails and looked for ways to combine it with cabbage
Genetic Engineering Medicinal eggs - scientists have created a breed of genetically modified hens that produce cancer-fighting medicines in their eggs. The animals have had human genes added to their DNA so that human proteins are secreted into the whites of their eggs, along with complex medicinal proteins similar to drugs used to treat skin cancer and other diseases. Web spinning goats - Researchers inserted a spiders’ dragline silk gene into the goats’ DNA in such a way that the goats would make the silk protein only in their milk. This “silk milk” could then be used to manufacture a web-like material called Biosteel.
Cloning • Clones: Using the DNA of one organism to create another exact copy of the organism
Plant and Animal Breeding • Cloning is a way of producing living things with identical desirable traits. • Breeding: the bringing together of two living things to produce offspring • Selective breeding: can bring out the desired traits of living things • examples: dog breeding, agriculture • Knowing what to expect tells us which living things to breed for certain traits.
Designer Babies Using genetic engineering to choose the traits of your offspring Savior Siblings - children conceived with the initial purpose of acting as donors for a sick brother or sister.
Gene Therapy • Technique aimed at correcting mutated genes that cause diseases • Scientists insert a normal gene into a chromosome to replace a dysfunctional gene
The Human Genome Project The genetic blueprint for a human being The mapping of the genome was finished in 2003, and scientists are continuing to discover what each gene does and how it functions.