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DNA

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Matthew Halloran

on 8 March 2018

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Transcript of DNA

Watson and Crick Model of DNA
- DNA consists of 2 complementary chains of nucleotides arranged in a ladder type configuration and then twisted into a double helix
DNA Replication
- DNA Replication is the copying of DNA into new strands. It occurs during interphase prior to mitosis and meiosis
Modern Genetics
- study of DNA (Deoxyribonucleic Acid) which is the hereditary material found in the nucleus of cells
- Nucleic Acid: a polymer of repeating units called nucleotides
Protein Synthesis
- DNA -> mRNA -> tRNA-amino acid -> protein
Gene: sequence of nucleotides in a DNA molecule responsible for synthesizing (making) a polypeptide (protein)
- control of cellular activities involves both DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
Protein Synthesis (Part 1 and 2)
DNA

Watson and Crick Model of DNA
- the uprights are composed of alternating phosphate and deoxyribose molecules
- each rung is composed of a pair of nitrogenous bases held by a relatively weak hydrogen bond
Watson and Crick Model of DNA
- the bases pair according to Chargoff's rules:

A-T (Adenine with Thymine)
C-G (Cytosine with Guanine)
Mystery of DNA
- Mendel is known as the "father of genetics" but he had no knowledge of DNA or genetic material
Nucleotide
- a nucleotide has three parts
- phosphate
- sugar (deoxyribose)
- nitrongenous base (A, T, G, C)
Frederick Griffith
- studied mice infected with a certain strain of bacteria
- theorized that bacteria had "transformed" by transferring some type of molecules
Oswald Avery
- DNA is the material responsible for transformation
- many scientists were skeptical about DNA being the genetic material
Erwin Chargaff
- discovered that nitrogenous bases occur in specific ratios
- Adenine equal with Thymine
- Guanine equal to Cytosine
- "Chargaff's rules"
Alfred Hershey and Martha Chase
- using viruses with radioactive DNA they determined that DNA was in fact the genetic material
Maurice Wilkins and Rosalind Franklin
- using x-ray diffraction they determined that the shape of DNA was a double helix
James Watson and Francis Crick
- discovered that the shape of a DNA molecule must be a double helix
Nitrogenous Bases
A = Adenine
T = Thymine
C = Cytosine
G = Guanine
Process of Replication
- Double stranded DNA "unwinds and unzips" along weak hydrogen bonds between the nitrogenous bases with the help of enzymes (DNA helicase)
Process of Replication
- free nucleotides in the nucleus are then incorporated in sequence
Process of Replication
- two double strands of DNA are formed - each consisting of one old strand and one new strand
- both strands are identical to the original molecule
Process of Replication
- work through the example in your notes to show yourself how the process works
- the end product: 2 new DNA molecules with one new strand and one old strand
Mutations
- gene mutations involve a random change in the chemical nature of DNA
- bases are added or deleted in the DNA sequence or the wrong base may be deleted during replication
Ex: T for a C
- may be visible in the phenotype
Ex: Sickle Cell Anemia - change in 1 base alters normal hemoglobin to sickled hemoglobin
RNA
- there are three types of RNA
1. mRNA (messenger)
2. tRNA (transfer)
3. rRNA (ribosomal)
RNA vs. DNA
1. Sugar
- RNA has ribose and DNA has deoxyribose
2. # of strands
- RNA is single stranded while DNA is double stranded
3. Bases
- RNA uses Uracil (U) instead of Thymine (T), Adenine, Cytosine, and Guanine are the same
Transcription (Part 1)
- DNA -> mRNA (uses enzyme RNA polymerase)
- takes place in the nucleus
- DNA serves as a template for the synthesis of mRNA from free RNA nucleotides in the nucleus
- the mRNA molecules are complementary to the DNA
Codon: every three nucleotides in a mRNA sequence will code for one amino acid
Translation (Part 2)
- mRNA -> tRNA-amino acid -> protein
- Protein = sequence of amino acids
- takes place in the cytoplasm
- mRNA (made during transcription) moves into the cytoplasm where it becomes associated with ribosomes
- specific tRNA molecules (cloverleaf shaped RNA molecules with a 3 base sequence called the anticodon on one side and an amino acid attachment site on the opposite side) pick up amino acids and bring them to the ribosomes in the order determined by DNA
- the anticodon base pairs with a specific codon in the protein. This whole process is catalyzed by enzymes
Example
mRNA -> tRNA -> string of amino acids -> protein

mRNA: AAU UCG CCA

use the mRNA to find the tRNA and also to find the associated amino acids (use the codon chart)
Modern Genetics
- the environment interacts with genes in the development and expression of inherited traits
Examples
Effect of Light on Chlorophyll Production
- when light is present, chlorophyll is produced and leaves are green
Himalayan Rabbit
- when there is a temperature change hair turns black because a gene that codes for a black pigment is turned on
Identical Twin Studies
- twins separated at birth and reunited later in life will show striking similarities (heredity / nature) and striking differences (environment / nurture)
Genetic Engineering
- the transfer of genetic information from one organism to another resulting in the formation of recombinant DNA
- Involves the use of bacterial plasmids as vectors for transferring genes
- enables scientists to insert missing or defective genes into cells which allows those cells to make the corresponding proteins
Cloning
- the process of producing a group of genetically identical offspring from the cells of an organism
- used primarily in agriculture
- plants with desirable qualities can be rapidly produced from the cells of a single plant
- cloning of animals
- occurring since the 1950's
- first tadpole was cloned in 1952
- Dolly the sheep was the first cloned mammal (1996)
- nuclear transfer technology has been used to clone pigs, sheep, goats, cats, mice, dogs, and rabbits
Polyploid Plants
Polyploid: multiple sets of chromosomes in an individual
Triploid: 3N (three copies of each chromosome)
Tetraploid: 4N (four copies of each chromosome)
- these plants tend to be larger and more vigorous than diploid varieties. However some are sterile (seedless)
Types of DNA Mutations
Silent Mutations
- silent mutations are a type of point mutations (1 base change) that DO NOT change the amino acid
Missense Mutations
- type of point mutation where the amino acid changes
Nonsense Mutations
- type of point mutation where the amino acid changes to a stop instruction
Addition (Insertion) Mutation
- a type of frame shift mutation where bases are added to the sequence
Deletion Mutation
- a type of frameshift mutation where bases are deleted from the sequence
Full transcript