Investigation 3: DNA & RNA By Connor Erickson & Madison Shelpuk

DNA - Structure of DNA DNA is an organic compound. Its made up of repeating subunits called nucleotides. Each DNA molecule consists of two long chains of nucleotides. A DNA nucleotide has three parts: A sugar molecule called deoxyribose. A phosphate group which consists of a phosphorus , P, atom surrounded by oxygen, O, atoms. A molecules that is referred to as a nitrogen-containing base because it contains a nitrogen, N, atom. The four nitrogen-containing bases found in DNA nucleotides are adenine, guanine, cytosine, and thymine.

Structure of DNA continued Adenine and guanine have two rings of carbon, C, and nitrogen, N, atoms. In contrast, cytosine and thymine have only one ring of carbon and nitrogen atoms. Bases with two rings of carbon and nitrogen atoms, such as adenine and guanine, are called purines. Pyrimidines are bases with one ring of carbon and nitrogen atoms, like cytosine and thymine.

The Double Helix In 1953, James Watson and Francis Crick decided the model for the structure of DNA should be the double spiral helix.

Complementary Base Pairing Cytosine pairs with guanine, and adenine pairs with thymine. The DNA nucleotides usually pair in these combinations. These pairs are called complementary base pairs. Complementary base pairs are connected to each other by hydrogen bonds. The complementary nucleotide chains in the DNA model led to suggestions of how DNA might copy itself.

Replication of DNA The process of copying DNA in a cell is called replication. During replication, the two nucleotide chains separate by unwinding, and each chain serves as a template for a new nucleotide chain. The first step is the separation of the two nucleotide chains. The point at which the two chains separate is called the replication fork. The chains are separated by enzymes called helicases. As the helicase enzymes move along the DNA molecule, they break hydrogen bonds between the complementary bases, and the chains separate. Enzymes called DNA polymerases bind to the separated chains of DNA. As DNA polymerases move along the separated chains, new chains of DNA are assembled using nucleotides in the surrounding medium that are complementary to the existing DNA chains. Nucleotides are joined to the new chains by covalent bonds between deoxyribose sugars and phosphate groups. They are joined to the original nucleotide chain by hydrogen bonds.

Replication of DNA continued When replication is completed, two new exact copies of the original DNA molecule are produced and the cell is ready to undergo cell division. Each new DNA molecule consists of one new nucleotide chain joined by hydrogen bonds to a nucleotide chain from the original DNA molecule.

Accuracy and Repair The process of DNA replication is extremely accurate – there is about one error in every 10,000 paired nucleotides. A change in the nucleotide sequence at even one location is called a mutation and can have serious effects in new cells. A repair process helps to keep the error rate to one in 1 billion nucleotides. DNA can also be damaged by a variety of things such as ultraviolet radiation from the sun or chemicals.

RNA – Structure of RNA Like DNA, RNA is a nucleic acid made up of repeating nucleotides, but the structure is much different. The sugar molecule is ribose, and uracil replaces thymine. Uracil – not thymine – pairs with adenine in RNA.

Types of RNA Messenger RNA (mRNA) Made up of RNA nucleotides in the form of a single uncoiled chain. mRNA carries genetic info from the DNA in the nucleus to the cytosol of a eukaryotic cell. Transfer RNA (tRNA) Made up of a single chain of about 80 RNA nucleotides folded into a hairpin shape that binds to specific amino acids. Ribosomal RNA (rRNA) The most abundant form of RNA. rRNA is made of RNA nucleotides in a globular form. Joined proteins, rRNA makes up the ribosomes where proteins are made.

Transcription One function of RNA is to carry genetic information from DNA in the nucleus to the cytosol where it can produce proteins.

Products of Transcription The products of transcription are called transcripts and are the different types of RNA molecules including mRNA, tRNA, and rRNA.

Fundamentals of Genetics

Genetics Genetics is the field of biology devoted to understanding how characteristics are transmitted from parents to offspring. The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding. Genes correspond to regions within DNA, a molecule composed of a chain of four different types of nucleotides—the sequence of these nucleotides is the genetic information organisms inherit. DNA naturally occurs in a double stranded form, with nucleotides on each strand complementary to each other. Each strand can act as a template for creating a new partner strand—this is the physical method for making copies of genes that can be inherited.

Recessive and Dominant Traits There are  two types of genes for each trait: Dominant, and Recessive. The combination determines the trait to be expressed at the time of conception, sperm cell fuses with the ovum to create a new cell called Zygot with 46 (23 pairs) chromosomes. On each pair of Chromosomes, there are two genes that determine the inherited trait. This gene pair is called allele. If the two pair of allele are identical (one pair from each parent), the off spring will express that trait.

Chromosomes and Genes A chromosome is made of a very long strand of DNA and contains many genes . The genes on each chromosome are arranged in a certain and particular sequence, that each gene has a particular location on the chromosome . In addition to DNA, chromosomes contain other chemical components that influence gene function. Sex Chromosomes: The pair of sex chromosomes determines whether a fetus becomes male or female. Males have one X and one Y chromosome. A male's X comes from his mother and the Y from his father. Females have two X chromosomes, one from the mother and one from the father. In certain ways, sex chromosomes function differently than non-sex chromosomes. A gene is a segment of DNA containing the code used to synthesize a protein. Genotype: is a persons unique combination of genes. The genotype is a complete set of instructions on how that persons body synthesizes proteins and how the body is supposed to function and be built.

Genotype and Phenotype Genotype: is the "outward, physical manifestation" of the organism. Which are the physical parts, the sum of the atoms, molecules, macromolecules, cells, structures, metabolism, energy utilization, tissues, organs, reflexes and behaviors. Anything that is part of the observable structure, function or behavior of a living organism. Phenotype: is the "internally coded, inheritable information" are carried by all living organisms. This stored information is used as a "blueprint" or set of instructions for building and maintaining a living creature. These instructions are found within almost all cells, they are written in a coded language (the genetic code). They are also copied at the time of cell division or reproduction and are passed from one generation to the next ("inheritable"). These instructions are intimately involved with all aspects of the life of a cell or an organism. They control everything from the formation of protein macromolecules, to the process of metabolism and synthesis.

Incomplete Dominance & Condominance Incomplete Dominance: is a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele. This in which results in a combined phenotype. Codominance: is a condition which both alleles of a gene pair in a heterozygote are fully expressed, with neither one being dominant or recessive to the other.