DNA DE - OXY - RIBO - NUCLEIC ACID
DNA Structure DNA consists of two molecules that are arranged into a ladder- like structure called a Double Helix. A m olec ule of DN A is m ade up of millions of tiny subunits called Nucleotides. Each nucleotide consists of: 1. Phosphate group 2. Pentose/Ribose sugar 3. Nitrogen base
Nucleotides Phosphate Nitrogen Base Deoxyribose Sugar
Nucleotides The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the rungs or steps of the ladder. * There are four types of nitrogen bases.
Nucleotides A Adenine T Thymine C Cytosine G Guanine
Nucleotides Each base will only bond with one other specific base. Adenine (A) pairs with Thymine (T) Cytosine (C) pairs with Guanine (G)
DNA Structure Because of this Complementary Base Pairing, the order of the bases on one side of the DNA molecule/ ladder determines the order of the bases in the other, opposite side of the ladder.
One side of the DNA molecule Opposite side of the DNA molecule A T C T C A The complimentary Nitrogen bases fit together chemically like puzzle pieces. G A G T G C T A
DNA Structure To crack the genetic code found in DNA we need to look at the sequence of bases. The bases are arranged in triplets called codons. * YOU give it a try. A G G - C T G - A A G - T C C - T A G T C C - G A C - T T C - A G G - A T C
DNA Structure A segment of DNA is known as a gene. Each gene has a unique sequence of nitrogen bases. These gene sequences are specific instructions for making proteins and proteins are V ERY im portant building blocks of organisms. It is these proteins (and com binations of proteins) that build cells & tissues or work as enzymes (c hem ic al communicators) in organisms. Proteins are m ade of m any c hains of amino acids.
The sequence of the nitrogen bases is a code for instructions/information much the same way a bar code provides an each way for organizations to identify products, services, accounts, vehicles, even people.
Morse Code is another form of information hidden in a sequence. Interpret the follow Morse Code message: _.. _.._._.._. _._..... _
The sequence of nitrogen bases in the gene determines the order of the amino acids in the protein. A change in the amino acid order results in a different protein being made. Different proteins create different tissues or give instructions for different traits in organism s.
DNA Gene Protein Trait
DNA Structure Video - 1:19
Steps to Copying DNA: During the S1 Phase of Interphase 1. Enzymes act to separate the sides of the DNA at the bond between the nitrogen bases. (like a zipper unzipping) * Occasionally the DNA replication process doesn t go perfectly and that can lead to problems called Mutations. We will discuss this later. 2. Nucleotides, floating freely around the molecule, then attach themselves like magnets at the nitrogen base bonding sites of both halves of the molecule. 3. When all open nitrogen base bonding sites are full, a new, complete, HOPEFULLY identical DNA molecule is formed. There now are two. Both are copies of each other. 4. The nucleus & cell are now ready to undergo cell division.
* Genes (all instructions) are found in the nucleus of cells. * Proteins are synthesized in the ribosomes in the cells. So, if the instructions are in the nucleus for making proteins is in the nucleus and proteins are made in the ribosomes how do these instructions get from the nucleus to the ribosomes? * The instructions in the genes, for constructing the proteins, are carried from the nucleus to the ribosomes of the cell by another type of nucleic acid, known as ribonucleic acid or RNA
* RNA molecules are similar to DNA. But, instead of the sugar Deoxyribose, RNA has the sugar Ribose. Also, instead of the nitrogen base Thymine (T), it contains the nitrogen base Uracil (U). * Three main types of RNA are: Messenger RNA (mrna) Ribosomal RNA (rrna) Transfer RNA (trna)
Controlling Genes: Since all somatic/body cells of the same organism have all the same DNA, it's important to know, each cell can turn-off or turn-on only the genes needed for that particular type of cell. THIS is IMPORTANT...imagine if your muscle cells didn't know they were muscle cells and produced proteins for bone cells?
Mutations Sometimes mistakes happen when DNA is being copied. If DNA is not copied exactly, the proteins made from the instructions might not be made correctly. These mistakes are known as mutations, which are any permanent changes to the DNA sequence. Outside factors can affect the DNA replication. Xrays, sunlight, other forms of radiation and some chemicals are known to cause mutations.
Results of a Mutation *Without correctly coded proteins, an organism may not be able to grow, repair, or maintain itself. *A change in a gene or chromosome can change the traits of an organism. *If a change occurs in a somatic cell, all the cells that form from that cell will have the same change. (cancers) *If the change occurs in a gamete, then the change may be in every cell of the offspring's body. *Most times we think of mutations as being negative, but some mutations can actually be beneficial. (natural selection)
THE END Now, study these notes a few minutes each night! (There could be a surprise assessment in your future!)