DNA The Secret of Life Deoxyribonucleic Acid DNA
DNA The Secret of Life
Deoxyribonucleic Acid • DNA is the molecule responsible for controlling the activities of the cell • It is the hereditary molecule • DNA directs the production of protein
Structure of DNA • In 1953, Watson and Crick proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases. • Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring.
Structure of DNA • Because DNA is composed of two strands twisted together, its shape is called double helix. • A double helix resembles a twisted ladder.
Nucleotides • DNA is made up of subunits called nucleotides • Nucleotides consist of the backbone, which is made of sugar (deoxyribose) and phosphate, as well as a nitrogenous base
Nucleotide Nitrogen base Phosphate Sugar
How Did DNA Get its Name? • Based on what you just learned, how do you think deoxyribonucleic acid (DNA) got its name?
Nucleotides • A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen. • In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine (A) Guanine (G) Cytosine (C) Thymine (T)
Nucleotide Sequence • The four nucleotides are represented by the first letter in their name – Adenine – Guanine – Thymine – Cytosine
Nucleotide Sequence • In DNA, Adenine always pairs with Thymine • Cytosine always pairs with Guanine
Nucleotides • Nucleotides stack on top of one another forming the double helix, or twisted ladder
DNA Building • Click here to link to a DNA building activity online!
Go Get It Moment! • When you hear “Move it!” you will have 30 seconds to come get one piece of paper with an A, G, T, or C on it. • Then find someone else in the room whose letter correctly matches with your nucleotide letter and stand by that person. • What are the questions? • “Move it!”
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Go Get It Moment! • When you hear “Double Helix”, you will have 1 minute to make a classroom DNA strand by standing next to another pair of nucleotides • What questions are there? • “Double Helix”
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DNA Replication • In order for cells to divide, DNA must be able to make exact copies of itself – This process is known as DNA Replication
DNA Replication • DNA Replication occurs before mitosis and meiosis • Replication results in two identical DNA daughter strands from one mother strand
Process of DNA Replication • The DNA strand is unzipped at the hydrogen bonds by an enzyme named helicase. • Nucleotides in the nucleus then find their corresponding nucleotides on each of the two open DNA strands and produce two new DNA double helixes.
Link to DNA Replication Animation • Click here to see how DNA Replication works
Protein Synthesis • The main job for DNA is to direct the production of protein • Protein makes tissues and organs and carries out the organism’s metabolism • Proteins are polymers (chains) of amino acids
Protein Synthesis • The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein
RNA • RNA is a nucleic acid composed of nucleotides that is crucial in making protein • There are three differences between DNA and RNA – RNA is a single strand – The sugar in RNA is called Ribose instead of DNA’s Deoxyribose – Like DNA, RNA has 4 nitrogenous bases, but instead of Thymine, Uracil is the 4 th base
RNA as a Single Strand • You recall that DNA looks like a twisted ladder and is referred to as a double helix • RNA looks like half a ladder – There is only one side to RNA
RNA Contains Ribose • Remember how DNA got it’s name? – It is a nucleic acid with deoxyribose as the sugar on the backbone – Hence the name Deoxyribonucleic acid • Ribonucleic acid (RNA) has the sugar ribose on it’s backbone
RNA Has Uracil • Remember the base pairs in DNA? – Adenine pairs with Thymine – Guanine pairs with Cytosine
RNA Has Uracil • In RNA – Adenine pairs with URACIL – Guanine pairs with Cytosine
Making Protein • Protein production starts with DNA • DNA passes instruction to RNA • RNA carries out the work of linking together chains of amino acids
Three Types of RNA • There are three types of RNA involved in Protein Synthesis – Messenger RNA (m. RNA) – Ribosomal RNA (r. RNA) – Transfer RNA (t. RNA)
Messenger RNA • Messenger RNA (m. RNA), brings instructions from DNA in the nucleus to the cell’s factory floor, the cytoplasm – On the factory floor, m. RNA moves to the assembly line, a ribosome – Remember that a ribosome is either a free-floating small dot in the cell or is attached to the endoplasmic reticulum making it “rough” ER
Ribosomal RNA • The ribosome, made of Ribosomal RNA (r. RNA) binds to the m. RNA and uses the instructions to assemble the amino acids in the correct order
Transfer RNA • Transfer RNA (t. RNA) is the supplier • Transfer RNA delivers the amino acids to the ribosome to be assembled into a protein
Genetic Engineering • The manipulation of genes within a cell or organism • Gene Mapping – finding location of genes on the chromosomes.
Gene Splicing • • • Locate DNA Sequence Enzymes are used to separate the DNA of a particular location on the gene. New DNA can be spliced in or RECOMBINED with the remaining DNA. – This is known as Recombinant DNA
Gene Splicing • • The new DNA will have new characteristics. First use of this new technology was to manufacture human insulin for diabetics.
Gene Splicing • One of the most interesting feats accomplished by genetic engineering is the splicing DNA from fire flies into a tobacco plant – The plant will glow in the dark.
Transcription • The production of messenger RNA (m. RNA) is known as Transcription • DNA acts as a template for the RNA molecule • To View a Link to Transcription Animation Click Here.
Transcription • The main difference between DNA Replication and transcription is that transcription results in one single strand of RNA rather than an exact duplicate of a double stranded DNA molecule • Much of the information on the m. RNA strand codes for specific amino acids to make protein
The Genetic Code • A code is necessary to turn the language of RNA into the language of amino acids and proteins • The four nitrogenous bases make up the code – The code letters are A, G, T, and C • A set of three letters makes a “word” called a Codon – There are 64 possible codons
Codon
Amino Acids • There are 20 different amino acids that make up proteins
The Genetic Code • As you could see on the chart of amino acids, there are more than one codon that code for certain amino acids – This results in fewer errors in protein synthesis
The Genetic Code • All organisms use the same genetic code • This provides evidence that all life on earth may have evolved from the same origin
Ribosomes • The newly produced strand of m. RNA travels from the nucleus to the cytoplasm where it attaches to a ribosome • The ribosome is the actual site for protein synthesis
Translation: From m. RNA to Protein • The process of “reading” the three letter “words” , or codons, is known as translation • Translation takes place at the ribosomes in the cytoplasm – The amino acids are free-floating in the cytoplasm and congregate at the ribosome during protein synthesis
The Process of Protein Synthesis • The first codon is usually A-U-G, methionine, which starts the production of a new protein • Following the start codon, the remaining codons call for amino acids in the order in which they appear on the m. RNA strand
Transfer RNA (t. RNA) Amino acid • At the ribosome, Transfer RNA (t. RNA) identifies the code through translation and finds the appropriate amino acid matching the codons – Each t. RNA molecule only attaches to one specific amino acid – The Anticodon on the bottom of the t. RNA molecule corresponds with the codons on the m. RNA strand Transfer RNA molecule Chain of RNA nucleotides Anticondon
Protein Synthesis Animation – Click Here to Link to An Animation
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