Presentation on theme: "DNA, RNA, and Protein Synthesis Chapter 10. Discovery of DNA 1928- Fredrick Griffith –He found that when harmless bacteria are mixed with dead harmful."— Presentation transcript:
Discovery of DNA 1928- Fredrick Griffith –He found that when harmless bacteria are mixed with dead harmful bacteria, the harmless will absorb the genetic material of the harmful and become harmful themselves –Transfer of genetic material is called transformation
Discovery of DNA 1940s- Avery and colleagues –Wanted to know what caused transformation (DNA, RNA, or protein) –They separated these individual parts and tested them. –They found DNA was the cause of transformation –In other words, they found if harmless bacteria took in harmful bacteria’s DNA, the harmless became harmful.
Discovery of DNA 1952- Hershey and Chase –Wanted to test whether DNA or protein was the genetic material that viruses pass on when they infect an organism. –They used viruses that infect bacteria (called bacteriophages) –They radioactively labeled the DNA and the protein (this allowed them to trace the path of each) –They found DNA was injected into the bacteria to infect it, not protein. So DNA was the genetic material
Discovery of DNA 1950s- Watson, Crick, Franklin, and Wilkins –Franklin and Wilkins discover DNA is helical –Watson and Crick build a model of DNA and determine it is a double helix
DNA Structure Made of nucleotides (so nucleotides are the monomers of DNA!) –Nucleotides have 3 parts: 1.Nitrogenous base (there are 4 kinds) 2.Phosphate Group 3.5 carbon sugar called deoxyribose
DNA Structure Nitrogenous bases: –Contain nitrogen and is a base –Purines- (double ringed) Adenine (A) Guanine (G) –Pyrimidine's- (single ringed) Cytosine (C) Thymine (T)
DNA Structure DNA is made up of 2 straight chains of nucleotides The bases on each of those chains are attracted to each other and form hydrogen bonds The force of thousands or millions of hydrogen bonds keeps the two strands of DNA held tightly together
DNA models Since the sugar- phosphate “backbone” of DNA never change, we often simplify DNA into the letters of the nitrogenous bases. For example, this DNA strand can be simplified to… TGAC ACTG
DNA Structure Base pairing rules in DNA: –Hydrogen bonds form between specific pairs –Adenine ALWAYS pairs with Thymine –Cytosine ALWAYS pairs with Guanine –These pairs (A-T and C-G) are called complementary base pairs –Each complimentary pair contains one single and one double ringed base
DNA Structure Because of the base pairing rules, one strand of DNA is complementary to the other strand (otherwise they would not stick together!) –The order of the nitrogenous bases on DNA is called its base sequence –So if one strand has a base sequence of TGCC, the other strand will have ACGG.
Let’s Practice Write the complimentary strand for… TGACCGAT TGGCCAATATA
DNA Replication DNA Replication is the process by which DNA is copied in a cell before the cell divides.
DNA Replication Step 1: Enzymes called Helicases separate the two strands of DNA Hydrogen bonds are broken Replication fork : Y-shaped region formed as bonds are broken
DNA Replication Step 2: Enzymes called DNA polymerases add nucleotides to the separated strands Nucleotides are found floating free in the nucleus The addition of new nucleotides occurs in opposite directions addition towards the replication fork addition away from the replication fork
DNA Replication In Eukaryotes, several replication forks form and replication continues until all of the DNA has been replicated. –If only 1 was formed it would take too long to replicate DNA (53 days for humans!!) Once replication is complete, 2 DNA molecules exist. –Each molecule is made from one old strand and one new This is called semi-conservative replication since each new strand has kept one of the original strands.
DNA Replication Replication is usually very accurate –There is only about 1 error for every BILLION nucleotides added! –The reason is that DNA Polymerases also “proof-reads” the DNA and fixes any errors during replication
DNA Replication If an error does occur, it results in a different nucleotide sequence in the new DNA strands called a mutation –A change in even one nucleotide can be very harmful to an organism –Some mutations can affect the growth of cells, causing growth to accelerate, resulting in cancer –Changes can be good - mutations sometimes lead to adaptations and therefore evolution
Protein Synthesis DNA is the “code” for hereditary characteristics. The genetic code is how organisms store hereditary information which is first translated into amino acids DNA codes for all of the body’s proteins (like enzymes)
Protein Synthesis –Genes are sequences located in DNA that code for specific characteristics –The code (or gene) for the production of the protein melanin is in your DNA and creates your hair and skin color
Protein Synthesis The “code” or “recipe” within DNA cannot be read directly- –DNA cannot leave the nucleus and proteins are made in the cytoplasm of cells –So the code is transcribed (copied) and translated (turned into something useful) by ribonucleic acid ( RNA ) However,
Protein Synthesis Remember, proteins make us who we are –Responsible for chemical reactions hereditary characteristics (such as eye color) –Recall the monomers of proteins are amino acids –DNA holds the recipe for the amino acid sequence of all the proteins we make
DNA vs RNA Both are made of nucleotides Both are involved in protein synthesis DNA has the sugar deoxyribose, while RNA has the sugar ribose RNA uses the nitrogenous base uracil (U) instead of thymine (T) used in DNA RNA is single stranded, while DNA is double stranded RNA is usually MUCH shorter than DNA
Protein Synthesis Transcription The first step in protein synthesis is transcription: –RNA polymerase (enzyme) binds to a genes promoter region A promoter is just a specific nucleotide sequence where the RNA polymerase can attach –The RNA attaches to the RNA polymerase and the DNA begins to uncoil
Transcription cont. The RNA polymerase adds complimentary nucleotides resulting in a straight chain RNA molecule –The DNA code determines what bases will be added –Example if the DNA code for a gene is ATCCGTT, then the RNA will be UAGGCAA –Remember, RNA does not have Thymine, it has Uracil!!
The copying of DNA continues until the RNA polymerase reaches a termination signal –That is a specific sequence of nucleotides that tells the RNA polymerase to “STOP” and release the RNA and DNA –The RNA is called mRNA, because it is the messenger of the “code” from the DNA to the ribosomes Transcription cont.
Once the newly made RNA leaves the nucleus it attaches to a ribosome at the promoter region. Ribosomes will “read” 3 nucleotides in the RNA code at a time –These 3 nucleotides are called codons. –Each Codon codes for START signal Amino Acid STOP signal Protein Synthesis - Translation
Example, the sequence AUG codes for the amino acid Methionine a START signal (This is the only start signal) –ALL mRNA molecules start with AUG, otherwise, they would not have a start region for protein synthesis Translation cont.
So, in translation, the RNA is translated into amino acids, which are put together to form proteins (or polypeptides) The translation occurs with the help of tRNA, which carries the amino acids Translation cont.
When the ribosome reads the start sequence (AUG), a tRNA molecule comes along with the anticodon –The anticodon is the complementary sequence. –The complementary bases bond with each other and the amino acid methionine begins the protein synthesis within the ribosome –So, tRNA transfers amino acids to the ribosome Translation cont.
Recall there are only 20 amino acids Most amino acids have more than one codon –Example, Leucine’s codons are UUA, UUG, CUU, CUC, CUA, and CUG But each codon codes for ONLY 1 amino acid –Example, CUU only codes for Leucine and nothing else Amino Acids
After the start sequence, the ribosome moves to the next codon. –Let’s say the next codon is GUC –Now a tRNA that has the anticodon for that codon attaches to the ribosome carrying the amino acid Valine. –The amino acid Valine attaches to the Methionine from before (now we have a dipeptide!) Translation cont.
This process continues and the polypeptide grows until the STOP codon is reached –UAA, UAG, and UGA are the only stop codons –The protein, ribosome and all RNA is released to perform other needed functions Translation cont.
Protein Synthesis - Overview Amino Acids are listed by their CODON!!! –That would be the 3 nucleotide sequence on the mRNA
Protein Synthesis - Overview Now use the CODON chart to figure out the amino acid sequence