DNA Transcription Ribosome mRNA Translation Polypeptide (protein) IntroductionThe Central Dogma of Molecular Biology Cell
DOGMA? This central dogma was develop by Crick. This was a hypothesis on how the code was read from DNA then used to make proteins. Scientists did not like this term for this hypothesis because it sounds like a problem!
DOGMA! Principle, idea, or statement that is considered to be absolutely true. Kind of like a theory!!!!! But Crick called it a DOGMA!!! DNA ---- RNA ----- Proteins!!!!!!
Central Dogma of Biology The flow of information in the cell starts at DNA,
What is the purpose for proteins? antibody: fight diseases Muscle contractions Enzymes Hormones Hair, feathers, beaks, nails, horns, etc. Egg whites Transport proteins: blood(hemoglobin)
Protein Structure Made up of amino acids Polypeptide- string of amino acids ONLY 20 amino acids are arranged in different orders to make a variety of proteins!!!! Amino acids are in the cytoplasm. Assembled on a ribosome
DNA vs. RNA DNA Double Helix Deoxyribose sugar Adenine pairs with Thymine (A-T) Stays in nucleus RNA Single strand Ribose sugar Uracil replaces Thymine! Leaves nucleus to do the work
DNA vs. RNA DNA RNA Deoxyribose Ribsose Thymine Uracil is one of the bases in RNA. There is thymine no thymine. This means A goes with U and G still goes with C. Double Strand Single Strand
Steps to Protein Synthesis Transcription – process where DNA message is changed into mRNA then out of nucleus to the ribosomes!!! 2. Translation – process when mRNA is translated into amino acid chains(protein) on the ribosomes.
How does a protein get built?? • This is where RNA becomes involved. • DNA is too large to get out of the nuclear membrane pores. • SO RNA has to be made to go to the ribosomes!!!
SO, HOW DOES AN AMINO ACID CHAIN GET BUILT? RNA stands for ribonucleic acid
Stars of Translation and Transcription • mRNA • DNA • rRNA • tRNA • Ribsomes • RNA polymerase
Three types of RNA: 1. mRNA “messenger” RNA Carries code for proteins from DNA Carries “codon” 2. tRNA “transfer” RNA Attaches specific Amino Acids to the protein chain by matching the mRNA codon with the anticodon.
RNA TRANSCIPTION There are three (3) types RNA: 1. Messanger RNA – (mRNA) carries messages from the DNA in the nucleus to the ribosomes.
tRNA 2. Transfer RNA – (tRNA) 20 different kinds which are only able to bond with one (1) specific type of amino acid.
rRNA 3. Ribosomal RNA – (rRNA) major component (part) of the ribosomes
3. Ribosomal RNA rRNA Where Protein synthesis occurs
How Does RNA polymerase(complex) know where to start and stop? • Promoter site: starting point on DNA. Specific base sequences that represents a gene. • Termination site: Place where RNA polymerase stops!!! • REMEMBER - only a gene is being read to make mRNA not all of your DNA.
Step 1: RNA polymerase complex attaches to DNA at special places that serve as the start signal(promoter sites). Only one gene!!!!!
Step 2: DNA splits at site of RNA polymerase. RNA polymerase attaches matching bases to form new RNA strand from DNA template.
Step 3: RNA polymerase leaves DNA when reaches the stop signal. RNA strand is released and goes to cytoplasm. DNA rewinds itself into the double helix.
Results of Transcription Strand of mRNA made from the DNA
FYI RNA polymerase doesn’t check for mistakes in the code. Doesn’t cause mutations when there is a few mistakes in proteins unlike replication.
Making mature mRNA Original mRNA transcribed is not mature mRNA Exons:readable segments Of mRNA that go to the ribsome Introns: nonreadable Segments that must be removed before leaving Nucleus.
Exons vs. Introns Once introns removed, mRNA is ready to leave the nucleus!!!!
Cytoplasm Nuclear pores AAAAAA AAAAAA DNA Transcription RNA RNA Processing G G mRNA Export Nucleus Eukaryotic Transcription
Prokaryotic Protein Synthesis • All occurs in the cyotplasm!!!
Transcription is done…what now? Now we have mature mRNA transcribed from the cell’s DNA. It is leaving the nucleus through a nuclear pore. Once in the cytoplasm, it finds a ribosome so that translation can begin. We know how mRNA is made, but how do we “read” the code?
Translation Translationis the process of decoding a mRNA molecule into a polypeptide chain orprotein. ALWAYS read mRNA!!!!!! Three RNAs play the key roles!!
RNA TRANSLATION Protein Synthesis: the formation of a protein using information coded on DNA and carried out by RNA in the assembly of amino acids. • Proteins are: • Amino acids in chains – 20 kinds • Made of 10’s or 100’s or 1000’s of amino acids • Must be arranged in a specific sequence for each type of protein • Function & type of protein is determined by amino acid sequence • DNA makes RNA • RNA constructs amino acids
mRNA - Codons • Read 3 bases at a time on the mRNA called CODONS!!!! • Each combination of 3 nucleotides on mRNA is called a codon or three-letter code word. • Each codon specifies a particular amino acid that is to be placed in the polypeptide chain (protein).
OH NH2 P HO O Adenine N N O N N CH2 O B A S E S H O O Guanine P HO O N NH O SUGAR-PHOSPHATE BACKBONE N NH2 N CH2 O Arginine H O NH2 Adenine P HO O N N O N N CH2 O OH H A Codon
Start codons and Stop codons For translation to begin, there is a START codon. AUG: is the 3 letter codon that starts the process. UAA, UGA, UAG: Stop codons.
Start Codon • Start codon: codon AUG also serves as the “initiator” codon, which starts the synthesis of a protein.
Stop Codon • STOP codon: Codon that signal the end of the protein. (UAA, UAG, & UGA • Besides selecting the amino acid methionine, the codon AUG also serves as the “initiator” codon, which starts the synthesis of a protein
Protein Synthesis: Translation A three-letter code is used because there are 20 different amino acids that are used to make proteins. If a two-letter code were used there would not be enough codons to select all 20 amino acids. That is, there are 4 bases in RNA, so 42 (4x 4)=16; where as 43 (4x4x4)=64.
Translation Therefore, there is a total of 64 codons with mRNA, 61specify a particular amino acid. This means there are more than one codon for each of the 20 amino acids.
Protein Synthesis: Translation Transfer RNA (tRNA) Each tRNA molecule has 2 important sites of attachment. One site, called the anticodon, binds to the codon on the mRNA molecule. The other site attaches to a particular aminoacid. During protein synthesis, the anticodon of a tRNA molecule base pairs with the appropriate mRNA codon.
tRNA Transfer RNA Bound to one amino acid on one end Anticodon on the other end complements mRNA codon If they do not match then the tRNA is rejected!!!!
Methionine A C C 73 1 72 2 71 3 70 4 69 5 68 6 67 59 7 66 Py A* U* 65 64 63 62 C 16 Pu 17 9 A Pu 17:1 13 12 Py 10 49 50 51 52 G C T y G* Py 22 23 Pu 25 47:16 G A 26 47:15 20 20:2 20:1 27 1 43 44 28 42 45 46 29 41 47 30 40 47:1 31 39 Py* 38 U Pu* U 34 36 C 35 A Anticodon Met-tRNA
Parts of a Ribosomes - rRNA Ribosomes are composed of 2 subunits separate in cytoplasm Large Small Contain 3 binding sites – helps tRNA align to codon. E P A