Week 2 Notes
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This 7 page Class Notes was uploaded by Whitney Marie Halaby on Friday September 9, 2016. The Class Notes belongs to BIO 190 at Towson University taught by Dr. Elizabeth O'Hare in Fall 2016. Since its upload, it has received 102 views. For similar materials see Introductory Biology for Health Professions in Biology at Towson University.
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Date Created: 09/09/16
BIO 190 Notes Week 9/69/8 DNA has multiple functions o Stores and passes on genetic info 2 type of nucleic acids: DNA & RNA RNA o Single stranded o Has U instead of T o The sugar is ribose o 3 part nucleotide: 5 carbon sugar (ribose that is negatively charged), phosphate group o RNA is made from a DNA template o Polynucleotide sequence Nucleotides are linked together by dehydration reactions o DNA is transcribe to make RNA o G – C o A – U o Using the base pair rules makes it possible to predict RNA sequence o DNA Sequence: TAC GCG TAT GAG CTA o Complementary Strand: ATG CGC ATA CTC GAT o RNA Strand: AUG CGC AUA CUC GAU o It is important that cells make 2 identical copies of DNA during replication o RNA molecules carry accurate instruction for making proteins DNA Replication o Also known as semiconservative model o DNA replicates in the opposite directiom o Purpose: cell production, wound repair, organismal growth (growth in size) o Replicated DNA must be an exact copy when it isn’t an exact match it is a mutation o Advantages: Make sure all cells carry genetic info Have genetic instructions available for gamete development o How it happens – Brief Overview: 1. Two strands of parental DNA separate 2. Free nucleotides are going to bind to the parent strand following the base pairing rules 3. Enzymes (ligates – blue) generate new sugar phosphate backbone – the phosphate of one nucleotide is linked to the sugar group of the adjacent nucleotide 4. Two identical daughter strands are formed – half of the parent strand half of the daughter strand – the daughter strand is called the semiconservative model o Detailed Overview of how it happens: 1. Proteins attach to each ori causing a separation of the 2 strands – the opening DNA causes bubbles to form. Topoisomerase (an enzyme): unwinds DNA. Helicase ( an enzyme): pry’s apart the double helix, breaks the hydrogen bond and makes the bubble bigger 2. DNA polymerase (RNA primer provides the location) adds nucleotides to 3 prime –OH the phosphate group (carbon 5) on the incoming nucleotide attaches to the –OH group (carbon 3) of the first nucleotide nucleotides are added in the 5 prime to 3 prime direction a. RNA primer is complementary to DNA sequence b. RNA primer laid down gives RNA polymerase a 3 prime OH to attach to a 5 prime phosphate c. Where there is RNA primer U will be used instead of T – but only there – it will eventually all be DNA only one or two nucleotides d. DNA made in a 5 prime to 3 prime direction but read templates 3 prime to 5 prime e. DNA polymerase requires a 3 prime hydroxyl group before synthesis can be initiated f. DNA polymerase has proof reading ability – changing nucleotides out that have been affected by radiation and toxic chemicals g. Leading strand: the strand that is continuously synthesized, works towards a forking point h. Lagging Strand: strand that is NOT continuously synthesized since new DNA is only made outward (5 prime to 3 prime) i. Okazaki fragments: DNA fragments – fragments are attached by DNA ligase j. A& C are the leading strands o Challenges: Complex coordination of multiple enzymes – proteins untwist – recruit nucleotides – solidify covalent bonds One out of one billion nucleotides is incorrectly paired Speed of the process – takes about one hour to copy the genome of e.coli and a few hours for a human 3. How does Replication happen so fast? Happens at multiple places along the chromosome The slower it goes the more prone it is to errors Ori: origin of replication DNA creates a bubble at ori and DNA replication occurs at multiple ori’s Transcription o Protein synthesis o RNA made from DNA o Provide genetic messages in the form of RNA o RNA polymerase looks for the promoter to know where to start o Steps 1. Initiation: RNA polymerase attaches to the promoter (this marks the beginning of RNA synthesis) – once attached RNA polymerase starts to synthesize RNA 2. Elongation: new RNA strand grows as RNA polymerase continues to add nucleotides – RNA nucleotides are linked together – free nucleotides form H bonds with bases of DNA template – as synthesis continues growing RNA molecules peel away from the DNA template, allowing the two separated DNA strands to come back together in the region already transcribed 3. Termination: when RNA polymerase reaches the terminator DNA sequence the RNA polymerase molecule detaches from newly made pre mRNA strands and the gene o Components needed DNA Nucleotides RNA polymerase—an enzyme that forms new RNA strands by following the base pair rules Promoter: determines were transcription starts and on which strand Termination sequence: DNA signal at the end of the gene which marks the end of the gene o First step to creating proteins o Prokaryote: bacteria, pro meaning before, karyo meaning no nucleus in the bacteria, transcription and translation take place in the cytoplasm o Eukaryotic: mammals, plants, transcription takes place in the nucleus and is then processed then exits into the cytoplasm and proteins are made off of mRNA – translation happens in the cytoplasm o Genes control phenotypic traits through expression of proteins o Genotype: genetic make up of organisms o Phenotype: physical manifestation of genotypes – genotypes are linked to phenotypes by proteins o Protein synthesis: genes that control phenotypic traits mRNA Processing o Prior to nuclear export, mRNA is modified or processed o Addition to nucleotides (that are not encoded in the sequence) to end mRNA o Modifications to mRNA: Addition of extra nucleotides to end of premRNA that are not incorporated into peptide sequence Small cap: a modified form of a G nucleotide and the 5 prime end and 5 prime cap Large cap: a chain of 50250 A nucleotides at the 3 prime end (polyA tail) Facilitate export of mRNA from nucleus Protect mRNA from degradation by cellular enzymes Help ribosomes bind to mRNA RNA Splicing: Cutting introns out of the mRNA and the joining of exons together prior to the mRNA leaving the nucleus – ONLY IN EUKARYOTES Provides a means to provide multiple polypeptides from a single gene into processing in eukaryotes Archibald Garrod o Worked to discover the relationship between genes and proteins o Broad hypothesis o Specific hypothesis o First person to link phenotype to genotypes o Studied pee Beadle and Tatum o Mold o Showed that each mutation had a mutation in a single gene o Proteins were malformed o One gene on an enzyme/protein synthesis Translation o Makes proteins that carry out cellular function o Steps of Translation 1. Initiation: brings together mRNA and tRNA bearing the first amino acid (Met) and the two subunits for a ribosome – establishes where translation will begin – initiation establishes exactly where translation will begin this ensures mRNA codons are translated into the correct AA sequence translation does not start on the exact end of the mRNA (ribosome looks for AUG [Met] start signal – initiation occurs in two steps 1. mRNA molecule binds to a small ribosomal subunit and anticodon of tRNA Met basepairs with a start codon 2. Initiator tRNA carries Met with anticodon UAC and basepairs with start codon AUG 2. Elongation: amino acids are added one by one to the previous amino acid (this occurs in a 3 step process) 1. The anticodon on incoming tRNA molecule is carrying the appropriate AA then pairs with mRNA codon in ribosomal A site 2. The growing polypeptide separates from old tRNA onto the P site and attaches by a new peptide bond to an AA carried by the tRNA in the A site ribosome catalyzes formation of the peptide bond 3. P site tRNA (which doesn’t have an AA) leaves the ribosome and the ribosome translocate (moves) to the other tRNA (holding the growing peptide) from A site to P site 3. Termination: occurs when a stop codon reaches the ribosome’s A site – stop codons are UAA, UAG, UGA which are not amino acids but they act as signals to stop translation – the completed polypeptide is then freed from the last tRNA – ribosome splits back into two subunits o mRNA is made into protein 3 letter ‘words’ of nucleic acids (codons) are converted to the amino acid ‘word’ proteins DNA RNA Protein Nucleic Acid Nucleic Acids Amino Acids o Purpose: produce polypeptides o Needs: mRNA: instructions for making the new polypeptide amino acid supply tRNA: a molecule used to interpret the instructions (mRNA) enzymes: for adding the amino acid to the tRNA ATP: used for energy to add the amino acid to the tRNA by the enzyme Ribosomes: a large protein structure in the cytoplasm that coordinates the functions of mRNA and tRNA and catalyzes the synthesis of polypeptides a big protein that is only in the cytoplasm because that is where translation occurs – it also coordinates the function of mRNA and tRNA o Two subunits o Large subunit: made up of proteins and a kind of ribosomal RNA (rRNA) o Small subunit: made up of proteins and a kind of rRNA o Two subunits come together and work as a vice/clamp holds tRNA and mRNA molecules close, allowing AA to be carried by tRNA molecule to be connected to a polypeptide o 20 different amino acids o tRNA: a special type of RNA that converts 3 letter ‘words’ of codons (nucleic acids) on mRNA amino acid ‘words’ of proteins – tRNA must carry out two functions o 1. Pick up the appropriate amino acid – one specific amino acid attaches to a specific tRNA (each AA is joined to the correct tRNA by a specific enzyme using a molecule of ATP as energy to drive the reaction) – 1 enzymes is specific for each different type of AA (although all tRNA molecules are similar, there is a slightly different variety of tRNA for each AA) o 2.Recognize the appropriate codon in the mRNA using the tRNA’s anticodon Anticodon: a special triplet of bases that is complementary to the codon triplet on the mRNA – during translation anticodons on tRNA recognizes a specific codon on the mRNA by using basepairing rules o Essential amino acid: amino acids we need to get from our environment to survive o Non essential amino acid: an amino acid that is not essential to be part of an individuals diet because the body can produce them on their own o 3 bases ( a triplet code) are encoded for 1 amino acid – the number 3 is needed which means 64 triplet possibilities o Genetic Code Marshal Nierburg: deciphered first codon, 1961, synthesized an artificial RNA molecule – experiment: add uracils to a test tube with ribosomes and other ingredients used to carry out translation this resulted in protein being composed of only one amino acid (phenylaline Phe) 3/64 triplets do NOT designate amino acids but serve as stop codons that mark the end of translation AUG has a dual function – it signals where translation occurs – codes for amino acid (Met) – provides a start signal for protein polypeptide chains 61/64 triplets code for amino acids DNA: TAC TTC AAA ATC mRNA: AUG (indicates start site for translation) AAG UUU UAG Protein (use the chart): met. Lys. Phe. Stop (not an amino acid) – Met. Lys. Phe. All are amino acids Nearly all organisms share the same genetic code, this allows scientists to create o Genetic therapies o Research purposes o Agriculture benefits o For fun The genetic code outlines that all organisms must share a common ancestor which means we are all related evolution
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