General Biology Lecture 5 Notes
General Biology Lecture 5 Notes 101-NYA-05
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This 7 page Class Notes was uploaded by CatLover44 on Sunday September 25, 2016. The Class Notes belongs to 101-NYA-05 at Dawson Community College taught by Virginia Hock in Fall 2016. Since its upload, it has received 3 views. For similar materials see General Biology 1 in Biology at Dawson Community College.
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Date Created: 09/25/16
General Biology Course Number: 101-NYA-05 Lecture no. 5 Date: Wednesday, September 7, 2016 Professor: Virginia Hock Topics Covered: protein synthesis; functions and types of nucleic acids, the steps involved in protein synthesis (transcription and translation), which molecules are involved with which steps of protein synthesis, transcribing and translating DNA (codons and anti-codons) Nucleic Acids and Flow of Genetic Information • Nucleic acids store and transmit hereditary information in genes, which are the units for inheritance o DNA gives instructions, and RNA follows those instructions o DNA has oxygen in its sugar molecules, RNA doesn't • Nucleic acids are made of nucleotides that connect and form polynucleotides • Easy ways to distinguish between RNA and DNA: o DNA is double-stranded, RNA is single-stranded o RNA doesn't contain thymine (T), it's version of thymine is uracil (U), so if you see U, you know you're looking at RNA. o MEMORIZE THIS TABLE! • There are three types of RNA: mRNA, tRNA, and rRNA. o mRNA = messenger RNA, tRAN = transfer RNA, rRNA = RNA + protein. • We need DNA for cell replication: it contains genes that determine which proteins are made. DNA Assembly: Complementary Base Pairing • Recall: A only binds with T, and C only binds with G (DNA TO RNA). This forms the basis of complementary base pairing. • DNA will not exit our nucleus, mRNA is DNA’s “helper” in this sense because it leaves the nucleus for it. • Note: DNA’s double-stranded structure makes it more stable than RNA. • Our height, eye colour, hair colour, and muscle mass are determined by nucleotide sequences. o A change in a nucleotide sequence causes a different protein to be made. • We need DNA, RNA, and genes to make proteins. • Remember the four structures of proteins, and their properties! o 1. Primary structure: monomers that connect to each other to make polymers. Controls shape and function (most important structure) o 2. Secondary structure: alpha coils and beta pleated sheets. Beta pleated sheets make up the core of globular proteins. H-bonds formed between amino and carboxyl groups in a polypeptide backbone. Like a telephone cord because they can withstand some tension, but too much tension will cause these structures to break. o 3. Tertiary structure: held together by many attractive forces (hydrogen bonding, ionic bonding, non-polar interactions, disulfide bridges), and contains more than one polypeptide. The 3-D structure of a polypeptide is determined by the four different attractive forces listed, and the interactions between the R groups of amino acids. o 4. Quaternary structure: fusion of two or more polypeptides. This structure is formed by the interactions within the polypeptide chains that comprise the protein. Many proteins are made of two or more polypeptide chains that stick together to make one macromolecule. Transcription and Translation Transcription • In the transcription process (inside the nucleus), a strand of DNAs copied (template strand). o DNA is copied, and turned into a form that RNA understands. 2 o The part of the gene that is meant to be copied is separated before transcription occurs. o Transcription of a RNA molecule that's complementary to DNA according to the base pair rule. • To make a protein properly, genes must control how amino acids are arranged. • There is no thymine (T) in RNA, so T is replaced by U (uracil). • Note: proteins are made outside of the cell's nucleus. • In thetranslation process (outside the nucleus) , DNA is copied into mRNA. • Coding tells the nucleotides when to start and stop copying DNA. • Note: DNA’s double-stranded structure makes it stronger than RNA, which is only single- stranded. • mRNA is synthesized in the nucleus with the help of enzymes and DNA . It contains the information from one gene. • The nucleotides arranged into groups of three are called codons, which tell nucleotides when to start and stop copying. o AUG (methionine) is always the start codon; o The last three codons are stop codons which don't code for anything, they just mark the end of the coding process. o Codons determine how cells decide which amino acid to add. o Each codon indicates an amino acid. o The transcription process is over when mRNA is released from the enzyme. • In the transcription process (outside the nucleus) the primary structure of proteins are made according to the codon sequence on the mRNA. o mRNA is turned into protein; o Codons on mRNA provide the sequence that amino acids must be arranged in; o mRNA has the information, but doesn't do the work; o Amino acids are not nucleic acids so they have nothing to do with the base pair rules; o The cell needs a way to match up amino acids on the codons (on mRNA) to the anti- codons on tRNA; o tRNA is the second type of RNA. It's called the decoder. o Transfer RNA communicates between mRNA and amino acids. Each mRNA codon has its own specific anti-codon that it can bind to (complementary tRNA anti- codon). Each tRNA has a unique anti-codon that carries a corresponding amino acid. o There are many different kinds of tRNA, but they are all different because they have their own unique anti-codons, and they can only bind to one type of amino acid. § So only one kind of amino acid can be placed at a particular codon site by one tRNA molecule. § Many amino acids can have several codons: 1 start codon and 3 stop codons, and 61 codons code for 20 amino acids. 3 • You need to know how to read this table for tests and quizzes! • tRNA anti-codons must always match correctly to mRNA codons. If one tRNA existed for each codon, there should be 61 codons but there are more than 61. Some tRNA are able to bind to more than 1 mRNA codon. • Ribosomes are large RNA and complex proteins. They link mRNA and tRNA to make other proteins. They continue link them to each other until the whole length of mRNA has been read. You can think of them as tiny machines. • The third type of RNA is rRNA, which are made of proteins and RNA. o The first tRNA attaches to a P site on the ribosome o Each new tRNA attaches to an A site o Each tRNA caries an amino acid • As the ribosome moves along (reads) the mRNA it aligns their tRNA and their amino acids. o The transcription process starts when a tRNA attaches itself to the P site of a ribosome. Each tRNA has its own amino acid attached to it. o The amino acids from the tRNA at the P site are transferred to the other tRNA at the A site, and are then joined by an enzyme. o After this is done, the tRNA at the P site moves to the E site (exit site) and detaches itself from the ribosome. o At this point the tRNA at the A site moves to the P site, and a new tRNA with the next amino acid attaches to the empty A site. 4 o These steps repeat until the end of the mRNA molecule is reached, and then the amino acid chain is released into the cytoplasm. o Elongation occurs until the stop codon arrives at the A site (UAG, UAA, or UGA), then a protein (release factor) binds to the A site, which causes a water molecule to be added to hydrolyze the chain from the tRNA at the A site (hydrolysis means a bond is broken with the addition of a water molecule). It releases a polypeptide. o Once this process is complete, the ribosome detaches itself and waits for a new mRNA to “read”. o This is how rRNA helps with the assembly of amino acids to make proteins. 5 Summary of Translation Process 6 Transcription mRNA Note: you'll be asked to translate long chains into mRNA from DNA, and from mRNA to tRNA on tests. 7