Chapter 17 Reading Journal

What are the three steps of transcription?
First it starts with a transcription unit this is the whole strand of DNA that is transcribed into RNA. 1. Initiation is when the RNA polymerase binds to the promoter. In eukaryotes it must first receive help from transcription factors so that the polymerase can bind. 2. Elongation: is when the polymerase moves along the strand of DNA producing a strand of RNA with the complementary sequence. 3. Termination: the terminator sequence of DNA causes the RNA to be released and then it detaches ready for modification before translation.

What is the difference between a codon and anti-codon and what do they do?
A codon is a sequence of three bases on an mRNA molecule that will be translated into a protein. The anti-codon is the complementary strand on the tRNA that allow the codon to bind. Codons come into the tRNA at the A site where amino acids are added and then the amino acids from the codon in the P site to the codon in the A site. Then the Codon in the A site shifts to the P site while that codon moves to the E site and exits so that the whole process may start again.

What are the different types of mutations?
Point mutations change only one base in a sequence and they account for either missense or nonsense mutations. Missense is when the codon still makes a protein though that protein may be dysfunctional. Nonsense is when a normal codon is turned into a stop codon so that no protein is made. Insertions and deletions are the adding and removal of certain sequences, if these come in threes they are often not very harmful but if not they can cause a frame shift and through off all the codons down the line.

Facts:
-Mutagens are substances that cause mutations in DNA sequences
-In modification mRNA gets a 5’ cap and poly-A-tail
-RNA splicing takes out the introns which are the portions of the RNA that don’t code for anything so they are removed
-Many codons code for the same proteins even when they have a different last base this is called the wobble effect
-The template strand is the strand of DNA that the polymerase binds to in order to make the RNA strand



This is the codon table, used to determine what amino acid a certain codon makes and then from there what amino acid sequences and therefore proteins a certain strand of DNA or RNA will produce once translated.

Summary:
DNA codes for RNA which then translates into proteins this is how something goes from being a gene to being expressed, if the protein of a certain gene isn’t made then that gene isn’t being expressed. First DNA is transcribed into a complementary RNA sequence after the RNA is processed and modified it is translated into a protein although some RNA is never translated but still useful in its transcribed form. RNA polymerase allows the synthesis of RNA after it attaches to the promoter. Translation uses a ribosome small and large subunit and tRNA that allows the codons to attach to the anti-codon. Mutations with the DNA cause problems in the organism because they effect protein production by either stopping it or changing it into different proteins that aren’t as useful to the cell. RNA doesn’t have to be modified in bacteria like it does in eukaryotes because it doesn’t have to be packaged to pass the nuclear envelope.