RNA Structure and Gene Expression - Biology Notes PDF

RNA Structure and Use Ribonucleic Acid- is the nucleic acid, which acts as a messenger between DNA and the Ribosome. RNA carries out the process which makes proteins from amino acids. Structure is similar to DNA, 5 carbon sugar (ribose), phosphate group, Nitrogen...

RNA Structure and Use Ribonucleic Acid- is the nucleic acid, which acts as a messenger between DNA and the Ribosome. RNA carries out the process which makes proteins from amino acids. Structure is similar to DNA, 5 carbon sugar (ribose), phosphate group, Nitrogenous base (uracil replaces thymine) and is single stranded (still 5’-3’) Transcription is making RNA from DNA – In transcription 1 strand of DNA is copied into a complementary strand of RNA. This is done by an enzyme, RNA Polymerase. – mRNA carries genetic information from DNA in the nucleus to the ribosomes in the cytoplasm  Three Types of RNA messenger RNA - carry information from DNA to other parts of the cell ribosomal RNA - forms an important part of both subunits of the ribosome transfer RNA - carries amino acid  Transcription Segments of DNA serve as templates to produce complementary RNA molecules. Requires RNA polymerase (assembles nucleotides into RNA) RNA polymerase only binds to a promoter (regions of DNA that have specific base sequences) Its like send a copy of a transcript instead of the “official”  RNA Editing Introns- portions of pre-RNA that are cut out and discarded Exons- the remaining pieces of RNA – expressed Why?? Scientists are unsure.....hence, Evolution? What is “important” to some isn’t to others… not always the “chosen” ones   Translation Translation is the decoding of a mRNA message into a polypeptide chain (protein). Transfer RNA carries amino acids to the ribosomes and has a cruciform shape Ribosomal RNA makes up a major part of the ribosome’ The Anticodon (three exposed nucleotides) on tRNA matches up with the correct codon on the mRNA Ribosomes assemble the polypeptide chain by making the peptide bonds between the amino acids Study figure 7-19 Figure 12–18 Translation Figure 12–18 Translation (continued)  Protein Synthesis The nature of the Genetic code is as follows: DNA-> mRNA-> Codon-> Protein A codon is a combination of 3 nucleotides on the mRNA Each codon specifies a particular amino acid that is added to the polypeptide chain. AUG is the initiator sequence (shine-Dalgarno sequence) UAA, UAG, UGA are all stop codons Figure 12–17 The Genetic Code  Mutations Mistakes may occur in genes while duplication genetic information. – The mistakes are changes in the genetic material. – Mutations are not always harmful. There are two types of mutations: Gene and Chromosomal Gene mutations mutate a particular gene. – Caused by a chemical change to DNA – Point mutations change a single nucleotide. – Frameshift mutations shift the groupings by adding or deleting a nucleotide. If these mutations occur in an activated gene proteins may not be made properly.  Chromosomal Mutations Chromosomal mutations involve the whole, parts, or even sets of chromosomes. They change the structure or number of chromosomes There are five types of chromosomal mutations: – Deletion- loss of part of a chromosome – Duplication- segment of DNA is repeated – Inversion- oriented in reverse of its normal direction. – Translocation- part of a chromosome breaks off and attaches to another chromosome. – Nondisjunction- failure of chromosomes to separate during meiosis. Leads to polyploidy. Down’s Syndrome (trisomy 21) Chromosomal Mutations Deletion Duplication Inversion Translocation  Gene Expression & Regulation in Prokaryotes DNA acts as a template to make RNA. mRNA is used by the ribosome to make polypeptides All DNA cannot be turned on (expressed) at the same time. Operons express the gene which is to make protein - this is the part of the gene that is turned on. – An operon is a segment of DNA, which has several genes that often work together. Fig. 10-17 (book) – The Operon consists of : A gene cluster An Operator A promoter  Operons Start The GeneTranslation cluster is a group of genes that work together The operator is a region of DNA in front of the gene cluster The promoter is a segment of DNA in front of the operator. - BINDING SITE OF RNA The Promoter acts as a start here sign for RNA polymerase The promoter usually has an inducer (chemical) which triggers the formation of mRNA.  An Operon at Repressors stop transcription Work by attaching to the operator and prohibits RNA polymerase from transcribing the gene. (this happens when glucose in not present) The shape of the repressor determines which operon it attaches to. The inducer binds to the repressor & changes its shape The repressor with its changed shape falls off the operator and RNA Polymerase can make mRNA  Gene Expression Genes are only turned “on” when they have to work! It’s like a light bulb – no need to have it on unless you are going to use it! The lac operon (group of several genes (LACTOSE) working together) only works whenever lactose is present. If lactose is not present – it is not on! NO NEED TO WASTE ENERGRY BY KEEPING GENES ON WHEN THEY ARE NOT BEING USED!  Gene Expression in Eukaryotes DIFFERENT FROM PROKARYOTES – much more complex! DNA is used to make mRNA but not all the mRNA is used to make the proteins Exons are the portions of mRNA which are expressed or turned into protein. Introns are the portions, which intervene the expressed mRNA. These are cut out. This splicing of mRNA takes place in the nucleus. NO Ribosomes present.  Gene Expression in Eukaryotes Most eukaryotic genes are controlled individually and are more complex than the lac operon. The TATA box positions the RNA Polymerase. About 25-30 bp before the start of the gene(TATA OR TATAAA_ Enhancer Proteins help transcription of the DNA and make the process more complex The complexity allows for cell specialization  Typical Gene Structure Regulatory Promoter (RNA polymerase sites DNA strand binding site) Start transcription Stop transcription  Development and Differentiation All cells come from the same fertilized egg and must differentiate into specialized cells. (why we only need certain genes turned on in certain cells!) Homeotic genes (Hox) – master control center! A series of genes called the hox genes controls embryo development and differentiation in all animals. – They are arranged in order of presence The hox genes are remarkably similar in all species. External factors – temperature, acidity, salinity