Control Mechanisms and Mutations - 2 Day Presentation PDF

Control Mechanisms and Mutations Take care of your sperm!!!  Background There are approximately 20,000 genes that code for proteins in humans However not all proteins are required at all times Think about the hormone insulin – when would it be needed? ...

Control Mechanisms and Mutations Take care of your sperm!!!  Background There are approximately 20,000 genes that code for proteins in humans However not all proteins are required at all times Think about the hormone insulin – when would it be needed?  Genes Some genes are always needed and are constantly being made called housekeeping genes. Transcription factors – proteins that turn genes on when required, by binding to DNA and helping the RNA polymerase to bind Transcription factor  Gene Regulation Gene’s can be turned on or off depending on the organisms requirements – 4 levels of control Transcriptional – Regulates which genes (DNA – mRNA) are transcribed Posttranscriptional – Which Introns and exons are spliced  Gene Regulation Translational – Controls how often/rapidly mRNA transcripts will be translated into proteins Posttranslational – Proteins must pass through the cell membrane to be functional – this affects the rate at which they become active  Mutations Are errors made in the DNA sequence that are inherited. These errors may have negative, positive or no side effects for an organism. Diploid organisms have two copies of each gene; hence, if an error was made in one copy, the other copy may compensate.  Mutations Mutations fall into one of two general categories, – Single gene mutations – involve changes in the nucleotide sequence of one gene – Chromosome mutations – involve changes in chromosomes, and may involve many genes  Types of Mutations Mutations in the somatic cells of an organism will usually go unnoticed unless a significant number of cells are involved (not passed onto next generation). More serious mutations are found on gametes (Can be passed on to the offspring). The following mutations are called point mutations as they are specific to a base pair.  Silent Mutation A mutation that does not result in a change in the amino acid coded for and, therefore, does not cause any phenotypic change Ex. Change in the amino acid coding: Switch for a U to a C - UUU and UUC both code for Phe. Usually they happen in the mRNA introns – therefore they are normally cut out  Missense mutation Arises when a change in the base sequence of DNA alters a codon, leading to a different amino acid being placed in the protein sequence. Sickle cell anemia is an example Other cases of Cystic Fibrosis and ALS (amyotrophic lateral sclerosis) have been reported as well Can be beneficial when making new anitbodies  Nonsense mutation occurs when a change in the DNA sequence causes a stop codon to replace a codon specifying an amino acid. During translation, only the part of the protein that precedes the stop codon is produced, and the fragment may be digested by cell proteases. Often lethal to the cell Both these two mutations arise from substitutions  Beta Thalassemia People with ß Thalassemia cannot synthesize ß globin, part of normal hemoglobin ß globin is usually 146 amino acids in length. The mutated gene codes for a stop codon in the position 39. This causes individuals with ß thalassemia to have small RBC’s that rupture easily – leading to many blood transfusions throughout life  Deletion Occurs when one or more nucleotides are removed from the DNA sequence. The protein can be drastically altered and will inevitably result in a defective protein. – AUG GGA UUC AAC etc – AUG GAU UCA AC etc – This changes the amino acids therefore changing the protein  Insertion the placement of an extra nucleotide in a DNA sequence. Can result in similar effects to a deletion When a mutation changes the reading frame, it is called a frameshift mutation – Insertion and deletion are frameshifts  Translocation At the chromosomal level - the relocation of groups of base pairs from one part of the genome to another. Usually occurs b/w two nonhomologous chromosomes. A segment of one chromosome breaks and releases a fragment, while the same event takes place with another chromosome.  Translocation When unrelated gene sequences are touching and are transcribed and translated, the result is a fusion protein with a completely altered function, if any.  Inversion Is a chromosomal segment that has reversed its orientation in the chromosome. There is no gain or loss of genetic material, but the gene my be disrupted or come under other transcriptional control  Deletion and Duplication You can also have part of your chromosome deleted and part of it duplicated  Causes of Mutations Some mutations are simply caused by error of the genetic machinery and are known as spontaneous mutations. Mutations may also arise from exposure to mutagenic agents and can induce mutations. Ex, UV rays, benzene, nuclear energy etc.  Cancer is a group of diseases that are characterized by abnormal cell division – Loss of regulatory mechanisms which control cell growth and differentiation  Cancer In cancer cells, genes coding for: – Differentiation are repressed or imperfect e.g. tumor suppressor genes – Proliferation are left on e.g. proto- oncogenes P53 gene – stops the cell from progressing – Rapid division often produces an abnormal lump of cells called a tumour  Questions 1-8 on page 263 Also do reading of THE OPERONs on page 255 – 257 of textbook – Make own notes