Presentation on theme: "This lesson you should be able to... Grade B/A- Grade B/A- Explain genetic control of protein production in a prokaryote using the lac operon. OCR F215-Control,"— Presentation transcript:
This lesson you should be able to... Grade B/A- Grade B/A- Explain genetic control of protein production in a prokaryote using the lac operon. OCR F215-Control, Genomes and Environment A2
Key terms you need to know....... Operon – length of DNA made from structural genes and control sites Structural genes – code for protein Control sites – operator and promoter region of the DNA
Starter Exam Question Jan 2011 idea of change to, DNA / base(s) / nucleotide(s) natural / directional, selection ;
regulatory idea that makes, repressor protein / transcription factor idea that product switches (structural / another) gene, on / off structural -idea that makes, enzyme / polypeptide / protein ; relationship between the 2 idea that regulatory gene, controls / affects, the expression of structural gene ; lactose has been, removed / digested / respired / broken down (by bacteria) ; to, lactic acid / lactate / other sugars ; yogurt still a good source of, calcium / vitamins ;
There are ~20,000 genes in each of our cells. But a particular cell will not make use of each of them. For example – white blood cell and skin cell- A white blood cell will contain the gene coding for the protein melanin, but will not be expressed. A skin cell will contain the gene to make antibodies, but it will not be expressed “not switched on.”
We know that....... mRNA – codes for a particular protein The code on the mRNA is complementary to the base sequence on the DNA template strand Therefore that code on the mRNA is a copy of the base sequence on the DNA coding strand Proteins are specified by mRNA
Background information Bacteria can synthesise different enzymes (proteins) depending on what food substrate they are growing on. E.Coli can synthesise over 3000 different enzymes. Enzymes involved in basic cell functions are synthesised at a constant rate. Inducible enzymes are synthesised as and when they are needed.
E.Coli can adapt to its environment by producing enzymes to metabolise certain nutrients.......... but only when those particular nutrients are present E.Coli normally respires using glucose but can also respire using lactose (sugar found in milk/disaccharide) Needs to synthesise ß-galactosidase & lactose permease Background information
ß-galactosidaseß-galactosidase – hydrolyses lactose into glucose & galactose. lactose permease – transport protein that becomes embedded in the e.coli membrane – helps transport more lactose into the cell. When placed in a lactose substrate, e.coli increases the synthesis of these two proteins by 1000x. Lactose triggers the enzymes production – inducer molecule. Background information
Lac system genes (in the bacterial DNA) form the operon – consists of structural genes and control genes. ß-galactosidase Z - ß-galactosidase lactose permease Y - lactose permease O – operator region – switches Z & Y on and off RNA polymerase P – promoter region-Binding site for RNA polymerase for transcription of Z & Y repressor I- Regulator:-Codes for the repressor protein The lac operon
If lactose is absent Regulator gene Regulator gene is expressed and produces repressor protein Repressor protein binds to the operator region (P & O) Partially covers the promoter region (P) RNA polymerase can’t bind – Z & Y genes can’t be translated Z & Y are switched off
If lactose is present Inducer molecule (lactose) binds to the repressor protein Repressor protein dissociates from the operator region Promoter is now unblocked RNA polymerase can now bind promoter region Z &Y can now be transcribed – mRNA produced ß-galactosidase /lactose permease can now be synthesised
The lac operon As a result of the 2 enzymes being made, e.coli can now..... lactose permease Take up lactose from its environment because lactose permease acts a transport protein. ß-galactosidase, Using ß-galactosidase, lactose (disaccharide) can be hydrolysed into glucose & galactose E.coli can use these sugars for respiration E.coli is gaining energy from the lactose
ß-galactosidase ß-galactosidase (lactase) – hydrolyses lactose to glucose and galactose Background information
The Lac Operon – Summary Genes responsible for lactose digestion and their regulation. Physical presence of lactose results in transcription of genes to produce lactose permease and Beta-galactosidase. A regulatory gene produces a repressor protein. When no lactose is present, it joins with the operator region. RNA polymerase joins to the promoter region. If the repressor protein is attached to the operator region, the RNA polymerase cannot move further along and transcript structural genes to produce enzymes for lactose digestion. If lactose is present, it binds with the repressor protein and causes a conformational change, so the repressor protein can’t bind with the operator region. RNA polymerase can travel along and the enzymes for lactose digestion can be produced.
Exam Question Jan 2011 lactose binds to repressor protein ; changes, shape / structure (of protein) ; removes it from / stops it binding to, operator ; RNA polymerase binds to promoter ; idea that (so that Z and Y) are, transcribed / mRNA made
This lesson you should be able to... Grade B/A- Grade B/A- Explain that the genes that control development of body plans are similar in plants, animals and fungi, with reference to homeobox sequences. OCR F215-Control, Genomes and Environment Mrs Funk A2
Controlling development All organisms begin life as a single cell. This cell divides and the new cells produced start to differentiate and specialize. ‘Switching on’ the expression of a gene or keeping it switched off determines the development of features. homeobox genes Many organisms contain similar genes that control development of body plans. For example groups of genes called the homeobox genes play an important role in the development of many multicellular organisms.
Homeobox genes transcriptional factors Homeobox genes code for transcriptional factors. These regulate the expression of other genes important in development. homeobox genes. The genome of the fruit fly contains one ‘set’ or cluster of homeobox genes. These control development, including the polarity of the embryo, polarity of each segment and the identity of each segment. Mutations in homeobox genes can cause changes in the body plan. For example a mutation in the gene controlling leg placement can cause legs to grow where the antennae are normally found.
Drosophilia Fruit fly body plan pg 114 Maternal effect genes Maternal effect genes – determine embryo polarity (which end head, which end tail) Segmentation genes Segmentation genes – specify polarity of each segment (which part of head is brain which part is mouth piece) Mutation Example 1: Has a homeobox gene called Ubx, which prevents formation of wings in T3 ( a part of the body). Mutation in both forms of Ubx = wings grow in T3 Fruit fly has two sets of wings – cannot fly Mutation Example 1 Antennapedia – where the antennae look more like legs http://www.youtube.com/watch?v=LFG-aLidT8s
There is little variation in many regions of the homeobox genes in different organisms. This suggests that these have been highly conserved throughout evolutionary history. They are thought to be especially important to the basic development of organisms. Homeobox genes are present in the genomes of most organisms. They control development of body parts in similar ways. Homeobox genes
The homeobox regulatory gene is found in the genome of segmented animals from annelids to humans. The genes contain a 180 bp homeobox sequence that codes for polypeptides including transcription factors, which bind to genes upstream initiating transcription switching genes on and off. This regulates the expression of other genes. Homeobox genes work in similar ways in vertebrates plants and fungi. Genetic Control
Homeobox genes are genes whose activity switches a whole set of other genes on or off, affecting an organism’s body plan (overall design of an organism’s body). hox clustersThey are found in clusters called hox clusters Most animals have very similar homeobox genes. Genes are highly conserved (have not evolved much) Code for production of transcription factors. These can bind to certain sections of DNA and cause it to be transcribed. Thalidomide disrupted the homeobox genes in developing foetuses, so arms and legs did not develop properly. Homeobox genes summary
Many of the effects of retinoic acid on development occur through the ability of retinoic acid to regulate gene expression in various specific cell types. Retinoic acid binds to proteins in the steroid receptor family, and it is this RA receptor complex which mediates gene expression. Retinoic Acid
The activation of Hox genes also explains the teratogenenicity of Retinoic Acid (Isoretinoin, Accutane), a vitamin A derivative used for the treatment of cystic acne. Despite label warnings, Accutane has been taken by at least 160,000 women of childbearing age. The most common abnormality found is cleft palate and other head and neck malformations. Formation of the palate roof through fusion of the palate is a complex process, and the cells in this region of the anterior head do not express genes of the Hox complexes. Retinoic Acid
Plenary Exam Question Jan 2012 homeotic / regulatory, (gene) ; contains, 180 bp / homeobox, sequence ; that codes for homeodomain (on protein) ; (gene product) binds to DNA ; initiates transcription / switch genes, on / off ; control of, development / body plan ; these genes very important ; mutation would, have big effects / alter body plan ; many other genes would be affected / knock-on effects ; mutation likely to be, lethal / selected against ;
protein synthesis / transcription and translation ; respiration ; DNA replication ; mitosis ; cytokinesis ; apoptosis ; differentiation / gene switching ; fungi / plants