GENE EXPRESSION/ENGINEERING

Concepts/Ideas/Notes

1. in eukaryotes gene expression is partly related to the coiling and uncoiling of DNA
2. although both introns and exons are transcribed into mRNA, when mRNA migrates to the cytoplasm, introns are excised, and exons are spliced together, a nitrogen base attaches to each end of the gene, forming a cap and tail.  This shortened mRNA strand then migrates to the ribosomes, where protein synthesis occurs.
3. The expression of genes is regulated through chromosome uncoiling, control of the enhancer region, and cleavage (hydrolysis) of mRNA that has been formed by the gene.

Definitions:

1. Gene Expression – activation of a gene that results in the formation of a protein.  By controlling gene expression cells regulate which proteins are active at any given time.
2. lac Operon – DNA segment on a chromosome that codes for the splitting of lactose into glucose and galactose and the altering of the cell’s membrane to allow lactose to pass through.
3. Operon – functioning unit of key nucleotide sequences which controls gene expression and consists of three segments.  These three segments which are controlled as a unit produce messenger RNA (mRNA), in the process of protein transcription.
1. Promoter – specific nucleotide sequences of DNA which act as start signals for RNA transcription
2. Operator – sequence of nucleotides located between the promoter and the structural genes.  It may overlap the promoter, and /or the structural gene(s).  It is the site at which a repressor protein can bind.  It is basically like an on off switch.
3. Structural Genes – genes that code for proteins, often enzymes that work sequentially in a particular reaction pathway.
4. Repressor – molecule attached to an operon, which inhibits a gene from being expressed.  It is the protein that precedes the operator, that binds to the operator and obstructs (inhibits) the promoter.  It is the binding site for RNA polymerase.  The repressor molecule prevents the action of the enzyme RNA polymerase, which is needed to make the mRNA that will produce the enzymes that break down lactose
5. Regulator Gene – codes for the repressor, it releases the repressor molecule.  Located anywhere on a bacterial chromosome, it codes for a protein called the repressor, which binds to the operator, obstructing the promoter.  No mRNA transcription can occur if this occurs.
6. Inducer – molecule that initiates gene expression
7. Nucleosomes – DNA tightly wrapped around histones to form beadlike structures
8. Heterochromatin – tightly coiled form a DAN which contains inactive genes (not expressed)
9. Euchromatin – uncoiled form of DNA after the chemical bonds are broken in the nucleosomes which is the site of active transcription of DNA into mRNA.  The degree to which DNA uncoils indicates the degree of gene expression.
10. Enhancer – region on a gene which must be activated for the gene in the euchromatin to be expressed.
11. Intron – inert segment or region of DNA, which does not code for proteins
12. Exons – the segment of DNA that function as the codons during protein synthesis
13. Effector – depending on the operon, an effector can either activate or inactivate the repressor for that particular operon.
14. Morphogenesis – the development of form in an organism
15. Blastula – after a zygote forms and begins to grow it forms a hollow ball of cells called a blastula.
16. Gastrula – once a pocket forms on the surface of the blastula it is called a gastrula.  Further cell differentiation here forms the tissue of the embryo and the adult organism.
17. Cell Differentiation – the change in the morphology or physiology of a cell in relation to its neighboring cells which begins in the blastula.
18. Homeotic – genes that control the development of specific adult structures
19. Oncogenes – mutations of normal genes that cause cancer
20. Anti-oncogenes – tumor-growth suppressor genes
21. Imaginal Disks – in fruit flies, disk-shaped tissue, which are triggered by hormones to develop into a specific structure characteristic (imago). Each imaginal disk always develops into the same specific adult structure.
22. Imago – specific adult structure formed from an imaginal disk

Inactive DNA coiled in chromosomes during mitosis and meiosis à DNA uncoils as genes, where inactive mRNA is produced à inactive mRNA with both introns and exons moves from nucleus into cytoplasm à enzymes activate mRNA by eliminating introns; exons now join and move to ribosomes for protein synthesis.

Cancer:

1. Sarcoma – cancer in bone and muscle
2. Lymphoma – solid tumors that grow in the tissue that form in blood cells
3. Leukemia – uncontrolled production of immature white blood cell caused by tumors blood forming tissues
4. Tumor – an abnormal mass of cells that results from ungoverned cell division.

A.     Benign Tumor – cells remain in the mass and generally pose no threat to life.

B.     Malignant Tumor – cells break away (metastasis) and cause new tumors to form in other locations.

a.       carcinomas – malignant tumors that grow in skin and nerves

b.      sacomas – malignant tumors that grow in bone and muscle

c.       lymphomas – malignant tumors that grow in the tissue that form blood cells.

5. Carcinogen – refers to any substance that causes cancer
6. Oncogenes – mutations of normal genes that cause cancer
7. Anti-oncogenes – tumor-growth suppressor genes 

Applied Genetics:

1. Applied Genetics – the manipulation of the heredity characteristics of an organism to improve or create specific traits in offspring
2. Controlled Breeding – manipulating the hereditary characteristics of offspring by selecting parents with specific phenotypic traits.  This allows a breeder to develop new strains of a species or to maintain existing strains.

1. Mass selection – process of choosing a few individuals from a larger pool of individuals to act as parents (those with a better trait hopefully!).
2. Inbreeding – the breeding of individuals with similar phenotypes to maintain or to intensify desirable traits.  Inbreeding can eventually produce weaker organisms because it increases the incidence of harmful homozygous recessive traits.
3. Hybridization – two different but related species or varieties of plants or animals are crossed.  Hybrids posses a different genotype and usually phenotype different from either parent.  Hybridization increases the number of heterozygous genes in an organism, thus reducing the likelihood that a harmful, recessive allel will be expressed.

3. Hybrid Vigor – hybrids that grow faster and larger and are healthier than either parent.
4. Induced Mutation – the use of x-rays and chemicals to induce mutations which are then selected to be passed on to offspring.
5. Polyploidy – the condition in which cells contain multiple, complete sets of chromosomes.  This condition often happens naturally in plants and polyploid plants are often larger and hardier than their parents.  Polyploidy is induced by administering the chemical colchicine which prohibits the formation of the cell plate causing two complete sets of chromosomes to exist in the same cell after cell division.
6. Genetic Engineering – direct manipulation of genes often using recombinant DNA, segments of DNA from at least two different organisms.
7. Recombinant DNA – segments of DNA from at least two different organisms.
8. Interferon – protein produced by the human body that inhibits the growth of viruses.  It is now being produced by a genetically engineered bacteria.
9. Restriction Enzymes – proteins that cut DNA molecules into pieces.  Different restriction enzymes cut different sequences of nucleotides or codons.
10. Gene Splicing – process by which a gene from one organism is placed into the DNA of another organism.
11. Plasmid – small ring of DNA in bacteria
12. Gene Cloning – process by which a human gene is replicated during genetic engineering
13. Gene Sequencing – process of determining the exact order of bases in a fragment of DNA
14. Electrophoresis – technique that identify gene markers (small segments of DNA) by separating  by determining how far each type of DNA can travel in an electric field.

Process of Genetic Engineering:

1. isolating the human gene that codes for for a particular trait
2. splicing the human gene into a strand of bacterial DNA (plasmid) from one bacterium
3. inserting recombinant DNA (human gene now within the other bacterial plasmid) into another bacterium.
4. cloning the bacterium and collecting the product.