DNA and Gene Expression

1. DNA and Gene Expression

2. DNA • Deoxyribonucleic Acid • Double helix • Carries genetic information • Located in the nucleus • The monomer is a nucleotide • A phosphate • A ribose sugar • A nitrogenous base

3. What are the bases in DNA • A – adenine • T – thymine • C – cytosine • G – guanine • Base pair rules

4. Where is DNA located in the Cell?

5. Where are the genes located? • Genes are located on the chromosomes. • Every species has a different number of chromosomes. • There are two types of chromosomes: autosomes and sex chromosomes

6. Genes are located on the chromosomes which are found in the nucleus of a cell. • When a cell is undergoing cell reproduction, the chromosomes are visible. Chromosomes appear when the chromatin condenses and become visible. • Most of the time (90%) the genetic material in the form of chromatin. • A genome is the complete genetic information contained in an individual. • (gene + chromosome)

7. What is gene expression? Gene expression is the activation of a gene that results in a protein.

8. Prokaryotes No membrane bound organelles (nucleus) More primitive organisms Only one circular chromosome Bacteria are the only organisms that are prokaryotes. Eukaryotes Membrane bound organelles ( specialize in function –nucleus, mitochondria, chloroplast) Chromosomes are in pairs and not circular All organisms that are not bacteria: protist, fungi, plants and animals Gene expression takes place differently in prokaryotes and eukaryotes. What is a prokaryotes? Eukaryotes?

9. In Eukaryotes, following mitosis or meiosis, DNA recoils but certain regions remain relaxed for transcription. The areas of relaxed DNA are called euchromatin. • Transcription is the Reading of the DNA and Changing the code to mRNA. • Translation is changing The mRNA into a trait by Using tRNA to interpret the mRNA.

10. DNA in eukaryotes has regions of coding and noncoding DNA. The regions of DNA that code for proteins or traits are called EXONS, while the regions that do not code for proteins are called INTRONS. cytoplasm cytoplasm

11. In prokayotes, transcription and translation occur in the cytoplasm. • In eukaryotes, transcription occurs inside the nucleus in a two step sequence of events. • Pre-mRNA includes both introns and exons for the gene. • mRNA is only the coding portion (exons). • Translation occurs in the cytoplasm at the ribosomes. • Reminder: The are three (3) types of RNA • Messenager (mRNA) • Transfer (tRNA) • Ribsomal (rRNA)

12. Translation • RNA • Single stranded • Does not contain thymine but has uracil instead. • tRNA carries 3 base pair code for specific amino acid. • Amino acids compose polypeptid chains. • One or more polypeptide chains compose a protein • proteins provide the “blueprints” for our characteristics and functions.

13. In Prokaryotes there are three (3) regulatory elements that control gene expression. • Structural genes – genes that code for a specific polypeptide (protein). • Promoter – DNA segment that recognizes RNA polymerase. • Operator – element that serves as a binding site for an inhibitor protein that blocks transcription.

14. Enhancer Control • Eukaryote genes on a DNA strand also have noncoding control sequences that facilitate transcription. • These are called enhancers. • Transcription factors are additional proteins that bind to RNA polymerase and enhancers to help with transcription.

15. Cell Differentiation • Cell differentiation is the development of cells into cells with specialized functions. • Examples: muscle cells, liver cell, red blood cells • As organisms grow and develop, organs and tissues develop to produce a characteristic form. The process is call morphogenesis.

16. Homeotic Genes • Homeotic genes are regulatory genes that determine where certain anatomical structures, such as appendages, will develop in an organism during morphogenesis. • These seem to be the master genes of development Mutant with legs growing out of head Normal

17. Homeobox • In Drosophila (fruit flies) the specific DNA sequence within a homeotic gene that regulates patterns of development is the homeobox. • The same or very similar homeobox sequences have been found in many other eukaryotic organisms

18. Cancer • Leading cause of death in the United States • A genetic disease caused by a mutation in the genes that control cell division

19. Tumor – abnormal proliferation of cells that results from uncontrolled, abnormal cell division • Benign – a tumor that remains within a mass • Malignant tumor- uncontrolled dividing cells that invade and destroy healthy tissue elsewhere in the body • Metastasis – spread of cancer cells beyond their original site

20. Kinds of Cancer • Carcinomas – grow in skin and tissues that line the organs of the body • Example: lung and breast • Sarcomas – grow in bone and muscle tissue • Lymphomas – solid tumors that grow in tissues that form blood cells • Example: leukemia

21. In normal cells, that frequency of cell division is governed by several factors: • Adequate nutrition • Attachment to other cells, membranes or fibers • Division stops if cell become crowded (usually after 20 – 50) divisions • Cancer cell continue dividing and ignore the normal messages to stop dividing.

22. What Causes Cancer? • Mutations that alter the genes coding for growth factors. • May occur spontaneously • Result from exposure to an carcinogen ( any substance that increases the risk of cancer.) • Usually there is more than one mutation. • There are two types of genes that control cell division • Proto-oncogens • Tumor suppressing genes (p53 gene)