Gene Expression

1. Gene Expression General Biology KEY

2. Central Dogma of Molecular Biology • DNA determines a cell or organism’s traits • physical (the structures of a cell or organism) • Physiological (how a cell or organism acts) • Possibly behavioral traits (how an organism acts) • You know that DNA contains a code, but how does DNA’s code actually do anything? DNA RNAproteins  traits

3. Gene Expression needs RNA • Gene Expression = How traits result from genes. • DNA is stored and protected in the nucleus in eukaryotic cells. • Proteins are built at the ribosomes which are outside the nucleus. • RNA acts as a go-between to get DNA’s message out of the nucleus to where it can be used to build proteins.

4. What is a gene? • A gene can be defined in several ways: • A unit of heredity which can pass on traits by cell reproduction • A section (segment) of DNA that holds the code for the production of an RNA molecule • A section (segment) of DNA that holds the code for a polypeptide or protein • A section (segment) of DNA that holds the code for a trait (or part of a trait)

5. What’s RNA? How is it different from DNA? • RNA = Ribonucleic Acid • Made of nucleotides • Each nucleotide has a phosphate, sugar and Nitrogen base • Single Stranded • Three types: mRNA, rRNA, tRNA • Is able to leave the nucleus • Contains the Nitrogen Bases A, C, G, and U • Uracil instead of Thymine Ribose!

6. There are 3 types of RNA mRNA rRNA tRNA

7. Protein Synthesis • Building Proteins (protein synthesis) takes place in two major steps: Transcription (in the nucleus) then Translation (at the ribosomes)

8. Transcription • =Building RNA using DNA as a template. • Takes place in the Nucleus. • Uses an Enzyme called RNA Polymerase. • Click DNA  RNA  protein  trait

9. Steps of Transcription • DNA unwinds & the DNA base pairs separate at the location of the gene to be expressed. • The enzyme RNA polymerase builds an RNA strand that is complementary to one side of the DNA at the gene location. • When it’s finished the RNA can leave the nucleus and the DNA returns to normal.

10. Transcription Practice*Don’t forget – use U instead of T EXAMPLE 1. • DNA: T A C C C A A G G C CC A T T • mRNA: A U G GG U U C C G GG U A A EXAMPLE 2. • DNA: T A C G G C A T A G C G A C T • mRNA: A U G C C G U A U C G C U G A

11. How does the RNA message get translated into a protein? • Every 3 nucleotides on a mRNA is called a codon. • Each codon codes for a particular amino acid.

12. mRNA codon Chart 3rd

13. Translation • =Building a protein (polypeptide) using RNA as a template. • The RNA message is “decoded” or “translated” by building a protein. • Takes place at the ribosomes. • Click DNA  RNA  protein  trait

14. Proteins • Proteins have many functions and make up many structures in cells and organisms. • Amino acids are the monomer units of proteins. • The polymers are called polypeptides (chains of amino acids connected by covalent bonds called peptide bonds) • Once the polypeptide is properly folded and is functional, it can be called a PROTEIN.

16. Proteins are made of amino acids Amino Acid Polypeptide An immature polypeptide folds to become a functional PROTEIN Proteins differ from each other by which amino acids they contain and what order they are in. folds polypeptide protein

17. Practice: Translation EXAMPLE 1. • mRNA: A U G GG U U C C G GG U A A • Polypeptide: Met - Gly - Ser - Gly - stop EXAMPLE 2. • mRNA: A U G C C G U A U C G C U G A • Polypeptide: Met - Pro - Tyr - Arg - stop

18. Steps of Translation 1 2 3 • The ribosome attaches to the mRNA. • As the mRNA moves through the ribosomes, the tRNAs bring in the amino acids one by one and they bond to each other to form a long polypeptide chain. • The tRNA’s are recycled. • When the polypeptide is finished it is released and the mRNA is recycled.

19. Summary of Protein Synthesis (Gene Expression)

20. Mutations • Despite proofreading, sometimes mistakes are made when the DNA is copied. • Mutation = a spontaneous change in the DNA code. • Gene Mutations change the genetic code in a single gene (one or a few nucleotides). This may cause the gene to make a different protein or a nonfunctional one. This could change the resulting trait. • Mutations are not always bad. Some may be helpful or neutral (no effect).

21. What causes mutations? • Sometimes mutations are just errors that occur during the DNA replication process • Sometimes cells can repair the damage, but when they cannot, the DNA base sequence changes permanently. The cell may die or malfunction. • Some mutations arise from MUTAGENS • Mutagens are chemical or physical agents in the environment • Some chemicals • Radiation (UV light, gamma rays, x-rays) • Some viruses (ex. HPV) • In sexually reproducing organisms, mutations only pass on to the next generation if they occur in the sex cells.

22. Gene Mutations: Types of Point Mutations

23. Point Mutations • Frameshift Mutations • Addition/Insertion: One or more nucleotides is added/inserted into the gene • Deletion: One or more nucleotides is removed/deleted from the gene • Substitution: One or more nucleotides is substituted or swapped with a different nucleotide. *usually the least harmful**

24. Types of Chromosomal Mutations

25. Chromosomal Mutations • Deletion: Part of the chromosome is deleted • Duplication: One or more gene(s) on the chromosome gets duplicated (repeated) • Inversion: Parts of a chromosome are reversed • Translocation: Part of one chromosome breaks off and attaches to another chromosome.

26. Sickle Cell Anemia: An example of a Substitution Mutation

27. Do Genes Control everything? • No…a cell/organism’s DNA is only part of the story. • Gene expression can be heavily influenced by environmental factors. • Nature vs. nurture argument

28. Does every section of the genome (DNA) code for something? • Not necessarily… • Genes are known as “coding” regions, since they code for polypeptides and determine traits. • Scientists used to think that most of DNA’s code was made up of “non-coding” regions. These regions apparently did not code for any polypeptides. • Recent studies suggest that much of the ‘noncoding’ regions are important in regulating the expression of the ‘coding’ regions. • Simpler organisms (ex. Sponges) have less non-coding regions than more advanced organisms (ex. Humans)

29. Does every cell express every gene in the genome? • Not necessarily. • A cell will only express the genes that it needs for its own particular traits. • Each organism started life as just one cell. During the development process, an organism’s cells become more and more differentiated and specialized for particular functions. This is called cellular specialization.

30. Differentiation in C. elegans • A fertilized egg develops into an adult worm after many cell divisions. Daughter cells from each cell division follow a specific path toward a role as a particular kind of cell. This involves each cell type expressing (making proteins from) only the genes it needs.

31. Stem Cells • Stem cells are undifferentiated cells. • They can specialize to become any type of cell in the body. • Early embryos are made entirely of embryonic stem cells. • Adults also have some stem cells for example in bone marrow.

32. CloningCombine an egg cell with a donor nucleus to make a cloned embryo

33. Gene TherapyUse normal genes to add to or replace defective genes

34. Transgenic Organisms • GMO = Genetically Modified Organism click • Ex) GM Glowing Animals click • Ex) GM crops - ex) insect resistance • EX) GM bacteria producing insulin and growth hormone • There are some concerns about the unintended consequences that a shift to GM farming and ranching may have on agriculture. click • Many (not all) companies label foods so consumers can decide whether or not to use GM products