1. KEY CONCEPT 8.5 Translation converts an mRNA message into a polypeptide, or protein.

2. Genetic Code: mRNA is read by tRNA 3 bases at a time Each 3 base sequence of mRNA is called a codon Each codon codes for a certain amino acid (20 aa’s) The genetic code matches each RNA codon with its amino acid or function.

3. The genetic code matches each codon to its amino acid or function. –three stop codons –one start codon, codes for methionine The genetic code matches each RNA codon with its amino acid or function.

5. A change in the order in which codons are read changes the resulting protein. Regardless of the organism, codons code for the same amino acid.

6. AMINO ACIDS ARE LINKED TO BECOME A PROTEIN. An anticodon is a set of three nucleotides that is complementary to an mRNA codon. An anticodon is carried by a tRNA.

7. Ribosomes consist of two subunits. The large subunit has three binding sites for tRNA. The small subunit binds to mRNA.

8. AMINO ACIDS ARE CODED BY MRNA BASE SEQUENCES. Step 2: Translation converts mRNA messages into polypeptides. A codon is a sequence of three nucleotides that codes for an amino acid. codon for methionine (Met) codon for leucine (Leu)

9. 1. For translation to begin, tRNA binds to a start codon and signals the ribosome to assemble. 2. A complementary tRNA molecule binds to the exposed codon, bringing its amino acid close to the first amino acid.

10. 3. The ribosome helps form a polypeptide bond between the amino acids. 4. The ribosome pulls the mRNA strand the length of one codon.

11. 5. The now empty tRNA molecule exits the ribosome. 6. A complementary tRNA molecule binds to the next exposed codon. 7. Once the stop codon is reached, the ribosome releases the protein and disassembles. Protein assembly Protein assembly

14. EXAMPLE OF PROTEIN SYNTHESIS: Strand of DNA: T A C G C A T G G mRNA codon: tRNA anticodon: amino acids:

15. THE STUDENT IS EXPECTED TO: 5C DESCRIBE THE ROLES OF DNA, RIBONUCLEIC ACID (RNA) AND ENVIRONMENTAL FACTORS IN CELL DIFFERENTIATION; 6C EXPLAIN THE PURPOSE AND PROCESS OF TRANSCRIPTION AND TRANSLATION USING MODELS OF DNA AND RNA; 6D RECOGNIZE THAT GENE EXPRESSION IS A REGULATED PROCESS; 6E IDENTIFY AND ILLUSTRATE CHANGES IN DNA AND EVALUATE THE SIGNIFICANCE OF THESE CHANGES

16. KEY CONCEPT 8.6 Gene expression is carefully regulated in both prokaryotic and eukaryotic cells.

17. PROKARYOTIC CELLS TURN GENES ON AND OFF BY CONTROLLING TRANSCRIPTION. A promoter is a DNA segment that allows a gene to be transcribed. An operator is a part of DNA that turns a gene “on” or “off.” An operon includes a promoter, an operator, and one or more structural genes that code for all the proteins needed to do a job.

18. In prokaryotes, The lac operon acts like a switch. The lac operon is “off ” when lactose is not present. The lac operon is “on” when lactose is present.

20. Eukaryotic Genes TATA box - may help to position RNA polymerase. Enhancer sequence – proteins bind to the enhancer sequence and may open up chromatin, attract RNA pol, or act as repressor proteins Eukaryotic genes are more complex than prokaryotic genes – why?

21. EUKARYOTES REGULATE GENE EXPRESSION AT MANY POINTS. Different sets of genes are expressed in different types of cells.

22. Transcription in eukaryotes is controlled by regulatory DNA sequences and protein transcription factors. Most eukaryotes have a TATA box promoter. Enhancers and silencers speed up or slow down the rate of transcription. Each gene has a unique combination of regulatory sequences.

23. RNA processing is also an important part of gene regulation in eukaryotes. 3 major steps: Introns are removed and exons (coding regions) are spliced together. A cap is added. A tail is added.

24. ENVIRONMENTAL FACTORS INFLUENCE GENE EXPRESSION, RESULTING IN DIFFERENT CELL TYPES. Internal factors can affect cell differentiation.  Uneven distribution of proteins, mRNA, and organelles within a cell can affect gene expression.  Surrounding cells can influence one another by sending and receiving signal molecules.

25. Factors in an organism’s external environment can also affect gene expression.  Too much oxygen in an organism’s environment can prevent transcription proteins from being made by the cells.  Temperature can influence gene expression.  Drugs or chemicals in the external environment can influence cell differentiation.  Light can change the way that genes are expressed.

26. THE STUDENT IS EXPECTED TO: 6E IDENTIFY AND ILLUSTRATE CHANGES IN DNA AND EVALUATE THE SIGNIFICANCE OF THESE CHANGES

27. KEY CONCEPT 8.7 Mutations are changes in DNA that may or may not affect traits.

28. SOME MUTATIONS AFFECT A SINGLE GENE, WHILE OTHERS AFFECT AN ENTIRE CHROMOSOME. A mutation is a change in an organism’s DNA. Many kinds of mutations can occur, especially during replication. A point mutation substitutes one nucleotide for another. mutated base

29. EXAMPLE OF A POINT MUTATION: CYSTIC FIBROSIS In around 70% of cases CF is caused by a triplet deletion, resulting in the removal of an amino acid from the polypeptide chain produced. Cystic fibrosis (CF) is a recessive inherited disease. It is caused by point mutations in the CFTR gene, which codes for a transmembrane protein that acts as an ion pump. The CFTR gene is found on chromosome 7. It codes for 1480 amino acids. There are over 1000 known mutations, which can affect the function of the CFTR gene in different ways.

30. MUTATIONS

33. A frameshift mutation inserts or deletes a nucleotide in the DNA sequence.

34. Deletion Duplication Inversion Translocation FIGURE 12–20 CHROMOSOMAL MUTATIONS Section 12-4

35. Chromosomal mutations affect many genes. –Chromosomal mutations affect many genes. –Gene duplication results from unequal crossing over. Chromosomal mutations may occur during meiosis (will study this soon)

36. Translocation results from the exchange of DNA segments between different chromosomes.

37. MUTATIONS MAY OR MAY NOT AFFECT TRAITS. Chromosomal mutations tend to have a big effect. Some gene mutations change phenotype.  A mutation may cause a premature stop codon.  A mutation may change protein shape or the active site.  A mutation may change gene regulation. blockage no blockage

38. Some gene mutations do not affect phenotype. A mutation may be silent. A mutation may occur in a noncoding region. A mutation may not affect protein folding or the active site.

39. Mutations in sex cells can be harmful or beneficial to offspring. Natural selection often removes mutant alleles from a population when they are less adaptive. Mutations in body cells do not affect offspring.

40. MUTATIONS CAN BE CAUSED BY SEVERAL FACTORS. Replication errors can cause mutations. Mutagens, such as UV ray and chemicals, can cause mutations. Some cancer drugs use mutagenic properties to kill cancer cells.