GENETICS and the DNA code NOTES

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1 GENETICS and the DNA code NOTES BACKGROUND DNA is the hereditary material of most organisms. It is an organic compound made of two strands, twisted around one another to form a double helix. Each strand is composed of repeating units of nucleotides, which themselves are composed of deoxyribose sugar, a phosphate group, and a nitrogen base. There are four nitrogen bases in DNA adenine (A), thymine (T), cytosine (C), and guanine (G). The sequence of these nitrogen bases is the genetic code. Every three bases, or letters, codes for an amino acid, the building block of proteins. Like DNA, RNA is a nucleic acid made of repeated nucleotides. An RNA nucleotide consists of ribose sugar, a phosphate group, and a nitrogen base. RNA is very similar to DNA, but differs in a few important structural details: in the cell, RNA is usually single stranded, while DNA is usually double stranded; RNA nucleotides contain ribose, while DNA contains deoxyribose (a type of ribose that lacks one oxygen atom); and RNA has the nucleotide uracil, rather than thymine, which is present in DNA. Through the processes of transcription and translation, the cell makes proteins using the code from DNA. Transcription takes place in the nucleus and involves transferring the information in DNA through messenger RNA (mrna). The mrna is a single strand that is the complement of the template DNA, except that it uses uracil (U) instead of thymine (T). Once the mrna is formed, it leaves the nucleus and goes into the cytoplasm. Translation takes place in the cytoplasm and is the process of creating a polypeptide from the information carried on the mrna. The mrna binds with a ribosome, which is the site where protein synthesis takes place. The mrna moves through the ribosome three nitrogen bases at a time; these three nitrogen base segments are called a codon, and each codon codes for a particular amino acid. The transfer RNA (trna) has an anticodon that is the complement of the codon and carries the appropriate amino acid for that codon. This process of adding amino acids continues until there is a stop codon, signaling the end of the polypeptide. This polypeptide is then folding to make a protein. Some proteins are made of a single polypeptide, while others are made up of multiple polypeptides bonded together. Mutations are changes in a gene in the DNA, which may cause the protein to not form correctly. These changes can be passed on from a parent, or they can occur during an individual s lifetime. The impact of the mutation depends on where and when the change occurs. Some changes occur in non-coding regions or involve a change that still codes for the same amino acid sequence, since multiple nitrogen base combinations can code for the same amino acid. These are called silent mutations and are considered to be neutral. Other mutations can change the protein structure, which will change the traits of an organism. These changes can be either positive or negative for the organism. RNA DNA # strands Nitogen bases Sugar Location Primary function In nucleus and cytoplasm Trasnfers genetic information to aid cell in protein synthesis Long-term storage of genetic information; codes fro proteins

2 Replication: in nucleus 1. Unzip DNA helix by breaking hydrogen bonds 2. Add DNA nucleotides to exposed strands Transcription: in nucleus 1. Unzip section of DNA to copy 2. And RNA nucleotides to one side of DNA exposed 3. Modify mrna by cutting out introns (noncoding mrna) leaving only exons (coding mrna) 4. Mature mrna leaves nucleus Translation: in cytoplasm 1. Ribosome reads mrna code at START codon 2. trna with anitcodon that complements mrna brings correct amino acid 3. Ribosome attaches amino acids together 4. Ribosome release mrna and complete amino acid chain when hits STOP codon

3 Use the information above to help complete the activity. Turn the DNA sequence into an amino acid chain. Also include the trna anitcodon. 1. Complimentary DNA Original DNA mrna codons Amino acid sequence 3 T A C T C G G G G C G C A T C C A A G A G 5 trna anticodon 2. Complimentary DNA Original DNA mrna codons 3 T A C G A T C G A T A G C T A G C T A G C 5 Amino acid sequence trna anticodon 3. Complimentary DNA Original DNA mrna codons 3 T A C A C G T A T C T T G G C T A G C T A 5 Amino acid sequence trna anticodon

4 Mutations NOTES Identify each type of DNA mutation: point, frameshit (insertion), frameshift (deletion) Which type of mutation (point or frameshift, causes more damage? Why? Identify each type of chromosomal mutation: insertion, deletion, substitution, inversion, translocation How are the chromsomal mutations above different from the effects of nondisjunction? Identify the mutations as: silent muation, missense mutation, nonsense mutation, stop codon mutation 1. : results in same amino acid; same function 2. : results in code for different amino acid; affects range (ex. Sickle cell anemia 3. : results in early stop codon; harmful affects (ex. Cystic fibrosis) 4. : results in stop codon turned into another amino acid (chain gets too big); harmful affects (ex. Familial British dementia)

5 Name Period date DNA Replication and Central Dogma Identify each figure below: replication, transciption, translation Where does replication occur? 3. Where does transciption occur? 4. Where does tranlation occur? 5. Which process results in amino acid chains? 6. Which process results in mrna? 7. Which process results in more DNA for cellular division? Making complimentary DNA (cdna) strands: 8. 3 A A T T C G C C G G T A T T A G A C G T T T A T C C C G G A G A G G T C C A A T G C A T C G G G G A A T T A C C C G T T A A 5

6 11. What is a codon? 12. What codon means start? 13. What 3 codons act as termination signals? 14. List ALL of the codons for leucine. 15. Name one amino acid that has more than one codon. 16. Name an amino acid that has only one codon If the DNA sequence is --- AAA TAT CCG TAG CAA ATG, write the mrna sequence, trna anticodon sequence, and the six amino acids for this. DNA: AAA TAT CCG TAG CAA ATG 17. mrna: 18. Amino acids: 19. trna: 20. Given the following three mrna sequences, 2 code for the same protein. Which two? Circle the correct sequences a) AGU UUA GCA ACG AGA UCA b) UCG CUA GCG ACC AGU UCA c) AGC CUC GCC ACU CGU AGU 21. A geneticist found that a particular mutation had no effect on the protein coded by a gene. What do you think is the most likely type of mutation in this gene? Why?

7 22. Look at the following sequence: THE FAT CAT ATE THE RAT. Delete the first H and regroup the letters in groups of three- write out the new groups of three. Does the sentence still make sense? What type of mutation is this an example of? Below is the base sequence for the normal protein for normal hemoglobin and the base sequence for the sickle cell hemoglobin. Normal GGG CTT CTT TTT Sickle GGG CAT CTT TTT 23. Transcribed and translate the normal and sickle cell DNA. Normal Sickle Cell 24. Is sickle cell caused by a point or frameshift mutation. Explain. 25. If the base sequence read GGG CTT CTT AAA instead, would this result in sickle cell hemoglobin? Explain why or why not.

8 Fill in the Chart cdna ORIGINAL mrna codon trna anticodon Amino Acid strand DNA triplet 20. AAG 21. GGC 22. CAG 23. UUA 24. AAA 25. GTA 26. CUC 27. ACA 28. TAT 29. AGC 30. AUU 31. CCA 32. GGC mrna CODON CHART for Amino Acids