Expert Questions Chapter 4 Answers

1. What is a nucleotide? What are its parts? - Building block of DNA/Mrna - sugar, phosphate, base 2

2. Explain Chargaff’s rule about nitrogenous bases and describe which bases bond together. He discovered that the amounts of A and T were always equal and the amounts of C and G were always equal. Concluded that A and T always bond together and C and G always bond together. 3

3. Describe the structure of DNA. Sides are made of alternating sugar and phosphate. Sugars attach to rungs. Rungs contain 2 bases (A and T or C and G) Rungs are held together by hydrogen bonds. 4

4. Draw DNA 5

5. What does semi-conservative mean? 6 Each new DNA is ½ new and ½ old Replication

6. Steps of replication. DNA replication DNA unzips Complementary nucleotides move in Product is 2 identical DNAs (1/2 new and ½ old) 7

6. When and why does DNA replication occur? At the end of interphase before mitosis. Because each new cell needs a complete copy of the DNA. 8

8. Why are proteins important? 9 Found throughout cells Control cellular functions Determine physical traits such as: Skin Color Eye color How tall you grow What colors you can see Whether your hair is curly or straight

9. What are proteins made of? 10 proteins are made of amino acids The code is made up of 3 bases (codon) The order of the amino acids is determined by the mRNA which is determined by the DNA.

10. Why do cells go through protein synthesis? 11 To make proteins which form the building blocks of all parts of the organism and are responsible for all traits and characteristics

11. Process of protein sythesis 1. Transcription – a gene is copied onto mRNA 1.) The cell gets a message that a protein is needed. 2.) DNA unzips at hydrogen bonds exposing only one gene. 3.) Complementary nucleotides move into one side of the gene forming mRNA. 4.) mRNA leaves the nucleus to go into the cytoplasm. 5.) DNA rezips at the hydrogen bonds. 2. Translation – the gene is decoded and the amino acids it codes for are assembled in the ribosome 12 1.) mRNA goes through the cytoplasm to meet the ribosome. 2.) mRNA goes through the ribosome in groups of 3 bases at a time called codons 3.) The arrangement of bases in a codon creates a specific amino acid. 4.) Amino Acids get connected by a peptide bond. 5.) Many amino acids connected together makes a protein.

12. DNA/mRNA 13 DNAmRNA Longer shorter Thousands/millions of genes 1 gene Double stranded (helix) Single stranded (helix) Bases - ATGC Bases – AGCU (U = Uracil) Stays in the nucleus Goes from nucleus to cytoplasm and ribosome Produced in DNA Replication Produced in Transcription Deoxyribose Sugar Ribose Sugar

13.What is a mutation? An error in DNA or mRNA 14

14.What are 3 kinds of mutations? Describe how each affects the DNA insertion – adds a base deletion – removes a base substitution – replaces a base with a different one 15

15. List 3 types of mutations and give an example of what could be the sequence ATC CCA GTA insertion –______________________ deletion –______________________ substitution –______________________ 16

16. When do mutations occur? How? During replication or transcription. Randomly or because of mutagens. 17