Unit 6: Gene Expression Review Questions and Answers Topic 1: Genes and DNA 1. Where is DNA located in a prokaryotic cell? DNA is tocated in the circular chromosame of a prokaryotic cell. 2. Where is DNA located in a eukaryotic cell? DNA is tocated in the chromosomes, which are found in the nucleus of a eukaryotic cell. 3. What are the building blocks of a nucleic acid, such as DNA? Nucleotides are the building blocks of a nucleic acid. 4. What are the three parts of a nucleotide? The three parts of a nucleotide are a sugar, a phosphate group, and a nitrogen base. 5. How are nucleotides arranged in a DNA molecule? A DNA molecule consisfs of two chains of nucleotides. ln each chain, the sugar of one nucleotide is joined to the phosphate group of the nert nucleotide. Each nitrogen base in one chain is attached to a nitrogen base in the other chain. Topic 2: Replication Copying DNA 1. Where does DNA replication occur in a eukaryotic cell? DNA replication occurs in the nucleus of a eukaryotic cell. 2. What are the basepairing rules for DNA? Adenine always pairs with thymine, and guanine always pairs with cytosine. 3. What would be the complementary strand for the DNA strand ATTCGGATC?
The complementary strand would be TAAGCCTAG. 4. How do the two new DNA molecules that result from DNA replication compare with each other? The two new DNA molecules that result from DNA replication are identical. Both molecules have the same sequence of nitrogen bases in their two strands of nucleotides. 5. How does each new DNA molecule that results from DNA replication compare with the DNA molecule from which it was made? Each new DNA molecule that results from DNA replication is identicalto the DNA molecule from which it was made. Both motecules have the same sequence of nitrogen bases in their two strands of nucleotides. Topic 3: The Genetic Code 1. What is the genetic code? The genetic code is the "language" in which the instructions for assembling proteins are written. 2. What are triplets? Triptets are the threebase sequences of one side of a DNA molecule. Each triplet causes a specific amino acid to be placed into a protein. 3. lf you know the sequence of nitrogen bases in a gene, how can you determine the sequence of amino acids that willbe found in the protein produced by the gene? A sequence of nitrogen bases in a gene can be'translated" into a sequence of amino acids by using a tabte showing the codons and their corresponding amino acids. 4. What do biologists call a permanent change in the sequence of nitrogen bases in a DNA molecule? a mutation 5. How might a change in the sequence of nitrogen bases in a gene affect the protein 2
the gene produces? A change in the nitrogenbase sequence of a gene can result in the production of a protein with a sequence of amino acids that is different from that of the original protein. As a result, the protein may not be able to carry out its normalactivities. Topic 4: Three Types of RNA 1. What are the three main ways in which the structure of RNA molecules differs from the structure of DNA molecules? RNA motecules have onty one strand of nucleotides, while DNA molecules have two strands. RNA molecules contain the sugar ribose instead of the deoxyribose found in DNA. RNA motecules contain the nitrogen base uracil instead of the thymine found in DNA. 2. What is the relationship among DNA triplets, mrna codons, and IRNA anticodons? Each of these is a sequence of three nitrogen bases in a strand of nucleotides, and each corresponds to a particular amino acid. 3. What is the role of mrna in gene expression? Messenger RNA, or nrna, carries the instructions for making proteins from DNA in the nucleus to ribosomes in the cytoplasm. 4. What is the role of IRNA in gene expression? Transfer RNA, or IRNA, carries specific amino acids to the ribosomes. Each IRNA molecule carries the amino acid that is specified by the molecule's anticodon. 5. What is the role of rrna in gene expression? Ribosomal RNA, or rrna, is part of the structure of ribosomes. Topic 5: Transcription Making RNA 1. Where in a cell does transcription occur? Transcription occurs in the nucleus of a eukaryotic cell and in the cytoplasm of a 3
prokaryotic cell. 2. What types of molecules are made by transcription? Att three types of RNA moleculesmrna, frna, and rrnaare made by transcription. 3. How does transcription compare with DNA replication? ln transcription, the instructions in DNA are rewritten as RNA molecules that serue as working copies of the instructions. ln DNA replication, the instructions in DNA are copied exactly; one DNA molecule is used to make two identical DNA molecules. 4. How are the basepairing rules for transcription different from the basepairing rules for replication? tn reptication, A always pairs with T, and C always pairs with G. ln transcription, A pairs with T or U, and C always pairs with G. 5. What is the mrna strand that will be made by the transcription of the DNA strand ATCG CCTACTAG? U A G. C G. G A U G A U C Topic 6: Translation Protein Synthesis 1. Where in a cell does translation occur? Translation occurs at the ribosomes in the cytoplasm of a cell. 2. What types of molecules are made by translation? Proteins are made by translation. 3. How is an mrna molecule used during translation? During translation, the sequence of nitrogen bases along an nrna molecule is used to line up amino acids carried by IRNA in order to make a protein. The amino acids line up in the order specified by the instructions in DNA as IRNA anticodons form base pairs with mrna codons. 4
4. What are the IRNA anticodons that willform base pairs with the mrna codons CGA CUA UCG GCU? GCU GAU AGC CGA 5. What sequence of DNA triplets produced the mrna codons in question 4? GCU GAT AGC CGA 5