1. For each pair of terms, explain how the meanings of the terms differ. a. purine and pyrimidine:
Purine: a nitrogenous base that has a double-ring structure; one of the two general categories of nitrogenous bases found in DAN and RNA; either adenine or guanine. Pyrimidine: a nitrogenous base that has a single-ring structure; one of the two general categories of nitrogenous bases found in DNA and RNA; thymine, cytosine, or uracil.
Purine has a double-ring structure and pyrimidine only has a single ring structure. Both are found in nitrogenous bases however, purine is found in adenine or thymine and pyrimidine is found in thymine, cytosine or uracil. b. ribosome and ribosomal RNA:
Ribosome: a cell organelle composed of RNA and protein; the site of protein synthesis. Ribosomal RNA: an organelle that contains most of the RNA in the cell and that is responsible for ribosome function.
Ribosomal RNA is part of the structure of ribosomes that aids in protein synthesis. c. messenger and transfer RNA:
Messenger RNA: a single-stranded RNA molecule that encodes the information to make a protein. Transfer RNA: an RNA molecule that transfers amino acids to the growing end of a polypeptide chain during translation.
Messenger RNA only transfers information whereas transfer RNA transfers amino acids. d. termination signal and stop codon:
Termination signal: a specific sequence of nucleotides that marks the end of a gene. Stop Codon:
Termination signal is in transcription and stop codon is in translation. e. transcription and translation:
Transcription: the process of forming a nucleic acid by using another molecule as a template; particularly the process of synthesizing RNA by using one strand of a DNA molecule as a template. Translation: the portion of protein synthesis that takes place at ribosomes and that uses the codons in mRNA molecules to specify the sequence of amino acids in polypeptide chains.
Transcription occurs in the nucleus, where DNA acts as a template for directing the synthesis of RNA. Translation occurs in the cytoplasm, where a ribosome then attaches and the mRNA acts as a template for directing the tRNA in bringing the right protein. 5. Summarize Griffith’s transformation experiments.
Frederick Griffith conducted four experiments, in 1928, using one virulent and one not virulent strain and mice. He was studying the bacterium that causes pneumonia. In his first experiment he injected the mice with non-virulent [R] cells and all the mice survived. In the second experiment the mice were injected with virulent [S] cells and all died. In the third experiment the mice were injected with heat-killed [S] cells and all the mice survived. In the last experiment, Griffith injected the mice with non-virulent [R] cells and heat killed [S] cells. All the mice died. Griffith concluded that the heat-killed [S] cells transferred genetic material from one cell to the live harmless cells. 6. Describe how Avery’s experiments led to the understanding of DNA as the molecule of heredity in bacteria.
In Avery’s three experiments he destroyed protein, DNA and RNA individually to find out which one was the transforming agent in Griffith’s experiment. In this experiment they found that after destroying RNA and protein the R cells could still transform into S cells, however with the DNA was missing the transformation did not occur. This led to the understanding that DNA was responsible for the transformation in bacteria. 7. Describe the contributions of Hershey and Chase to the understanding that DNA is the hereditary molecule in viruses.
Martha Chase and Alfred Hershey wanted to know whether DNA or protein was the hereditary material viruses transfer when they enter bacterium. They used radioactive isotopes to label the protein and DNA in the phage. They used radioactive sulfur to label the protein and radioactive sulfur to label DNA. Then they allowed the protein labeled and DNA labeled phages to separately infect the E. coli. Chase and Hershey removed the coats from the cells in a blender and used a centrifuge to separate the phage from the E. coli. All of the viral DNA but only a little of the protein entered the E. coli. They concluded that the DNA was the hereditary molecule in viruses. 12. Summarize the major steps that occur during DNA replication.
In step one a helicase separates the DNA strand. This forms a y-shaped region that is called a replication fork. In step two the DNA polymerase adds complementary nucleotides found floating to form a leading strand. Covalent bonds form between the Deoxyribose sugar of one nucleotide and the phosphate group of the next nucleotide on the growing strand. Hydrogen bods form between the complementary nitrogenous bases on both the original and new strands. DNA ligase joins the Okazaki fragments into a continuous strand of DNA called the lagging strand. In step three DNA polymerases are released and two identical molecules of DNA are created. 19. Summarize how RNA is formed from a gene during the process transcription.
Transcription occurs in the nucleus. In step one RNA polymerase binds to the promoter and initiates transcription. DNA strand unwinds and separates. In step two RNA polymerase adds free RNA nucleotides that are complementary to the nucleotides on the DNA strand. The result is mRNA. In step three the RNA polymerase reaches a termination signal. This signal tells RNA polymerase to release the DNA and RNA. The mRNA moves into the cytoplasm. 20. Identify the function of the genetic code.
The genetic code is the term for the rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid. 21. Differentiate the functions of the three types of RNA involved in protein synthesis.
The mRNA is transcribed from the DNA. It exits through the nucleus and goes through the cytoplasm to the ribosome. The tRNA binds to the amino acids. 26. Why is it unlikely that any particular mutations would have any noticeable effect in a population?
It is unlikely that any particular mutations would have any noticeable effect in a population because 27. A segment of DNA has the following sequence: TACGGTCTCAGC. Write the mRNA transcript from this sequence of DNA. Next, write the tRNA anticodons that would pair with the mRNA transcript. Use table 10-1 to write the names of the amino acids coded for by the mRNA transcript. 28. A DNA molecule replicates to produce two new DNA molecules. Both of the two new DNA molecules then replicate to form four more new DNA molecules. Are any nucleotides chains from the original DNA present in the last four new DNA molecules? If so, how many?
Pg. 250: #’s 1, 5-6, 8, & 11-16
1.For each of the following terms explain how the meanings of the terms differ. a.Germ-cell mutation and somatic-cell mutation:
Germ-cell mutation: mutation that occurs in an organism’s gametes. Somatic-cell mutation: a mutation that occurs in a body cell. Germ-cell mutations occur in the organisms gametes. Somatic-cell mutations occur in an organism’s body cells. Germ-cell mutation does not affect the organism but it does affect the offspring. Somatic-cell mutations affect the organism. b.Multiple allele and polygenic:
Multiple allele: more than two alleles for a genetic trait. Polygenic: describes a characteristic that is influenced by many genes
Multiple alleles have more than two alleles but polygenic is the characteristic that shows because of the many genes. c.Sex-linked trait and sex-influenced trait:
Sex-linked trait: a trait that is determined by a gene found on one of the sex chromosomes, such as the X or Y chromosome in humans. Sex-influenced trait: an autosomal trait that is influenced by the presence of male or female sex hormones.
A sex-influenced trait is influenced by the presence of the different genders of sex hormones. A Sex-linked trait is directly linked with the chromosome such as X or Y chromosome in humans. d.Amniocentesis and chorionic villi sampling:
Amniocentesis: a procedure used in fetal diagnosis in which amniotic fluid is removed from the uterus of the pregnant woman. Chorionic villi sampling: a procedure in which the chorionic villi to are analyzed to diagnose fetal genotypes.
Both procedures allow technicians to analyzed fetal cells, chromosomes, proteins and detect genetic diseases. Amniocentesis is done between the 14th and 16th weeks of pregnancy and Chorionic villi sampling is done between the 8th and 10th weeks of pregnancy. 5. Compare sex chromosomes and autosomes.
Sex chromosomes determine the gender of the individual. Autosomes are the remaining chromosomes that are not directly involved in determining the sex of the individual. 6. Identify the evidence that led Morgan to hypothesize that the gene for eye color in Drosophila melanogaster is carried on the X chromosome.
Morgan noticed that one male fruit fly had white eyes. He crossed the white-eyed male with a normal red-eyed female and found that all the F1 offspring had red eyes. Then he crossed the F1 males with the F1 females. The F2 generation had three red-eyed flies to one white-eyed fly. All white-eyed flies, however, were males. 8. Relate how X-linked genes affect the inheritance of sex-linked traits.
11. Differentiate between nondisjunction and translocation mutations.
Translocation is when a piece of chromosome breaks off and reattaches to a nonhomologous chromosome. Nondisjunction is what a chromosome fails to separate from its homologous chromosome during meiosis. One gamete receives an extra copy of a chromosome and another gamete receives no copies. 12. State the type of information that is obtained by analyzing a pedigree.
A pedigree shows how a trait is inherited over several generations. If a trait is autosomal it will appear in both sexes equally and if a trait is sex-linked, it is usually seen only in males because most sex-linked traits are recessive. 13. Describe the pattern of inheritance in Huntington’s disease.
The pattern of inheritance in Huntington’s disease is an autosomal dominant condition characterized by forgetfulness and irritability. 14. Predict the possible genotypes for a person whose ABO blood group is type A.
IAIA or IAi
15. Summarize two ways in which geneticists can detect genetic disorders. Geneticists can detect genetic disorders through genetic screening that involves two techniques, amniocentesis and chorionic villi sampling. Amniocentesis is a procedure used in fetal diagnosis in which amniotic fluid is removed from the uterus of the pregnant woman. Chorionic villi sampling is a procedure in which the chorionic villi to are analyzed to diagnose fetal genotypes. 16. Describe how gene therapy is used to treat genetic disorders.
Gene therapy is a technique that places a healthy copy of a gene into the cells of a person whose copy of the gene is defective. Gene therapy relies on knowing gene sequences.