Exam 2
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
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| What is a nucleic acid? | Macromolecules composed of repeating units of nucleotides
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| What are the three parts of a nucleotide? | 5 carbon sugar; phosphate group; nitrogen base
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| What chemical bonds hold nitrogen bases together? | Hydrogen bonds
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| What bonds hold the sugar-phosphate backbone of nucleic acid together? | Covalent bonds
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| Name three differences between DNA and RNA. | DNA is double stranded, RNA is single stranded; DNA contains deoxyribose sugar, RNA has ribose sugar; DNA contains thymine base, RNA has uracil base
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| Name three kinds of RNA. | mRNA, rRNA, tRNA
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| What is the purpose of each kind of RNA? | mRNA (messenger) takes DNA code to ribosomes; rRNA (ribosomal) ribosomal RNA plus proteins equals ribosomes; tRNA (transport) brings amino acids to ribosomes to make a protein
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| What is a chromosome? | A threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
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| How are the chromosomes of prokaryotes different than eukaryotes? | Eukaryotes: usually multiple, straight, paired chromosomes; Prokaryotes: usually one, circular, unpaired chromosome attached to plasma membrane
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| What is a gene? | Segment of a chromosome; Sequence of nucleotides that code for enzymes and other proteins
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| What is the difference between genotype and phenotype? | Genotype—genetic code; Phenotype—the expression of a gene; what we see
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| Why are there no recessive traits in bacteria? | Because bacteria only have one chromosome
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| Replication | the process of making a duplicate copy of DNA in a cell.
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| Transcription | process of making RNA from a DNA template by complementary base pairing
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| Translation | process of translating the DNA code from mRNA into an enzyme or other protein
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| What is the role of the enzyme DNA polymerase? | DNA polymerase attaches new nucleotides to each parent strand by complementary base pairing
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| What is the role of the enzyme RNA polymerase? | RNA polymerase attaches to a site called the promoter. This is what determines which strand of DNA is copied
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| Know how nitrogen bases pair in DNA. | Adenine-Thymine; Cytosine-Guanine
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| Know how nitrogen bases pair in RNA. | Adenine-Uracil; Cytosine-Guanine
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| What is the difference between the coding and template strand of DNA? | Coding strand: strand of DNA that codes for a protein; the strand that is the same as mRNA except for the substitution of bases - uracil for thymine. Template stand: complimentary to sense strand; this is the strand that is transcribed to make mRNA
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| What are introns? | DNA sequences that don’t code for anything
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| What are exons? | DNA sequences that are translated into proteins
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| How do prokaryotic and eukaryotic cells differ in regards to introns and exons? | Introns must be excised from mRNA in eukaryotic cells before ribosomes can read the code; Prokaryotic DNA and mRNA do not contain introns
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| What is a codon? | Three consecutive base pairs on mRNA
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| Why is the code called a “degenerate” code? | 61 codes for 21 amino acids and 3 stop codes
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| What is an anticodon? Where is it found? | Complimentary base code on tRNA to an mRNA codon. Determines the amino acid that tRNA brings back to the ribosomes
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| How do triphosphate deoxyribonucleotides and triphosphate ribonucleotides provide energy for replication and transcription and translation? | Three phosphate groups are linked together with high energy bonds. When energy is needed, a high energy bond is broken.
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| What is an operon? | a group of genes that work together
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| What is the difference between an inducible and repressible operon? | Inducible – genes not usually transcribed and must be activated by an inducer; Repressible – always transcribed until deactivated by a repressor
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| Be able to explain how the lac operon works. | The lactose operon or lac operon results in the production of proteins that allow bacteria to use the sugar lactose as an energy source
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| What is a mutation? | Change in the base sequence of the genetic code
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| Explain the difference between point mutations and frameshift mutations. | Point mutation—Change in one base pair; Frameshift mutation—One or more bases deleted or inserted
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| Which kind of mutation would usually have the worst consequences for a cell? | Frameshift mutation
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| What is a mutagen? | An agent, such as a chemical, ultraviolet light, or a radioactive element, that can induce or increase the frequency of mutation in an organism
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| What is a base analog? | a chemical that is similar to a nitrogen base, used for complimentary base pairing in place of the normal nitrogen base
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| What does UV light do to nucleic acid and how does it interfere with replication? | causes thymine dimers; Thymines bind with each other instead of complimentary bases
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| Why is ionizing radiation so destructive to living cells? | Ionizing radiation (x-ray and gamma rays) causes electrons to pop out of energy shells and react with other molecules. Can break DNA.
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| Base-excision repair | enzymes pull an incorrect nucleotide from DNA if DNA proofreading did not catch it
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| Light Repair | light activated enzymes break the bonds between nucleotides
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| Dark Repair | enzymes cut the damaged section of DNA with dimers out of the strand
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| Mismatch Repair | enzymes cut out mistakes in new strands of DNA before they are methylated and insert correct bases.
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| SOS Repair | new DNA polymerases are made that can copy the damaged DNA. Many mistakes are made, but a few cells survive.
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| What is a recombinant cell? | Cell that has received DNA from another cell
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| What is horizontal gene transfer? | Transformation, conjugation, and transduction are examples of horizontal gene transfer
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| What is transformation? | Genes transferred from one bacteria to another as “naked” DNA
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| Describe Frederick Griffith’s experiment. | Worked with Streptococcus pneumonia and mice
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| What do we mean by “competence” of a cell? | cell surface properties
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| What is conjugation? | the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells
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| How do Gram-positive and Gram-negative bacteria conjugate? | Gram-positive—“clumping factors” bring cells together. Pores form between cells. Gram-negative—one of two mating types must have a plasmid that codes for pili.
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| F+ cells | have pili code on a plasmid
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| F- cells | do not have the code for a pili
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| Hfr (high frequency) cells | have pili code but the plasmid has been integrated into the host chromosome
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| How does a bacterial cell acquire new DNA through transduction? | Through a virus
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| What are transposons? | “jumping” genes; Small pieces of DNA that can move from one region of DNA to another on the same or different chromosome. Can also move from one organism to another via plasmids or viruses.
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| What is the definition of a recombinant cell? | Cell that has received DNA from another cell
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| How does bioengineering differ from conjugation, transformation and transduction? | Deliberate DNA recombination
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