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Microbiology exam
| Question | Answer |
|---|---|
| What are the three main components of a DNA nucleotide? - | A phosphate group, a deoxyribose sugar, and a nitrogenous base. |
| Which nitrogenous bases are classified as purines? - | Adenine and Guanine. |
| Which nitrogenous bases are classified as pyrimidines? - | Thymine and Cytosine. |
| What type of bond connects nucleotides to form the sugar-phosphate backbone? - | Phosphodiester bonds. |
| What does it mean for the DNA double helix to be antiparallel? - | The two strands run in opposite directions, with one strand oriented 5'-3' and the other 3'-5'. |
| According to Chargaff's rules, which bases pair together in DNA? - | Adenine pairs with Thymine, and Guanine pairs with Cytosine. |
| What type of bonds hold complementary base pairs together in DNA? - | Hydrogen bonds. |
| What are the primary structural differences between DNA and RNA? - | RNA is single-stranded, contains ribose sugar instead of deoxyribose, and uses uracil instead of thymine. |
| What is the function of messenger RNA (mRNA)? - | It acts as an intermediary that carries a copy of a gene from DNA to the site of protein synthesis. |
| What is the function of ribosomal RNA (rRNA)? - | It aligns mRNA and tRNA and catalyzes peptide bond formation during protein synthesis. |
| What is the function of transfer RNA (tRNA)? - | It carries specific amino acids to the ribosome during translation. |
| Define genotype. - | The full collection of genes within an organism. |
| Define phenotype. - | The observable characteristics resulting from the expression of genes. |
| How does eukaryotic DNA packaging differ from prokaryotic DNA packaging? - | Eukaryotic DNA is wrapped around histone proteins, whereas prokaryotic DNA is supercoiled without histones. |
| What is extrachromosomal DNA in prokaryotes called? - | Plasmids. |
| What is the central dogma of molecular biology? - | The flow of genetic information from DNA to RNA to protein. |
| What does it mean for DNA replication to be semiconservative? - | Each new daughter molecule consists of one original parent strand and one newly synthesized strand. |
| Why are Okazaki fragments formed during DNA replication? - | Because DNA polymerase can only synthesize in the 5' to 3' direction, the lagging strand must be synthesized in short, discontinuous segments. |
| What are the two primary functions of the genome? - | Inheritance (passing DNA to offspring) and the production of RNA/proteins for cellular function. |
| Where is extrachromosomal DNA found in eukaryotic cells? - | In the mitochondria and chloroplasts. |
| What is the primary difference between the leading and lagging strands during replication? - | The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously away from the fork. |
| How can environmental factors influence phenotype? - | Environmental conditions (like temperature) can determine whether specific genes are expressed, even if the genotype remains the same. |
| What is the structural form of the prokaryotic chromosome? - | A single, circular, double-stranded DNA molecule. |
| What are the three stages of bacterial DNA replication? - | Initiation, Elongation, and Termination. |
| What is the function of Topoisomerase II (DNA gyrase) in DNA replication? - | It unwinds the supercoiled DNA. |
| What enzyme breaks hydrogen bonds to separate DNA strands during replication? - | Helicase. |
| What is the role of single-stranded binding proteins in DNA replication? - | They coat the DNA strands to prevent them from rewinding into a double helix. |
| What enzyme creates the RNA primer required to start DNA replication? - | Primase. |
| How does DNA polymerase III function on the leading strand? - | It moves toward the replication fork and synthesizes one continuous strand of DNA. |
| What are Okazaki fragments? - | Short segments of DNA synthesized on the lagging strand during replication. |
| What is the function of DNA ligase in DNA replication? - | It seals the gaps between Okazaki fragments. |
| What enzyme separates replicated chromosomes in bacteria at the end of replication? - | Topoisomerase IV. |
| How do eukaryotic chromosomes differ from prokaryotic chromosomes regarding replication? - | Eukaryotic chromosomes are linear, larger, more complex, and have multiple origins of replication. |
| What is the function of telomerase in eukaryotic cells? - | It maintains the ends of linear chromosomes. |
| Define transcription. - | The process of making an RNA copy of a gene from DNA. |
| Where does transcription occur in bacteria? - | In the cytoplasm within the nucleoid region. |
| What is the role of the promoter in transcription? - | It is the section of DNA where RNA polymerase binds to initiate transcription. |
| What is the direction of mRNA synthesis during transcription? - | 5' to 3' direction. |
| How does eukaryotic transcription differ from bacterial transcription? - | It occurs in the nucleus, involves only one gene per RNA transcript, and requires RNA processing. |
| Define translation. - | The process of protein synthesis by reading genetic information in mRNA. |
| What is the genetic code's degeneracy? - | The fact that most amino acids are coded by more than one codon. |
| What is the start codon for translation and which amino acid does it code for? - | AUG, which codes for methionine. |
| What are the three stop codons? - | UAA, UAG, and UGA. |
| What is the role of transfer RNA (tRNA) in translation? - | It carries specific amino acids to the ribosome based on its anticodon. |
| What is an anticodon? - | A three-nucleotide sequence on tRNA that is complementary to a codon on mRNA. |
| What are the three steps of translation? - | Initiation, Elongation, and Termination. |
| What is the function of the A site in the ribosome during translation? - | It is the site where tRNA carrying the next amino acid enters. |
| What occurs at the P site of the ribosome? - | Peptide bonds form between the amino acids. |
| What is the role of the E site in the ribosome? - | It is the exit site for tRNA molecules. |
| What happens during the termination phase of translation? - | A release factor binds to the stop codon, causing the ribosome, mRNA, tRNA, and finished protein to be released. |
| How does prokaryotic transcription and translation differ from eukaryotic processes? - | In prokaryotes, they occur simultaneously in the cytoplasm; in eukaryotes, transcription is in the nucleus and translation is in the cytoplasm. |
| What is a point mutation? - | A mutation caused by the substitution of one base for another in a gene. |
| What is a frameshift mutation? - | A mutation caused by the insertion or deletion of bases, which shifts the reading frame. |
| What is a silent mutation? - | A base change that does not alter the amino acid coded by the codon. |
| What is a missense mutation? - | A base change that results in a different amino acid being coded. |
| What is a nonsense mutation? - | A base change that creates a premature stop codon, terminating protein synthesis. |
| What causes thymine dimers in DNA? - | Exposure to UV light (nonionizing radiation). |
| How does photoreactivation repair DNA? - | An enzyme called photolyase binds to thymine dimers and is activated by light to repair the bonding. |
| What is the difference between vertical and horizontal gene transfer? - | Vertical transfer is from parent to offspring; horizontal transfer is the acquisition of genes from non-parent organisms. |
| What is transformation in bacteria? - | The process of taking up 'naked' DNA from the environment released by a dead donor cell. |
| What is transduction? - | The transfer of DNA from a donor to a recipient cell via a bacteriophage. |
| What is conjugation? - | A mode of genetic exchange where a plasmid is transferred via a direct connection like a pilus. |
| What are transposons? - | Segments of DNA that can move to different places within the genome. |
| What are constitutive genes? - | Genes that code for proteins needed by the cell at all times. |
| What are the four components of an operon? - | Regulatory gene, promoter, operator, and structural genes. |
| What is the function of the operator in an operon? - | It is the site where the repressor protein binds. |
| What is a repressible operon? - | An operon that is usually active but can be turned off when its product is abundant. |
| What is an inducible operon? - | An operon that is usually inactive but can be turned on in the presence of a specific substrate. |
| How does the trp operon function? - | It is a repressible operon that is turned off when tryptophan binds to the repressor, activating it to block transcription. |
| How does the lac operon function? - | It is an inducible operon that is turned on when lactose binds to the repressor, inactivating it so it cannot block transcription. |
| What is the role of DNA ligase in mismatch repair? - | It joins the corrected DNA sequence to the existing DNA molecule. |
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