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BIOL2161
| Question | Answer |
|---|---|
| Do prokaryotes have a nucleus? | No, instead DNA floats freely in the cytoplasm |
| Do eukaryotes have a nucleus? | Yes, and membrane-bound organelles |
| What is the size difference between prokaryotic and eukaryotic cells? | Eukaryotes are around 10x larger |
| What is the form of DNA in prokaryotes? | Circular chromosomes (and plasmids) |
| What is the form of DNA in eukaryotes? | Linear chromosomes with histones |
| Where does transcription occur in prokaryotes? | Same place as translation |
| Where does transcription occur in eukaryotes? | Nucleus (separate from translation) |
| Do prokaryotes have organelles? | No |
| Do eukaryotes have organelles? | Yes |
| What are the three components of a nucleotide? | Sugar, phosphate and nitrogenous base |
| What is the difference between ribose and deoxyribose? | Ribose has 2'-OH; deoxyribose has 2'-H |
| What are purines? | Adenine and guanine (two rings) |
| What are pyrimidines? | Cytosine, thymine and uracil (one ring) |
| What bond forms the DNA backbone? | Phosphodiester bond |
| What is the shape of DNA? | Double helix |
| Strand orientation in DNA? | Antiparallel (5'->3' and 3'->5') |
| Base pairing rules? | A-T (2 bonds) G-C (three bonds) |
| Where are bases located in DNA? | Inside the helix |
| Where is the backbone located? | Outside |
| Why can DNA strands separate easily? | Hydrogen bonds are relatively weak |
| DNA vs RNA strands? | DNA double-stranded; RNA single-stranded |
| Sugar in DNA vs RNA? | DNA: deoxyribose; RNA: ribose |
| Base difference? | DNA uses T; RNA uses U |
| Which is more stable, DNA or RNA? | DNA |
| Function of DNA? | Long-term information storage |
| Function of RNA? | Messaging and catalytic roles |
| Which direction does DNA polymerase synthesise? | 5'->3' |
| What does helicase do? | Unwinds DNA |
| What does primase do? | Makes RNA primers |
| What does DNA polymerase III do? | Main elongation enzyme |
| What does RNA polymerase I do? | Removes primers and fills gaps |
| What are Okazaki fragments? | Short DNA fragments on lagging strand |
| Leading vs lagging strand? | Leading= continuous; lagging= discontinuous |
| What provides energy for DNA synthesis? | Release of pyrophosphate (PPi) |
| What is the sense strand? | Matches mRNA (T->U) |
| What is the antisense strand? | Template for transcription |
| What is a mutation? | Permanent change in DNA sequence |
| Germline vs somatic mutation? | Germline= heritable; somatic= not heritable |
| What do silent mutations do? | No amino acid change |
| What causes UV DNA damage? | Pyrimidine dimers |
| What is a pyrimidine dimer? | Covalent bond between adjacent pyrimidines |
| Effect of pyrimidine dimers? | Distorts DNA and blocks replication |
| What is nucleotide excision repair (NER)? | Removes damaged DNA and replaces it |
| What happens if DNA damage is not repaired? | Mutations or cell death |
| How many DNA repair enzymes exist? | Around 130 |
| Human mutation rate? | Around 3x10^-8 per base per generation |
| Why do longer genes mutate more? | Larger target size |
| Why do RNA viruses mutate rapidly? | Error-prone replication |
| Why is high viral mutation important? | Enables rapid evolution |
| What causes cancer at the molecular level? | Accumulation of mutations |
| What types of genes are affected in cancer? | Oncogenes, tumour suppressors, repair genes |
| Why is cancer considered multigenic? | Requires multiple mutations |
| Why is DNA a good storage molecule? | Stable, high-density information storage |
| What creates genetic variation? | Mutations and imperfect repair |
| What is forward genetic screening? | Start with a phenotype and identify the responsible genes |
| What is reverse genetic screening? | Start with a known gene/ genotype and observe the resulting phenotype |
| Which type of screening is used in the lac operon practical? | Forward genetic screening |
| What is the main goal of the lac operon screen in E. coli? | Isolates mutants affecting lac operon function |
| What was Thomas Hunt Morgan famous for discovering? | White-eye mutation in Drosophila linked to the X chromosome. |
| Why was Morgan’s discovery important? | It provided the first evidence of sex-linked inheritance |
| What did Beadle and Tatum propose? | The “one gene → one enzyme” hypothesis. |
| What did Crick and Brenner discover using frameshift mutations? | The triplet nature of the genetic code. |
| What did Jacob and Monod discover? | The regulatory mechanism of the lac operon |
| What mutagen is used in the practical? | UV light (~254 nm). |
| What type of DNA lesion is primarily caused by UV radiation? | Pyrimidine dimers, especially thymine dimers |
| What is a pyrimidine dimer? | A covalent linkage between adjacent pyrimidine bases caused by UV exposure. |
| Why are pyrimidine dimers harmful? | They distort DNA and block replication and transcription. |
| What can happen if UV damage is not repaired? | Replication fork stalling, blocked transcription, and cell death. |
| What enzyme performs photoreactivation? | Photolyase |
| What does photolyase do? | Breaks the covalent bond in pyrimidine dimers |
| Does photoreactivation require light? | Yes, visible/near-UV light. |
| What repair pathway removes a damaged DNA segment around UV lesions? | Nucleotide excision repair (NER). |
| Which proteins are involved in bacterial NER? | UvrA, UvrB, UvrC, DNA polymerase I, and DNA ligase. |
| How does NER repair DNA damage? | Excises a short DNA segment containing the lesion, resynthesizes DNA, and ligates the strand. |
| What defect does the UV-R A PHR strain have? | Defective nucleotide excision repair and photoreactivation. |
| What is measured in a UV kill-curve experiment? | Survival of bacteria after increasing UV exposure. |
| What is plotted on a kill curve? | Log CFU vs UV exposure time. |
| What does CFU stand for? | Colony-forming units |
| Why are serial dilutions used before plating? | To obtain countable colony numbers |
| Why is kanamycin included in the agar plates? | To select for experimental strains and suppress contaminants. |
| Which strain should be more UV-sensitive: wild-type or UV-repair mutant? | The UV-repair mutant |
| What does lacZ encode? | β-galactosidase. |
| What does β-galactosidase do? | Hydrolyzes lactose into glucose and galactose. |
| What does lacY encode? | Lactose permease |
| What is the function of lactose permease? | Imports lactose into the cell |
| What does lacA encode? | Transacetylase |
| What controls transcription of lacZ, lacY, and lacA? | A shared promoter and operator region |
| What is an operon? | A group of genes transcribed together under one promoter |
| What is X-Gal? | A colorless substrate cleaved by β-galactosidase. |
| What color appears when β-galactosidase cleaves X-Gal? | Blue |
| What do blue colonies indicate on X-Gal plates? | Functional lac operon activity |
| What do white colonies indicate on X-Gal plates? | Potential lac operon mutants |
| Why are white colonies isolated for further study? | They may contain mutations affecting lac operon function |
| What is the purpose of a β-galactosidase assay? | Quantify lac operon enzyme activity. |
| What is plasmid complementation? | Introducing a functional gene copy to determine which gene is mutated. |
| What does successful complementation indicate? | The plasmid supplied the missing functional gene. |
| What is PCR used for in the ASC component? | Amplifying the lac operon region for sequencing |
| Why sequence lac operon mutants? | To identify the exact mutation responsible for the phenotype. |
| What is the purpose of sequence alignment? | Compare mutant DNA to a reference sequence to locate mutations. |
| Why is Escherichia coli widely used in genetics? | Easy to grow, genetically manipulate, and study. |
| What is the relationship between DNA, RNA, and protein? | DNA → RNA → protein. |
| What process converts DNA into RNA? | Transcription |
| What process converts RNA into protein? | Translation |
| What is a frameshift mutation? | An insertion/deletion that shifts the reading frame. |
| Why are frameshift mutations often severe? | They alter downstream codons and protein structure. |
| Why are upstream mutations in operons especially damaging? | They can disrupt downstream genes in the same transcript. |
| What is a phenotype? | Observable traits or characteristics |
| What is a genotype? | The genetic makeup of an organism |
| What is a mutation? | A heritable change in the DNA sequence |
| What is mutagenesis? | The process of generating mutations |
| Why are controls important in experiments? | They allow comparison and validate conclusions |
| What is the purpose of comparing wild-type and mutant strains? | Determine the effect of specific mutations |
| Why are DNA repair pathways biologically important? | They maintain genome stability and cell survival. |
Created by:
Samara Hayes