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Molecular Genetics
| Question | Answer |
|---|---|
| What are the 4 types of DNA nucleotides? | Adenine (A), Thymine (T), Guanine (G), Cytosine (C) |
| What are the 4 types of RNA nucleotides? | Adenine (A), Uracil (U), Guanine (G), Cytosine (C) |
| What is mRNA? | Messenger RNA — a single-stranded template for protein synthesis |
| What is tRNA? | Transfer RNA — clover-shaped molecule that transports amino acids to their mRNA codon |
| What is rRNA? | Ribosomal RNA — globular RNA that forms part of ribosomes |
| What is DNA replication? | The copying of genetic information in cells, starting at the origin of replication |
| What does helicase do? | Separates the DNA double helix into single strands, forming a replication fork |
| What does topoisomerase do? | Relieves the stress caused by unwinding DNA by breaking and rejoining strands |
| What are single-stranded binding proteins? | Proteins that bind to single-stranded DNA near the replication fork to keep the two strands apart |
| What does primase do? | Creates a small strip of RNA primer that DNA polymerase needs to begin synthesizing a new DNA strand |
| What does DNA Polymerase III do? | Synthesizes the new DNA strand in the 5' → 3' direction by adding nucleotides to the RNA primer |
| What does DNA Polymerase I do? | Removes the RNA primer and replaces it with newly synthesized DNA |
| What does ligase do? | Seals the gaps in the phosphodiester backbone of DNA between Okazaki fragments |
| What is the leading strand? | The strand synthesized continuously as DNA unzips |
| What is the lagging strand? | The strand synthesized discontinuously, producing Okazaki fragments |
| What are Okazaki fragments? | Short stretches of nucleotides formed as the lagging strand is synthesized |
| What are telomeres? | Segments of DNA added to the ends of chromosomes to prevent loss of genomic information as chromosome ends wear down |
| In which direction is DNA synthesized? | 5' → 3' direction; nucleotides are added only to the 3' end |
| What is transcription? | The process of synthesizing RNA from a DNA template for a specific gene |
| How does transcription differ from DNA replication? | Transcription transcribes a specific gene; DNA replication copies the entire genome |
| What are transcription factors? | Proteins that bind to the promoter and other regulatory sequences to control transcription of a target gene |
| What is the promoter region? | The DNA sequence where RNA polymerase attaches; located upstream of the transcribed DNA |
| What is the most effective way to prevent a gene from being expressed? | Delete the promoter region |
| What are the three steps of transcription? | Initiation (RNA polymerase attaches to promoter and unzips DNA), Elongation (RNA polymerase synthesizes RNA using one DNA strand as template), Termination (RNA polymerase reaches a stop sequence and detaches) |
| What post-transcriptional processing occurs before translation? | Adding a 5' cap to the 5' end, adding a poly-A tail to the 3' end, and RNA splicing |
| What is RNA splicing? | The removal of introns from pre-mRNA and reconnection of the remaining exons to produce mature mRNA |
| What are exons? | Protein-coding regions of the genome |
| What are introns? | Non-coding regions in mRNA that do not encode functional proteins |
| What is alternative splicing? | A process that allows production of multiple protein types from a single gene by using different combinations of exons |
| What is translation? | The synthesis of proteins based on the sequence of mRNA nucleotides |
| What are the three steps of translation? | Initiation, Elongation, Termination |
| What happens during translation initiation? | The small ribosomal subunit binds to mRNA, methionine-tRNA binds to the AUG start codon, and the large ribosomal subunit joins to form a complete ribosome |
| What happens during translation elongation? | tRNAs bring amino acids to the growing polypeptide chain; they enter at the A site, shift to the P site, then exit at the E site |
| What happens during translation termination? | A stop codon (UAG, UAA, or UGA) is encountered, release factors recognize it, and the polypeptide chain is released |
| What is a point mutation? | A single nucleotide change causing substitution, insertion, or deletion |
| What is a silent mutation? | A codon change that, due to codon redundancy, still codes for the same amino acid — protein function is unchanged |
| What is a missense mutation? | A mutation that results in a new codon encoding a different amino acid |
| What is a nonsense mutation? | A mutation that converts an amino acid codon into a stop codon, producing a truncated, usually non-functional protein |
| What is a frameshift mutation? | A mutation caused by insertion or deletion that shifts the reading frame of the RNA transcript, causing different amino acids to be translated |
| What is the difference between a forward and backward mutation? | A forward mutation changes a wild-type allele to a mutant allele; a backward mutation reverts a mutant allele back to wild type |
| How do bacteria reproduce? | Binary fission — DNA is duplicated and the cell divides into two daughter cells |
| How does bacterial DNA replication differ from eukaryotic mitosis? | In bacteria, no mitotic spindle forms, and DNA replication and separation occur simultaneously |
| What are plasmids? | Small, circular double-stranded DNA molecules separate from the main prokaryotic chromosome; they carry non-essential but potentially beneficial genes and replicate independently |
| What is an operon? | A gene cluster that controls transcription, consisting of a promoter, operator, and structural genes |
| What is the operator in an operon? | A region that can block RNA polymerase if occupied by a repressor |
| What are structural genes in an operon? | Genes that code for the proteins to be produced |
| What is a repressor? | A protein that binds to the operator of prokaryotic genes to decrease transcription |
| What is an activator (enhancer)? | A protein that binds to prokaryotic operators to increase transcription and assists RNA polymerase attachment to the promoter |
| What is the lac operon? | A prokaryotic operon that encodes genes required for processing lactose; presence of lactose induces the operon to produce lactose-breakdown enzymes. Performs best with glucose absent, lactose present |
| What is the trp operon? | A group of genes necessary to synthesize tryptophan in prokaryotic cells; when tryptophan is present, the trp repressor binds to the operator and blocks RNA synthesis (repressible) |
| What is conjugation? | DNA transfer from a living donor bacterium to a living recipient via cell-to-cell contact using a pilus |
| What is transformation? | A process where a competent recipient bacterium takes up free DNA from its surrounding environment (like w plasmids) |
| What is transduction? | DNA transfer from one bacterium to another via a bacteriophage (a virus that infects bacteria) |
| What is the genome? | The complete genetic information of an organism; the majority of the human genome consists of non-coding DNA |
| What is the transcriptome? | The complete set of all RNA molecules that can be produced by a cell |
| What is the proteome? | The complete set of proteins expressed in an organism |
| What is genome size? | The total number of nucleotides an organism has |
| Is genome size related to organism complexity? | No — for example, a grape may have a larger genome than a human |
| How do eukaryotic and prokaryotic genome sizes compare? | Eukaryotes have larger genomes than prokaryotes; prokaryotes lack introns and have less "junk DNA" |
| What is gene number? | The total number of genes (sequences of nucleotides that code for a product) an organism has |
| Is there a correlation between genome size and gene number? | No — there is no correlation between genome size and number of genes |
| Do eukaryotes or prokaryotes have more genes? | Eukaryotes have more genes than prokaryotes |
| Why do humans have fewer genes than expected for their complexity? | Because of alternative splicing — a single gene can be used to make multiple different protein products |
| What is gene density? | The ratio of gene number to genome size |
| Why do eukaryotes have lower gene density than prokaryotes? | Because the majority of the eukaryotic genome is noncoding DNA |
| What are the approximate proportions of the human genome by category? | Transposable elements 44%, introns 20%, repetitive DNA 15%, unique noncoding DNA 14%, regulatory sequences 5%, exons 2% |
| What is epigenetics? | The study of changes in gene expression that do not involve alterations to the nucleotide sequence |
| What is DNA methylation and what does it do? | An epigenetic mechanism that stops gene expression by tightening chromatin organization, making DNA less accessible for transcription — without altering the nucleotide sequence |
| What is histone acetylation and what does it do? | An epigenetic mechanism that increases gene expression by loosening chromatin organization, making DNA more accessible for transcription |
| What are histone tails made of? | Lysine amino acids — if mutated, gene expression can be increased or decreased |
| What is temperature-dependent sex determination? | A process seen in reptiles where gender is determined by environmental temperature during a thermosensitive period of embryonic development |
| What is Pattern I temperature-dependent sex determination? | Males develop in cold temperatures and females develop in warm temperatures (e.g., turtles) |
| What is Pattern II temperature-dependent sex determination? | Females develop in cold or hot temperatures and males develop in medium temperatures (e.g., crocodiles) |
| What epigenetic mechanisms are involved in temperature-dependent sex determination? | DNA methylation, histone acetylation, and non-coding RNAs — these modify which hormone pathway is expressed, leading to different sex organ development |
| How does epigenetics explain the queen bee phenotype? | The queen larva is fed royal jelly, which blocks DNA methylation, allowing different genes to be expressed and resulting in a different phenotype (larger size, longer lifespan, faster development, functional ovaries) |
| What is genomic imprinting? | A process where certain genes are expressed depending on which parent they are inherited from; the body expresses genes from only one parent's chromosome while the imprinted genes on the other chromosome are silenced via epigenetic mechanisms |
| What is Prader-Willi Syndrome? | A condition caused by mutation or deletion of genes on the father's copy of Chromosome 15; a set of genes on that chromosome is only expressed from the father's copy, while the mother's copy is imprinted (silenced) |
| What is Angelman Syndrome? | A condition caused by deletion or mutation of genes on the mother's copy of Chromosome 15; a different set of genes on that chromosome is only expressed from the mother's copy, while the father's copy is imprinted (silenced) |
| How do Prader-Willi and Angelman Syndromes differ? | Both involve imprinting on Chromosome 15, but they affect different sets of genes — Prader-Willi results from loss of the paternal copy's expression, while Angelman results from loss of the maternal copy's expression |
Created by:
smurtab