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Genetics: 3
A deck of flashcards for Undergraduate Study of Biology.
| Question | Answer |
|---|---|
| Translation | The process in which cellular ribosomes create proteins. In translation, messenger RNA (mRNA)—produced by transcription from DNA—is decoded by a ribosome to produce a specific amino acid chain, or polypeptide. |
| What nucleic acids are involved in translation? | Messenger RNA (mRNA) and transfer RNA (tRNA). mRNA is translated into a protein with the help of tRNA. |
| Transfer RNA (tRNA) | An adaptor molecule composed of RNA, that serves as the physical link between the mRNA and the amino acid sequence of proteins. They are not identical, each carrying a specific AA and has an anticodon on the other end. |
| Anticodon | A sequence of three nucleotides forming a unit of genetic code in a transfer RNA molecule, corresponding to a complementary codon in messenger RNA. |
| Conditions for accurate translation | A correct match between a tRNA and an amino acid, done by the enzyme aminoacyl tRNA synthetase, and a match between the tRNA anticodon and an mRNA codon. |
| Wobble | The third base with less discriminatory for the amino acid than the other two bases. This third position in the codon is referred to as the wobble position. |
| Ribosomal RNA (rRNA) | The RNA component of the ribosome, and is essential for protein synthesis in all living organisms. It constitutes the predominant material within the ribosome, which is approximately 60% rRNA and 40% protein by weight. |
| What are the three binding sites for tRNA in a ribosome? | The P site, A site and E site. |
| The P site | Holds the tRNA that carries the growing polypeptide chain. |
| The A site | Holds the tRNA that carries the next amino acid to be added to the chain. |
| The E site | The exit site where discharged tRNA leave the ribosome. |
| What are three stages of translation? | Initiation, Elongation and Termination. |
| Initiation stage in translation | A stage of translation that brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits (rRNA). A small ribosomal subunit binds with mRNA and a special initiator tRNA. |
| The start codon | AUG |
| Elongation stage in translation | A stage of translation where amino acids are added one by one to the preceding amino acid. Each addition involves proteins called elongation factors through: codon recognition, peptide bond formation and translocation. |
| Termination stage in translation | A stage of translation when a stop codon in the mRNA reaches the A site of the ribosome. The A site accepts a protein called a release factor which causes the addition of H2O molecules rather than AA. This reaction releases the polypeptide. |
| Polyribosome (polysome) | A number of ribosomes which translates a single mRNA simultaneously. |
| Two populations of ribosomes in the cell | Free ribosomes (in the cytosol) and bound ribosomes (attached to the RER). |
| Are ribosomes identical? | Yes, they can also switch from free to bound. |
| Free ribosomes | Mostly synthesizes proteins that function in the cytosol. |
| Bound ribosomes | Makes proteins of the endomembrane system and proteins that are secreted from the cell. |
| Where does polypeptide synthesis begin? | Polypeptide synthesis always begins in the cytosol. |
| When does synthesis does not finish in the cytosol? | Only when the polypeptide signals the ribosome to attach to the ER. |
| Signal peptide | A mark found on polypeptides destined for the ER or for secretion. A signal-recognition particle (SRP) binds to the signal peptide and brings it and its ribosome to the ER. |
| Mutations | Changes in the genetic material of a cell or virus. |
| Point mutation | Chemical changes in just one base pair of a gene. |
| Two general categories of point mutations | Base-pair substitutions and Base-pair insertions or deletions. |
| Base-pair substitution | Replaces one nucleotide and its partner with another pair of nucleotides. |
| Silent mutations | Mutation with no effect on the amino acid produced by a codon because of redundancy in the genetic code. |
| Missense mutations | Mutation that still code for an amino acid, but not necessarily the right one. |
| Nonsense mutations | Mutation which changes an amino acid codon into a stop codon, nearly always leading to a non-functional protein. |
| Frameshift mutation | Where insertion or deletion (addition or losses) of nucleotide pairs in a gene alters the reading frame of the RNA. |
| Mutagen | Physical or chemical agents that can cause mutations. |
| How genes are transcribed/translated in: Bacteria, Eukarya and Archaea | Bacteria; simultaneously. Eukarya: Separated by nuclear envelope. Archaea: Likely coupled. |
| Defining a "Gene" | It is considered a discrete unit of inheritance, a region of specific nucleotide sequence in a chromosome & a DNA sequence that codes a specific polypeptide chain. |
| Summary of a gene | A region of DNA that can be expressed to produce a final functional product, either a polypeptide or an RNA molecule. |
| Gene expression | The process by which DNA directs protein synthesis, which includes two stages: transcription and translation. |
| How was the fundamental relationship between genes and proteins discovered? | Evidence from the study of metabolic defects and nutritional mutants in Neurospora. |
| RNA | The intermediate between genes and the proteins for which they code. |
| Transcription | A process which produces messenger RNA (mRNA) |
| Primary transcript | The initial RNA transcript from any gene. |
| How are the flow of information from gene to protein based? | On a triplet code: a series of non-overlapping, three nucleotide words. These triplets are the smallest units of uniform length that can code for all the amino acids. |
| Template strand | One of the two DNA strands during transcription which provides a template for ordering the sequence of nucleotides in an RNA transcript. |
| Codons | mRNA base triplets, read in the 5' to 3' direction during translation. It must be read in the correct reading frame(groupings) in order for the specified polypeptide to be produced. |
| RNA polymerase | The enzyme which catalyzes RNA synthesis by prying the DNA strands apart and hooks together the RNA nucleotide. RNA synthesis follows the same base-pairing rules as DNA, except uracil substituted for thymine. |
| Promoter | The DNA sequence where RNA polymerase attaches |
| Transcription unit | The stretch of DNA that is transcribed. |
| The 3 stages of transcription | Initiation, Elongation and Termination. |
| Initiation stage in transcription | Promoters signal the initiation of RNA synthesis. |
| How the initiation stage of transcription happens in bacteria? | RNA polymerase recognizes and binds to the promoter. |
| How the initiation stage of transcription happens in Eukaryotes? | Transcription factors mediate the binding of RNA polymerase. |
| Transcription initiation complex | The completed assembly of transcription factors and RNA polymerase II bound to a promoter. |
| TATA box | A promoter which is crucial in forming the initiation complex in eukaryotes. |
| Elongation stage in transcription | RNA polymerase moves along the DNA, untwisting the double helix, 10 - 20 bases at a time. |
| Rate of transcriptions in eukaryotes | Transcription progresses at a rate of 40 nucleotides per second in eukaryotes. |
| Termination stage in transcription for bacteria | The polymerase stops transcription after it transcribes the terminator (the sequence that signals the end of the transcription). |
| Termination stage in transcription for eukaryotes | The polymerase transcribes a sequence on the DNA called the polyadenylation signal sequence, which codes for a polyadenylation signal (AAUAAA) in the pre-mRNA. |
| Introns | These non-coding regions, they are also called intervening sequences. |
| Exons | The other regions, that are eventually expressed, usually translated into amino acid sequences. |
| RNA splicing | A process which removes introns and joins exons, creating a mRNA molecule with a continuous coding sequence. In some case, it may be carried out by spliceosome. |
| Spliceosome | Consists of a variety of proteins and several small nuclear ribonucleoproteins (snRNP). It interacts with certain sites along an intron, releasing the intron and joining together the two exons that flanked the intron. |
| Ribozymes | Catalytic RNA molecules that function as enzymes and splice RNA. The discovery of ribozymes rendered obsolete the belief that all biological catalysts were proteins. |
| The three properties of RNA that enable it to function as an enzyme | It can form a three-dimensional structure because its ability to base pair with itself. Some bases in RNA contain functional groups. RNA may hydrogen-bond with other nucleic acid molecules. |
| Alternative RNA splicing | Variations from genes that can encode more than one kind of polypeptide, depending on which segments are treated as exons during RNA splicing. |
| Domains | Proteins often have a modular architecture consisting of discrete regions. |
| What may result in exon shuffling? | The evolution of new proteins. |
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theecloud
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