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Genetics: 3

A deck of flashcards for Undergraduate Study of Biology.

QuestionAnswer
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.
Created by: theecloud