10.10 - 10.14 Flashcards
Messenger RNA
The type of ribonucleic acid that encodes genetic information from DNA and conveys it to ribosomes, where the information is translated into amino acids.
Note 1 —-»
Messenger RNA is transcribed from DNA, and the information in the mRNA is then translated into polypeptides. In prokaryotic cells, which lack nuclei, transcription and translation occur in the same place: the cytoplasm. In eukaryotic cells, however, mRNA molecules must exit the nucleus via the nuclear pores and enter the cytoplasm, where the machinery for polypeptide synthesis is located.
Intron
An internal, noncoding region of a gene that does not become part of the final messenger RNA molecule and is therefore not expressed.
Exon
The part of a gene that becomes part of the final messenger RNA and is therefore expressed.
RNA Splicing
The removal of introns and joining of exons in eukaryotic RNA, forming an mRNA molecule with a continuous coding sequence.
Explain why most eukaryotic genes are longer than the mRNA that leaves the nucleus.
These genes have introns, noncoding sequences of nucleotides that are spliced out of the initial RNA transcript to produce mRNA.
Transfer RNA
A type of RNA that acts as an interpreter in translation.
Note 2 —-»
The function of a tRNA is to transfer amino acids from the cytoplasmic pool to a growing polypeptide in a ribosome. To perform this task, tRNA molecules must carry out two functions: (1) picking up the appropriate amino acids and (2) recognizing the appropriate codons in the mRNA. The unique structure of tRNA molecules enables them to perform both tasks.
Anticodon
A specific sequence of three nucleotides that is complementary to a codon triplet on mRNA on a tRNA.
Note 3 —-»
There is a family of 20 versions of these enzymes, one enzyme for each amino acid. Each enzyme specifically binds one type of amino acid to all tRNA molecules that code for that amino acid, using a molecule of ATP as energy to drive the reaction. The resulting amino acid–tRNA complex can then contribute its amino acid to a growing polypeptide chain.
What is an anticodon, and what is its function?
It is the base triplet of a tRNA molecule that couples the tRNA to a complementary codon in the mRNA. This is a key step in translating mRNA to polypeptide.
Ribosomal RNA
The type of RNA, that with proteins, makes up ribosomes.
Note 4 —-»
The ribosomes of bacteria and eukaryotes are very similar in function, but those of eukaryotes are slightly larger and different in structure. The differences are medically significant. Certain antibiotic drugs can inactivate bacterial ribosomes while leaving eukaryotic ribosomes unaffected. These drugs, such as tetracycline and streptomycin, are used to combat bacterial infections.
Note 5 —-»
A fully assembled ribosome has a binding site for mRNA on the small subunit and binding sites (referred to as the P site and the A site) for tRNA on the large subunit. The subunits of the ribosome act like a vise, holding the tRNA and mRNA molecules close together, allowing the amino acids carried by the tRNA molecules to be connected into a polypeptide chain. In the next two modules, we examine the steps of translation in detail.
How does a ribosome facilitate protein synthesis?
A ribosome holds mRNA and tRNAs together and connects amino acids from the tRNAs to the growing polypeptide chain.
Note 6 —-»
Translation can be divided into the same three phases as transcription: initiation, elongation, and termination.
Start Codon
The specific three-nucleotide sequence that to which an initiator tRNA molecule binds, starting the translation of genetic information on mRNA.
P site
One of ribosome’s binding sites for tRNA during translation.
A site
One of ribosome’s binding sites for tRNA during translation.
What would happen if a genetic mutation in a gene changed a start codon to some other codon?
The messenger RNA transcribed from the mutated gene would be nonfunctional because ribosomes could not initiate translation correctly.
Stop Codon
One of three triplets in mRNA that signals gene translation to stop.
What would happen if a mutation caused a codon in the middle of an mRNA to change from UUA to UAA?
Translation would stop prematurely because a stop codon was introduced.
