Chapter 17 Flashcards
Explain how making proteins in cells involves going from one ‘chemical language’ to another?
First, the original DNA is copied into mRNA in a process called transcription. Then, mRNA is used by ribosomes to make proteins in the cytoplasm, in a process known as translation.
What are codons, and in what molecule are they found?
A codon is a three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code. They are located on a strand of RNA.
How many codons are there?
There are 64 codons
How many specify (or ‘code for’) amino acids? How many do not specify amino acids?
61 represent amino acids and the remaining three represent stop signals.
Clearly explain the roles of the codons AUG
AUG codes for the amino acid methionine (Met) but also functions as a “start” signal for ribosomes to begin translating the mRNA at that point.
Clearly explain the roles of the codons UGA, UAG and UAA in TRANSLATION.
UGA, UAG, and UAA functions as “stop” signals, marking where ribosomes end translation.
Describe the initiation of transcription of a gene, explaining the role of the promoter and template strand
During initiation, in eukaryotes, the transcription factors mediate the RNA polymerase to bind to the promoter sequence of the DNA, the polymerase unwinds the DNA for the initiation at this point to start transcribing the template strand
Describe the elongation of transcription of a gene, explaining the role of the RNA polymerase.
During elongation, RNA polymerase moves along the DNA template stand and untwists the double helix; this allows 10 to 20 nucleotides to be paired with DNA at a time. The new RNA nucleotides peel away from the DNA template and the double helix re-forms.
Describe the termination of transcription of a gene, explaining the role of the terminator.
During termination, in eukaryotes, the termination sequence causes the polymerase to detach from the DNA and release the transcribed RNA.
In what direction does RNA polymerase read a template strand, and in what direction does it synthesize a new polynucleotide chain?
RNA polymerase reads a template strand in the 3’ to 5’ direction. It synthesizes polynucleotide from the 5’ to 3’ direction.
In what direction does DNA polymerase read a template strand, and in what direction does it synthesize a new polynucleotide chain?
DNA polymerase reads in the 3’ to 5’ direction. It synthesizes polynucleotide in the 5’ to 3’ direction.
In what direction is an mRNA transcript translated?
Messenger RNA transcript is translated from the 5’ to 3’ direction.
What is rRNA?
Ribosomal RNA is RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.
What protein-like function does rRNA have?
Ribosomal RNA associates with a set of proteins to form ribosomes. These complex structures, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains
Where does rRNA come from?
Molecules of ribosomal RNA are synthesized in a specialized region of the cell called the nucleolus, which appears as a dense area within the nucleus and contains the genes that encode rRNA.
What are tRNAs, and why are they necessary for translation?
Transfer RNA is an RNA molecule that functions as a translator between nucleic acid and protein languages by carrying specific amino acids to the ribosome, where they recognize the appropriate codons in the mRNA.
What are anticodons and where are they found in a tRNA?
Anticodon is a nucleotide triplet at one end of a tRNA molecule that base pairs with a particular complementary codon on an mRNA molecule.
Where are amino acids attached, and how?
The amino acids are attached to the 3’ end of tRNA. They are attached by an enzyme called aminoacyl-tRNA synthetases, which requires the use of ATP, losing two phosphate groups and becoming AMP.
Where do tRNAs come from?
Transfer RNA is produced by RNA polymerase III from the nucleus and exported out to the cytoplasm.
Explain why tRNAs depend on aminoacyl-tRNA synthetases to perform their function.
Transfer RNA needs aminoacyl-tRNA synthetases to catalyze the covalent attachment of the amino acid to its tRNA, which is a process driven by the hydrolysis of ATP.
How many different types of these enzymes are found in cells?
There are twenty different types of aminoacyl-tRNA synthetases, one for each type of amino acid.
What are the substrates of this enzyme?
The tRNA and its specific amino acid are the substrates of the enzyme
Understand the causes and effects of the various mutations mentioned in this chapter
frameshift, nonsense, missense, and silent mutation
Silent mutation
is a nucleotide-pair substitution that has no observable effect on the phenotype; for example, within a gene, a mutation that results in a codon that codes for the same amino acid.
