Ch. 13 Concept Check & Check Your Understanding Flashcards
An inborn error or metabolism is caused by..
A mutation in a gene that causes an enzyme to be inactive
The reason why Beadle and Tatum observed four different categories of mutants that could not grow on media without methionine is because..
Four different enzymes are involved in a pathway for methionine biosynthesis
What is the genetic code?
The relationship between a three-base codon sequence and an amino acid
The reading frame begins with a ___ and is read ___.
Start codon, in groups of three bases
The fourth codon in an mRNA-coding sequence is GGG, which specifies glycine. If we assume that no amino acids are removed from the polypeptide, which of the following statements is correct?
The fourth amino acid from the N-terminus is glycine
A type of secondary structure found in proteins is..
- alpha helix
- B sheet
Let’s suppose a researcher mixed together nucleotides with the following percentage of bases: 30% G, 30% C, and 40% A. If RNA was made via polynucleotide phosphorylase, what percentage of the codons would be 5’-GGC-3’?
2.7%
In the triplet-binding assay of Nuremberg and Leder, an RNA triplet composed of three bases was able to cause the..
Binding of a tRNA carrying the appropriate amino acid
If a tRNA has an anticodon with the sequence 5’-CAG-3’, which amino acid does it carry?
Leucine
The anticodon of a tRNA is located in the..
Loop of the second stem-loop
An enzyme known as ___ attaches an amino acid to the ___ of a tRNA, thereby producing ___.
Aminoacyl-tRNA synthetase
3’ single-stranded region of the acceptor stem
A charged tRNA
Each ribosomal subunit is composed of..
- multiple proteins
- rRNA
The site(s) on a ribosome where tRNA molecules may be located include the..
- A site
- P site
- E site
During the initiation stage of translation in bacteria, which events occur?
- IF1 and IF3 bind to the 30S subunit
- the mRNA binds to the 30S subunit and tRNA binds to the start codon in the mRNA
- IF2 hydrolyzes its GTP and is released; the 50S subunit binds to the 30S subunit
The Kozak rules determine..
The choice of the start codon in complex eukaryotes
During the peptidyl transferase reaction, the polypeptide, which is attached to a tRNA in the ___, becomes bound via ___ to an amino acid attached to a tRNA in the ___.
P site, a peptide bond, A site
A release factor is referred to as a “molecular mimic” because its structure is similar to..
A tRNA
The metabolic pathway of phenylalanine breakdown.
Which disease occurs when homogentisic acid oxidase is defective?
Alkaptonuria occurs when homogentisic acid oxidase is defective.
An example of an experiment that supported Beadle and Tatum’s one-gene/one-enzyme hypothesis.
What enzymatic function is missing in the strain 2 mutants?
The strain 2 mutants are unable to convert O-acetylhomoserine into cystathionine.
The relationships among the DNA coding sequence, mRNA codons, tRNA anticodons, and amino acids in a polypeptide.
Describe the role of DNA in the synthesis of a polypeptide.
The role of DNA is to store the information that specifies the amino acid sequence of a polypeptide. It is a storage role.
The amino acids that are incorporated into polypeptides during translation.
Which two amino acids do you think are the least soluble in water?
Tryptophan and phenylalanine are the least soluble in water.
Levels of structures formed in proteins.
What type of bonding is responsible for the formation of the two types of secondary structures?
Hydrogen bonding promotes the formation of secondary structures in proteins.
The triplet-binding assay.
Explain how the use of radiolabeled amino acids in this procedure helped to reveal the genetic code.
Only one radiolabeled amino acid was found in each sample. If radioactivity was trapped on the filter, this meant that the codon triplet specified that particular amino acid.
Recognition between tRNAs and mRNA.
What are the two key functional sites of a tRNA molecule?
A tRNA has an anticodon that recognizes a codon in the mRNA. It also has a 3’ acceptor site where the correct amino acid is attached.
Catalytic function of aminoacyl-tRNA synthetase.
What is the difference between a charged tRNA versus an uncharged tRNA?
A charged tRNA has an amino acid attached to it.
Wobble position and base-pairing rules.
How do the wobble rules affect the total number of different tRNAs that needed to carry out translation?
The wobble rules allow for a smaller population of tRNAs to recognize all of the possible mRNA codons.
Overview of the stages of translation.
Explain how mRNA plays a role in all three stages.
A site in mRNA promotes the binding of the mRNA to the ribosome. The codons are needed during elongation to specify the polypeptide sequence. The stop codon is needed to terminate transcription.
The locations of the Shine-Dalgarno sequence and the start codon in bacterial mRNA.
Why does a bacterial mRNA bind specifically to the small ribosomal subunit?
The Shine-Dalgarno sequence in mRNA is complementary to a region in the 16S rRNA within the small ribosomal unit. These complementary sequences hydrogen bond with each other.
The elongation stage of translation in bacteria.
What is the role of peptidyl transferase during the elongation stage?
Peptidyl transferase catalyzes the peptide bond formation between amino acids in the growing polypeptide chain.
The termination stage of translation in bacteria.
Explain why release factors are called “molecular mimics.”
The structures of release factors, which are proteins, resemble the structures of tRNAs.
