Translation (DP IB Biology: HL)

What is the correct sequence of events during the initiation stage of translation in eukaryotes?

1. Small subunit of the ribosome binds to the 5’ end of mRNA
2. Large ribosomal subunit binds to form the ribosome complex
3. The ribosomal subunit moves along the mRNA until it locates a start codon
4. An initiator tRNA binds
5. Elongation of the polypeptide chain can begin                                                                                                                                  

   	first	→	→	→	last
   A	I	II	III	V	IV
   B	II	I	IV	III	V
   C	I	II	III	IV	V
   D	I	IV	III	II	V

Which of the following is not a function of tRNA?

During the elongation stage of translation the ribosome ‘translocates’ along the mRNA moving in a 5’ → 3’ direction.

What is the immediate effect of this directional movement?

Which statements best describe ribosomes?

In eukaryotic cells, ribosomes can be either free or bound.

Which of the following proteins would most likely be synthesised by bound ribosomes?

In prokaryotes, the processes of transcription and translation are said to be coupled, which means they can proceed simultaneously.

Which is the key cellular feature of prokaryotes that allows this to happen?

The bacterium Staphylococcus aureus (S. aureus) is one of the main human pathogens and can cause many serious infectious diseases. Mutations in the mec A gene has allowed S.aureus to become resistant to many antibiotics. The table below shows a (Clustal W) partial nucleotide sequence alignment of mec A for different isolates of S. aureus. The drug resistant strain has a base substitution mutation (shown in bold) which changes the amino acid residue from serine to threonine.

Which of the following statements most likely explains how an amino acid change can cause antibiotic resistance?

Which interactions or features differentiate tertiary structure from secondary structure in proteins?

1. Hydrogen bonds
2. Disulphide bridges
3. Hydrophobic interactions
4. Alpha-helices
5. Interactions between R-groups of amino acids

Which of the following best describes the quaternary structure of proteins?

The diagram below represents an electron micrograph of eukaryotic polysomes.

What is the main advantage that polysomes give to a eukaryotic cell?

Which of the following enables tRNA activating enzymes to link an amino acid to a tRNA molecule?

Which of the following applies to both free and bound ribosomes?

1. They produce polypeptides that are destined to be used for processes occurring in the cytosol
2. Translation is interrupted and then re-initiated once movement of the ribosome is complete
3. They are found in all eukaryotic cells and may be either 70S or 80S
4. They facilitate the binding of mRNA and tRNA and catalyse the formation of peptide bonds
5. They have four binding sites to allow the molecules involved with translation to attach to its subunits

Ustilago maydis is a fungal pathogen affecting maize. It secretes toxins, known as killer toxins, with the best-characterised one being the KP6 toxin. This particular toxin consists of two small polypeptides that are not linked by covalent bonds. The diagram below shows the ribbon structure of one of the polypeptides of the KP6 toxin.

Which of the following is the most accurate description of the structure of this polypeptide?

Leucine is an essential amino acid (EAA) that plays an important role in initiating the process of translation. Scientists investigated the effect of leucine on the process of protein synthesis and protein breakdown in muscles. Participants of the study were divided into three equal groups. Each group were given the same diet that was supplemented with different amounts of leucine (High, low and no added leucine) and the rate of protein synthesis and protein breakdown were monitored over time.

The diagram below shows the results of this study.

Which of the following provides the most plausible conclusion that can be drawn from the data?

The following steps describes the events taking place during the elongation of a polypeptide in no particular order.

1. Free tRNA molecules bind to their corresponding amino acids due to their specific anticodon and transport it to the ribosome 
2. A tRNA with a complementary anticodon binds to the "A" site bringing its specific amino acid along
3. The initiator tRNA moves from the "P" to the "E" site on the ribosome where it initiates translation
4. The amino acid carried by the tRNA at the "P" site is linked to the polypeptide chain by a peptide bond
5. tRNA carrying the peptide chain moves from the "A" site to the "P" site as the ribosome moves in the 5' → 3' direction along the mRNA molecule

Which of these steps contain incorrect information?