LS7A: Week 6

Which of the following brings amino acids to the ribosome for use in translation? tRNA mRNA rRNA

tRNA

Imagine you are following a particular tRNA, called tRNAQ, through the process of translation in a eukaryote. In what order does tRNAQ go through the steps listed below? (Note that some steps may be used more than once.) 1. The polypeptide is transferred to tRNAQ. 2. tRNAQ binds the A site of the ribosome. 3. tRNAQ binds the P site of the ribosome. 4. The ribosome shifts, with tRNAQ still bound. 5. tRNAQ binds the E site of the ribosome. 2, 4, 1, 4, 2, 4, 5 3, 1, 4, 2, 4, 5 5, 1, 4, 3, 4, 5 3, 4, 1, 4, 2, 4, 5 2, 1, 4, 3, 4, 5

2, 1, 4, 3, 4, 5

Assuming A-U and G-C pairing between the anticodon and the codon, what anticodon in tRNAMet would pair with the codon 5'-AUG-3'? 5'-CAU-3' 5'-ATG-3' 5'-AUG-3' 5'-GUA-3' 5'-UAC-3'

5'-CAU-3'

Which of the following sequences of events correctly describes the progress of a protein that will be secreted from the cell? 1. SRP binds to the growing polypeptide chain and to the ribosome. 2. Translation resumes. 3. SRP binds to its receptor. 4. The signal sequence is cleaved. 5. Protein synthesis begins in the cytosol. 6. Translation pauses.

5-->1-->6-->3-->2-->4

Enzymatic catalysis of the peptide bond between the growing polypeptide and the next incoming amino acid takes place in which binding site? Question 2 choices Choice A., A site , Choice B., P site , Choice C., E site Choice D., combined A and P sites

A

How is the amino acid held on the charged tRNA? Question 2 choices Choice A., covalent bond , Choice B., hydrogen bonds Choice C., It can be a combination of all bond types.

A

What do you think happened to the mutations that decreased survival or reproduction of the parasites?

A mutation that decreases survival or reproduction will likely decrease in number in each generation because nonmutant forms leave more offspring. Eventually, the harmful mutation may disappear from the population because its final carriers failed to survive or reproduce. In the extreme case when the harmful mutation causes death or sterility, it can disappear in only one generation.

The interactions between amino acids are major factors in determining the shape of a protein. These interactions can be affected by the environment surrounding a protein. Which of the following would have an effect on the shape of a protein? whether the other molecules in the environment are predominantly hydrophilic or hydrophobic the pH of the environment the concentrations of ions present in the environment the temperature of the environment All of the other answer options are correct.

All of the other answer options are correct.

If a mutation rendered the signal recognition particle receptor nonfunctional such that it is no longer able to dissociate from the SRP, what would be the most obvious effect on the cell? Proteins destined for the nucleus would remain in the cytosol. Translation of most proteins would be incomplete. No proteins would arrive at their proper destinations within the cell. All proteins normally secreted by the cell would remain in the cytosol. All proteins normally secreted by the cell would remain partially formed and attached to the endoplasmic reticulum.

All proteins normally secreted by the cell would remain in the cytosol. All proteins normally secreted by the cell would remain partially formed and attached to the endoplasmic reticulum.

Which of the following occurs in the A site of the ribosome during translation? An uncharged tRNA is ejected from this site as the ribosome slides to the next codon. An incoming charged tRNA binds to this site. None of the other answer options is correct. The tRNA carrying the growing polypeptide moves to this site as the ribosome slides to the next codon.

An incoming charged tRNA binds to this site.

Which of the following occurs in the E site of the ribosome during translation? None of the other answer options is correct. The tRNA carrying the growing polypeptide moves to this site as the ribosome slides to the next codon. An uncharged tRNA is ejected from this site as the ribosome slides to the next codon. An incoming charged tRNA binds to this site.

An uncharged tRNA is ejected from this site as the ribosome slides to the next codon

How many aminoacyl-tRNA synthetase enzymes must be present in cells to properly synthesize proteins? Question 3 choices Choice A., 3, one for each base in a codon Choice B., 4, one for each base in the mRNA Choice C., 20, one for each amino acid Choice D., 64, one for each possible codon

C

The ribosome ______BLANK subunit has _______BLANK binding sites for tRNA molecules. Question 1 choices Choice A., large; two Choice B., small; two Choice C., large; three Choice D., small; three Choice E., large; four

C

Which of the following is the actual event that translates the language of nucleic acids (the sequence of bases, A, T (U), C, and G) to the language of proteins (determining which amino acid will be added to the polypeptide)? Question 1 choices Choice A., binding of charged tRNA to the ribosome A site Choice B., catalysis of a new peptide bond from the growing polypeptide to the next amino acid Choice C., release of the finished polypeptide at the stop codon , Choice D., attachment of the appropriate amino acid to the tRNA by aminoacyl tRNA synthetase Choice E., establishing the correct reading frame by the ribosome

D

In a protein-coding region, a mutation that replaces a single nucleotide for another always changes the resulting amino acid. True False

False

Protein families contain proteins with identical primary, secondary, and tertiary structures. False True

False

What is the consequence for a growing RNA transcript if an abnormal nucleotide with a 3′ H is incorporated rather than a 3′ OH? How about a 2′ H rather than a 2′ OH?

The incorporation of a nucleotide with a 3′ H rather than a 3′ OH will stop subsequent elongation because the 3′ OH is necessary to attack the high energy phosphate bond of the incoming nucleoside triphosphate. The incorporation of a nucleotide with a 2′ H rather than a 2′ OH will have no effect on elongation, as this group is not involved in the polymerization reaction.

A mutation leads to a change in one amino acid in a protein. The result is that the protein no longer functions properly. How is this possible?

The sequence of amino acids in a protein determines how a protein folds, so a change in even a single amino acid can affect the way the protein folds and can disrupt its function. For example, if the hydrophobic R groups of two amino acids must aggregate for proper structure and function, then a mutation that changes one of the hydrophobic amino acids for an acidic or a basic amino acid will prevent this aggregation and disrupt structure and function. Similarly, if proper folding requires interaction between the R groups of an acidic and a basic amino acid, then, if either one of them is changed to a hydrophobic amino acid, proper folding will not take place.

Which of the following occurs in the P site of the ribosome during translation? An incoming charged tRNA binds to this site. The tRNA carrying the growing polypeptide moves to this site as the ribosome slides to the next codon. An uncharged tRNA is ejected from this site as the ribosome slides to the next codon. None of the other answer options is correct.

The tRNA carrying the growing polypeptide moves to this site as the ribosome slides to the next codon.

Bacterial DNA containing an operon encoding three enzymes is introduced into chromosomal DNA in yeast (a eukaryote) in such a way that it is properly flanked by a promoter and a transcriptional terminator. The bacterial DNA is transcribed and the RNA correctly processed, but only the protein nearest the promoter is produced. Can you suggest why?

With proper eukaryotic processing, the RNA transcript from the bacterial DNA will be capped at the 5′ end. The initiation complex will form at the 5′ cap and move along the mRNA until the first AUG codon is encountered, and then translation begins. When one of the termination codons is encountered, the polypeptide is released. Translation of the downstream polypeptides cannot take place because the Shine-Dalgarno sequences preceding them are not recognized by the eukaryotic translational machinery.

Match the organelle with its description. Responses may be used multiple times or not at all. A. endoplasmic reticulum B. Golgi apparatus C. nuclear envelope 1. involved in the sorting of lipids and proteins 2. composed of two membranes 3. composed of multiple cisternae 4. involved in the synthesis of lipids and proteins 5. connected to the endoplasmic reticulum

b,c,b,a,c

Where are ribosomes found inside a cell? in the cytosol attached to the rough endoplasmic reticulum both in the cytosol and attached to the rough endoplasmic reticulum attached to the Golgi apparatus

both in the cytosol and attached to the rough endoplasmic reticulum

Which of the following actions would affect the secondary, but not primary, structure of a protein? break the ionic bonds between amino acids break the hydrogen bonds between amino acids change the sequence of amino acids disrupt the interactions between two different polypeptide chains

break the hydrogen bonds between amino acids

Proteins that prevent inappropriate folding of newly synthesized proteins are called: chaperones. ribosomes. enzymes. polymerases. synthetases.

chaperones.

Where does synthesis of transcription factor proteins occur?

cytoplasm

Which of the following accurately describes the path traveled by a new protein as it is synthesized and released from the cell? cytosol → Golgi → ER → vesicle → plasma membrane → external environment cytosol → ER → Golgi → vesicle → plasma membrane → external environment nuclear envelope → ER → vesicle → Golgi → plasma membrane → external environment plasma membrane → ER → vesicle → Golgi → cytosol → external environment nucleus → ER → Golgi → vesicle → plasma membrane → external environment

cytosol → ER → Golgi → vesicle → plasma membrane → external environment

The unfolding of a protein by heat or chemical treatment is referred to as: depolymerization. denaturation. disaggregation. hydrolysis. uncoupling.

denaturation.

A region of a polypeptide that folds in a particular way, relatively independently of the rest of the molecule, is a folding: exon. lariat. segment. domain. region.

domain

The process of a vesicle fusing with the plasma membrane and depositing its contents into the extracellular space is referred to as: bridging. active transport. endocytosis. budding. exocytosis.

exocytosis.

Secondary structure is characterized by which one of the following types of interactions? a covalent bond between two cysteines ionic bonding between an acidic R group and a basic R group the covalent bond between an amino nitrogen and a carboxyl carbon hydrogen bonding within the peptide backbone hydrogen bonding between R groups of amino acids

hydrogen bonding within the peptide backbone

When a charged tRNA is about to bind to the vacant A site of a ribosome, where is the growing polypeptide? The polypeptide is equally likely to be in any of the three sites. in the A site in the E site in the P site

in the P site

Which of the following are processed in the Golgi apparatus? (Select all that apply.) enzymes required for the synthesis of phospholipids mRNA molecules for the removal of introns integral membrane proteins of the plasma membrane proteins that will be broken down by lysosomes proteins that are secreted from the cell

integral membrane proteins of the plasma membrane proteins that will be broken down by lysosomes proteins that are secreted from the cell

Which of the following organelles could be considered recycling centers of eukaryotic cells? smooth endoplasmic reticulum the nucleus Golgi apparatus lysosomes mitochondria

lysosomes

In a population of organisms, beneficial and harmful random mutations are retained or eliminated through the process of: expression. folding. conservation. selection. translation.

selection.

Ribosomes in prokaryotes and eukaryotes are: identical in structure and translate using the same genetic code. similar in structure and translate using different genetic codes. similar in structure and translate using the same genetic code. identical in structure but translate using different genetic codes.

similar in structure and translate using the same genetic code.

The fully folded structure of a functional protein composed of a single polypeptide chain is referred to as the _____ structure. quaternary secondary tertiary primary

tertiary

Disorders of which organelle are often associated with defects in transport from compartment to compartment, resulting in poor sorting of protein components within the cell? plasma membrane endoplasmic reticulum the Golgi apparatus plasmids nucleus

the Golgi apparatus

Binding sites for tRNA are located in: both ribosomal subunits. the small ribosomal subunit. neither ribosomal subunit. the large ribosomal subunit.

the large ribosomal subunit.

A protein with an internal signal sequence is MOST likely to be located in: the extracellular space. the nucleus. the cytoplasm. a mitochondrion. a chloroplast.

the nucleus.

Two major types of protein secondary structures are referred to as: amino and carboxyl. ionic and covalent. α helix and β sheet. elementary and primary. residual and permanent.

α helix and β sheet.