Workspace▸ Science▸ Test 18
← Back to Science
Science · Drill 18

Science practice 18

15 questions ~9 min recommended
⏱ 00:00
Score
—

α-T mRNA Transcripts1

Smooth muscle CAH
Striated muscle D COHHHH
Striated muscle CCOOHU
Myoblast CH00-00
Brain 0+-

α-T Gene2

Exon 1 2 3 4 9 10 11 12
Amino Acids 1-38 39-80 39-80 81-125 126-164 165-188 189-213 214-234 235-257 258-284 None 258-284

3456789101112131415

A gene is composed of a series of exon and intron segments. Exons are the coding regions of a gene, the segments that contain the instructions for building a protein. A gene's exons are connected by noncoding regions, or introns.

To build a protein, the cell must first transcribe the gene into messenger RNA (mRNA). Then a process called RNA splicing removes the noncoding introns and connects all of the exons to produce an mRNA transcript that can be used to build the protein.

Tropomyosins are a family of proteins that help maintain the cytoskeleton structure in all cells and support the contraction of muscle cells. In the late 1980s, a group of scientists discovered that the alpha-tropomyosin (α-TM) gene can code for several different tropomyosin proteins within different tissues of the same organism.

Figure 6.1 shows the structure of the seven mRNA transcripts identified as the result of the scientific study. In each transcript, each box represents an exon. Each transcript was found to be a product of the same α-TM gene.

Figure 6.1

Source: http://www.bio.utexas.edu/research/tuckerlab/bright/phylo_3_10_04/index.html.

Scientists continue to study the α-TM gene as a model of alternative splicing, in which mRNA transcripts containing different combinations of exons can lead to the production of different proteins. Figure 6.2 shows the structure of the α-TM gene, which is composed of 12 exons connected by 11 introns.

Figure 6.2

Each exon in a gene codes for a specific series of amino acids in the corresponding protein. The complete α-TM gene codes for a protein composed of 284 total amino acids. Table 6.1 shows the series of amino acids coded by each of the 12 exons in the α-TM gene.

TABLE 6.1 Alpha-Tropomyosin Exon

Source: http://www.bio.utexas.edu/research/tuckerlab/bright/phylo_3_10_04/index.html.

1. To produce a tropomyosin protein, which of the following steps must occur first?

2. According to the passage, each mRNA transcript in Figure 6.1 is produced from:

3. In Figure 6.1, what is the maximum number of exons present in an mRNA transcript?

4. Constitutive exons are present in all mRNA transcripts of a gene and are thought to be integral in the proteins' basic structure. Which of the following exons appears to be constitutive?

5. Alternatively spliced exons (ASEs) are those that only appear in certain mRNA transcripts. Which of the following cell types appears to have the least number of ASEs?

6. Which exons do not appear in any of the same mRNA transcripts?

7. Two types of muscle tissues-skeletal and cardiac-are both striated. Based on Figure 6.1, how do the α-TM mRNA transcripts of skeletal and cardiac muscle tissues differ?

8. The total number of exons in the α-TM gene is:

9. Based on the data in Table 6.1, which α-TM exon codes for the longest sequence of amino acids?

10. Which α-TM mRNA transcript is missing amino acids 258-284?

11. Based on Table 6.1, which mRNA transcript contains a repeated sequence of amino acids?

12. A myoblast is an embryonic cell that can differentiate into a muscle cell. Based on Figure 6.1, which of the following happens to the α-TM mRNA transcript when a myoblast differentiates into a smooth muscle cell?

13. Untranslated regions (UTRs) are sequences that exist at the beginning and end of every mRNA transcript. Instead of coding for amino acids, UTRs regulate the expression of the transcribed gene. In the α-TM mRNA, Exons 1 and 12 both contain UTRs. Based on the data in Table 6.1, which other exon contains a UTR?

14. The passage states that in addition to their function in all cells, tropomyosins also support contraction in muscle cells. It can be inferred that this extra function is related to which of the following sequences of amino acids?

15. A hepatoma is a tumor that forms within the liver. Based on Figure 6.1, it can be inferred that tumor formation may correlate to a loss of which exon?

← Prev test Next test →
Jump to