Chapter 15 Biology 1610

Match each description with the correct type of point mutation.

a. Changes a codon for one amino acid into a different codon for the same amino acid. Silent mutation b. One or a few base pairs are replaced by different base pairs. Substitution c. One or a few base pairs are lost. Deletion d. Changes a codon for one amino acid into a codon for a different amino acid. Missense mutation e. Changes a codon for one amino acid into a stop codon. Nonsense mutation f. An addition or deletion that alters the codons downstream from the mutation. Frameshift mutation g. This type of mutation causes Huntington's disease and has only been observed in humans and mice. Triplet repeat expansion h. One or a few base pairs are gained. Addition i. An addition or deletion that alters the codons upstream from the mutation. None of these

Indicate whether each of the following statements about the processing of mRNA transcripts is true or false.

1. Processing of mRNA transcripts occurs in prokaryotes only. false 2. Before the mRNA is processed, it is called the primary transcript. true 3. The final processed form of mRNA is called the mature mRNA. true 4. Transcript processing takes place in the cytoplasm. false 5. During transcript processing, a methylated GTP is added to the 3' end of the transcript. false 6. During transcript processing, a series of adenine residues are added to the 5' end of the transcript. false 7. During transcript processing, noncoding regions, called exons, are removed and the coding regions, called introns, are spliced together. false 8. The poly-A tail appears to play a role in the stability of mRNAs by protecting them from degradation. true 9. A single primary transcript can be spliced into different mature mRNAs by the inclusion of different exons, a process called alternative splicing. true

Animation: mRNA Synthesis (Transcription) The complimentary messenger RNA strand that would be synthesized from the DNA base sequence of 5' CTGAC 3' would be...

3' GACUG 5'

Animation: Protein Synthesis 3 New amino acids (other than the initial f-Met) enter at which site? At the E site What is unusual about the initiator tRNA? What stimulates the ribosome to move down one codon? If an aminoacyl-tRNA synthetase added the wrong amino acid to a tRNA, what would happen?

A transfer RNA is released It carries a modified amino acid The formation of a bond between the peptide in the P site and the amino acid in the A site The tRNA would carry the wrong amino acid, and it would be incorporated into the growing protein

Fill in each blank with the correct enzyme.

In eukaryotes, RNA polymerase II transcribes mRNA and some small nuclear RNAs. In eukaryotes, RNA polymerase I transcribes rRNA. In eukaryotes, RNA polymerase III transcribes tRNA and some other small RNAs.

Fill each blank with the correct type of RNA

Messenger RNA is translated by the ribosomes and contains the code that specifies the sequence of amino acids in a polypeptide chain. Ribosomal RNA combines with protein to form the 2 ribosomal subunits. Transfer RNA transports amino acids to the ribosomes for use. Small nuclear RNA plays a key role in the splicing reaction that removes introns from eukaryotic pre-RNA. SRP RNA combines with protein to form particles that help ribosomes attach to the endoplasmic reticulum in eukaryotes. Micro RNA acts to cleave target mRNAs or inhibit the translation of target mRNAs present in the cytoplasm of eukaryotes.

Place the following in order, starting with the smallest (#1) and ending with the largest (#4).

Nucleotide: 1 Chromosome: 4 Gene: 3 Codon: 2

The following sentences describe the process of transcription in prokaryotes. Fill in each blank using the terms provided and then arrange the sentences in the correct order, beginning with the event that occurs first.

RNA polymerase binds to a region of the DNA called the promoter. RNA polymerase begins to unwind and separate the 2 strands of the DNA double helix. Actual synthesis of the RNA transcript begins at the start site. Successive RNA nucleotides are added to the 3' end of the growing RNA chain during a process called elongation. When RNA polymerase reaches a terminator sequence, the RNA transcript and RNA polymerase separate from the DNA, and the DNA within the transcription bubble rewinds.

The following sentences describe various types of chromosomal mutations. Complete each sentence using the terms provided.

Segments of a chromosome that are lost are called deletions. Segments of a chromosome that are broken in 2 places, reversed, and then put back together are called inversions. Segments of a chromosome that are repeated are called duplications. Segments of a chromosome that break off and attach to another chromosome are called translocations. If a duplication occurs directly next to the original segment, it is termed a tandem duplication. If two chromosomes are broken and they exchange non-homologous segments, this is called a reciprocal translocation.

Animation: How Spliceosomes Process RNA The snRNPs are also called Which of the following do snRNPs bind to? Introns are generally considered 'free to mutate,' meaning that if a mutation occurs within the intron, it will not effect the functional protein. What is an exception to this axiom? Which of the following statements about RNA splicing is FALSE?

snurps. 5' and 3' ends of the intron If there is a mutation in the 3' or 5' splice site, the snurp won't recognize it, and it will not be removed from the mRNA. all of these choices are true

Animation: How Translation Works Which of the following occurs as the ribosome shifts down the mRNA by a distance of three nucleotides? Translation is terminated when a stop codon is presented at the ________ site. What stimulates the ribosome to move down one codon? A mutation occurred in the third codon position of a gene, but the protein still functions normally. How is this possible?

the tRNA that was in the P site moves into the E site A The formation of a bond between the peptide in the P site and the amino acid in the A site The genetic code is redundant, so that mutations in the third position of the codon often result in the same amino acid being specified.