chapter 17

Why is a frameshift missense mutation more likely to have a severe effect on phenotype than a nucleotide-pair substitution missense mutation in the same protein?

A substitution missense affects only one codon, but a frameshift missense affects all codons downstream of the frameshift. Many genetic diseases are caused by missense mutations.

What amino acid sequence does the following DNA nucleotide sequence specify?

Before mRNA can be translated into an amino acid sequence, the mRNA must first be synthesized from DNA through transcription. Base pairing in mRNA synthesis follows slightly different rules than in DNA synthesis: uracil (U) replaces thymine (T) in pairing with adenine (A). The codons specified by the mRNA are then translated into a string of amino acids.

Amino Acids

CAC GCA UGC AUC ACU AAA

This chart shows how to decode an example mRNA sequence. Labels indicating directionality (for example, 5' → 3') are not needed when writing amino acid sequences.

Example mRNA sequence 5−AUGUCGACUAAGGGA−3′ Codon sequence AUG-UCG-ACU-AAG-GGA Amino acid sequence(three-letter abbreviation) Met Ser Thr Lys Gly

RNA plays important roles in many cellular processes, particularly those associated with protein synthesis: transcription, RNA processing, and translation. Drag the labels to the appropriate bins to identify the step in protein synthesis where each type of RNA first plays a role. If an RNA does not play a role in protein synthesis, drag it to the "not used in protein synthesis" bin.

In eukaryotes, pre-mRNA is produced by the direct transcription of the DNA sequence of a gene into a sequence of RNA nucleotides. Before this RNA transcript can be used as a template for protein synthesis, it is processed by modification of both the 5' and 3' ends. In addition, introns are removed from the pre-mRNA by a splicing process that is catalyzed by snRNAs (small nuclear RNAs) complexed with proteins. The product of RNA processing, mRNA (messenger RNA), exits the nucleus. Outside the nucleus, the mRNA serves as a template for protein synthesis on the ribosomes, which consist of catalytic rRNA (ribosomal RNA) molecules bound to ribosomal proteins. During translation, tRNA (transfer RNA) molecules match a sequence of three nucleotides in the mRNA to a specific amino acid, which is added to the growing polypeptide chain. RNA primers are not used in protein synthesis. RNA primers are only needed to initiate a new strand of DNA during DNA replication.

During translation, nucleotide base triplets (codons) in mRNA are read in sequence in the 5' → 3' direction along the mRNA. Amino acids are specified by the string of codons. What amino acid sequence does the following mRNA nucleotide sequence specify? 5′−AUGGCAAGAAAA−3′ Express the sequence of amino acids using the three-letter abbreviations, separated by hyphens (e.g., Met-Ser-Thr-Lys-Gly).

met- ala-arg-lys An amino acid sequence is determined by strings of three-letter codons on the mRNA, each of which codes for a specific amino acid or a stop signal. The mRNA is translated in a 5' → 3' direction.

Which of the following terms associated with transcription describe regions of nucleic acid?

promoter gene terminator The gene itself, the promoter, and the terminator are all DNA deoxyribonucleic acid) sequences. The RNA (ribonucleic acid) that is produced is another. The RNA polymerase enzyme that performs transcription is a protein and therefore not a nucleic acid.

in a process called, ----- non-coding regions of the RNA transcript are removed.

splicing

Codon

A specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid

What is the start codon? opened hint Identify the start codon, also known as methionine

AUG

Transcription

(genetics) the organic process whereby the DNA sequence in a gene is copied into mRNA

Think about the DNA coding sequence of a gene. If an A were swapped for a T, what kind of mutation could it cause and why?

It could cause a silent, missense, or nonsense mutation because those are the types that can be caused by a nucleotide-pair substitution like this one. When the sequence of bases in a gene is changed by a single nucleotide-pair substitution, it can have different effects on the product depending on where it is and whether or not the mutated codon codes for the same amino acid as the original codon.

Translation

Process by which mRNA is decoded and a protein is produced

not used in protein synthesis

RNA primers

4. The final RNA template for protein synthesis in eukaryotes is different from the RNA that was produced from the DNA template because of

RNA processing.

in eukaryotes, the initiation and regulation of transcription involve DNA-binding proteins called transcription factors. Which of the following statements correctly describe the role of transcription factors in the initiation of transcription? Select all that apply. Which of the following statements correctly describe the role of transcription factors in the initiation of transcription? Select all that apply.

Some transcription factors bind to both strands of the DNA, whereas others bind specifically to either the template or coding strand. Binding of a transcription factor to DNA requires a specific sequence of bases in the DNA binding region. Some transcription factors must bind to the promoter before RNA polymerase II can bind. Transcription factors are a group of DNA-binding proteins involved in the initiation and regulation of transcription. Many transcription factors bind to the promoter sequence of a gene. These transcription factors enable RNA polymerase II to bind to the promoter in the correct orientation (facing in the right direction on the DNA) to copy the template strand.

What are the stop codons? opened hint Enter the three stop codons, separated by commas.

UAG UGA UAA

Polypedtide

a long chain of chemically bonded amino acids

2. The attachment of a free amino acid to a specific RNA molecule is the key step in -----

charging of tRNA.

The completed mRNA contains the gene's ----joined together in the correct order.

exons

Anticodon

group of three bases on a tRNA molecule that are complementary to an mRNA codon

Regions of the RNA transcript that contain non-coding bases are called ----- These regions are not present in the mRNA that leaves the nucleus.

introns.

transcription/RNA processing

mRNA, pre-MRNA, snRNA

Molecular complexes called ---- carry out RNA splicing in the nucleus.

spliceosomes

translation

tRNA, rRNA

1. The formation of a strand of RNA that is complementary to one strand of the nuclear DNA is called-----

transcription.

3. In ------ the nucleotide sequence of a piece of RNA is converted into a sequence of amino acids in a polypeptide.

translation,

Place the events in the transcription of a gene in their proper order from left (first event) to right (last event). Rank from first event to last event.

1. RNA polymerase binds promoter. 2. RNA polymerase transcribes gene. 3.RNA polymerase reaches terminator. 4. RNA polymerase exits gene, RNA is released.

After transcription begins, several steps must be completed before the fully processed mRNA is ready to be used as a template for protein synthesis on the ribosomes. Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus?

Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA. A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. Once RNA polymerase II is bound to the promoter region of a gene, transcription of the template strand begins. As transcription proceeds, three key steps occur on the RNA transcript: Early in transcription, when the growing transcript is about 20 to 40 nucleotides long, a modified guanine nucleotide is added to the 5' end of the transcript, creating a 5' cap. Introns are spliced out of the RNA transcript by spliceosomes, and the exons are joined together, producing a continuous coding region. A poly-A tail (between 50 and 250 adenine nucleotides) is added to the 3' end of the RNA transcript. Only after all these steps have taken place is the mRNA complete and capable of exiting the nucleus. Once in the cytoplasm, the mRNA can participate in translation.

Enter the sequence of bases as capital letters with no spaces and no punctuation. Begin with the first base added to the growing RNA strand, and end with the last base added.

There are three principles to keep in mind when predicting the sequence of the mRNA produced by transcription of a particular DNA sequence. The RNA polymerase reads the sequence of DNA bases from only one of the two strands of DNA: the template strand. The RNA polymerase reads the code from the template strand in the 3' to 5' direction and thus produces the mRNA strand in the 5' to 3' direction. In RNA, the base uracil (U) replaces the DNA base thymine (T). Thus the base-pairing rules in transcription are A→U, T→A, C→G, and G→C, where the first base is the coding base in the template strand of the DNA and the second base is the base that is added to the growing mRNA strand.

During transcription in eukaryotes, a type of RNA polymerase called RNA polymerase II moves along the template strand of the DNA in the 3'→5' direction. However, for any given gene, either strand of the double-stranded DNA may function as the template strand. For any given gene, what ultimately determines which DNA strand serves as the template strand? View Available Hint(s)

the base sequence of the gene's promoter In eukaryotes, binding of RNA polymerase II to DNA involves several other proteins known as transcription factors. Many of these transcription factors bind to the DNA in the promoter region (shown below in green), located at the 3' end of the sequence on the template strand. Although some transcription factors bind to both strands of the DNA, others bind specifically to only one of the strands. Transcription factors do not bind randomly to the DNA. Information about where each transcription factor binds originates in the base sequence to which each transcription factor binds. The positioning of the transcription factors in the promoter region determines how the RNA polymerase II binds to the DNA and in which direction transcription will occur.