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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. Submit

Ribosomes provide the scaffolding on which tRNAs interact with mRNA during translation of an mRNA sequence to a chain of amino acids. A ribosome has three binding sites, each of which has a distinct function in the tRNA-mRNA interactions. Drag the appropriate tRNAs to the binding sites on the ribosome to show the configuration immediately before a new peptide bond forms. Note that one of the binding sites should be left empty.

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In the sequence alignment (Figure 1), count the number of each base at position 1. Order them from most frequent to least frequent.

10 T, 0 A, 0 C, 0 G

Life as we know it depends on the genetic code: a set of codons, each made up of three bases in a DNA sequence and corresponding mRNA sequence, that specifies which of the 20 amino acids will be added to the protein during translation. Imagine that a prokaryote-like organism has been discovered in the polar ice on Mars. Interestingly, these Martian organisms use the same DNA → RNA → protein system as life on Earth, except that there are only 2 bases (A and T) in the Martian DNA, and there are only 17 amino acids found in Martian proteins. Based on this information, what is the minimum size of a codon for these hypothetical Martian life-forms?

5 bases

To show how sequence logos are made, the potential ribosome-binding regions from 10 of the E. coli genes are shown in a sequence alignment (Figure 1). Select Figure 2 from the dropdown menu above the sequence alignment. That figure is the sequence logo derived from the aligned sequences (Figure 2). Note that the DNA shown is the nontemplate (coding) strand, which is how DNA sequences are typically given. In the sequence logo, the horizontal axis shows the primary sequence of the DNA by nucleotide position. Letters for each base are stacked on top of each other according to their relative frequency at that position among the aligned sequences, with the most common base as the largest letter at the top of the stack. The height of each letter represents the relative frequency of that base at that position. In the sequence alignment (Figure 1), count the number of each base at position -9. Order them from most frequent to least frequent.

7 G, 2 A, 1 C, 0 T Submit

In the sequence alignment (Figure 1), count the number of each base at position 0. Order them from most frequent to least frequent.

8 A, 1 G, 1 T, 0 C Submit

Which of these is currently considered the best definition of a gene?

A gene codes for either a polypeptide or an RNA molecule. Submit

Which one of the following is true of tRNAs?

Each tRNA binds a particular amino acid.

Where does RNA polymerase begin transcribing a gene into mRNA?

It starts after a certain nucleotide sequence called a promoter.

What is the function of RNA polymerase?

It unwinds the double helix and adds nucleotides to a growing strand of RNA.

Which of the following molecules are produced by transcription?

Messenger RNA Ribozymes

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′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

Part C - The role of DNA in determining amino acid sequences. Part complete Before a molecule of mRNA can be translated into a protein on the ribosome, the mRNA must first be transcribed from a sequence of DNA.

Met-Ser-Cys-His

The average length of a transcription unit along a eukaryotic DNA molecule is about 27,000 nucleotide pairs, whereas an averaged-sized protein is about 400 amino acids long. What is the best explanation for this fact?

Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that are not translated.

The DNA in a cell's nucleus encodes proteins that are eventually targeted to every membrane and compartment in the cell, as well as proteins that are targeted for secretion from the cell. For example, consider these two proteins: Phosphofructokinase (PFK) is an enzyme that functions in the cytoplasm during glycolysis. Insulin, a protein that regulates blood sugar levels, is secreted from specialized pancreatic cells. Assume that you can track the cellular locations of these two proteins from the time that translation is complete until the proteins reach their final destinations. For each protein, identify its targeting pathway: the sequence of cellular locations in which the protein is found from when translation is complete until it reaches its final (functional) destination. (Note that if an organelle is listed in a pathway, the location implied is inside the organelle, not in the membrane that surrounds the organelle.)

PFK: cytoplasm only insulin: ER - Golgi - Outside cell

Based on the logo, what five adjacent base positions in the 5' UTR region (the untranslated region at the 5' end of the mRNA) are most likely involved in ribosome binding? Explain.

Positions -12 to -8 have the tallest stacks in the 5' UTR region; therefore, they represent the most likely sequence for the ribosome binding site.

Which positions in the logo have the least predictable bases? How can you tell?

The 12 positions showing no bases have the lowest predictive power (-18, -17, -16, -12, -11, -6, -5, -4, -2, 5, 6, and 8). Submit

Suppose that a portion of double-stranded DNA in the middle of a large gene is being transcribed by an RNA polymerase. As the polymerase moves through the sequence of six bases shown in the diagram below, what is the corresponding sequence of bases in the RNA that is produced? 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.

UGAGCC

What is a ribozyme?

a biological catalyst made of RNA

What does a mutagen cause?

a change in the sequence of DNA

Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene?

a frameshift deletion at the beginning of the gene

Based on the genetic code chart above, which of the following would be the result of this single base-pair substitution?

a nonsense mutation resulting in early termination of translation

Label the four mutated DNA segments shown below according to the type of point mutation each represents. Use the codon table above to determine how each mutation would affect the amino acid coding for each segment. Drag the labels to their appropriate locations to identify the type of point mutation shown.

a: silent mutation b: nonsense mutation c: missense mutation d: frameshift mutation

If a segment of DNA were replicated without any errors, the replicated strand would have the following sequence of nucleotides: 5' - ACTACGTGA - 3' Sort the following replicated DNA sequences by the type of point mutation each contains (frameshift, base substitution, or neither), as compared to the correct sequence shown above. Sort the items into the appropriate bins.

frameshift mutation : 5'-ACTTACGTGA-3' 5'-ACTCGTGA-3 base substitution mutation: 5'-ACTACGTGT-3' 5'-ACTAAGTGA-3' neither:

The flow of information in a cell proceeds in what sequence?

from DNA to RNA to protein

After an RNA molecule is transcribed from a eukaryotic gene, what is removed and what is spliced together to produce an mRNA molecule with a continuous coding sequence?

introns ... exons

Complete the following vocabulary exercise related to the process of translation of mRNA to protein by the ribosome.

not in the same order as in homework!!!

In the actual experiment, the researchers used 149 sequences to build their sequence logo, as opposed to just 10. Select Figure 3 from the dropdown menu (Figure 3). Now there is a stack at each position, even if short, because the sequence logo includes more data. Which three positions in the sequence logo in Figure 3 have the most predictable bases? Name the most frequent base at each position.

position 0 (A); position 1 (T); position 2 (G) Submit

The height of a stack of letters in a logo indicates the predictive power of that stack (determined statistically). If the stack is tall, we can be more confident in predicting what base will be in that position if a new sequence is added to the logo. For example, at position 2, all 10 sequences have a G; the probability of finding a G there in a new sequence is very high, as is the stack. For short stacks, the bases all have about the same frequency, so it's hard to predict a base at those positions. Which two positions in the logo sequence have the most predictable bases, and which bases would you predict at those two positions in a newly sequenced gene?

position 1 (T) and position 2 (G) Submit

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?

the base sequence of the gene's promoter

The sequence logo can help you predict where certain gene features lie. Gene features such as the ribosome binding site and the start codon occur in highly conserved parts of the DNA sequence. In other words, base positions with tall stacks of letters likely represent a feature common to a large number of genes. What gene feature is represented by the bases in positions 0-2?

the translation start codon AUG Submit

A codon consists of __________ bases and specifies which __________ will be inserted into the polypeptide chain.

three ... amino acid

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.

transcription/RNA processing : snRNA pre-mRNA mRNA translation: rRNA tRNA not used in protein synthesis : RNA primers Submit