DNA, RNA, and Proteins - SAT Subject Test in Biology

By definition, a missense mutation will still code for an amino acid, but not the desired amino acid. Silent mutations will have a different base pair, but due to the redundancy of genetic code, it will still code for the desired mutation. Nonsense mutations code for an amino acid that leads to a stop codon, which terminates the translation of mRNA into protein. Insertions and deletions result in a shifted reading frame and typically are detrimental.

The correct answer is "allosteric site." A molecule that binds to an enzyme's allosteric site induces a conformational change in the enzyme, decreasing or increasing the affinity of the enzyme’s binding sites to the substrate. The binding site binds and orients the substrate. The catalytic site lowers the activation energy of the reaction. The binding site and the catalytic site together make up the active site. Cofactors are parts of certain enzymes and are required for those enzymes to function.

The correct answer is a ribosome bound to the rough endoplasmic reticulum. The rough endoplasmic reticulum is covered with bound ribosomes, giving it its “rough” appearance. Proteins that are to be secreted from the cell are translated by ribosomes in the rough ER before moving through the Golgi apparatus and eventually ending up in a vesicle to be secreted from the cell. There are no ribosomes found in the nucleus, bound to smooth ER, or bound to the plasma membrane.

The correct answer is "tertiary." Translation is a process performed by ribosomes to link amino acids together in a chain, and the order of the amino acids is based on a code from mRNA. The order of the amino acids in the chain is the primary structure. The secondary structure is the folding in that chain, mainly based on hydrogen bonds between parts of the chain and the surrounding water molecules. The tertiary structure is the actual three-dimensional structure of the protein. Disulfide bonds are covalent bonds between cysteine residues and are stronger than hydrogen bonds and give a stable, three-dimensional structure to what was originally just a chain of amino acids.

There are generally considered to be three major differences between DNA and RNA. 1) DNA has a main sugar of deoxyribose and RNA has a main sugar of ribose, 2) RNA uses uracil instead of thymine, and 3) RNA is almost exclusively a single-stranded nucleic acid. Further, DNA is generally the template that an organism uses to create RNA (except in specific organisms which use reverse transcriptase and use RNA to create DNA).

The main three types of RNA necessary to create a polypeptide are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). snRNA is also important and can help modify the primary mRNA transcript, but it is only found in eukaryotes and is not absolutely essential to polypeptide formation. Micro RNA (miRNA) is also useful for post-transcriptional modification, but plays a minor role when compared to mRNA/tRNA/rRNA.

mRNA, or messenger RNA, carries genetic information from DNA into a three-letter code that encodes the amino acid sequence of a polypeptide (protein).

DNA contains the genetic instructions for structure and development of living things and stores genetic information over the long term.

tRNA, or transfer RNA, brings amino acids to ribosomes during translation of RNA to protein.

rRNA, or ribosomal RNA, is a component of ribosomes along with ribosomal proteins. Ribosomes are the cell organelles responsible for translating mRNA to protein.

snRNA, or small nuclear RNA, forms complexes with proteins used in RNA processing. snRNA is found only in eukaryotes.

The nuclear envelope separates transcription from translation in a eukaryotic cell. Translation cannot occur until transcription is finished, which is the opposite of what occurs in a prokaryotic cell. In eukaryotic cells, transcription occurs in the nucleus where mRNA will be produced. Once mRNA is produced, it will exit the nucleus through pores and then proceed to be translated into protein in the cytoplasm.

With an inducible system, the operon is off, meaning its repressor is active, or actively repressing the system from turning on. Inducible operons are opposite to a repressible operon, which is always on until it is repressed.

With a repressible system, the operon is on, meaning the repressor is inactive. Repressible operons are the opposite of inducible operons, which are always off until their repressor is inactivated.

Transcription is the first process of gene expression and happens before translation.

UAG, UAA, and UGA are stop codons so when they enter the A site of a ribosome they will initiate the termination of translation.

The question specifies that this is DNA replication. U (uracil) is found only in RNA and T (thymine) is found only in DNA. In DNA, A (adenine) pairs with T (thymine) and G (guanine) pairs with C (cytosine) so the complementary strand will have "A" where the original has "T," "G" where the original has "C," "C" where the original has "G" and "T" where the original has "A."

DNA strands run antiparallel, so the 3' end on the new strand will go opposite the 5' end on the original and vice versa. In this case, that means the complementary strand will run from 5' to 3' to read 5' - TAGCTTCACG - 3'. This sequence is shown in bold below:

5' - TAGCTTCACG - 3'

3' - ATCGAAGTGC - 5'

According to Chargaff's rule, DNA nucleotides pair in a 1:1 ratio. Therefore, if we know how much of the particular gene is made up of one nucleotide, we can extrapolate that known variable to find the other three unknown variables.

To do so, you must remember that adenine pairs with thymine, and cytosine pairs with guanine (A-T, C-G), and that since the ratio between each pair is 1:1 then a gene with 33% adenine must also have 33% thymine. Combine these numbers and subtract from 100: the number leftover is the % of total cytosine and guanine in the gene.

100% - 66% = 34%

Finally, since we know that 34% of the DNA is both C and G, and that the ratio between C-G is 1:1, C and G must both be 17%.

This question is designed to catch a) students who are not reading the question carefully, and b) students unsure of which nucleotides pair with which.

The correct answer is 29%, because cytosine pairs with guanine in a 1:1 ratio. If you answered 21%, then you likely thought the question was more complex than it was.

The correct answer is hydrogen bonding, and each nucleotide attracts its pairing mate because they have corresponding number of hydrogen bonds. Adenine is attracted to thymine to create two hydrogen bonds, and cytosine is attracted to guanine to form three hydrogen bonds. While phosphodiester bonds are very important in creating the strand of DNA, they are not the bond that keeps the two strands in the double helix structure.

The function of an enzyme is to speed up chemical reactions. They do this by lowering the activation energy, which is the minimum energy that must be available for a chemical reaction to occur. If the energy required is lowered, the reaction can go faster. Thus the correct answer is an enzyme changes "the activation energy of the reaction."

A reactant is a substance that undergoes change during a reaction. During an enzyme reaction specifically, the reactant is called the substrate, as a substrate is the substance in which an enzyme acts on and changes.

Both pH and temperature can affect how productive an enzyme is. If an enzyme is functioning in an environment that is not at its optimal pH or optimal temperature, the enzyme's activity will decrease.

Denature means to destroy the properties of a protein or other biological macromolecule. If an enzyme (which is a protein) stops working, it has denatured.