Austrian chemist Erwin Chargaff discovered that the amount of cytosine was equal to the amount of guanine in the cell, and the amount of adenine was equal to the amount of thymine in the cell. This discovery was important in determining that cytosine always pairs with guanine and that adenine always pairs with thymine. 

In RNA, uracil pairs with adenine and cytosine pairs with guanine, whereas in DNA, thymine pairs with adenine and cytosine pairs with guanine. Uracil is unique to RNA and thymine is unique to DNA. 

G-C is held together by three hydrogen bonds, while A-T is held together by two hydrogen bonds. Having more hydrogen bonds means that boiling points would be higher, so the set of base pairs with the most C-G bonds will have the highest boiling point.

Since adenine pairs with thymine in DNA, this would mean there are also 270 thymine bases. Similarly, cytosine and guanine pair up as well. This would mean there are also 430 cytosine bases. Adding all those together would give you 1400 bases total.

A nucleotide comprises of a purine/pyrimidine base, sugar, and a phosphate group. This is easy remember by focusing on the "t" in the terms "nucleotide" and "phosphate."

A nucleoside comprises only a purine/pyrimidine base and sugar. There is no "t" in "nucleoside" and hence, no phosphate.

All of these are actual nucleic acids, except xDNA, which does not exist. Therefore, we can eliminate this answer right away. mtDNA, or mitochondrial DNA, is a small portion of a person's DNA that is housed within the mitochondria. It is significant in that it is inherited solely from the mother and is thought to have evolved separately from "normal" DNA. However, it isn't involved with amino acids at all, so it too can be eliminated as a choice.

RNA (ribonucleic acid) is heavily involved in protein synthesis (the creation of new proteins, which are just long chains of amino acids). The first part of the process is transcription, in which the double-stranded DNA (deoxyribonucleic acid) is "unzipped" by the enzyme helicase. Another enzyme, RNA polymerase, "reads" this single strand and produces a chain of nucleotides exactly opposite to the DNA's nucleotides, and this chain, in its mature form, is called mRNA (messenger RNA). Living up to its name, mRNA travels outside the nucleus, where DNA is housed, and out into the rest of the cell, to the ribosome.

At this point, translation begins. Every trio of nucleotides on the mRNA, called a codon, represents a specific amino acid. Another type of RNA, tRNA (transfer RNA) can "translate" the codon into the appropriate amino acid, since it carries a three-nucleotide-long anticodon on one segment, which can form a bond with the corresponding codon on the mRNA, and an amino acid on the other segment. In this way tRNA brings amino acids to the growing protein chain. Another involved nucleic acid is rRNA (ribosomal RNA) which makes up a large part of the ribosome itself and is responsible for helping to properly attach each amino acid that the tRNA brings to the amino acid sequence being built.

Based on the question, which asks about the molecule that retrieves amino acids so that they can be added to the protein being built, the correct answer is tRNA.

All of these are actual nucleic acids, except xDNA, which does not exist. Therefore, we can eliminate this answer right away. mtDNA, or mitochondrial DNA, is a small portion of a person's DNA that is housed within the mitochondria. It is significant in that it is inherited solely from the mother and is thought to have evolved separately from "normal" DNA; however, it isn't involved with amino acids at all, so it too can be eliminated as a choice.

RNA (ribonucleic acid) is heavily involved in protein synthesis (the creation of new proteins, which are just long chains of amino acids). The first part of the process is transcription, in which the double-stranded DNA (deoxyribonucleic acid) is "unzipped" by the enzyme helicase. Another enzyme, RNA polymerase, "reads" this single strand and produces a chain of nucleotides exactly opposite to the DNA's nucleotides, and this chain, in its mature form, is called mRNA (messenger RNA). Living up to its name, mRNA travels outside the nucleus, where DNA is housed, and out into the rest of the cell, to the ribosome.

At this point, translation begins. Every trio of nucleotides on the mRNA, called a codon, represents a specific amino acid. Another type of RNA, tRNA (transfer RNA) can "translate" the codon into the appropriate amino acid, since it carries a three-nucleotide-long anticodon on one segment, which can form a bond with the corresponding codon on the mRNA, and an amino acid on the other segment. In this way tRNA brings amino acids to the growing protein chain. Another involved nucleic acid is rRNA (ribosomal RNA) which makes up a large part of the ribosome itself and is responsible for helping to properly attach each amino acid that the tRNA brings to the amino acid sequence being built.

Based on the question, which asks you to identify the nucleic acid that helps carry the protein "message" from the nucleus to the ribosome, the correct answer is mRNA.

In DNA transcription and translation, the start codon is the first codon, among those transcribed into the mRNA sequence, that is translated during protein synthesis. In humans, this is always AUG, which codes for the amino acid methionine.

Of the other answer choices, three function as a stop codon: UAA, UGA, and UAG. The other choice, CUG, codes for the amino acid leucine.

A mnemonic for remembering that AUG is the start codon is to make the connection that the school year typically starts in August.

According to Chargoff's rules, we know that the ratios of Adenine:Thymine and Guanine: Cytosine will be approximately 1:1. Once you know that the percentage of Adenine is 18%, you can multiply by two to find the total percentage of Thymine and Adenine (36%), then, you can subtract that number from 100% to find the percentage of Cytosine and Guanine - 64% (because the total percentage has to equal 100%), finally you can divide it in half to get the percentage of Guanine bases (32%).

Because of the presence of Deoxyribose sugar, you know that the genome is composed of DNA. Only RNA contains Uracil bases, so the answer is 0%.