Bio1334 Genetics - Molecular Genetics - From DNA To RNA (Lecture Two)

mRNA, or messenger RNA, is a type of nucleic acid that carries genetic information from the DNA in the nucleus of a cell to the ribosomes in the cytoplasm. It acts as a "messenger" because it carries the instructions for protein synthesis. mRNA is transcribed from DNA during the process of transcription, and it is then translated into proteins during the process of translation. This allows the genetic code stored in the DNA to be converted into functional proteins, which are essential for various cellular processes and functions.

Ribose is the correct answer because it is the sugar present in RNA. RNA, or ribonucleic acid, is a molecule that plays a crucial role in protein synthesis and gene expression. It is composed of a chain of nucleotides, and each nucleotide consists of a sugar (ribose), a phosphate group, and a nitrogenous base. Ribose is a five-carbon sugar that forms the backbone of the RNA molecule, connecting the nucleotides together. It is different from the sugar found in DNA, which is deoxyribose.

In RNA, thymine is replaced by a different base called uracil. Thymine is found in DNA, but in RNA molecules, uracil takes its place. This substitution is due to the fact that RNA uses uracil instead of thymine to pair with adenine during the process of protein synthesis. Uracil is a pyrimidine base, just like thymine, and it plays a crucial role in the structure and function of RNA molecules.

FALSE: RNA is less stable than DNA, both genetically and chemically.

RNA is chemically less stable than DNA because it is more reactive than DNA. RNA molecules have a hydroxyl group on the 2' carbon of the ribose sugar, while DNA molecules have a hydrogen atom at the same position. This hydroxyl group makes RNA more susceptible to hydrolysis and other chemical reactions, leading to its relatively shorter lifespan compared to DNA. Additionally, RNA is often involved in various enzymatic reactions, making it more prone to degradation.

During the processing of mRNA before it leaves the nucleus, non-coding sequences called introns are removed or 'spliced' from the mRNA. Introns are sections of the mRNA that do not code for any specific protein and are therefore unnecessary for protein synthesis. The removal of introns ensures that only the coding sequences, called exons, are present in the mature mRNA molecule, which can then be translated into proteins by the ribosomes.

Transcription is the process by which an mRNA molecule is synthesized using a DNA template. The mRNA molecule is complementary to one of the DNA strands, meaning that the sequence of bases in the mRNA molecule is the opposite of the sequence in the DNA strand. This complementary relationship allows the mRNA molecule to carry the genetic information from the DNA to the ribosomes for protein synthesis.

RNA polymerase is the enzyme responsible for synthesizing RNA from a template strand of DNA during the process of transcription. It binds to the DNA template and catalyzes the formation of phosphodiester bonds between the nucleotides, resulting in the synthesis of an RNA molecule that is complementary to the DNA template. RNA polymerase plays a crucial role in gene expression by transcribing the genetic information encoded in DNA into RNA, which can then be translated into proteins.

RNA is synthesized in the 5' to 3' direction. This means that the RNA polymerase enzyme adds new nucleotides to the growing RNA strand starting from the 5' end and moving towards the 3' end. The 5' end of the RNA molecule contains a phosphate group, while the 3' end contains a hydroxyl group. This directionality is important for the proper functioning of RNA in processes such as translation and gene expression.

mRNA undergoes processing before it leaves the nucleus. One of the modifications that occur is the addition of a tail of poly-A nucleotides to the 3′ end of the mRNA. This poly-A tail plays a crucial role in the stability and translation of the mRNA molecule. It helps protect the mRNA from degradation and assists in the binding of ribosomes during the process of translation. Therefore, the correct statement is that the 3′ end of the mRNA gets a tail of poly-A nucleotides.

The term "transcriptome" refers to the complete set of RNA molecules present in a cell or a specific cell type, including mRNA. It encompasses all the RNA transcripts that are produced by the transcription of DNA in the cell. The transcriptome provides valuable information about the gene expression patterns and can be used to study various biological processes and diseases.

RNA polymerase binds to the promoter region of DNA to initiate transcription. However, it requires the assistance of other proteins called transcription factors to properly bind to the promoter. Transcription factors help in stabilizing the binding of RNA polymerase to the promoter and initiate the transcription process. These proteins play a crucial role in regulating gene expression by facilitating the recruitment of RNA polymerase to the promoter region.

RNA is more reactive than DNA because its sugar, ribose, has a 2' OH group. This hydroxyl group can participate in chemical reactions, making RNA more chemically reactive compared to DNA. The presence of the 2' OH group allows RNA to undergo various enzymatic and non-enzymatic reactions, including cleavage, ligation, and modification, which are crucial for its functions in gene expression and protein synthesis. In contrast, DNA lacks the 2' OH group, making it more stable and less prone to chemical reactions.

The splicing reaction is primarily performed by small nuclear RNA molecules (snRNAs) that bind to proteins to form small nuclear ribonucleoprotein particles (snRNPs) that form the core of the spliceosome. The spliceosome is a large complex composed of snRNPs and other proteins that catalyzes the removal of introns from pre-mRNA molecules during mRNA processing. It recognizes specific sequences at the splice sites and brings them together to form a catalytic center, allowing for the precise removal of introns and joining of exons to generate mature mRNA molecules.

The DNA template strand is read in the 3' to 5' direction. This means that the RNA polymerase enzyme moves along the DNA template strand in the 3' to 5' direction and synthesizes the RNA molecule in the 5' to 3' direction. The RNA molecule is complementary to the DNA template strand, so it has a sequence that is identical to the coding (non-template) strand, except that it contains uracil (U) instead of thymine (T).

Small nuclear RNAs (snRNAs) are responsible for performing the splicing reaction of introns from mRNA. These snRNAs are a class of RNA molecules that are found in the nucleus of eukaryotic cells. They form complexes with proteins to create small nuclear ribonucleoproteins (snRNPs), which are involved in the splicing process. During splicing, snRNPs recognize the splice sites on the pre-mRNA molecule and catalyze the removal of introns, allowing the exons to be joined together to form the mature mRNA molecule. Therefore, snRNAs play a crucial role in the removal of non-coding regions from mRNA, ensuring the production of functional proteins.

mRNA processing involves the addition of a cap structure to the 5' end of the mRNA molecule. This cap is composed of a modified nucleotide called an atypical nucleotide. The cap structure plays a crucial role in mRNA stability, transport, and translation initiation. Therefore, the statement that the 5' end is "capped" with an atypical nucleotide is correct.

During transcription, the molecules that line up along the DNA template strand are called nucleoside triphosphates (NTPs). NTPs are the building blocks of RNA and are used by RNA polymerase to synthesize a complementary RNA strand. Nucleoside triphosphates consist of a nitrogenous base (adenine, cytosine, guanine, or uracil), a ribose sugar, and three phosphate groups. As RNA polymerase moves along the DNA template strand, it incorporates NTPs that are complementary to the DNA bases, resulting in the formation of an RNA molecule with a sequence complementary to the original DNA strand.

During the process of polymerization of the mRNA strand, pyrophosphate is lost from the nucleoside triphosphate (NTP). This loss of pyrophosphate leads to the breakage of the phosphoanhydride bond, which in turn provides the energy needed for polymerization. The breakage of the phosphoanhydride bond releases energy that is utilized in the formation of the phosphodiester bond between the nucleotides of the growing mRNA strand.

RNA is genetically less stable than DNA because it is single stranded, which means there is no backup of genetic information. Additionally, RNA is more prone to mutate because it contains cytosine, which can mutate into uracil and cannot be detected and repaired.