The nucleus is the largest and the most important cell organelle in a eukaryotic cell. A nucleus is a membrane-bound organelle that houses the genetic material of eukaryotes in DNA. The nucleus consists of protein fibres or the DNA inside chromatin fibres. Nucleoids contain the genetic material of prokaryotes in the cytoplasm. The nucleoids usually consist of a single chromosome.
Let us look at more difference between nucleus and nucleoid in the table given below.
Answer:
Production of nitrogen oxides is the event which occurs first in the formation of photochemical smog.
Explanation:
Photochemical smog is a type of smog which occurs when volatile gases such as nitrogen oxide react with the sunlight in the atmosphere. Due to this reaction, smog is formed which is brown in color. This nitrogen oxide gas is produced when the fossil fuel burns in the engines of vehicles. Nitrogen oxide is volatile gas which means it directly goes in the atmosphere and contribute in air pollution and global warming.
Third Quarter or Last Quarter, they mean the same thing just phrased different.
Answer: RNAs are not processed before translation in prokaryotes, this process only takes place in eukaryotes.
Explanation:
Messenger RNA or mRNA is a single-straded ribonucleic acid that transfers the genetic information from the DNA (deoxyribonucleic acid) molecule of the cell nucleus to a ribosome (which are the machinery responsible for protein synthesis) in the cytoplasm. mRNA determines the order in which the amino acids of a protein will be joined and acts as a template or pattern for the synthesis of that protein. To accomplish this, the DNA molecule must be transcribed into an RNA molecule, which is used for protein synthesis.
The messenger RNA obtained after transcription is known as primary transcribed RNA or precursor RNA or pre-mRNA, which in most cases is not released from the transcription complex in a fully active form, but in eukaryotes it must undergo modifications before it can perform its function (RNA processing or maturation). These modifications include:
- Elimination of fragments (splicing): In most cases, the <u>mRNA undergoes the removal of internal, non-coding sequences called introns, and the connection of exons. This does not occur in prokaryotic cells</u>, as they do not have introns in their DNA.
- Protection by CAP: <u>Addition to the 5' end of the structure called "cap" or "capping"</u>, which is a modified guanine nucleotide, 7-methylguanosine triphosphate, via a 5'-5' triphosphate linkage, instead of the usual 3',5'-phosphodiester linkage. This cap is necessary for the normal RNA translation process and to maintain its stability.
- Polyadenylation signal: <u>Addition to the 3' end of a poly-A tail, a long polyadenylate sequence, whose bases are all adenine</u>. Its addition is mediated by a sequence or polyadenylation signal (AAAAAA), located 11-30 nucleotides upstream of the original 3' end. This tail protects the mRNA from degradation, and increases its half-life in the cytosol, so that more protein can be synthesized.
The mature mRNA (in eukaryotes) is transferred to the cytosol of the cell through pores in the nuclear envelope. Once in the cytoplasm, ribosomes are coupled to the mRNA. However, in prokaryotes, ribosome binding occurs while the mRNA strand is being synthesized. After a certain amount of time, the mRNA is degraded into its component nucleotides by ribonucleases. So, the transcription and translation processes are carried out in a similar way as in eukaryotic cells but they occur simultaneously. But, the fundamental difference is that, in prokaryotes, the messenger RNA does not undergo a maturation process and, therefore, no cap or tail is added and no introns are removed. Moreover, it does not have to leave the nucleus as in eukaryotes, because in prokaryotic cells there is no defined nucleus.
So, RNAs are not processed before translation in prokaryotes, this process only takes place in eukaryotes.
A heart murmur is a condition in which abnormal heart sounds
are determined with the help of a stethoscope. Normally, a heart valve makes a
distinct clicking sound when it snaps shut. With a murmur, the click is
replaced by a sound similar to blowing. This abnormal sound can indicate the
turbulent flow of blood through a narrowed valve or backward (retrograde) flow
back toward the atria then through a broken valve.
