Any Biology experts out there?

Question

Can you answer all or any of these questions?
1. Describe the process of post-transcriptional modification beginning with the primary mRNA transcript.

2. Distinguish between the three types of RNA and describe the role of each in protein synthesis.

3. Describe the steps in translation of a protein beginning with attachment of a ribosome to mRNA and ending with release of a polypeptide from the ribosome. Include the diferences of RNA.

Answer 1

well Mark and smarties have given quite nice answers... let me know if you want additional details.

Answer 2

Post-transcriptonal modification is the process in which precursor mRNA is converted to mature mRNA. While the mRNA molecule is still being transcribed and it consists of 30 nucleotides, the 5' end of the mRNA is "capped" with a guanosine nucleotide. Then, a poly-adenine tail is added to the 3' end of the mRNA once it has been cleaved. The final step of PTM is removing the introns from the mRNA and exons are joined together. Introns are the parts of the mRNA that do not code for proteins while exons are the parts that do.

The three types of RNA are: messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA). mRNA is the "blueprint for whatever protein the DNA gene was coded for. It is the template, consisting of a series of tri-nucleotide codes called codons, in which tRNA binds to during translation. tRNA is a short strand of RNA that has a three base pair (anticodon) key and is attached to an amino acid, which is specific to each anti codon. rRNA acts like an enzyme and forms the "active site" of the ribosome where translation occurs.

The mRNA moves from the nucleotide and binds with the "active site" of the ribosome, which is made up of rRNA. There, rRNA acts like a catalyst and matches up codons on mRNA to the anticodons of tRNA. At the other end of the tRNA is an amino acid. As neighboring molecules of tRNA + amino acid are joined, peptide bonds form between the amino acids. This process continues until the termination codon of mRNA causes translation by the rRNA to cease. The tRNA molecules detach from their aminos acids shortly after the peptide bonds are formed and reattach to other amino acids in the cell. The mRNA can the be used again in another ribosome to synthesize another protein. In fact, it's possible for one mRNA molecule to be used by multiple ribosomes simultaneously producing multiple proteins simultaneously. The poly peptide or protein is then released out of the ribosome into the endoplasmic reticulum where it's packaged be transfered elsewhere in the cell.

That concludes our journey. I hope you enjoyed the ride.

Answer 3

1- I'm not sure about this one.

2- Messenger RNA (mRNA)

Messenger RNA is RNA that carries information from DNA to the ribosome sites of protein synthesis in the cell. Once mRNA has been transcribed from DNA, it is exported from the nucleus into the cytoplasm (in eukaryotes mRNA is "processed" before being exported), where it is bound to ribosomes and translated into protein. After a certain amount of time the message degrades into its component nucleotides, usually with the assistance of RNA polymerases.

Transfer RNA (tRNA)

Transfer RNA is a small RNA chain of about 74-93 nucleotides that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. It has sites for amino-acid attachment and an anticodon region for codon recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding. It is a type of non-coding RNA.

Transfer RNA (tRNA) contains about 75 nucleotides, three of which are called anticodons, and one amino acid. The tRNA reads the code and carries the amino acid to be incorporated into the developing protein.

There are at least 20 different tRNA's - one for each amino acid. The basic structure of a tRNA is shown in the left graphic. Part of the tRNA doubles back upon itself to form several double helical sections. On one end, the amino acid, phenylalanine, is attached. On the opposite end, a specific base triplet, called the anticodon, is used to actually "read" the codons on the mRNA.

The tRNA "reads" the mRNA codon by using its own anticodon. The actual "reading" is done by matching the base pairs through hydrogen bonding following the base pairing principle. Each codon is "read" by various tRNA's until the appropriate match of the anticodon with the codon occurs.

In this example, the tRNA anticodon (AAG) reads the codon (UUC) on the mRNA. The UUC codon codes for phenylalanine which is attached to the tRNA. Remember that the codons read from the mRNA make up the genetic code as read by humans.

Ribosomal RNA

Ribosomal RNA (rRNA) is a component of the ribosomes, the protein synthetic factories in the cell. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S, and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. rRNA molecules are extremely abundant. They make up at least 80% of the RNA molecules found in a typical eukaryotic cell.

3- for info about protein synthesis read the related section on this site: http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookPROTSYn.html#Protein%20Synthesis

Answer 4

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