Problem 23 - Anatomy and Physiology of Animals

Question

Which of the following is not made out of RNA? a. the carriers that shuffle amino acids to a growing polypeptide strand b. the ribosome C. the messenger molecule that provides the code for protein synthesis d. the intron

Step-by-Step Solution

Answer

b. the ribosome

Step 1: Understand the Question

The question asks us to identify which option is not made out of RNA. RNA, or ribonucleic acid, is a nucleic acid present in cells that plays several roles in the synthesis of proteins.

Step 2: Analyze Option (a)

Option (a) refers to carriers that shuffle amino acids to a growing polypeptide strand. These are known as tRNA or transfer RNA molecules, which are indeed made from RNA.

Step 3: Analyze Option (b)

Option (b) refers to the ribosome. Ribosomes are composed of rRNA (ribosomal RNA) and proteins, meaning some parts of a ribosome are made of RNA, but ribosomes are not entirely RNA.

Step 4: Analyze Option (c)

Option (c) refers to the messenger molecule that provides the code for protein synthesis, which is mRNA or messenger RNA. This is made entirely out of RNA.

Step 5: Analyze Option (d)

Option (d) refers to an intron. Introns are non-coding sections of an RNA transcript that are removed during RNA splicing, and they are indeed made of RNA.

Step 6: Identify the Correct Answer

Based on the analysis, option (b) doesn't solely consist of RNA, as it is part of a ribo-protein complex, while the other options are made fully or primarily out of RNA.

Key Concepts

tRNA

tRNA, or transfer RNA, is a special molecule involved in the protein synthesis process. Its main role is to carry amino acids to the ribosome, where proteins are made. Each tRNA molecule is linked to a specific amino acid, and it matches amino acids with the appropriate codons on mRNA through its anticodon.
This ensures that the amino acids are added in the correct sequence, resulting in functional proteins.

• Structure: tRNA has a unique cloverleaf shape, featuring loops and a stem.
• Function: It decodes mRNA sequences into amino acids and helps in assembling proteins at the ribosome.

It's fascinating to note that tRNA reads the genetic code from mRNA one codon at a time, demonstrating the precision of molecular biology.

rRNA

Ribosomal RNA, or rRNA, is a crucial component of ribosomes. Ribosomes are the cellular machines where proteins are synthesized. rRNA combines with proteins to form the ribosomal subunits that facilitate the binding of mRNA and tRNA.

• Function: rRNA helps to catalyze the formation of peptide bonds between amino acids.
• Structure: It forms a significant structural and functional framework of ribosomes.

Interestingly, rRNA is one of the most abundant types of RNA in the cell due to its role in building the ribosome's core structure and aiding in protein synthesis.

mRNA

Messenger RNA, or mRNA, is like a blueprint for protein construction. It carries genetic information from DNA to the ribosomes, where proteins are made. mRNA is transcribed from DNA and then translated into amino acids by the ribosome.

• Transcription: mRNA is synthesized in the nucleus through a process called transcription.
• Translation: Once mRNA reaches the ribosome, it guides the assembly of amino acids into a protein.

The remarkable function of mRNA is to act as an intermediary, ensuring that the genetic code is faithfully translated into functional proteins, driving the function of cells and organisms.

Intron

Introns are like the quiet parts of an orchestra, often hidden but essential. Unlike their neighboring exons that code for proteins, introns are non-coding regions within an RNA sequence. During a process called RNA splicing, introns are removed while exons are joined together to form a mature mRNA strand.

• Non-coding: Although not directly involved in coding for proteins, introns play significant roles in gene expression.
• Splicing: The removal of introns and joining of exons is crucial for creating the correct mRNA sequence for protein synthesis.

Introns can influence how genes are expressed, demonstrate how diverse RNA processing is, and play a role in alternative splicing, leading to multiple proteins from a single gene. Introns showcase the complexity and versatility of genetic regulation mechanisms.