ribosome

(noun)

protein/mRNA complexes found in all cells that are involved in the production of proteins by translating messenger RNA

Related Terms

Examples of ribosome in the following topics:

  • The Initiation Complex and Translation Rate

    • The first step of translation is ribosome assembly, which requires initiation factors.
    • The complex consisting of mRNA, charged tRNAi, and the small ribosomal subunit attaches to the large ribosomal subunit, which completes ribosome assembly.
    • Once ribosome assembly is complete, the charged tRNAi is positioned in the P site of the ribosome and the empty A site is ready for the next aminoacyl-tRNA.
    • The eIF5-GTP allows the 60S large ribosomal subunit to bind.
    • Discuss how eukaryotes assemble ribosomes on the mRNA to begin translation

  • The Mechanism of Protein Synthesis

    • The 60S ribosomal subunit is recruited to the pre-initiation complex by eIF5-GTP, which hydrolyzes its GTP to GDP to power the assembly of the full ribosome at the translation start site with the Met-tRNAi positioned in the ribosome P site.
    • The ribosome moves three nucleotides down the mRNA.
    • This allows the large ribosomal subunit to assemble on top of the small subunit, generating the intact 80S ribosome, and places the Met-tRNAi in the P site of the intact ribosome .
    • The growing polypeptide chain is attached to the tRNA in the ribosome P site.
    • The ribosome translocates once codon on the mRNA.

  • The Nucleus and Ribosomes

    • The nucleolus is a condensed region of chromatin where ribosome synthesis occurs.
    • Ribosomes, large complexes of protein and ribonucleic acid (RNA), are the cellular organelles responsible for protein synthesis.
    • This mRNA travels to the ribosomes, which translate the code provided by the sequence of the nitrogenous bases in the mRNA into a specific order of amino acids in a protein .
    • Ribosomes are made up of a large subunit (top) and a small subunit (bottom).
    • During protein synthesis, ribosomes assemble amino acids into proteins.

  • The Protein Synthesis Machinery

    • Mitochondria and chloroplasts also have their own ribosomes, and these look more similar to prokaryotic ribosomes (and have similar drug sensitivities) than the cytoplasmic ribosomes.
    • Mammalian ribosomes have a small 40S subunit and a large 60S subunit, for a total of 80S.
    • The E site holds empty tRNAs just before they exit the ribosome.
    • The complete mRNA/poly-ribosome structure is called a polysome.
    • The large ribosomal subunit sits atop the small ribosomal subunit and the mRNA is threaded through a groove near the interface of the two subunits.

  • Types of RNA

    • The mRNA then carries the code out of the nucleus to organelles called ribosomes for the assembly of proteins.
    • Once the mRNA has reached the ribosomes, they do not read the instructions directly.
    • The ribosome acts like a giant clamp, holding all of the players in position, and facilitating both the pairing of bases between the messenger and transfer RNAs, and the chemical bonding between the amino acids.
    • The ribosome has special subunits known as ribosomal RNAs (rRNA) because they function in the ribosome.
    • These subunits do not carry instructions for making a specific proteins (i.e., they are not messenger RNAs) but instead are an integral part of the ribosome machinery that is used to make proteins from mRNAs.

  • Processing of tRNAs and rRNAs

    • Mature rRNAs make up 50-60% of each ribosome.
    • The eukaryotic ribosome is composed of two subunits: a large subunit (60S) and a small subunit (40S).
    • The bacterial ribosome is composed of two similar subunits, with slightly different components.
    • The two subunits join to constitute a functioning ribosome that is capable of creating proteins.
    • Each different tRNA binds to a specific amino acid and transfers it to the ribosome.

  • The Endoplasmic Reticulum

    • The rough endoplasmic reticulum (RER) is so named because the ribosomes attached to its cytoplasmic surface give it a studded appearance when viewed through an electron microscope .
    • Ribosomes transfer their newly synthesized proteins into the lumen of the RER where they undergo structural modifications, such as folding or the acquisition of side chains.
    • The smooth endoplasmic reticulum (SER) is continuous with the RER but has few or no ribosomes on its cytoplasmic surface.

  • The Central Dogma: DNA Encodes RNA and RNA Encodes Protein

    • This method of synthesizing proteins is directed by the mRNA and accomplished with the help of a ribosome, a large complex of ribosomal RNAs (rRNAs) and proteins.
    • The main function of tRNA is to transfer a free amino acid from the cytoplasm to a ribosome, where it is attached to the growing polypeptide chain. tRNAs continue to add amino acids to the growing end of the polypeptide chain until they reach a stop codon on the mRNA.
    • The ribosome then releases the completed protein into the cell.
    • Ribosomes are able to read the genetic information inscribed on a strand of messenger RNA and use this information to string amino acids together into a protein.

  • Molecular Analyses and Modern Phylogenetic Trees

    • These data come from a variety of molecular sources, such as mitochondrial DNA, nuclear DNA, ribosomal RNA (rRNA), and certain cellular proteins.
    • For constructing an evolutionary tree from proteins, for example, the sequences are aligned and then compared. rRNA (ribosomal RNA) is typically used to compare organisms since rRNA has a slower mutation rate and is a better source for evolutionary tree construction.
    • Since the ribosomes are critical to the function of living organisms, they are not easily changed through the process of evolution.
    • Woese compared the minuscule differences in the sequences of ribosomes among a great array of bacteria and showed that they were not all related.

  • Characteristics of Eukaryotic Cells

    • Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes.
    • Therefore, the nucleus houses the cell's DNA and directs the synthesis of proteins and ribosomes, the cellular organelles responsible for protein synthesis.
    • Mitochondria are oval-shaped, double membrane organelles that have their own ribosomes and DNA.
    • The nucleus stores chromatin (DNA plus proteins) in a gel-like substance called the nucleoplasm.The nucleolus is a condensed region of chromatin where ribosome synthesis occurs.The boundary of the nucleus is called the nuclear envelope.It consists of two phospholipid bilayers: an outer membrane and an inner membrane.The nuclear membrane is continuous with the endoplasmic reticulum.Nuclear pores allow substances to enter and exit the nucleus.