2006-10-12 05:22:28 · 4 answers · asked by Austin K 1 in Science & Mathematics ➔ Biology
Ribosomes are organelles found in the cytoplasm of all cells. In humans they are found floating free in the cytoplasm and attached to the endoplasmic reticulum. They are used to synthesize proteins from mRNA, mainly.
2006-10-12 05:24:40 · answer #1 · answered by pdigoe 4 · 0⤊ 0⤋
A ribosome is a complex of RNA and proteins that can translate mRNA into a polypeptide chain (e.g., a protein). Ribosomes are found in the cytosol (the internal fluid of the cell) of all cells. . Ribosomes consist of two subunits that fit together ( and work as one to tranlate the mRNA into a polypeptide chain. (Each subunit consiste of one or two very large RNA molecules (known as ribosomal RNA or rRNA) and several smaller protein molecules.
Free ribosomes occur in all cells, and also in mitochondria and chloroplasts in eukaryotic cells. Several free ribosomes can associate on a single mRNA molecule to form a polyribosome or polysome. Free ribosomes usually produce proteins that are used in the cytosol or in the organelle they occur in. When certain proteins are synthesized by a ribosome, it can become "membrane-bound", associated with the membrane of the nucleus and the rough endoplasmic reticulum (in eukaryotes only) for the time of synthesis. They insert the freshly produced polypeptide chains directly into the ER, from where they are transported to their destinations. Bound ribosomes usually produce proteins that are used within the cell membrane or are expelled from the cell via exocytosis.
The ribosomal subunits of prokaryotes and eukaryotes are quite similar. However, prokaryotes use 70S ribosomes, each consisting of a (small) 30S and a (large) 50S subunit, whereas eukaryotes use 80S ribosomes, each consisting of a (small) 40S and a (large) 60S subunit.[The unit S means Svedberg units, a measure of the rate of sedimentation of a particle in a centrifuge, where the sedimentation rate is associated with the size of the particle. Svedberg units are not additive - two subunits together can have Svedberg values that do not add up to that of the entire ribosome.]
2006-10-12 06:34:59 · answer #2 · answered by FarzaneH 2 · 0⤊ 0⤋
It is infact one of the few non protein enzymes. It is known as an RNA enzyme because there are no protiens anywhere near the active site. The proteins in it are there merely to hold the RNA in place. Ribosomes take mRNA transcripts and recruit tRNA's bound to amino acids and use them to creat polypeptides.
2006-10-12 06:02:16 · answer #3 · answered by Bacteria Boy 4 · 0⤊ 0⤋
cluster of proteins and RNA: a submicroscopic cluster of proteins and RNA, occurring in great numbers in the cytoplasm of living cells, that takes part in the manufacture of proteins
2006-10-12 05:24:45 · answer #4 · answered by Burhan 2 · 0⤊ 0⤋