ribosome
TRANSCRIPT
To familiarize the students with the cell biology at molecular levelCELLBIOLOGYCourse Title Mid Practical Theory Total
MBB 503 [3+0] Molecular Cell Biology 30 - 120 150
The CellBasic unit of life…
• Cell have tiny granular structures known as Ribosomes
• Ribosomes are Ribonucleo-Protein Particles
• Ribosomes serves as workbenches, with mRNA acting as the blueprint in the process of protein synthesis
What are Ribosomes?
George Palade was the first person to study them in 1955
Discovery of Ribosomes
J. Biophysics and Biochem. Cytosol., 1955, Vol. 1, No. 1http://jcb.rupress.org/content/1/1/59.full.pdf+html
• Protein Builders+ Synthesizers
• Read the RNA’s information and use it to create proteins (translation)
WHAT DO THEY DO?
• 5-10 nm larger in eukaryotic cells
• Made out of complexes of RNAs and proteins
• 2 subunits:
• smaller attaches to mRNA
• Larger binds to the tRNA and amino acids
• Then they split
WHAT DO THEY LOOK LIKE?
• Prokaryotes: free forms in cytoplasm and protoplasm
• Eukaryotes:• free in cytoplasm for use inside cell• attached to outer membrane of
endoplasmic reticulum for use outside of cell
WHERE DO THEY LIVE?
• The number of Ribosomes differs greatly• A rapidly growing E.coli cell may have as many as 15,000 to 20,000
ribosomes, about 15% of the cell mass
Number
I. Matrix Ribosomes: These synthesize proteins destined to remain within the cell
II. Plasma Membrane Ribosomes: These make proteins for transport to the outside
Types of Ribosomes
There are two domains of Ribosomes
Translational Domain: The region responsible for translation is called the Translational domain
Both subunits contribute to this domain, located in the upper half of the small subunit and in the associated areas of the large subunit
Exit Domain: The growing peptide chain emerges from the large subunit at the exit domain
This is located on the side of the subunit
Domains of Ribosomes
• Prokaryotic Ribosomes are commonly called 70S Ribosomes• These have dimensions of about 14 to 15nm by 20nm• A Molecular Weight of approximately 2.7 million daltons(2.7×106 daltons)• These are constructed of
a 50S and a 30S subunit
Dimensions of Ribosomes
• Ribosomes are not bounded by membrane
• Prokaryotic Ribosomes are smaller and less dense than Eukaryotic Ribosomes
• Ribosomes are composed of two subunits, each of which consists of protein and a type of RNA called Ribosomal RNA (rRNA)
Structure of Ribosomes
• Each subunit is constructed from one to two rRNA molecules and many polypeptides
• 30S smaller Subunit
• 50S larger Subunit
Ribosomal Subunits
• The S in 70S and similar values stand for Svedberg units
• The faster a particle travels when centrifuged, the greater its Svedberg value or Sedimentation coefficient
• The sedimentation coefficient is a function of a particles molecular weight, volume and shape
• Heavier and more compact particles normally have larger Svedberg numbers or sediment faster
Svedberg Unit
• 30S Subunit is smaller and has a molecular weight of 0.9×106 daltons
• It is made up of 16S rRNA and 21 Polypeptide chains
30S Subunit
The 50S subunit is larger one and has a molecular weight of about 1.8×106 daltons
It consists of 5S rRNA, 23S rRNA and 34 Polypeptide chains
50S Subunit
• rRNA is transcribed from certain portions of DNA by the same energy-requiring process used for the synthesis of mRNA and tRNA
• rRNA is thought to have two roles
i. The 16S rRNA of the 30S subunit may aid in the initiation of protein synthesis
The 3` end of the 16S rRNA complexes with an initiating signal site on the mRNA and helps position the mRNA on the ribosome
ii. 16S rRNA binds initiation factor-3 and the 3` CCA end of aminoacyl-tRNA
Ribosomal RNA and its Role
The ribosome has three
sites for binding tRNA
• The Peptidyl or Donor site
(the P site)
• The Aminoacyl or Acceptor Site
(the A site)
• The Exit Site
(the E site)
Sites of Ribosome
The Ribosome is involved in the process of Protein Synthesis
Protein Synthesis is divided into three stages:
1. Initiation
2. Elongation
3. Termination
Function of Ribosomes
WHAT HAPPENS WHEN THEY DON’T WORK RIGHT?
Diamond-Blackfan Anemia• 5 infants/million • Heart and skeletal abnormalities, not enough red blood cells• The 7 mutated genes give faulty instructions on how to make ribosomal proteins
Cartilage Hair Hypoplasia• Relatively rare, but 1/19 of the Amish population are carriers• Anemic, short limbs, leukopenia (low white blood cell count) and thrombocytopenia (low platelet count)• The gene mutation causes a buildup of one enzyme which builds ribosomal RNA
Shwachman-Diamond Syndrome• 1/100,000 children• Neutropenia (low white blood cell count) and Pancreatic problems that lead to steatorrhea (fatty bowel
movement) because there aren’t enough enzymes to digest fats, anemia• The gene mutation is causing a low amount of enzymes made out of proteins
Dyskeratosis Congenita• 1/million children• Hair, nail, skin, lungs, blood, digestive and immune system abnormalities, aplastic anemia (bone marrow doesn’t
make enough platelets, red or white blood cells), • Caused by gene mutation that causes ribosome deficiency
• Several antibiotics work by inhibiting protein synthesis on prokaryotic ribosomes
• Antibiotics such as Streptomycin and gentamicin attach to the 30S subunit and interfere with protein synthesis
• Other Antibiotics, such as Erythromycin and Chloramphenicol, interfere with protein synthesis by attaching to the 50S subunit
Effect of Antibiotics on Protein Synthesis
Because of differences in prokaryotic and eukaryotic ribosomes, the microbial cell can be killed by the antibiotic
while the eukaryotic host cell remains unaffected
Point to Ponder
PHOTO CREDITS
Slide 2: http://biology.about.com/b/2008/11/29/what-are-ribosomes.htm
Slide 3: http://barrett-group.mcgill.ca/teaching/nanotechnology/ribosome.jpg
Slide 4:http://web.jjay.cuny.edu/~acarpi/NSC/images/cell.gif
Slide 6:http://illnessesanimalsplants.wikispaces.com/file/view/plantcell.jpg/31816717/plantcell.jpg
http://images.protopage.com/view/721661/caa3z4ysta5s87lr2asekq5ng.jpg
BIBLIOGRAPHY
• http://en.wikipedia.org/wiki/Ribosome (February 2011)
• http://www.biology4kids.com/files/cell_ribos.html (February 2011)
• http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Ribosomes/Ribosome.HTML (February 2011)
• http://www.livestrong.com/article/208980-what-is-a-list-of-ribosomes-diseases/ (February 2011)