RIBOSOME

SUBMITTED TO

Dr. R P SINGH

SUBMITTED BY

Pandya Dilipbhai k

CUG/2014/1078

Introduction

• It is a large & complex molecule.

• Found in all living cells prokaryote & eukaryote.

• That serves as the primary site of biological protein synthesis.

• Ribosome was first observed in 1953s by romanian cell biologist george emil palade using a electrone microscope.

george emil palade (1953)

• In prokaryote free form in cytoplasm & protoplasm

• In eukaryote free in cytoplasm inside the cell attach to the outer membrane in endoplasmic reticulum

STRUCTURE

• It is without cell membrane.

• Two subunits are attach by a different angles.

Large subunit

Small subunit

The subunits of the ribosome are synthesized by the nucleolus.

• The subunits of ribosomes join together

when the ribosomes attaches to the

messenger RNA during the process of

protein synthesis.

• Ribosomes along with a transfer RNA

molecule (tRNA), helps to translate the

protein-coding genes in mRNA to proteins.

Ribosome Function

• Ribosome basically a protein factory. Subunits each have role in making of proteins

• To understand exactly what each subunit does, it’s necessary to walk through protein synthesis step by step

Protein synthesis

• Process starts from DNA through “transcription”

• “Translation” is where ribosome comes in. Translation occurs when protein formed from code on mRNA

• Ribosome carries out the translation of the nucleotide triplets

Protein synthesis

• Chart - visual image of transcription and translation in protein synthesizing

• DNA and RNA have nucleotides that determine kind of protein

• 3 nucleotides = 1 amino acid of a protein

Ribosome and RNA

• mRNA with code for proteins located at 30S subunit

• tRNAs responsible for carrying amino acids to mRNA. Each tRNA has own nucleotide triplet which binds to matching triplet on mRNA, ex., tRNA with code AAA (triple adenine) would match up with mRNA that has code UUU (triple uracil)

Initiation:The first phase of translation

• Translation begins when mRNA attaches to the 30S

• tRNA comes and binds to mRNA where nucleotide code matches

• This triggers 50S binding to 30S. 50S is where all tRNAs will bind. Now we move on to elongation

Elongation:The second phase

• Two binding sites on 50S: A site and P site, which aid in continuing translation

• First tRNA connected at A site. Now moves to P site as another tRNAapproaches

• Second tRNA binds to A site

Elongation (continued)

• Peptide bond forms between amino acids of tRNAs (methionine and proline)

• First tRNA now detached from its amino acid, and it leaves ribosome. Second tRNA still has proline and methionine attached

Elongation (continued)

• The tRNA left now moves to P site. Ribosome ready to accept another tRNAand continue process

• Each tRNA adds another amino acid to growing peptide chain (thus “elongation”)

• Eventually process has to finish, however

End of translation

• Ribosome was moving along nucleotide triplets one by one

• Ribosome reaches “stop codon,” peptide chain finished. Last tRNAleaves ribosome, leaving behind completed peptide

End of translation (continued)

• Ribosome separates from mRNA

• Ribosome subunits also separate, and will remain this way until another mRNA comes along to restart the process