Post on 15-Apr-2017
Protein Synthesis in Cell
05/03/2023 Dept. of Physiology, MSRMC
Learning Objectives• Importance of proteins• Site of protein synthesis• Steps of protein synthesis• Regulation of protein synthesis• Applied aspects
05/03/2023 Dept. of Physiology, MSRMC
Proteins: their importance• Membrane proteins• Structural proteins• Enzymes• Hormones• Antigens
05/03/2023 Dept. of Physiology, MSRMC
Site of Protein Synthesis
05/03/2023 Dept. of Physiology, MSRMC
Site of Protein Synthesis
05/03/2023 Dept. of Physiology, MSRMC
DNA• DNA has two functions.
– self-renewing data repository that maintains a constant source of genetic information for the cell.
– serve as a template for the translation of genetic information into proteins, which are the functional units of the cell.
05/03/2023 Dept. of Physiology, MSRMC
Basic building blocks of DNA• Phosphoric acid• Sugar• Nitrogenous base
05/03/2023 Dept. of Physiology, MSRMC
Genetic Code• The gene consists of a segment of DNA that
is transcribed into RNA.• The genetic code consists of successive
"triplets" of bases on the DNA.• Each three successive bases is a code word.• The successive triplets eventually control the
sequence of amino acids in a protein molecule that is to be synthesized in the cell.
05/03/2023 Dept. of Physiology, MSRMC
Pathway from Genes to Proteins
05/03/2023 Dept. of Physiology, MSRMC
• Central dogma of molecular biology: genetic information flows unidirectionally from DNA to proteins.
05/03/2023 Dept. of Physiology, MSRMC
Steps of Protein Synthesis• Transcription
• Translation
• Post translational modificaton
05/03/2023 Dept. of Physiology, MSRMC
Transcription• Definition: Transcription is the synthesis
of RNA from a DNA template, mediated by an enzyme called RNA polymerase.
• Site: Nucleus
05/03/2023 Dept. of Physiology, MSRMC
• Requirements:
– DNA template
– RNA polymerase
– Activated ribonucleotides
Transcription contd.
05/03/2023 Dept. of Physiology, MSRMC
Building blocks of RNA• Phosphoric acid
• Sugar
• Nitrogenous base
05/03/2023 Dept. of Physiology, MSRMC
• The basic building blocks of RNA form RNA nucleotides.
• RNA nucleotides are then activated by RNA Polymerase.
05/03/2023 Dept. of Physiology, MSRMC
• RNA polymerase recognises the promoter region in DNA and binds to it.
• Unwinding of a segment of DNA
• Attachment of activated ribonucleotides to the DNA segment
05/03/2023 Dept. of Physiology, MSRMC
• Polymerase moves along the DNA strand
• Breakage of 2 phosphate radicals from RNA nucleotides
• Covalent linkage of 3rd phosphate with ribose
05/03/2023 Dept. of Physiology, MSRMC
• RNA polymerase reaches end of DNA gene (chain terminating sequence)
• Breaking away of polymerase & RNA chain
• Formation of RNA transcript
05/03/2023 Dept. of Physiology, MSRMC
• The code that is present in the DNA strand is eventually transmitted in complementary form to the RNA chain.
• The ribose nucleotide bases always combine with the deoxyribose bases in a fixed combination.
05/03/2023 Dept. of Physiology, MSRMC
DNA Base RNA BaseGuanine…………………………….……CytosineCytosine ………………………..…….… GuanineAdenine …………………………………… UracilThymine ………………………………… Adenine
05/03/2023 Dept. of Physiology, MSRMC
05/03/2023 Dept. of Physiology, MSRMC
• The RNA that is initially transcribed from a gene is called the primary transcript.
• Most eukaryotic genes contain exons, DNA sequences that are present in the mature mRNA, alternating with introns, which are not present in the mRNA.
05/03/2023 Dept. of Physiology, MSRMC
• Splicing• Addition of 5’ methyl cap• Cleavage of RNA transcript downstream
from polyadenylation signal• Addition of poly A tail
Processing of The Primary Transcript
05/03/2023 Dept. of Physiology, MSRMC
05/03/2023 Dept. of Physiology, MSRMC
Types of RNA• mRNA• tRNA• rRNA• miRNA
05/03/2023 Dept. of Physiology, MSRMC
mRNA• mRNA molecules are long, single RNA
strands that are suspended in the cytoplasm.
• They contain codons that are exactly complementary to the code triplets of the DNA genes.
05/03/2023 Dept. of Physiology, MSRMC
• Carrier for specific amino acids from cytoplasm to mRNA
• Has sites for binding amino acid & mRNA
tRNA
05/03/2023 Dept. of Physiology, MSRMC
rRNA• Functions in association with tRNA &
mRNA
• Present in ribosomes
05/03/2023 Dept. of Physiology, MSRMC
miRNA• Non-coding RNA
• Regulate gene expression
05/03/2023 Dept. of Physiology, MSRMC
Translation • Definition: Translation is the synthesis
of protein from RNA.
• Site: Ribosomes
05/03/2023 Dept. of Physiology, MSRMC
• Requirements:– Amino acids– mRNA– tRNA– ATP
Translation contd.
05/03/2023 Dept. of Physiology, MSRMC
• Begins at AUG• Ends at UAG, UAA, UGA
Translation contd.
05/03/2023 Dept. of Physiology, MSRMC
• Amino acid + ATP
• Activated amino acid + AMP
• tRNA
• Amino acid tRNA complex
• Binds to mRNA
05/03/2023 Dept. of Physiology, MSRMC
• Peptide bonds formed between successive amino acids
• Process stops at chain termination codon
• Release of polypeptide
Translation contd.
05/03/2023 Dept. of Physiology, MSRMC
05/03/2023 Dept. of Physiology, MSRMC
• It is common to have more than one ribosome on a given mRNA chain at a time.
• The mRNA chain plus its collection of ribosomes is visible under the electron microscope as an aggregation of ribosomes called a polyribosome.
05/03/2023 Dept. of Physiology, MSRMC
05/03/2023 Dept. of Physiology, MSRMC
Post-translational Modification
• Folding• Hydroxylation• Carboxylation• Glycosylation• Phosphorylation • Cleavage of peptide bonds
05/03/2023 Dept. of Physiology, MSRMC
Regulation of Gene Expression
• Step 1: Chromatin remodeling• Step 2: Initiation of transcription• Step 3: Transcript elongation• Step 4: Termination of transcription• Step 5: RNA processing• Step 6: Nucleocytoplasmic transport• Step 7: Translation• Step 8: mRNA degradation
05/03/2023 Dept. of Physiology, MSRMC
05/03/2023 Dept. of Physiology, MSRMC
Applied physiology
05/03/2023 Dept. of Physiology, MSRMC
Mutation • Definition: change in the DNA structure of
a gene• Types:
– Point mutation (transition, transversion)– Frame shift mutation(deletion, insertion)
• Mutations can lead to genetic diseases, cancers.
• Some mutations may be silent.
05/03/2023 Dept. of Physiology, MSRMC
Genetic diseases• Sickle cell anaemia• Cystic fibrosis• Phenylketonuria• Huntington’s chorea• Haemophilia
05/03/2023 Dept. of Physiology, MSRMC
• Gene therapy: methods to cure an inherited disease by providing a patient with correct copy of a defective gene.
• Gene therapy has been successful in– Cystic fibrosis– Severe combined immunodeficiency
Gene therapy
05/03/2023 Dept. of Physiology, MSRMC
Summary