Proteins are essential functional units in cells that are synthesized through a multi-step process involving transcription of DNA in the nucleus to mRNA, which is then transported to the cytoplasm and translated by ribosomes to produce a protein. During translation, tRNA molecules carry amino acids to the ribosome according to the mRNA codon sequence to form the polypeptide chain. The protein then undergoes post-translational modifications to achieve its functional structure before carrying out important cellular roles such as enzymatic reactions, transport, structure, and signaling. Regulation of protein synthesis ensures only necessary proteins are produced at the right times and places in the cell.

1. Protein Synthesis in Cell

2. Learning Objectives
• Importance of proteins
• Site of protein synthesis
• Steps of protein synthesis
• Regulation of protein synthesis
• Applied aspects
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3. Proteins: their importance
• Membrane proteins
• Structural proteins
• Enzymes
• Hormones
• Antigens
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Site of Protein Synthesis

5. Site of Protein Synthesis
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6. 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.
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7. Basic building blocks of DNA
• Phosphoric acid
• Sugar
• Nitrogenous base
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8. 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.
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9. Pathway from Genes to Proteins
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10. • Central dogma of molecular biology:
genetic information flows unidirectionally
from DNA to proteins.
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11. Steps of Protein Synthesis
• Transcription
• Translation
• Post translational modificaton
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12. Transcription
• Definition: Transcription is the synthesis
of RNA from a DNA template, mediated by
an enzyme called RNA polymerase.
• Site: Nucleus
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13. • Requirements:
– DNA template
– RNA polymerase
– Activated ribonucleotides
Transcription contd.
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14. Building blocks of RNA
• Phosphoric acid
• Sugar
• Nitrogenous base
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15. • The basic building blocks of RNA form
RNA nucleotides.
• RNA nucleotides are then activated by
RNA Polymerase.
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16. • 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
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17. • Polymerase moves along the DNA strand
• Breakage of 2 phosphate radicals from
RNA nucleotides
• Covalent linkage of 3rd phosphate with
ribose
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18. • RNA polymerase reaches end of DNA
gene (chain terminating sequence)
• Breaking away of polymerase & RNA
chain
• Formation of RNA transcript
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19. • 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.
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20. DNA Base RNA Base
Guanine…………………………….……Cytosine
Cytosine ………………………..…….… Guanine
Adenine …………………………………… Uracil
Thymine ………………………………… Adenine
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22. • 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.
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23. • Splicing
• Addition of 5’ methyl cap
• Cleavage of RNA transcript downstream
from polyadenylation signal
• Addition of poly A tail
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Processing of The Primary
Transcript

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25. Types of RNA
• mRNA
• tRNA
• rRNA
• miRNA
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26. 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.
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27. • Carrier for specific amino acids from
cytoplasm to mRNA
• Has sites for binding amino acid & mRNA
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tRNA

28. rRNA
• Functions in association with tRNA &
mRNA
• Present in ribosomes
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29. miRNA
• Non-coding RNA
• Regulate gene expression
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30. Translation
• Definition: Translation is the synthesis
of protein from RNA.
• Site: Ribosomes
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31. • Requirements:
– Amino acids
– mRNA
– tRNA
– ATP
Translation contd.
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32. • Begins at AUG
• Ends at UAG, UAA, UGA
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Translation contd.

33. • Amino acid + ATP
• Activated amino acid + AMP
• tRNA
• Amino acid tRNA complex
• Binds to mRNA
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34. • Peptide bonds formed between
successive amino acids
• Process stops at chain termination codon
• Release of polypeptide
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Translation contd.

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36. • 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.
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38. Post-translational Modification
• Folding
• Hydroxylation
• Carboxylation
• Glycosylation
• Phosphorylation
• Cleavage of peptide bonds
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39. 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
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41. Applied physiology
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42. 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.
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43. Genetic diseases
• Sickle cell anaemia
• Cystic fibrosis
• Phenylketonuria
• Huntington’s chorea
• Haemophilia
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44. • 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
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Gene therapy

45. Summary
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