1. Cell Physiology
Protein Synthesis

2. Protein Synthesis DNA serves as a blueprint for making proteins
Gene: DNA segment that carries a blueprint for building one protein or polypeptide chain
Proteins have many functions
Fibrous (structural) proteins are the building materials for cells
Globular (functional) proteins act as enzymes (biological catalysts)
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3. Protein Synthesis DNA information is coded into triplets Triplets
Contain three bases
Call for a particular amino acid
For example, a DNA sequence of AAA specifies the amino acid phenylalanine
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4. Protein Synthesis
Most ribosomes, the manufacturing sites of proteins, are located in the cytoplasm
DNA never leaves the nucleus in interphase cells
DNA requires a decoder and a messenger to build proteins, both are functions carried out by RNA (ribonucleic acid)
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5. Protein Synthesis How does RNA differ from DNA? RNA:
Is single-stranded
Contains ribose sugar instead of deoxyribose
Contains uracil (U) base instead of thymine (T)
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6. Role of RNA Transfer RNA (tRNA) Ribosomal RNA (rRNA)
Transfers appropriate amino acids to the ribosome for building the protein
Ribosomal RNA (rRNA)
Helps form the ribosomes where proteins are built
Messenger RNA (mRNA)
Carries the instructions for building a protein from the nucleus to the ribosome
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7. Role of RNA Protein synthesis involves two major phases:
Transcription
Translation
We will detail these two phases next
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8. Protein Synthesis Transcription
Transfer of information from DNA’s base sequence to the complementary base sequence of mRNA
Only DNA and mRNA are involved
Triplets are the three-base sequence specifying a particular amino acid on the DNA gene
Codons are the corresponding three-base sequences on mRNA
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9. Protein Synthesis Example of transcription: DNA triplets AAT-CGT-TCG
mRNA codons UUA-GCA-AGC
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10. Figure 3.16 Protein synthesis.
Slide 1
Nucleus (site of transcription)
DNA
Cytoplasm (site of translation) 1
mRNA specifying one polypeptide is made on DNA template. 2
mRNA leaves nucleus and attaches to ribosome, and translation begins.
Amino acids
mRNA
Nuclear pore
Nuclear membrane
Correct amino acid attached to each species of tRNA by an enzyme
Synthetase enzyme 4
As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain.
Growing polypeptide chain
Met 3
Incoming tRNA recognizes a complementary mRNA codon calling for its amino acid by binding via its anticodon to the codon.
Gly
Ser
Phe
Ala
Peptide bond 5
Released tRNA reenters the cytoplasmic pool, ready to be recharged with a new amino acid.
tRNA “head” bearing anticodon
Large ribosomal subunit
Codon
Direction of ribosome advance; ribosome moves the mRNA strand along sequentially as each codon is read.
Portion of mRNA already translated
Small ribosomal subunit

11. Figure 3.16 Protein synthesis (1 of 2).
Slide 2
Nucleus (site of transcription)
DNA
Cytoplasm (site of translation)
mRNA specifying one polypeptide is made on DNA template. 1
Amino acids
mRNA
Nuclear pore
Nuclear membrane
Correct amino acid attached to each species of tRNA by an enzyme
Synthetase enzyme

12. Protein Synthesis Translation
Base sequence of nucleic acid is translated to an amino acid sequence
Amino acids are the building blocks of proteins
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13. Protein Synthesis Translation (continued)
Steps correspond to Figure 3.16 (step 1 covers transcription)
mRNA leaves nucleus and attaches to ribosome, and translation begins
Incoming tRNA recognizes a complementary mRNA codon calling for its amino acid by binding via its anticodon to the codon.
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14. Figure 3.16 Protein synthesis (1 of 2).
Slide 3
Nucleus (site of transcription)
DNA
Cytoplasm (site of translation)
mRNA specifying one polypeptide is made on DNA template. 1 2
mRNA leaves nucleus and attaches to ribosome, and translation begins.
Amino acids
mRNA
Nuclear pore
Nuclear membrane
Correct amino acid attached to each species of tRNA by an enzyme
Synthetase enzyme

15. Figure 3.16 Protein synthesis (2 of 2).
Slide 4
Incoming tRNA recognizes a complementary mRNA codon calling for its amino acid by binding via its anticodon to the codon. 3
tRNA “head” bearing anticodon
Large ribosomal subunit
Codon
Direction of ribosome advance; ribosome moves the mRNA strand along sequentially as each codon is read.
Portion of mRNA already translated
Small ribosomal subunit

16. Protein Synthesis Translation (continued)
Steps correspond to Figure 3.16
As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain.
Released tRNA reenters the cytoplasmic pool, ready to be recharged with a new amino acid.
© 2015 Pearson Education, Inc.

17. Figure 3.16 Protein synthesis (2 of 2).
Slide 5 4
As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain.
Growing polypeptide chain
Met
Incoming tRNA recognizes a complementary mRNA codon calling for its amino acid by binding via its anticodon to the codon. 3
Gly
Ser
Phe
Ala
Peptide bond
tRNA “head” bearing anticodon
Large ribosomal subunit
Codon
Direction of ribosome advance; ribosome moves the mRNA strand along sequentially as each codon is read.
Portion of mRNA already translated
Small ribosomal subunit

18. Figure 3.16 Protein synthesis (2 of 2).
Slide 6 4
As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain.
Growing polypeptide chain
Incoming tRNA recognizes a complementary mRNA codon calling for its amino acid by binding via its anticodon to the codon. 3
Met
Gly
Ser
Phe
Ala
Peptide bond 5
Released tRNA reenters the cytoplasmic pool, ready to be recharged with a new amino acid.
tRNA “head” bearing anticodon
Large ribosomal subunit
Codon
Direction of ribosome advance; ribosome moves the mRNA strand along sequentially as each codon is read.
Portion of mRNA already translated
Small ribosomal subunit