Protein Synthesis (Eukaryotes)

1. Protein Synthesis (Eukaryotes) By Antara, Carla, Clariss and Theantay

2. DNA • DNA is located in the nucleus of a cell. It is a double helix shape and contains sequences of nucleotides. • Each nucleotide has one of the 4 bases: Adenine (A) which always bonds with Thymine (T), and Cytosine (C) which always bonds with Guanine (G). Each stand of DNA is complementary to the other. • The order of these nucleotides determines holds the genetic code for a protein. Nucleotides

3. DNA Unwinds • The section of DNA that codes for the protein being synthesized is unwound and unzipped by the enzyme helicase. Helicase

4. Two strands of DNA • One half of the DNA is the template strand. This is the strand that will be transcribed into mRNA. • The other strand is the coding (anti-sense) strand. This has a complementary sequence of bases as in the template stand so contains the same sequence of nucleotides as will be in the mRNA that will be produced. Template Strand Coding Strand

5. RNA Synthesis • RNA polymerase attaches to the template strand and creates a complementary length of mRNA. This is the primary mRNA. • The coding stand of DNA is not used. RNA Polymerase Coding Strand Template Strand mRNA

6. Differences between RNA and dna • RNA: • Has the bases Adenine, Cytosine, Guanine and Uracil • Relatively short • The sugar-phosphate backbone is made of ribose sugar • Single stranded • DNA: • Has the bases Adenine, Cytosine, Guanine and Thymine • Very long • The sugar-phosphate backbone is made of deoxyribose sugar • Double stranded

7. RNA Processing • During RNA processing, which occurs in the nucleus, the introns in the primary mRNA are spliced out leaving only the exons in the mature mRNA. Primary mRNA Exon Intron

8. Leaving the Nucleus • The mature mRNA leaves the nucleus through a nuclear pore to go into the cytoplasm. mRNA Nuclear Pore Nucleus Cytoplasm

9. Translation • The ribosome attaches to the mRNA in the cytoplasm. • It reads the codons (3 bases) in the mRNA that each code for a specific amino acid. • The tRNA with the complementary anticodon to the codon will carry the specific amino acid. Amino Acid tRNA loaded with Amino Acids Ribosome mRNA

10. Translation • The tRNA with the correct anticodon will be attracted to the binding site in the ribosome. • The ribosome will add the amino acid it carries to the growing polypeptide chain and the tRNA will be released. • The unloaded tRNA will be reattached to another of the same amino acid. Binding Site Loaded tRNA Polypeptide Chain Unloaded tRNA Ribosome mRNA

11. Primary proteins • The completed chain of amino acids, called a polypeptide chain, is a primary protein. Polypeptide chain - Primary protein

12. Secondary proteins The polypeptide chain arranges into two common shapes to form a secondary protein: the alpha helix (left) and the beta-pleated sheet (right). These are held in place by hydrogen bonds.

13. Tertiary Proteins • The alpha helix and beta pleated sheets fold into a complex 3 dimensional shape which is called a tertiary protein. For some proteins, this is the end of the road and the protein goes away to do what is was synthesized to do.

14. Quaternary proteins • Quaternary proteins are clusters of tertiary proteins which bind together to form one protein that does a specific job.