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Leaving Cert Biology Genetics – section 2.5 Genetics 2.5 2.5.4( RNA), 2.5.5, 2.5.15 Leaving Cert Biology Genetics – section 2.5 2.5.4 RNA Structure • RNA (ribonucleic acid) is another nucleic acid. • It is made up of nucleotide units • Each nucleotide unit has a backbone one of four nucleotide bases: Adenine A, Guanine G, Cytosine C, and Uracil U (instead of thymine!) U Leaving Cert Biology Genetics – section 2.5 RNA Structure Unlike DNA, RNA is single stranded! Leaving Cert Biology Genetics – section 2.5 2.5.5 Protein synthesis • Every protein has a particular sequence of amino acids that it is made up of. 1. Our DNA contains the instructions (in the form of a code) to make proteins 3-D image of Melanin Leaving Cert Biology Genetics – section 2.5 Protein synthesis 2.The code contained in our DNA is transcribed (copied) to make messenger RNA (mRNA). Leaving Cert Biology Genetics – section 2.5 Protein synthesis 3. The mRNA carries the code into the ribosome The mRNA The protein chain Leaving Cert Biology Genetics – section 2.5 The function of mRNA in protein synthesis is to carry a copy of the DNA instructions (codes) from the nucleus to the ribosomes. Leaving Cert Biology Genetics – section 2.5 Protein synthesis 4. In the ribosome the code is translated and the amino acids are assembled into the correct sequence to make the protein. Leaving Cert Biology Genetics – section 2.5 Protein synthesis 5. The protein folds into its functional shape. Leaving Cert Biology Genetics – section 2.5 Protein synthesis – higher level • 1. Enzymes unwind the double helix Leaving Cert Biology Genetics – section 2.5 2. Transcription • RNA nucleotide bases bond with one strand of exposed DNA. • The enzyme RNA polymerase assembles these bases to form mRNA. •mRNA has a series of bases that are complementary to those in DNA ! Leaving Cert Biology Genetics – section 2.5 The function of mRNA in protein synthesis is to carry a copy of the DNA instructions (codes) from the nucleus to the ribosomes. Leaving Cert Biology Genetics – section 2.5 Leaving Cert Biology Genetics – section 2.5 3. mRNA sequence • mRNA moves into the cytoplasm • Each three base sequence of mRNA carries a genetic code (codon) that specifies either: a starting codon, a particular amino acid or a stop codon. Leaving Cert Biology Genetics – section 2.5 4. The ribosome • Ribosome subunits (rRNAs) attach to the mRNA. • These subunits form the ribosome, the site of protein synthesis. Leaving Cert Biology Genetics – section 2.5 5. tRNA • Free floating tRNAs with their attached amino acids, within the cytoplasm are attracted to the complementary mRNA already attached to the ribosome. • This ensures the amino acids are aligned in a sequence determined by the codons of the mRNA Leaving Cert Biology Genetics – section 2.5 6. Protein synthesis • Aligned amino acids bond to form links of the new protein molecule Leaving Cert Biology Genetics – section 2.5 7. End of Translation • tRNAs continue to move to the ribosome, until a stop codon on the mRNA code sequence tells the ribosome that the process is complete and the protein is synthesised. Leaving Cert Biology Genetics – section 2.5 8. Protein folding 5. The protein folds into its functional shape. Leaving Cert Biology Genetics – section 2.5 Can you.. • • • • • Tell what RNA stands for Explain how mRNA is made Give the function of mRNA Tell the location of transcription Describe what happens to mRNA after it leaves the nucleus • Explain how the code of mRNA is translated