Unraveling Gene Expression: A Deep Dive into RNA Structure & Translation Across Human Cells

1. Higher Human Biology Unit 1 Human Cells KEY AREA 3: Gene Expression

2. Human Cells Learning Intentions KEY AREA 3 – Gene Expression • Gene Expression • RNA Structure & Function • Transcription • Translation • Post-translation

3. 3a) Gene Expression The genetic composition of a cell is called the cell genotype The cell genotype is determined by the sequence of DNA bases in its genes Only a fraction of the genes in a cell are expressed

4. 3b) Gene Expression Gene expression is controlled by the regulation of Transcription and Translation The order of bases on DNA determines the sequence of amino acids that are made The sequence of amino acids joined together in polypeptide chains determine the structure, shape, function of the protein produced

5. 3c) RNA Structure & Function RNA is a single strand of RNA nucleotides RNA nucleotides contain a ribose sugar, a phosphate and a base RNA nucleotides contain the bases Adenine, Uracil, Cytosine, Guanine Transcription and translation involve 3 types of RNA: mRNA (messenger RNA) carries a copy of a section of the DNA code for a specific protein from the nucleus to the ribosome rRNA (ribosomal RNA) and proteins form a ribosome tRNA (transfer RNA) carries a specific amino acid

6. 3c) RNA Structure & Function mRNA is linear and carries the DNA code in the form of mRNA codons (3 bases=a codon) A mRNA codon is complementary to the triplet of bases on the original DNA strand tRNA is found in the cytoplasm tRNA is folded on itself due to hydrogen bonds forming between bases tRNA exposes triplets of bases called tRNA anticodons tRNA anticodons are complementary to a mRNA codon tRNA pick up specific amino acids (with its attachment site) in the cytoplasm and carry them to the ribosome mRNA codons and tRNA anticodons translate the genetic code into the correct sequence of amino acids to make a protein

7. 3d) Transcription Transcription is the copying of the DNA code for a specific protein into mRNA Transcription of DNA into primary and mature RNA transcripts occurs in the nucleus 1. A promotor region of DNA initiates transcription 2. RNA polymerase enzyme moves to the specific section of DNA and unwinds the DNA double helix from that point by breaking hydrogen bonds between bases 3. RNA nucleotides pair with complementary DNA base pairs (A-U, G-C) forming mRNA 4. RNA polymerase can only add nucleotides to the 3’ end of mRNA 5. RNA polymerase joins the nucleotides together to form a new sugar- phosphate backbone 6. The mRNA becomes separated from the DNA template, and is called the primary transcript of mRNA

8. 3d) Transcription

9. 3e) Transcription- RNA Splicing Not ALL nucleotides in a gene play a role in the coding for the amino acids sequence Introns are non-coding regions of genes Exons are coding regions of genes Introns are found between the Exons Introns are cut out and removed from the primary transcript Exons are spliced together (RNA splicing) to form mRNA with a continuous sequence exons (this is called the mature transcript of mRNA) this does not change the order of the exons The mature transcript of mRNA moves from the nucleus through the cytoplasm to a ribosome Transcription Animation (1:52)

10. Splicing (1:37)

11. 3f) Stages of Translation • mRNA codons AUG complementary to tRNA anticodon UAC codes for the amino acid methionine (met) AND acts as the START CODON • mRNA codons UAA, UAG & UGA do not code for amino acids, but they act as STOP CODONS • Translation begins at a start codon and ends at a stop codon • Mature mRNA binds to the ribosome • Each tRNA anticodon binds to a complementary codon on the mRNA lining up the amino acids (being carried by tRNA) in a specific order • Peptide bonds form between the amino acids to form a growing polypeptide chain • When the tRNA detaches from its amino acid, it then collects another

12. 3f) Translation

13. 3f) Translation

14. 3f) Translation

15. 3f) Translation

16. 3h) One gene, many proteins One gene can create many proteins as a result of alternative RNA splicing Different mature mRNA molecules are produced from the same primary transcript this is dependent on which exons are retained during RNA splicing

17. 3i) Final Protein Structure Amino acids are linked by peptide bonds to form polypeptides polypeptide chains fold to form three dimensional shape of a protein the folding is caused by hydrogen bonds and other interactions between individual amino acids Proteins have a large variety of shapes which determines their functions a cell’s phenotype is its physical and chemical state a cell’s phenotype is determined by the proteins it produces along with environmental factors that can influence the cell Translation animation (2:04)

18. Human Cells Questions KEY AREA 3 – Gene Expression • Testing Your Knowledge 1 Page 37 Q’s 1-4 2. Testing Your Knowledge 2 Page 43 Q’s 1-4 • What you Should Know Page 43 Q’s 1-15 • Quick Quiz