3.2 Review PBS

1. 3.2 Review PBS

2. What is the DNA code? What is the connection between genes and proteins? • DNA is read in segments, called genes • A gene is a particular sequence of nucleotide bases that code for a protein. • The sequence of bases determines what sequence the amino acids are in, which determines the protein

3. How are proteins produced in a cell? How does the sequence of nucleotides in DNA determine the sequence of amino acids in a protein? • Step 1: Transcription • DNA is too large and fragile to leave the nucleus. • So it is copied into a mRNA template by RNA polymerase • mRNA acts a “messenger”, which takes the gene code out of the nucleus to the ribosome

4. How are proteins produced in a cell? How does the sequence of nucleotides in DNA determine the sequence of amino acids in a protein? • Step 2: Translation • mRNA binds to a ribosome • Ribosome reads the mRNA in three bases at a time (called codons) These determine which amino acid is brought • tRNA come and bind to the codons using anticodons • This tRNA brings a specific amino acid • This process repeats until the whole protein is made • Therefore the sequence of DNA determines the codons in mRNA, which determines the sequence of amino acids, which determines the protein being made.

5. How are proteins produced in a cell? How does the sequence of nucleotides in DNA determine the sequence of amino acids in a protein?

6. What determines the shape of a protein? • Many amino acids have different properties (positive, negative, or neutral charge). Therefore the amino acids present and their order in the chain affect the shape of the protein due to the following forces: • Van der Waals forces – random attractive forces between atoms • Electrostatic charge – positive amino acids will attract negative amino acids and repel positive amino acids • S-S – Covalent bonds between amino acids with sulfur, these are stronger forces that hold the protein shape steady • Hydrogen bonds – bond formed between two molecules that are polar… (continues on next slide)

7. What determines the shape of a protein? • Polar amino acids are said to be hydrophilic • Hydrophilic amino acids like water because they are polar like water and will attract water. • Nonpolar amino acids are said to be hydrophobic • Hydrophobic amino acids are “afraid” of water because they are not polar and will repel water (fats are hydrophobic, which is why they do not mix with water) • Hydrophilic amino acids will attract each other and form hydrogen bonds. They will repel hydrophobic amino acids.

8. Is the shape of a protein affected by its surrounding environment? • In water hydrophilic amino acids will spread out (attracted to water) and hydrophobic amino acids will clump up (repelled by water) • In oil hydrophilic amino acids will clump up (repelled by hydrophobic oil) and hydrophobic amino acids will spread out.

9. What is a mutation?How does a change in the DNA code affect the shape of a protein? • A mutation is change in one base (point mutation) or bases (frameshift mutation due to addition or deletion of base) of DNA. • This can change the codon, which then can change the amino acid(s). • If an amino acid of one property is replaced with an amino acid of another property this can change in the interactions of the amino acids and the shape of the protein.

10. Can changing just one nucleotide in a gene change the shape of a protein? • Yes, examples: Tay Sachs and Sickle Cell • A single base changes glutamic acid (hydrophilic amino acid) to change to valine (hydrophobic amino acid) • This change causes valine(a hydrophobic amino acid) to to stick to the hydrophobic pocket of another hemoglobin. • The hemoglobin sticking together causes the cell to be sickle shaped.

11. Key points to understand from your portfolio: • Page 1: Describe the 4 different types of proteins • Pages 2, 3, & 5: Be able to describe what happens with transcription & translation (using terms from pg. 5), and be able to walk through those processes. Also, describe what happens with protein synthesis with individuals with sickle cell anemia (what kind of mutation, and how does this work?)

12. Key points to understand from your portfolio: • Page 4: Compare/contrast sickle cell & Tay Sacs. Describe the 4 forces discussed on this page. Compare glutamic acid and valine. Include specifics like hydrophobic or hydrophilic, charge, and how they behave in water. This information should help you understand the difference in the shape of normal RBCs compared to sickle cells. • Page 6: Do you understand this concept map?