Molecular biology Flashcards
Why DNA instead of RNA for info storage?
RNA has an extra 2’ hydroxyl group, which makes it more reactive with water and with the phosphate of the backbone, making it less stable. There would be a lot more sequence breaks if RNA was used.
How does the properties of nucleotides contribute to the structure of the DNA helix?
A: The sugar and phosphate of the nucleotides are up the back bone because they interact with water, shielding the hydrophobic nitrogenous bases. Phosphate has a negative charge and repulses opposite side.
Why do we have RNA?
A: RNA acts as a catalyst for reactions in the cell. It is also easier to replicate/proliferate.
Why Thymine instead of Uracil in DNA?
A: Cytosine deaminates into Uracil causing alteration of the sequence due to different base-pairing. Instead of C-> base pairs with G in RNA, you get C->U-> base pairs with A.
Why does low temp decrease specificity in hybridization experiment?
A: DNA hybridization = annealing (bringing two strands together), which is the opposite of melting (pulling two strands apart.) Melting temp is higher in strands that complement each other better, so if the temperature decreases, the snips observed will include ones that hybridized with sequences that are not as complementary as well as those that are complementary.
Why high salt decrease specificity in hybridization experiment?
A: Positive ions meet up with negative ions in the backbone, which opens up the middle where the nitrogenous bases are - more available for hybridization with RNA snips.
Why are proteins more abundant/necessary when there is RNA?
A: Proteins have a wider variety of properties due to variety of amino acids, and can therefore catalyze a wider variety of chemical reactions and have more shapes. They can also make structures that DNA/RNA cannot, like transmembrane proteins.
Why is protein so much more abundant than RNA and RNA so much more abundant than DNA?
A: Amplification, DNA ->RNA -> protein.
How do cells become different from one another? What is the protein that does this and how does it work?
A: Gene expression. Transcription factors bind to promoter and induce gene expression. Some TF are common, some are specific to certain types of genes such as cardiac gene expression.
Why do genes need to be expressed at different rates at different times, in different cells?
A: Because they need to make different proteins based on their function.
How do transcription factors influence the proteins made in the cell?
A: They bind to the enhancer sequence and bring the RNAP to the start site and split strands apart for transcription, though they cannot initiate transcription alone - need other activator proteins and mediator complex.
How does the cell regulate proteins that are made?
A: The genes themselves encode regulators: transcription factors proteins, and proteins that directly control metabolic function.
How does the cell respond to the external environment and changes in its cytoplasm?
A: via signal transduction pathways that change location, amount, and type of transcription factors.
What do the different RNAPs do:
A: RNAP I makes rRNA, RNAP II makes mRNA -> proteins, RNAP III makes tRNA.
What modifications occur before mRNA is released into the cytoplasm and what are their roles?
A: introns are spliced, and some exons depending on function/type of protein (differential splicing), then 5’ cap (signal it is mRNA to protein synthesis machinery) and poly-A tail (export signal and stabilizer) are added.
