Quiz questions Flashcards
properties of an organelle that imply it evolved from a symbiotic relationship
double membrane
own DNA
what is implied from the fact that all eukaryotic cells contain mitochondria
endosymbiotic relationship happened early in evolution in a current ancestor of all current lineages
what is implied from the fact that aside from animals, other eukarotic lineages are unicellular
multicelluarity evolved multiple times after the split between plant and non plant lineages (wouldnt have occurred in a common ancestor of plants and animals)
The acquisition of chloroplasts must have occurred in a common ancestor of green plants and red algae, as all of these organisms contain chloroplasts. However, there are also some (but not all) protozoa that contain chloroplasts, including Euglena, diatoms, and brown algae. The structure of chloroplasts is also much more diverse than that of mitochondria. This indicates that the endosymbiotic events that led to the acquisition of chloroplasts have occurred multiple times during evolution, even after the split between plants and nonplant lineages. The absence of chloroplasts in all animals indicates that chloroplasts did NOT evolve in a common ancestor of plants and animals.
plasma vs ER membrane
plasma: thicker, stiffer, less permeable
ER has more water molecules in the hydrophobic core
order for rate molecules move across membranes
slowest to fastest
ions
larger, uncharged polar molecules like glucose and amino acids
small uncharged polar molecules like water
small non polar molecules
The Na+-K+ pump binds to Na+ ions on the inside of the liposome and is then phosphorylated by a phosphate from the ATP, which is also inside the liposome. The pump changes conformation in response to phosphorylation, releasing the Na+ on the outside. K+ from the outside of the liposome can then bind to the pump and trigger dephosphorylation. Dephosphorylation of the pump triggers switching of conformation back to the original conformation, leading to a release of K+ inside the liposome. The pump is then ready to repeat the cycle of pumping Na+ out and K+ into the liposome. The Na+ and ATP must be inside the liposome and K+ outside the liposome for pumping of ions to occur
RNA capping, a part of RNA processing, takes place as an RNA is being transcribed. Eukaryotic genes contain both introns and exons, and both are transcribed. Soon after transcription begins, within the first 25 nucleotides added to the growing RNA strand, a modified guanine nucleotide is added to the 5’ end of the RNA. Once the cap is added and as transcription is continuing along the gene, splicing to remove introns can begin. After transcription is complete, further modification of the RNA transcript must occur, including the addition of the 3’ poly-A tail, before the mature mRNA can exit the nucleus to be translated by ribosomes in the cytosol.
An aminoacyl-tRNA binds to the vacant A site on the ribosome; a peptide bond forms; the large subunit of the ribosome translocates, moving the bound tRNAs to the E and P sites; the small subunit of the ribosome translocates, ejecting the tRNA from the E site.
The ribosomal RNA is the critical component in the active site as this site is made of only ribosomal RNA. The protein helps support the RNA but does not participate in the catalysis of peptide bond formation. The ribosomal RNA base-pairs with the tRNA holding the growing polypeptide, helping to position it in the correct orientation. Other RNA nucleotides base-pair with the incoming tRNA to position the amino acids. Further hydrogen-bonding positions the amino acids, facilitating new peptide bond formation.
The hydrogen bonds formed between ribosomal RNA and tRNAs position the aminoacyl-tRNAs to catalyze peptide bond formation.
D. The RNA in the P site makes hydrogen bonds with the 3’ end of the aminoacyl-tRNA.
Ribosomes (which catalyze peptide bond formation) and spliceosomes (responsible for splicing introns out of pre-mRNAs) contain both RNA and protein, but it is the RNA component that is catalytic, hence both are ribozymes. Ribozymes may represent molecular fossils of the proposed RNA world, a scenario in which RNA predates both DNA and proteins. In this scenario, over time DNA took over the information storage role and proteins took over the majority of enzymatic activity in the cell, with RNA still serving a central role in the transfer of information from DNA to protein.
The initial binding site for a ribosome is the 5’ end of an mRNA molecule, upstream of the important AUG that serves as the start translation signal. Initiation of translation is outlined in the steps shown in the figure below. Pay special attention to how the small ribosomal subunit, pre-loaded with an initiator tRNA and other translation initiation factors, binds to the 5’ untranslated region and then slides along the mRNA until it reaches the start AUG codon. Once this happens, the rest of the ribosome complex can assemble so that translation can begin in earnest.
