A __________ is a chemical messenger that binds to receptors on a cell and brings about
metabolic, physiological, or behavioral responses in the organism.
a. hormone
b. enzyme
c. nucleus
d. growth factor
A
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You begin an experiment involving metabolic processes in human liver cells, but you discover your liver tissue samples have been contaminated with a strain of obligate anaerobic bacteria. Theoretically, how could you kill the bacteria while minimizing damage to the liver cells?
a. soak the tissue samples in pure ethanol b. put the sample through an autoclave c. expose the samples to gaseous oxygen d. dehydrate the tissue samples overnight
What extracellular plant signaling molecules can exert their effects at very low concentrations?
a. hormones b. peptide c. enzymes d. pheromones e. plasmodesmata
The following F2 results occur from a typical dihybrid cross:
purple: A_B_ 9/16 white: aaB_ 3/16 white: A_bb 3/16 white: aabb 1/1 If a double heterozygote (AaBb) is crossed with a fully recessive organism (aabb), what phenotypic ratio is expected in the offspring?
NASA has discovered an alien life-form. You are called in to help NASA scientists to deduce the genetic code for this alien
Surprisingly, this alien life-form shares many similarities with life on Earth: this alien uses DNA as its genetic material, makes RNA from DNA, and reads the information from RNA to make protein using ribosomes and tRNAs. Even more amazing, this alien uses the same 20 amino acids, like the organisms found on Earth, and also codes for each amino acid by a triplet codon. However, the scientists at NASA have found that the genetic code used by the alien life-form differs from that used by life on Earth. NASA scientists drew this conclusion after creating a cell-free protein-synthesis system from alien cells and adding an mRNA made entirely of uracil (poly U). They found that poly U directs the synthesis of a peptide containing only glycine. NASA scientists have synthesized a poly AU mRNA and observe that it codes for a polypeptide of alternating serine and proline amino acids. From these experiments, can you determine which codons code for serine and proline? Explain. Bonus question. Can you propose a mechanism for how the alien's physiology is altered so that it uses a different genetic code from life on Earth, despite all the similarities?