Chemistry of Life
Describe why hydrogen bonds form between water molecules.
slightly negatively charged O atom in one water molecule is attracted to one of the slightly positively charged H atoms in another water molecule, so that a weak hydrogen bond forms between the two water molecules. The strong electronegativity of O pulls the electrons shared with each H atom within a single water molecule toward the O atom, concentrating more negative charge at the O end of the molecule and giving the H atoms a slight positive charge. (Water is polar)
Describe how plants absorb photons of light energy. (hint:what structure allows plants to do this...don't say photosynthesis)
plants contain pigments such as chlorophylls that absorb photons of light (of certain wavelengths).
Describe how genetic information is carried in chloroplasts and mitochondria.
chloroplasts and mitochondria contain DNA and RNA
Referring to the handout: Describe why the amount of light available to the Chlorella culture might affect the growth dynamics of the alga.
light is an energy source for photosynthesis.
Describe why DNA replication is said to be a semiconservative process
one strand of DNA serves as the template for the synthesis of a new strand of complementary DNA .
Identify the type of monomer of which enzymes are composed of.
amino acids are the monomers of which this enzyme is composed.
Describe the effect on chlorophyll-containing photosystems when the chlorophyll molecules absorb photons of light.
electrons in the photosystems are boosted to higher energy levels.
Describe TWO events that are common to both mitosis and meiosis that ensure the resulting daughter cells inherit the appropriate number of chromosomes.
Spindle elements (microtubules) form/attach to chromosomes
· Chromatin condenses
· Alignment of chromosomes across center of cell prior to chromosome separation
· Separation of chromatids/centromeres to daughter cells
· G2/M checkpoint occurs in both processes
· Replication or synthesis of DNA precedes mitosis/meiosis
· Cytokinesis separates daughter cells after mitosis/meiosis
Referring to the handout: Under harsh environmental conditions, C. elegans produces a pheromone, a complex of molecules that affects other C. elegans. One effect of the pheromone is to cause developing larvae to temporarily arrest as larvae rather than mature to reproductive adults. Predict the relative amount of pheromone most likely produced by C. elegans that are only weakly attracted to one of the test chemicals.
a relatively large amount of the pheromone will be produced by C. elegans that are only weakly attracted to one of the test chemicals.
Explain how random mutations such as those in pathogens with a mutator phenotype may arise in the DNA of an organism.
errors in DNA replication or in DNA repair mechanisms or changes induced by external factors (such as radiation or certain chemicals) can introduce or not correct errors in nucleotide sequence.
The pH of a solution determines the charge of certain R groups. The pH of pineapple fruit ranges from 3.5 to 5.2. Predict the effect on the activity of the enzyme bromelain if it is used in a product with a pH of 11.
activity of bromelain will decrease.
Predict the effect on shrubs growing in one area if they are treated with a compound that blocks electron flow through the electron transport chains of chloroplasts. Provide reasoning to justify your prediction.
The shrubs will die / will eventually die /will not be able to make sugars. Blocking electron flow prevents formation of the proton gradient required to produce the ATP used for sugar production.
How does the function and structure of the chromosome differ in prokaryotes vs eukaryotes?
· shape (circular/nonlinear/loop)
· less complex (no histones/less elaborate structure/folding)
· size (smaller size/less genetic information/fewer genes)
· replication method (single origin of replication/theta replication)
· transcription/translation may be coupled
· generally few or no introns (noncoding)
· majority of genome expressed
· operons—gene regulation
No points for plasmids—more common but not unique to prokaryotes/not part of prokaryote chromosome.
referring to the handout: If the Chlorella culture is maintained for an additional 120 days, predict the most likely effect on the number of cells counted every five days. Provide reasoning to justify your prediction.
the concentration of cells will gradually decrease. nutrients will become limiting and wastes will build up.
Describe why translation of an mRNA can start before transcription of the mRNA is complete in prokaryotes but not in eukaryotes.
prokaryotes do not have a nuclear envelope that separates the genome from ribosomes in the cytoplasm of the cell, whereas eukaryotes do.
The arrangement of the water molecules in ice causes the ice to float. Explain how ice floating on the surface of a body of water affects the water in a way that is beneficial to the organisms in it.
The floating ice will reduce heat loss from the water below the ice, resulting in warmer water that is not likely to freeze to the bottom of the body of water.
Scientists claim that a plant that has more than one type of photosynthetic pigment has greater fitness than a plant that has only one type of photosynthetic pigment. Provide reasoning to justify this claim.
The plant will be able to absorb a greater range of wavelengths, which should increase its ability to perform photosynthesis and thus to survive and reproduce.
The genetic composition of daughter cells produced by mitosis differs from that of the daughter cells produced by meiosis. Describe TWO features of the cell division processes that lead to these differences.
# of divisions
- Mitosis 1 division/2 cells resulting
- meiosis 2 divisions / 4 cells resulting
Ploidy of daughter cells
- Mitosis = same as parent cell, diploid, 2n --> 2n
- meiosis half of parent cell, haploid, 4n --> 2n, 2n --> n
Chromatids sparate?
Mitosis = yes
meiosis = ONLY in meiosis II, NOT meiosis I
Crossing over?
Mitosis = no
meiosis = yes
Independent assortment of chromosomes?
mitosis - no
meiosis - yes!
Referring to the handout: Justify the scientists’ use of two different spots on each petri dish and the counting of worms at each of the two spots.
comparing the number of worms at each spot is a control for the completely random movement or repulsion of the worms (and the comparison also confirms that ethanol is an appropriate diluent for the chemicals because it neither attracts nor repulses the worms).
Referring to Figure 1 (handout), explain the process illustrated between Step 1 and Step 2.
the growing polypeptide chain attached to the tRNA aligned with codon 3 of the mRNA is transferred to the amino (NH2 ) terminus of amino acid 4 (AA4 ) attached to the tRNA aligned with codon 4 of the mRNA .
The enzyme bromelain works by breaking the enzymes that cause fruit browning into smaller molecules. Explain how the reaction that breaks up the enzymes occurs.
bromelain acts by enabling the hydrolysis of the protein/polypeptide/amino acid chain, breaking apart the peptide bonds holding the amino acids together OR that bromelain breaks the bond between amino acids by using water as a reactant.
Researchers studied the growth and photosynthetic ability of a plant that contained a mutant form of one of the enzymes required for chlorophyll biosynthesis. Identify an appropriate control that the researchers should use when they study the growth and photosynthetic ability of the plant with the mutant enzyme.
an appropriate control is a wild-type (normal) plant of the same species that does not have any mutant chlorophyll biosynthesis enzymes and is grown under identical conditions.
all of the F1 flies from the students’ crosses have the identical phenotype with respect to body color and wing shape, but the F2 flies have four different phenotypes. Describe how fertilization contributes to this genetic variability.
Fertilization joins gametes with different allele combinations of the genes for body color and wing shape.
Referring to the handout: Describe why the location and quality of food sources in the soil are sometimes likely to stimulate random movements by C. elegans, but at other times are more likely to stimulate directed movements.
if the C. elegans do not detect a good food source close by, they are likely to utilize random movements as they hunt. It also indicates that if they detect a good food source close by, they are likely to move directly toward it.
Referring to the figure provided, explain why the polypeptide produced when the transformed bacteria translate the introduced eukaryotic mRNA provides evidence for the common ancestry of all living organisms.
the polypeptide produced by translation of a processed eukaryotic mRNAmRNA by a eukaryotic cell or a prokaryotic cell into which it has been introduced should have the same amino acid sequence because the genetic code is almost universal and the same codon chart can be used for both prokaryotic and eukaryotic organisms.