AP Bio Midyear: Long Responses
Cells regulate both protein synthesis and protein activity. Discuss TWO specific mechanisms of gene regulation in eukaryotic cells.
- In Eukaryotic cells, genes are regulated by the prezygotic gene regulation mechanism of alternate RNA splicing. This occurs after unneeded sections of RNA called introns are cut out of the RNA chain and are left inside the nucleus of the cell. Then, the regions exiting the cell, called exons, are spliced together in different orders. These different orders regulate genes by allowing some genes to be expressed while others are not. -Another example is allosteric regulation, which is the regulation of activities of enzymes and proteins, caused by the binding of regulators at a site other than the active site of the enzyme or protein. This causes the active site to change shape and prevent the binding of the substrate.
The human genome illustrates both continuity and change. a. Describe the essential features of TWO of the procedures/techniques below. For each of the procedures/techniques you describe, explain how its application contributes to understanding genetics. -The use of a bacterial plasmid to clone and sequence a human gene -Polymerase chain reaction (PCR) -Restriction fragment length polymorphism (RFLP) analysis
-The use of a bacterial plasmid to clone and sequence a human gene Description: use restriction enzymes to cut out a piece of the plasmid cut human sequence with the corresponding restriction enzyme insert the new DNA from the plasmid into the human cell use gel electrophoresis to separate the fragments and read the sequence Contribution: used to create transgenic organisms used to create human proteins highly helpful in the development of treatment for genetic diseases can produce insulin -Polymerase chain reaction (PCR) Description: uses heat to separate DNA strands add primers add polymerase and/or nucleotides allows for the amplification of a piece of DNA Contribution: used to study a particular segment of DNA can be used in forensic studies or studies in which a scientist only has a small portion of DNA and needs more to be able to fully analyze it
Charles Darwin proposed that evolution by natural selection was the basis for the differences that he saw in similar organisms as he traveled and collected specimens in South America and on the Galapagos Islands. a. Explain the theory of evolution by natural selection as presented by Darwin.
-individuals in a population vary some traits are more favorable -more offspring are produced than can survive; (competition) -those individuals w/ favorable traits have an increased -reproduction rate which thereby increases the favorable traits in the population
Codons
A set of three nucleotides that code for an amino acid. A ribosome reads the codon and attach the tRNA while pairing the anticodon to the codon, which carries that corresponding protein thus forming a polypeptide chain.
Each of the following relates to an aspect of evolution by natural selection. Explain four of the following. -Convergent evolution -Natural selection and the formation of insecticide-resistant insects or antibiotic-resistant bacteria -Speciation and isolation -Natural selection and behavior such as kinesis, fixed-action-pattern, dominance hierarchy, etc. -The heterozygote advantage
Convergent evolution- the evolution of organisms not closely related that causes them to evolve similar traits based on their ecological niches. This relates to natural selection because it is when the environment in which an organism lives affects the organism by causing better suited traits to be passed on, thus causing organisms with those same favored traits to evolve similarly. Natural selection and the formation of insecticide-resistant insects or antibiotic-resistant bacteria- bacteria are better fit to survive when compared to larger more complex organisms because they are quick to reproduce, thus allowing them to more quickly change and evolve. As antibiotics are released into the environment, mutations occurring in at least some bacteria within a population are likely to be resistant. Therefore, as the resistant bacteria survive and reproduce, the newly formed offspring will have acquired the resistant traits to the drug, thus making it no longer affective on the population. Speciation and isolation- During allopatric isolation, organisms of a species are separated into different populations (geographically separated) and gene flow is cut off, causing them to evolve to better fit their new niche. This evolution occurs over time, as the organisms better fit for the new environment survive and pass on their favored genes. Eventually, the changes in the DNA of the separated organisms will accumulate to form a new species, separate from the old one and better adapted to the environment. These new species will not be able to interbreed to form fertile offspring. In sympatric isolation, the organisms are "reproductively isolated", meaning the organisms still live in the same area but are still separated. Other forms of isolation are geographic isolation, ecological isolation, temporal isolation, behavioral isolation, mechanical isolation, and gametic isolation, which are all pre-zygotic. Post-zygotic isolations include reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown. The two different types of rates of speciation are gradualism, which is a gradual accumulation of small changes over time, or punctuated equilibrium, which is rapid bursts of change mixed with long periods of little or no change. The heterozygote advantage- In some species, possessing the heterozygous genome is better than possessing either the homozygous dominant or recessive genotypes. An example of this is with the gene for sickle-cell anemia, in which it is better to have the heterozygous genome than either homozygous genome. This is because organisms with the homozygous recessive trait have sickle-cell anemia in its entirety. However, heterozygotes for this disease benefit from having the one carrier gene because they are more resistant to malaria, which is common in people living in Africa.
All humans are nearly identical genetically in coding sequences and have many proteins that are identical in structure and function. Nevertheless, each human has a unique DNA fingerprint. Explain this apparent contradiction.
Every human has a unique DNA fingerprint because although all humans have nearly identical DNA sequences, the combination of DNA and the traits inherited by offspring from their parents differ between each human. This causes slight differences between people that are phenotypically expressed. Additionally, while human DNA is nearly identical, mutations can occur and cause differences between people that were not present before and were not expected.
A new species of fly was discovered on an island in the South Pacific. Several different crosses were performed, each using 100 females and 100 males. The phenotypes of the parents and the resulting offspring were recorded. Cross I: True-breeding bronze-eyed males were crossed with true-breeding red-eyed females. All the F1 offspring had bronze eyes. F1 flies were crossed, and the data for the resulting F2 flies are given in the table below. F2 Phenotype Male Female Bronze eyes 3,720 3,800 Red eyes 1,260 1,320 Cross II: True-breeding normal-winged males were crossed with true-breeding stunted-winged females. All the F1 offspring had stunted wings. F1 flies were crossed, and the data for the resulting F2 flies are given in the table below. F2 Phenotype Male Female Normal wings 1,160 1,320 Stunted wings 3,600 3,820 Cross III: True-breeding bronze-eyed, stunted-winged males were crossed with true-breeding red-eyed, normal winged females. All the F1 offspring had bronze eyes and stunted wings. The F1 flies were crossed with truebreeding red-eyed, normal-winged flies, and the results are shown in the table below. Phenotype Male Female Bronze eyes, stunted wings 2,360 2,220 Bronze eyes, normal wings 220 300 Red eyes, stunted wings 260 220 Red eyes, normal wings 2,240 2,180 (a) What conclusions can be drawn from cross I and cross II? Explain how the data support your conclusions for each cross. (b) What conclusions can be drawn from the data from cross III? Explain how the data support your conclusions. (c) Identify and discuss TWO different factors that would affect whether the island's fly population is in Hardy-Weinberg equilibrium for the traits above.
From the data from cross I and cross II, we can conclude that the alleles that code for the bronze-eyed trait and the stunted-wing traits are both dominant traits. Due to the fact that all of the offspring in the F1 generations from both crosses showed these traits, it proves these are the dominant traits since the offspring was created by two pure-breed parents, and if a trait is recessive it would have been hidden. In addition the 3:1 ratios that are in generation 2 of both cross I and II further support the cross of heterozygotes in which the dominant phenotype represents the 3 in the ratio and the recessive phenotype is represented by the 1. Also, the cross showed that both the traits are autosomal because they are equally common in females as they are in males It can be concluded from the data from cross III that the genes coding for wing length and eye color are linked, and that crossing over has occurred within the population. This is shown in the data through the bronze eyed with normal wings and the red eyes with stunted wings because there is no set 1:1:1:1 ratio as would be expected in independent assortment. The parental phenotypes were present in 90 percent of the offspring but rather a small number of individuals out of the total population with not common phenotypes. This small number of irregular combinations provide evidence for crossing over between the two linked genes. The population would need to be large enough for there to be no genetic drift among the flies and they would need to mate randomly, so that there would be no change in the gene pool due to mating preferences. Additionally, there would have to be no mutations so that no new alleles are introduced to the population, no emigration/immigration from the area to keep the gene pool from changing due to the addition or loss of alleles, and natural selection could not be occurring so that no alleles are favored or disfavored by the environment.
Ribosomes
Reads RNA and attaches amino acids together; site of protein synthesis; mRNA is processed there; and the codons are read as they pass through the A site P site and E site in the ribosome.
In a laboratory population of diploid, sexually reproducing organisms a certain trait is determined by a single autosomal gene and is expressed as two phenotypes. A new population was created by crossing 51 pure-breeding (homozygous) dominant individuals with 49 pure breeding (homozygous) recessive individuals. After four generations, the following results were obtained: Number of Individuals Generation Dominant Recessive Total 1 51 49 100 2 280 0 280 3 240 80 320 4 300 100 400 5 360 120 480 a. Identify an organism that might have been used to perform this experiment, and explain why this organism is a good choice for conducting this experiment. b. On the basis of the data, propose a hypothesis that explains the change in the phenotypic frequency between generation 1 and generation 3. c. Is there evidence indicating whether or not this population is in Hardy-Weinberg equilibrium? Explain.
The fruit fly might have been used to perform this experiment. This organism is a good choice for this particular experiment because it is small and does not require a lot of attention with regards to its health, it reproduces very quickly, and humans are not overly attached to the species, as they could be for other species such as dogs or cats. If the organisms in the first generation are homozygous for their given genotype, then the organisms in generation 2 will be all heterozygotes, therefore causing the organisms in generation 3 to be a ratio of 3:1 because of the cross that would have occurred between all heterozygotes. This population is in Hardy-Weinberg equilibrium because the 3:1 ratio remains constant from generation 3 through generation 5. Because the ratio remains the same, the equilibrium is maintained and the p and q values do not change. p^2=.75 and q^2=.25
Many biological structures are composed of smaller units assembled into more complex structures having functions based on their structural organization. For the following complex structures, describe the smaller units, their assembly into the larger structures, and one major function of these larger, organized structures. inner membrane of a mitochondria an enzyme
a. an inner membrane of a mitochondria- The inner membrane of the mitochondria is made of a phospholipid bilayer, with the hydrophobic tails facing in while the hydrophilic heads point outward. Additionally, many closely associated proteins are embedded inside this lipid bilayer, which compose electron transport chains occupying the highly folded inner membrane. The greater surface area created by the folded bilayer allows for more electron transport chains to be present, thus creating a greater chemiosmotic gradient. This gradient is needed in the production of ATP within the mitochondria, which is then used throughout the cell. b. an enzyme- An enzyme is made up of amino acids that come together to form a polypeptide chain. These amino acids are made of a carboxyl group, an R group, a carbon atom, and an amino group. The enzyme forms when the protein folds onto itself in a unique structure, specific to its function. Enzymes are catalysts for many reactions, meaning they speed up chemical reactions that occur within cells.
RNA polymerase
responsible for the synthesis of RNA from DNA. Binds to the Activator during transcription.
tRNA
transport DNA; carries amino acids over to ribosomes to form polypeptide chains.
