AP Biology Semester II Exam I Study Guide

AP Biology Semester II Exam I Study Guide

What is the RNA world hypothesis and what is the reasoning behind it?

RNA as first genetic material: RNA World Hypothesis 1. According to the RNA World Hypothesis, RNA not DNA was the first informationstorage molecule. 2. Ribozymes are RNA molecules that can catalyze chemical reactions (act as a catalyst). 3. Ribozymes allow RNA to self-replicate.

1953 Stanley Miller- Harold Urey Experiment 1. What was the goal of the experiment? 2. Summarize the design of the experiment: 3. What was the outcome of the experiment?

1953 Stanley Miller- Harold Urey Experiment Goal = simulate early Earth conditions could organic molecules spontaneously form? Water simulated primitive oceans NH 4, NH 3, H 2, H 2 0 simulated the early atmosphere Heat & spark simulated the inputs of free-energy Outcome: amino acids (monomers of protein) conditions present on the early Earth could produce the organic molecules necessary for life

The 1953 Miller/Urey experiment came under attack because new data suggested that the conditions present on the early Earth were different from those modeled by this classic experiment. Given this, what is the current understanding regarding the possibility of organic molecules forming spontaneously and abiogenically on the early Earth?

In 2008 Miller used the updated information about the early Earth and simulated a volcanic eruption, again producing amino acids.

What are the conditions that we believe are necessary for abiogenesis (regardless of planet)?

1. Initially at least, oxygen-free atmosphere (oxygen is very reactive strong oxidizer and thus would interfere with the formation of initial organic molecules from inorganic precursors). 2. The presence of water. 3. A source of free-energy (such as as volcanism, lightening, electromagnetic radiation). 4. A system with all of the elements found in great abundance in organisms: CHNOPS

1 What are some differences between eukaryotic and prokaryotic cells? 2

One of the main differences between prokaryotic and eukaryotic organisms is the presence of membrane-bound organelles in eukaryotic cells (i.e. nucleus, lysosomes, E.R., Golgi Apparatus, mitochondria, chloroplasts). What is a major advantage of having membrane-bound organelles?

Membrane-bound organelles compartmentalize (separate) chemical reactions allowing incompatible reactions to occur simultaneously and allowing for different microenvironments within the cell that increase the efficiency of those reactions.

Unlike eukaryotic cells, prokaryotic cells: 1. Possess cell walls that have the substance peptidoglycan (plant and fungal cell walls lack this substance) 2. Have a single circular chromosome 3. Do not have a nuclear membrane 4. Do not possess membrane-bound organelles 5. Although both cell types posses ribosomes, those of prokaryotes are somewhat smaller

How does what we know about molecular genetics provide robust evidence for shared common ancestry?

Evidence that all life on Earth shares a common ancestor 1. All existing organisms share a common genetic code (A,T,C,G nucleotides of DNA). Whether bacteria or human, all genes are composed of the same four nucleotide monomers. 2. All living things share other molecular building blocks, such as the same amino acids (form proteins). 3. As a result of these similarities, the human insulin gene has been inserted into bacteria, which are able to produce this human hormone protein.

Summarize a robust line of evidence in support of shared common ancestry from the field of metabolism:

Glycolysis (sugar-splitting) is the most widespread metabolic process on Earth both prokaryotic and eukaryotic cells share this common method of converting some of the chemical potential energy in fuel into the chemical potential energy in ATP. Glycolysis does not require a mitochondrion or even oxygen (neither were present early on in the development of life).

1. What is the endosymbiotic theory on the origin of chloroplasts and mitochondria? 2. Summarize lines of evidence in support of this theory:

1. The endosymbiotic theory proposes that one free-living prokaryote engulfed (but did not digest) another free-living prokaryote. The latter became the mitochondrion/chloroplast. 2. Lines of evidence in support of this theory include: - Double membrane - Own DNA (circular chromosome with bacterial gene structure) - Own ribosomes (bacterial in structure) - They are the size of bacteria - They reproduce, just like bacteria, by binary fission

How is the double-membrane structure of the mitochondrion connected to its function?

Only as a result of two membranes, can there be two environments, and thus a H + concentration gradient. The electron transport chain protein pumps use the loss of potential energy of electrons (stripped from fuel molecules) to actively pump H + ions into the intermembrane space. When these ions diffuse down their electrochemical gradient through ATP synthase, the enzyme catalyzes the reaction ADP + P i ATP

What conclusion can you make from the data presented below?

Those bacteria that are resistant to an antibiotic have a survival and thus reproductive advantage. As a result, we see evolution through natural selection acting over many generations of bacteria (several years), favoring those bacteria that are resistant to antibiotics.

Most of the chemical energy on Earth is trapped in cellulose. It is the most abundant organic compound on Earth: plants produce 10 11 (100 billion) tons of it per year (your paper is cellulose). But animals do not have enzymes to digest it! How do termites and ruminants such as cows get energy out of the cellulose in their diets?

Termites have a mutualistic relationship with bacteria and protista endosymbionts that breakdown cellulose into glucose for their hosts.

They have mutualistic (endosynmbiotic) relationship with bacteria and/or protists that have the necessary enzymes

Explain how bacteria can evolve so quickly:

Why Can Bacteria Evolve Very Quickly? Short generation time + Mutation Large population Evolution via Natural Selection Chance for mutation Parent Cell Daughter Cell Vertical Transmission Cell A Cell B Transformation Transduction Conjugation Genetic recombination Horizontal Transmission

What is a potential danger to excessive, unnecessary use of antibiotics?

When antibiotics are use unnecessarily, for example added to paints on our walls or used to promote faster growth rates in livestock, we are unintentionally setting up a selective pressure that will select for resistant mutants that will eventually fail antibiotic treatments in humans.

Suppose a few bacterium have ampicillin resistant plasmids and that these bacteria can pass these plasmids through conjugation. 1. What would happen to the percentage of the population possessing these plasmids if the population were exposed to ampicillin and why? 2. What would happen to this percentage if ampicillin was not used anymore but instead kanamycin were used and why?

Suppose a few bacterium have ampicillin resistant plasmids and that these bacteria can pass these plasmids through conjugation. 1. What would happen to the percentage of the population possessing these plasmids if the population were exposed to ampicillin and why? The frequency of the ampicillin resistant bacteria would increase because it confers a survival (and thus reproductive advantage). 2. What would happen to this percentage if ampicillin was not used anymore but instead kanamycin were used and why? The frequency of the ampicillin resistant bacteria would decrease because it does not offer a survival advantage, but the allele would not disappear because it is also not being selected against.

Although bacteria reproduce via a cloning cell division called binary fission, there are three ways that genetic recombination can occur among bacteria. Describe the three mechanisms:

3 Ways to Genetic Recombination in Bacteria Recombination = combining DNA from more than 1 source Transformation Uptake of naked, foreign DNA (plasmids) from the environment Transduction Viruses carry DNA from one bacterial host to another Conjugation One-way transfer of DNA between two bacterial cells

1. Describe the lysogenic replication-cycle in viruses 2. Explain how this cycle can result in altered phenotype of the infected host cell 3. Give an example: 4. Why do RNA viruses (such as influenza) and retroviruses (such as HIV) have a particularly fast rate of evolution?

Lysogenic Cycle

Lysogenic Cycle (Continued) Unlike lytic cycle, allows replication of phage genome without destroying the host cell An environmental signal usually triggers the switch from lysogenic to lytic mode Can result in new properties for the host such as increased pathogenicity in bacteria. Viral genes cause bacteria to make toxins that result in human disease: - Cholera - Diphtheria - Botulism - Scarlet fever

Bacterium: Vibrio cholerae The bacterium Vibrio cholera is harmless unless a lysogenic bacteriophage provides the gene coding for the cholera toxin, which converts the bacterium to the virulent form that causes cholera.

The genetic material of RNA viruses is RNA. The genetic material of retro viruses is RNA that is then converted to DNA by the enzyme reverse transcriptase. In both cases, a copying mechanism different from that used in our cells is used. As a result, proofreading (and repair) is not performed, resulting in a much higher rate of mutations proceeding into successive generations.

Describe the process of phagocytosis:

1. How long does it take the primary response to A to peak? 2. How long does the secondary response take? 3. What accounts for this difference? 4. Why does the response to B take so long?

The peak response to antigen A takes about two weeks, because it was the first exposure; however, the response to the second exposure if rapid and stronger because the memory B cells are in existence and can thus secrete large amounts of free antigen quickly. Similarly, the initial response to B is slow, but a secondary response would be quick.

What is the key difference between the nonspecific and specific immune response?

In the nonspecific immune response, the body detects foreign invaders, but does not identify them as a specific virus, for example. Examples include: phagocytosis, inflammatory response, interferon, antimicrobial proteins However, in the specific immune response, there is a lock-key relationship between a specific antigen and a specific antibody such that there is a unique response to each type of virus.

Summarize the role of B-cells in the humoral immune response:

1. An antigen binds with the corresponding receptor on a B-cell 2. This stimulates the B-cell to proliferate 3. The cells differentiate into a clone of memory cells (building long term immunological memory) 4. And a clos of plasma cells that secrete large amounts of free antibodies into the circulatory system