20201 Foundations of BiologyiSpring 2018 Practice questions for Exam 1 2. The fo

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20201 Foundations of BiologyiSpring 2018 Practice questions for Exam 1 2. The following is incorect regarding mitochondria and plastids Page 3 of 8 A) They originated by invagination. B) MRochondrial DNA is homologous to that of rickettsias. C) Chloroplasts originated from cyanobacteria. D) They have bacterialk-type 70S rnbosomes. E) None of the above 13. The basis for Carl Woese's classification of living organisms in a Three Domain system( and A) (mineral, plant, and animal atomic and molecular composition B) (animals, plants, and fungilymulticellularity vs, unicellularity (Bacteria, Archaeaand Euknyayphylogeny based on genetic studes, mostly rRNA (Planta, Anmala, and Protista>that bacteria and archaea are not hing organisms (eukaryotes, prokaryotes, and virusesV that eukaryotes and peokaryotes are cellular organisms E) 14. This is an advantage for prokaryotic cells to have polycistronic mRNAs A) Enzymes involved in entire metabolic pathways are encoded in a single message. B) All proteins in a polycistronic mFINA can be translated simultaneoushy C) Faster adaptation to the environment when compared to eukaryotic organisms D) Protein synthesis (translation) can occur while RNA synthesis (transcription) is still happening E) All of the above 15 pH and is an indicator of -the- the pH. the higher the concentration of protons in a solution. [A-MAH], density; higher B) log [H-], acidity, lower C) -log IOH-1 alkalinity, lower D) pKa, alkalinity, higher E) None of the above 16. What is the proportion of HaN-CHa-COO-+HaN-CH2-COOH at pKat? A) B) C) D) E) 100%0% 75%/25% 50%150% 25%75% 0%/100% 17. What is the proporson of HaN-CH-COO/-HIN-CHa-COO-at pH 10.267 A) B) 100%0% 75%)25% 50%/50% D) 25%/75% 0%/100%

Explanation / Answer

Ans. #12. Correct option – A. They originated by Invagination.

Invagination is the inward folding of plasma membrane into the cytoplasm. The invagination of plasma membrane into cytoplasm of a prokaryotic cell might have led to the formation of nucleus (invagination of plasma membrane formed nuclear membrane around host genome), thus lead to the evolution of eukaryotic cell.

# Evolution of mitochondria and chloroplast is explained by endosymbiosis- in which heterotrophic bacteria and cyanobacteria engulfed by an Archean cell lead to the evolution of mitochondria and chloroplast, respectively.

# Mitochondrial DNA is homologous to that of rickettsias (a prokaryote) because both are essentially prokaryotes in nature.

# Both the chloroplasts and mitochondria have 70s ribosomes (cytoplasmic ribosomes of eukaryotic cell are 80s) because they originated from prokaryotic cells.

#13. Correct option- C. (Bacteria, Archaea, and Eukarya) (phylogeny based----)

Carl Woese (and co-workers) were working on following things that lead to the establishment of Domain Archaea-

I. Sequencing of 16S ribosomal rRNA yields a distinct evolutionary descent from rest of bacteria.

II. Unlike other bacteria, these members lacked peptidoglycan in their cell wall. Instead, their cell wall was composed of pseudomurein.

# These quite unique characteristics along with some unique coenzymes and metabolic pathways led Woese classify the prokaryotes in domain Archaea and Bacteria.

Carl R Woese and George E Fox, 1977, reported the ‘Archaea’ as the third domain of life, being Bacteria and Eukarya the other two. The kingdom Archaebacteria under the domain Archaea, kingdom Eubacteria (previously termed Monera in five kingdom system) under the domain Bacteria are the prokaryotic forms of life. The eukaryotic kingdoms Protista, Animalia, Plantae and Fungi were grouped under the domain Eukarya.

#14. Correct option- E. All of above

#15. Correct option- B. –log [H+], acidity, lower

#16. Correct option- C- 50% / 50%

Note that the two chemical species differ only at the –COOH group.

pKa1 is the acid dissociation constant of the alpha-acidic group of amino acid. At pH = pKa1, the –COOH is 50% dissociated, i.e. [-COO-] = [-COOH].

# Also, note that [NH3+] remains constant.

Therefore, [NH3+-CH2-COO-] / [NH3+-CH2-COOH] , i.e. [COO-] / [COOH] = 50% / 50%

#17.

Note that the two chemical species differ only at the –NH2 group.

pKa2 is the acid dissociation constant of the alpha-amine group of amino acid.

pKa2 is generally around 9.5.

At pH > pKa2, the –NH2 is predominantly in protonated state (NH3+). When pH is lower than pKa2 at least 2 units, there is 100% protonation (i.e. all NH2 would be in form of NH3+). Since pH is lower than pKa2 by less than 2 unit but differ by 1 unit, the [NH2] < [NH3+], where NH2 is less than 50% but greater than 0%.

So, correct option is- D. [NH2] / [NH3+] = 25 % / 75%

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