Topic 2A

Question 1

RNA has properties of both:

Answer 1

DNA (information storage) and proteins (enzymes-facilitates chemical reactions)

Question 2

RNA world hypothesis

Answer 2

the hypothesis that the earliest organisms relied on RNA for both catalysis and information storage

Question 3

what did Szostak’s experiment do?

Answer 3

demonstrated how RNA molecules can evolve over time and act as catalysts

Question 4

if RNA was the origin of life, why do cells use DNA for info storage and protein for other cellular processes?

Answer 4

because RNA is less stable than DNA and proteins are more versatile-each is specialized for different functions

Question 5

ribose

Answer 5

the sugar in RNA, carries a hydroxyl group on the 2’ C which is very reactive (why RNA is less stable than DNA)

Question 6

uracil (U)

Answer 6

a pyrimidine base in RNA, where it replaces the thymine found in DNA

Question 7

while the 5’ end of DNA is typically a monophosphate…

Answer 7

the 5’ end of an RNA molecule is typically a triphosphate

Question 8

what is shorter? RNA or DNA

Answer 8

RNA

Question 9

DNA molecules are double stranded, RNA molecules are….

Answer 9

single stranded-form 3D structure by folding to enhance stability

Question 10

RNA transcript

Answer 10

the RNA sequence synthesized from a DNA template

Question 11

RNA transcript is produced by polymerization of :

Answer 11

ribonucleoside triphosphates

Question 12

RNA polymerase

Answer 12

the enzyme that carries out polymerization of ribonucleoside triphosphates from a DNA template to produce an RNA transcript

Question 13

nontemplate strand

Answer 13

the untranscribed partner of the template strand of DNA used in transcription

Question 14

all nucleic acids (DNA and RNA) being synthesized, have nucleotides added to the:

Answer 14

3’ end, grow in a 5’-to-3’ direction

Question 15

the DNA template and the RNA transcript are:

Answer 15

antiparallel

Question 16

genetic code

Answer 16

the correspondence between three-letter nucleotide codons in RNA and amino acids, in which 20 amino acids are specified by 64 codons:

Question 17

initiation codon

Answer 17

the codon at which translation begins, coded by AUG (Met)

Question 18

which direction are polypeptides synthesized from:

Answer 18

the amino end to the carboxyl end

Question 19

the AUG codon that initiates translation is preceded by:

Answer 19

regions in the mRNA that is not translated

Question 20

the position of the initiator AUG codon in the mRNA establishes:

Answer 20

the reading frame that determines how the downstream codons are to be read: i.e. must start here, so where it goes from now

Question 21

briefly describe the process of synthesizing new polypeptide chain

Answer 21

once initial Met creates the amino end of chain, downstream codons read in groups of 3, ribosome binds to tRNA with complementary anticodon and that amino acid is attached to chain to become new carboxyl end. process stops when a “stop” codon is encountered

Question 22

what are the “stop” codons?

Answer 22

UAA, UAG, UGA

Question 23

what happens when the polypeptide encounters a “stop” codon/is finished?

Answer 23

it is released into the cytosol

Question 24

what experiment deciphered the standard genetic code?

Answer 24

Khorana (1960)-made synthetic RNA of known sequence which was added to a solution containing all components needed for translation. Adjusting certain factors (ex. magnesium concentration) would effect synthesis

Question 25

many amino acids are specified by more than one codon, therefore, the genetic code is:

Answer 25

redundant or degnerate

Question 26

what are some features of translation (that can account for redundancy)?

Answer 26

1. tRNA anticodons’ 5’ base that pairs with 3’ base in the codon is chemically modified into a form that can pair with two or more bases at the third position
2. there less imperfect alignment between third position of codon and complementary anticodon in the ribosome, so base pairing is relaxed (this codon-anticodon interaction is called the wobble)

Question 27

what are the three steps of translation?

Answer 27

initiation, elongation, termination

Question 28

initiation

Answer 28

the stage of translation in which methionine (AUG codon) is established as the first amino acid in a new polypeptide chain

Question 29

elongation

Answer 29

the process in protein translation in which successive amino acids are added one by one to the growing polypeptide chain

Question 30

termination

Answer 30

in protein translation, the time at which the addition of amino acids stops and the completed polypeptide chain is released from the ribosome.