DNA to RNA to Protein

Question 1

what is the purpose of RNA as an intermediary

Answer 1

allows for genes to be expressed with different efficiencies

Question 2

what are the differences between RNA and DNA

Answer 2

• ribose vs deoxyribose sugars
• uracil vs thymine

Question 3

what is the purpose of the template strand

Answer 3

to be used for transcription

Question 4

what is the purpose of the coding strand

Answer 4

to provide sequence of the final product

Question 5

what does RNA polymerase do

Answer 5

transcribes DNA to RNA

Question 6

what are the characteristics of RNA polymerase

Answer 6

• catalysis of ribonucleotide linkage
• doesn’t need primer
• makes more mistakes than DNA polymerase b/c it lacks exonuclease activity

Question 7

what are the types of RNA made by cells

Answer 7

mRNA, rRNA, tRNA

Question 8

what are the steps in transcription

Answer 8

binding, initiation, elongation, termination

Question 9

what are the next steps for mRNA

Answer 9

• must leave nucleus for translation
• exits thru nuclear pores

Question 10

what are the mechanisms of mRNA processing

Answer 10

RNA capping and polyadenylation

Question 11

describe RNA capping

Answer 11

• methylated guanosine (guanine attached to ribose ring) added to 5’ end
• allows ribosome to bind mRNA

Question 12

describe polyadenylation

Answer 12

series of adenine nucleotides added to 3’ end

Question 13

what is the purpose of eukaryotic mRNA processing

Answer 13

to increase the stability of mRNA and indicates transcript is ready for translation

Question 14

describe exons vs introns

Answer 14

exons are coding sequences, whereas introns are noncoding sequences

Question 15

define spliceosomes

Answer 15

complex of proteins and RNA molecules that splice RNA

Question 16

how are introns removed

Answer 16

• excised by snRNPS (small ribonucleoprotein complexes)
• the snRNPS recognize specific nucleotide sequences and determine where cuts should be made for intron removal

Question 17

describe translation

Answer 17

the process of reading the genome after protein synthesis

Question 18

what is the start codon; what is the name for it

Answer 18

AUG; methionine

Question 19

what are the stop codons

Answer 19

UAA, UAG, UGA

Question 20

what are codons

Answer 20

mRNA decoded in sets of 3 nucleotides, representing an amino acid

Question 21

how is a strand read

Answer 21

from 5’ to 3’ ends

Question 22

what is an anticodon

Answer 22

sequence of 3 nucleotides that base-pairs with a codon in mRNA

Question 23

what is a tRNA

Answer 23

molecular adaptor; reads the code and makes the proteins for it

Question 24

what two adaptors act together to translate the genetic code

Answer 24

aminoacyl-tRNA synthetase and tRNA

Question 25

briefly describe the process of translating the genetic code

Answer 25

- aminoacyl-tRNA synthetase couples amino acids to the corresponding tRNA - anticodon forms base pairs with codon on mRNA

Question 26

describe the structure of a ribosome

Answer 26

- one large and one small subunit - vary between prokaryotic and eukaryotic structures

Question 27

what are the types of ribosomes; where are they

Answer 27

bound and free; attached to ER and in cytoplasm respectively

Question 28

what is the function of bound ribosomes

Answer 28

make proteins for membranes and secretion

Question 29

when do ribosomal subunits dissociate

Answer 29

when translation of protein is complete

Question 30

what are the 3 binding sites for tRNAs

Answer 30

aminoacyl (A), peptidyl (P) and exit (E) sites

Question 31

what sites does the tRNA fit to and in what condition(s)

Answer 31

A & P; only when tRNA anti-codon binds to mRNA codon

Question 32

describe how a polypeptide is assembled at the ribosome

Answer 32

- tRNA enters A site, where an anticodon binds to mRNA codon - 2 amino acids link to e/o and the large ribosomal subunit shifts - the first amino acid is rejected and mRNA moves 3 nucleotides further through the small ribosomal subunit

Question 33

describe how translation stops

Answer 33

- needs presence of stop codon - when stop codon reaches A site, chain release factors bind instead of another tRNA amino acid - peptidyl transferase catalysis water addition to COOH to free the chain - the subunits dissociate, thereby the tRNA, mRNA and release factors releasing

Question 34

what are chemical examples of practical applications for translation inhibition

Answer 34

tetracycline, streptomycin, chloramphenicol, erythromycin, rifamycin

Question 35

describe tetracycline's role in translation inhibition

Answer 35

blocks binding of aminoacyl tRNA to A site of ribosome (prevents the 1st step of translation)

Question 36

describe chloramphenicol's role in translation inhibition

Answer 36

blocks peptidyl transferase reaction on ribosomes (prevents 2nd step of translation)

Question 37

describe erythromycin's role in translation inhibition

Answer 37

blocks translation reaction on ribosomes (prevents 3rd step of translation)