Chapter 7

Question 1

What do mRNAs code for?

Answer 1

proteins

Question 2

RNAs that form the core of a ribosome

Answer 2

rRNAs

Question 3

regulate gene expression

Answer 3

miRNAs

Question 4

the process by which the information encoded in a DNA sequence is translated into a product that has some effect on a cell or organism

Answer 4

gene expression

Question 5

start/stop sites of transcription

Answer 5

promoter / terminator

Question 6

Is the promoter region transcribed? Terminator?

Answer 6

no / yes

Question 7

RNA polymerase always moves in this direction

Answer 7

3’ ——> 5’

Question 8

Initiation of transcription in bacteria:

Answer 8

• sigma factor binds to promoter
• RNA synthesis is initiated
• sigma subunit dissociates
• chain elongation continues until terminator sequence
• RNA polymerase halts and releases the DNA and RNA transcript
• polymerase reassociates with the sigma factor

Question 9

accessory proteins in eukaryotes that assemble on the promoter where they position the RNA polymerase and pull apart the DNA double helix, allowing RNA polymerase to begin transcription

Answer 9

general transcription factors

Question 10

How the transcription factors assemble:

Answer 10

1. ) TFIID binds to TATA box causing a distortion in the DNA
2. ) TFIID enables the binding of TFIIB
3. ) more transcription factors and RNA polymerase II bind
4. ) TFIIH uses ATP to pull apart DNA at the transcription start site
5. ) TFIIH also phosphorylates RNA polymerase II
6. ) RNA polymerase is released from complex

Question 11

post-transcription professing

Answer 11

5’ cap
poly A tail
splicing

Question 12

Is the poly A tail transcribed?

Answer 12

no

Question 13

Purposes of modifications after transcription:

Answer 13

• marks transcript as mRNA
• facilitates exports to cytoplasm
• increases stability of mRNA

Question 14

Where does post-transcription modifications occur?

Answer 14

nucleus

Question 15

DMD gene (dystrophin)

Answer 15

• 78 introns
• occupies 2,000,000 base pairs on chromosome X
• mRNA is 14,00 nucleotides long

Question 16

process of removing introns and stitching exons together

Answer 16

RNA splicing

Question 17

When does splicing occur?

Answer 17

after capping

Question 18

What structure does the intron form when it is cut out?

Answer 18

lariat structure

Question 19

How does the lariat structure form?

Answer 19

1. ) branch point adenine in the intron sequence attacks the 5’ splice site and cuts the sugar-phosphate backbone of the RNA
2. ) the cut 5’ end of the intron becomes covalently linked to the 2’-OH group of the ribose of the A nucleotide
3. ) the free 3’-OH end of the exon sequence reacts with the start of the next exon sequence, joining the two together

Question 20

carries out RNA splicing

Answer 20

snRNAs

Question 21

snRNAs are packaged with proteins to form?

Answer 21

snRNPs (U1, U2, U4, U5, U6)

Question 22

the large assembly of RNA and protein molecules that carries out RNA splicing in the nucleus

Answer 22

spliceosome

Question 23

form the core of the spliceosome

Answer 23

snRNPs

Question 24

mediate the transport of RNA out of the nucleus

Answer 24

nuclear pore complexes

Question 25

mRNA lifetime is longer in eukaryotes or prokaryotes?

Answer 25

eukaryotes

Question 26

serves as an adaptor that “reads” a codon in mRNA and adds the correct amino acid to the growing polypeptide chain

Answer 26

tRNA

Question 27

a set of three consecutive nucleotides that bind to the complementary codon in an mRNA molecule

Answer 27

anticodon

Question 28

What does wobble mean?

Answer 28

some tRNAs require base-pairing only at the first two positions of the codon and can tolerate a mismatch at the third position

Question 29

covalently couple each amino acid to it’s appropriate set of tRNA molecules

Answer 29

aminoacyl-tRNA synthetases

Question 30

What is the large subunit of a ribosome composed of?

Answer 30

small proteins and rRNAs

Question 31

function of large subunit? small subunit?

Answer 31

* large subunit— catalyzes peptide binds | * small subunit— matches mRNA codons to tRNAs

Question 32

RNA molecules that posses catalytic activity

Answer 32

ribozymes

Question 33

start and stop sites of translation

Answer 33

``` start codon (AUG) stop codon (UGA, UAG, UAA) ```

Question 34

always carries that amino acid Met

Answer 34

initiator tRNA

Question 35

mRNA that codes for several different proteins, each of which is translated from the same mRNA molecule (only in prokaryotes)

Answer 35

polycistronic

Question 36

Do stop codons code for an amino acid?

Answer 36

no

Question 37

What stops translation?

Answer 37

release factor enters A site, peptidyl transferase catalyzes the addition of water instead of an amino acid, polypeptide chain is released

Question 38

many ribosomes working simultaneously on a single mRNA molecule

Answer 38

polyribosomes

Question 39

specialized pathways that break down proteins

Answer 39

proteolysis

Question 40

the enzyme that degrades proteins

Answer 40

professes

Question 41

large proteins machines in eukaryotes that break down proteins

Answer 41

proteasomes

Question 42

Where are proteasomes found?

Answer 42

cytosol and nucleus

Question 43

How do proteasomes select which proteins should be degraded?

Answer 43

proteins marked with ubiquitin

Question 44

Post-translational modifications:

Answer 44

* covalent modifications (phosphorylation) * the binding of small-molecule cofactors * association with other protein subunits