Chapter 16: Transcription and Translation

Question 1

What is transcription?

Answer 1

Using DNA to code for RNA molecules

Question 2

What main molecules are required for transcription?

Answer 2

• DNA template
• RNA polmerase
• rNTP (ribonucleotide triphosphate)

Question 3

How many RNA polymerases are in bacteria? Eukaryotes?

Answer 3

1 in bacteria, 3 in eukaryotes (RNA pol. I, II, III)

Question 4

The structure of rNTP

Answer 4

a base, ribose sugar and 3 phosphates

Question 5

What is the strand that is read by RNA polymerase called?

Answer 5

template strand

Question 6

The sequence of mRNA matches with what strand?

Answer 6

coding (non-template) strand

Question 7

What protein does RNA polymerase need in order initiate transcription?

Answer 7

a sigma protein

Question 8

What does a sigma protein do?

Answer 8

• creates a holoenzyme by binding to RNA polymerase
• guide RNA pol. to specific locations (promoters) where transcription should begin
• a regulatory protein

Question 9

What binds to DNA first?

Answer 9

sigma protein (not RNA pol.)

Question 10

Where on the DNA does sigma bind to?

Answer 10

promoter region

Question 11

What are promoters?

Answer 11

initiates transcription (NOT actual start)

Question 12

What the 2 promoter regions of bacterial DNA?

Answer 12

• 35 box (TTGACA)

- 10 box (TATAAT)–10 bases from where RNA pol. starts transcription

Question 13

What place does bacterial transcription actually begin?

Answer 13

the +1 region

Question 14

Are sigma proteins present in eukaryotes?

Answer 14

No.

Question 15

In eukaryotes, what acts analogous to a sigma in bacteria?

Answer 15

basal transcription factors (need many to begin transcription)

Question 16

What does RNA pol. I do?

Answer 16

synthesis of large ribosomal units

Question 17

What does RNA pol. II do?

Answer 17

synthesis or mRNA

Question 18

What does RNA pol. III do?

Answer 18

synthesis of small ribosomal units and tRNA

Question 19

In eukaryotes, what is the promoter?

Answer 19

TATA box located 30 bases upstream to transcription site

Question 20

What happens once sigma is released from promoter?

Answer 20

initiation ends, synthesis (elongation) begins

Question 21

Once DNA helix unwinds to form what (in transcription of Protein synthesis)?

Answer 21

Transcription bubble

Question 22

What is elongation?

Answer 22

when RNA pol. begins synthesizing mRNA

Question 23

What do zipper amino acids do?

Answer 23

help separate the mRNA from the template DNA strand

Question 24

What do rudder amino acids do?

Answer 24

help maneuver the template and non-template strand through the channels of RNA pol.

Question 25

How does transcription ends?

Answer 25

when RNA pol. reaches a termination signal, RNA loops on itself to form a hairpin, therefore disrupting the interaction between RNA pol. and the mRNA

Question 26

What is the difference between a nucleotide and a nucleoside?

Answer 26

nucleosides are similar to nucleotides except that they don't have a phosphate group

Question 27

How many phosphates can a nucleotide have?

Answer 27

up to 3

Question 28

What are ribonucleosides?

Answer 28

RNA base + ribose sugar

Question 29

What are deoxyribonucleosides?

Answer 29

DNA base + deoxyribose sugar

Question 30

What is nucleic acid?

Answer 30

a polymer of nucleotide monomers linked together

Question 31

Why does transcription and translation happen simultaneously in bacteria?

Answer 31

because bacterial (prokaryotic) cells lack a nucleus

Question 32

What is an exon?

Answer 32

coding region of pre mRNA that is kept after splicing

Question 33

What is an intron?

Answer 33

non-coding region of pre mRNA that is removed by spliceosomes

Question 34

In eukaryotes, what types of RNA processing are needed before mRNA can be translated?

Answer 34

1) Capping with 5' cap 2) Poly A tail at the 3' end of RNA strand 3) Splicing out the introns

Question 35

What is the purpose of capping the 5' end of mRNA?

Answer 35

- to protect the 5' end from degradation by exonucleases - to stabilize mRNA before translation - recognition site for translation?

Question 36

What is the purpose of adding a row of adenine to the 3' end of mRNA (poly A tail)?

Answer 36

-to protect the end from degradation

Question 37

snRNPs are known as:

Answer 37

small nuclear ribonucleoproteins

Question 38

In vitro hybridization of mRNA and their DNA templates produce loops of mRNA-DNA hybrids. These loops are

Answer 38

single-stranded DNA and they represent introns

Question 39

What happens to the mature mRNA after post-transcriptional processing (in eukaryotes)?

Answer 39

exported for translation

Question 40

What is the advantage of alternative splicing?

Answer 40

- a variety of mRNA transcripts can be produced | - this leads to the synthesis of many different proteins

Question 41

What is translation?

Answer 41

peptides and proteins are sythesized from mRNA

Question 42

What is a peptide?

Answer 42

a short chain of amino acids linked together by a peptide bond (ie. dipeptides, tri-peptides, polypeptides, etc.)

Question 43

What molecules are required for translation?

Answer 43

- mRNA - tRNA - ribosome - amino acids

Question 44

What is an aminoacyl tRNA?

Answer 44

tRNA + amino acid

Question 45

What are the main components of tRNA?

Answer 45

-anticodon, attached amino acid to CCA region and nucleotides (loops and secondary structured stem)

Question 46

What are ribosomes made up of?

Answer 46

large and small subunits

Question 47

What does the large subunit of ribosomes do?

Answer 47

-where peptides are formed

Question 48

What does the small subunit of ribosomes do?

Answer 48

holds the mRNA in place during translation

Question 49

What are anticodons?

Answer 49

set of 3 ribonucletides that form base pairs with the mRNA codon

Question 50

What the 3 sites of ribosomes involved in translation?

Answer 50

- A (acceptor or aminoacyl) site - P (peptide formation)site - E (exit) site

Question 51

The A site is responsible for:

Answer 51

bringing in the tRNA with AA attached

Question 52

What happens in the P site?

Answer 52

tRNA holds the growing polypeptide chain

Question 53

What happens in the E site?

Answer 53

the tRNA has no AA attached

Question 54

What is the ribosomal binding site?

Answer 54

the mRNA sequence that forms complimentary base pairs with the rRNA from the small subunit -the start of initiation of translation

Question 55

When is initiation complete?

Answer 55

when the large sununit joins the ribosomal complex

Question 56

The process of initiation (translation)

Answer 56

1) mRNA binds to small subunit via complimentary base pairing 2) Aminoacyl tRNA carrying f-met binds to AUG codon of mRNA 3) Large subunit binds, completing complex and leaving the initiator aminoacyl tRNA in the P site

Question 57

The process of elongation (translation)

Answer 57

1) arrival of aminoacyl tRNA to A site 2) peptide bond forms (peptide chain is transferred from tRNA in P site to tRNA in A site) 3) translocation-repeat down the length of mRNA (ribosome moves down length of mRNA in 5' to 3' direction)

Question 58

Do tRNAs have a stop anticodon?

Answer 58

No.

Question 59

How does protein synthesis end?

Answer 59

when release factor fills the empty A site

Question 60

What do release factors do?

Answer 60

- fills A site because similar in shape, size as tRNA - hydrolyzes the bond linking tRNA in P site to polypeptide chain - releases polypeptide chain

Question 61

What sequences in the tRNA should be conserved? variable?

Answer 61

Conserved: the nucleotide part Variable: the anticodon and amino acid part