Chapter 15

Question 1

The central dogma of molecular biology (Crick) genetic info flows in one direction:

Answer 1

DNA > Transcription > RNA > Translation > protein

Question 2

DNA code is … into messenger RNA.

Answer 2

transcribed

Question 3

Ribosomes “read” the genetic code in mRNA and … it to attach amino acids together to form a protein.

Answer 3

translate

Question 4

codon

Answer 4

a set of 3 nucleotides specifying a specific amino acid

Question 5

reading frame

Answer 5

the series of nucleotides that produces the correct protein when translated in sets of 3

Question 6

The amino acids encoded by 60 different codons were determined, plus…

Answer 6

• Start codon – AUG - used to signify the start of translation
• Stop codons – UUA, UGA, UAG – used to terminate translation

Question 7

The code is degenerate:

Answer 7

meaning that most AAs are specified by two or more codons

Question 8

template (-)DNA strand

Answer 8

used to transcribe RNA, 3’ to 5’

Question 9

coding (+)DNA strand

Answer 9

is complementary to the template strand (but is not used in transcription), 5’ to 3’

Question 10

RNA polymerase enzyme

Answer 10

synthesizes the primary (+) RNA transcript (5’ to 3’) using the template DNA strand

Question 11

transcription

Answer 11

• initiation: RNA polymerase identifies a specific starting DNA sequence
• elongation: ribonucleotides are added to the 3’ end of the new RNA
• termination: RNA polymerase stops when it encounters a terminating DNA sequence.

Question 12

translation

Answer 12

• initiation: a specific tRNA and ribosome come together at a start codon on mRNA.
• elongation: tRNAs bring amino acids to the ribosome to build the polypeptide
• termination: ribosome encounters a stop codon on the mRNA and releases the polypeptide

Question 13

Gene expression requires 6 types of RNA:

Answer 13

• messenger RNA (mRNA)
• ribosomal RNA (rRNA)
• transfer RNA (tRNA)
• small nuclear RNA (snRNA)
• signal recognition particle (SRP)
• micro-RNA (miRNA)

Question 14

messenger RNA (mRNA)

Answer 14

carries the information from DNA that encodes proteins

Question 15

ribosomal RNA (rRNA)

Answer 15

is a component of the ribosome (along with proteins)

Question 16

transfer RNA (tRNA)

Answer 16

carries amino acids to the ribosome for translation

Question 17

small nuclear RNA (snRNA)

Answer 17

is involved in processing pre-mRNA

Question 18

signal recognition particle (SRP)

Answer 18

is composed of protein and RNA and involved in directing mRNA to the RER

Question 19

micro-RNA (miRNA)

Answer 19

is very small and have several functions – some involved in mRNA “silencing”.

Question 20

The transcriptional unit (often containing more than one gene) starts at a … and ends at a … of the DNA molecule.

Answer 20

promoter sequence, terminator sequence

Question 21

The promoter is composed of

Answer 21

• a DNA sequence to which RNA polymerase binds
• the start site (+1) – the first base to be transcribed into RNA

Question 22

Prokaryotic cells contain a single type of RNA polymerase found in 2 forms:

Answer 22

• core polymerase can elongate RNA but cannot initiate transcription
• holoenzyme = core polymerase plus a sigma factor which is required to initiate transcription

Question 23

During elongation

Answer 23

the transcription bubble moves along the DNA template strand.

Question 24

The RNA strand grows in the … direction as ribonucleotides are added.

Answer 24

5’ to 3’

Question 25

transcription bubble

Answer 25

contains RNA polymerase, the DNA template strand, and the growing RNA transcript

Question 26

After the transcription bubble passes,

Answer 26

the now-transcribed DNA is rewound.

Question 27

During elongation,

Answer 27

RNA polymerase moves along the (-)DNA template, synthesizes (+) mRNA in the 5' to 3' direction, and unwinds and rewinds the DNA as it is read.

Question 28

Transcription stops when the transcription bubble encounters a ...

Answer 28

terminator DNA sequence – often with a series of A-T base pairs

Question 29

In prokaryotes, transcription and translation often occur at ...

Answer 29

the same time

Question 30

operon

Answer 30

includes related genes that can be regulated as a single unit.

Question 31

RNA polymerase I

Answer 31

makes rRNA

Question 32

RNA polymerase II

Answer 32

makes mRNA and some snRNA

Question 33

RNA polymerase III

Answer 33

makes tRNA and other small RNAs

Question 34

Initiation of mRNA transcription requires a series of transcription factors -

Answer 34

proteins that bind RNA polymerase II to a promoter

Question 35

The primary RNA transcript is modified by:

Answer 35

- addition of a 5’ cap and a 3’ poly-A tail - removal of non-coding introns leaving the coding exons that will be translated

Question 36

snRNAs within the spliceosome

Answer 36

recognize and remove the introns, then splice the exons.

Question 37

Single primary RNA transcript can be

Answer 37

spliced into different mRNAs by the inclusion of different sets of exons

Question 38

tRNAs carry amino acids to the ribosome to build polypeptides

Answer 38

- aminoacyl-tRNA transferases (synthetases) add amino acids to the acceptor arm of each tRNA - the anticodon loop of tRNA contains nucleotide sequences complementary to mRNA codons

Question 39

tRNA molecules

Answer 39

one end accepts a certain amino acid, and the anti-codon end is complementary to a certain mRNA codon.

Question 40

Aminoacyl-tRNA transferase

Answer 40

to “charge” a specific tRNA molecule with a specific amino acid.

Question 41

“Charged” tRNA

Answer 41

has an amino acid added using energy from ATP; allows amino acids to form peptide bonds without additional energy

Question 42

Ribosomes do not ...

Answer 42

verify amino acid attached to tRNA, so mistakes can happen.

Question 43

The ribosome has two functions:

Answer 43

- decode the mRNA - form peptide bonds between AAs using the enzyme peptidyl transferase (enzymatic component of the ribosome)

Question 44

The ribosome has 3 tRNA binding sites:

Answer 44

- A site: binds the tRNA attached to the growing polypeptide - P site: binds the tRNA that carried the last amino acid in the chain - E site: temporarily binds the empty tRNA until it is discharged and can go pick up another amino acid.

Question 45

In prokaryotes, initiation of translation requires an ...

Answer 45

initiation complex

Question 46

initiation complex includes

Answer 46

- an initiator tRNA with N-formylmethionine bound to the P site, with E and A sites empty - small and large ribosomal subunits - mRNA with a ribosome binding sequence (RBS)

Question 47

Elongation during translation involves the addition of amino acids

Answer 47

- a charged tRNA binds to the A site if its anticodon is complementary to the A site codon - peptidyl transferase forms a peptide bond - the ribosome moves “one codon” down the mRNA in a 5’ to 3’ direction

Question 48

The ribosome moves along the mRNA,

Answer 48

and the polypeptide chain forms.

Question 49

Entry of a release factor into the A site

Answer 49

terminates translation and the components dissociate.

Question 50

Elongation continues until the ribosome encounters a

Answer 50

stop codon

Question 51

Stop codons are recognized by

Answer 51

release factors which release the polypeptide from the ribosome.

Question 52

chaperone proteins

Answer 52

help fold newly formed proteins into proper tertiary shapes

Question 53

translation may occur either

Answer 53

on ribosomes in cytoplasm or on the rough endoplasmic reticulum (RER)

Question 54

signal sequences

Answer 54

at the beginning of the polypeptide sequence bind to the signal recognition particle (SRP)

Question 55

The signal sequence and SRP are then

Answer 55

recognized by RER receptor proteins.

Question 56

The signal sequence/SRP complex

Answer 56

holds the ribsomes on RER

Question 57

As the polypeptide is synthesized

Answer 57

it passes through a pore into the interior of the ER.