20.4 - Information Flow in Biological Systems

Question 1

central dogma

Answer 1

in cells the flow of genetic information contained in DNA is a one-way street that leads from DNA to RNA to protein

Question 2

The process by which a single strand of DNA serves as a template for the synthesis of an RNA molecule is called

Answer 2

transcription

Question 3

The process by which the message is converted into protein is called

Answer 3

translation

Question 4

Unlike transcription, the process of translation involves converting the information from

Answer 4

one language to another

Question 5

In this case, the genetic information in the linear _________ is being translated into a protein, a linear ________

Answer 5

sequence of nucleotides

sequence of amino acids.

Question 6

Three classes of RNA molecules are produced by transcription

Answer 6

messenger RNA, transfer RNA, and ribosomal RNA.

Question 7

Messenger RNA (mRNA)

Answer 7

carries the genetic information for a protein from DNA to the ribosomes. It is a complementary RNA copy of a gene on the DNA.

Question 8

Ribosomal RNA (rRNA)

Answer 8

a structural and functional component of the ribosomes, which are “platforms” on which protein synthesis occurs. There are three types of rRNA molecules in bacterial ribosomes and four in the ribosomes of eukaryotes.

Question 9

Transfer RNA (tRNA)

Answer 9

translates the genetic code of the mRNA into the primary sequence of amino acids in the protein.

Question 10

secondary and tertiary structures of tRNA

Answer 10

cloverleaf-shaped secondary structure resulting from base pair hydrogen bonding (A─U and G─C) and a roughly L-shaped tertiary structure

Question 11

The sequence CCA is found at the 3′ end of the tRNA. The 3′-OH group of the terminal nucleotide, adenosine, can be

Answer 11

covalently attached to an amino acid

Question 12

Three nucleotides at the base of the cloverleaf structure form the

Answer 12

anticodon

Question 13

the anticodon, this triplet of bases forms hydrogen bonds to a

Answer 13

codon

Question 14

codon

Answer 14

complementary sequence of bases on a messenger RNA (mRNA) molecule on the surface of a ribosome during protein synthesis.

Question 15

This hydrogen bonding of codon and anticodon brings the

Answer 15

correct amino acid to the site of protein synthesis at the appropriate location in the growing peptide chain.

Question 16

transcription is catalyzed by

Answer 16

the enzyme RNA polymerase

Question 17

transcription occurs in 3 stages

Answer 17

initiation
elongation/synthesis of the RNA transcript
termination

Question 18

initiation

Answer 18

involves binding of RNA polymerase to a specific nucleotide sequence, the promoter, at the beginning of a gene.

Question 19

This interaction of RNA polymerase with specific promoter DNA sequences allows RNA polymerase to recognize

Answer 19

the start point for transcription.

and also determines which DNA strand will be transcribed

Question 20

Unlike DNA replication, transcription produces a

Answer 20

complementary copy of only one of the two strands of DNA.

Question 21

As it binds to the DNA, RNA polymerase separates the two strands of DNA so that it can

Answer 21

“read” the base sequence of the DNA.

Question 22

chain elongation

Answer 22

begins as the RNA polymerase “reads” the DNA template strand and catalyzes the polymerization of a complementary RNA copy.

Question 23

With each step, RNA polymerase transfers a _______to the end of the growing RNA chain and catalyzes the formation of a _______ bond between the_________group of the incoming ribonucleotide and the_______ group of the last ribonucleotide of the growing RNA chain.

Answer 23

complementary ribonucleotide
3′–5′ phosphodiester
5′-phosphoryl
3′-hydroxyl

Question 24

The final stage of transcription is

Answer 24

termination

Question 25

The RNA polymerase finds a ______sequence at the end of the gene and _____the newly formed RNA molecule.

Answer 25

termination

releases

Question 26

In eukaryotes, transcription produces a

Answer 26

primary transcript that must undergo extensive post-transcriptional modification before it is exported out of the nucleus for translation in the cytoplasm.

Question 27

Eukaryotic primary transcripts undergo three post-transcriptional modifications.

Answer 27

These are the addition of a 5′ cap structure and a 3′ poly(A) tail, and RNA splicing.

Question 28

In the first modification, a ___ structure is ____ added to the__′ end of the primary transcript.

Answer 28

cap
enzymatically
5

Question 29

The cap structure consists of

Answer 29

7-methylguanosine attached to the 5′ end of the RNA by a 5′–5′ triphosphate bridge.

Question 30

The first two nucleotides of the mRNA are also

Answer 30

methylated

Question 31

The cap structure is required for

Answer 31

efficient translation of the final mature mRNA.

Question 32

The second modification is the enzymatic addition of a

Answer 32

poly(A) tail to the 3′ end of the transcript

Question 33

Poly(A) polymerase uses ___ and catalyzes the stepwise polymerization of 100–200 adenosine nucleotides on the______

Answer 33

ATP

3′ end of the RNA.

Question 34

The _____ protects the 3′ end of the mRNA from enzymatic degradation and thus _________

Answer 34

poly(A) tail

prolongs the lifetime of the mRNA.

Question 35

The third modification

Answer 35

RNA splicing

Question 36

RNA splicing

Answer 36

involves the removal of portions of the primary transcript that are not protein coding.

Question 37

These sequences that do not code for proteins are called

Answer 37

intervening sequences or introns.

Question 38

The primary transcript contains both

Answer 38

the introns and the protein-coding sequences, called exons.

Question 39

The presence of introns in the mRNA would make it ____ for the process of translation to synthesize the ____ protein. Therefore, they must be removed, which is done by the process of ____

Answer 39

impossible
correct
RNA splicing

Question 40

As you can imagine, RNA splicing must be very precise. If too much, or too little, RNA is removed, the mRNA will

Answer 40

not carry the correct code for the protein.

Question 41

there are “signals” in the DNA to mark the boundaries of the

Answer 41

introns

Question 42

The sequence ____ is always found at the intron’s 5′ boundary and the sequence ___ is found at the 3′ boundary.

Answer 42

GpU

ApG

Question 43

Recognition of the splice boundaries and stabilization of the splicing complex requires the assistance of particles called

Answer 43

spliceosomes

Question 44

Spliceosomes are composed of a variety of

Answer 44

small nuclear ribonucleoproteins (snRNPs, read “snurps”).

Question 45

Each snRNP consists of a

Answer 45

small RNA and associated proteins.

Question 46

The ____ components of different _____ are complementary to different sequences involved in ____

Answer 46

RNA
snRNPs
splicing

Question 47

By hydrogen bonding to a splice boundary or intron sequences, the snRNPs

Answer 47

recognize and bring together the sequences involved in the splicing reactions.

Question 48

it is the small RNA molecules that

Answer 48

catalyze the splicing reactions. Such catalytic RNAs are called ribozymes.