Chapter 17 Questions

Question 1

Which specific regions of DNA are transcribed?

Answer 1

Genes ?

Question 2

Which two processes carryout gene expression?

Answer 2

Transcription and Translation

Question 3

Which two molecules produced because of gene expression are considered “worker” molecules?

Answer 3

RNA and Proteins

Question 4

Which type of RNA is considered the intermediate between DNA and proteins?

Answer 4

Messenger RNA ?

Question 5

What are the three main differences between DNA and RNA?

Answer 5

• RNA contains ribose instead of deoxyribose
• RNA is typically single stranded while DNA is usually double stranded
• RNA contains uracil instead of thymine

Question 6

What are the three types of RNA that are produced by transcription and what specific role does each play during protein synthesis?

Answer 6

• Messenger RNA (mRNA)- contains the code for proteins
• Ribosomal RNA (rRNA)- major component of ribosomes
• Transfer RNA (tRNA)- carries amino acids to ribosomes during protein synthesis

Question 7

What cellular location does transcription take place in bacteria? What location does translation take place in bacteria?

Answer 7

Since bacteria lack nuclei, they can undergo transcription and translation at the cytoplasm simultaneously

Question 8

What cellular location does transcription take place in eukaryotes? What cellular location does translation take place in eukaryotes?

Answer 8

transcription occurs in the nucleus, while translation occurs in the cytoplasm

Question 9

What are the main differences between transcription and translation in bacteria vs. eukaryotes?

Answer 9

Eukaryotes have three different RNA polymerases (one for mRNA, one for tRNA, and one for rRNA) while bacteria only have one RNA polymerase that make all three forms of RNA

Question 10

What is the strand of DNA that used during transcription called?

Answer 10

Template strand

Question 11

Which direction does RNA polymerase adds complementary nucleotides to DNA?

Answer 11

5’ to 3’ direction

Question 12

How can only four DNA nucleotides be used to encode all 20 different amino acids.

Answer 12

since each position in a three nucleotide codon has four possibilities (one for each of the four RNA bases) there are 43 different codons

Question 13

How many RNA nucleotides make up a codon?

Answer 13

Three

Question 14

Do some amino acids have multiple codons?

Answer 14

Yes

Question 15

Know how to add the correct complementary mRNA nucleotides to the template

Answer 15

?

Question 16

Know how to use the resulting mRNA sequence to encode the correct amino acid sequence using a codon chart

Answer 16

?

Question 17

What type of mutation leads to a change in the correct reading frame of mRNA?

Answer 17

frame shift mutation

Question 18

What are the three main stages of transcription and what happens during each stage for both prokaryotes and eukaryotes?

Answer 18

Initiation
Elongation
Termination

Question 19

What does RNA polymerase recognize and bind to in order to initiate transcription in bacteria?

Answer 19

RNA polymerase itself recognizes and binds to the promoter and initiate transcription

Question 20

How does initiation of transcription begin in eukaryotes? (i.e. describe the eukaryotic transcription initiation complex)

Answer 20

transcription factors must first bind to a specific sequence in the promoter called the TATA box; the bound transcription factors then recruit RNA polymerase II to bind to the promoter and initiate transcription

Question 21

During elongation, can multiple RNA polymerase molecules transcribe the same gene at one time?

Answer 21

Yes

Question 22

What molecule is responsible for separating double stranded DNA during transcription?

Answer 22

RNA polymerase

Question 23

Which direction does RNA polymerase add complementary nucleotides to the DNA template strand?

Answer 23

5’ to 3’ direction

Question 24

What is the difference between bacterial and eukaryotic termination?

Answer 24

• In bacteria, the polymerase stops transcription at the end of the terminator sequence and the mRNA can be translated without further modification
• In eukaryotes, RNA polymerase II transcribes the polyadenylation signal sequence (AAUAAA); the pre-RNA transcript is released 10–35 nucleotides past this polyadenylation sequence
• In eukaryotes, the pre-mRNA will then undergo processing prior to being translated; no processing is needed for bacterial mRNA and the mRNA is translated as it is being made

Question 25

What are the three ways that mRNA is processed after transcription?

Answer 25

• The 5’ end receives a 5’ cap made of a modified guanine nucleotides
• The 3’ end receives a poly A tail made of 50-250 adenine nucleotides
• Introns are removed through RNA splicing

Question 26

What are the functions of the 5’ cap and poly A tail?

Answer 26

They facilitate the export of mRNA out of the nucleus
They protect mRNA from hydrolytic enzymes
They help ribosomes attach to the 5′ end

Question 27

Why are introns removed from the primary transcript?

Answer 27

The nucleotide sequences of introns are not used for translation and therefore, must be removed prior to translation

Question 28

Explain what is involved in the process of intron removal

Answer 28

RNA splicing is a process that removes introns and joins exons to create an mRNA molecule with a continuous coding sequence

Question 29

What types of special enzymes are used for intron removal?

Answer 29

RNA splicing is carried out by a protein and RNA enzyme complex called a spliceosome
The RNA molecules in the spliceosome are ribozymes

Question 30

Describe the structure of tRNA molecules:
Single or double stranded?
Two-dimensional vs three dimensional shape?
What are located at each end of tRNA molecules?

Answer 30

• single strand of RNA (~80 nucleotides long)
• tRNA is able to fold upon itself to form a three dimensional structure
• At one end of the tRNA is an amino acid attachment site. At the other end is an anticodon on the other end (the anticodon base-pairs with a complementary codon on mRNA)

Question 31

What is the name of the enzyme that attaches amino acids to tRNA?

Answer 31

aminoacyl-tRNA synthetase

Question 32

What does the anticodon on tRNA bind to?

Answer 32

mRNA codon

Question 33

Can some tRNA bind to multiple codons? Is this an exact complementary match?

Answer 33

There are 61 different amino acid codons, but only 45 different tRNAs; this means that some tRNAs can bind to more than one codon through “wobble” binding

Question 34

What type of molecules make up ribosomes?

Answer 34

proteins and ribosomal RNA (rRNA)

Question 35

What are the two ribosomal subunits called?

Answer 35

The two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA)

Question 36

How many tRNA binding sites are there on the ribosome and what are they called?

Answer 36

3. The P site, the A site, and the E site.

Question 37

What does the initiation complex consist of?

Answer 37

mRNA, an initiator tRNA , and the two ribosomal subunits

Question 38

What are the three steps of elongation?

Answer 38

codon recognition, peptide bond formation, and translocation

Question 39

Describe the process of polypeptide elongation starting with the binding of the initiator tRNA to how amino acids are added to the growing polypeptide chain, to the process of translocation and finally termination.

Answer 39

During elongation, amino acids are added one by one to the growing polypeptide chain
Each addition involves proteins called elongation factors and occurs in three steps: codon recognition, peptide bond formation, and translocation.
Termination occurs when a stop codon in the mRNA reaches the A site of the ribosome

Question 40

What are the two major ways that polypeptides are processed after being translated?

Answer 40

• Folding

- Post translational modifications (addition of other molecules or functional groups to polypeptide)

Question 41

Where do proteins synthesized by cytosolic ribosomes function in the cell?

Answer 41

cytoplasm

Question 42

Where happens to proteins synthesized by ER ribosomes?

Answer 42

Ribosomes bound to the ER make proteins that will go through the endomembrane system to form, secretory proteins, membrane proteins, or proteins that will go to various organelles within the cell (lysosome, mitochondrial, chloroplast, etc.)