Chapter 17

Question 1

Explain how making proteins in cells involves going from one ‘chemical language’ to another?

Answer 1

First, the original DNA is copied into mRNA in a process called transcription. Then, mRNA is used by ribosomes to make proteins in the cytoplasm, in a process known as translation.

Question 2

What are codons, and in what molecule are they found?

Answer 2

A codon is a three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code. They are located on a strand of RNA.

Question 3

How many codons are there?

Answer 3

There are 64 codons

Question 4

How many specify (or ‘code for’) amino acids? How many do not specify amino acids?

Answer 4

61 represent amino acids and the remaining three represent stop signals.

Question 5

Clearly explain the roles of the codons AUG

Answer 5

AUG codes for the amino acid methionine (Met) but also functions as a “start” signal for ribosomes to begin translating the mRNA at that point.

Question 6

Clearly explain the roles of the codons UGA, UAG and UAA in TRANSLATION.

Answer 6

UGA, UAG, and UAA functions as “stop” signals, marking where ribosomes end translation.

Question 7

Describe the initiation of transcription of a gene, explaining the role of the promoter and template strand

Answer 7

During initiation, in eukaryotes, the transcription factors mediate the RNA polymerase to bind to the promoter sequence of the DNA, the polymerase unwinds the DNA for the initiation at this point to start transcribing the template strand

Question 8

Describe the elongation of transcription of a gene, explaining the role of the RNA polymerase.

Answer 8

During elongation, RNA polymerase moves along the DNA template stand and untwists the double helix; this allows 10 to 20 nucleotides to be paired with DNA at a time. The new RNA nucleotides peel away from the DNA template and the double helix re-forms.

Question 9

Describe the termination of transcription of a gene, explaining the role of the terminator.

Answer 9

During termination, in eukaryotes, the termination sequence causes the polymerase to detach from the DNA and release the transcribed RNA.

Question 10

In what direction does RNA polymerase read a template strand, and in what direction does it synthesize a new polynucleotide chain?

Answer 10

RNA polymerase reads a template strand in the 3’ to 5’ direction. It synthesizes polynucleotide from the 5’ to 3’ direction.

Question 11

In what direction does DNA polymerase read a template strand, and in what direction does it synthesize a new polynucleotide chain?

Answer 11

DNA polymerase reads in the 3’ to 5’ direction. It synthesizes polynucleotide in the 5’ to 3’ direction.

Question 12

In what direction is an mRNA transcript translated?

Answer 12

Messenger RNA transcript is translated from the 5’ to 3’ direction.

Question 13

What is rRNA?

Answer 13

Ribosomal RNA is RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.

Question 14

What protein-like function does rRNA have?

Answer 14

Ribosomal RNA associates with a set of proteins to form ribosomes. These complex structures, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains

Question 15

Where does rRNA come from?

Answer 15

Molecules of ribosomal RNA are synthesized in a specialized region of the cell called the nucleolus, which appears as a dense area within the nucleus and contains the genes that encode rRNA.

Question 16

What are tRNAs, and why are they necessary for translation?

Answer 16

Transfer RNA is an RNA molecule that functions as a translator between nucleic acid and protein languages by carrying specific amino acids to the ribosome, where they recognize the appropriate codons in the mRNA.

Question 17

What are anticodons and where are they found in a tRNA?

Answer 17

Anticodon is a nucleotide triplet at one end of a tRNA molecule that base pairs with a particular complementary codon on an mRNA molecule.

Question 18

Where are amino acids attached, and how?

Answer 18

The amino acids are attached to the 3’ end of tRNA. They are attached by an enzyme called aminoacyl-tRNA synthetases, which requires the use of ATP, losing two phosphate groups and becoming AMP.

Question 19

Where do tRNAs come from?

Answer 19

Transfer RNA is produced by RNA polymerase III from the nucleus and exported out to the cytoplasm.

Question 20

Explain why tRNAs depend on aminoacyl-tRNA synthetases to perform their function.

Answer 20

Transfer RNA needs aminoacyl-tRNA synthetases to catalyze the covalent attachment of the amino acid to its tRNA, which is a process driven by the hydrolysis of ATP.

Question 21

How many different types of these enzymes are found in cells?

Answer 21

There are twenty different types of aminoacyl-tRNA synthetases, one for each type of amino acid.

Question 22

What are the substrates of this enzyme?

Answer 22

The tRNA and its specific amino acid are the substrates of the enzyme

Question 23

Understand the causes and effects of the various mutations mentioned in this chapter

Answer 23

frameshift, nonsense, missense, and silent mutation

Question 24

Silent mutation

Answer 24

is a nucleotide-pair substitution that has no observable effect on the phenotype; for example, within a gene, a mutation that results in a codon that codes for the same amino acid.

Question 25

Missense mutation

Answer 25

is a nucleotide-pair substitution that results in a codon that codes for a different amino acid.

Question 26

Nonsense mutation

Answer 26

is a mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

Question 27

Frameshift mutation

Answer 27

is a mutation occurring when nucleotides are inserted in or deleted from a gene and the number inserted or deleted is not a multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons.

Question 28

What is the current definition of a gene?

Answer 28

A gene is a region of DNA that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule.

Question 29

How does protein synthesis compare and contrast between prokaryotes and eukaryotes (in transcription) ?

Answer 29

• In transcription, bacteria have a single type of RNA polymerase that synthesizes not only mRNA but also other types of RNA that function in protein synthesis, such as ribosomal RNA. In contrast, eukaryotes have at least three types of RNA polymerase in their nuclei; the one used for pre-mRNA synthesis is called RNA polymerase II. The other polymerases transcribe RNA molecules that are not translated into protein.
• In bacteria, part of the RNA polymerase itself specifically recognizes and binds to the promoter. In eukaryotes, a collection of proteins called transcription factors mediates the binding of RNA polymerase and initiation of transcription.

Question 30

How does protein synthesis compare and contrast between prokaryotes and eukaryotes (in termination) ?

Answer 30

The mechanism of termination differs between bacteria and eukaryotes. In bacteria, transcription proceeds through a terminator sequence in the DNA. The transcribed terminator functions as the termination signal, causing the polymerase to detach from the DNA and release the transcript, which requires no further modification before translation. In eukaryotes, RNA polymerase II transcribes a sequence on the DNA called the polyadenylation signal sequence, which specifies a polydenylation signal (AAUAAA) in the pre-mRNA. Then, at a point about 10-35 nucleotides downstream from the AAUAAA, these proteins cut it free from the polymerase, releasing the pre-mRNA.

Question 31

How does protein synthesis compare and contrast between prokaryotes and eukaryotes (in Initiation) ?

Answer 31

In the initiation of translation in bacteria, the small subunit of a ribosome can bind to mRNA and a specific initiator tRNA in any order. In eukaryotes, the small subunit, with the initiator tRNA already bound, binds to the 5’ cap of the mRNA and then moves, or scans, downstream along the mRNA until it reaches the start codon; the initiator tRNA then hydrogen-bonds to the AUG start codon.

Question 32

How does protein synthesis compare and contrast between prokaryotes and eukaryotes (Major difference) ?

Answer 32

major difference between protein synthesis in prokaryotes and eukaryotes is that transcription and translation can happen at the same time in bacteria but not in eukaryotes.