UNIT 5

The codon chart shown here uses the three base sequence found on the mRNA molecule after the information is copied from DNA during transcription. If the mRNA message is AAC UAC UGC, what was the original DNA base sequence?

• Asn--Tyr--Cys

• UUG AUG ACG

• AAC TAC TGC

• TTG ATG ACG

Answer explanation

TTG ATG ACG This is the only answer that makes sense. Choice A is wrong, because the mRNA transcript is complementary to the original DNA. DNA contains T instead of U, so choice B is wrong. A translates to T, C to G, and U to A.

A ___________ chain is a sequence of amino acids that is the foundation for the basic structure of a protein.

• polyunsaturated

• polynomial

• polysaccharide

• polypeptide

Answer explanation

"Poly-" means "many," while "peptide" refers to "protein."

Messenger RNA carries a(n) ___________ of the DNA’s instructions out of the nucleus to the ___________.

• transcript; ribosome

• exact copy; mitochondria

• transcript; mitochondria

• exact copy; ribosome

Answer explanation

The mRNA transcript is carried to the ribosome.

During replication, the DNA segment in a somatic cell undergoes the mutation seen here.

What type of mutation has occurred? If this DNA molecule proceeds to transcription and translation, explain the impact of this mutation on the production of a protein?

Responses

• This is a frameshift mutation, resulting from the substitution of one nitrogen base. If this strand of DNA is used for transcription, it will result in all of the amino acids being placed incorrectly in the protein.

• This is a point mutation, resulting from the addition of one nitrogen base. This strand can no longer be used for transcription or translation due to its mutation.

• This is a frameshift mutation, resulting from the addition of one nitrogen base. This strand can no longer be used for transcription or translation due to its mutation. If this strand of DNA is used for transcription, it will affect the coding of multiple amino acids, causing an incorrect protein to be assembled.

• This is a point mutation, resulting from the substitution of one nitrogen base. If this strand of DNA is used for transcription, it will affect the coding of ONE amino acid, resulting in placing the correct amino acid in the protein, placing the wrong amino acid in the protein, or coding for the protein to stop building.

Answer explanation

If this strand of DNA is used for transcription, it will affect the coding of ONE amino acid, resulting in placing the correct amino acid in the protein, placing a wrong amino acid in the protein, or coding for the protein to stop building.

A single strand of DNA contains the following nine nucleotides in this order: ACT TAT GGA. What sequence of bases will be present on the complementary strand of DNA?

• ACU UAU GGA

• UGA AUA CCT

• ACT TAT GGA

• TGA ATA CCT

Answer explanation

TGA ATA CCT A pairs with T, G pairs with C. Remember this is asking for DNA and not for the mRNA transcript.

Protein synthesis is vital for cell growth and metabolism. Transcription and translation are known as the central dogma of biology in which proteins are synthesized from DNA. How is transcription similar to translation in terms of base pairing?

• transcription starts at the promoter; translation begins at the start codon

• in transcription, RNA is formed; in translation, a polypeptide is formed

• in transcription, C pairs with G and A pairs with T to make mRNA; in translation, A pairs with U and G pairs with C to make tRNA

• in transcription, DNA binds to mRNA; in translation, codons bind to anti-codons

Answer explanation

Transcription and translation are very similar in terms of pairing. In transcription, DNA must bind with mRNA to make a transcript to send outside of the nucleus. In translation, codons bind with anti-codons to make amino acids which then form proteins.

During _____________, the cell uses information from messenger RNA to produce proteins.

• translation

• amino acid sequencing

• transcription

• respiration

Answer explanation

Translation is the process of translating the genetic code from messenger RNA into an amino acid chain.

Translation of the DNA sequence AAGCTGGGA would result in

• an mRNA strand with the sequence UUGCACCCU.

• an mRNA strand with the sequence TTCGACCCT.

• a sequence of three amino acids linked by peptide bonds.

• a DNA strand with the base sequence TTCGACCCT.

Answer explanation

Translation produces proteins from mRNA, which was at one time, DNA code.

What is deoxyribose?

• a nitrogenous base found in DNA and RNA

• an acid found in DNA

• a pigment found in RNA

• a sugar found in DNA

Answer explanation

Deoxyribose is a sugar found in DNA.

What process IMMEDIATELY preceeded protein synthesis at the ribosome?

• translation

• transcription

• duplication

• replication

Answer explanation

Transcription immediately preceeded protein synthesis or translation at the ribosome.