DNA structure
A researcher separates the two strands of DNA. One strand reads 3′–TACGGA–5′. What is the complementary strand?
5′–ATGCCT–3′
What enzyme unwinds and separates the two DNA strands?
Helicase
What is the process of making an RNA copy from DNA?
Transcription.
What cellular structure is responsible for reading mRNA and building a protein?
Ribosomes.
A DNA sequence changes from ATG–CCA–GGA to ATG–CTA–GGA. What type of mutation occurred?
Substitution.
A DNA sample contains 18% guanine. What percentage is cytosine, adenine, and thymine?
C = 18%, A = 32%, T = 32%
DNA polymerase adds new nucleotides in which direction?
5′ → 3′
What type of RNA carries the genetic instructions copied from DNA?
mRNA.
What type of RNA brings amino acids to the ribosome?
tRNA.
A nucleotide is removed from a DNA sequence. What type of mutation is this?
Deletion.
A mutation prevents hydrogen bonds from forming between complementary bases. How would this affect DNA structure?
The two DNA strands would not properly bind together, disrupting the double-stranded structure.
One new DNA strand is made continuously while the other is made in short pieces. What are these strands called?
Leading strand and lagging strand.
If the DNA template strand is 3′–TAC GGA CTT–5′, what is the mRNA sequence?
5′–AUG CCU GAA–3′
What is the three-nucleotide sequence on mRNA that determines an amino acid called?
A codon.
Why can adding or removing one nucleotide be more disruptive than substituting one nucleotide?
It can cause a frameshift, changing how the nucleotides are grouped into codons.
A student writes:
5′–ATCG–3′
5′–TAGC–3′
The bases are correctly paired. What is wrong?
DNA strands are antiparallel. The second strand should be 3′–TAGC–5′ since the strand is read in the opposite direction.
Primase is blocked, but DNA polymerase is still working. Why can't DNA replication properly begin?
Primase makes the RNA primer that gives DNA polymerase a starting point.
A cell has a gene in its DNA that contains instructions for making a protein. Why does the DNA need to be transcribed before the protein can be made?
The DNA stays in the nucleus, so its information is copied into mRNA, which can carry the instructions to the ribosome.
An mRNA codon is 5′–GCU–3′. What is the complementary tRNA anticodon?
3′–CGA–5′
An mRNA codon changes from GAA → GAG, but the same amino acid is still produced. What type of mutation is this?
Silent mutation.
A researcher finds that the two strands of a DNA molecule can separate from each other, but the individual nucleotides within each strand remain connected.
Hydrogen bonds → hold the complementary nitrogenous bases between the two DNA strands together.
Covalent bonds → connect the sugar and phosphate groups along each DNA strand, forming the backbone.
A cell has many short DNA fragments on one newly synthesized strand. Which enzyme creates these fragments, and which enzyme connects them together?
DNA polymerase creates the fragments, and DNA ligase connects them.
A mutation occurs in the DNA template, changing one nucleotide. During transcription, what would you expect to happen to the resulting mRNA?
The mRNA would contain a corresponding change in its nucleotide sequence.
An mRNA mutation changes a codon that normally codes for an amino acid into a stop codon. What will happen during translation?
Translation will stop too early, producing a shortened protein that may not function properly.
A mutation occurs in a DNA sequence, but it happens in a region that does not contain instructions for making a protein. Would you expect the mutation to always change the protein? Explain why or why not.
No. If the mutation does not affect a region involved in producing the protein, it may have no effect on the protein.