DNA Reverse Complement Flashcards

Question 1

In double-stranded DNA, which bases pair with adenine (A) and cytosine (C), respectively?

Accepted Answer

Thymine (T) pairs with A. Guanine (G) pairs with C.

Question 2

Two DNA strands are aligned base by base. The top strand has its 5′ end on the left. Which end of the bottom strand is on the left?

Accepted Answer

The 3′ end. The strands are antiparallel, so their directions are opposite.

Question 3

Write the complementary DNA strand directly below 5′–CATGGA–3′, pairing the bases in the same columns. Label its ends.

Accepted Answer

3′–GTACCT–5′

The aligned partner runs 3′ to 5′ from left to right.

Question 4

A DNA strand is written 5′ to 3′. How do you get its reverse complement?

Accepted Answer

Pair each base, then read the paired bases in reverse order. The result gives the partner strand from its 5′ end to its 3′ end.

Question 5

What is the reverse complement of 5′–GTTCA–3′?

Accepted Answer

5′–TGAAC–3′

The aligned partner is 3′–CAAGT–5′. Read it from the right.

Question 6

Which two bases fill the blanks in the bottom DNA strand, from left to right?

5′–G C T A G–3′
3′–C _ A _ C–5′

Accepted Answer

G, then T. They pair with C and A in the top strand.

The completed bottom strand is 3′–CGATC–5′.

Question 7

Write the same DNA strand 5′ to 3′ if it is shown as 3′–TGGAC–5′.

Accepted Answer

5′–CAGGT–3′

Start from the right. The bases stay the same because you're reading the same strand.

Question 8

Write the strand that pairs with 3′–ACCTGA–5′. Give your answer 5′ to 3′.

Accepted Answer

5′–TGGACT–3′

The aligned partner already has its 5′ end on the left.

Question 9

Someone gives CGTGAC as the reverse complement of 5′–CAGTGC–3′. What step did they miss?

Accepted Answer

They still need to complement each base. CGTGAC is the original sequence read backward. The reverse complement is 5′–GCACTG–3′.

Question 10

A DNA strand ends with G at its 3′ end. What is the first base of its reverse complement, written 5′ to 3′?

Accepted Answer

C. The original 3′ end lines up with the partner's 5′ end, and C pairs with G.

Question 11

Write the reverse complement of 5′–ACGCTAA–3′.

Accepted Answer

5′–TTAGCGT–3′

Pair the bases to get 3′–TGCGATT–5′, then read from the right.

Question 12

Is 5′–AGCATGCT–3′ a reverse-complement palindrome?

Accepted Answer

Yes. Its reverse complement is 5′–AGCATGCT–3′ again.

Question 13

Someone gives AGGCAT as the reverse complement of 5′–TCCGTA–3′. What step did they miss?

Accepted Answer

They still need to reverse the order. AGGCAT is the aligned partner read 3′ to 5′. Read it from the other end to get 5′–TACGGA–3′.

Question 14

A DNA strand's reverse complement is 5′–CGAACTG–3′. What was the original sequence, written 5′ to 3′?

Accepted Answer

5′–CAGTTCG–3′

Taking the reverse complement a second time restores the original sequence.

Question 15

Find the exact + strand match to 5′–GATA–3′ on the printed + reference 5′–TCGGATACCAA–3′. Count the leftmost reference base as position 1 and include both ends of the match.

Accepted Answer

Positions 4–7 (+). Those bases read GATA from left to right.

Question 16

You split a 5′→3′ DNA sequence into a left block and a right block. Which block provides the 5′ end of the reverse complement?

Accepted Answer

The right block. The original 3′ end is on the right, across from the partner's 5′ end.

Question 17

An exact DNA query matches the + strand at reference positions 4–8. Which reference position holds the query's 5′ end?

Accepted Answer

Position 4. The query runs left to right on the + strand.

Question 18

To find a − strand match to 5′–GCTAC–3′, what sequence should you look for on the printed 5′→3′ + reference?

Accepted Answer

5′–GTAGC–3′

That's the reverse complement of the query.

Question 19

Can a five-base DNA sequence made from A, C, G, and T equal its own reverse complement?

Accepted Answer

No. Its middle base would have to pair with itself, and each of those four bases pairs with a different base.

Question 20

Search the printed + reference 5′–ACTAGGATTCCTAGT–3′ for 5′–CTAGG–3′ on either strand. Give each exact match's strand and 1-based inclusive reference positions.

Accepted Answer

Positions 2–6 (+) and 10–14 (−).

The reference has CTAGG at 2–6 and CCTAG, the query's reverse complement, at 10–14.

Question 21

One base in the bottom DNA strand is paired incorrectly. Which base should replace it, and at what position from the left?

5′–A T C G C–3′
3′–T A A C G–5′

Accepted Answer

G at position 3. The top strand has C there.

The corrected bottom strand is 3′–TAGCG–5′.

Question 22

A window on the printed + reference is 5′–CGAG–3′. Does its − strand exactly match the query 5′–CTCA–3′?

Accepted Answer

No. The − strand at that span reads 5′–CTCG–3′. Its last base differs from the query.

Question 23

Find the exact − strand match to 5′–CCGA–3′ on the printed + reference 5′–GACTCGGAATC–3′. Give the 1-based inclusive reference positions.

Accepted Answer

Positions 4–7 (−). The printed bases at 4–7 are TCGG. The opposite strand reads CCGA in the 5′→3′ direction.

Question 24

An exact DNA query matches the − strand at reference positions 6–10. Which reference position holds the query's 5′ end?

Accepted Answer

Position 10. The query runs right to left on the − strand.

Question 25

A query of 5′–CGCG–3′ exactly matches the + strand at reference positions 3–6. How many strands match at that same span?

Accepted Answer

Two. CGCG equals its own reverse complement, so positions 3–6 match on both strands.

DNA Reverse Complement Flashcards

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