UAT-UK SPEC CODE: B6 (Gene technologies)ASSUMED MATHS 1 PREREQUISITE: M3.5FREQUENCY: MEDIUM
Recombinant DNA: Restriction Endonucleases, Sticky Ends, Ligase & Plasmid Marker Screening
Deconstructed from 5 past UAT-UK questions (2.15% of all historical Biology papers). Students using standard A-Level classroom methods spend an average of 130s on this archetype—blowing past the 90s ESAT budget. Using the 2-line Sub-90 heuristic below compresses solve time to 35s (saving 95s per question).
Historical Frequency
5 Past Qs
2.15% of Biology
Classroom Trap Time
130s
+40s over 90s budget
Sub-90 Target Time
35s
Banks +95s on the clock
Dominant UI Format
1-2-3 Statement
Maths 1 Skill: M3.5
Card 1 & Card 2 Preview: The Classroom Time Trap vs. Sub-90 2-Line Rule
Excerpted from our interactive 6-Step Topic Lesson for ARCH-B-07.
CARD 1 OF 6 • THE CLASSROOM TIME TRAP (130s)
Why Students Bleed Time:
Evaluate each statement against recombinant DNA biochemistry:
1. Prokaryotes cannot splice eukaryotic introns, so mature -cell mRNA is reverse-transcribed into intron-free cDNA (1 is correct).
2. Digesting both vector and insert with the same restriction endonuclease produces complementary single-stranded overhangs ('sticky ends') (2 is correct).
3. Hydrogen bonds form spontaneously by base-pair complementarity; DNA ligase seals nicks in the sugar-phosphate backbone by forming covalent phosphodiester bonds (3 is incorrect).
1. Prokaryotes cannot splice eukaryotic introns, so mature -cell mRNA is reverse-transcribed into intron-free cDNA (1 is correct).
2. Digesting both vector and insert with the same restriction endonuclease produces complementary single-stranded overhangs ('sticky ends') (2 is correct).
3. Hydrogen bonds form spontaneously by base-pair complementarity; DNA ligase seals nicks in the sugar-phosphate backbone by forming covalent phosphodiester bonds (3 is incorrect).
In 5 past UAT-UK questions (2.15% of Biology), candidates lose 95s by confusing the cutting enzyme with the joining enzyme, or claiming ligase forms hydrogen bonds between bases (hydrogen bonds form spontaneously!). Instead, apply B6 with Maths 1 skill M3.5.
CARD 2 OF 6 • THE 2-LINE SUB-90 HEURISTIC (<35s)
Classic ESAT trap: Ligase = Phosphodiester backbone, NOT hydrogen bonds eliminate 3 immediately 1 and 2 only.
Classic ESAT trap: Ligase = Phosphodiester backbone, NOT hydrogen bonds eliminate 3 immediately 1 and 2 only.
Sanity & Limit Check: Verify units/signs against
multi_statement_linchpin_foil (Swapping restriction endonuclease (cuts phosphodiester backbone at specific recognition sequence) with DNA ligase (joins sugar-phosphate backbone via phosphodiester bonds)) and fence_post_or_domain_trap (Cutting a circular plasmid at n restriction sites and getting n+1 fragments instead of n fragments (versus n+1 fragments for a linear DNA molecule)).Examiner Distractor Blueprint for ARCH-B-07
FOIL #1multi_statement_linchpin_foil
Swapping restriction endonuclease (cuts phosphodiester backbone at specific recognition sequence) with DNA ligase (joins sugar-phosphate backbone via phosphodiester bonds)
Confusing the cutting enzyme with the joining enzyme, or claiming ligase forms hydrogen bonds between bases (hydrogen bonds form spontaneously!).
FOIL #2fence_post_or_domain_trap
Cutting a circular plasmid at n restriction sites and getting n+1 fragments instead of n fragments (versus n+1 fragments for a linear DNA molecule)
Fence-post topology trap: n cuts on a closed circle give n fragments; n cuts on a linear strand give n + 1 fragments.
FOIL #3sign_or_direction_flip
Selecting bacteria that GROW on tetracycline when the foreign gene was inserted INTO the tetracycline-resistance gene (insertional inactivation)
Successful recombinant plasmids have their second antibiotic resistance gene disrupted, so they grow on Ampicillin but DIE on Tetracycline.
FOIL #4multi_statement_linchpin_foil
Cutting human DNA and bacterial plasmid with two DIFFERENT restriction enzymes that produce non-complementary sticky ends
Both donor DNA and vector plasmid must be cut with the SAME restriction enzyme to generate complementary sticky ends.
Try 1 Live Sample Question Under the 90-Second Stopwatch
Press W to open the 2-line dry-wipe scratchpad, select A–E, and lock in to reveal the Dual-View solution.
sub90 ESATARCH-B-07: Recombinant DNA: Restriction Endonucleases, Sticky Ends, Ligase & Plasmid Marker Screening (Sample)Biology
00:00.0
SUB-90 ZONE (<35S)
0.0s35s Sub-9090s ESAT Budget150s Classroom
Right-click any option to cross out • Keys
A–E + EnterQuestion 1 of 1 • 90s Target
Ready to Start Question 1?
The question stem, diagram, and answer options are hidden behind this pre-start gate. When you click below, the question will reveal and your 90-second split stopwatch will immediately begin ticking.
Biology•ARCH-B-07•Standard 5-Option
or press Enter to start