DSE Biology | Genetic Engineering and Biotechnology Lesson Prep (for tutors)

DSE Biology | Genetic Engineering and Biotechnology Lesson Prep (for tutors) | Enzymes, Vectors and PCR

2026-11-03

Tutor lesson-prep guides · Secondary Biology

Students remember “cut with a restriction enzyme” but lose the thread by step three. This lesson fixes the process as four moves, cut, join, deliver, select, each with the tool and the reason for using it.

Objectives — Students can: (1) state the four stages of genetic engineering in order with the tool used at each; (2) explain the three temperature stages of PCR and calculate the amplification; (3) argue both sides of the genetically modified food issue with supporting evidence.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
DNA structure	Which bases pair together	A with T, C with G
Enzymes	What an enzyme does	Lowers activation energy, speeds up the reaction
Cells	Which cells carry plasmids	Bacteria

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-10 min	Diagnose	Order four process cards	Name the tool for each
10-24 min	Cut and join	Restriction and ligase enzymes	Sticky ends
24-36 min	Deliver and select	Transformation and screening	Marker gene
36-48 min	PCR	95, 55 and 72 degrees	Calculate the fold increase
48-56 min	Issue question	GM food for and against	Two points each side
56-60 min	Exit check	Three questions collected	Independent

03 Teaching script (read it out)

Scene 1: Cut and join: the ends must match

A restriction enzyme cuts DNA at a specific sequence and leaves sticky ends. Only ends cut by the same enzyme pair up, so the vector and the gene must be cut with the same enzyme.
DNA ligase seals the sugar-phosphate backbone and forms the recombinant DNA.
Make them answer: what goes wrong with blunt ends (poor pairing, possible reverse insertion).

Tutor move: scissors and tape, the cuts must line up before the tape holds.

Scene 2: Deliver and select: without screening nothing works

Putting the recombinant plasmid into bacteria is transformation, but most bacteria take up nothing, so a marker gene such as antibiotic resistance is used to screen.
Only colonies that grow on the antibiotic can carry the plasmid, and a second test confirms the insert and its orientation.
Trap: calling transformation infection, or assuming every bacterium succeeds.

Tutor move: ask what you would get without screening (a plate of ordinary bacteria).

Scene 3: PCR: three temperatures, one purpose

95 degrees denatures and separates the strands, 55 degrees anneals the primers, 72 degrees extends with polymerase. After 30 cycles the target is amplified 2^30 = 1,073,741,824 fold.
PCR only amplifies; it does not alter the sequence and does not replace the other steps.
Warning: asked why heat is needed, answer that hydrogen bonds break to separate the strands, not that cells are killed.

Tutor move: three temperatures on a timeline, then one full cycle spoken aloud.

04 Question types and worked steps

Type	Example	Steps	Answer
Order	Arrange the stages	Cut, join, deliver, select	Name the tool at each stage
Explain	Why a stage is needed	Tool, action, consequence	Say what happens without it
Calculate	PCR fold increase or fragment length	Two to the power of the cycles	State the cycle count
Issue	Benefits and risks of GM food	Two points each with evidence	A stance alone is not enough

Sanity check (teach this): Every stage must answer: which tool, why, and what happens without it. Each extra PCR cycle doubles the product. An issue answer with a stance but no evidence earns half marks at most.

05 Independent practice (3 questions)

Question	Answer	What to watch
Fold increase after 30 PCR cycles	1,073,741,824 fold	Two to the power of cycles
Why the same enzyme for gene and vector	Identical sticky ends can join	Ends must be complementary
Why screening is needed	Most bacteria take up no plasmid	Marker gene separates them

06 Common mistakes and what to say

Mistake	Student writes	Say this
No screening	Process stops at insertion	“How do you know which bacterium worked? Screen them.”
Tools swapped	Ligase used to cut	“Scissors cut, tape joins. Never swap them.”
PCR as editing	Thinking PCR changes the gene	“PCR photocopies; it does not edit.”
Stance only	Just “GM food is harmful”	“Where is the evidence? Name one specific risk.”

07 Homework (paper, section and question numbers)

Genetic engineering flow (in-house) — Questions 1-3: order the stages and name the tools
PCR and issue question (in-house) — Questions 4-6: calculate the fold increase and argue both sides

08 Exit check (last 5 minutes)

Question	Answer	Decision
Fold increase after 30 cycles	1,073,741,824	Wrong: reteach powers of two
Which enzyme joins recombinant DNA	DNA ligase	Wrong: reteach the tools
Why screening is needed	Most bacteria take up no plasmid	Wrong: reteach marker genes

09 Tutor FAQ

Does a restriction enzyme cut the host DNA

It can, so a specific sequence is chosen and work is done in vitro.

Why does PCR need primers

They supply a free 3-prime end for the polymerase to start from.

Is GM food always harmful

Judge each case on evidence; state both risk and benefit.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.