Untitled Flashcards Set

D1.1 DNA Replication

Theme: Continuity and Change

First Exams 2025

Level of Organisation: Molecules

SL and HL

Combined Content

IB Guiding Questions

How is new DNA produced?

How has knowledge of DNA replication enabled

applications in biotechnology?

SL and HL Content

SL & HL Content:

D1.1: DNA Replication

SL and HL Content

D1.1.1:

DNA replication as production of exact copies of DNA with

identical base sequences

D1.1.2:

Semi-conservative nature of DNA replication and role of

complementary base pairing

D1.1.3: Role of helicase and DNA polymerase in DNA replication

D1.1.4: Polymerase chain reaction and gel electrophoresis as tools for

amplifying and separating DNA

SL & HL Content:

D1.1: DNA Replication

D1.1.5:

Applications of polymerase chain reaction and gel

electrophoresis

SL and HL Content

Note: The sequence of subtopics have been changed for the SL section

of this topic, to improve clarity.

SL & HL Key Terms

SL and HL Content

DNA

Nucleotide

DNA Replication

Helicase

DNA Polymerase

Complementary Base Pairs

Semi-Conservative

Polymerase Chain Reaction (PCR)

Primers

Taq DNA Polymerase

Denaturation

Annealing

Gel Electrophoresis

DNA Profile

Restriction Endonuclease

DNA Markers

Diagram of DNA

Draw a labelled diagram of DNA

Structure of DNA

Deoxyribonucleic acid (DNA) contains

the genetic information for the

development and growth of cells and

multicellular organisms.

You may want to review your notes from

Topic A1.2 Nucleic Acids

Labelled Diagram of DNA

Phosphate

Hydrogen Bonds

Deoxyribose

Covalent

Bond

Nucleotide

Nitrogen Base

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D1.1.1: DNA replication as production of exact

copies of DNA with identical base sequences

Students should appreciate that DNA replication is required for

reproduction and for growth and tissue replacement in multicellular

organisms.

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DNA Replication

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DNA replication is the production of identical copies of

DNA.

DNA Replication

The new copies of DNA will have identical nucleotide

sequences to each other and to the original DNA molecule.

DNA replication is carried out in the cell before mitosis and

meiosis in eukaryotic cells.

DNA replication before mitosis is required for growth and

tissue replacement in multicellular organisms.

DNA replication before meiosis is required for

reproduction.

Limit to the role of helicase in unwinding and breaking hydrogen bonds

between DNA strands and the general role of DNA polymerase.

D1.1.3: Role of helicase and DNA polymerase in

DNA replication

SL and HL Content

DNA Replication

SL and HL Content

Enzymes are

involved in the

process of DNA

replication.

Explain DNA

replication,

highlighting the

roles of the

enzymes

helicase and

DNA

polymerase.

Helicase

The enzyme helicase

unwinds the DNA double

helix by breaking the

hydrogen bonds between

complementary nucleotides.

Helicase unzips the DNA Double Helix

The two separated strands

will act as templates to

produce new strands of DNA.

DNA Polymerase

DNA polymerase moves

along each strand of DNA

linking nucleotides to

form a growing chain of

nucleotides using the

pre-existing strand as a

template.

DNA polymerase catalyzes the formation of a new strand of DNA

The complementary base

pairs are:

Adenine – Thymine

Guanine – Cytosine

DNA Polymerase

The complementary

bases are held together

by hydrogen bonds.

DNA polymerase catalyzes the formation of a new strand of DNA

DNA replication produces

two identical strands of

DNA.

Each strand will have one

strand from the original

DNA and one new strand.

D1.1.2: Semi-conservative nature of DNA

replication and role of complementary base

pairing

Students should understand how these processes allow a high degree of

accuracy in copying base sequences.

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DNA Replication is Semi-Conservative

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DNA replication is a

semi-conservative process as

new DNA molecules have one

parent strand and one newly

synthesized strand.

DNA Replication is Semi-Conservative

DNA replication is

semi-conservative and highly

accurate due to complementary

base pairing.

Students should understand the use of primers, temperature changes

and Taq polymerase in the polymerase chain reaction (PCR) and the

basis of separation of DNA fragments in gel electrophoresis.

D1.1.4: Polymerase chain reaction and gel

electrophoresis as tools for amplifying and

separating DNA

SL and HL Content

Polymerase Chain Reaction

The polymerase

chain reaction (PCR)

is a method for

amplifying (making

many copies of) a

DNA sequence from

a small sample.

Explain how the

polymerase chain

reaction amplifies

a DNA sequence.

Polymerase Chain Reaction

The polymerase chain reaction uses cycles of heating and cooling to

amplify a sample of DNA.

Cycles of the Polymerase Chain Reaction (PCR)

Polymerase Chain Reaction

The Polymerase Chain Reaction (PCR) allows scientists to amplify

(produce many copies of) the DNA.

The following materials are required:

DNA to be amplified

Buffer solution, which allows the reactions to occur

Primer to attach to the DNA to be copied

Taq DNA Polymerase - this attaches to the primer and creates a

new strand of DNA nucleotides by complementary base pairing.

DNA nucleotides - these will be linked by Taq DNA polymerase to

create a new strand of DNA.

Polymerase Chain Reaction

The steps of the polymerase chain reaction include:

Denaturation: The DNA sample is heated to 95°C to break hydrogen

bonds and separate the two DNA strands.

Annealing: Temperature is reduced to 54°C which allows DNA

primers to bind to both strands of DNA, next to the sequence to be

copied.

The temperature is increased to 72°C which allows Taq DNA

polymerase to replicate both strands, starting at the primer. This

produces two identical double-stranded DNA molecules. Both of

these are exact copies of the original DNA molecule.

Steps #1 - #3 are repeated many times to produce many copies of the

DNA.

Taq DNA Polymerase

Taq DNA polymerase is obtained from a

bacterium (Thermus aquaticus) which is

adapted to living in hot springs, so the

enzyme is not denatured at the

temperatures involved in the PCR process.

Thermus aquaticus survives in hot springs

Explain why human DNA polymerase is

not used for PCR.

The PCR process uses high temperatures. These temperatures would

denature human proteins, including DNA polymerase. If DNA polymerase is

denatured it will not catalyse the reactions to produce new strands of DNA.

Electrophoresis

Gel electrophoresis

is a technique used

to separate charged

molecules like DNA

or proteins.

Gel electrophoresis

can be used to

produce DNA

profiles, which are

commonly referred

to as DNA

fingerprints.

Gel Electrophoresis of DNA

DNA is an acid, and dissociates to

become negatively charged in water.

Restriction endonuclease enzymes cut

DNA into many negatively charged

fragments.

The DNA fragments move from the

negative electrode to the positive

electrode in an electrophoresis chamber.

Complete the online gel electrophoresis

activity.

DNA fragments move towards the positive electrode

DNA Profiles

A DNA profile is a pattern created from

an individual's DNA fragments, using gel

electrophoresis.

DNA profiles for an individual are unique,

and they are used in forensic science and

paternity testing.

DNA Profiles

Explain how gel electrophoresis can be

used to produce a DNA Profile.

Electrophoresis and DNA Profiles

A sample of DNA is obtained and amplified using PCR.

DNA sample is cut into fragments using restriction endonucleases.

The DNA is inserted into wells in agar gel which is in a salt solution.

Electricity is run through the salt solution.

The (negatively charged) DNA fragments move towards the positive

electrode.

Small (lighter) fragments move faster than bigger (heavier) fragments.

When a dye is added, a pattern becomes visible. The pattern is the DNA

profile.

Students should appreciate the broad range of applications, including

DNA profiling for paternity and forensic investigations.

Nature of Science: Reliability is enhanced by increasing the number of

measurements in an experiment or test.

In DNA profiling, increasing the number of markers used reduces the

probability of a false match.

D1.1.5: Applications of polymerase chain

reaction and gel electrophoresis

SL and HL Content

Applications of PCR and Gel Electrophoresis

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There is a broad range of uses for the polymerase chain reaction and gel

electrophoresis.

Two common uses include:

Forensic investigations: DNA from crime scenes can be processed

to produce a DNA profile. The crime scene DNA profile can be

compared to DNA profiles from individuals suspected of

committing the crime.

Paternity testing: A child shares half of its DNA with each parent.

The bands in the child’s DNA profile will match either the mother

or father. It is possible to determine if a man is the child’s father

using DNA profiles from the mother, suspected father and child.

Jimmy’s Lollipop - Solve a Crime

Complete the online activity to determine who stole Jimmy’s lollipop.

Identify the person who stole Jimmy’s lollipop.

DNA Profiles and Crime Scenes

All of the bands on a DNA

profile of a suspect, and a

profile from a crime scene, have

to match to identify the suspect.

Identify the suspect who was

at the crime scene.

Suspect 2 was at the crime

scene.

DNA Profiles and Paternity

DNA Profiles can be used to determine

paternity (and maternity, although

usually the mother is known).

The bands in the DNA profile of the

child must appear in either the

mother’s or father’s DNA profile.

If all of the bands on the child’s profile

match either the mother or father,

then they are both the parents.

Paternity Testing using DNA profiles

Increasing Reliability of DNA Profiles

Nature of Science:

It is important that DNA profiles correctly match suspects with a crime.

It is important that DNA profiles produce reliable results, and do not

provide a false match.

DNA markers are sections of DNA used to create a DNA profile.

Scientists can increase the reliability of DNA profiles by increasing the

number of markers.

Review and Discuss: SL & HL Key Terms

SL and HL Content

DNA

Nucleotide

DNA Replication

Helicase

DNA Polymerase

Complementary Base Pairs

Semi-Conservative

Polymerase Chain Reaction (PCR)

Primers

Taq DNA Polymerase

Denaturation

Annealing

Gel Electrophoresis

DNA Profile

Restriction Endonuclease

DNA Markers