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IB BIOLOGY > D1.1 DNA Replication > Flashcards

D1.1 DNA Replication Flashcards

1
Q

DNA replication is?

A

DNA replication is the production of exact copies of DNA with identical base sequences

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2
Q

what are the purposes of DNA replication?

A
  1. Cell division
  • new cells need new DNA for growth and tissues repair
  1. Reproduction
  • gametes require DNA to pass on genetic information
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3
Q

What does “semi-conservative” mean in DNA replication? + give general overview of how the process works

A

“Semi-conservative” refers to the process of DNA replication where each new DNA molecule consists of one original (parent) strand and one newly synthesized strand.

IN SEMI-CONSERVATIVE REPLICATION:

  • One strand of the ‘parent’ DNA is kept in the ‘daughter’ molecule. This is called the template strand
  • Other half = determined by the code on the template strand and is built up from free nucleotides (this takes place in the nucleus)

–> during this, nucleotides are added one by one to the new strand according to the rules of complementary base-pairing

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4
Q

How does semi-conservative replication work? (5 specific steps)

A
  1. hydrogen bonds between the nitrogenous bases are broken
  2. free nucleotides are present in the nucleus
  3. free nucleotides pair up with complementary exposed bases
  4. the new strand is linked together
  5. there are now two DNA molecules. each one contains one old strand and one new one
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5
Q

During semi-conservative replication, when are hydrogen bonds formed?

A

Hydrogen bonds are formed during the pairing of nucleotides between the template strand and the newly synthesized strand

(they can only form when the correct bases are paired up)

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6
Q

the output of semi-conservative replication?

A

The new DNA molecule has kept half of the parent DNA and then used this to create a new, daughter strand

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7
Q

what is the role of complementary base pairing in DNA replication?

A

It ensures that DNA is copied accurately.

The specific pairing of bases on the two strands ensures that the new strand is an exact copy of the original.

(otherwise, you’d have a mutation ㅠㅠ)

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8
Q

the only correct method of DNA replication is?

A

a semi-conservative method!

there were other ideas throughout history, but they’re not correct

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9
Q

why must DNA strands be separated prior to replication?

A

The DNA strands must be separated before replication so they can act as templates for making new DNA strands

The two strands of the DNA double helix are held together by their base pairs, making the molecule stable under normal conditions. SO, to replicate, enzymes break these hydrogen bonds and separate the strands

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10
Q

what is the role of helicase in DNA replication?

A

it unwinds and unzips the DNA by breaking the hydrogen bonds between bases

it unwinds the double-stranded DNA at the replication fork

(This process is essential for allowing the DNA polymerase to read the template strands and synthesize the new DNA strands)

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11
Q

what is created via semi conservative replication?

A

semi-conservative replication creates two double-helix DNA molecules, each containing one original (parent) strand and one newly synthesized (daughter) strand.

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12
Q

DNA replication is? (replisome)

A

a multi-stage process that is carried out by an assemblage of functional subunits called a replisome

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13
Q

what is DNA polymerase?

A

a type of protein that is an essential part of replisomes

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14
Q

what is the role of DNA polymerases in DNA replication? (+ 3 steps of its job)

A
  • It assembles new strands of DNA, using the two original strands as templates
  1. The DNA polymerases move along the template strands, adding one nucleotide at a time
  2. DNA polymerase ensures the correct nucleotide is added to the new strand by matching it with the complementary base on the template strand
  3. Once the correct nucleotide pairs and hydrogen bonds form, DNA polymerase links it to the new strand by creating a covalent bond between the phosphate of the free nucleotide and the sugar of the last nucleotide in the strand
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15
Q

there are ___ DNA polymerases for each strand of _____ in the ___

A

there are separate DNA polymerases for each strand of template DNA in the replisome

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16
Q

what is the PCR? what is its function?

A

PCR = polymerase chain reaction

  • it is an automated method of DNA replication
  • PCR machines follow a cycle of steps repeatedly, doubling the quantity of DNA with each cycle
  • Only a very small quantity of DNA is required at the start (in theory, a single molecule)
  • The steps in a PCR cycle are triggered by changes of temperature, so a PCR machine is known as a thermal cycler or thermocycler
17
Q

outline the process of the PCR, including the use of primers, temperature changes, and Taq polymerase

A
18
Q

how would you deduce the number and relative size of DNA fragments from the number of bands in an electrophoresis gel?

A

TO FIND NUMBER OF FRAGMENTS:

  • Number of Bands = Number of DNA Fragments (each band represents a separate DNA fragment)
  • Smaller fragments travel further and faster
  • Larger fragments travel shorter distances and move slower

TO FIND RELATIVE SIZE:

  1. USE A DNA LADDER
  • Compare your bands to the known size markers in the ladder ( top band = larger fragment, bottom band = smaller fragment)
  1. ESTIMATE EXACT SIZE:
  • Use a standard curve based on the ladder to estimate the size of your fragments based on migration distance
19
Q

what is DNA electrophoresis? why do we do it?

A
  • DNA electrophoresis = a technique using an electric current to separate DNA strands based on their size and amount of charge
  • we do it because: sometimes, scientists need to know more about an individual’s DNA than can be seen in a karyotype, but determining the sequence of the entire genome would be excessive (so they identify the alleles at a few loci via electrophoresis)

Samples taken from different sources can be compared and used for forensic analysis = another reason why it is done

20
Q

outline the procedure for DNA electrophoresis (8 step process)

A
  1. Prepare the Gel: Use a gel sheet (3-4 mm thick) with rectangular holes (wells) near one end.
  2. Set Up the Tank: Place the gel in a shallow tank with electrodes at both ends.
  3. Add Electrolyte Solution: Pour an electrolyte solution to cover the gel.
  4. Load DNA Samples: Pipette DNA samples into the wells.
  5. Apply Voltage: Apply an electric current across the electrodes to create an electric field.
  6. DNA Migration Happens: DNA molecules, being negatively charged, move towards the positive anode.
  7. Visualize the Bands: After sufficient time, switch off the voltage, remove the gel, and stain it with dye to make DNA visible.
  8. Use a Ladder: Use a DNA ladder in the right lane to estimate fragment sizes based on their migration distance.
21
Q

How and why do DNA fragments separate during electrophoresis? What is the result of electrophoresis?

A

WHY?

  • DNA’s Negative Charge: DNA molecules are negatively charged due to phosphate groups in the sugar-phosphate backbone.

HOW?

  • Electric Field: When an electric field is applied, DNA moves towards the positive anode.
  • Size-Based Separation: The gel’s mesh resists the movement of molecules; smaller DNA fragments move faster and further than larger ones
    &
  • Fragment Separation: This difference in speed results in the separation of DNA fragments based on their size (smaller fragments travel further)

RESULT?

DNA fragments of the same size form bands at the same position along the gel

22
Q

List applications of the PCR (5)

A
  • Testing for viral infections (ex. coronavirus)
  • Paternity testing (using PCR to amplify specific regions for comparison)
  • Detection of genetic mutations or inherited disorders
  • Gene cloning to produce copies of specific genes
  • DNA fingerprinting for criminal investigations or ancestry testing
23
Q

Outline the use of the PCR in testing for viral infection (5 steps)

A
  1. Sample Collection: A swab is taken from the nose or throat, and viral RNA is rinsed off into a saline solution.
  2. RNA to DNA Conversion: The enzyme reverse transcriptase converts the viral RNA into complementary DNA (cDNA).
  3. PCR Amplification: PCR amplifies specific viral DNA sequences that act as markers for the virus strain being tested.

4 Fluorescent Markers: Fluorescent markers are attached to the DNA as it is amplified.

  1. Result Monitoring: Fluorescence is monitored during PCR, and if it reaches a target level, the test result is positive for the virus.
24
Q

Discuss advantages and disadvantages of using the PCR test for viral infections

A

Advantages:

  • High sensitivity: Detects even minuscule amounts of viral RNA
  • Specificity: Primers can be designed to detect only specific virus strains

Disadvantages:

  • Expensive: Requires specialized materials and equipment, often only available in labs
  • Time-consuming: Thermal cycling takes time, so results aren’t immediately available
25
Q

Outline the process of DNA profiling (5 steps)

A
  1. Sample Collection: DNA is obtained from an individual or an unknown source
  2. PCR Amplification: Specific tandem repeats are selected and copied using PCR (at least 13 different repeats)
  3. Gel Electrophoresis: The DNA fragments are separated by size based on the number of repeats in the sequences
  4. Band Pattern: A unique pattern of DNA bands is created, forming an individual’s DNA profile
  5. Analysis: The DNA profile is analyzed for comparison (ex. in paternity testing)
26
Q

List applications of DNA profiling (4)

A
  • Paternity testing to confirm biological relationships
  • Forensic investigations for identifying suspects or victims in criminal cases
  • Identification of human remains (in disaster scenarios)
  • Genetic research for studying inheritance patterns and genetic disorders
27
Q

why are the applications of DNA profiling and PCR so similar?

A

Because DNA profiling is the end result of using techniques like PCR!

28
Q

Analyze a DNA profile to determine relatedness or forensic guilt

A

For Relatedness:

  • Compare the DNA profiles of the child, mother, and potential father
  • Bands in the child’s profile that are not present in the mother’s or potential father’s profile suggest that the potential father is not the biological father

Children inherit bands from both parents, so a matching band pattern indicates biological relationship

For Forensic Guilt:

  • Compare the DNA profile of a suspect to DNA found at a crime scene
  • If the bands match, the suspect may be linked to the crime scene
29
Q

List example sources of DNA that can be used in DNA profiling (5)

A
  1. Blood
  2. Saliva
  3. Hair
  4. Skin cells
  5. Urine

IB BIOLOGY (11 decks)

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