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Biology > D1.1: DNA Replication > Flashcards

D1.1: DNA Replication Flashcards

1
Q

State what DNA replication is

A

The production of exact copies of DNA with identical base sequences.

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2
Q

Outline the purposes of DNA replication.​

A
  • to provide a complete copy of the organism’s DNA so that the organism grows from a fertilised egg cell to a large multicellular organism
  • repairing damaged tissues
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3
Q

Describe the meaning of “semi conservative” in relation to DNA replication.

A

the products of DNA replication each contain one of the original DNA strands and one new strand

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4
Q

Explain the role of complementary base pairing in DNA replication.

A

The complimentary base pairing rule ensures the new strands built are exact copies of the original & genetic code remains intact between generations
- A binds with T
- C binds with G

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5
Q

State why DNA strands must be separated prior to replication.

A
  • each strand of the original DNA molecule acts as a template for the new DNA strands that are being built
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6
Q

Outline the role of helicase in DNA replication.

A

Helicase is an enzyme attaching to DNA
- It moves along the molecule unwinding the DNA helix and separating the 2 strands by breaking H bonds betw. the bases

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7
Q

Outline the role of DNA polymerases in DNA replication.

A
  • DNA Polymerase III moves along template strand from 3’ to 5’ and assembles new strands of DNA in the 5’ to 3’ direction. Replicates continuously on the leading strand, replicates lagging strand discontinuously.
  • DNA Polymerase I removes RNA nucleotides of the RNA primers and replaces them with the correct DNA nucleotides
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8
Q

State the arrangement of DNA polymerase and template DNA for each strand

A

There are separate DNA polymerases for each stand of template DNA.

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9
Q

State the function of the PCR.

A

Amplifies a specific DNA sequence, producing multiple copies of it

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10
Q

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

A

denaturation phase;
- DNA heated at around 98*C to break the H bonds that hold the 2 strands of the double helix tgt

annealing phase (cooling);
- The sample cools at around 60*C and the short RNA primer sequences bond to complementary sequences in the DNA sample.

extension phase;
- The bonding of RNA primers allows Taq Polymerase to replicate DNA using the RNA primer was a starting point at around 72*C; the DNA polymerases are only able yo extend existing strands and not able to add the first nucleotide of a DNA strand. DNA strands are heated and the process repeats

Process is repeated and the region of interest is amplified exponentially

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11
Q

Deduce the number and relative size of DNA fragments from the number of bands in an electrophoresis gel.

A

250 to 30k base pairs

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12
Q

Outline the procedure for DNA electrophoresis.

A
  • Gel electrophoresis uses electrical currents to move molecules through a gel
  • DNA separated by size and amount of charge
  • DNA fragments get digested using restriction endonuclease enzymes which cut the backbone of DNA double helix making shorter DNA segments
  • samples of DNA fragments loaded into wells on one end of the gel which is submerged in a buffer solution
  • DNA samples begin near negative pole so that they can spread out as they are drawn towards positive pole because PO4 3- group of DNA is negatively charged
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13
Q

Describe how and why DNA fragments separate during electrophoresis.​ ​

A
  • samples of DNA fragments loaded into wells on one end of the gel which is submerged in a buffer solution
  • DNA samples begin near negative pole so that they can spread out as they are drawn towards positive pole
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14
Q

List applications of the PCR.

A
  • DNA profiling
  • Cloning of genes
  • Identification of bodies
  • To sequence the DNA of extincr species and other life forms
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15
Q

Outline the use of the PCR in testing for viral infection.

A

pk

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16
Q

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

A

advantages:
- pk
- pk

disadvantages:
- pk
- pk

17
Q

Outline the process of DNA profiling.

A
  • There are short repeated DNA sequences called tandem repeats
  • Amplification with PCR
  • The resulting mix of DNA fragments gets separated using gel electrophoresis
18
Q

List applications of DNA profiling.

A

Unique patterns of bands can be used:

  • in forensics, can compare the pattern from a crime scene to patterns of victims/suspects
  • in paternity testing, pattern of an individual is compared with patterns of possible parents
19
Q

Analyze a DNA profile to determine relatedness or forensic guilt.

A

sharing of a unique feature

20
Q

List example sources of DNA that can be used in DNA profiling.​

A
  • residue on a doorknob
  • a drinking glass
  • a piece of clothing
21
Q

Identify the 5’ ends and 3’ ends of a strand of DNA.

A
  • 5’ end is the line connecting deoxyribose sugar and phosphate group
  • 3’ is counted clockwise from O at top of deoxyribose
22
Q

Describe the formation of the covalent bond between adjacent nucleotides during DNA replication.

A
  • These phosphodiester bonds occur between the phosphate group attached to the 5ʹ carbon of the deoxyribose of one nucleotide and the hydroxyl group on the 3ʹ carbon of deoxyribose on the next nucleotide
23
Q

State what DNA polymerases can only add to an existing DNA strand.

A

DNA polymerases can only add free nucleotides to an existing DNA strand.

24
Q

State what DNA polymerases can only add the 5’ phosphate of a free nucleotide to of the elongating strand.

A

DNA polymerases can only add the 5’ phosphate of a free nucleotide to the 3’ deoxyribose of the elongating strand.

25
Q

Explain why replication is different on the leading and lagging strands of DNA.

A

Leading Strand:
- DNA Polymerase III moves along template strand in 3’ to 5’ direction and new strand is synthesised continuously in 5’ to 3’ direction

Lagging Strand:
- DNA Polymerase III moves along template strand in 3’ to 5’ direction and new strand is synthesised discontinuously in 5’ to 3’ direction hence, creating Okazaki fragments which are short fragments of DNA.
- Ligase joins Okazaki fragments together by catalysing the formation of a phosphodiester bond

26
Q

Compare the pace and direction of replication on the leading and lagging strands of DNA.

A

Leading strands of DNA (similar to the sense strand as it mirrors the sequence of the RNA produced) :
- faster pace
- Direction of replication is 5’ to 3’

Lagging strands of DNA (similar to the antisense strand as it serves as a template for building a new strand):
- slower pace
- Direction of replication is 5’ to 3’

27
Q

Outline the formation of Okazaki fragments on the lagging strand.

A
  • discontinuous replication occurs on the lagging strand
  • DNA polymerase replicates the new strand in sections having to repeatedly move further along the strand to continue replicating it
  • These sections of newly formed but short and disconnected DNA are Okazaki fragments that are joined on the lagging strand by DNA Ligase
28
Q

Explain the need for RNA primers in DNA replication.

A

RNA primers allow DNA Polymerase to attach and begin assembling the free nucleotides into a new strand of DNA - without the RNA primers, DNA polymerase is unable to attach to the DNA strand properly

29
Q

Compare the number of RNA primers on the leading and lagging strands.

A
  • a single RNA primer is required on the leading strand as replication is continuous
  • primers need to be placed at regular intervals on the lagging strand to allow DNA polymerase to attach at multiple points necessary for discontinuous replication that occurs on this strand
30
Q

Outline the function of the enzyme DNA primase.

A

Attaches RNA primers made of RNA nucleotides to the template strand

  • This allows DNA polymerase to attach and begin assembling the free nucleotides into a new strand of DNA
31
Q

Outline the function of the enzyme DNA polymerase III.

A
  • Assembles new strands of DNA by placing free nucleotides in the correct sequence according to the base sequence of the template strand and the complementary base pairing rule
  • Replicates continuously on leading strand but must replicate lagging strand discontinuously meaning it must replicate the strands in short sections called Okazaki fragments
32
Q

Outline the function of the enzyme DNA polymerase I.

A

Removes RNA nucleotides of the RNA primers and replaces them with the correct DNA nucleotides

33
Q

Explain why there are gaps between adjacent Okazaki fragments on the lagging strand.

A
  • Discontinuous replication that occurs in the lagging strand as DNA polymerase III can only add nucleotides in the 5’ to 3’ direction
34
Q

Outline the function of the enzyme DNA ligase.

A

Catalyses the formation of the phosphodiester bonds between the Okazaki fragments. This makes the replicated strand built using the lagging strand into a single strand that can function normally.

35
Q

State the function of DNA proofreading.

A

corrects errors during replication.

36
Q

Outline the process of DNA proofreading by DNA polymerase III.

A
  • DNA PIII adds an incorrect nucleotide whilst building the new strand of DNA (due to mispairing)
  • DNA PIII identifies the error of the mismatched base at the 3’ end of the mismatched strand
  • DNA PIII splits phosphodiester bond between mismatched nucleotide
  • DNA PIII removes incorrect nucleotide
  • DNA PIII adds correct nucleotide

Biology (20 decks)

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