DNA Replication

Question 1

What is cDNA?

Answer 1

DNA synthesised from single stranded RNA (e.g. mRNA or micro RNA) template in a reaction catalysed by the enzyme reverse transcriptase. cDNA is often used to clone eukaryotic genes in prokaryotes

Question 2

What is centrifugation?

Answer 2

A process that is used for the separation of fluids, gas or liquid based on density

Question 3

What is conservative replication?

Answer 3

A type of replication that results in one of the daughter molecules containing all the parent DNA and the other daughter molecule containing none of it

Question 4

What is dispersive replication?

Answer 4

A type of replication that results in all off the daughter molecules having segments of DNA from their parent and the rest is new DNA

Question 5

What is DNA cloning?

Answer 5

(1) the act of making may identical copies of a DNA molecule - the amplification of a particular DNA sequence. (2) also, the isolation of a particular stretch of DNA from the rest of the cells genome

Question 6

What is a DNA library?

Answer 6

Collection of cloned DNA molecules representing either an entire genome (genomic library) or complementary DNA copies of the mRNA produced by a cell (cDNA library)

Question 7

What is DNA polymerase?

Answer 7

An enzyme that synthesises DNA by joining nucleotides together using a DNA template as a guide

Question 8

What is gel electrophoresis?

Answer 8

A laboratory method used to seperate mixtures of DNA, RNA, or proteins according to molecular size

Question 9

What is a genomic library?

Answer 9

Collect of cloned DNA molecules representing an entire genome

Question 10

What is helicase?

Answer 10

A type of enzyme that separates double-stranded DNA into single strands allowing each strand to be copied

Question 11

What is hybridisation?

Answer 11

The process whereby two complementary nucleic acid strands forms a base paired duplex DNA-DNA, DNA-RNA, or RNA-RNA molecule. Forms the basis of a powerful technique for detecting specific nucleotide sequences

Question 12

What is ligase?

Answer 12

A specific type of enzyme that facilitates the joining of DNA strands together by catalysing the formation of a phosphodiester bond

Question 13

What is a plasmid vector?

Answer 13

Small, circular molecules of double stranded DNA derived from plasmids that occur naturally in bacterial cells; widely used for gene cloning

Question 14

What is a poly a tail?

Answer 14

A stretch of RNA that has only adenine bases

Question 15

What is polymerase chain reaction?

Answer 15

Technique for amplifying specific regions of DNA by the user sequence specific primers and multiple cycles of DNA synthesis, each cycle being followed by a brief heat treatment to separate complementary strands

Question 16

What is primase?

Answer 16

An enzyme that synthesises a short strand of RNA on a DNA template, producing a primer for DNA synthesis

Question 17

What is a primer?

Answer 17

A short strand of RNA that serves as a starting point for DNA synthesis

Question 18

What is recombinant DNA technology?

Answer 18

Collection of techniques by which DNA segments from different sources are combined to make new DNA, often called recombinant DNA. Recombinant DNAs are widely used in the cloning of genes, in the genetic modification of organisms, and in the production of large amounts of rare proteins

Question 19

What is replication cell senescence?

Answer 19

Phenomenon observed in primary cell cultures in which cell proliferation slows down and irreversibly halts

Question 20

What are restriction nucleases?

Answer 20

One of the large number of nucleases that can cleave a DNA molecule at any site where a specific short sequence of nucleotides occurs. Extensively used in recombinant DNA technology

Question 21

What is semi-conservative replication?

Answer 21

A type of replication that results in both daughter molecules having a parent strand of DNA and a new strand. DNA synthesis is semi-conservative

Question 22

What is shelterin?

Answer 22

A protein complex known to protect telomeres in many eukaryotes from DNA repair mechanisms, as well as regulate telomerase activity

Question 23

What are single-stand binding proteins?

Answer 23

A protein that binds to the single strands of the opened up DNA helix, preventing helical structures from reforming while the DNA is being replicated

Question 24

What are somatic cells?

Answer 24

Any cell of a plant or animal other than the cells of the germ line

Question 25

What is strand-directly mismatch repair?

Answer 25

A proofreading system that removes DNA replication errors missed by the DNA polymerase proofreading exonuclease. It detects the potential for DNA helix distortion from noncomplememtary base pairs the recognises the excises the mismatch in the newly synthesised strand and resynthesises the excised segment using the old strand as a template

Question 26

What is taq polymerase?

Answer 26

An enzyme found in the bacillus Thermus aquaticus, which lives in hot springs; it is heat resistant and thus can endure the high temperatures of the polymerase chain reaction

Question 27

What are tautomeric forms?

Answer 27

Constitutional isomers of the main forms of nucleotides that may cause mistakes in base pairing

Question 28

What is telomerase?

Answer 28

Enzyme that elongates telomere sequences in DNA, which occurs at the ends of eukaryotic chromosomes

Question 29

What is a telomere?

Answer 29

End of a chromosome, associated with a characteristic DNA sequence that is replicated in a special way. Counteracts the tendency of the chromosome to otherwise shorter. With each round of replication

Question 30

How many origins of replications occur in prokaryotes?

Answer 30

One

Question 31

How many origins of replication occur in eukaryotes?

Answer 31

Multiple

Question 32

What enzyme opens up the DNA?

Answer 32

Helicase

Question 33

What is responsible for stabilising unwound DNA?

Answer 33

Single-strand binding protein

Question 34

Which enzyme is responsible for adding nucleotides to the growing polynucleotide chain? What direction does it synthesise in?

Answer 34

DNA polymerase | 5' to 3'

Question 35

How do enzymes know where to start replicating the DNA?

Answer 35

The replication sites have short sequences to attract the initiator proteins and stretches of DNA that are easy to open

Question 36

Is eukaryotic or prokaryotic replication quicker?

Answer 36

Prokaryotic

Question 37

Replication requires RNA primers, what enzyme(s) add these primers to the DNA?

Answer 37

DNA primase

Question 38

How are old primers removed from the DNA?

Answer 38

They are erased by a combined action of DNA polymerase and RNase H

Question 39

What does the clamp loader do?

Answer 39

Holds the DNA polymerase onto the DNA as it moves

Question 40

Which enzyme is responsible for relieving helical winding?

Answer 40

DNA topoisomerases

Question 41

How often does a mistake occur in DNA replication?

Answer 41

1 in a billion

Question 42

In the rare tautomeric form, what base can C pair with?

Answer 42

A instead of G

Question 43

After covalent binding, what is the next error correcting reaction?

Answer 43

Exonucleolytic proofreading by DNA polymerase in the 3' to 5' direction

Question 44

How does exonucleolytic prrofreading work?

Answer 44

Correct nucleotide pairing has a higher affinity for polymerase. If an incorrect pairing occurs, the polymerase chews back to create a base-paired 3' -OH end on the primer strand. It then continues the process of adding nucleotides correctly

Question 45

What would happen if the strand-directed mismatch repair system was not able to differentiate between the new strand and old strand?

Answer 45

It would correct the wrong nucleotide 50% of the time

Question 46

What allows the strand-directed mismatch repair system to differentiate between the new strand an the old strand?

Answer 46

Newly synthesised lagging-strand DNA transiently contains nicks (that haven't yet been sealed by DNA ligase) and such nicks provide the signal that directs the mismatchprrofreading to the appropriate strand

Question 47

What enzyme adds telomere sequences to the end of chromosomes?

Answer 47

Telomerase

Question 48

What is the proteins that form a protective chromosome cap called?

Answer 48

Shelterin

Question 49

What does shelterin do?

Answer 49

Shelterin hides telomeres from the cell's damage detectors that continually monitor DNA

Question 50

What happens when there is no telomere sequence left?

Answer 50

The cell enters replicative cell senescence, withdrawing them permanently from the cell cycle and preventing them from dividing