Chapter 6: DNA and Biotechnology

Question 1

_____________ are composed of a five-carbon sugar (pentose) bonded to a nitrogenous base and are formed by covalently linking the base to C-1’ of the sugar.

Answer 1

Nucleosides

Question 2

_____________ are formed when one or more phosphate groups are attached to C-5’ of a nucleoside.

Answer 2

Nucleotides

Question 3

If the pentose is __________, the nucleic acid is RNA.

Answer 3

Ribose

Question 4

If the pentose is _______________ (ribose with the 2’ -OH group replaced by -H), then it is DNA.

Answer 4

Deoxyribose

Question 5

____________ contain 2 rings in their structures. The two found in nucleic acids are adenine (A) and guanine (G).

Answer 5

Purines

Question 6

______________ contain only one ring in their structure. The three are cytosine (C), thymine (T), and uracil (U).

Answer 6

Pyrimidines

Question 7

Because of the specific-base pairing, the amount of A equals the amount of T, and the amount of G equals the amount of C. Thus, total purines will be equal to total pyrimidines overall. These properties are known as _________________.

Answer 7

Chargaff’s rules

Question 9

The double helix of most DNA is a right-handed helix, forming what is called __________. The helix in __________ makes a turn every 3.4 nm and contains about 10 bases within that span. Major and minor grooves can be identified between the interlocking strands and are often the site of protein binding.

Answer 9

B-DNA

Question 10

Another form of DNA is called ____________ for its zigzag appearance; it is a left-handed helix that has a turn every 4.6 nm and contains 12 bases within each turn.

Answer 10

Z-DNA

Question 11

The DNA that makes up a chromosome is wound around a group of small basic proteins called histones, forming ______________.

Answer 11

Chromatin

Question 12

The histone proteins that form the histone core:
_________, __________, __________, __________.

Answer 12

• H2A
• H2B
• H3
• H4

Question 13

Two copies each of the histone proteins H2A, H2B, H3, and H4 form a histone core and about 200 base pairs of DNA are wrapped around this protein complex, forming a _______________.

Answer 13

Nucleosome

Question 14

Histones are one example of ________________ (proteins that associate with DNA).

Answer 14

Nucleoproteins

Question 15

A small percentage of chromatin remains compacted during interphase and is referred to as ________________. It appears dark under light microscopy and is transcriptionally silent.

Answer 15

Heterochromatin

Question 16

The dispersed chromatin is called _____________, which appears light under microscopy. It contains genetically active DNA.

Answer 16

Euchromatin

Question 17

______________ are a region of DNA found in the centre of chromosomes. They are often referred to as sites of constriction because they form noticeable indentations. This part of the chromosome is composed of heterochromatin, which is in turn composed of tandem repeat sequences that also contain high GC-content.

Answer 17

Centromeres

Question 18

The ___________ or _________________ is a set of specialized proteins that assist the DNA polymerases.

Answer 18

• Replisome
• Replication complex

Question 19

Proteins are required to hold the double stranded DNA strands apart: ________________________ will bind to the unraveled strand, preventing both the reassociation of the DNA strands and the degradation of DNA by nucleases.

Answer 19

Single-stranded DNA-binding proteins

Question 20

______________ is a wrapping of DNA on itself as its helical structure is pushed ever further toward the telomeres during replication; picture an old-fashioned telephone cord that’s become tangled on itself.

Answer 20

Supercoiling

Question 21

To alleviate the torsional stress from supercoiling and reduce the risk of strand breakage, ___________________ introduce negative supercoils.

Answer 21

DNA topoisomerase

Question 22

The _________________ works ahead of helices, nicking one or both strands, allowing relaxation of the torsional pressure, and then resealing the cut strands.

Answer 22

DNA topoisomerase

Question 23

The replication process is termed _________________ because one parental strand is retained in each of the two resulting identical double-stranded DNA molecules.

Answer 23

Semiconservative

Question 24

____________________ (prokaryotes) or ________________, _____, and ______ (eukaryotes) will then begin synthesizing the daughter strands of DNA in the 5’ tot 3’ manner.

Answer 24

• DNA polymerase III
• DNA polymerases alpha, delta, and epsilon

Question 25

The RNA primers must eventually be removed to remain integrity of the genome. This is accomplished by the enzyme ________________ (prokaryotes).

Answer 25

DNA polymerase I

Question 26

The RNA primers must eventually be removed to remain integrity of the genome. This is accomplished by the enzyme ________________ (eukaryotes).

Answer 26

RNase H

Question 27

The enzyme _______________ (prokaryotes) or ________________ (eukaryotes) then adds DNA nucleotides where the RNA primer had been.

Answer 27

- DNA polymerase I (prokaryotes) - DNA polymerase delta (eukaryotes)

Question 28

_____________ seals the ends of DNA molecules together, creating one continuous strand of DNA.

Answer 28

DNA ligase

Question 29

_______________ replicates mitochondrial DNA.

Answer 29

DNA polymerase gamma

Question 30

________________ and ______ are important the process of DNA repair.

Answer 30

DNA polymerase beta and epsilon

Question 31

________________ and _______ are assisted by the PCNA protein, which assembles into a trimer to form the sliding clamp.

Answer 31

DNA polymerase delta and epsilon

Question 32

The ______________ helps to strengthen the interaction between the DNA polymerase units and the template strand.

Answer 32

Sliding clamp

Question 33

To lengthen the time that cells can replicate and synthesize DNA before necessary genes are damaged, chromosomes contain _____________. They are located at the very tips of the chromosome and consist of repetitive sequences with a very high GC-content.

Answer 33

Telomeres

Question 34

Cancer cells are able to migrate by local invasion or _____________, a migration to distant tissues by the bloodstream or lymphatic system.

Answer 34

Metastasis

Question 35

Mutated genes that cause cancer are termed ______________.

Answer 35

Oncogenes

Question 36

Before oncogenes are mutated, they are often referred to as _______________.

Answer 36

Proto-oncogenes

Question 37

Tumour suppressor genes, like p53 or Rb (retinoblastoma), encode proteins that inhibit the cell cycle or participate in DNA repair processes. They normally function to stop tumour progression, and are sometimes called _______________.

Answer 37

Antioncogenes

Question 38

____________, which closes the gaps between Okazaki fragments, lack proofreading ability.

Answer 38

DNA ligase

Question 39

Cells also have machinery in the G2 phase of the cell cycle for ________________; these enzymes are encoded by genes MSH2 and MLH1, which detect and remove errors introduced in replication that were missed during the S phase of the cell cycle in eukaryotes.

Answer 39

Mismatch repair

Question 40

The MSH2 and MLH1 in mismatch repair are homologues of ________ and __________ in prokaryotes, which serve a similar function.

Answer 40

MutS and MutL

Question 41

Ultraviolet light induces the formation of __________ between the adjacent thymine residues in DNA.

Answer 41

Dimers

Question 42

Thymine dimers are eliminated from DNA by a ____________________ (______) mechanism, which is a cut-and-patch process.

Answer 42

Nucleotide excision repair (NER) mechanism

Question 43

An __________________ makes nicks in the phosphodiester backbone of the damaged strand on both sides of the thymine dimer and removes the defective oligonucleotide in NER mechanism.

Answer 43

Excision endonuclease

Question 44

Thermal energy can be absorbed by DNA and may lead to cytosine deamination. This is the loss of an amino group from cytosine and results in the conversion of cytosine to ___________ in a DNA molecule.

Answer 44

Uracil

Question 45

In base excision repair, the affected base is recognized and removed by a glycosylase enzyme, leaving behind an _______________ (______) site, also called an ___________ site.

Answer 45

- Apurinic/apyrimidinic (AP) site - Abasic site

Question 46

The AP site is recognized by an _________________ that removes the damaged sequence from the DNA.

Answer 46

AP endonuclease

Question 47

_______________ technology allows a DNA fragment from any source to be multiplied by either gene cloning for polymerase chain reaction (PCR).

Answer 47

Recombinant DNA

Question 48

_____________ is a technique that can produce large amounts of a desired sequence.

Answer 48

DNA cloning

Question 49

Cloning requires that the investigator ligate the DNA of interest into a piece of nucleic acid referred to as a vector, forming a ___________________.

Answer 49

Recombinant vector

Question 50

_________________ (__________________) are enzymes that recognize specific double-stranded DNA sequences. These sequences are palindromic, meaning that the 5' to 3' sequence of one strand is identical to the 5' to 3' sequence of the other strand (in antiparallel orientation).

Answer 50

Restriction enzymes (restriction endonuclease)

Question 51

_______________ are large collections of known DNA sequences; in sum, these sequences could equate to the genome of an organism.

Answer 51

DNA libraries

Question 52

_______________ contain large fragments of DNA, and include both coding (exon) and noncoding (intron) regions of the genome.

Answer 52

Genomic libraries

Question 53

_________ (__________________) libraries are constructed by reverse-transcribing processed mRNA.

Answer 53

cDNA (complementary DNA)

Question 54

___________ lacks noncoding regions, such as introns, and only includes the genes that are expressed in the tissue from which the mRNA was isolated. For that reason, these libraries are sometimes called _______________.

Answer 54

- cDNA - Expression libraries

Question 55

_________ library can be used for gene therapy or constructing transgenic animals.

Answer 55

cDNA (expression) library

Question 56

The preferred gel for DNA electrophoresis is ______________, and - just like proteins in polyacrylamide gel - the longer the DNA strand, the slower it will migrate in the gel.

Answer 56

Agarose gel

Question 57

A PCR reaction requires __________ that are complementary to the DNA that flanks the region of interest. The __________ has high GC content (40-60% is optimal), as the additional hydrogen bonds between G and C confer stability.

Answer 57

Primer

Question 58

In DNA sequencing, a modified base called a _________________ is added in lower concentrations. These include ddATP, ddCTP, ddGTP, and ddTTP that contain a hydrogen at C-3', rather than a hydroxyl group; once one of these modified bases has been incorporated, the polymerase can no longer add to the chain.

Answer 58

Dideoxyribonucleotide

Question 59

The DNA fragments in DNA sequencing can be separated by size using __________________.

Answer 59

Gel electrophoresis

Question 60

_____________ now offers potential cures for individuals with inherited diseases. It is intended for disease in which a given gene is mutated or inactive, giving rise to pathology. By transferring a normal copy of the gene into the affected tissues, the pathology should be fixed, essentially curing the individual.

Answer 60

Gene therapy

Question 61

_____________ mice are altered at their germ line by introducing a cloned gene into fertilized ova or into embryonic stem cells.

Answer 61

Transgenic mice

Question 62

The cloned gene that is introduced in transgenic mice is referred to as a ______________.

Answer 62

Transgene

Question 63

In _____________ mice, in which a gene has been intentionally deleted (knocked out) has similar approach as transgenic mice.

Answer 63

Knockout mice

Question 64

_____________ is evident if the two cell lineages (transgenic cells and host blastocyst) come from mice with different coat colours.

Answer 64

Chimera