Chapter 2-Nucleic Acids

Question 1

Define purines

Answer 1

9-member double ring with 4N and 5C

- adenine and guanine

Question 2

Define pyrimidines

Answer 2

6 member ring with 2N and 4C

- cytosine, thymine, uracil

Question 3

How many nucleotides to make a complete turn of dna double helix?

Answer 3

10 nucleotids, 3.4nm (34 angstroms)

Question 4

What is the diameter of DNA double helix?

Answer 4

1nm

Question 5

Significance of DNA supercoiling (2)

Answer 5

1. Compaction of DNA in nucleus

2. Easier strand separation for replication and transcription

Question 6

List the types of coiled dna in increasing order in terms of distance travelled during agarose gel electrophoresis.

Answer 6

Nicked, linear, supercoiled, circular and ss

Question 7

Describe the hairpin loop of RNA

Answer 7

2 regions of the same strand that are complementary in nucleotide sequence base pair to form a helix but ends in an unpaired stem/loop

Question 8

Name 5 secondary structures of RNA

Answer 8

1. Helix
2. Hairpin Loop
3. Bulge loop
4. Interior loop
5. Multi-branched loop

Question 9

Describe what is a tRNA

Answer 9

• associated with 1 aa and carries a specific anticodon which will pair with codon sequence of mRNA in protein synthesis (translation)
• has an anticodon region that can base pair with the codon region on mRNA
• small chain of around 80 nucleotides
• 5 arms; 3 arms are hairpin loops, 1 arm is bulge loop

Question 10

Describe micro RNA (miRNA)

Answer 10

• class of cellular RNAs that regulate protein expression at the translational level
• bind to complementary sequences of mRNA to inhibit translation (gene silencing)

Question 11

Describe Long non-coding RNA (lncRna)

Answer 11

• > 200 nucleotides in length
• not translated into proteins
• found to alter mrna splicing and interact with splicing factors
• modify epigenetic state by recruiting chromatin remodelling proteins
• recruit/block transcription factors to affect gene expression
• often have little homology between species

Question 12

Define splicing

Answer 12

Precursor mrna transcript is transformed into a mature mrna transcript where introns are excised and exons are splices together by spliceosomes

Question 13

Benefits of studying nucleic acids

Answer 13

1. New treatments and biomarkers for gene therapy, vaccines and personalised medicine
2. New ways of manipulating cells by using siRNA and CRISPR

Question 14

Difficulties in studying nucleic acids

Answer 14

Many methods require further development before they can reach the clinic

Question 15

Describe alkylating agents (used in chemotherapy)

Answer 15

• induce covalent modifications of DNA, creating adducts not readily removed by the cell’s repair machinery
• cell either repairs or undergoes apoptosis—> results in cell cycle arrest and stops proliferation
• eg cisplatin

Question 16

Describe anti-metabolites (used in chemotherapy)

Answer 16

• interfere with normal cell metabolism of nucleic acids or the enzymes that produce them
• some are purine/pyrimidine analogues that prevent biosynthesis or become incorporated into DNA
• eg methotrexate

Question 17

Define biomarkers

Answer 17

A characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes or pharmacological responses to therapeutic intervention.

Question 18

Describe short interfering RNA (siRNA)

Answer 18

• short SYNTHETIC RNA designed to specifically target an RNA for degradation
• same mechanism of action as miRNA (but r synthetic)
• can be introduces to cell via transfection, electroporation or chemical modifications

Question 19

Define gene therapy

Answer 19

Experimental technique that uses genetic principles to treat disorders

Question 20

Define gene therapy

Answer 20

Experimental technique that uses genetic principles to treat disorders

Question 21

Advantages of mRNA vaccines

Answer 21

1. Less time-consuming bc mRNA molecules are easier to produce than non-infectious viruses

Question 22

At what wavelength does DNA and RNA most efficiently absorb UV light?

Answer 22

260nm

Question 23

What concentration of DNA and RNA give 1 ABS?

Answer 23

In 1cm cuvette, 50ug/ml dsDNA or 40ug/ml ssRNA

Question 24

Define the Tm of DNA

Answer 24

• temperature at which half of DNA are dsDNA and half are ssDNA