6.1 DNA Structure [HY]

Question 1

Where is the bulk of DNA found?

Answer 1

• in chromosomes in the nucleus of eukaryotic cells, some are also present in mitochondria and chloroplasts

Question 2

Nucleosides

Answer 2

• composed of pentose bonded to a nitrogenous base
• formed by covalently linking the base to C-1′ of the sugar

Question 3

Nucleotides

Answer 3

• formed when one or more phosphate groups are attached to C-5′ of a nucleoside
• these molecules are named
  according to the number of phosphates present
• high-energy compounds because of the energy associated with the repulsion between closely associated negative charges on the
  phosphate groups
• the building blocks of DNA
• both purines and pyrimidines
  contain nitrogen in their aromatic rings. Nucleic acids are thus imbued with exceptional stability

Question 4

How does ATP power cells?

Answer 4

• Due to all the negative charges in close proximity,
  removing the terminal phosphate from ATP actually releases energy (exothermic)

Question 5

How are Nucleic acids classified?

Answer 5

• according to the pentose they contain

Question 6

Which nucleotide only exists in DNA?

Answer 6

Thymine

Question 7

Difference between RNA and DNA?

Answer 7

• DNA uses Thymine
• RNA uses Uracil
• DNA uses deoxyribose as its pentose
• RNA uses ribose as its pentose

Question 8

Four Nitrogenous bases of DNA?

Answer 8

Adenine, Guanine, Cytosine and Thymine

Question 9

Four Nitrogenous bases of RNA?

Answer 9

Adenine, Guanine, Cytosine and Uracil

Question 10

Backbone of DNA composed of?

Answer 10

• alternating sugar and phosphate groups
• determines the directionality of the DNA
• read from 5′ to 3′
• a phosphate group links the 3′ carbon of one sugar to the 5′
  phosphate group of the next incoming sugar in the chain
• DNA and RNA are negative b/c of the phosphates
• Polarity is created by the distinct 5’ and 3’ ends. (The 5′ end of DNA, for instance, will have an −OH or phosphate group bonded to C-5′ of the sugar, while the 3′ end has a free −OH on C-3′ of the sugar)

Question 11

How is the base sequence of a nucleic acid strand read and written?

Answer 11

• 5’ to 3’
• If written backwards, the ends must be labeled: 3′—GTA—5′

Question 12

MCAT nomenclature for phosphates and deoxyribose?

Answer 12

• The position of phosphates may be shown: pApTpG
• “d” may be used as shorthand for deoxyribose: dAdTdG

Question 13

Purines

Answer 13

Adenine, Guanine

Question 14

Pyrimidines

Answer 14

Cytosine, Uracil, and Thymine

Question 15

Complementary base-pairing?

Answer 15

A-T and G-C

Question 16

Chargaff’s rules

Answer 16

• 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.
• total purines will be equal to total pyrimidines overall.
• %A = %T
  %G = %C

Question 17

Probe DNA

Answer 17

• When probe DNA binds to target DNA sequences, this may provide evidence of the presence of a gene of interest