2.5 DNA Flashcards
2.5 i) Know the basic structure of mononucleotides (deoxyribose or ribose linked to a phosphate and a base, including thymine, uracil, cytosine, adenine or guanine) and the structures of DNA and RNA (polynucleotides composed of mononucleotides linked through condensation reactions). ii) Know how complementary base pairing and the hydrogen bonding between two complementary strands are involved in the formation of the DNA double helix.
What is DNA?
- deoxyribonucleic acid
- the genetic code/information which dictates all the inherited characteristics of an organism
Where is DNA located?
- in the nuclei of cells
- in the cytoplasm if there is no nucleus
What is the function of DNA?
controls the manufacture of proteins
How does the DNA of different species differ?
- differences in DNA means different proteins are produced, so organisms are different
- organisms of different species show bigger differences between their DNA than organisms of the same species
What is the structure of DNA?
- DNA is a polymer - it is a chain of nucleotides (the monomer is the mononucleotide)
- DNA is made of two chains in a double-helix structure
What is the basic structure of a mononucleotide? How are they formed?
- pentose sugar (5 carbon sugar) - [in DNA this is deoxyribose, in RNA this is ribose]
- phosphate group
- organic base containing nitrogen
- these 3 molecules are joined by condensation reactions
What is the basic structure of a mononucleotide of DNA?
- deoxyribose (pentose sugar)
- phosphate group
- organic base containing nitrogen (A,T,C,G)
What are four bases of DNA?
- adenine (A)
- thymine (T)
- cytosine (C)
- guanine (G)
What is the basic structure of a mononucleotide of RNA?
- ribose (pentose sugar)
- phosphate group
- organic base containing nitrogen (A,U,C,G)
What are four bases of RNA?
- adenine (A)
- uracil (U) - replaces thymine
- cytosine (C)
- guanine (G)
How do mononucleotides link to form DNA/RNA?
- mononucleotides join together by condensation reactions between the sugar of one nucleotide and the phosphate of the other
- this forms a chain of mononucleotides - a polynucleotide
- both DNA and RNA mononucleotides form polynucleotides (DNA and RNA are polymers)
What is the bond formed between mononucleotides in the sugar-phosphate backbone called?
phosphodiester bond
How many polynucleotide strands are DNA and RNA made of?
- DNA is made of two polynucleotide stands in a double helix
- RNA is made of one polynucleotide stand
Describe the double helix structure of DNA:
- two polynucleotide strands twist around each other to form a double helix
- the strands are antiparallel because they run in opposite directions
How do the two polynucleotide stands of DNA join together?
by hydrogen bonding between the bases
What is complementary base pairing?
each base can only pair up with another particular base
How do the bases of DNA pair up?
- A always pairs with T
- C always pairs with G
How many hydrogen bonds form between the base pairs of DNA? What dictates this?
- 2 hydrogen bonds form between A and T
- 3 hydrogen bonds form between C and G
- the shape and chemical structure of the bases dictates how many hydrogen bonds form
