Download b8 nucleic acids

B8: Nucleic acids
B.8.1  Describe the structure of nucleotides and their condensation polymers (nucleic acids or
polynucleotides).
[Nucleic acids are polymers made up of nucleotides. A nucleotide contains a phosphate group, a pentose
sugar and an organic nitrogenous base. Students should recognize, but do not need to recall, the structures
of the five bases: adenine(A), cytosine(C), guanine(G), thymine(T) and uracil (U). Nucleic acids are joined
by covalent bonds between the phosphate of one nucleotide and the sugar of the next, resulting in a
backbone with a repeating pattern of sugar-phosphate-sugar-phospate. Nitrogenous bases are attached to the
sugar of the backbone.]
Nucleic acids = polymers made up of nucleotides
Examples:
 deoxyribonucleic acid (DNA)
 ribonucleic acid (RNA)
*More on the complete structures of DNA and RNA later.
A. Nucleotides
Nucleotides consist of:
1. a phosphate group:
2. a pentose sugar:
*DNA contains  deoxyribose
*RNA contains  ribose
3. an organic base:
*DNA contains adenine(A), cytosine(C), guanine(G),and thymine(T)
*RNA contains  adenine(A), cytosine(C), guanine(G), and uracil (U]
DNA bonding base pairs
*Uracil replaces thymine in RNA
Examples of Complete Nucleotides:
B. Polynucleotides
Nucleotides condense to form polynucleotides. Each nucleotide is joined by a phophodiester bond between C3
of the sugar and the neighbouring phosphate group.
or
C. Nucleic acids  DNA and RNA
B.8.3  Explain the double helical structure of DNA.
[The structure has two nucleic acid strands that spiral around an axis. Students should describe the hydrogen bonding between
specific pairs of nucleotide bases.
TOK: What are the implications of the discovery of the molecular basis of life in other areas of knowledge?]
RNA
B.8.2  Distinguish between the structures of DNA and RNA.
[RNA has ribose as its pentose sugar; DNA has deoxyribose. Deoxyribose lacks an oxygen atom on C2. RNA has uracil instead of
thymine as its base. RNA is a single-stand nucleic acid; DNA is a double-strand nucleic acid.]
Summary:
Pentose sugar
Bases
# of nucleic acid
strands
DNA
deoxyribose
adenine hydrogen bonds to thymine
double
RNA
ribose
adenine H-bonds to uracil
i.e. uracil replaces thymine
single
B.8.4  Describe the role of DNA as the repository of genetic information, and explain its role in protein
synthesis.
[DNA is the genetic material that an individual inherits from its parents. It directs mRNA synthesis
(transcription) and, through mRNA, directs protein synthesis (translation) using a triplet code.]
Protein Synthesis (Steps)
1. Transcription = synthesis of mRNA (i.e. messenger RNA) via “unzipping” of DNA
 mRNA base sequence is complementary to that on a section of DNA
e.g. DNA base seqenence
A G G C T C G A G G T T
Complementary mRNA strand 
 Transcription takes place in the nucleus of the cell.
 Upon completion of transcription, the mRNA travels into the cytoplasm of the cell.
2. Translation = synthesis of polypeptide chain via the “decoding” of base sequences on the mRNA strand
 Each three base sequence (i.e. each triplet code) on the mRNA codes for an amino acid.
 There are 64 (i.e. 44) possible triplet codes and only 20 amino acids. Therefore, most amino acids are
represented by more than one triplet code. (e.g. GCU, GCC, GCA, GCG all code for alanine.)
Some sequences code for start and end of the chain.
8.8.5  Outline the steps involved in DNA profiling and state its use.
[Aim 8: Include forensic and paternity cases.]