B.8.1 Describe the structure of nucleotides and their condensation polymers
Nitrogenous Bases:
- nucleic acids are polymers made up of nucleotides
- a nucleotide contains a phosphate group, a 5-carbon sugar, and an organic nitrogenous base
- in DNA (deoxyribonucleic acid), the 4 nitrogenous bases are adenine (A), guanine (G), cytosine (C), and thymine (T)
- in RNA (ribonucleic acid), uracil (U) replaces thymine but the other 3 bases are still present
- nucleic acids are joined by covalent bonds between the phosphate on carbon-5 of one nucleotide and the -OH group on carbon-3 of the next (called a 5'-3' linkage), resulting in a backbone with a repeating pattern of sugar-phosphate-sugar-phosphate
- the bonds are called phosphodiester linkages
- nitrogenous bases are attached to the sugar of the backbone
Nitrogenous Bases:
- adenine and guanine have double rings and are purines
- cytosine, thymine, and uracil have a single ring and are pyrimidines
- A vs G: G has 2 substitutions (C=O and -NH2) while A has 1 substitution (-NH2 at same place as C=O for G)
- T vs U: T has a -CH3 substituent while U has no substitutions
- C vs T/U: C has 2 substituents (-NH2 and C=O) while T has 2 substituents (2 C=O)
- the nitrogenous base always attaches to the -OH group sticking upwards on carbon-1
B.8.2 Distinguish between the structures of DNA and RNA
- RNA has ribose as its pentose (5 carbon) sugar while DNA has deoxyribose (which lacks an oxygen atom on C2)
- RNA has uracil instead of thymine as a nitrogenous base
- RNA is a single-stranded nucleic acid while DNA is double-stranded
B.8.3 Explain the double helical structure of DNA
- the structure has 2 nucleic acids strands that spiral around an axis
- the 2 strands are anti-parallel, meaning that one strand has a 5'-3' linkage from top the bottom while the other has 3'-5' and it essentially flipped upside down
- a helix is formed because the bond angles between phosphate and sugar and the phosphate-phosphate repulsion result in a right-handed twist
- nitrogenous bases are packed horizontally and pairs are hydrogen-bonded together
- the center of the helix is not the center of the base pairs so a major and minor groove results
- B-DNA is approximately 10 nucleotides/turn (~3.4 nm), ~2 mm thick
B.8.4 Describe the role of DNA as the repository of genetic information, and explain its role in protein synthesis
- DNA holds the basic genetic information that defines an organism and is inherited from parents
- DNA replicates itself so genetic information can be transferred to the next generation
- replication is semi-conservative: each parent strand is the template for the new strand
- mutations include insertion/deletion, substitution, and transposition
- DNA directs mRNA synthesis (transcription)
- messenger RNA provides the sequence of amino acids to synthesize proteins, transfer RNA delivers amino acids to protein synthesis mechanism (ribosome), and ribosomal RNA is part of the protein synthesis structure
- regulatory regions are where proteins that control the rate of transcription bind
- DNA also directs protein synthesis (translation) by converting mRNA into protein using a triplet code that specifies each amino acid
- tRNA has a specific amino acid code and transfers amino acids to the mRNA/ribosome complex to be added to protein
B.8.5 Outline the steps involved in DNA profiling and state its use
Variable Tandem Nucleotide Repeats (VNTR):
Procedure:
- DNA profiling is the production of a genetic fingerprint or characteristic set of markers for an individual
- general idea: To generate DNA fragments from specific areas with a high degree of variation (usually VNTR regions are used), and then to separate the patterns to produce a pattern characteristic of an individual
Variable Tandem Nucleotide Repeats (VNTR):
- these are sections in human DNA where short (4-10 base pairs) sections have been duplicated back to back (4-40 times depending on the individual)
- analysis of these sections gives lengths of nucleic acid that can be different for each individual
Procedure:
- polymerase chain reaction is used to amplify (make many copies of) multiple of these VNTR sections per person
- the amplified sample is subjected to electrophoresis where negatively charged DNA will be separated according to size
- visualization of bands on the gel is either by stain or by inclusion of radioactive/fluorescent/luminescent or other labels into the nucleotides used to make copies
- profile patterns are then compared - certain people can be excluded from consideration if their pattern differs from or could not generate a specific pattern examined
- e.g.) profiling is used at crime scenes (to link locations, weapons, suspects), and for paternity tests