Theme A: A1 Molecules - A1.2 Nucleic Acids Flashcards
DNA
stands for deoxyribonucleic acid. the molecule that provides the long-term stored genetic information for all organisms in Earth.
structure of a nucleotide (single-stranded - RNA)
nucleotides are made up of a phosphate group, a pentose sugar, and a nitrogenous base. nucleotides form a chain/polymer as a result of condensation reactions that form covalent bonds between the sugar of 1 nucleotide and the phosphate group of the next. this is also known as sugar-phosphate bonding that forms a strong backbone in the molecule.
nitrogenous bases
4 bases in RNA: guanine, adenine, cytosine, uracil.
4 bases in DNA: guanine, adenine, cytosine, thymine.
The sequence of nitrogenous bases are genes or genetic messages that mainly code for amino acids, which are molecules that combine to form proteins.
condensation reaction
the reaction releases a water molecule when synthesising DNA or RNA molecules.
complementary bases
adenine (A) always bonds with thymine (T).
cytosine (C) always bonds with guanine (G).
structure of DNA
has a double helix shape made of 2 antiparallel strands of nucleotides. the strands are linked by hydrogen bonds between complementary bases.
similarities between DNA and RNA
they’re both linear polymers consisting of sugars, phosphates, and bases.
difference between DNA and RNA
DNA: double stranded
RNA: single stranded
DNA: deoxyribose sugar
RNA: ribose sugar
DNA: thymine is 1 of the 4 bases
RNA: uracil is 1 of the four bases
DNA: double helix shape
RNA: variety of shapes depending on type of RNA
DNA: permanent genetic code of a cell/organism
RNA: only RNA viruses contain permanent genetic code
difference between deoxyribose and ribose sugars
ribose has 1 more oxygen atom which can be exemplified through their molecular formulas:
deoxyribose: C5H10O4
ribose: C5H10O5
examples of nucleic acids
1) messenger RNA (mRNA)
2) transfer RNA (tRNA)
3) ribosomal RNA (rRNA)
4) adenosine triphosphate (ATP)
why is complementary base pairing useful?
it plays an essential role in DNA replication. when a protein called helicase breaks the hydrogen bonds between the DNA into 2 singe strands, these free-floating individual nucleotides pair with unmatched nucleotides to make an exact copy of the original molecule.
triplet codon (“triplet”)
every 3 bases represent a meaningful piece of genetic information called a triplet or triple codon.
directionality of RNA and DNA strands
strands of DNA and RNA are synthesised starting with the 5’ (5 prime) end and working towards the 3’ (3 prime) end. the 5’ end of a single strand is the unbound phosphate group and the 3’ end terminates with a sugar.
purine-to-pyrimidine bonding
purine is always bonded to a pyrimidine. therefore, the 2 DNA strands maintain the same distance from one another with 3 rings in total, leading to a stable double helix shape.
purines (double ring size and thus larger): adenine and guanine
pyrimidines (single ring size and thus smaller): thymine and cytosine
structure of a nucleosome
the DNA wraps twice around the 8 histone proteins at the nucleosome’s core. 1 additional histone is used to maintain its shape. linker DNA then connects it to the next nucleosome
efficient packaging solution of DNA
DNA, which is very long, wraps around 8 histone proteins to make nucleosomes that are connected via linker DNA. nucleosomes coil around other proteins into a condensed shape known as a chromosome. A human cell contains 46 chromosomes in its nucleus.
resources and techniques used in the Hershey-Chase experiment
Alfred Hershey and Martha Chase used a bacteriophage (a virus that infects bacteria; it’s composed of a protein outer coats and inner core of DNA) to infect the bacterium E.coli. they also used the radioisotopes phosphorus 32 (found in DNA) and sulfur 35 (found in 2 of the 20 amino acids present in protein).
conclusion of the Hershey-Chase experiment
The E.coli infected by the bacteriophage with phosphorus had radioactivity detected inside of the cell, meaning the DNA was passed from the virus to bacteria. Whereas the one infected by the phage with sulfur in the protein coat had no radioactivity detected inside of it, meaning the protein was not passed on. This allowed them to conclude that DNA, not protein, is the genetical material.
techniques that lead to Chargaff’s rule
Erwin Chargaff developed paper chromatography to show the proportion of nitrogenous bases in various sources of DNA.
discoveries from Chargaff’s experiment
Chargaff’s experiment revealed that the proportion of adenine (A) is equal to thymine (T), and the proportion of guanine (G) is equal to cytosine (C), a finding now known as Chargaff’s rules. This discovery helped to falsify the tetranucleotide theory, which suggested that DNA consisted of a repetitive sequence of the four nucleotide bases in equal amounts (A, T, G, and C) and was therefore too simple to carry genetic information.
