A1.2 Nucleic Acids

DNA

the genetic material of all living organisms

Virus genetic material

RNA, but they're not living organisms

Nucleotide

monomers of nucleic acids like DNA & RNA

Sugar-phosphate bonding

makes a continuous chain of covalently bonded atoms in each strand of DNA or RNA nucleotides

Covalent bond

forms the strong backbone

RNA

polymer formed by condensation of nucleotide monomers

Condensation reaction

two molecules combine to form a larger molecule producing a small molecule such as H2O

Ribose

sugar used in RNA

Deoxyribose

sugar used in DNA

Uracil

base used in RNA instead of thymine

Double helix

two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs

DNA bases

Adenine Thymine Cytosine Guanine

RNA bases

Adenine Cytosine Guanine Uracil

DNA strands

2

RNA strands

1

Types of nucleic acids

DNA RNA tRNA mRNA rRNA

tRNA (transfer RNA)

coding

mRNA (messenger RNA)

coding

rRNA (ribosomal RNA)

non-coding made in the nucleolus

5'

phosphate is attached to the 5th carbon

3'

phosphate is attached to the 3rd carbon

Transcription

5 → 3

Translation

3 → 5

Start codon

AUG

Complementary base pairing

allows genetic information to be replicated and expressed

Hydrogen bonds

provide selectivity bases fit together like lock-and-key

DNA/RNA polymerase

incoming nucleotide only stays if it forms correct H-bond pair

Diversity of DNA sequences

limited diversity of possible DNA base pairings

Purine-to-pyrimidine bonding

required for DNA helix stability

Adenine-thymine and cytosine-guanine

pairs have equal length

Nucleosome

DNA molecule wrapped around a core of eight histone proteins held together by an additional histone protein attached to linker DNA

Histones

small positively charged proteins

Histone core composition

2xH2A 2xH2B 2xH3 2xH4

Beads on a string structure

appearance of nucleosomes under an electron microscope

DNA charge

negative

Histone charge

positive

H1 histone

does not form part of the octamer

H1 function

locks DNA in place helps pack nucleosomes provides stability and regulates access to DNA

Hershey and Chase experiment

confirmed DNA not protein is the transforming principle

35S radioactive labeling

sulfur is a component of proteins but not DNA

32P radioactive labeling

phosphorus is in DNA and not protein

Centrifugation

used to separate infected bacteria and viral parts

Transforming principle

DNA injected into bacteria

Technological developments

radioactive tagging with radioisotopes

Chargaff's rule

falsified tetranucleotide hypothesis

Inductive conclusion

conclusions are never guaranteed to be true only supported by evidence

Karl Popper's solution

science should aim for certainty through falsification