Unit 7: Nucleic Acids

genetic material of all living organisms (deoxyribose nucleic acid) polymer made of monomers called nucleotides Some viruses use RNA as their genetic material but viruses are not considered to be living.

pentose sugar, phosphate group and nitrogenous base see A1.2.2 on iPad

see A1.2.3 on iPad for structure Covalent bonds can be specified = phosphodiester bonds this forms a strong sugar/phosphate backbone

DNA: adenine, thymine, cytosine, guanine RNA: adenine, uracil, cytosine, guanine Purines: Adenine and Guanine Pyrimidines: Cytosine, Uracil, Thymine

single strand of nucleotides, formed by condensation (removal of water to create a bond) of nucleotide monomers see A1.2.5 on iPad for structure

a double helix made of two antiparallel strands of nucleotides with two strands linked by hydrogen bonding between complementary base pairs antiparallel = parallel in opposite directions see A1.2.6 on iPad for structure

similarities: polymer of nucleotide cytosine + guanine differences: DNA: double stranded, deoxyribose sugar, adenine + thymine RNA: single stranded, ribose sugar, adenine + uracil

DNA replication is semi conservative (each resulting copy is made of one parent strand and one new strand. Parent strands are used as templates to make the new strands see A1.2.8 on iPad for structure gene expression: using codes in DNA to synthesise protein

DNA molecules vary in length many possibilities for unique sequences DNA is only 2nm in diameter, so cells can store long lengths of DNA limitless capacity of DNA for storing information

same codons on RNA code for the same amino acids in almost every organism = universal genetic code

carbons are numbered (see A1.2.11) New nucleotides can only be added to the 3’ end

each complementary pair has 1 purine and 1 pyrimidine all pairs are equal length, increasing stability

DNA wrapped twice around a core of 8 histone proteins (see A1.2.13) additional h1 histone stabilises the nucleosome and helps condense DNA eukaryotes have nucleosomes, prokaryotes have naked DNA

which was responsible for transmitting hereditary info: DNA or proteins? Viruses are made of DNA and protein Viruses inject their host with their genetic material grew 2 types of bacteriophage to identify genetic material, with different radioactive cultures. 1. ^35S (sulfur) adheres to proteins 2. ^32P (phosphorus) adheres to DNA then allowed them to infect cells Spun the cells in a centrifuge cells will fall to the bottom, virus particles will remain outside cells contained 32P –> DNA

would expect all 4 nucleotides to have equal amounts = tetranucleotide hypothesis (that DNA consists of a repeating sequence of 4 nucleotides in equal amounts and proteins were the genetic material) but actually, there were different amounts there is variation across all life forms (falsification of the tetranucleotide hypothesis) complementary base pairings = A&T are equal, C&G are equal

production of exact copies of DNA with identical base sequences reproduction: passing hereditary info to offspring growth and repair: cell division to create new cells (requires replication of DNA

semi-conservative = one strand is original, one new strand this is to prevent errors

helicase: enzyme that breaks the hydrogen bonds between bases to separate the parent strands and unwind the double helix (unzipping the genes lol) DNA polymerase: adds free nucleotides to the new strand, creating a bond between the phosphate of the free nucleotide and the sugar of the last nucleotide on the strand

PCR (polymerase chain reaction) - amplifies DNA - heat breaks the hydrogen bonds of DNA template and separates into single strands - add in primer (to signal where to start copying) - add in Taq polymerase (heat-tolerant) (to insert nucleotides and extend the new strand) gel electrophoresis - separates DNA molecules by length - put DNA fragments into one end of porous gel - apply electricity (neg. electrode at DNA end) - DNA is also negative, so repelling force moves DNA through the gel - shorter fragments go farther

paternity testing (gel electrophoresis), forensic investigations, coronavirus testing

replication fork = site of separation when helicase separates DNA strands leading strand: - original strand starts at 3’, so new strand goes from 5’ to 3’ towards the fork lagging strand: - original strand starts at 5’, so short segments of nucleotides are added in the 5’3’ away from the fork (Okazaki fragments)

DNA primase: lays down RNA primer DNA polymerase I: removes RNA primers and replaces with correct DNA nucleotides DNA polymerase III: adds new nucleotides in the 5’ to 3’ direction and attaches the nucleotides together & proof-reading DNA ligase: connects Okazaki fragments

using DNA polymerase III errors result in mutations replaces incorrect nucleotide with correct one

using a strand of DNA as a template to synthesise a strand of RNA RNA polymerase: enzyme that separates the strands, adds RNA nucleotides and creates the sugar phosphate bonds to create a continuous strand RNA has uracil instead of thymine