Molecular Genetics

Nucleoside

ribose sugar and nitrogenous base

nucleotide

ribose sugar, nitrogenous base, phosphate group

RNA

ribose sugar with hydroxyl groups on 2’ and 3’ carbons

DNA

deoxyribose sugars with 3’ carbon with hydroxyl group and 2’ carbon does not

purines

double ringed

A and g

pyrimidines

single ringed

C,T,U

origin of replication

where DNA strands first spearate to initiate DNA replication

what type of replication is DNA

semiconsiverative

steps of DNA replication

initiation, elongation, termination

what happens in initiation

origins of replication at the A-T pairs split

• helicase comes to unzip, creating a replication fork

helicase

breaks the bonds in the DNA

what happens in elongation

new DNA strands are produced

• single strand binding proteins keep the DNA from attaching

• Topoisomerase holds and keep it from coiling

• primase place RNA primers along the strands for nucleotide addition

• sliding clamp proteins hold DNA polymerase onto the template strand

• DNA polymerase add free nucleoside triphosphate to the 3’ end.

• leading strand continues producing

• lagging strands produce okazaki fragments and are short

• DNA polymerase replaces RNA primers with DNA

• DNA ligase glues fragments of DNA together

what happens in termination

DNA replication ends

• telomeres is noncoding and tell when it reaches the end. It is lost at the end

• telomerase extend the telomeres to prevent DNA loss

nucleosomes

complexes of DNA wrapped around histone proteins

chromatin

overall packaging of DNA and histones

euchromatin

nucleosomes that are loosely packed so DNA can be used for transcription

heterochromatin

nucleosomes that are tightly packed. inactive DNA

what does the acetylation of histones do

removes positive charges, relaxing the DNA histones attraction and allow more transcription to occur

what happens when the deacetylation of histones occur

increases positive charges, tightening DNA histone attraction and decreasing transcription

methylation of histones

add methyl groups, either decrease or increase transcription

genes

instructions within DNA that code for proteins

• need to be transcribed into RNA first then protein

  • promoter → gene → operator → gene

mRNA how are they produced

DNA undergoes transcription

steps of transcription

initiation, elongation, termination

translation: initiation

promoter next to the gene attracts RNA polymerase to transcribe the gene

transcription: Elongation

transcription bubble forms and RNA polymerase travels from 3’ - 5’ direction on the template strand

transcription: termination

terminator sequence signals the RNA polymerase to stop

what is the template strand

strand used to transcribe the mRNA

what is the coding strand

other DNA strand; equivalent to transcribed mRNA

T is replaced with U