Fundamentals of DNA, RNA & Proteins Flashcards
what is DNA (very general)
2 polymers of nucleotides joined together by hydrogen bonds & form a double helix
nucleotides of DNA are comprised of
deoxyribose sugar
nitrogen base
phosphate group
Purines
adenine & guanine
Pyrimidine
thymine & cytosine
C & G hydrogen bonds
3 hydrogen bonds
stronger than A & T
A & T hydrogen bonds
2 hydrogen bonds
weaker than C & G
DNA polarity
based on the phosphodiester backbone
(covalent bonds)
DNA strands have 5’-3’ polarity
ANTI-PARALLEL strands that are complementary to each other
histones
proteins in the nucleus that wrap DNA around it to aid in condensing & organizing DNA
DNA replications direction
synthesis of new DNA: 5’-3’
reading parent strand of DNA in 3’-5’
Helicases
unwind & untangle DNA from histones
primase
synthesizes a short RNA sequence to prime DNA synthesis
polymerases
catalyze formation of the phosphodiester bonds
DNA pol III replicates most
DNA pol I removes RNA primer & catalyzes short stretch of DNA
Ligases
catalyze formation of a single phosphodiester bond
close up ‘nicks’ in Okazaki fragments
DNA vs RNA
- DNA is double stranded; RNA is single stranded
- DNA has deoxyribose sugars; RNA has RIBOSE sugars
- DNA contains thymine; RNA contains URACIL
types of RNA
Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA) heteronuclear RNA small nuclear RNA MicroRNA (miRNA) short interfering RNA double stranded RNA many short RNAs
RNA Transcription: Initiation
RNA synthesis begins at the promotor
RNA pol II & accessory proteins assemble on DNA @ this site
TATA box
transcription starts at +1 base site
RNA transcription: Elongation
RNA polymerase synthesizes mRNA from DNA strand reading in the 3’-5’ direction
RNA Transcription: Termination
at the end of the functional gene coding region there will be a string of T’s on the DNA & produce a string of Adenine tails on the mRNA
the longer the poly A tail, the more stable the mRNA
RNA secondary structure
bases bind to each other creating a 3D structure
especially with tRNA
RNA transcription vs DNA replication
Transcription: no priming slower lower fidelity more processive - ability of an enzyme complex to finish what it starts
total RNA within a cell
ribosomal RNA = 94%
messenger RNA=2%
transfer RNA= 3%
28S rRNA should be double 18S rRNA
central dogma
DNA w/ promotor & functional coding site –> transcription –> splicing out introns –>translation –> post translational modifications –> finished protein
Epigenetics
non-sequence specific heritable traits transcriptional gene silencing: selective gene methylation imprinting x-inactivation
post transriptional gene silencing (PTGS):
RNA induced silencing complex
selective gene methylation
CpG islands are sites of methylation in human DNA (strings of CGCGCGC etc)
when methylated these genes will not be expressed
genomic imprinting (silencing)
imprinting is unique to mammals & flowering plants
expression of a certain gene can be contributed to a certain parental gene
Growth factor gene X
male Donkey: 99%
female donkey: 1%
coding region or open reading frame
ordered sequence of nucleotides on a chromosome that encodes a specific functional product
charging tRNAs
aminoacyl-tRNA synthetases specifically attach amino acids to 3’ end of tRNA
protein translation: initiaion
AUG is start codon
ribosome on mRNA accepts tRNA at A site
protein translation: elongation
growing polypeptide as tRNA gets moved to P site & ribosome catalyzes a peptidyl reaction
protein translation: termination
stop codons:
UAA, UAG, UGA
polysome formation
multiple ribosomes translating multiple proteins off of one mRNA strand
protein turnover
lysosomal -10%
proteasomal -90%
