ap bio unit 6 Son Im Crine

pyrimidines vs purines

single ring (u, c, t) vs double ring (a, g)

prokaryotic vs eukaryotic genomes

prokaryotic:

• circular

• smaller

eukaryotic:

• linear, multiple

• larger

both contain plasmids which are circular double stranded dna molecules (cytosol in prokaryotes and nucleus in eukaryotes)

what does uracil replace in dna

it replaces thymine (so AU and GC pair up)

what does DNA replication being semiconservative mean

when a DNA molecule replicates, the two resulting DNA double helices each consist of one original (parental) strand and one newly synthesized strand

5 prime vs 3 prime end

5 prime: phosphate terminus (Five and PHosphate)

3 prime: hydroxyl terminus

nucleotides can only be added in the __ direction, and this means…

5’ to 3’

one strand will always be synthesized continuously (leading strand)

one strand will always be synthesized discontinuously (lagging strand) (the fragments are called okazaki)

what are the enzymes involved in replication and what do they do

helicase: unwinds the dna

primase: synthesizes short RNA primers (starting from 3’ on the template strand, strands are antiparallel so at that spot the other strand is 5’) that provide starting points for DNA synthesis

topoisomerase: prevents strands from being over twisted at the replication fork (the place where the strands are separated)

dna polymerase: adds complementary DNA nucleotides to the growing strand in the 5′ → 3′ direction and proofreads for errors

ligase: joins dna fragments on lagging strand

central dogma

DNA → RNA → protein

DNA transcription

1. initiation: RNA polymerase binds to a sequence of a DNA gene called the promoter and separates the two strands

2. elongation: one strand is the template (noncoding, antisense) and the other is non-template (coding). the RNA polymerase synthesizes a new RNA strand (5’ → 3’) using the template which is the same as non-template but with uracil

3. termination, we have a new mRNA and DNA is put back to normal

3 types of RNA

mRNA:

carries genetic info from DNA to ribosomes, 3 base sequence is codon

tRNA:

transfers specific amino acids to the ribosome; contains anticodon that pairs with mRNA codons to ensure the correct amino acid is added to the growing polypeptide chain

rRNA:

forms core and structure of ribosomes

eukaryotic mRNA modifications

addition of poly-A tail

100-200 adenine nucleotides that helps stability (green circles)

addition of GTP cap

modified guanine nucleotide that helps protect it and allow ribosome to attach

introns

sequences of mRNA that do not code for amino acids. they’re removed during RNA processing (this is called alternative splicing) and are thus not a part of the mRNA transcript

exons

sequences of mRNA that do code for amino acids and are used in processing and then connected to each other to make mature mRNA transcripts

what happens if introns are not removed

they’ll be translated along with the exons and create gibberish