nucleic acids Flashcards
DNA gyrase
moves in advance of helicase and relives strains in the DNA molecule that are created when teh double helix is uncoiled to prevent the strands from forming tight supercois
Helicase
uncoild the DNA double helix and splits in into two template strands.
Single stranded binding proteins
keep the strands apart long enough to allow the template strand to be copied
DNA polymerase lll
adds nucleotides in a 5’ to 3’ direction. on teh leading strand it moves in the same direction as the replication fork, close to helicase. starts next to the primer.
DNA primase
adds a short length of RNA attached by base pairing to a template strand of DNA polymerase to bind and begin replication
Okazaki fragments
short lengths of DNA formed between RNA primers on teh lagging starnd due to teh movement of DNA polymerase III from 5’ to 3’
DNA polymerase l
removes the RNA primer and replaces it with DNA. a nick is left in the sugar-phosphate backbone where to nucleotides are still unconnected
DNA ligase
seals up the nick left by DNA polymerase l by making a sugar phosphate bond
coding sequences
transcribed and translated when a cell requires a protein they code for
non-coding sequences
regulates gene expression, some are sites where a protein can bind that aither promote or supress teh transcription
introns
non-coding. removed from mRNA before translation
exons
coding. spliced together to form mature mRNA
tandem repeats
regions where adjacent sections of DNA have the same base sequence within genomes of humans and otehr species.
structure of nucleotides
8 histone proteins with DNA srapped twice around teh core and DNA linker countinuing towards teh next nucleosome
gene expression
the production of mRNA by transcription of a gene and then the production of polypeptides by translation of the mRNA
promoter
a base sequence close to the start of a gene (non-coding)
RNA polymerase
binds to the promoter in prokaryotes and then starts transcribing
repressor proteins
bind to the promoter ans prevents transcription
transcription factors
bind to the proteins, allowing RNA polymerase to bind and then initiate transcription
methylation
addition of a methyl group - inhibits transcription
methylation
addition of a methyl group - inhibits transcription
small sub-unit of ribosome
a binding site for mRNA
large sub-unit of ribosome
three binding sites for tRNA; A site for tRNA bringing in an aminoacid, P site for tRNA carrying a growing polypeptide, and E site for tRNA exiting the ribosome
stages of translation
small subunit bind to mRNA with a strat codon. tRNA with a comeplementary anticodon binds. teh large subunit bind to teh small subunit. mRNA is positioned to that teh initiator tRNA is in the P site. a tRNA with a complementray anticodon to the adjacent bind to A site. a peptide bodn form between aminoacids held by tRNA in the P and A sites.
stages of elongation
the ribosome moves three bases on along teh mRNA towards the 3’ end, causing the tRNA in the P site to the E site and the tRNA carring the polypeptide from teh A to the P site. A become vacant. tRNA in the E site detaches and moves away, E site is also vacant. tRNA with complementary anticodon binds to A site . the growing polypeptide is linked with the aminoacid on the tRNA in the A site by teh formation of peptide bonds
termination of translation
ribosome moves along the mRNA until it reaches a stop codon. polypeptide is released from the tRNA in the P site. tRNA detaches from P site, mRNA detaches from the small subunit, and large and small subunits seperate
primary structure
polypeptide chain
secondary structure
hydrogen bonds develop between amino acids in the polypeptide chain, forming either beta-pleated sheets or an alpha helix.
tertiary structure
formed when polypeptide chains fold up after translation
quaternary structure
fomed by linking two or more polypeptides to form a single protein
crick and watson
DNA structure
meselson and stahl
semi conservative DNA replication
polymerase chain reaction (PCR)|
used for copying DNA artificially. taq DNA polymerase is usedto copy the original molecule multiple times,
