IB biology unit 7 nucleic acids

histones

histones only found in eukaryotic cells, four types of pairs of different histones, have DNA wrapped around it

linkers

in the histones allows more than one to link together

nucleosomes contain:

histones, dna, linkers

why 5-3 direction

because nucleotides can only be added to pre-existing one, RNA synthase provides attachment point for DNA polymerase

what stops replication

deoxyribonucleic acid to prepare for sample base sequence, deoxyribonucleic will be incorporated they will stop the replication

non-coding RNA gene

coding for RNA molecules that are not translated into proteins including genes for tRNA

introns

non-coding sequence within the gene are removed by RNA splicing prior to the formation of mRNA

telomeres

region of repeating DNA at the tips of the chromosomes preventing against chromosomal deterioration during replication

single strand binding (SSB)

bind to the DNA strand after they have been separated and prevent them to get together again

helicase

breaks hydrogen bond between complementary base pairing

DNA ligase

bind to Okazaki fragments together to form a continuous strand

initiation of transcription

starts with RNA polymerase bind to the DNA at the promotor region and the double helix unwinds

elongation of transcription

when mRNA becomes longer and nucleotides are added to the 3OH group

termination of transcription

mRNA synthesis is complete and the complex DNA, RNA polymerase and mRNA disassembles

when does transcription occur in prokaryotes

mRNA have been synthesised transcription occurs

when does transcription occur in eukaryotic

the mRNA is produced needs to be prepared for transcription

introns

DNA sequence that contain no coding information

splicing of introns

involves spliceosomes that act like enzymes in the splicing process to remove introns and bind extrons together

extrons

DNA sequence that code for polypeptide

splicing allows

several proteins to synthesise from the same gene,

lac operator

set of genes all linked by a promotor

promotor in DNA

This molecule plays a crucial role in activating gene expression by binding to DNA and recruiting RNA polymerase to the promoter region.

promotor effects transcription

by controlling if RNA polymerase can access the gene shown in the lac operon of prokaryotic

E-coli and lactose

the breakdown of lactose results in genes being turned off, a lactose repressor protein is disactivated, one lactose has been broken the repressor protein no longer deactivated and blocks the expression of lactose

activator

protein binds to enhancer while the repressor protein bind to silencer to increase or decrease rate of transcription

enhancer and silencer

Enhancer: A DNA sequence that increases the rate of transcription by binding to transcription factors.

Silencer: A DNA sequence that decreases the rate of transcription by binding to repressor proteins.

non-coding sequance

repressor protein

blocks the transcription of specific genes

methylation and transcription can cause

chemical change to both the histones and the DNA

* histones bind to DNA they block specific genes not allowing transcription
* tail of histones can be acetylated adding acyl group repventing the binding of nucleosomes

what happens when DNA becomes methylated

when a group of methly is added to cytosine found in DNA molecule, they are usually not expressed and can cause tumour formation

antisense strand transcription

transcribed into RNA and sequence is complementary to the RNA sequence and will be the DNA version of the tRNA anticodon sequence

sense strand transcription

not transcribed into RNA and will be the DNA version of the RNA sequance is reffered as coding strand

cpoding sequance

afterRNA polymerase bound to promoter it causes the DNA strand to unwind and separate the region of DNA that transcribed by the RNA polymerase

modifiying mRNA after transcription: capping

addition of methyl group to the 5’ end of transcribed RNA the methylated cap provides protection against degradation of exonucleaases also allow the transcription to be recognised by the cell translational mechaninery

polyadenylation

addition of a long chain of adenine nucleotides to teh 3’end of the transcription the poly-a-tail improves the stability of the RNA transcription and facilitates the exports from the nucleus

modifying mRNA after transcription

capping, polyadenylation, splicing occur after transcription in order to form mature mRNA

alternative splicing

can cause the removal of exon, result in the formation of different polypeptides from a single gene sequence

chromatin

when DNA is supercoiled it is not accessible for transcription it exits as condensed heterochromatin

euchromatin

region with high transcriptional activity are loosely packed

heterochromatin

region with low or no transcription actively are densely packed

structure of ribosome

* made up of protein and ribosomal RNA
* large subunit contain 3 large tRNA binding site an aminoacyl (A) site, peptidyl (P) site and an exit (E) site

where are ribose found

either floating in cytoplasm or in the ER

structure of tRNA

* acceptor stem carried an amino acid
* the anticodon associated with the MRNA codon complementary base pairing
* t arm associated with ribosome
* d arm associated with tRNA activating enzyme responsable to adding amino acid to the acceptor

tRNA process

* binds with specific amino acids in the cytoplasm in a reaction catalyzed by tRNA activating enzyme (each amino acid recognized enzyme)

ATP in tRNA

* creates a high energy bond that allows transfer to the tRNA molecules this stored energy will provide the majority of the energy required for peptide bonds

post translation eukaryotic

* ribosome separate from the genetic material by the uncles
* after transcription the mRNA must be transported from the nucleus prior to translation by the ribosome
* the transport requires modification to the RNA

post translation prokaryotic

* ribosome may have been translating the mRNA molecules while still being transcribed from the DNA template

translation only works when

tRNA molecules in the cell are located with correct amino acid corresponding to the codon on the mRNA involved the aminoacyl-tRNA syntheses