1. transcription factors

HOW TARGET GENES ARE EXPRESSED

• GENES- sections of DNA that contain coded info in form of bases

  • code for specific AAs

• gene is expressed when mRNA is actively produced using genes base sequence during transcription

• mRNA carries code to produce a sequence of AAs i.e. a polypeptide

• polypeptides then used to produce proteins, some of which control cell activities e.g. enzymes

CELL DIFFERENTIATION

• in multicellular organisms every cell contains same DNA but perform diff functions

  • bc differentiate to form tissues and organs

• as this happens diff types of cell produce more proteins specific to their function

• shape of cell and arrangement of organelles will be diff as cell is now specialised

• can measure degree of differentiation between cells by comparing proteins they produce using gel electrophoresis

GENE PROBES AND GENE EXPRESSION

• gene probes allow particular sections of DNA and RNA to be identified

• gene probes find unique sequences of nucleotides on DNA using RNA that is complimentary to it (DNA-RNA hybridisation)

• DNA from cells is isolated and heated to denature it

• fluorescently labelled RNA for the required gene (probe) is added

• any hybridisation shows required gene is present

CONTROLLING GENE EXPRESSION

• transcription of DNA to mRNA

• translation of mRNA into proteins

• having controls in place at any of these stages gives control over gene expression

• can also change a protein once it has been synthesised

DNA STRUCTURE (RECAP)

• when DNA condenses it has to be packaged efficiently

• achieved using histones which are pos charged proteins

• DNA winds round histone to form nucleosomes

• interact to produce more coiling and then supercoiling

• in supercoiled areas genes are not available to be copied to make proteins

• one way cells are differentiated

TRANSCRIPTIONAL FACTORS (TF)

• protein that controls transcription of genes by binding to a specific region of DNA

• all have a DNA binding site which binds to either a promoter region in DNA or an enhancer region

TF- BINDING TO PROMOTER REGIONS

• sequences of nucleotides next to a gene

• if a TF binds here it can either enable or prevent binding of RNA polymerase at gene

• if it enables binding- mRNA will be built and can be used in translation to make protein

• if it prevents binding- prevents transcription so no mRNA is made

• some TFs can perform both roles for diff genes

TF- BINDING TO ENHANCER REGIONS

• binding sites in DNA that might be far away from gene itself

• regulate transcription by changing structure of chromatin causing DNA to be more or less open to RNA polymerase

• open chromatin structure makes a gene accessible so its available for transcription while a closed one makes it inaccessible so not available

TF- 2

• often several diff TFs will be involved in expression of a gene, giving many levels of control

• equally, a single TF might control expression of many diff genes

• might stimulate expression of one and suppress expression of another

• allows some genes to be expressed (switched on) and others to be repressed (switched off) at diff stages of development of an organism