7.2 Flashcards
rna splicing
pre-mrna is modified to remove introns and exons
the exons join with spliceosomes to produce mature mrna by the process of rna splicing
many ways of joining so can produce several versions of mrna from the same section of DNA
so can ultimately produce different phenotypes
pre mrna
rna produced in nucleus from transcription of all the DNA in a gene including exons and introns
epigenetics
changes that affect gene activation
involved in differentiation
involved in changes in proteins synthesised
factors that affect gene control are :
-dna methylation
-histone modification
-non coding rna
dna methylation
addition of a methyl group to a base
added by DNA methyltransferase enzyme
can also modify the structure of the histones
changes arrangement of DNA and prevents transcription
switch off genes which cannot be switched on so proteins cannot be transcribed
dna demethylation
removal of methyl group
genes become active so can be transcribed
histone modifacation
positively charged proteins
dna helices wind around histones to form chromatin
-makes up chromasomes
when densely supercoiled and condensed genes are not available to be copied (heterochromatin)
active chromatin is loose with uncoiled regions opening up more genes for transcription
histone acetylation
acetyl group is added to one of the lysines in histone
opens up structure and activates chromatin allowing transcription
removing group produces heterochromatin again
histone methylation
methyl group is added to a lysine in histone
depending on the position of lysine methylation may cause inactivation of the DNA or activation of a region
methylation is often linked to silencing of a gene
regulation of gene expression
genes can be switched off when not needed preventing resources from being wasted
transcription factors
proteins which increase the rate of transcription
bind to specific DNA promoter region at the start of their target gene inviting rna to bind
1- activator
stimulate or increase rate of transcriptions by helping rna polymerase to bind to start of gene and activate transcription
2- repressors
inhibit or decrease the rate of transcription by preventing rna polymerase from binding
enhancer sequences
specific regions of dna to which transcription factors bind and regulate the activity of the DNA by changing the structure of the chromatin making it more or less available to rna polymerase and so either stimulating or preventing transcription of gene
gene probe
finds the unique sequence of nucleotides on the DNA that make up the gene
pluripotent
can differentiate into most cells
-blastocyst
totipotent
can differentiate into any cell
-zygote
multipotent
can only differentiate into a few cells
-cells in embryo
