Bio A Midterm 2 - 11/10

gene regulation

-the process of turning genes on and off during development to make a brain cell look and act different from a liver cell or a muscle cell

-also allows cells to react quickly to changes in their environments

gene expression

the process of turning on a gene to produce RNA and protein

each cell controls ____ and ___ its genes are expressed?

when and how

difference between eukaryotes and prokaryotes in gene transcription

unlike prokaryotes, eukaryotic RNA polymerase requires other proteins or transcription factors to facilitate transcription initiation

similarity between eukaryotes and prokaryotes in gene transcription?

it requires the actions of an RNA polymerase to bind to a sequence upstream of a gene to initiate transcription

transcription factors

-proteins that bind to the promoter sequence and other regulatory sequences to control the transcription of the target gene

-RNA polymerase by itself cannot initiate transcription in eukaryotic cells

-these must bind to the promoter region first and recruit RNA polymerase to the site for transcription to be established

promoter region

-immediately upstream of the coding sequence

-region can be short (only a few nucleotides in length) or quite long (hundreds of nucleotides long)

-the longer it is, the more available space for proteins to bind

-length is gene-specific and can differ dramatically between genes

what is the purpose of the promoter?

to bind transcription factors that control the initiation of transcription

enhancer

-a DNA sequence that promotes transcription; binding sequences/sites for transcription factors

-each one is made up of short DNA sequences called distal control elements

-activators bound to the distal control elements interact with mediator proteins and transcription factors

-don’t necessarily have to be close to the genes they enhance

transcriptional repressors

can bind to promoter or enhancer regions and block transcription; respond to external stimulo to prevent the binding of activating transcription factors

epigenetic changes

-modifications where chemical compounds added to single genes regulate their activity

-modifications remain as cells divide and may be inherited through the generations

-can help determine whether genes are turned on or off and can influence the production of proteins in certain cells, ensuring that only necessary proteins are produced

epigenome

-comprises all of the chemical compounds that have been added to the entirety of one’s DNA (genome) as a way to regulate the activity (expression) of all the genes within the genome

-the chemical compounds of the epigenome are not part of the DNA sequence, but are on or attached to DNA

histone

-DNA strands are wound around this as the first level of organization/packing

-these proteins package and order DNA into nucleosomes (structural units)

nucleosome complexes

-can control the access of proteins to the DNA regions

-can move to open the chromosomes structure to expose a segment of DNA

euchromatin

active open regions of chromatin

euchromatic

describes regions of the genome that are transcriptionally active

heterochromatin

tightly wound regions of chromatin

heterochromatic

describes regions of the genome that are typically silenced and transcriptionally inactive

what is the function of chemical tags added to histone proteins and DNA?

these temporary signals alter how tightly wound the DNA is around the histone proteins and tell the histones if a chromosomal region should be open or closed

epigenetic regulation

a type of gene regulation where temporary changes to the histones and DNA alter the chromosomal structure as needed without changing the sequences of bases within the DNA

DNA methylation

-a type of epigenomic modification that involves attaching small molecules (methyl groups) to DNA nucleotides or the amino acids that make up the histone proteins

-adds to cytosine nucleotides in specific regions—CpG islands

-when methyl groups are added to a particular gene, that gene is turned off or silenced, and no protein is produced from that gene → DNA is inaccessible and gene is inactive

histone code hypothesis

-the hypothesis that transcription of a gene is in part regulated by modifications made to histone proteins, primarily on their somewhat floppy ends

-concept that histone modifications serve to recruit other proteins by specific recognition of the modified histone, rather than through simply stabilizing or destabilizing the interaction between histone and the underlying DNA

histone methylation

the specific amino acid in the histone tail that gets methylated is very important for determining whether it will tighten or loosen chromatin structure

histone acetylation

-histone tails can also be modified by the addition of an acetyl group

-when histone tails are acetylated, this typically causes the tails to loosen from around the DNA, allowing the chromatin to loosen

-DNA is accessible and gene is active

errors in epigenetic process

can lead to abnormal gene activity or inactivity; can cause genetic disorders

EX: cancers, metabolic disorders, degenerative disorders