1) Gene expression in eukaryotes is regulated at multiple levels, including transcription, epigenetic modifications to DNA and histones, alternative splicing of mRNA, and microRNAs inhibiting translation.
2) Transcription is regulated through the binding of transcription factors to enhancer and silencer regions near gene promoters. DNA methylation and histone modifications can alter chromatin structure and gene activity.
3) Alternative splicing of pre-mRNA and the actions of microRNAs introduce additional regulatory mechanisms by generating different protein isoforms from a single gene or inhibiting specific mRNAs post-transcriptionally.
regulation of gene expression in eukaryotes is a complex mechanism involved many factors. out of many levels of regulations, chromosomal and transcription level of regulation are discussed in this slides.
Regulation of gene expression in eukaryotesAnna Purna
Presence of nucleus and complexity of eukaryotic organism demands a well controlled gene regulation in eukaryotic cell. Tissue specific gene expression is essential as they are multicellular organisms in which different cells perform different functions. This PPT deals with various control points for the gene regulation and expression within a cell.
REGULATION OF
GENE EXPRESSION
IN PROKARYOTES & EUKARYOTES .
This presentation is enriched with lots of information of gene expression with many pictures so that anyone can understand gene expression easily.
Gene expression is the process by which the information encoded in a gene is used to direct the assembly of a protein molecule.
Gene expression is explored through a study of protein structure and function, transcription and translation, differentiation and stem cells.
It is the process by which information from a gene is used in the synthesis of a functional gene product.
These products are often proteins, but in non-protein coding genes such as ribosomal RNA (rRNA), transfer RNA (tRNA) or small nuclear RNA (snRNA) genes, the product is a functional RNA.
The process of gene expression is used by all known life - eukaryotes (including multicellular organisms), prokaryotes (bacteria and archaea)
Regulation of gene expression:
Regulation of gene expression includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products (protein or RNA).
Gene regulation is essential for viruses, prokaryotes and eukaryotes as it increases the versatility and adaptability of an organism by allowing the cell to express protein when needed.
CLASSIFICATION OF GENE WITH RESPECT TO THEIR EXPRESSION:
Constitutive ( house keeping) genes:
Are expressed at a fixed rate, irrespective to the cell condition.
Their structure is simpler.
Controllable genes:
Are expressed only as needed. Their amount may increase or decrease with respect to their basal level in different condition.
Their structure is relatively complicated with some response elements.
TYPES OF REGULATION OF GENE:
positive & negative regulation.
Steps involving gene regulation of prokaryotes & eukaryotes.
Operon-structure,classification of mechanisms- lac operon,tryptophan operon ,
and many things related to gene expression.
This is a video slide so anyone can understand this topic easily by seeing pictures included in this slide.
regulation of gene expression in eukaryotes is a complex mechanism involved many factors. out of many levels of regulations, chromosomal and transcription level of regulation are discussed in this slides.
Regulation of gene expression in eukaryotesAnna Purna
Presence of nucleus and complexity of eukaryotic organism demands a well controlled gene regulation in eukaryotic cell. Tissue specific gene expression is essential as they are multicellular organisms in which different cells perform different functions. This PPT deals with various control points for the gene regulation and expression within a cell.
REGULATION OF
GENE EXPRESSION
IN PROKARYOTES & EUKARYOTES .
This presentation is enriched with lots of information of gene expression with many pictures so that anyone can understand gene expression easily.
Gene expression is the process by which the information encoded in a gene is used to direct the assembly of a protein molecule.
Gene expression is explored through a study of protein structure and function, transcription and translation, differentiation and stem cells.
It is the process by which information from a gene is used in the synthesis of a functional gene product.
These products are often proteins, but in non-protein coding genes such as ribosomal RNA (rRNA), transfer RNA (tRNA) or small nuclear RNA (snRNA) genes, the product is a functional RNA.
The process of gene expression is used by all known life - eukaryotes (including multicellular organisms), prokaryotes (bacteria and archaea)
Regulation of gene expression:
Regulation of gene expression includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products (protein or RNA).
Gene regulation is essential for viruses, prokaryotes and eukaryotes as it increases the versatility and adaptability of an organism by allowing the cell to express protein when needed.
CLASSIFICATION OF GENE WITH RESPECT TO THEIR EXPRESSION:
Constitutive ( house keeping) genes:
Are expressed at a fixed rate, irrespective to the cell condition.
Their structure is simpler.
Controllable genes:
Are expressed only as needed. Their amount may increase or decrease with respect to their basal level in different condition.
Their structure is relatively complicated with some response elements.
TYPES OF REGULATION OF GENE:
positive & negative regulation.
Steps involving gene regulation of prokaryotes & eukaryotes.
Operon-structure,classification of mechanisms- lac operon,tryptophan operon ,
and many things related to gene expression.
This is a video slide so anyone can understand this topic easily by seeing pictures included in this slide.
mRNA stability and localization.RNA is critical at many stages of gene expression. How frequently it will be translated, how long it is likely to survive, and where in the cell it will be translated. RNA cis-elements & associated proteins
This presentation deals with DNA replication in mamalian mitochondria. Mammalian mtDNA is replicated by proteins distinct from those used for nuclear DNA replication. According to the strand displacement model, replication is initiated from two distinct origins, OH and OL.
Recombination
Breaking and rejoining of two parental DNA molecules to produce new DNA molecules
Types of recombination
Definition of recombination
Gene Conversion – Characteristics
Holliday model
Holliday junction cleavage
This presentation is about the transcription machinery that is required for the transcription in eukaryotes. The comparison between the transcription factors involved in prokaryotes and eukaryotes. The initiation of transcription and how it helps in producing a mRNA.
mRNA stability and localization.RNA is critical at many stages of gene expression. How frequently it will be translated, how long it is likely to survive, and where in the cell it will be translated. RNA cis-elements & associated proteins
This presentation deals with DNA replication in mamalian mitochondria. Mammalian mtDNA is replicated by proteins distinct from those used for nuclear DNA replication. According to the strand displacement model, replication is initiated from two distinct origins, OH and OL.
Recombination
Breaking and rejoining of two parental DNA molecules to produce new DNA molecules
Types of recombination
Definition of recombination
Gene Conversion – Characteristics
Holliday model
Holliday junction cleavage
This presentation is about the transcription machinery that is required for the transcription in eukaryotes. The comparison between the transcription factors involved in prokaryotes and eukaryotes. The initiation of transcription and how it helps in producing a mRNA.
Most bacteria are free-living organisms that grow by increasing
in mass and then divide by binary fission.
Growth and division are controlled by genes, the expression
of which must be regulated appropriately. Genes
whose activity is controlled in response to the needs of a
cell or organism are called regulated genes. All organisms
also have a large number of genes whose products
are essential to the normal functioning of a growing and
dividing cell, no matter what the conditions are. These
genes are always active in growing cells and are known as
constitutive genes or housekeeping genes; examples include
genes that code for the enzymes needed for protein
synthesis and glucose metabolism. Note that all genes are
regulated on some level. If normal cell function is impaired
for some reason, the expression of all genes, including
constitutive genes, is reduced by regulatory
mechanisms. Thus, the distinction between regulated
and constitutive genes is somewhat arbitrary.
regulation of Transcription in prokaryotes can be done under operons and cascade of gene expression ; also we can divide it into negative and positive responses which the lac operon is a good example of it.
Regulation of gene expression.
It can be helpful for the students of Biotechnology, Genetics, Molecular Biology, Microbiology and othe Biology related courses.
If you've got any queries, you can directly mail me to pratimasingdan@gmail.com.
I hope this will help you a lot.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
How to Build a Module in Odoo 17 Using the Scaffold MethodCeline George
Odoo provides an option for creating a module by using a single line command. By using this command the user can make a whole structure of a module. It is very easy for a beginner to make a module. There is no need to make each file manually. This slide will show how to create a module using the scaffold method.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
Thinking of getting a dog? Be aware that breeds like Pit Bulls, Rottweilers, and German Shepherds can be loyal and dangerous. Proper training and socialization are crucial to preventing aggressive behaviors. Ensure safety by understanding their needs and always supervising interactions. Stay safe, and enjoy your furry friends!
Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
This slide is special for master students (MIBS & MIFB) in UUM. Also useful for readers who are interested in the topic of contemporary Islamic banking.
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
Normal Labour/ Stages of Labour/ Mechanism of LabourWasim Ak
Normal labor is also termed spontaneous labor, defined as the natural physiological process through which the fetus, placenta, and membranes are expelled from the uterus through the birth canal at term (37 to 42 weeks
MATATAG CURRICULUM: ASSESSING THE READINESS OF ELEM. PUBLIC SCHOOL TEACHERS I...NelTorrente
In this research, it concludes that while the readiness of teachers in Caloocan City to implement the MATATAG Curriculum is generally positive, targeted efforts in professional development, resource distribution, support networks, and comprehensive preparation can address the existing gaps and ensure successful curriculum implementation.
2. Chapter 11 Regulation of Gene Expression
Key Concepts
• 11.1 Several Strategies Are Used to
Regulate Gene Expression
• 11.2 Many Prokaryotic Genes Are
Regulated in Operons
• 11.3 Eukaryotic Genes Are Regulated by
Transcription Factors and DNA Changes
• 11.4 Eukaryotic Gene Expression Can Be
Regulated after Transcription
3. Chapter 11 Opening Question
How does CREB regulate the expression
of many genes?
4. Concept 11.1 Several Strategies Are Used to Regulate Gene
Expression
Gene expression is tightly regulated.
Gene expression may be modified to
counteract environmental changes, or
gene expression may change to alter
function in the cell.
Constitutive proteins are actively
expressed all the time.
Inducible genes are expressed only when
their proteins are needed by the cell.
6. Concept 11.1 Several Strategies Are Used to Regulate Gene
Expression
Genes can be regulated at the level of
transcription.
Gene expression begins at the promoter
where transcription is initiated.
In selective gene transcription a “decision” is
made about which genes to activate.
Two types of regulatory proteins—also
called transcription factors—control
whether a gene is active.
7. Concept 11.1 Several Strategies Are Used to Regulate Gene
Expression
These proteins bind to specific DNA
sequences near the promoter:
• Negative regulation—a repressor protein
prevents transcription
• Positive regulation—an activator protein
binds to stimulate transcription
10. Concept 11.1 Several Strategies Are Used to Regulate Gene
Expression
Acellular viruses use gene regulation to
take over host cells.
A phage injects a host cell with nucleic acid
that takes over synthesis.
New viral particles (virions) appear rapidly
and are soon released from the lysed cell.
This lytic cycle is a typical viral
reproductive cycle—in a lysogenic phase,
the viral genome is incorporated into the
host genome and is replicated too.
11. Concept 11.1 Several Strategies Are Used to Regulate Gene
Expression
A bacteriophage may contain DNA or RNA and
may not have a lysogenic phase.
The lytic cycle has two stages:
• Early stage—promoter in the viral genome
binds host RNA polymerase and adjacent
viral genes are transcribed
Early genes shut down transcription of host
genes, and stimulate viral replication and
transcription of viral late genes.
Host genes are shut down by a
posttranscriptional mechanism.
Viral nucleases digest the host’s chromosome
for synthesis in new viral particles.
12. Concept 11.1 Several Strategies Are Used to Regulate Gene
Expression
• Late stage—viral late genes are
transcribed
They encode the viral capsid proteins and
enzymes to lyse the host cell and release
new virions.
The whole process from binding and
infection to release of new particles takes
about 30 minutes.
13. Figure 11.3 A Gene Regulation Strategy for Viral Reproduction
14. Concept 11.1 Several Strategies Are Used to Regulate Gene
Expression
Human immunodeficiency virus (HIV) is a
retrovirus with single-stranded RNA.
HIV is enclosed in a membrane from the
previous host cell—it fuses with the new
host cell’s membrane.
After infection, RNA-directed DNA synthesis
is catalyzed by reverse transcriptase.
Two strands of DNA are synthesized and
reside in the host’s chromosome as a
provirus.
16. Concept 11.1 Several Strategies Are Used to Regulate Gene
Expression
Host cells have systems to repress the
invading viral genes.
One system uses transcription “terminator”
proteins that interfere with RNA
polymerase.
HIV counteracts this negative regulation
with Tat (Transactivator of transcription),
which allows RNA polymerase to
transcribe the viral genome.
19. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
Prokaryotes conserve energy by making
proteins only when needed.
In a rapidly changing environment, the most
efficient gene regulation is at the level of
transcription.
E. coli must adapt quickly to food supply
changes. Glucose or lactose may be
present.
20. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
Uptake and metabolism of lactose involve
three proteins:
∀β-galactoside permease—a carrier protein
that moves sugar into the cell
∀β-galactosidase—an enzyme that
hydrolyses lactose
∀β-galactoside transacetylase—transfers
acetyl groups to certain β-galactosides
If E. coli is grown with glucose but no
lactose present, no enzymes for lactose
conversion are produced.
21. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
If lactose is predominant and glucose is low,
E. coli synthesizes all three enzymes.
If lactose is removed, synthesis stops.
A compound that induces protein synthesis
is an inducer.
Gene expression and regulating enzyme
activity are two ways to regulate a
metabolic pathway.
23. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
Structural genes specify primary protein
structure—the amino acid sequence.
The three structural genes for lactose
enzymes are adjacent on the
chromosome, share a promoter, and are
transcribed together.
Their synthesis is all-or-none.
24. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
A gene cluster with a single promoter is an
operon—the one that encodes for the
lactose enzymes is the lac operon.
An operator is a short stretch of DNA near
the promoter that controls transcription of
the structural genes.
Inducible operon—turned off unless needed
Repressible operon—turned on unless not
needed
26. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
The lac operon is only transcribed when a
β-galactoside predominates in the cell:
• A repressor protein is normally bound to
the operator, which blocks transcription.
• In the presence of a β-galactoside, the
repressor detaches and allows RNA
polymerase to initiate transcription.
The key to this regulatory system is the
repressor protein.
29. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
A repressible operon is switched off when
its repressor is bound to its operator.
However, the repressor only binds in the
presence of a co-repressor.
The co-repressor causes the repressor to
change shape in order to bind to the
promoter and inhibit transcription.
Tryptophan functions as its own co-
repressor, binding to the repressor of the
trp operon.
32. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
Difference in two types of operons:
In inducible systems—a metabolic substrate
(inducer) interacts with a regulatory protein
(repressor); the repressor cannot bind and
allows transcription.
In repressible systems—a metabolic product
(co-repressor) binds to regulatory protein,
which then binds to the operator and
blocks transcription.
33. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
Generally, inducible systems control
catabolic pathways—turned on when
substrate is available
Repressible systems control anabolic
pathways—turned on until product
concentration becomes excessive
34. Concept 11.2 Many Prokaryotic Genes Are Regulated in Operons
Sigma factors—other proteins that bind to
RNA polymerase and direct it to specific
promoters
Global gene regulation: Genes that encode
proteins with related functions may have a
different location but have the same
promoter sequence—they are turned on at
the same time.
Sporulation occurs when nutrients are
depleted—genes are expressed
sequentially, directed by a sigma factor.
36. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Transcription factors act at eukaryotic
promoters.
Each promoter contains a core promoter
sequence where RNA polymerase binds.
TATA box is a common core promoter
sequence—rich in A-T base pairs.
Only after general transcription factors
bind to the core promoter, can RNA
polymerase II bind and initiate
transcription.
37. Figure 11.10 The Initiation of Transcription in Eukaryotes (Part 1)
38. Figure 11.10 The Initiation of Transcription in Eukaryotes (Part 2)
39. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Besides the promoter, other sequences bind
regulatory proteins that interact with RNA
polymerase and regulate transcription.
Some are positive regulators—activators;
others are negative—repressors.
DNA sequences that bind activators are
enhancers, those that bind repressors are
silencers.
The combination of factors present
determines the rate of transcription.
41. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Transcription factors recognize particular
nucleotide sequences:
NFATs (nuclear factors of activated T cells)
are transcription factors that control genes
in the immune system.
They bind to a recognition sequence near
the genes’ promoters.
The binding produces an induced fit—the
protein changes conformation.
42. Figure 11.11 A Transcription Factor Protein Binds to DNA
43. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Gene expression can be coordinated, even
if genes are far apart on different
chromosomes.
They must have regulatory sequences that
bind the same transcription factors.
Plants use this to respond to drought—the
scattered stress response genes each
have a specific regulatory sequence, the
dehydration response element.
During drought, a transcription factor
changes shape and binds to this element.
45. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Gene transcription can also be regulated by
reversible alterations to DNA or
chromosomal proteins.
Alterations can be passed on to daughter
cells.
These epigenetic changes are different
from mutations, which are irreversible
changes to the DNA sequence.
46. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Some cytosine residues in DNA are
modified by adding a methyl group
covalently to the 5′ carbon—forms 5′-
methylcytosine
DNA methyltransferase catalyzes the
reaction—usually in adjacent C and G
residues.
Regions rich in C and G are called CpG
islands—often in promoters
49. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
This covalent change in DNA is heritable:
When DNA replicates, a maintenance
methylase catalyzes formation of 5′-
methylcytosine in the new strand.
However, methylation pattern may be
altered—demethylase can catalyze the
removal of the methyl group.
50. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Effects of DNA methylation:
• Methylated DNA binds proteins that are
involved in repression of transcription—
genes tend to be inactive (silenced).
• Patterns of DNA methylation may include
large regions or whole chromosomes.
51. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Two kinds of chromatin are visible during
interphase:
Euchromatin—diffuse and light-staining;
contains DNA for mRNA transcription
Heterochromatin—condensed, dark-
staining; contains genes not transcribed
52. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
A type of heterochromatin is the inactive X
chromosome in mammals.
Males (XY) and females (XX) contain
different numbers of X-linked genes, yet
for most genes transcription, rates are
similar.
Early in development, one of the X
chromosomes is inactivated—this Barr
body is identifiable during interphase and
can be seen in cells of human females.
54. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Another mechanism for epigenetic
regulation is chromatin remodeling, or
the alteration of chromatin structure.
Nucleosomes contain DNA and positively-
charged histones in a tight complex,
inaccessible to RNA polymerase.
Histone acetyltransferases change the
charge by adding acetyl groups to the
amino acids on the histone’s “tail.”
56. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
The change in charge opens up the
nucleosomes as histone loses its affinity
for DNA.
More chromatin remodeling proteins bind
and open the DNA for gene expression.
Thus, histone acetyltransferases can
activate transcription.
58. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Histone deacetylase is another kind of
chromatin remodeling protein.
It can remove the acetyl groups from the
histones, repressing transcription.
59. Concept 11.3 Eukaryotic Genes Are Regulated by Transcription
Factors and DNA Changes
Environment plays an important role in
epigenetic modifications.
Even though they are reversible, some
epigenetic changes can permanently alter
gene expression patterns.
If the cells form gametes, the epigenetic
changes can be passed on to the next
generation.
Monozygotic twins show different DNA
methylation patterns after living in different
environments.
60. Concept 11.4 Eukaryotic Gene Expression Can Be Regulated
after Transcription
Eukaryotic gene expression can be
regulated after the initial gene transcript is
made.
Different mRNAs can be made from the
same gene by alternative splicing.
As introns and exons are spliced out, new
proteins are made.
This may be a deliberate mechanism for
generating proteins with different
functions, from a single gene.
61. Concept 11.4 Eukaryotic Gene Expression Can Be Regulated
after Transcription
Examples of alternative splicing:
• The HIV genome encodes nine proteins,
but is transcribed as a single pre-mRNA.
• In Drosophila the Sxl gene with four exons
is spliced differently to produce different
combinations in males and females.
63. Concept 11.4 Eukaryotic Gene Expression Can Be Regulated
after Transcription
MicroRNAs(miRNAs)—small molecules of
noncoding RNA—are important regulators
of gene expression.
In C. elegans, lin-14 mutations cause the
larvae to skip the first stage—thus the
normal role for lin-14 is to be involved in
stage one of development.
lin-4 mutations cause cells to repeat stage
one events—thus the normal role for lin-4
is to negatively regulate lin-14, so that
cells can progress to the next stage of
development.
64. Concept 11.4 Eukaryotic Gene Expression Can Be Regulated
after Transcription
lin-4 encodes not for a protein but for a 22-
base miRNA that inhibits lin-14 expression
posttranscriptionally by binding to its
mRNA.
Many miRNAs have been described—once
transcribed they are guided to a target
mRNA to inhibit its translation and to
degrade the mRNA.
66. Concept 11.4 Eukaryotic Gene Expression Can Be Regulated
after Transcription
mRNA translation can be regulated.
Protein and mRNA concentrations are not
consistently related—governed by factors
acting after mRNA is made.
Cells either block mRNA translation or alter
how long new proteins persist in the cell.
67. Concept 11.4 Eukaryotic Gene Expression Can Be Regulated
after Transcription
Three ways to regulate mRNA translation:
• Inhibition of translation with miRNAs
• Modification of the 5′ cap end of mRNA
can be modified—if cap is unmodified
mRNA is not translated.
• Repressor proteins can block translation
directly—translational repressors
70. Answer to Opening Question
The CREB family of transcription factors can
activate or repress gene expression by
binding to the cAMP response element
(CRE) sequence found in the promoter
region of many genes.
CREB binding is essential in many organs,
including the brain, and has been linked to
addiction and memory tasks as well as to
metabolism.