How do genes know where they are on the body?

C

Candide

Registered Senior Member
How do genes know where they are on the body?

why don't we start growing fingernails on our nose? why doesn't a heart start growing where our bladder is and vice versa?
 
Genes don't 'know' where they go. Its like a really complex chemical reaction which is regulated by chromosomes. You could say that its not the genes that 'know', but the chromosomes.

Have you learned about transcription, translation, the different phases and all that? It makes perfect sense after you understand the processes.
 
i haven't. i am a layperson who just thought one day, we have all these cells, and in each there is DNA, now how does a cell in a foot know to grow "foot" and a cell in the eye to grow "eye"?

i probably sound a bit simple for saying this. how do chromosomes know where they are?

okay, let me guess. i might say that cells in all different parts of the body are different. the plan of these cells began in the womb. skin cells work in such a way that they only read off "skin cell" sections of DNA, not "eye cell" bits

is that close? if you want i'll continue but i think i've embarassed myself enough for one night. ;o)
 
You are close, but it is more complex. All cells have the same DNA, and all have the same genes in them. These genes all code for a protein or RNA product (most genes code a protein end product) via transcription in which proteins read the DNA and produce RNA, and then translation, in which an RNA-protein complex reads the RNA transcription product and creates a protein.

The difference between each cell type, is what combination of genes are expressed (which means they are transcribed and translated), which leads to a different combination of proteins in each cell type. These protein combinations are what lead to the phenotype (what we see) of the cell. These proteins also decide what the function is.

Now, there are various ways that genes can be silenced, or not expressed. There can be proteins that bind to sections of the DNA and prevent transcription, there can be other genes that produce an RNA product that binds to the RNA transcript and prevents it from being translated, etc. There are also chemical signals, which can be in the form of sugars, steroid hormones, proteins and a whole slough of other molecules that can induce gene expression. These dictate which gene is expressed when and where during development, and essentially leads to cells being specialized.

I hope that helps a little.
 
The details differ per metazoan species, but basically positional information present in the fertilized egg is used to create more detailed positional information. And combining different sets of positional information generates more positional information.

that's just general...

want to go into detail?
 
hello all, thank you for your responses. the question has been answered for me. if you would like to go into more detail I for one will read on.
 
Idle Mind said:
You are close, but it is more complex. All cells have the same DNA, and all have the same genes in them. These genes all code for a protein or RNA product (most genes code a protein end product) via transcription in which proteins read the DNA and produce RNA, and then translation, in which an RNA-protein complex reads the RNA transcription product and creates a protein.

The difference between each cell type, is what combination of genes are expressed (which means they are transcribed and translated), which leads to a different combination of proteins in each cell type. These protein combinations are what lead to the phenotype (what we see) of the cell. These proteins also decide what the function is.

Now, there are various ways that genes can be silenced, or not expressed. There can be proteins that bind to sections of the DNA and prevent transcription, there can be other genes that produce an RNA product that binds to the RNA transcript and prevents it from being translated, etc. There are also chemical signals, which can be in the form of sugars, steroid hormones, proteins and a whole slough of other molecules that can induce gene expression. These dictate which gene is expressed when and where during development, and essentially leads to cells being specialized.

I hope that helps a little.
Click to expand...

very excellent explanation!
 
thank you very much again Idle Mind, it is a concise explanation that has interesting detail.

"The details differ per metazoan species, but basically positional information present in the fertilized egg is used to create more detailed positional information. And combining different sets of positional information generates more positional"

this sounds interesting too. is this related to growing through childhood & puberty?

also mitosis, the dividing of somatic cells. this obviously happens but i find it hard to imagine when i look at my skin... how can something be actively splitting down there? in the diagrams in biology books the cells tend to float about.
 
Candidethank you very much again Idle Mind said:
Yes it was good. As he/she stated, although all cells in the body have all the genes that comprise the genome, only a small percentage of those genes will be active at a given time in a given cell. ie. only those genes that are relevant to the cell’s specific function and those genes that are involved in basic cellular processes such as DNA maintenance and repair, DNA replication and energy production. (The so-called “housekeeping genes”.) Although Idle Mind mention a few mechanisms by which genes are silenced, the most fundamental mechanism a cell uses to permanently silence irrelevant genes is via repressive chromatin structure. In other words, the chromosomal regions encompassing these genes adopt a tight structure that physically prevents access to the genes by the necessary proteins needed to activate it, such as RNA polymerases and transcription factors.

Candide said:
this sounds interesting too. is this related to growing through childhood & puberty?
Click to expand...

No, SM is referring to the earliest mechanisms by which development from a single-celled zygote occurs. It doesn’t really apply to your question.

Candide said:
also mitosis, the dividing of somatic cells. this obviously happens but i find it hard to imagine when i look at my skin... how can something be actively splitting down there? in the diagrams in biology books the cells tend to float about.
Click to expand...

Your body is a giant matrix of interconnected proteins, predominantly collagen. Nearly all the cells of your body are “encased” inside this scaffold. So, as you can now imagine, nearly all cell-cell interactions, cell migration, cell division and cell functioning occurs whilst in contact with the extracellular matrix.
Click to expand...
 
use search terms morphogen gradient, transcription factors, positional information, embryogenesis, developmental genetics.

i could probably dig up a paper i wrote on drosophila wing imaginal disc development. it goes into all the chemical interactions and selective gene expression i think you're asking about.

i'm excited to see spurious summarize it. this is a lifetime of study to get just a small part of the story. i can't wait to see what he says.
 
thank you more! i'm learning a lot.

"Your body is a giant matrix of interconnected proteins, predominantly collagen. Nearly all the cells of your body are “encased” inside this scaffold. So, as you can now imagine, nearly all cell-cell interactions, cell migration, cell division and cell functioning occurs whilst in contact with the extracellular matrix."

this collagen stops the cells falling off the body and cell mechanics happens inside this glue. that makes sense.

it's amazing that each part of the body sings off only a small part of the DNA songsheet. what determines the size of the choir?

one wonders how genes coordinate macro features like height or weight. how can size be "in one's genes" - it's a property of groups of genes working together.

i will continue to ask questions because i think that shows you are listening. don't feel obliged to answer them!
 
there's no one gene for any given thing. each little bitty characteristic results from the complex interaction of hundreds of genes, most of them indirectly.
 
surely a giant has more cells than a dwarf. i can understand why cells on different parts of the body do their different things. but what makes someone taller? we don't all have the same number of cells in our body. tall is a physiological concept that refers to collection of cells. the size of the choir of cells is mostly determined during initial development of cells within the womb and the process of childhood, with environmental and genetic causes.
 
Idle Mind said:
You are close, but it is more complex. All cells have the same DNA, and all have the same genes in them. These genes all code for a protein or RNA product (most genes code a protein end product) via transcription in which proteins read the DNA and produce RNA, and then translation, in which an RNA-protein complex reads the RNA transcription product and creates a protein.

The difference between each cell type, is what combination of genes are expressed (which means they are transcribed and translated), which leads to a different combination of proteins in each cell type. These protein combinations are what lead to the phenotype (what we see) of the cell. These proteins also decide what the function is.

Now, there are various ways that genes can be silenced, or not expressed. There can be proteins that bind to sections of the DNA and prevent transcription, there can be other genes that produce an RNA product that binds to the RNA transcript and prevents it from being translated, etc. There are also chemical signals, which can be in the form of sugars, steroid hormones, proteins and a whole slough of other molecules that can induce gene expression. These dictate which gene is expressed when and where during development, and essentially leads to cells being specialized.

I hope that helps a little.
Click to expand...

If I were Candide I would now have asked how the combinations of genes, proteins and whatever know where to be expressed themselves that provide knowledge for other genes to know where they are on the body.
 
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