Some questions on DNA and genes

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ronaldofan717
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Some questions on DNA and genes

Post by ronaldofan717 » Mon Feb 04, 2008 2:57 am

Hi! I don't really get these questions and thought that maybe someone could help me out:)
1. What are three types of polypeptides encoded by DNA? and what are their functions?(if you just give me a type, I'm sure I'll find it online somewhere, so don't worry too much about the functions)

2. Do two different genes make the same protein? Could you explain that too?

3. A house fly has 15,000 genes, so how many different proteins does it make?
Thanks a lot!!

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mith
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Post by mith » Mon Feb 04, 2008 6:39 am

1. no idea...
2. splicing
3. def of gene(actually this can vary)
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Post by dr. dugmore » Mon Feb 04, 2008 7:13 am

A house fly has 15,000 genes, so how many different proteins does it make?

not sure, but can you estamate how many proteins are made just by how many genes? im not sure you can.... correct me if im wrong
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MrMistery
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Post by MrMistery » Mon Feb 04, 2008 9:12 pm

well it's a bit tricky, as Dave implied.
First of all, 15000 genes means proteins+RNA that is not translated(such as rRNA, tRNA, SRP-RNA etc). So from this point of view i guess the estimate would be a bit less than 15000. But generally an organism has many more proteins than genes - us humans have 25000 genes and more than 50000 proteins. THere are a number of mechanisms that allow this, such as alternative splicing, poly-A site choice etc.
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Re: Some questions on DNA and genes

Post by Cat » Fri Feb 15, 2008 12:27 am

1. What are three types of polypeptides encoded by DNA? and what are their functions?(if you just give me a type, I'm sure I'll find it online somewhere, so don't worry too much about the functions)

I don't know what you mean by type. Most likely you mean transcription factors, enzymes, and structural proteins, but I don’t know for sure.

2. Do two different genes make the same protein? Could you explain that too?

You can argue both ways: if you define "gene" as DNA sequence responsible for protein production, then two genes can have the same coding sequence (or slightly different, since if you look up translation you will notice that some changes in the DNA bases do not result in the change of the protein sequence) but different in terms of non-coding regions (hence, different expression patterns or levels etc...) however, that usually happens when gene gets duplicated and sequences diverge over time. Now, if you define "gene" as any DNA sequence responsible for the production of a particular protein, then the answer is NO and the different DNA sequences are just different versions of the same gene (different alleles of the same gene if they are located on the sister chromatids). There is no consensus on the definition of the gene yet so you can decide.

3. A house fly has 15,000 genes, so how many different proteins does it make?
Thanks a lot!!

A lot more than that. Before functional protein is made, sequences have a potential to be modified post-transcriptionally (e.g. splicing), during translation (e.g. alternative start codons), post-translationally (e.g. protein splicing) and then undergo additional modifications (such as glycosylation).

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