Two questions on gene -> protein synthesis

Discussion of all aspects of biological molecules, biochemical processes and laboratory procedures in the field.

Moderators: honeev, Leonid, amiradm, BioTeam

Post Reply
loom91
Garter
Garter
Posts: 2
Joined: Fri Jul 27, 2007 9:50 am

Two questions on gene -> protein synthesis

Post by loom91 » Fri Jul 27, 2007 11:06 am

Hi,

I gave up biology in the tenth grade because the endless terminology of descriptive biology was too boring for me, but I've continued to independently study the parts I like (biochemistry, MCB, genetics, evolution). Two questions occurred to me:

1)Every chromosome is one long DNA molecule with a long chain of nucleotide base pairs. Yet a single chromosome encodes the synthetic blueprint of many proteins. So how do the ribosomes recognise when they should stop making a protein and interpret the later DNA as the instructions for another different protein?

2)During crossing-over in meiotic division, chromosomes are spliced and glued at random. How does this process ensure that the resulting haploid set contains a workable set of instructions? For example, say a certain sequence encodes the synthetic information for a particular protein. When it is spliced down the middle and joined to something else, what's the guarantee that the resulting sequence does not encode some toxic, or at least useless protein?

Thanks.

Molu

blcr11
Viper
Viper
Posts: 672
Joined: Fri Mar 30, 2007 4:23 am

Post by blcr11 » Fri Jul 27, 2007 11:38 am

1. In eukaryotes, mRNAs are almost exclusively mono-cistronic, that is, they code for only one message for one polypeptide. There are initiation and termination signals that the polymerase complex responds to. The ribosomes only have to translate one message/polypeptide at a time.

2. The crossing over isn't as random as all that. The crossing over events don't happen just any old place, but within homologous sections of paired chromosomes. You're exchanging corresponding pieces of maternal and paternal chromosomes which may contain different alleles of the same genes, but you won't, in general, be jumping into the middle of different genes, as you seem to think. Things like that can happen, but they are rare events.

loom91
Garter
Garter
Posts: 2
Joined: Fri Jul 27, 2007 9:50 am

Post by loom91 » Fri Jul 27, 2007 12:10 pm

blcr11 wrote:1. In eukaryotes, mRNAs are almost exclusively mono-cistronic, that is, they code for only one message for one polypeptide. There are initiation and termination signals that the polymerase complex responds to. The ribosomes only have to translate one message/polypeptide at a time.

2. The crossing over isn't as random as all that. The crossing over events don't happen just any old place, but within homologous sections of paired chromosomes. You're exchanging corresponding pieces of maternal and paternal chromosomes which may contain different alleles of the same genes, but you won't, in general, be jumping into the middle of different genes, as you seem to think. Things like that can happen, but they are rare events.


Thanks.

1)I don't get what you mean by ribosomes only having to translate one message/polypeptide at a time. Do you mean that DNA contains termination instructions? That is, the ribosomes stops synthesising the current protein once it encounters some particular code?

2)Say there's one protein for a blue pigment and one for a red pigment. They correspond to alleles. Now if I take half of the blue gene and append it to half of the pink gene, isn't it highly likely that the resulting mashed-up protein may not produce pigments at all? A mix-n-match of two different molecules does not, in general, have close resemblances to either!

Molu

User avatar
khenwood
Death Adder
Death Adder
Posts: 65
Joined: Thu Jun 21, 2007 3:15 pm
Location: Washington DC

Post by khenwood » Fri Jul 27, 2007 3:15 pm

1 - Stop Codon

2 - This really depends on how & where the two genes were joined. But yes, it's possible that the resulting combination will be dysfunctional & won't product a pigment. Or a mosaic. Or just one pigment, depending what the dominant/recessive characteristics are.
scienceboard.net

Post Reply

Who is online

Users browsing this forum: Bing [Bot] and 5 guests