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Biological Information

Brother Gregory speaks to his class,

The subjects for today's lesson is the nature and expression of biological information, or how if the genetic code interpreted and used? You must follow the lesson and try to answer the questions.

"Let us begin .......

"Life on earth has formed a continuous thread of unbroken existence for 3.5 billion years. During that time, as generation followed generation, the link between ancestors and descendants was DNA and the genetic information it carried.

the outward, physical manifestation of internally coded, inheritable information.


definition -|- phenotype -|- genotype -|- relationship
trait -|- red petals -|- pigment -|- role of proteins
proteins are polyers -|- genes and codes


"This definition defines the relationship between the stored library of information each cell and organism carries within it, and the physical presence of an organism in its world and environment.

"It also tells us the relationship between these two ideas; information and what the information produces.

"In my experiments in pea hybridizations I have tried to find out how this biological information can be inherited, but how the biological information is expressed as parts of the organisms body and behavior is more complex.

"What is needed is a simple concept - a small, easily studied part of the overall body of the creature. This is the idea of a genetic trait such as the red color seen in the petals of a flower.

"By studying how the stored biologicial information in the cells of the plant produce the red color seen in the petal flowers, it is possible to determine how all biological information is processed and expressed.

"There is a flow of information from the codes in the DNA molecules to the final production of redness in the flower petals.



flow of information -|- genetic code

The Genetic Code - how the information is stored.

"The structure of the DNA molecule was determined by Watson and Crick. They showed that each DNA molecule was a double helix in which two polynucleotide strands were twisted around one another.

"The genetic code took longer to break, but is now known to consist of a series of three letter 'words', each one of which codes for the insertion of a specific amino acid at that point on a polypeptide chain.

Breaking the genetic code
find out what the codes words mean

"So, how did it go? "How long did it take you to find out which amino acides are coded for by which three letter words?

"I would like to see your results and conclusions some time... but first, why don't you answer some simple questions about what you did and what you found ...


ribosomes -|- tRNA -|- translation:Start translation:Elongation
translation:End -|- protein completion

Transcription and Translation - getting the message out

"Once the required gene has been identified, the double stranded DNA molecule is unwound. This is not a simple process and requires the use of specialized unwinding proteins and ATP energy.

"During the process of transcription a single strand of RNA is synthesized using a double stranded DNA molecule as a template. This forms a messenger molecule that will carry the information onto the next stage.

"The process of transcription is catalyzed by a multisubunit enzyme called RNA polymerase, which needs as substrates double stranded DNA, and the ribonucleotides ATP, UTP, CTP and GTP.

"At the end of the transcription process the cell has made a molecule of RNA that now holds all the codes and code words needed for the correct sequence of a polypeptide chain; this is the messenger RNA (mRNA) molecule.

"When it is finished, messenger RNA is a single strand of RNA that has been copied from DNA molecule.

"The mRNA moves into the cytoplasm where it finds all the tools and supplies it needs to start the process, of translation - making the polypeptide chain.

"An important tool in the next part of the process is a small RNA molecule called transfer RNA, or (tRNA) - which has two important roles in decoding the messsage.

"This molecule carries a single amino acid joined to one end, and at a bend in the molecule a region known as the anticodon, which will be important in the translation process.

"Ribosomes are where the translation occurs. Each ribosome is a complex of proteins and special RNA called ribosomal RNA (rRNA). In both prokayotes and eukaryotes active ribosomes are composed of two subunits called the large and small subunit. Bacterial ribosomes (prokaryotic) are smaller than eukaryotic ribosomes.

Translation
- the full sequence

"Translating the genetic code takes place on the surface of the ribosome. It proceeds in a number of steps and stages that bring tRNA molecules to the surface of the ribosome where the codon (on the mRNA) is matched up with the anticodons (on the tRNAs).



mutations -|- mutagenesis


Mutations - damaging the message

"A mutation occurs when a DNA gene is damaged or changed in such a way as to alter the genetic message carried by that gene.

"A normal gene consists of a string of letters in which is written the genetic code. A DNA molecule is transcribed into mRNA and then the messsage is correctly translated into a polypeptide sequence.

"A mutated gene also consists of a string of letters in which is written the genetic code. But, in this message, for example, one of the letters is changed, or mutated to a different letter. This is a point mutation.

"Mutations fall into several common categories depending on the kind and type of damage or alteration that has taken place. In all cases, however, the damage to the DNA results in an alteration of the message being made from this DNA and thus, at least potentially, damage to the phenotype of the organism.

Control of genes

"Even simple organisms such as bacteria have as many as 3000 genes, producing protein products such as enzymes, cell wall components, building proteins, ribosomal proteins and many others.

"It would be both wastefull and inefficient to make all proteins continuously. The cell, therefore, needs some method of controling when and where these many different proteins are made

The Operon:

"Four regions of the DNA control the production of a protein - these are the activator, promoter and operator regions which lie just ahead of the structural part of the gene which carries the needed codes and code words, and is used to make mRNA.

"Often located in a different region of the DNA, the regulator gene codes for a small protein molecule called the repressor.

Induction:

"Inducible genes are those that are normally turned off - that is, not producing mRNA or protein - until they are needed. The tiny protein molecule produced by the regulator gene binds to the operator region of a structural gene and prevents it from being transcribed.

Repression:

"Other genes are normally active and able to be constantly transcribed, because the repressor protein is produced in an inactive form. On the arrival and binding of the corepressor molecule the complex can act as a functional repressor and block the structural gene by binding at the operator site.

"This turns the gene off - or represses the production of the mRNA and structural gene protein.


definition -|- phenotype -|- genotype -|- relationship
trait -|- red petals -|- pigment -|- role of proteins
proteins are polyers -|- genes and codes

ribosomes -|- tRNA -|- translation:Start translation:Elongation
translation:End -|- protein completion

mutations -|- mutagenesis

Science@a Distance
© 2004, Professor John Blamire