Gene Expression and Regulation
03:17
DNA is the instructions (program) that tells the cell what to do
•
Proteins are the results of those instructions
•
The study of metabolic defects provided evidence that genes lead to proteins
•
This relationship was first proposed by Archibald
o
Suggested that some metabolic disorders were caused by a blocked
pathway
o
Inherited diseases were the result of the lack of an enzyme
o
A Blockage in pathway not only stops the production of something we
need but it also may lead to the accumulation of something we don’t want.
o
The suggestions of Garrod were confirmed in the 1930’s
George Beadle and Edward Tatum conducted experiment with bread
mold, Neurospora crassa, and demonstrated that different mutants
(generated by x-rays) had the pathway of arginine (an amino acid)
synthesis blocked at different steps.
Beadle and Tatum deduced that the 3 different mutant types each
lacked a different enzyme in the pathway which synthesizes arginine
From these results they formulated the one gene-one enzyme
hypothesis
DNA
RNA
Proteins
Step 1-DNA to RNA
This process is called transcription
Transcription is the synthesis of RNA using DNA as a template
The RNA is complementary to the DNA
RNA that is synthesized from a gene coding for a protein is called
messenger RNA (mRNA)
Differences between DNA and RNA
•
1. Sugar- deoxyribose (DNA) verses ribose (RNA)
•
2. Base thymine (DNA) is replaced by uracil (RNA)
This
preview
has intentionally blurred sections.
Sign up to view the full version.
During transcription of a gene, only one strand (template strand) of
the DNA’s two strands is read
Different genes use different strands as the template strand
Step 2- RNA to protein
This process is called translation
Translation is the synthesis of a polypeptide directed by mRNA
Why translation?
•
Converting the language of nucleic acids into the language of
proteins
o
4 bases in nucleic acids
o
20 amino acids in proteins
translation occurs on the ribosomes
during translation, proteins are synthesized according to the genetic
message of sequential codons in the mRNA
transfers RNA (tRNA) and ribosomal RNA (rRNA) acts as the
“interpreter” between the nucleotide “language” of mRNA and the
amino acid “language” of proteins
In genetic code, a triplet of nucleotides specifies an amino acid
Dictated by the math, since there are 4 nucleotides and 20 amino
acids
•
4 different nucleotides, combining as codons, which are 3 –
nucleotide sequences
•
there could potentially be as many as 64 amino acids
•

This is the end of the preview.
Sign up
to
access the rest of the document.
- Spring '10
- Crousillac
- Cell Cycle, DNA, Mitosis, Proteins, daughter cells
-
Click to edit the document details