Gene Expression: From Gene to Protein
How do we get from DNA to expressed traits? (Not a direct relationships, intermediary (proteins) )
DNA code for proteins, proteins give us phenotypes
Central Dogma of Molecular Biology
DNA replicates itself, DNA is transcript RNA and then translated to proteins
Genes Code for Protein
How was this discovered?
The study of metabolic defects
Archibald Garrod (1857-1936)
attributed biochemical roles to genes
Beadke and Tatum ( 1941)
Link between genes and enzymes
One gene-one enzyme hypothesis
RNA
Types
Characteristics
Transfer (tRNA)
Messenger (mRNA)
Ribosomal (rRNA)
Single strand, base of uracikl instead of thymine, sugar is ribose, no specific 3-D shape
Transcription
Overview
Main Players: Template DNA (double strand), RNA polymerase (enzyme that does the transcribing) mRNA (transcribed from template
DNA template to generate RNA, adds nucleotides from 3' end of RNA
3'- 5' strand of DNA= Template
5' - 3' RNA molecule generated (INSERT DIAGRAM)
RNA Polymerase
Types
one RNA Polymerase
Three RNA polymerases (I, II, III in nuclei)
RNA polymerase II is used for mRNA synthesis in eukaryotic
Three stages
Initiation:
Elongation: ONLY IN EUK CELLS
Termination
Starts at promotor (RNA binds here)
"Upstream" of gene
In prokaryotes, RNA poly recognize and binds direct to promoters
Eukaryotes: a special transcription factor recognizes the TATA (AT rich region) box within the promotor. RNA Polymerase II binds the promoter. Other transcription factors also bind to the promotor
A single gene can be transcribed simultaneously by several RNA polymerases
Termination sequences in the DNA that allows it to stop (insert chart for pro and euk difference for termination)
Following transcription, the sequence of the RNA transcript is complementary to which of the following? Template Strand (base pairing rule)
Prior, modified guanine nucleotide to the 5' end (5' cap) and a adenine nuceotide add to the 3' end (Poly A tail). Adds stability
RNA splicing is also occurring in which introns are cut out, exon are spliced together are kept in for the mature mRNA (this is because not all are coding sequences)
Done by spliceosomes
Translation
In Prokaryotes: Transcription and translation occur simultaneously
In Eukaryotes, translation is occured at the ribosomes
Series of nucleotides are used to translate to proteins.
Genetic Code: Triplet Code: 3 bases = codon = 1 amino acids
Read 5' 3 ' direction, there are redundancy but NO ambiguity (several different codons code for secific amino acid, but any one codon indicates only one amino acid), no overlapping, reading frame encodes proteins, and there are start and stop codons
no. of nucleotides per mRNA = 3x no. amino acids
Cracking the code
Matching each codon to its specific amino acid
Marshal Nirenberg (1961)
First to crack the code, UUU (phenylalanine)
Codon Table: 61 of 64 triplets code for amino acids
AUG indicate the start of translation (Met)
Three condon signal termination of translation
One gene: One enezyme hypothesis (NEED MORE INFO ON THESE THREE HYPOTHESIS)
One Gene one protein hypothesis
One Gene one polypetide hypothesis *