Transcription

• The major research advances that led to our modern understanding of DNA were investigated in the 1920s - 1950s.
• The genetic material, DNA or proteins, was investigated in the 1920s - 1950s.
• Griffith (1928) discovered that genetic traits can be transferred between cells, using an unknown substance from virulent bacteria to transform harmless bacteria.
• Avery, MacLeod, & McCarty (1944) demonstrated that DNA is the transforming substance, by sequentially inactivating RNA, protein, and DNA.
• Nucleotide structure, consisting of a 5 carbon sugar, a phosphate group, and a nitrogenous base, was known since the 1920s.
• Chargaff’s (1950) Rule states that the number of A=T and the number of C=G are constant in DNA.
• Rosalind Franklin (1953) discovered that DNA is shaped like a helix (corkscrew) and has a consistent diameter.
• Watson & Crick (1953), based on Franklin’s work, proposed that DNA is a double helix with a sugar-phosphate backbone on the outside.
• Watson & Crick (1953) stated that the two strands of DNA are held together by hydrogen bonds between complementary base-pairs.
• Watson & Crick (1953) stated that the two stands of DNA are antiparallel, running in opposite directions 5’-3’.
• DNA synthesis, where DNA is synthesized in the 5’- > 3’ direction only, is a key aspect of DNA replication.
• DNA replication involves a replication fork, a Y-shaped region where parental strands are unwound.
• RNA (ribonucleic acid) contains ribose, contains uracil (U), is usually single-stranded, is shorter than DNA, and is temporary.
• DNA (deoxyribonucleic acid) contains deoxyribose, contains thymine (T), is usually double-stranded, is longer than RNA, and is permanent.
• Transcription (Gene expression) involves converting the information in DNA into a protein.
• A is the same, why do your blood cells look and act different than your skin cells? Different cells express different proteins. This is called differential gene expression.
• RNA polymerase synthesizes a strand of mRNA in the 5’ to 3’ direction, transcription begins at a promoter sequence and ends at a terminator sequence.
• The process of splicing involves a complex of snRNA and proteins, the spliceosome, which forms a lariat, cuts mRNA, and joins exons.
• In prokaryotes, the entire process of gene expression occurs in the cytoplasm, translation begins before transcription ends, and one mRNA may contain multiple genes (operon).
• Splicing: removes introns (noncoding segments) and joins exons (coding segments).
• Transcription: Synthesis of mRNA from DNA.
• 5’ Cap: Methylated GTP added “backwards” to 5’ end of pre-mRNA, protects from degradation, helps translation initiation.
• In eukaryotes, transcription occurs in the nucleus, RNA is processed before leaving the nucleus, and translation occurs in the cytoplasm.
• RNA polymerase moves down DNA, elongating RNA transcript (5’ ® 3’).
• In eukaryotes, transcription produces pre-mRNA, processing in the nucleus forms mature mRNA, ends are modified, and some segments are removed.
• RNA is produced 5’ to 3’ (just like DNA) so to transcribe from DNA to mRNA, what end of the template DNA strand should you start on?
• Gene: sequence of DNA that codes for a protein.
• Terminator sequences at the end of gene cause mRNA and DNA to dissociate, RNA polymerase releases DNA.
• Translation: Synthesis of protein from mRNA.
• 3’ poly-A tail: string of A nucleotides added to 3’ end of pre-mRNA, protects from degradation, helps with exiting nucleus.
• Alternative splicing: the same mRNA molecule can be spliced in different ways to produce different proteins.
• In eukaryotes, transcription factors help RNA polymerase find the promoter and initiate transcription.
• Transcription involves transcribing a given sequence of DNA.
• Griffith (1928): Genetic traits can be transferred between cells
• Franklin discovered that DNA is shaped like a helix
• Watson & Crick proposed double-helical structure of DNA
• Avery, MacLeod, & McCarty (1944): DNA is the transforming substance. DNA has to be active for transformation to occur.
• Chargaff’s (1950) Rule: # of A=T and # of C=G
• Initiation of transcription is controlled by the binding of RNA polymerase to the promoter.
• Elongation of transcription is the process by which the RNA polymerase moves along the DNA strand, adding nucleotides in the 5' to 3' direction