is transcription
GGU one of the codons for the amino acid glycine. Which of the following is another codon for glycine? A. B. C. D. E. GGA AGU GAU AAA UUU
A 16th century scribe
GGU is one of the codons for the amino acid glycine. Which of the following is another codon for glycine? A. B. C. D. E. GGA* AGU GAU AAA UUU
Remember, DNA is the genetic material, but proteins are the workhorses of the cell enzymes cytoskeleton hormones receptors transporters channels etc, etc. Not all cells make all proteins name some housekeeping proteins microtubules, enzymes of glycolysis name some cell-specific proteins RUBISCO, hemoglobin
DNA --> RNA --> protein
Protein is made in 2 steps: DNA --> RNA (transcription) RNA --> protein (translation) Both phases contribute to the control of gene expression. Why is there an RNA step?
several types of RNA are transcribed Some genes use one strand of the double helix, others use the other strand mRNA, rRNA, tRNA are the most common
3 5 5 mRNA tRNA mRNA 3 mRNA rRNA mRNA tRNA DN AN R A
mRNA
tRNA
mRNA
mRNA
rRNA
mRNA
tRNA
DNA RNA
protein protein protein protein protein
protein
protein
protein
only mRNA codes for protein most of the RNA in a cell is rRNA
RNA nucleotides are added to the 3 end of the RNA strand
Transcription
bacteria fungi protists plants insects mollusks bony fish amphibians reptiles birds mammals human
106
107 108 109 1010 1011 1012 number of nucleotides per haploid genome (log scale!!!
genome sizes compared
20 nucleotides/sec in eukaryotes, 50/sec in prokaryotes. Why slower in eukaryotes?
Transcription
By convention, the DNA sequence is written as the non-template strand, so it corresponds to the RNA sequence.
Transcription
this will be the pre-mRNA
Transcription
Which is most accurate, DNA replication or transcription?
Transcription
Which is most accurate, DNA replication or transcription?
Over 100 proteins are present in the eukaryote initiation complex. this will be the pre-mRNA this will be the pre-mRNA
There are typically about 10-15 copies of a mRNA for an expressed gene in a cell, but the number can vary a lot.
You Tube has nice animations of all aspects of molecular biology.
transcription of newt DNA
As the RNA polymerase moves along the DNA, another one can start.
Modification of pre-mRNA in eukaryotes
Modification of pre-mRNA in eukaryotes Sally is a molecular biologist. She needs to find a region of a gene that is unique so that the gene can be distinguished from other, similar genes. Where Sally should look for a small, unique sequence of nucleotides? A) B) C) D) E) 5 cap 5 UTR protein coding segment polyadenylation signal poly-A tail
Modification of pre-mRNA in eukaryotes
RNA splicing in eukaryotes Sally is a molecular biologist. She needs to find a region of a gene that is unique so that the gene can be distinguished from other, similar genes. Where should Sally look for a small, unique sequence of nucleotides? A) B) C) D) E) 5 cap 5 UTR * protein coding segment polyadenylation signal poly-A tail
Introns can be a lot longer than exons Over evolution introns have become more numerous and longer. Dont bother with Fig. 17.11 or related text on splicesomes, or Ribozymes
Exons and domains
For a given gene, only 1 of the 2 sides of the double helix is transcribed. Why? A. only one of the DNA strands runs in a transcribable direction B. the other side is gibberish (nonsense) C. there is not enough room within RNA polymerase to make 2 RNAs D. clustered genes must all be transcribed in the same direction E. RNA transcribed from the other side will produce protein with the correct amino acids, but lined up in the wrong direction
Why have introns? alternative splicing (later lecture) exon shuffling (exons used in different genes over evolutionary time) regulatory sequences
Only 1 of the 2 sides of the double helix is transcribed. Why? A. only one of the DNA strands runs in a transcribable direction B. the other side is gibberish (nonsense) * C. there is not enough room within RNA polymerase to make 2 RNAs D. clustered genes must all be transcribed in the same direction E. RNA transcribed from the other side will produce protein with the correct amino acids, but lined up in the wrong direction
(by convention read as RNA)
The genetic code
Assume A pairs with B, B with C etc. - --- i - - - -u fephbufu f i sbu- - - --- - - - thedogate --- thera - - - t - --
Mutations
Mutations
template strand
What happens if this G mutates to an A?
Mutations
Mutations
What happens if this G mutates to an A? mRNA would read GGU i.e. glycine this is a silent mutation
What happens if this T mutates to an A?
Mutations
Mutations
What happens if this T mutates to an A? the codon reads UAG i.e. Stop nonesense mutation
Where would the addition of an A have the most profound effect?
*
Mutations
Wave Goodbye!!
Where would the addition of an A have the most profound effect? A frameshift mutation near the start of a gene has the most profound effect.
http://www.youtube.com/watch?v=vS6ORxPXBNM