Lecture 21: The Eukaryotic Genome Flashcards
Genome
All the DNA in an organism
How many genes do humans have and how many base pairs?
30000 genes
3000 million base pairs
Exons
Coding section of mRNA that encode for a protein
Introns
Regions of non-coding mRNA that are found between exons
Splcing
Mechanism by which introns are removed from mRNA and exons are joined together
snRNPs
small ribonucleoprotein particle, used to catalyze the splicing reaction
How do snRNPs work?
snRNPs can recognize the boundaries of introns and exons.
-One snRNP binds to an exon-intron boundary and another binds to another exon-intron boundary
-The two snRNPs then come together and cut one end of the splice site
-Then they loop the intron together and bind the exons
5’ cap
- 5’ cap is added to the 5’ end of the mRNA
- Helps with stability, translation and so that the cell recognizes it as mRNA and not a virus
Poly A tail
-At the 3’ end of the mRNA the sequence AUAAA is recognized
-Another enzyme come in and cuts of the end of the mRNA after the stop codon
-Then it adds approximately 100 A’s(poly A Tail)
What happens at the end of the chromosome?
At the end of the chromosome(5’), there is no upstream okazaki fragment to fill in the gap with DNA
(above where the primer was)
How does the cell avoid DNA getting shorter and shorter?
-Cells put on the end of their chromosomes “junk” DNA, DNA that doesn’t do anything
-Junk DNA gets lost during replication instead of encoding DNA
-Telomeres
What does telomerase do?
Adds telomeres to the ends of chromosomes so DNA do not shrink
-Prevents loss of genes
Centromeres
-Region of non-coding DNA associated with the centric region of the chromosome
-May be involved in the binding of the kinetochore
-Information about how the chromosome should organise themselves in division
Transposable Elements
-elements that can hop around the genome
DNA Transposons
-Splice themselves out of the genome then jump back in by encoding a gene called transposase
-parasitic DNA
-Most of the time it is put in one of the big spaces of genes encoding for no proteins
-However sometimes it will pop it into a gene and cause a disruption resulting in a phenotype
-If they jump into germ cells they can introduce new alleles in a population
Retrotransposons
-Make copies of themselves by being transcribes(act like RNA)
-Use reverse transcriptase to turn their RNA into DNA
-The DNA is then inserted back into the genome
LINES
-Don’t look like a retrovirus but do encode for reverse transcriptase, endonuclease inserts them into the genome
Alu elements
-Dont code for reverse transcriptase and uses the pre made enzymes to jump into the genome
Pseudogenes
Reverse transcriptase often make copies of not only retrotransposons but also they’ll make copies of your genes. Specifically, the gene that is only exons(processed pseudogenes)
Ribozymes
-RNA enzymes
-They can splice out their own introns without snRNPs
Slef-Splicing Introns
Intorns that can splice themselves out without needing snRNPs
Proof of the RNA world being first
-RNA could be both genetic material and enzymes
-RNA polymerase can self-replicate
How are ribosomes a good example of RNA world first?
-Ribosomes catalyze the peptide bond formation between amino acids
- Ribosomes are also completely made up of RNA
Tetraploids?
-4n
-Bigger due to more DNA
-Same number of cells but the cells are twice as big
How can cells be used to estimate genome size?
Cells that make bones, secrete bone around cells and when the cell dies it leaves a hole the size of the cell(this tells us how big their cells were)
