Lecture 21: The Eukaryotic Genome

Question 1

Genome

Answer 1

All the DNA in an organism

Question 2

How many genes do humans have and how many base pairs?

Answer 2

30000 genes
3000 million base pairs

Question 3

Exons

Answer 3

Coding section of mRNA that encode for a protein

Question 4

Introns

Answer 4

Regions of non-coding mRNA that are found between exons

Question 5

Splcing

Answer 5

Mechanism by which introns are removed from mRNA and exons are joined together

Question 6

snRNPs

Answer 6

small ribonucleoprotein particle, used to catalyze the splicing reaction

Question 7

How do snRNPs work?

Answer 7

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

Question 8

5’ cap

Answer 8

• 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

Question 9

Poly A tail

Answer 9

-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)

Question 10

What happens at the end of the chromosome?

Answer 10

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)

Question 11

How does the cell avoid DNA getting shorter and shorter?

Answer 11

-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

Question 12

What does telomerase do?

Answer 12

Adds telomeres to the ends of chromosomes so DNA do not shrink
-Prevents loss of genes

Question 13

Centromeres

Answer 13

-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

Question 14

Transposable Elements

Answer 14

-elements that can hop around the genome

Question 15

DNA Transposons

Answer 15

-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

Question 16

Retrotransposons

Answer 16

-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

Question 17

LINES

Answer 17

-Don’t look like a retrovirus but do encode for reverse transcriptase, endonuclease inserts them into the genome

Question 18

Alu elements

Answer 18

-Dont code for reverse transcriptase and uses the pre made enzymes to jump into the genome

Question 19

Pseudogenes

Answer 19

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)

Question 20

Ribozymes

Answer 20

-RNA enzymes
-They can splice out their own introns without snRNPs

Question 21

Slef-Splicing Introns

Answer 21

Intorns that can splice themselves out without needing snRNPs

Question 22

Proof of the RNA world being first

Answer 22

-RNA could be both genetic material and enzymes
-RNA polymerase can self-replicate

Question 23

How are ribosomes a good example of RNA world first?

Answer 23

-Ribosomes catalyze the peptide bond formation between amino acids
- Ribosomes are also completely made up of RNA

Question 24

Tetraploids?

Answer 24

-4n
-Bigger due to more DNA
-Same number of cells but the cells are twice as big

Question 25

How can cells be used to estimate genome size?

Answer 25

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)