Eukaryotic Chromosomal DNA and Gene Expression

Question 1

How big is the human genome?

Answer 1

3.2 Gigabases (3.2 x 10^9 bp)

Question 2

What are retrotransposons?

Answer 2

Retrotransposons are transposons that involve a RNA intermediate. They are transcribed into RNA, which is used as a template for DNA synthesis by a reverse transcriptase encoded by the transposon. This DNA is then randomly inserted into the genome.

Retrotransposons include endogenous retroviruses, LINES and SINES

Question 3

What are LINES?

Answer 3

Long interspersed elements. They are a type of retrotransposon that encode structural proteins, reverse transcriptase and endonuclease. LINE RNA, coupled with its structural proteins and reverse transcriptase, enter the nucleus, nick genomic DNA and use the 3’ end to prime RT off the RNA template.

• Thought to be important in neuronal plasticity.
• Promote inactivation of one X chromosome
• Insertions associated with cancers
• Inherited insertion mutations related to hemophilia and muscular dystrophy

Question 4

What are SINES?

Answer 4

SINEs do not encode a functional reverse transcriptase protein and rely on other mobile elements for transposition. The most common SINEs in primates are called Alu sequences. Alu elements are approximately 350 base pairs long, do not contain any coding sequences, and can be recognized by the restriction enzyme AluI (hence the name).

Question 5

What do the banding patterns in a Giemsa stain tell us?

Answer 5

Light bands = GC rich and contain expressed genes and SINES

Dark bands = AT rich and are rich in L1 repeats