Exam 1

Question 1

Briefly explain the process of protein glycosylation in yeast (e.g. which proteins
are glycosylated, where does glycosylation occur, glycosylation sites)

Answer 1

1. recognition of signal sequence at ER, co-translational translocation into ER
2. recognition of Asn-X-Ser glycosylation site while translocated into ER, transfer
   of core oligosaccharide onto Asn (N-linked) from membrane-bound dolichol
   carrier
3. subsequent trimming – Calnexin/Clareticulin cycle – cleavage of terminal
   glucose residues leaving mannose residues exposed
4. further trimming during passage through ER, Golgi until final secretion

Question 2

What is the purpose of protein glycosylation in Eukaryotes?

Answer 2

Trafficking through ER and golgi – secretion or to other organelles.
Protein quality control – folding, disulfide bridge formation, further posttranslational
modifications.

Question 3

True or False: Proteins that are typically secreted by their native hosts are more stable than
intracellular proteins.

Answer 3

TRUE

Question 4

True or False: Hypermannosylation of recombinant proteins is a common feature among
Saccharomyces, Pichia and Aspergillus expression systems.

Answer 4

FALSE: Hypermannoslation occurs in prokaryotes, NOT eukaryotes (all of those species are fungi)

Question 5

True or False: Gene expression in Saccharomyces cerevisiae is under negative control

Answer 5

FALSE: Saccharomyces is a eukaryote, thus its gene expression is under POSITIVE control

Question 6

True or False: A modified Ti-plasmid is used to transform plant cells

Answer 6

TRUE

Question 7

True or False: Pichia pastoris is a crabtree positive yeast

Answer 7

FALSE: It is crabtree negative

Question 8

True or False: Mating type switch is a characteristic of homothallic Saccharomyces strains

Answer 8

TRUE