Protein Synthesis & Collagen

Question 1

What is Fmoc?

Answer 1

AA residue. It’s a protective group. It protects amino group.

Question 2

Why are some codons less subject to causing a mutation in an amino acid sequence?

Answer 2

because of degeneracy or because of the abundance of such tRNAs
• There are 20 amino acids with 61 possible codons.
• Only Met and Trp have a single codon.

Question 3

Proteins with no targeting sequence go where?

Answer 3

remain in the cytosol

Question 4

The signal sequence on an emerging peptide is bound by what?

Answer 4

signal recognition particle (SRP)

Question 5

How are proteins for nucleus/chloroplast/mitochondria delivered ?

Answer 5

Proteins for mitochondria/chloroplast/nucleus bind chaperone proteins in the cytosol and are delivered to receptors/pores on the exterior of
the organelle.

Question 6

Which organelle doesn’t require the signal sequence to be removed?

Answer 6

Peroxisome (matrix)

Most sequences are found on the C-terminus instead of N-terminus which is special.

Question 7

What is the Sec61α complex ?

Answer 7

• The channel is shaped like a hourglass with a narrow constriction
• The pore is formed by a ring of isoleucine residues
• When there is no translocation the pore is blocked by a helical plug in red

Question 8

What is a translocon?

Answer 8

the complex that transports nascent polypeptides with a targeting signal sequence into the interior space of the endoplasmic reticulum from the cytosol

Question 9

ANY transmembrane protein needs to go where?

Answer 9

ER pathway

Question 10

What is the drawback of chemical synthesis?

Answer 10

Not 100% yield bc it’ll be a mixture of peptides in the solution.

Question 11

Why should anything longer than 20 AAs be done in vivo?

Answer 11

Bc ribosomes can incorporate 20 AAs with 100% yield.

Question 12

Difference between in vivo and in vitro protein synthesis?

Answer 12

In vivo- N—> C terminus

In vitro- C–> N terminus, Need 2 protect amino group and activate carboxyl group

Question 13

What is the structure of collagen?

Answer 13

• Collagen is an important constituent of connective tissue: tendons, cartilage, bones, cornea of the eye
• Each collagen chain is a long Gly- and Pro-rich left-handed helix
• Three collagen chains intertwine into a righthanded superhelical triple helix
• The triple helix has higher tensile strength than a steel wire of equal cross section
• Many triple-helices assemble into a collagen fibril

Question 14

Collagen types?

Answer 14

Procollagen to collagen. Collagen I and II where the basic unit is tropocollagen. Procollagen cleaved to tropocollagen.

Question 15

Collagen triple superhelix is suited to what type of AA composition?

Answer 15

Unusual amino acid composition

Repeating triplet: -(Gly-Pro- (Pro/HyP))

Question 16

Collagen has what 2 special elements?

Answer 16

4-Hydroxyproline and Lysine Cross-linking

Question 17

How are collagen cross links formed?

Answer 17

by covalent bonds between side chains that

have been post-translationally modified

Question 18

What type of channel does the translocon have?

Answer 18

The translocon has a central gated hydrophobic channel that allows passage of the peptide but not small ions. Pulls the protein through with no energy.