Protein Synthesis

Question 1

What happens during mRNA processing

Answer 1

Introns are removed
The 3’ end is polyadenylated (a string of adenine is added)
The 5’ end is capped with guanine

Question 2

What is alternative splicing

Answer 2

This refers to when the exons in an mRNA molecule are stuck back together in a different order to where they were in the chain before the introns were removed

This allows for a greater diversity of proteins that can be coded for by a single amino acid

Question 3

What is the function of UTRs

Answer 3

They perform functions such as stabilising the mRNA and modulating translation

Question 4

How is mRNA transported out the nucleus

Answer 4

It associates with nuclear proteins to form a messenger ribonucleoprotein particle (mRNP). The mRNP is the exported through nuclear pores

Question 5

How do ribosomes recognise mRNA

Answer 5

They identify the guanine cap at the 5’ end

Question 6

How does tRNA bring the correct amino acid to the ribosome

Answer 6

Each tRNA molecule is specific for each amino acid. The tRNA matches its anticodon to the codon in the mRNA sequence.

Question 7

What are the two pathways a polypeptide chain can take

Answer 7

-cytoplasmic pathway
-endomembrane pathway

Question 8

Where are proteins destined for the endomembrane system synthesised

Answer 8

Rough endoplasmic reticulum

Question 9

Where are proteins destined for the cytoplasm synthesised

Answer 9

Free floating ribosomes

Question 10

What is the endomembrane system

Answer 10

The membrane bound system which includes:
Golgi apparatus
Endoplasmic reticulum
Plasma membrane
Secretory vesicles

Question 11

How does the peptide know where it should be transported to

Answer 11

N-terminal signal peptides contain a target sequence for the proteins location. Depending on the sequence it could end up in the endomembrane system, other organelles and if there is no sequnce at all then it remains in the cytoplasm

Question 12

How are soluble and insoluble proteins sorted in the endomembrane system

Answer 12

Soluble proteins are usually needed in the cisternal spaces in the membrane, or they are secreted in vesicles

Insoluble proteins will stay in the membrane

Question 13

What is anterograde transport

Answer 13

Movement of proteins from the ER to the Golgi apparatus via vesicles

Question 14

What is retrograde transport

Answer 14

Movement of proteins from the Golgi to the ER via vesicles

Question 15

What are the 3 main types of proteins that coat vesicles

Answer 15

Clathrin
COP1
COP2

Question 16

What are the functions of vesicle coat proteins

Answer 16

Help target vesicles to the appropriate membrane
Force flat membranes into spherical buds
Prevent the premature fusing of membranes
Interacting with microtubles to move the vesicles

Question 17

What is constitutive secretion

Answer 17

The secretion of proteins from a cell that is completely unaffected by extracellular signals. This is the default pathway for proteins synthesised by the rough ER

Question 18

What is regulated secretion

Answer 18

Secretion that is effected by extracellular signals. The vesicles will wait at the plasma membrane until a signal molecule triggers them to fuse and secrete their contents

Question 19

What are proteins destined for lysosomes tagged with

Answer 19

Mannose-6-phosphate

Question 20

Which amino acids can have a carbohydrate attached to them via glycolysation

Answer 20

Serine
Threonine
Asparagine