2.1- Protein synthesis

Question 1

How is a protein made and secreted?

Answer 1

The gene that has the coded instructions for a protein such as insulin, housed on chromatin in the nucleus, is transcribed into a length of RNA, called messenger RNA (mRNA).

• Many copies of this mRNA are made and they pass out of the pores in the nuclear envelope to the ribosomes.
• At the ribosomes , the instructions are translated and insulin molecules are assembled.
• The insulin molecules pass into the cisternae of the rough endoplasmic reticulum (RER) and along these hollow sacs
• Vesicles with insulin inside are pinched off from the RER and pass, via microtubules and motor proteins , to the Golgi apparatus.
• The vesicles fuse with the Golgi apparatus, where the insulin protein molecules may be modified for release.
• Inside vesicles pinched off from the Golgi apparatus these molecules pass to the plasma membrane
• The vesicles and plasma membrane fuse, and the insulin is released to the outside of the cell.
• This is a type of bulk transport called exocytosis, an active process for whoch energy is needed

Question 2

How is insulin made?

USE THIS AS EXMAPLE

Answer 2

1) mRNA copy of the instruction (gene)for insulin is made in the nucleus.
2) mRNA leaves the nucleus through a nuclear pore.
3) mRNA attaches to a ribosome, in this case attached to rough endoplasmic reticulum. Ribosomes reads the instructions to assemble the protein (insulin).
4) Insulin molecules are pinched off in vesicles and travel towards Golgi apparatus.
5) Vesicles fuses with Golgi apparatus.
6) Golgi apparatus processes and packages insulin molecules ready for release.
7) Packaged insulin molecules are pinched off in vesicles from Golgi apparatus and move towards plasma membrane.
8) Vesicles fuses with plasma membrane.
9) Plasma membrane opens to release insulin molecules outside.