5.4 The end-membrane system

Question 1

What is the nuclear envelope?

Answer 1

perforated by membrane openings called nuclear pores. small molecules and ions can passively diffuse through pores, but large proteins and RNA require active transport.

Question 2

How do vesicles form?

Answer 2

by budding off an organelle taking with them a piece the membrane and internal contents

Question 3

What perts of the cell are involved in the end-membrane system? (8)

Answer 3

1. nuclear envelope
2. Endoplasmic reticulum
3. Golgi apparatus
4. vesicle
5. Lysosome
6. Plasma membrane
7. exocytosis
8. Endocytosis

Question 4

What is a nuclear pore and what is its function?

Answer 4

a large protein complex that allows molecules to move in and out of the nucleus

Question 5

what are ribosomes and what is their function?

Answer 5

the sires of protein synthesis in which amino acids are assembled into polypeptides.

Question 6

What does the ER produce and transport?

Answer 6

lipids and proteins used in and out of cell as well as transmembrane proteins and proteins destined for the yogi apparatus , lysosomes, or export out of cell.

Question 7

What are characteristics of the ER

Answer 7

• the ER is continuous throughout (lumen)
• maze like appearance
• convoluted membrane

Question 8

what is the rough ER and its function

Answer 8

studded with ribosomes, synthesizes transmembrane proteins and proteins that end up in the interior of organelles.

Question 9

What is smooth ER and its function?

Answer 9

lacks ribosomes and is the primary site of lipid synthesis (fatty acid and phospholipid biosynthesis)

Question 10

What are the 3 primary roles of the golgi apparatus?

Answer 10

1. it further modifies proteins and lipids produced by the ER
2. it acts as a sorting station to as proteins and lipids move into their final destination
3. the site of synthesis of most cells carbohydrates

Question 11

What is the structure of the golgi apparatus?

Answer 11

cisternae- series of membrane sacs that make up the golgi body
(can go against flow to send protein back to cisternae to fix)

Question 12

how is a protein or lipid modified in the Golgi body?

Answer 12

a sequence of steps performed in different regions of the organelle with different enzymes catalyzed for specific reactions

Question 13

What are lysosomes and their function?

Answer 13

• specialized vesicles derived from the Golgi apparatus that degrade damaged or unneeded macromolecules.
• contain a variety of enzymes that break down macromolecules and leave organelle as broken down macromolecules.

Question 14

what is the ideal pH of a lysosome and how is it maintained

Answer 14

pH 5 for optimum activity of enzymes maintained by protein pumps

Question 15

What is protein sorting and how does it occur?

Answer 15

• the process where proteins end up where they need to be

- directs proteins to the cytosol, the lumen, the membranes of end-membrane system, or even to of cell.

Question 16

How are proteins from free ribosomes sorted?

Answer 16

after they have been translated and contain an amino acid sequence called signal sequences which allowed them to be recognized and sorted.

Question 17

what happens to proteins with a signal sequence vs proteins without

Answer 17

without- stay in the cytosol
destined for the mitochondria and chloroplast- sequence at amino acids
destined for nucleus- sequence located internally

Question 18

what enables proteins to move through pores in the nuclear envelope

Answer 18

nuclear localizing signals.

Question 19

Protiens produced by ribosomes end up on the RER end up (3)

Answer 19

1. within the lumen of the end-membrane system
2. embedded in its membrane
3. sectreted out of the cell

Question 20

what is the name of the second sequence the prevents the polypeptide from continuing to the lumen?

Answer 20

signal anchor sequence

Question 21

what is the process for entering the lumen?

Answer 21

1. a signal receptor protein (SRP) binds to signalling sequence at amino end and halts translation
2. SRP receptor brings ribosome to transmembrane channel; SRP dissociates; protein synthesis resumes; polypeptide chain threaded through channel.
3. protein ends up in lumen of ER where is remakes, transporters, or secreted out

Question 22

transmembrane protein targeting

Answer 22

1. protein with signal anchor sequence threaded through channel in ER membrane until signal anchor sequence is reached
2. ER channel releases protein into the membrane
3. when translation is complete, the protein remains in the membrane