Endomembrane System and Bulk Transport Processes

Question 1

describe the Endomembrane System

Answer 1

• a membrane system interconnected by direct physical contact or transfer by vesicles

Question 2

• what does the endomembrane system include

Answer 2

• nuclear envelope
• endoplasmic reticulum (smooth + rough)
• Golgi apparatus
• Vesicles
• lysosomes
• vacuoles
• plasma membrane

Question 3

describe the er

Answer 3

• is composed of 2 regions

- Smooth ER (sER) and rough ER (rER)

Question 4

what are the functions of sER

Answer 4

• metabolism of carbohydrates
• lipid synthesis for membranes
• detoxification of drugs and poisons
• storage of calcium ions
• extensive sER in cells active in these processes
• the amount of sER can be increased or decreased to meet demand

Question 5

what are the functions of rER

Answer 5

• has a rough appearance due to ribosomes
• involved in protein synthesis
• secreted and membrane-bound proteins enter the lumen (interior) of the rER
• then they are processed by the rER and the rest of the endomembrane system for release at the cell or retention on the cell membrane

Question 6

what are the functions of the Golgi complex

Answer 6

• series of membrane sacs and associated vesicles
• receives, modifies, sorts and ships proteins that are arrive from the rER
• has polarity: cis and trans face
• vesicles from endoplasmic reticulum arrive at the cis face
• processed vesicle leaves at the trans face

Question 7

what are the 3 steps/function in the Golgi complex

Answer 7

• glycosylation
• sorting proteins
• directing vesicle trafficking

Question 8

what happens in the glycosylation stage

Answer 8

• the vesicles arrive from the rER
• addition of carbohydrates to proteins
• important for secreted or cell surface proteins
• Golgi also produces many polysaccharides which may also be secreted from the cell

Question 9

what happens in the sorting proteins stage

Answer 9

• adds molecular markers to direct proteins to the correct vesicles before ‘budding’ from the TRANS face

Question 10

what happens in the directing vesicle trafficking stage

Answer 10

• adds molecular ‘tags’ to vesicles leaving the trans face to direct them to the correct targets
• such tags are often short proteins exposed on the vesicles surface
• acts as docking sites when they reach their target
• some tags direct vesicles to lysosome
• other direct to secretory pathways
• important for release and surface expression

Question 11

With Bulk transport across the plasma membrane, what are the 5 types

Answer 11

• exocytosis
• endocytosis
• phagocytosis
• pinocytosis
• receptor-mediated endoctosis

Question 12

what happens in Exocytosis

also what are the 2 subtypes of exocytosis

Answer 12

• it transports material out of the cell or delivers it to the cell surface
• constitutive exocytosis: - releases extracellular matrix proteins
• regulated exocytosis: - releases hormones and neurotransmitters

Question 13

what happens in Endocytosis

Answer 13

• the cell takes in molecules and particular matter at the plasma membrane

Question 14

what happens in phagocytosis

Answer 14

• cell ‘eating’
• uptake of ‘food’ particles
• forms a phagocytic vacuole which is ‘digested’ by the lysosomes
• in humans this occurs in macrophages

Question 15

describe what pinocytosis

Answer 15

• cell ‘drinking’
• uptake of extracellular fluid containing various solutes such as protein and sugars
• uptake vesicle is formed with aid of a coat protein
• uptake in non-selective

Question 16

describe what receptor-mediated endocytosis is

Answer 16

• specialized form of pinocytosis
• allows the cell to take up bulk quantities of specific substances which may be present at only low concentrations in the extracellular fluid
• receptor proteins are used to selectively capture the required solute

Question 17

Describe lysosomes

Answer 17

• is an organelle that bounded by a membrane
• phagocytic vacuoles fuse with lysosomes
• lysosomes are membrane bound organelles, that are made up by rER and Golgi body containing hydrolytic enzymes

Question 18

what do Lysosomes do

Answer 18

• they degrade proteins, lipids, carbohydrates and nucleic acids, and release breakdown products into the cell
• the digest and recycle unwanted cellular materials
• processes is called autophagy

Question 19

what are vacuoles

Answer 19

• are large vesicles derived from the rER and Golgi
• are important in plants
• food vacuoles involved in phagocytosis
• can preform lysosome-like functions
• large central vacuole absorbs water allowing plant cell to go without a large increase in cytoplasm