5.4 The end-membrane system Flashcards
What is the nuclear envelope?
perforated by membrane openings called nuclear pores. small molecules and ions can passively diffuse through pores, but large proteins and RNA require active transport.
How do vesicles form?
by budding off an organelle taking with them a piece the membrane and internal contents
What perts of the cell are involved in the end-membrane system? (8)
- nuclear envelope
- Endoplasmic reticulum
- Golgi apparatus
- vesicle
- Lysosome
- Plasma membrane
- exocytosis
- Endocytosis
What is a nuclear pore and what is its function?
a large protein complex that allows molecules to move in and out of the nucleus
what are ribosomes and what is their function?
the sires of protein synthesis in which amino acids are assembled into polypeptides.
What does the ER produce and transport?
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.
What are characteristics of the ER
- the ER is continuous throughout (lumen)
- maze like appearance
- convoluted membrane
what is the rough ER and its function
studded with ribosomes, synthesizes transmembrane proteins and proteins that end up in the interior of organelles.
What is smooth ER and its function?
lacks ribosomes and is the primary site of lipid synthesis (fatty acid and phospholipid biosynthesis)
What are the 3 primary roles of the golgi apparatus?
- it further modifies proteins and lipids produced by the ER
- it acts as a sorting station to as proteins and lipids move into their final destination
- the site of synthesis of most cells carbohydrates
What is the structure of the golgi apparatus?
cisternae- series of membrane sacs that make up the golgi body
(can go against flow to send protein back to cisternae to fix)
how is a protein or lipid modified in the Golgi body?
a sequence of steps performed in different regions of the organelle with different enzymes catalyzed for specific reactions
What are lysosomes and their function?
- 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.
what is the ideal pH of a lysosome and how is it maintained
pH 5 for optimum activity of enzymes maintained by protein pumps
What is protein sorting and how does it occur?
- 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.
How are proteins from free ribosomes sorted?
after they have been translated and contain an amino acid sequence called signal sequences which allowed them to be recognized and sorted.
what happens to proteins with a signal sequence vs proteins without
without- stay in the cytosol
destined for the mitochondria and chloroplast- sequence at amino acids
destined for nucleus- sequence located internally
what enables proteins to move through pores in the nuclear envelope
nuclear localizing signals.
Protiens produced by ribosomes end up on the RER end up (3)
- within the lumen of the end-membrane system
- embedded in its membrane
- sectreted out of the cell
what is the name of the second sequence the prevents the polypeptide from continuing to the lumen?
signal anchor sequence
what is the process for entering the lumen?
- a signal receptor protein (SRP) binds to signalling sequence at amino end and halts translation
- SRP receptor brings ribosome to transmembrane channel; SRP dissociates; protein synthesis resumes; polypeptide chain threaded through channel.
- protein ends up in lumen of ER where is remakes, transporters, or secreted out
transmembrane protein targeting
- protein with signal anchor sequence threaded through channel in ER membrane until signal anchor sequence is reached
- ER channel releases protein into the membrane
- when translation is complete, the protein remains in the membrane
