19. Memrbane-limited organelles. ER. Annular Lamellae

Question 1

Membrane- limited organelles?

Answer 1

Most organelles in cytoplasm are membrane bound.

Membrane bound organelles only exist in eukaryotic cells.

Endoplasmic reticulum (smooth/rough ) have an interconnecting network of membranous tubules  cisternae

MEMBRANE BOUND/LIMITED:
ORGANELLES ARE PROTECTED BY SINGLE/DOUBLE PLASMA MEMBRANE.

1) RER,SER
2) Golgi apparatus
3) Lysosomes
4) Peroxisomes
5) Secretory vesicles
6) Mitochondria

Question 2

Cisterna definition?

Answer 2

CISTERNA/CISTERNAE: ONE OF THE SAC-LIKE VESICLES THAT CONSIST OF THE ENDOPLASMIC RETICULUM

Question 3

ER definition?

Answer 3

ENDOPLASMIS RETICULUM: A MEMBRANE SYS  TO TRNSPORT CHEMICAL COMPOUNDS WITHIN THE CELL

Question 4

Cytosol definition?

Answer 4

CYTOSOL: THE FLUID COMPONENT OF CYTOPLASM- EXCLUDING ORGANELLES AND INSOLUBLE CYTOPLASMIC COMPONENTS.

Question 5

Core functions of ER?

Answer 5

Endoplasmic Reticulum: Two x ER

The core functions of the Endoplasmic Reticulum are:

•Folding of protein molecules in sacs called cisternae

• Proteins are folded by many chaperone proteins (e.g. disulphide isomerase)
• The proteins folded correctly are transported to the Golgi apparatus
• Unfolded proteins case a stress response
• Transport of protein molecules in vesicles to the Golgi apparatus
• Protein synthesis (the Ribosomes on the RER only)

Question 6

RER? Structure? Functions? Cells where RER are prominent?

Answer 6

Rough Endoplasmic Reticulum: Continuous with outer layer of nuclear envelope

-Protein synthesis occurs here
-Structure:
• Consists of parallel stacks of flattened cisternae
• Cisternae - 7-8nm
• The outer (cytosolic) face of the RER is studded with ribosomes/polyribosomes ( they are not stable)
• They are not stable -continuously being released/rebound
• Ribosomes: site of protein synthesis

-Functions: Mainly to set apart proteins that are not for the cytosol 
•Manufacture of lysosomal enzymes
•Manufacture of secreted proteins
•Integral membrane proteins 
•Initial glycosylation of glycoproteins
•Phospholipid synthesis

Polyribosomes/ Ribosomes

• All protein synthesis begins on polyribosomes that aren’t attached to the ER
• The polyribosomes bind to the ER in the final stages of their protein synthesis (once a specific protein-nucleic acid complex forms in the cytosol)

Protein synthesising cells: In which RER’s are very prominent
•Fibroblast cells
•Exocrine gland cells
•Plasma cells
•Neurons

Question 7

SER? Structure? Functions? Cells where RER are prominent? How it transfers materials?

Answer 7

Smooth Endoplasmic Reticulum: Region of ER that lacks bound ribosomes/polyribosomes (degranulation of RER). Continuous with the RER

-Less abundant than RER’s in cells
-Structure:
•Cisternae is tubular
•Cisternae looks like channels instead of flattened stacks
•6-7 nm
•Lacks in ribosomes
•Contains enzymes:
- Steroid synthesising enzymes –> steroid hormones
- Has the enzymes ‘glucose-6-phosphate converting G6P –> glucose

-Functions:

• Lipid synthesis
• Synthesis of phospholipid molecules for - cellular membrane (transported from SER to other membranes)
• Detoxification of drugs in the liver (in the form  hepatocytes)
• Regulation of Ca+ concentration (in muscle cells - occurs in specialised SER - sarcoplasmic reticulum)
• Glycogen and Carbohydrate metabolism
• Synthesis of steroid hormones
• Forms vesicles to transport ER products to - GA or PM

Cells involved in the synthesis of things like; Lipids, Phospholipids and Steroids have abundance of SER such as:

• Cells of adrenal cortex
• Testes
• Ovaries
• Nerve cells
• Glandular cells (e.g. Sebaceous glands)

SER transfers these either via:

1. Direction communication to RER – allowing lateral diffusion
2. Vesicles detach, move and fuse with other membranous organelles
3. Carried individually by phospholipid transfer proteins

Question 8

Annular Lamellae? Structure? Functions? Cells it’s abundant in?

Answer 8

Annular Lamellae : Intermediate stage between ER and nuclear envelope

-Structure:
•Stacks of flattened membranous cisternae
•Contains numerous pore complexes
•Formed from the nuclear envelope

-Functions:
•Attachment site for stored RNA

Abundant in:

• Spermatozoa
• Human oocytes
• Sertoli cells (Tumour cells/ Testes)