Organelles

Question 1

Peroxisomes

Answer 1

• Main sites of oxygen utilisation
• contain oxidative enzymes (- catalase, urate oxidase)
• perform oxidation reaction without generation of energy
• oxygen –> a plant toxin
  -peroxisomes perform redox reactions
• also important for B-oxidation

Question 2

Autophagy

Answer 2

• The self-eating of cytosolic materials
• degrades damaged or unwanted proteins and organelles
  -nucleation and extension
  -closure
• fusion with lysosomes
  -digestion

Question 3

Lysosomes

Answer 3

• Safe container for ‘lethal’ digestive enzymes
• acidic pH ~5.0
• proton gradient maintained by H+-pump
• fusion with late endosomes
  –>endolysosome
• fusion with phagosomes
  –>phagolysosome
• heterogeneous: hydrolytically active, low pH compartments

Question 4

What materials if transported from lysosomes

Answer 4

Metabolites

Question 5

What materials is transported to lysosomes

Answer 5

There are three major routes exist for the transport of molecules to lysosomes for digestion.
- Heterophagy (phagocytosis and endocytosis)
- autophagy
-KFERQ - dependent import of cytosol proteins

Question 6

Functions of ER

Answer 6

• protein synthesis on rough ER (rER)
• protein processing (cleavage, glycosylation, disulphide bridge formation and prenylation)
• protein folding and assembly
  -protein sorting & quality control
  -biosynthesis of lipids (also for mitochondria and plastids)
  -calcium storage for signalling

The different regions of the ER specialise in certain functions

Question 7

ER-Golgi communication

Answer 7

• two way traffic
• ER does not communicate directly with secretory vesicles
• all onward traffic via Golgi
• Golgi-lock

Question 8

Transport from the ER to the Golgi apparatus

Answer 8

ER to the cis Golgi network is transported by microtubules, protein cargo is transported in COPII- coated vesicles from the ER to the cis-Golgi

cis Golgi network to the ER the protein cargo transported by retrieval transport and coated in COPI-coat

Question 9

Golgi Apparatus

Answer 9

• Consists of an Ordered Series of Compartments
• the cis FACE is the Golgi vesicle side
• trans FACE is the secretory vesicle side

Question 10

Ordered series of compartments

Answer 10

ER –> Golgi
Sorting- phosphorylation of oligosaccharides on lysosomal proteins - cis Golgi network

Removal of Man - cis cisterna

Removal of man and addition of GlcNAc - medial cisterna

addition of Gal and addition f NANA - trans cisterna

sulfation of tyrosine’s and carbohydrates - sorting (lysosomes, plasma membrane and secretory vesicle)

Question 11

Protein processing in the ER

Answer 11

cleavage of signal peptides
glycosylation of proteins

Question 12

Folding and quality control of proteins in the ER

Answer 12

Other proteins called chaperones use energy to fold proteins into their proper shape

Only proteins that are properly folded and assembled can leave the ER

Question 13

Biosynthesis of lipids in the ER

Answer 13

-almost all phospholipids synthesised in the ER
-transported as vesicles to destinations and plasma membrane
-lipid synthesis also for mitochondria and chloroplasts
-close physical relationship of ER and mitochondria and plasma membrane

The ER can exist without mitochondria, but mitochondria cannot exist without the ER

Question 14

Endocytosis

Answer 14

contents are taken up from the outside

Question 15

Exocytosus

Answer 15

Contents are released (secreted) to the outside

Question 16

Main route by which organelles of the endomembrane system interact

Answer 16

• Endoplasmic Reticulum 2 way traffic to the Golgi
• Golgi 2 way traffic to the Secretory vesicles
• Golgi 1 way traffic to the Extracellular Space
• Golgi 2 way traffic to early endosome
• Golgi 2 way traffic to late endosome
• Late endosome 2 way same direction traffic to lysosome
• cytosol to lysosome
• Early endosome 2 way same direction traffic to late endosome
• Early endosome to recycling endosome to extracellular space
  -Early endosome 2 way traffic to extracellular space

Question 17

Nuclear envelope

Answer 17

A double membrane that encloses the nucleus, regulating material exchange between the nucleus and cytoplasm via nuclear pores

Question 18

Nuclear pores

Answer 18

Protein complexes embedded in the nuclear envelop that control the passage of molecules like RNA and proteins between the nucleus and cytoplasm

Question 19

Nucleolus

Answer 19

A dense region within the nucleus responsible for the synthesis and assembly of ribosomal RNA and ribosome subunits

Question 20

Chromatin

Answer 20

DNA wrapped around histone proteins, which condenses to form chromosomes during cell division. It stores genetic information and regulates gene expression

Question 21

Nucleoplasm

Answer 21

The gel-like substance within the nucleus that suspends chromatin and nucleolus, providing structural support and medium for molecular interactions

Question 22

How molecules enter and leave the nucleus

Answer 22

Imported proteins carry a specific signal peptide: nuclear localisation signal (NLS)

Exported proteins also carry a specific signal peptide: nuclear export signal (NES)

Question 23

Centrosome

Answer 23

Composed of two centrioles and surrounding matrix of proteins.

• structure: it consists of two perpendicular centrioles made of microtubules, surrounded by the pericentriolar material, which contains proteins important for microtubule nucleation.

-function: the centrosomes serves as the main microtubule organising centre, playing a key role in cell division by organising the mitotic spindle and regulating microtubule dynamics for cell shape and intracellular transport

Question 24

Flagellum

Answer 24

Axoneme: A core structure made of nine outer microtubule doublets surrounding two central microtubules (9+2 arrangement)

Basal Body: Anchors the flagellum to the cell, similar to a centriole

Plasma membrane: Encases the flagellum, providing structural support

The coordinated movement of the axoneme microtubules allows the flagellum to enable cell motility.

Question 25

Origin of eukaryotic nucleus

Answer 25

Thought to have originated from an infolding of the plasma membrane

Question 26

Origin of flagellum

Answer 26

Originated from bacterial-like structures, such as bacterial pili or filaments