Cell Organelles

Question 1

How does the ribosome attach to the rER through the growing polypeptide

Answer 1

• SIGNAL PROTEIN on the polypeptide is COMPLEMENTARY to the RECEPTOR SITE on the membrane of rER
• growing polypeptide chain enters the lumen of the rER and PULLS THE RIBOSOME CLOSER to rER
• ribosome attached via weak bonds formation to membrane of rER

Question 2

Describe what happens to the newly synthesised polypeptides released from the rER

Answer 2

• TRANSPORT VESICLES containing the packaged proteins BUD OFF membrane of rER -> fuses with CIS FACE OF GOLGI APPARATUS
• Proteins enter lumen of golgi apparatus where they are CHEMICALLY MODIFIED
• SECRETORY VESICLES containing mature proteins BUD OFF from TRANS FACE of golgi apparatus
• secretory vesicolves move to the cell surface membrane via the CYTOSKELETON -> vesicle membrane FUSES with the CSM, releasing proteins via EXOCYTOSIS

Question 3

Features of mitochondrion

Answer 3

• cylindrical/rod-shaped
• double-membrane bound
• inner membrane extensively folded to form cristae (increases SA for proteins and enzymes to be embedded)
• 70s ribosomes

Question 4

Features of rER

Answer 4

• three dimensional structure network of interconnecting flattened membrane-bound sacs called cisternae
• ribosomes are attached to the cytoplasmic side of rER
• single-membrane bound
• membrane is continuous with the outer membrane

Question 5

Features of sER

Answer 5

• three dimensional structure network of interconnecting membrane-bound tubules called cisternae
• more tubular structure than rER
• lined with a thin single membrane
• no ribosomes attached to the outer surface

Question 6

Features of GA

Answer 6

• one or several stacks of flattened, curved membrane-bound sacs called cisternae
• single-membrane bound
• new cisternae constantly formed at cis face by fusing with transport vesicles

Question 7

Function of GA

Answer 7

• chemical modification of proteins and lipids (eg. glycosylation) to form glycoproteins and glycolipids respectively
• proteins transported to GA where they are temporarily stored and concentrated
• vesicles containing protein to be secreted and lysosomal enzymes bud off the GA as secretory vesicles and lysosomes respectively

Question 8

Function of rER

Answer 8

• folding of polypeptides into functional proteins
• site of protein synthesis by bound ribosomes
• transport of proteins to GA
• glycosylation (addition of short carbohydrate chains) to proteins

Question 9

Function of sER

Answer 9

• synthesis of lipids
• detoxification (by addition of hydroxyl group to harmful substances)

Question 10

Advantage to euk organelles having membrane-bound organelles

Answer 10

• different conditions to maintain optimum conditions for enzyme reaction
• increase surface area for embedding of enzymes and proteins into the membrane

Question 11

Roles for the vesicles formed at the maturing face of the GA

Answer 11

• secretory vesicles containing mature proteins bud off trans face of GA and move through the cytosal via cytoskeleton to the CSM
• vesicle membrane fuses with CSM and release content via exocytosis
• lysosome contains hydrolytic enzymes and remains in cell
• lysosome membrane fuses with membrane of phagocytic vesicle containing foreign particle
• hydrolytic enzymes digest contents into soluble products which dissolve into cytoplasm for cell use

Question 12

Function of mitochondria

Answer 12

• site of cellular respiration where oxidation of glucose synthesises adenosine triphosphate (ATP)
• synthesis of mitochondrial proteins

Question 13

Link between functions of rER and mitochondria

Answer 13

• proteins required by mitochondria for cellular respiration such as electron carriers are synthesised by ribosomes bound to the rER
• energy released by the mitochondria in the form of ATP via cellular respiration is required for protein synthesis at the endoplasmic reticulum

Question 14

Similarities between chloroplast and mitochondrion

Answer 14

• both bounded by a double membrane
• both have 70s ribosome
• both contain circular DNA
• both divide by binary fission
• both contain electron transport chain and stalked particles containing ATP synthase embedded in their inner membranes
• both are approximately 1-10 micrometer

Question 15

Structure of ribosome

Answer 15

• spherical
• 20nm in diameter
• non-membrane bound
• consists of a large and a small subunit
• each subunit is made up of rRNA and ribosomal proteins
• can exist as free ribosomes or are attached to the rER
• 70s ribosomes in prokaryotes and 80s ribosomes in eukaryotes

Question 16

Main identifying features of centrioles

Answer 16

• pair of rod-like structures
• positioned at right angles to each other
• composed of nine sets of triplet microtubules arranged in a ring

Question 17

Features of chloroplast

Answer 17

• cylindrical in shape
• size ranges from 5-10 micrometer
• double-membrane bound
• outer membrane is a smooth boundary whereas inner membrane gives rise to thylakoids stacked to for
  grana and lamellae
• stacking of thylakoids increase surface area for embedding of proteins, enzymes and pigments
• circular DNA
• 70s ribosomes
• enzymes of Calvin cycle
• starch grains