B2.2- organelles and compartmentalization

Question 1

what is/isn’t considered organelle

Answer 1

ARE NOT:
-cell wall
-cytoskeleton
-cytoplasm
ARE:
-nuclei
-vesicles
-ribosomes
-plasma membrane

Question 2

what are organelles

Answer 2

subunits of a cell that are adapted to perform specific functions

Question 3

use of centrifugation

Answer 3

-to isolate different organelles to be studied by structure and function

Question 4

why cells must be prepared in cold, isotonic, buffered solutions for centrifugation

Answer 4

cold= to reduce enzyme activity (when cell is opened, enzymes are released which could damage organelles)
isotonic= must have same water potential as organelles to prevent osmosis at is can cause organelles to shrivel/ burst.
buffered=kept at constant pH to prevent organelle damage

Question 5

steps to centrifugation

Answer 5

1) HOMOGENISATION=
cells broken open to release contents and blended in cold, isotonic, buffered solution. Then filtered
2) ultracentrifugation= spun at different speeds
and organelles are separated according to their densities (most dense at bottom)
-remove the pellet one by one and put the supernatant back to be spun further
RESULTS:
organelle in first pellet to last=
1) nucleus
2)chloroplast
3)mitochondria
4)lysosomes
5)ER
6)ribosomes

Question 6

what chromatography does

Answer 6

seperates pure substances (amino acids, proteins, carbs) . When mixture is separated, molecules separate depending on size and speed they travel through medium

Question 7

what gel electrophoresis does

Answer 7

separates molcules of different types by passing them through a gel using an electrical charge. Molecules separated based on size/charge

Question 8

advantages of separation of nucleus and cytoplasm

Answer 8

-DNA is protected in nucleus from harmful substances
-nucleus separates process of transcription from metabolism occurring in cytoplasm
-allows post-transcriptional modification of mRNA to occur in nucleus before translation in cytoplasm
-decreases chance of errors happening in production of polypeptides
-allows greater cell efficiency
(in prokaryotes= there is no isolation of the two processes- mRNA is immediately translated with no modification)

Question 9

advantages of compartmentalization in cytoplasm and examples

Answer 9

-enzymes kept in areas where they will be more effective
-reactions don’t interfere with each other
-enzymes for each process can be concentrated in specific area
-potential harmful enzyme don’t damage cell
EXAMPLES;
-lysosomes= contain destructive enzymes that breakdown waste, this could damage the cell if not isolated
-phagocytic vacuoles-prevents cell from coming in contact with pathogen

Question 10

what are phagocytic vacuoles

Answer 10

=when a bacteria is taken into cell by endocytosis
-lysosome fuses with it to form phagosome and lysosomes enzymes digest bacteria

Question 11

adaptations of mitochondria

Answer 11

1) outer membrane layer=
separates contents of mitochondria from rest of cell
2)matrix=
internal cytoplasm substance that contains enzymes for respiration
3)cristae=
tubular regions surrounding membrane to increase surface area for respiration
4)inner mitochondrial membrane=
membrane that contains enzymes/ granules/ribosomes for respiration
5)intermembrane space=
-small space which allows for accumulation of h+ ions (protons)

Question 12

adaptation of chloroplast

Answer 12

1) thylakoid membrane
-stacks of grana
-contain chlorophyll
-electron transport chain and ATP synthase
-large surface area for greater absorption of light
2) granum
-flattened discs of thylakoid membrane which increases surface area. Contain small thylakoid gaps in grana allowing accumulation of protons
3) stroma
-cytoplasm-like region with 70 ribosomes/ enzymes needed for Calvin cycle
4) double membrane
-isolates enzymes of chloroplast from cytoplasm

Question 13

importance of double membrane nucleus

Answer 13

-membrane separates production of mRNA in nucleus from cytoplasm
-maintains ideal conditions for transcription
-contain pores for mRNA to leave and be transcribed

Question 14

importance of double membrane of nucleus in terms of cell division

Answer 14

-nuclear membrane breaks down at beginning of cell division and the double membrane allows nucleus to break down into many small vesicles which fuse to reform nucleus after cell division

Question 15

structure of ribosome

Answer 15

composed of a large and a small subunit, both made of a protein and a rRNA.
-contain attachment sites on two subunits to allow multiple amino acids to bond

Question 16

where ribosomes are produced in relation to where they are used

Answer 16

-free ribosomes produce proteins used in cell (nucleus/mitochondria)

-ribosomes bound to membranes, produce proteins that are transported through ER and exported out of cell

Question 17

structure and function of golgi apparatus

Answer 17

located between RER (cis side) and plasma membrane (trans side)
-composed of flattened sacs (cristae)
function=
-vesicles containing proteins/ lipids fuse with cis side of Golgi apparatus, protein is modified (quaternary structure) to carry out specific function
-then packaged into vesicles and secreted from trans side and moves towards plasma membrane to secrete protein by exocytosis

Question 18

what is clathrin

Answer 18

-protein involved in formation of vesicles which transport specific molecules

Question 19

structure and function of clathrin

Answer 19

-triskelion shaped protein which attaches to recruiter proteins in a membrane forming a vesicle
-clathrin proteins polymerize to form clathrin cage, forcing membrane to form a rounded bud
-bud is cleaved off to form clathrin coated vesicle