Organelles & Compartmentalisation

Question 1

What is ultrastructure?

Answer 1

Biological structure and especially fine structure (as of a cell) not visible through an ordinary microscope.

Question 2

How are eukaryotic cells different than prokaryotic cells?

Answer 2

Eukaryotic cells have a more complex ultrastructure than prokaryotic cells.

Question 3

How is the cytoplasm of eukaryotic cells different?

Answer 3

The cytoplasm of eukaryotic cells is divided up into membrane-bound compartments called organelles. These compartments are either bound by a single or double membrane.

Question 4

What are organelles?

Answer 4

Organelles are structures that specialised for a specific function.

Question 5

What must structures lack which makes them NOT considered an organelle?

Answer 5

The absence of a membrane causes them to not be considered organelles.

Question 6

What structures lack a membrane, causing them to not be organelles?

Answer 6

-Cell wall
-Cytoskeleton
-Cytoplasm

Question 7

Which compartmentalised organelles do eukaryotic cells have?

Answer 7

-The nucleus
-Vesicles
-Ribosomes
-The plasma membrane

Question 8

What are the advantages of the compartmentalisation of the cell (eukaryotic cells)?

Answer 8

-Enzymes and substrates to be localised (maintained in a location so they can find their substrates readily) and therefore available at higher concentrations.
-damaging substances to be kept separated (e.g. digestive enzymes are stored in lysosomes so they do not digest the cell).
-Optimal conditions to be maintained for certain processes (e.g. pH for digestive enzymes).
-The number and location of organelles to be altered depending on requirements of the cell.

Question 9

What can happen to organelles in complex cells?

Answer 9

In complex cells, organelles can become specialised for specific functions.

Question 10

How do the specialised organelles (in complex cells) perform their functions?

Answer 10

The specialised organelles have specific adaptations to help them carry out their functions.
-e.g. the structure of an organelle is adapted to help carry out its function which is why each organelle looks very different from each other.

Question 11

Why is the separation of organelles from the rest of the cell via a membrane important?

Answer 11

It allows the organelle to carry out its own chemical reactions without interference from the rest of the cell.

Question 12

How has the study of the function of individual organelles become possible?

Answer 12

It has become possible following the invention of ultracentrifuges and methods of using them for cell fractionation have been developed.

Question 13

How can we study cells at a molecular level?

Answer 13

To study cells at a molecular level, we need to be able to separate out each each compartment and study them individually through cell fractionation.

Question 14

What is needed for cell fractionation?

Answer 14

-A pure sample containing only the specific organelle being studied.

Question 15

What are the three stages of cell fractionation?

Answer 15

-homogenisation
-filtration
-ultracentrifigation

Question 16

What happens during homogenisation?

Answer 16

The cell sample is broken up using a homogeniser which is a blender-like machine

Question 17

What happens during filtration?

Answer 17

The homogenate (containing the homogenised cells) is then filtered through a gauze

Question 18

What happens during ultracentrifugation?

Answer 18

The filtrate is placed into a tube and the tube is placed in a centrifuge.
-the speed can be altered to separate different components of the cell based on their molecular weight.

Question 19

What is a centrifuge?

Answer 19

A centrifuge is a machine that separates materials by spinning.

Question 20

How does the nucleus distinguish eukaryotic cells from prokaryotic cells?

Answer 20

Eukaryotic cells contain a nucleus while prokaryotic cells do not.

Question 21

What does the presence of a nucleus allow in eukaryotic cells?

Answer 21

The presence of a nucleus allow for many cell processes to take place more efficiently than in prokaryotes.

Question 22

What are the two processes that occur in both prokaryotes and eukaryotes?

Answer 22

-Gene transcription
-Gene translation

Question 23

How do gene transcription and translation occur in prokaryotes?

Answer 23

They occur simultaneously which allows for rapid responses to an environmental stimuli.

Question 24

How do gene transcription and translation occur in eukaryotes?

Answer 24

These processes occur separately due to the compartmentalisation of the nucleus.

Question 25

What is formed during transcription in a eukaryote? What does it need before translation?

Answer 25

During transcription, mRNA is formed using a template strand of DNA.
-the mRNA needs some modification before it can be used for translation.

Question 26

How does translation occur in a eukaryotic cell?

Answer 26

Modification of the mRNA can take place in isolation within the nucleus before it comes into contact with a ribosome which is where a translation occurs.

Question 27

Where does translation occur in a eukaryote?

Answer 27

In a ribosome

Question 28

How does translation occur in a prokaryote?

Answer 28

In prokaryotes, the mRNA immediately meets a ribosome which has higher risk of errors occurring in the mRNA code and therefore in the resulting protein following translation.

Question 29

How is the cytoplasm advantageous for eukaryotes?

Answer 29

The cytoplasm is not considered an organelle but it’s separate from organelles via their membranes in an advantage.

Question 30

What does the organisation of the eukaryotic cell into discrete membrane-bound organelles allow for?

Answer 30

It allows for the separation of incompatible biochemical processes.

Question 31

What does the separation of incompatible biochemical processes ensure?

Answer 31

It ensures that pathways requiring specific enzymes or metabolites run smoothly and are not at risk from interference from other cell structures or chemicals.

Question 32

What is an example of localising conflicting reactions in one organelle?

Answer 32

for example in plant cells a type of enzyme called nitrogenase (used for nitrogen fixation) is particularly sensitive to oxygen so it is positioned in an anaerobic part of the cytoplasm away from aerobic reactions

Question 33

How are lysosomes an example of compartmentalisation in the cytoplasm?

Answer 33

Lysosomes require lytic enzymes which could be harmful to the cell if they were not contained by the lysosome membrane

Question 34

How is a phagocytic vacuole an example of compartmentalisation in the cytoplasm?

Answer 34

During endocytosis a phagocytic vacuole forms around potentially toxic and harmful substances, such as bacteria; this keeps the contents separate from the cytoplasm and rest of the cell until a lysosome can safely digest the material

Question 35

What organelles have no membrane?

Answer 35

-Ribosomes
-Centrioles
-Microtubules

Question 36

Where can organelles with no membrane be found?

Answer 36

In prokaryotes and others

Question 37

What organelles have a single membrane?

Answer 37

-Golgi
-Lysosome
-Vacuoles and vesicles
-Endoplasmic Reticulum

Question 38

What organelles have a double membrane?

Answer 38

-Nucleus
Mitochondria
-Chloroplasts