Organelles & Compartmentalisation Flashcards
What is ultrastructure?
Biological structure and especially fine structure (as of a cell) not visible through an ordinary microscope.
How are eukaryotic cells different than prokaryotic cells?
Eukaryotic cells have a more complex ultrastructure than prokaryotic cells.
How is the cytoplasm of eukaryotic cells different?
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.
What are organelles?
Organelles are structures that specialised for a specific function.
What must structures lack which makes them NOT considered an organelle?
The absence of a membrane causes them to not be considered organelles.
What structures lack a membrane, causing them to not be organelles?
-Cell wall
-Cytoskeleton
-Cytoplasm
Which compartmentalised organelles do eukaryotic cells have?
-The nucleus
-Vesicles
-Ribosomes
-The plasma membrane
What are the advantages of the compartmentalisation of the cell (eukaryotic cells)?
-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.
What can happen to organelles in complex cells?
In complex cells, organelles can become specialised for specific functions.
How do the specialised organelles (in complex cells) perform their functions?
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.
Why is the separation of organelles from the rest of the cell via a membrane important?
It allows the organelle to carry out its own chemical reactions without interference from the rest of the cell.
How has the study of the function of individual organelles become possible?
It has become possible following the invention of ultracentrifuges and methods of using them for cell fractionation have been developed.
How can we study cells at a molecular level?
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.
What is needed for cell fractionation?
-A pure sample containing only the specific organelle being studied.
What are the three stages of cell fractionation?
-homogenisation
-filtration
-ultracentrifigation
What happens during homogenisation?
The cell sample is broken up using a homogeniser which is a blender-like machine
What happens during filtration?
The homogenate (containing the homogenised cells) is then filtered through a gauze
What happens during ultracentrifugation?
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.
What is a centrifuge?
A centrifuge is a machine that separates materials by spinning.
How does the nucleus distinguish eukaryotic cells from prokaryotic cells?
Eukaryotic cells contain a nucleus while prokaryotic cells do not.
What does the presence of a nucleus allow in eukaryotic cells?
The presence of a nucleus allow for many cell processes to take place more efficiently than in prokaryotes.
What are the two processes that occur in both prokaryotes and eukaryotes?
-Gene transcription
-Gene translation
How do gene transcription and translation occur in prokaryotes?
They occur simultaneously which allows for rapid responses to an environmental stimuli.
How do gene transcription and translation occur in eukaryotes?
These processes occur separately due to the compartmentalisation of the nucleus.
What is formed during transcription in a eukaryote? What does it need before translation?
During transcription, mRNA is formed using a template strand of DNA.
-the mRNA needs some modification before it can be used for translation.
How does translation occur in a eukaryotic cell?
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.
Where does translation occur in a eukaryote?
In a ribosome
How does translation occur in a prokaryote?
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.
How is the cytoplasm advantageous for eukaryotes?
The cytoplasm is not considered an organelle but it’s separate from organelles via their membranes in an advantage.
What does the organisation of the eukaryotic cell into discrete membrane-bound organelles allow for?
It allows for the separation of incompatible biochemical processes.
What does the separation of incompatible biochemical processes ensure?
It ensures that pathways requiring specific enzymes or metabolites run smoothly and are not at risk from interference from other cell structures or chemicals.
What is an example of localising conflicting reactions in one organelle?
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
How are lysosomes an example of compartmentalisation in the cytoplasm?
Lysosomes require lytic enzymes which could be harmful to the cell if they were not contained by the lysosome membrane
How is a phagocytic vacuole an example of compartmentalisation in the cytoplasm?
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
What organelles have no membrane?
-Ribosomes
-Centrioles
-Microtubules
Where can organelles with no membrane be found?
In prokaryotes and others
What organelles have a single membrane?
-Golgi
-Lysosome
-Vacuoles and vesicles
-Endoplasmic Reticulum
What organelles have a double membrane?
-Nucleus
Mitochondria
-Chloroplasts
