Cell Structure & Diversity 2 - Endomembrane System & Regulation of Animal Cell Shape Flashcards
What is included in the endomembrane system?
Nuclear envelope, endoplasmic reticulum (smooth and rough), Golgi complex, vesicles, lysosomes, vacuoles, plasma membrane
What is the endomembrane system?
A membrane system interconnected by direct physical contact or by vesicles transferring
What is the endoplasmic reticulum continuous with?
The nuclear envelope
What is the endoplamic reticulum structure?
Made of tubules with the open space between them called lumen
What is the two types of endoplasmic reticulum?
Smooth and rough
What are the functions of the smooth endoplasmic reticulum?
Metabolism of carbohydrates, lipid synthesis for membranes, detoxification of drugs and poisons, storage of calcium ions which are used as a signal in the cell
What is special about the amount of endoplasmic reticulum in cells?
The amount varies depending on the function of the cell and whether it is needing its function or not
Is there more smooth or rough ER in cells?
Rough
Why is rough endoplasmic reticulum rough?
Because it has ribosomes on it
What process is the rough ER involved in?
Protein synthesis
What is the role of the rough ER in the endomembrane system?
Secreted membrane bound proteins enter the lumen of the rough ER and are processed (synthesised and folded) by the rough ER and the rest of the endomembrane system for release from the cell or to be used in the cell membrane
What happens once the proteins are processed in the rough ER?
They accumulate in different areas, form a vesicle and then move to the Golgi complex
What is the Golgi complex?
A series of membrane sacs and associated vesicles which receives, modifies, sorts and ships proteins arriving from the rough ER
What are the two faces of the Golgi complex called?
Cis and trans
What face of the Golgi complex do vesicles arrive at?
The cis face
What face of the Golgi complex do vesicles leave?
The trans face
What are the 3 functions of the Golgi complex?
Glycosylation, sorting proteins and directing vesicle traffic
What is glycosylation?
Carbohydrates are added to proteins/ the proteins are modified which is important for secreted or cell surface proteins in fulfilling their function.
What is sorting proteins?
Molecular markers are added to direct the same types of proteins to the same area of the Golgi to be in the correct vesicles before budding from the trans face
What is directing vesicle traffic?
The molecular tags which are added to the surface of the vesicle leaving the trans face direct them to the correct target. Molecular tags can then act as docking sites
What are molecular tags usually?
Proteins
Where are vesicles directed?
Lysosomes and to secretory pathways so they can perform their function outside of the cell
What happens during exocytosis?
Material is transported out of the cell or to the cell surface and the vesicle membrane remains part of the plasma membrane.
What is constitutive exocytosis?
Exocytosis which is continuous
What is regulated exocytosis?
Exocytosis that requires a signal before the vesicles can leave the cell.
What does constitutive exocytosis release?
Extracellular matrix proteins
What does regulated exocytosis release?
Hormones and neurotransmitters
What is endocytosis?
When the cell takes in molecules and particulate matter from the external environment at the plasma membrane
What is phagocytosis?
The uptake of extracellular food particles
How does phagocytosis occur?
A pseudopodium pulls it in to form a phagocytic vacuole which is digested by the lysosomes
Where does phagocytosis occur?
In macrophage cells
What is pinocytosis?
The uptake of extra cellular fluid containing various solutes
How does pinocytosis occur?
A vesicle for uptake(coated pit) is formed with the help of coat proteins. The extracellular fluid and dissolved solutes flow in.
In endocytosis selective or non-selective?
Non-selective
What is receptor mediated endocytosis?
A specialised form of pinocytosis which allows the cell to uptake specific substances which may be present at only low concentrations in the extracellular fluid
What is the function of receptor proteins?
To selectively capture the required solute. Other things will also float into the coated pit.
What does it mean by receptors being recyclable?
They can be used again once they are outside the cell
What are lysosomes?
Membrane bound organelles made by the rough ER And Golgi complex which contain hydrolytic digestive enzymes
What is the pH in lysosomes and why?
Around 5 so that the enzymes can be cative
What do lysosomes do?
Phagocytic vacuoles fuse with lysosomes and they then degrade the proteins, lipids, carbohydrates and nucleic acids within the phagocytic vacuoles so that breakdown products can be released
What is autophagy?
The process when lysosomes digest and recycle unwanted and no longer useful cellular materials/parts. Whole cell death can also occur when lysosomal enzymes are released into the cytoplasm
What vacuoles may be found in animal cells?
Large vesicles derived from rough ER and Golgi as well as food vacuoles in phagocytosis.
What are animal cells surrounded by?
Extracellular fluid and may be connected to other cells
What is a feature of the shape of animal cells?
It is dynamic and the organelles aren’t fixed in position
What is the function of the cytoskeleton?
To maintain cell shape and the position of organelles within the cell
How can the cytoskeleton cause the cell to change shape?
By rapidly being amen to disassemble and reassemble depending on what the cell is needed for
What are the 3 components of the cytoskeleton?
Microtubules, microfilaments and intermediate filaments
What are microtubules made of?
Tubulin units arranged in a spiral structure
How are microtubules arranged?
They may be arranged beside each other or radiating out from the organising centre (centrosome) in a particular arrangement
What is the function of microtubules?
To resist compression so that cell shape is maintained and can also provide motility
What structures provide motility?
Flagella and cilia
What is the motion of flagella?
Snake-like
What is the motion of cilia?
rowing-like
Why is cell motility useful?
It means cells can move through fluid
Explain organelle motility
ATP powered motor proteins can walk organelles such as vesicles along microtubules allowing the vesicles or other organelles to be transported to specific targets in the cell
What are microfilaments made of?
Double chain of actin subunits twisted into strands
How are microfilament arranged?
Can form linear strands and 3D branched network structures
What are the functions of microfilaments?
The dense cortical network under the plasma membrane which is anchored to proteins helps make the region more rigid and maintain the cell shape. Therefore, tension can be resisted.
How do microfilaments support cell movement?
Interactions between motor proteins and actin allow for muscle contraction, amoeboid movement and cytoplasmic streaming
What are intermediate filaments made of?
Proteins including keratins in hair, lamins in the nucleus and neurofilaments in neurons which are supercoiled into cables
What is the function of intermediate filaments?
Because they are less dynamic, they form fairly permanent structures which means they can anchor organelles in place and maintain cell shape
What happens to intermediate filaments once the cell dies?
They remain
What are the 3 types of cell junctions?
Tight junctions, desmosomes and gap junctions
What is the function of tight junctions?
To hold together neighbouring cells which are tightly pressed beside each other and prevent movement of fluid across cell layer
What is the structure of tight junctions?
A continuous seal
What do tight junctions attach to?
Microfilaments
Are tight junctions all the same?
No, some have the ability to let some substances through (they are looser)
What are desmosomes?
Anchoring junctions that act like rivets
What is the function of desmosomes?
To provide attachments between sheets of muscle
What connects desmosomes to the cell?
Intermediate filaments which makes them really strong
How much space is between cells with desmosomes?
More space than in tight junctions
What are gap junctions?
A point of cytoplasmic contact between two cells where the cytoplasm connects and becomes continuous
What is the structure of gap junctions?
Proteins with a pore running through them
What is the function of gap junctions?
To allow ions and small molecules to pass from cell to cell and allow rapid intercellular communication
How do cells join together?
By the extracellular matrix
Do all cells join directly to other cells?
No, some are connected by the ECM
What is the composition of the ECM?
Material secreted by cells, proteins mainly glycoproteins especially collagen of which the fibres are embedded in a proteoglycan complex matrix
What are proteoglycans?
Proteins with extensive sugar additions
How does secretion into the extracellular matrix occur?
By constitutive exocytosis
What is the function of proteoglycans?
To trap water within the ECM which is needed because it resists compression and tissue shape is therefore maintained
What attaches cells to the ECM?
Glycoproteins called fibronectins
What attaches the ECM to the Cytoskelton?
Membrane proteins called integrins
Why are integrins important?
They provide a communication link from the ECM to the interior
