b2.2 compartmentalisation Flashcards
what are organelles?
organelles are the discrete subunits of a cell that are adapted to perform specific functions. the plasma membrane and ribosomes are universal organelles that are present in every living cell. complex cells possess additional membrane bound organelles that provide further functionality.
what isn’t considered an organelle?
certain cellular components are not considered to be organelles, such as the cell wall (extracellular component) and cytoskeletons (structural element).
what are the advantages of separating the nucleus and cytoplasm into separate comprtments?
the nucleus is a double membrane structure with pores that stores the genetic material of the cell. the presence of a nucleus allows eukaryotes to separate the processes of transcription and translation. this separation allows for the post-transcriptional modification of mRNA before it is translated by ribosomes. these modifications help to stabilise the mRNA transcript and remove non-coding sequences via splicing. this greatly improves the efficiency of protein synthesis and allows for tighter control of gene expression than is possible in prokaryotic cells.
what are the advantages of membrane bound organelles?
the presence of membrane bound organelles in the cytoplasm enables the organelles to maintain an internal chemistry that is different to the cytoplasm and allows for the concentration of key enzymes and metabolites needed to optimise the function of the organelle.
why are lysosomes evidence for the advantages of membrane bound organelles?
lysosomes and phagocytic vacuoles provide evidence for the advantage of compartmentalising the cytoplasm into discrete sections. these organelles contain hydrolytic enzymes that are responsible for digesting cellular debris or engulfed pathogenic materials. if these enzymes were not contained within a specific compartment, they would freely digest the contents of the cell.
how is the structure of the mitochondrion adapted to its function?
outer membrane - contains transport proteins that enable the shuttling or key materials from the cytosol
inner membrane - contains the ETC and ATP synthase
cristae - part of the inner membrane arranged into folds that increase the SA:V ratio
intermembrane space - small space between membranes maxmises hydrogen gradient upon proton accumulation
matrix - central cavity that contains appropriate enzymes and a suitable pH for the krebs cycle to occur
how is the structure of the chloroplast adapted to its function?
thylakoids - flattened discs that have a small internal volume to maximise hydrogen gradient upon proton accumulation
grana - thylakoids are arranged into stacks to increase the SA:V ratio of the thylakoid membrane
photosystems - pigments organised into photosystems in thylakoid membrane to maximise light absorption
stroma - central cavity that contains appropriate enzymes and a suitable pH for the calvin cycle to occur
lamellae - connects and separates thylakoid stacks, maximising photosynthetic efficiency
how does the double membrane of the nucleus benefit protein synthesis?
the nucleus is surrounded by a double membrane called the nuclear envelope, which is embedded with pores. this means that proteins synthesised by the ER can access the nucleus without requiring vesicular transportation. the nuclear envelope also functions as a barrier to separate the processes of transcription and translation. the presence of pores allows the cell to control the rate at which these interlinked processes can occur.
how does the double membrane of the nucleus benefit cell replication?
a double membrane is also beneficial to the processes of mitosis and meiosis. during these processes, the nuclear envelope must be disassembled to allow the chromosomes to be sorted and separated. because of the double membrane, the envelope can break down into vesicles - these can be reconstituted to reform the nuclear membrane at the end of the division process.
what is the structure of a ribosome?
ribosomes are comprised of two distinct subunits: the small subunit is responsible for binding to mRNA, while the large subunit binds to tRNA. when the two subunits form a complex, translation of an mRNA sequence can occur.
where can ribosomes be found and how does this affect their function?
in eukaryotes, ribosomes can either be located freely within the cytosol or embedded within the rER. free ribosomes synthesise proteins for use within the cytosol. ribosomes embedded within the rER synthesise proteins that will be packaged into vesicles and transported to other organelles. if the vesicles are transported to the golgi apparatus, then the proteins will be secreted from the cell for extracellular use.
what is the function of the golgi apparatus?
the golgi apparatus is responsible for sorting, storing, modifying and exporting cellular material. it is composed of a series of flattened sacs (called cisternae) that are located between the ER and the plasma membrane. proteins and lipids arrive in vesicles at the golgi body and are modified into functional molecules. in plant cells, much of the cell wall material passes through the golgi apparatus as well.
what types of secretion does the golgi apparatus control?
materials destined for secretion are packaged at the golgi body for exocytosis. these materials can either be released immediately (constitutive secretion) or stored in secretory vesicles for a sustained release (regulatory secretion). regulatory secretion is triggered by an external chemical signal binding to a specific receptor.
what are vesicles?
vesicles are membrane wrapped containers involved in shuttling materials between cellular compartments. most molecules are too large to pass directly through membranes and so are packaged into vesicles than can fuse with a membrane to deliver the material.
how does clathrin help vesicles form?
some vesicles form with the help of a coat protein called clathrin. clathrin is a triskelion-shaped molecule that is recruited to a membrane by adaptor proteins. the clathrin proteins then link together to form a rounded lattice that pulls the membrane into a bud. this bud is then cleaved by another protein to form a vesicle, at which point the clathrin architecture disassociates.
