cells Flashcards
process of cell fractionation
- cells homogenised in a blender to disrupt cell walls and membranes; organelles remain intact
- resulting centrifugal mixture, after being spun in a centrifuge at high speeds, separate organelles based on size and density
- most dense first sedimented out and then smaller components
what is in cytoplasm (3)
- cytosol: semi-fluid jelly substance, containing ion and organic cmpds
- organelles; discrete subcellular with specific function
- cytoskeleton: framework of protein filaments (microtubules and filaments)
functions of the nucleolus
- large concentration of rRNA, DNA and proteins
- site of assembly of ribosomal proteins and rRNA into ribosomal subunits
- site of synthesis of rRNA– ribosomes
2 nucleus main f(x)
- contain hereditary material
- control cell activities by regulating protein synthesis
what substances are exchanged inside and outside of nuclear envelope?
- inside: free nucleotides, ribosomal proteins, enzymes
- outside: ribosomal subunits, rRNA
describe ER
extensive network of membrane tubules and sacs called cisternae
RER’s appearance vs SER
- RER;s cisternae looks more flattened
- SER’s cisternae appears more tubular
f(x)s of RER
- glycosylation
- transport of protein: transport protein bud off from RER, carrying p to next destination
- membrane factory for the cell
describe gylcosylation
protein synthesised by bound ribosomes enters cisternal space, folded into 3D native conformation. Carbohydrates are added to the protein via glycosylation to form glycoproteins, which process is catalysed by enzyme within RER membrane
why is RER the membrane factory for the cell and how?
membrane grows as membrane proteins and phospholipids are added to it
ER membrane is transferred in form of transport vesicles to other components of endo systemes
what are SER’s functions
(many embedded enzymes that will catalyse the synthesis of a variety of carbohydrates and lipids)
- synthesise lipids
- detoxify drugs and poison (e.g. some enzymes of RER in liver cells)
e.g. SER in muscle cell, storing Ca2+ ions aka sarcoplasmic reticulum which orderly release triggers muscle contraction
what determines ribosomes’ positions
- certain protein have a stretch of polypeptides coded in respective genes known as signal peptide: first stretch of polypeptides synthesised
- signal peptide will be recognised by signal recognition particle (SRP) which will bind to receptor protein and bring ribosome to RER
- growing polypeptide translocated into RER
describe golgi apparatus
stack of flattened, membrane-bound sacs with sacs and associated vesicles (golgi vesicles)
functions of golgi (5)
- add short sugar chains to proteins and lipids via glycosylation to form glycoproteins and glycolipids
- modify existing glycoproteins and glycolipids by cleaving a sugar molecule from a sugar chain
- forming lysosomes
- produces polysaccharides (pectin) secreted by the trans face to form transport vesicles, fusing with the membrane
- sorts and targets completed materials to different parts of the cell/for secretion out
describe lysosome structure
- enclosed by a single membrane
- hydrolytic enzymes to digest macromolecules; acidic envt– optimal pH in acidic range
- and memb made by bound ribosomes
3D shape of protein shield vulnerable bonds i.e. from enzymatic attack such that it will not hydrolyse protein on inner surf of lysosomal memb and digestive enzymes
FUNCTIONS OF LYSOSOME
- autophagy
- autolysis
- digestion of materials taken in by endocytosis
- release of enzyme outside of cell by exocytosis
structure of mitochondrion
- enclosed by a double membrane
- smooth outer membrane
highly infolded inner membrane–> numerous cristae
why is the inner membrane of mitochondria highly infolded
- provide a large surface area for the attachment of proteins and enzymes for oxidative phosphorylation
- divides mitochondria into 2 internal compartments
1. intermembrane space btwn memb
2. matrix enclosed contains 70s ribosomes, circular DNA, various enzymes for Krebs Cycle
function of mitochondrion
- site of aerobic respiration: carry out metabolic processes to generate ATP through oxidation of sugars, fats and other fuels with o2 uptake
- krebs cycle occurs in matrix: oxidative phosphorylation occurs on cristae
what are chloroplasts’ structure
- enclosed by a double membrane, each phospholipid bilayer
- another membrane system with a seris of interconnected sacs: thylakoids, stacked up to form grana, joined by intergranal lamellae
- thylakoids extensively folded to increase surface area for attachment of chlorophyll, photosynthetic pigments
- stroma contains circular DNA, ribosomes, enzymes and starch granules sometimes
plant vacuole
structure
- large central surrounded by tonoplast
- contains cell sap: solution of mineral salts, sugars, enzymes, pigments, waste products
f(x)
- conc cell sap draw water to maintain turgour pressure for support from herbaceous plants
- cell growth: water intake will lead to minimal increase in cytoplasm size while vacuole enlarges
animal vacuole
structure:
- smaller and more numerous
- for storage of waste products, food
functions:
- enclose material for digestion by lysosomes
- fresh water protists: contractile vacuoles to pump excess water out to maintain suitable ion and molecule conc in cell
what are centrioles
a pair of cylindrical, rod like structures positioned at right angles of each other
each is made of 9 triplets of microtubules arranged in a ring
role of centrioles in animals
(cell division) replicate and move to opposite ends of the cell
-organise formation of spindle fibres, involved in the separation of chromosome during mitosis and meiosis
