Cell Structure & Function Flashcards
what are the three tenets of cell theory?
- all living organisms are composed of one or more cells
- the cell is the most basic unit of structure in all organisms
- all cells arise only from pre-existing cells
what are the differences between prokaryotic and eukaryotic cells?
prokaryotes have neither a true nucleus nor membrane bound organelles, whereas eukaryotes have both, and are generally much larger
for more, refer to table 1 on page 7 of notes
what are the five functions a cell (as a fundamental unit of life) are able to perform?
- intake of raw materials, and from these:
- extraction of useful energy and synthesising its own molecules
- growing in an organised manner
- reproducing after its own kind
- responding and adapting to external environment
what are the lower and upper limits of cell size?
lower limit: minimum amount of space needed to contain the essential elements of its function (eg. DNA and enzyme molecules)
upper limit: surface area to volume ratio needed for exchange of materials between the cell and its environment (as cell size increases, SA:V ratio decreases
why must cells be kept small, and how do increases in organism size thus have to arise?
to ensure the number of chemical exchanges (only transported through cell membrane) that can be performed with the extracellular environment would be adequate to maintain the cell, so most of the cytoplasm cannot be relatively far from the outer membrane
cell size kept small, hence increase in organism size is due to a greater number of cells
what are the units of measurement for cells and cell parts, and what is the approximate diameter of prokaryotic and eukaryotic cells?
cells / larger organelles: micrometer (um), 10^(-6)
smaller organelles (eg. ribosomes) / thickness of membranes: nanometer (nm), 10^(-9)
prokaryotic is 0.2-2.0um, eukaryotic is 10-100um
what does the cytoplasm consist of?
hint: cytosol, membranous / non-membranous organelles
cytosol is an aqueous matrix in which organelles and the nucleus are suspended
membranous: chloroplast, mitochondria, rough and smooth endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, chloroplasts (for plants)
non-membranous: cytoskeleton, centrioles, centrosomes (for animal), cilia, flagella, ribosomes
what is the cytoplasm?
it refers to all organelles and cytosol within the cell membrane, except the nucleus
cytoplasm = cytosol (aqueous solute rich matrix) + organelles
cytosol is 90% water, dissolved in it are essential ions and soluble organic molecules like sugars and aa, soluble proteins including enzymes, cytoskeleton (network of fine globular and fibrous protein strands, providing infrastructure and support to the cell
what are membranous organelles, and their advantages?
compartmentalised spaces within cytoplasm, surrounded by membranes (structurally and biochemically similar to plasma membrane)
- allows maintenance of characteristic differences between contents of each organelle and cytosol, compartmentalisation of specific reactions provides diff local environments, incompatible processes can occur simultaneously
- increases membrane SA, internal membranes have embedded enzymes and proteins, so more enzyme complexes can be embedded and increases efficiency of many reactions by providing optimal enzyme concentration
what is the nucleus and nuclear envelope? (microscope, size, function, structure)
largest organelle, easily seen with light microscope
5-20um
encloses genetic material, protects DNA from metabolically active cytoplasm, double membrane perforated with nuclear pores for substance exchange
nuclear envelope: double membrane (each a lipid bilayer), separates cytoplasm and nucleus’ contents, inner and outer membranes are continuous and region between is perinuclear space
describe the function and structure of the nucleoplasm and nucleolous
nucleoplasm: aqueous matrix within nucleus containing proteins, metabolites, ions, RNA, and chromatin (genetic material of the cell, coils of DNA wound around histone proteins)
- chromatin’s two forms: loosely coiled is euchromatin (light-coloured patches), tightly coiled is heterochromatin (dark-coloured patches)
nucleolus: dense mass in nucleus seen under electron microscope, composed of DNA carrying rRNA genes, RNA and protein, functioning to synthesise rRNA that forms a component of ribosomes
how are ribosomes synthesised in eukaryotic cells?
their two large and small ribosomal subunits are first synthesised at the rough endoplasmic reticulum’s ribosomes, then they are folded in the RER lumen and reenter the nucleus through nuclear pores, and meet up with the rRNA synthesised at the nucleolus
what is the endomembrane system?
it is composed of inter-related membrane sacs, related either by direct physical continuity or by transfer of membrane segments known as vesicles
components are: rough and smooth endoplasmic reticulum, Golgi apparatus / body, lysosomes, vacuoles
*the plasma membrane is not part of the endomembrane system, but continuously interacts with it
what is the endoplasmic reticulum (its structure and adaptations)?
extensive network of hollow, membranous tubules, sacs or sheets called cisternae (singular: cisterna)
internal space of the ER is known as the lumen, continuous with perinuclear space
extensive network of cisternae increases membrane surface area for synthesis
hollow cisternae accommodate newly synthesised substances and allow for packaging of contents into transport vesicles to the GA
what is the structure, function and significance of rough endoplasmic reticulum?
structure: sheet-like, rough due to presence of ribosomes that stud the cytosolic face of RER
function: RER-bound ribosomes are sites of protein synthesis, pp chain then enters ER lumen to be folded into its native conformation, and sent for export or targeted to various cellular organelles
significance: cells active in protein secretion are abundant in RER, some proteins synthesised in RER can also enter RER membrane to form ER membrane proteins
what is the structure and function of the smooth endoplasmic reticulum?
network of tubules which lack ribosomes, smooth appearance
functions in diverse metabolic processes
synthesis of lipids (cells active in hormone secretion usually have abundant SER)
metabolism of carbohydrates
detoxification of drugs and poisons
storage of calcium ions (for muscle contraction and cell signalling)
what is the structure, function and significance of the Golgi body (cis and trans faces)?
structure: stack of flattened, membrane-bound sacs called cisternae (singular: cisterna, each stack differs in thickness and molecular composition)
- distinct polarity: cis (forming) face, and a trans (maturing) face. new cisternae made of transport vesicle membranes formed at cis face by receiving transport vesicles from the ER, and secretory vesicles bud off at trans face to go to extracellular matrix or to form lysosomes
*Golgi vesicles transfer materials between cisternae, or transport substances to other organelles off the trans face
function: site of modification and packaging of ER products
- glycosylation: addition of sugar groups
- trimming: removal of excess monomers
*different cisternae have different enzymes, progressively modified at each cisterna between cis and trans faces
significance: any cell active in any form of secretion have abundant GA, increased SA for vesicle reception and budding. multiple cisternae: different modification processes can occur simultaneously
what is the structure and three major functions of lysosomes?
membranous organelle that is homogeneously electron-dense, contains hydrolytic enzymes (proteases, nucleases, lipases, acid phosphates) that digest most macromolecules, with an optimal acidic pH of 5, segregation of contents provides optimal pH for hydrolytic reactions and protects cellular contents from hydrolysis
- digestion: food particles or bacteria engulfed by endocytosis to fuse w lysosomes to form endosomes (with food) or phagocytic vacuole (with bacteria)
- autophagy of worn-out organelles: enclosing unwanted structures with membrane of unknown origin, forming autophagic vacuoles
- autolysis: self-destruction of cells is apoptosis, mass release of lysosomal contents in whole cell
what is the role and structure of vacuoles (in animal and plant cells)?
animal: small, mobile organelles that store and transport substances (eg. food vacuoles and phagocytic vacuoles)
plant: large central vacuole (single-membraned) known as a tonoplast that contains cell sap
functions include storage of organic compounds like proteins and inorganic ions like K+ and Cl-, disposal site for toxic metabolic by-products, contains pigments, plant protection by accumulating toxic or unpalatable compounds to consumers, cell growth and elongation by accumulating water and pushing cytoplasmic contents to periphery of cell so minimal investment in cytoplasm synthesis needed, and SA:V ratio not sacrificed when making plant cells bigger
what are both non-endomembrane system membranous organelles and energy transducers?
mitochondria and chloroplasts are energy transducers: not involved in endomembrane system, but they convert energy from one form into another
what is the structure, size, function, and significance of mitochondria?
elongated or spherical, ranging from between 1.0-10um
double membraned, smooth outer but highly convoluted inner with infoldings known as cristae to increase the SA
- synthesises ATP during cellular respiration!
space between membranes is inter-membrane space / perimitochondrial space
inner membrane encloses the mitochondrial matrix, storing enzymes, its own circular DNA, and own protein synthesis machinery (RNA and ribosomes), for mitochondria to synthesise its own proteins (site of the Krebs cycle)
compartmentalisation is necessary for proton gradient across inner mitochondrial matrix which is impermeable to protons
what is the structure, size, function, significance of chloroplasts?
sites of photosynthesis, convert solar energy to chemical energy, using sunlight to drive synthesis of organic compounds from CO2 and H2O
lens-shaped, 5-10um in length, only organelles other than nucleus visible under light microscope, double-membraned chloroplast envelope
inner membrane encloses semi-fluid compartment known as the stroma, contains DNA and protein synthesis machinery
sugars synthesised also stored as starch grains in stroma
thylakoids are the third set of membranes that enclose thylakoid lumen, forming thylakoid discs that stack up to form granum that are connected by intergranal lamellae, to increase SA for attachment of photosynthetic pigments
compartmentalisation is necessary for proton gradient
what is the structure, function, and location of ribosomes?
site of protein synthesis, consisting of two subunits (large and small ribosomal subunits made up of proteins and rRNA)
location: attached to RER, free in cytosol (self-sufficient: mitochondrial matrix and chloroplast stroma)
bound ribosomes synthesise proteins destined for export, insertion into membranes, or targeted to various membrane-bound organelles
free cytosolic ribosomes synthesise proteins that remain in the cell and function within the cytosol
what is the structure and function of the cytoskeleton (microtubules, microfilaments, intermediate filaments)
3D array of interconnected filaments and tubules: giving mechanical support and maintaining cell shape, allowing for anchorage and directing movement of organelles and molecules, providing cell motility (cilia and flagella)
microtubules: specialised arrangements arise from microtubule organising centers (MTOCs), involved in transport of substances
microfilaments: movement of cells
intermediate filaments: stabilise organelles or specialised cell junctions
