y5 bio: cluster 2 (organelles and compartmentalisation + cell specialisation + membrane transport)

which common structures are classified as organelles, and which are excluded?

included: plasma membrane, nucleus, ribosomes, vesicles. excluded: cell wall, cytoplasm, cytoskeleton

what is the key advantage of separating the nucleus from the cytoplasm in eukaryotic cells?

it allows post-transcriptional processing (e.g. splicing) and mRNA quality control to occur before translation begins

what are the three main advantages of cytoplasmic compartmentalisation?

1. concentration of enzymes/substrates

2. maintenance of optimal local microenvironments (e.g., pH)

3. isolation of incompatible biological processes

give an example of compartmentalisation isolating destructive processes in animal cells?

lysosomes isolate hydrolytic enzymes to prevent self-digestion of the surrounding cytoplasm

how does the structure of the inner mitochondrial membrane adapt to support ATP synthesis?

highly folded cristae maximise surface area for electron transport chains, while the narrow intermembrane space allows rapid proton gradient buildup

how are thylakoids structurally adapted for efficient light-dependent reactions in photosynthesis?

grana stack to provide a large surface area for photosystems and ETCs, while small internal lumen volumes allow quick proton accumulation

what is the function of the stroma in chloroplasts?

it isolates and concentrates Rubisco and other enzymes/substrates required for the light-independent calvin cycle

what is the functional difference between free ribosomes and bound ribosomes on the rough ER?

free ribosomes synthesize proteins intended for use within the cell

what is the path of a protein intended for secretion from synthesis to release?

rough er -> transport vesicle -> golgi apparatus -> secretory vesicle -> plasma membrane (exocytosis)

what are the main processing functions of the golgi apparatus?

modifying, sorting, and packaging proteins (including post-translational modifications like glycosylation and phosphorylation)

what is the structural role of clathrin in endocytosis?

clathrin forms a polymerised triskelion lattice/cage that bends the plasma membrane into an invaginated pit

what is the role of dynamin in vesicle formation?

dynamin uses GTP hydrolysis energy to pinch off (cause scission of) the newly formed vesicle from the membrane

what is the difference between constitutive secretion and regulated secretion?

constitutive secretion releases substances continuously, whereas regulated secretion stores vesicles until triggered by a specific extracellular signal

what is cell differentiation, and what signaling molecules direct it?

the process by which unspecialised cells become specialised, directed by signal gradients of morphogens that provide positional cue

what is a stem cell niche?

a specialized microenvironment within tissues that maintains stem cells and regulates their self-renewal and differentiation

what are two specific examples of stem cell niches in humans?

the bone marrow niche (hematopoiesis) and the hair follicle niche (hair/skin regeneration)

how do totipotent, pluripotent, and multipotent stem cells differ in potency?

totipotent cells can form any cell type (including extra-embryonic tissues)

pluripotent cells can form all embryonic tissues (3 germ layers)

multipotent cells can differentiate into a limited range of related cell types

what are the three embryonic germ layers formed by pluripotent cells?

ectoderm, mesoderm, and endoderm

how are type 1 and type 2 pneumocytes structurally adapted for their functions?

type 1: extremely thin with minimal cytoplasm to shorten gas diffusion distance

type 2: cuboidal shape with dense vesicles that secrete surfactant to prevent alveolar collapse

what are 3 key structural differences between cardiac muscle cells and striated (skeletal) muscle cells - in terms of length, branching and nucleated?

cardiac muscle cells are short, branched, and single-to-few nucleated BUT skeletal muscle cells are long, unbranched, and multinucleated

what is the function of intercalated discs in cardiac muscle tissue?

they contain gap junctions that allow rapid passage of ions between cells, enabling synchronised contraction

how are the midpiece and head of a sperm cell adapted for fertilization?

the midpiece contains abundant mitochondria for flagellar movement

the head contains an acrosome filled with digestive enzymes to penetrate the egg coat

what is the function of cortical granules in an unfertilized egg cell?

they release enzymes via exocytosis immediately after sperm entry to harden the zona pellucida, preventing polyspermy

why is the phospholipid bilayer described as amphipathic?

phospholipids have hydrophilic phosphate heads facing outwards and hydrophobic fatty acid tails facing inwards

what role does cholesterol play in animal cell membranes?

it regulates membrane fluidity and permeability across varying temperatures

what is the difference between integral and peripheral membrane proteins?

integral proteins penetrate the hydrophobic core of the bilayer, whereas peripheral proteins are bound to the membrane surface

what is passive transport and what are its main types?

movement of substances along a concentration gradient without ATP energy, including simple diffusion, facilitated diffusion, and osmosis

what is simple diffusion?

the net movement of small or non-polar particles from an area of higher concentration to lower concentration directly across the bilayer

what is facilitated diffusion?

the passive movement of polar or charged molecules across a membrane via transmembrane channel or carrier proteins

what is osmosis?

the net movement of water molecules across a selectively permeable membrane from a region of higher solute concentration to lower solute concentration

what is active transport?

the movement of substances against a concentration gradient across a membrane using ATP energy and protein pumps

how does the sodium-potassium pump function in animal cells?

it uses energy from ATP hydrolysis to pump 3 sodium ions out of the cell and 2 potassium ions into the cell

what is endocytosis?

the active process where the plasma membrane invaginates to engulf extracellular material, forming an intracellular vesicle

what is exocytosis?

the active process where an intracellular vesicle fuses with the plasma membrane to secrete its contents outside the cell

what property of the phospholipid bilayer allows endocytosis and exocytosis to occur?

membrane fluidity, which enables the lipid bilayer to break and reform without breaking the cell