Human Physio Cell Membrane

lecture 1 of human physio (not including intro)

Structure of phospholipid

Structure of phospholipid

Polar head & 2 nonpolar fatty acid tails

Components of plasma membrane

• cholesterol, phospholipid, carbohydrates, proteins

Functions of membrane proteins

STEM: Structure, transporters (channel proteins, carrier proteins), enzymes, and membrane receptor proteins

Functions of plasma membrane

PECS: physical barrier (separates between ICF and ECF), exchange of materials with environment, communication between cell and environment, structural support (cell shape maintained by cytoskeletal protein attached to membrane proteins)

2 different types of transport

passive and active transport

Passive transport

does not require ATP/energy and solutes move down concentration gradient, doesnt usually require a carrier

Types of passive transport

Diffusion, osmosis, facilitated diffusion

Diffusion

movement of solutes from high to low, does not require energy

Osmosis

movement of water molecules from high to low through a cell membrane, does not require energy

Crenation

Occurs in animal cells when there is too little water

Hemolysis

Occurs in animal cells when there is much water, cell ruptures

Plasmoylsis

too little water in plant cells, cell membrane pulls away from cell wall

Turgid

too much water, but the presence of cell wall doesnt cause cell to rupture

Facilitated diffusion

similar to simple diffusion but requires a carrier

Active transport

does not require ATP/energy and solutes move against concentration gradient, usually requires a carrier/transporter

Primary active transport

requires a carrier and energy (ATP)

Secondary active transport

Does not require ATP/energy and utilises potential energy stored in electrochemical gradients of ions to drive transport of another molecule (cotransporter), gradients established and maintained by carrier proteins that utilises ATP

Vesicular transport

Transport of large molecules across membrane, formation of membrane-enclosed vesicles (e.g. endocytosis, exocytosis)

Sodium-potassium pump

3 Cytoplasmic Na binds to pump proteins

Na binding promotes hydrolysis of ATP, energy release during reaction phosphorylates the pump

Phosphorylation causes the pump to change shape, expel Na to the outside

Two extracellular K binds to pump

K binding triggers release of the phosphate, the dephosphorylated pump resumes its original confirmation

Pump protein binds ATP releases K to the inside, and Na site are ready to bind Na again cycle repeats.

Secondary active transport

Co-transport molecules across the plasma membrane

Same direction (symport) - glucose and amino acids

Opposite directions (antiport) - Na and H ions

Endocytosis

uptake of substances

3 types of endocytosis

phagocytosis, pinocytosis, and receptor-mediated endocytosis

Phagocytosis

selective uptake of multimolecular particles

Pinocytosis

nonselective uptake of ECF fluid

Receptor-mediated endocytosis

selective uptake of large molecule

Exocyotsis

Process by which substance is transported out of cel

Different communication system

gap junctions, contact-dependent signals, paracrine, autocrine, endocrine, synaptic signalling

Gap junction

________ forms from connexons in 2 cells

contact-dependent signalling (juxtacrine)

a ligand on one surface binds to a receptor on another adjacent surface

autocrine

chemical signals act on cell that secrete it

paracrine

chemicals act on cells in the immediate vicinity of the cell secreting it

endocrine

cells of endocrine glands secrete hormone into ECF, hormones enter blood and carried by blood in cells in body, target cells respond to hormone

Synaptic signalling

neurotransmitters diffuses across synapses (rapid effect)

neurohormones

chemicals released by neurons into blood for action at distant targets

lipophilic signal molecules

bind to cytosolic (inside the cell) receptors or nuclear receptors (e.g. transcription in nucleus)

lipophobic signal molecules

stay in the ECF and bind receptor proteins

Membrane bound receptors

extracellular signals bind to membrane receptors alters intracellular molecules causing cellular response

Channel-linked receptors

has to bind with something first to be able to allow materials to enter/exit, different from a pump where transferring of materials take place

Enzyme linked receptors

Ligand binds to receptor, which triggers the enzyme, in this case it is tyrosine kinase. Tyrosine kinase adds phosphate onto a particular protein.

G protein-linked receptors

it is very specific and only respond to ligands by activating G proteins

modulation of signalling pathway

Target cell response - determined by receptor or its associated intracellular pathway

Multiple ligand for one receptor

one receptor may react to different ligands: primary ligand, agonist (activates receptor), antagonist (blocks receptor)

Multiple receptors for one ligand

epinepherine reacts with a-receptors or b-receptors to create different reactions

termination of signalling pathways

extracellular ligand degraded by enzymes, chemical messengers transported back into pre-synaptic cells for recycling, Endocytosis of receptor-ligand complex