Cellular Level

structure defines function

•the biochemical reactions occurring in a cell are dictated by the subcellular structures present in the cell

plasma membrane

defines the boundary of a cell

cytoplasm

the interior of the cell between the plasma membrane and the nucleus

Nucleus

contains the genes which control activities of the cell

plasma membrane = “fluid mosaic model”

Lipid bilayer exhibits fluidity and the membrane proteins are in constant flux - their shapes constantly change as in a kaleidoscope or a mosaic pattern

cholesterol

maintains the integrity of the plasma membrane by inserting between phospholipid tails

integral proteins

span the plasma membrane exposed on one surface or both surfaces of the plasma membrane

transmembrane proteins

Integral proteins exposed on both surfaces of the plasma membrane are called

peripheral proteins

attached to integral proteins or the phospholipids’ heads on the extracellular face of the plasma membrane

transport, enzymatic activity, receptors, intercellular joining, cell-cell recognition, attachment to the cytoskeleton

6 functions of membrane proteins

glycocalyx

“sugar coat”

protection

cushions the plasma membrane and protects it from chemical and physical injury

immunity to infection

enables the immune system to recognize and selectively attack foreign organisms

defense against cancer

changes in the glycocalyx of cancerous cells enable the immune system to recognize and destroy them

transplant compatability

forms the basis for compatibility of blood transfusions, tissue grafts, and organ transplants

call adhesion

binds cells together so tissues do not fall apart

fertilization

enables sperm to recognize and bind to eggs

embryonic development

guides embryonic cells to their destination in the body

tight/impermeable junctions

fusion of integral proteins in plasma membrane of adjacent cells that prevent the transfer of substances directly between adjacent cells

desmosomes/anchoring junctions

linker proteins extending from plaques on the cytoplasmic surface of the plasma membrane of adjacent cells interdigitate to hold the cells together and prevent their separation

gap/communicating junctions

formed by hollow cylinder called connexon; it allows for the rapid transfer of ions between cells; Gap junctions also known as

electrically

cells connected by gap junctions are ___________ coupled

passive membrane transport

substances cross the plasma membrane without any energy input.

Diffusion

movement of substances from area of higher concentration to area of lower concentration = down a concentration gradient

Osmosis, simple diffusion, facilitated diffusion

3 types of Diffusion

filtration

movement of solution from area of higher pressure to area of lower pressure = down a pressure gradient

active processes

the cell provides energy required to move substances across the plasma membrane

active transport/solute pumping

movements of solute from area of lower concentration to area of higher concentration against a concentration gradient

vesicular transport

bulk transport

exocytosis

movement of substances enclosed in vesicles out of the cell

endocytosis

movement of substances enclosed in vesicles into the cell

phagocytosis, pinocytosis, receptor-mediated endocytosis

3 versions of endocytosis

simple diffusion

nonpolar/hydrophobic/lipid-soluble substances diffuse through the plasma membrane. Ex. Oxygen, carbon dioxide

facilitated diffusion

transport of large/polar substances mediated by carrier proteins embedded in the plasma membrane;

exhibits saturation and specificity

Osmosis

movement of water from area of lower solute concentration to area of higher solute concentration through a semi-permeable membrane. Water moves through specific pores in the plasma membrane called aquaporins

Isotonic

concentration of solution inside and outside of the cells is the same; the same amount of water moves in/out of the cells and thus, the shape of cells remain unchanged

Hypotonic

•cells are placed in a solution with a lower concentration than solution inside cells;

     water moves via osmosis into the cells – cells swell and eventually lyse (burst)

Hypertonic

•cells placed in solution with a higher concentration than solution inside cells; water moves via osmosis from the cells; cell crenate ( shrink)

filtration

Capillary transfer of solution from blood across capillary walls into interstitial fluid occurs via

exocytosis

metabolic waste is secreted via

endocytosis

nutrients, fluids, hormones are taken into target cells in bulk

Phagocytosis

movement of solid particles from the exterior into the cell; solid particles such as clumps of bacteria or cell debris, are enclosed in vesicles called PHAGOSOMES

Pinocytosis

Bulk-flow endocytosis or fluid-phase endocytosis) – movement of solution into cells by enclosing the solution in vesicles called pinocytic vesicles. This is how cells take in nutrients in bulk and therefore all cells can perform

Receptor-mediated endocytosis

substances bind to specific receptors (carrier-mediated) on the surface of the cell and taken into the cell. ( LDL binds to LDL receptors on the surface of steroidogenic cells and taken in via receptor mediated endocytosis; cholesterol is released;

exhibits saturation and specificity

Transcytosis

Movement of substances enclosed in vesicles into a cell via endocytosis, travels  across the cell and released on  the opposite side of the cell via exocytosis

Vesicular Trafficking

Intracellular movement of substances in vesicles from organelle to  organelle within the cell

K+

concentration is higher inside the cell than outside; diffuses out of the cell down its electrochemical gradient

Na+

concentration is higher outside the cell than inside; diffuses into the cell down its electrochemical gradient

K+

selective permeability of the membrane favors __ diffusion

negative

membrane potential

is established when the movement

of K⁺ out of the cell equals K⁺

movement into the cell

Cytosol

the viscous, semitransparent fluid in which the organelles are suspended

mitochondria

“power plants”

ribosomes

site of protein synthesis

membrane factories

rough ER

smooth ER

lipid/drug metabolism

golgi apparatus

“traffic director”

Lysosomes

“demolition crew”

Peroxisomes

neutralize harmful free radicals

Cytoskeleton

cell skeleton

ribosomes, cytoskeleton

2 non membranous cytoplasmic organelles

LDL

bad cholesterol

HDL

good cholesterol

cholesterol is good

cholesterol is necessary for the body to stabilize the plasma membrane

cholesterol is bad

too much cholesterol is bad, especially LDL. Causes plaque buildup, leading to tissue death and heart attack/ischemic stroke