Bio 225 Exam 1 - Cellular Physiology - Lloyd

UofM Biology 225 Exam 1 - Intro and Cellular Physiology

What is the basic chemical composition of cells

Water - 70%, organic molecules and inorganic ions

Organic molecules in cells

carbohydrates, lipids, proteins, and nucleic acids

Inorganic molecules in cells (less than 1% of mass)

Na+, Mg2+. K+, Ca2+, Cl-, phosphate, bicarbonate, etc

plasma membrane functions (4)

• Helps maintain composition of intra and extracellular fluids

• Forms framework for protein components of cell

• Detects chemical messengers at cell surface

• Links adjacent cells together

Membrane junctions

tight junctions, desmosomes, and gap junctions

tight junctions

Functions as impermeable barrier

desmosomes and adherens junctions

(Spots and bands) Functions to anchor adjacent cells

gap junctions

Aids in communication between adjacent cells

Major structures of the plasma membrane

cholesterol, integral proteins, channel proteins, peripheral proteins, glycoprotein and sugar residues of glycoprotein

Relative permeability / diffusion thru plasma membrane of certain molecules.

refer to image

Steroid molecules are

lipids, nonpolar, and hydrophobic

Different ways that molecules move across the cell membrane

simple (passive) diffusion, facilitated diffusion, active transport, bulk transport (endo-/exo-cytosis)

integral protein

Tightly bound to the plasma membrane. Either embedded or span the entire bilayer and involved in structural support, signaling, and transport

peripheral protein

Attached to the surface of the plasma membrane. Interact with the membrane surface or with integral proteins

glycoprotein

Plasma protein with sugar chains attached. Can be integral or peripheral and involved in cell-cell recognition and binding (adhesion)

Molecules with high relative permeability through the plasma membrane include ___ and ___

hydrophobic molecules and small uncharged polar molecules

Molecules with low relative permeability (cannot diffuse freely through plasma membrane) include ___, ___, and ___

large uncharged polar molecules, ions, and charged polar molecules

what is a gradient

The difference between two points

diffusion is

A random dispersing process due to random thermal motion and entropy (second law of thermodynamics: entropy of a system must always increase or stay constant)

flux

A measure of the diffusion rate; a measure of the net gain of molecules by one side and the net loss from the other side

net flux is

the difference b/w the two one-way fluxes

T or F: Diffusion stops once equilibrium is reached

F

Equilibrium means

that the rate of the forward rxn equals the rate of the reverse rxn

simple (passive) diffusion

No metabolic energy (ATP) used, movement from high to low concentration, and net flux (rate of diffusion) = 0 at equilibrium

the movement of molecules due to the intrinsic kinetic energy of molecules (and entropy)

T or F: For passive diffusion, each substance diffuses against its own gradient, independent of the concentration gradients of other substances

T

The direction and magnitude of net flux depends on

permeability, concentration gradient, temperature, surface area, size of molecule, and distance:

T of F: Water can pass through the plasma membrane by simple diffusion

F ; water is excluded by the hydrophobic tails of the phospholipid bilayer

There is new evidence that shows that water can indeed pass thru the membrane via simple diffusion

Different types of gradients

chemical, electrical, or electrochemical

Gradients are forms of

energy storage (potential energy)

An electrochemical gradient is

a gradient of electrochemical potential; a concentration gradient and an electrical field gradient combined

osmosis is

Passive transport of water; Net diffusion of water from a region of high water concentration to a region of low water concentration

Direction of water movement is determined only by difference in total solute concentration, not type of solute

Aquaporins

integral channel proteins that facilitate osmosis

T or F: Direction of water movement is determined only by difference in total solute concentration, not type of solute

T

osmolarity is

Total concentration of solutes in a solution; depends on the total number of molecules not individual types

isosmotic

Same osmolarity (surrounding compared to cell)

hyperosmotic

Higher osmolarity (surrounding compared to cell)

hyposmotic

Lower osmolarity (surrounding compared to cell)

osmotic pressure

Pressure generated by water moving based on osmolarity

hydrostatic pressure

Pressure exerted by the standing column of water (gravity)

System used to transport molecules too large or too polar to diffuse across the plasma membrane

mediated transport system

facilitated diffusion

Transmembrane proteins facilitate diffusion of some polar or charged molecules across the plasma membrane. Molecules move down their electrochemical gradient. No metabolic energy (ATP) required for transport

channel proteins

Provide a corridor for polar or charged molecules to pass through the plasma membrane (facilitated diffusion)

specificity of channels depends on the charge and pore size

Ion channels may be

selective or non-selective

Selective ion channels include ___, ___, and ___ channels

Na+, K+, and Cl-

Non-selective ion channels are ______ ______ channels that allow ___, ___, and ___ ions to pass through

monovalent cation, Na+, K+, and Li+

constitutive channels

Channels that are always open

An example of a constitutive channel are ___

aquaporins

gated channels

Channels that open transiently in response to stimulus

The three types of gated channels are ___-gated channels, ___-gated channels, and ___-gated channels

ligand, voltage, and mechanically

ligand-gated channel

A signal molecule binds to the receptor/channel regulating the opening and closing of the gates (type of channel)

• eg) acetylcholine regulates entry of Na+ into muscle cell

voltage-gated channel

Regulated by the electrical state of the cell (type of channel)

ex: voltage-gated Na+ channels activated by membrane potential

mechanically-gated channel

Regulated by a physical change

ex: pressure

permease/carrier protein

Substrate binds to protein, undergoes a conformational change, and releases the substrate to the other side (a form of facilitated diffusion); down [] gradient

• ATP not needed

• eg) GLUT protein

molecules that are too large and/or polar to diffuse are transported across plasma membrane by mediated transport mechanisms:

facilitated diffusion, active transport, bulk transport

active transport

Transport where transported molecules must bind to the transporters. Metabolic energy (ATP) is required directly or indirectly.

types of active transport

secondary active transport and primary active transport

primary active transport

ATP is required directly and involved movement of solutes against their gradient. specific membrane-bound transport proteins involved

• Binding to recognition site of proteins that act as ATPase and convert ATP → ADP → Pi which causes a conformational change in the transport protein → movement of the solute across the membrane

• ex: Maintains electrochemical gradients

Primary active transport Example 1

Ca2+ ATPase/Pump: hydrolysis of ATP directly required for the function of the carriers. molecule or ion binds to the “recognition site” on one side of carrier protein —> binding stimulates phosphorylation (breakdown of ATP) of the carrier —> carrier protein undergoes conformational change —> hinge-like motion releases transported molecules to the opposite side of the membrane

Primary active transport Example 2

Na+/K+ ATPase/Pump

Carrier protein is also an ATPase enzyme that converts ATP to ADP and Pi. Actively exports 3Na+ and imports 2K+ inward against [] gradient.

functions of steep gradient (from Na+/K+ ATPase):

involvement in electrochemical impulses

promotes osmotic flow'

regulates resting calorie expenditure and basal metabolic rate

provides energy for “coupled transport” of other molecules

secondary active transport

No direct input of energy required but depends on the electrochemical difference established by primary active transport

“coupled” transport

Types of transporters

ion channels

antiporters

symporters

electroneutral cotransporters

electroneutral exchangers

uniporter

The specific transport of a single substance in or out of cells

symporters

transport moves 2 different molecules in the same direction. Both may or may not be charged

ex: SGLT transporters move sodium down electrochemical gradient into cell to concentrate glucose

antiporters

transport similarly charged molecules in opposite directions

ex: Na+/K+ ATPase

ion channels

move single ions down electrochemical or [] gradient

ex: CFTR

electroneutral cotransporters

move anions and cations in same direction

ex: NKCC transporters

electroneutral exchangers

reversible transporters driven by electrochemical gradients

ex: Cl-/HCO3- exchanger in RBCs

bulk transport

Simultaneous movement of many large molecules that cannot be transported by carriers

endocytosis and exocytosis

exocytosis

A process by which the contents (cellular products) of a cell vesicle are released to the exterior through fusion of the vesicle membrane with the plasma membrane

endocytosis

A process by which cells absorb external material by engulfing it with the cell membrane due to the interaction of the molecule and protein receptor

pinocytosis

The uptake of extracellular fluids and small molecules by a cell

phagocytosis

The process by which a cell engulfs and internalizes a large particle by extending its membrane around it

Unifying Theme: The ___ and ___ of a characteristic are connected.

form and function

Unifying Theme: In the face of environmental variation, ___ and ___ are used to compensate for environmental variation.

regulation and homeostasis

What is another word for a carrier protein?

permease