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Membrane structure and function - Coggle Diagram
Membrane structure and function
CONCEPT 7.1: Cellular membranes are fluid
mosaics of lipids and proteins
amphipathic
- containing hydrophobic (“water-fearing”) and hydrophilic (“water-loving”) regions
Cholesterol
- a membrane component in animal cells with different effects on membrane fluidity.... regards to temp.
warm temperatures= cholesterol
restrains movement of phospholipids
cool temp= it maintains fluidity by
preventing tight packing
fluid mosaic model
- membrane structure
depicts the membrane, as a mosaic of protein
molecules bobbing in a fluid bilayer of
phospholipids
Phospholipids
- form the main fabric of the
membrane..
proteins
- determine most of the
membrane’s functions
Peripheral proteins
- are bound to the surface of the
membrane
Integral proteins
- penetrate the hydrophobic core
Transmembrane proteins
- integral proteins
that span the membrane
Membrane Carbohydrates in Cell-
Cell Recognition
Glycolipids
- carbohydrates bonded to lipids
Glycoproteins
- carbohydrates bonded to
proteins
CONCEPT 7.2: Membrane structure results in
selective permeability
CONCEPT 7.3 - Passive transport is diffusion of
a substance across a membrane with no energy
investment
Diffusion
- is the movement of particles of any
substance, so that they spread out evenly into the
available space.
concentration
gradient
- Substances diffuse down their concentration
gradient, the region along which the density of a
chemical substance increases or decreases
facilitated diffusion
- transport proteins speed
the passive movement of molecules across the
plasma membrane
7.3 still
passive transport
- Passive transport is the movement of molecules across a cell membrane without energy input.
Osmosis
- is the diffusion of free water (water
molecules not clustered around another substance) across a selectively permeable membrane
osmoregulation
- control of solute
concentration and water balance
Water Balance of Cells Without Cell Walls -
Tonicity
- is the ability of a surrounding solution to cause a cell to gain or lose water
isotonic
- solution if its solute concentration is
the same as that inside the cell
Plant cells become
flaccid
-limp) in an isotonic
solution, and the plant wilts
hypertonic
- if the solute concentration
is greater than that inside the cell, Cells without cell walls will lose water, shrivel, and likely die in hypertonic solution
plasmolysis
- Plant cells experiencing lysis (rupturing of the plasma membrane)
hypotonic
- if the solute concentration
is less than that inside the cell, Cells without cell walls will gain water, swell and lyse (burst) in a hypotonic solution
turgid
- takes up water and swells until the inelastic wall, exerts back a pressure on the cell. ....... (very firm), the
healthy state for most plant cells
plasma membrane controls the exchange of
materials between the cell and its surroundings
selective permeability
- some
substances cross more easily than others
Permeability of the Lipid Bilayer
hydrophilic (polar) molecules - For example, sugars, water and ions pass through slowly, if at all
They NEED
transport proteins
- so substances can cross membranes more quickly by passing through
Channel proteins- hydrophilic channel that
certain molecules or ions can use as a tunnel
Carrier proteins = bind to molecules and change
shape to shuttle them across the membrane
aquaporins
- greatly
increase the rate of passage of water molecules
Ion channels
- facilitate the transport of ions
gated channels
- open
or close in response to a stimulus
Hydrophobic (nonpolar) molecules dissolve in the
lipid bilayer - hydrocarbons, CO2 and O2 pass easily
through the membrane
CONCEPT 7.4 Active transport uses energy to
move solutes against their gradients
Active transpor
-requires energy, usually in the
form of ATP hydrolysis , to move substances against
their concentration gradients
All proteins involved in active transport are carrier
proteins
Active transport enables cells to maintain solute
concentrationsthat differ from the environment
Cotransport
- occurs when active transport of a
solute indirectly drives transport of other substances
Membrane potential
-is the voltage across a
membrane
Voltage is created by differences in the distributionof positive and negative ions across a membrane
electrochemical gradient
- Two combined forces, drive the diffusion of ions across a membrane
An electrical force (the effect of the membrane potential on the ion’s movement)
A chemical force = (the ion’s concentration gradient)
electrogenic pump - is a transport protein that
generates voltage across a membrane, storing
energy that can be used for cellular work
animals -the sodium-potassium pump
plants, fungi, and bacteria-it is the
proton pump
,
which actively transports hydrogen ions out of
the cell
CONCEPT 7.5 - Bulk transport across the
plasma membrane occurs by exocytosis and
endocytosis
exocytosis
- transport vesicles migrate to the
membrane,fuse with it, and release their contents
outside the cell
For example, cells in the pancreas secrete insulin by
exocytosis
endocytosis
- macromolecules are taken into the
cell in vesicles
receptor-mediated endocytosis
- vesicle
formation is triggered by solute binding to receptors
pinocytosis
- molecules are taken up when
extracellular fluid is “gulped” into tiny vesicles
phagocytosis
-a cell engulfs a particle by
extending pseudopodia around it and packing it in a
membranous sac called a food vacuole
