Cell Membrane Structure and Function: Plasma Membrane, Transport, and Cell Junctions

Plasma Membrane

A selectively-permeable phospholipid bilayer forming the boundary of the cells

The design of the Membrane allows for

cannot pick and choose what goes in and out, can change in results due to the surroundings (2 layers of phospholipids)

3 ATES

Isolates, regulates, communicates

How do substances move across membranes

diffusion and active transport

Fluid Mosaic Model

Structural model of the plasma membrane, where molecules are free to move sideways within a lipid bilayer and are flexible

cholesteral

Makes the cell flexible, stops it from being able to explode, and stops it from becoming so small that the cell cannot let anything in or out

Why Flexibility of a cell is important

stops cells from breaking and needs to bring cells in and out

glycoprotein

A protein with one or more carbohydrates covalently attached to it.

Selective Permeability

A property of a plasma membrane that allows some substances to cross more easily than others.

Categories of Membrane Protein

Transport, receptor, and recognition

Transport Proteins

Carrier- Carries molecules across the membrane

Channel - Creates pores within the cells that allow water-soluble molecules to pass through

Receptor protein

cellular response when specific molecules in the extracellular fluid bind to them

Recognition Protein

identifies and cell-surface attachment site

Fluid

Any substance that can move or change shape in response to the environment

Consentration

the number of molecules in a given volume

Gradient

Physical difference in properties. The greater the gradient faster the diffusion

dynamic equilibrium

Result of diffusion where there is continuous movement of particles but no overall change in concentration (no net force)

Passive Transport

The movement of substances across a cell membrane without the use of energy by the cell (Diffusion, Facilitated Diffusion or Osmosis) High to low

active transport

Energy-requiring process that moves material across a cell membrane against a gradient. low to high

facilitated diffusion

process of diffusion in which molecules pass across the membrane through cell membrane channels with the help of transport proteins

Dialysis

a procedure to remove waste products from the blood of patients whose kidneys no longer function

Osmosis

Diffusion of water through a selectively permeable membrane

hypertonic

Having a higher concentration of salt than water.

hypotonic

more water than salt

Isotonic

equal salt to equal water

4 step process of Active Transport

1. Solute binding

2. Phosphorylation

3. Transport

4. Protein Reversion

Solute Binding

Solutes go into the transport protein in the cell membrane

Phosphorylation

ATP attaches to the transport protein, making a break

Transport

changes shape, changes to ADP, and releases one of the protiens

protein reversion

The phosphate group detaches, and the transport protein returns to its original shape

Breathing with diffusion

Inhalation of oxygen,

moves from the lungs' air sacs (alveoli) into the blood through diffusion,

the exhalation of carbon dioxide, which moves from the blood into the alveoli via diffusion to be expelled

excocytosis

process of exporting macromolecules

membrane-bound vesicles filled with macromolecules move through the cell to the plasma membrane

Endocytosis

process by which a cell takes material into the cell by the infolding of the cell membrane

3 types

3 types of endocytosis

phagocytosis, pinocytosis, receptor-mediated endocytosis

Phagocytosis

cell eating

false foot

wraps around its prey and packages it in a vesicle, then is digested by lysosomes

Pinocytosis

Cell drinking

droplets of fluid from its surroundings into tiny vesicles (ALL fluids not picky)

receptor-mediated endocytosis

When the target molecule is picked up, the vesicle will close and pull the molecules within the cell

cell surfaces - cell junctions

-Desmosomes

-tight junctions

-gap junctions

-plasmodesmala

Desmosomes

holds adjacent cells together

Prominent in skin and heart cells

tight junctions

cell-to-cell junction, prevents the movement of materials between cells

Prominent in epithelial and endothelial cells

gap junctions

channels connected to the cytoplasm between adjacent cells

made from proteins

allows nutrients, ions, etc.. to pass through

Prominent in cardiac muscles

Plasmodesma

- cell-to-cell junction in plants (gap junction in plants)

- almost all living plant cells are connected to one another because of this

-allows for water, nutrients, and hormones to pass freely between cells

Cell wall

Plants- cellulose and other polysaccharides

Fungi - chitin, a modified polysaccharide

Primary Cell Wall

created by secrete cellulose

joined by the middle lamella

Middle Lamella

thin and sticky layer of polysaccharides between primary walls of adjacent cells (separates and holds them together)

Secondary Cell Wall

thicker, and pushes the Primary Cell Wall away from the plasma membrane