Plasma Membrane Structure and Transport

Cell

The basic structural and functional unit of life

Between 30-40 trillion [blank] in body

Cytology

Scientific study of cells

When did cytology begin

When Robert Hooke coined the word cellulae to describe empty cell walls of cork in the 17th century

Who concluded that all animals are made of cells

Theodor Schwann around the 19th century

Who demonstrated that cells arise from other cells

Louis Pasteur in 1859 refuted that cells are formed by spontaneous generation

Cell Theory

All organisms composed of cells and cell products

An organism's structure and functions are due to activities of cells

Cells come from only preexisting cells

Cells of all species exhibit biochemical similarities

What is the tinniest cell in the body

Red blood cell

Cell Shape: Squamous

Thin, flat, scaly

Cell Shape: Cuboidal

Squarish-looking

Cell Shape: Columnar

Taller than wide

Cell Shape: Polygonal

Irregularly angular shapes, multiple sides

Cell Shape: Stellate

Star-like

Cell Shape: Spheroid to ovoid

Round to oval

Cell Shape: Discoidal

Disc-shaped

Cell Shape: Fusiform

Thick in middle, tapered toward the ends

Cell Shape: Fibrous

Thread-like

Can a cells shape appear different

Yes, if viewed in a different type of section

Ex. Longitudinal versus cross section

What are the four basic parts of human cells

Plasma membrane, Cytoplasm, Nucleus, Extracellular Fluid

Plasma Membrane

Flexible outer boundary made of proteins and lipids

Cytoplasm

A gel like intracellular fluid containing organelles

(Organelles, cytoskeleton, Inclusion (stored or foreign bodies), Cytosol (Intracellular fluid/ ICF)

Nucleus

The Control Center

Extracellular fluid (ECF(

Fluid outside of cells includes tissue (interstitial fluid)

Microscopy: Light Microscope (LM)

Revealed plasma membrane, nucleus, and cytoplasm (fluid between nucleus and surface)

Microscopy: Transmission electron microscope (TEM)

Improved resolution (ability to reveal detail)

Microscopy: Scanning electron microscope (SEM)

Improved resolution further, but only for surface features

Plasma membrane

Lipid bilayer with proteins in constantly changing fluid mosaic

Mainly phospholipids with some proteins

How does the plasma membrane appear with an electron microscope

Appears as dark parallel lines when viewed

What is the plasma membranes role in cellular activity

Defines cell boundaries, Governs interactions with other cells, Controls passage of materials in and out of the cell

Plasma membrane and ICF and ECF

It separates intracellular fluid from extracellular fluid

Interstitial fluid

IF= Extracellular fluid that surrounds cells

Membrane lipids: Phospholipids

Phospholipid bilayer

75% of membrane lipids are phospholipids

Amphipathic (contains both hydrophobic and hydrophilic components) molecules arranged in a bilayer

Hydrophilic phosphate heads face water on each side of membranes

Hydrophobic tails- are directed towards the center avoiding water

Drift laterally, keeping membrane fluid

Membrane lipids: Cholesterol

20% of the membrane lipids

Holds phospholipids still and can stiffen membrane

Membrane lipids: Glycolipids

5% of the membrane lipids

Phospholipids with short carbohydrate chains on extracellular face

Contributes to glycocalyx (Carbohydrate coating on cell surface.)

Glycocalyx

“Sugar covering” at cell surface

• Lipids and proteins with attached carbohydrates (sugar groups)

  • Ex. Glycoproteins, Glycolipids

Glycocalyx differentiation

Every cell type has different pattern of sugars

Specific biological markers for cell to cell recognition

Allows immune system to recognize self and non self

Cancerous cells change it continuously

Functions of the Glycocalyx

Protection, Immunity to infection, Defense against cancer, Transplant compatibility, Cell adhesion, Fertilization, Embryonic Development

Extensions of the cell surface: Microvilli

Minute fingerlike extensions of plasma membrane

Increase surface area for absorption

Core made of actin filaments for stiffening

(pushes the membrane up)

Extensions of the cell surface: Cilia

Hair like processes 7-10 μm long

Single, nonmotile primary cilium found on nearly every cell

“Antenna” for monitoring nearby conditions

Helps with balance in inner ear; light detection in retina

Extensions of the cell surface: Multiple nonmotile cilia

Found on sensory cells of nose

Extensions of the cell surface: Ciliopathies

Defects in structure and function of cilia

Extensions of the cell surface: Motile Cilia

Respiratory tract, uterine tubes, ventricles of brain, ducts of testes

50-200 on each cell

Beats in waves sweeping material across a surface in one direction (sweeping motion)

Extensions of the cell surface: Flagella

Whip-like structure with axoneme identical to cilium’s

Much longer than cilium

Stiffened by coarse fibers that support the tail

• Moves the entire cell (movement/pushes)

Tail of sperm-only functional flagellum in humans

Extensions of the cell surface: Pseudopods

Continually changing extensions of the cell that vary in shape and size

• Can be used for cellular locomotion, capturing foreign particles

Membrane proteins

2% of the molecules but 50% of the weight of membranes

Membrane proteins: Integral proteins

(Penetrate membrane)

Transmembrane proteins pass completely through

Hydrophilic regions contact cytoplasm, extracellular fluid

Hydrophobic regions pass through lipid of the membrane

Some drift in membrane; others are anchored to the cytoskeleton

• Imbedded in the plasma membrane

Membrane proteins: Peripheral Proteins

Adhere to one face of the membrane

Usually tethered to the cytoskeleton

• loosely attached to the membrane

Membrane proteins: Receptor

A [blank] that binds to chemical messengers such as hormones sent by other cells

Membrane proteins: Enzyme

A/An [blank] that breaks down chemical messenger and terminates its effect

Membrane proteins: Channel

A [blank] protein that is constantly open and allows solutes to pass into and out of the cell

Membrane proteins: Gated Channel

A [blank] that opens and closes to allow solutes through only at certain times

Membrane proteins: Cell-identity marker

A glycocalyx acting as a cell-identity marker distinguishes the body’s own cells from foreign cells

Membrane proteins: Cell adhesion molecule (CAM)

A cell-adhesion molecule (CAM) that binds one cell to another

Membrane proteins: Second messengers

Chemical first messenger (epinephrine) binds to a surface receptor

Receptor activates G protein

• An intracellular peripheral protien that gets its eneergy from guanosine triphosphate (GTP)

• G protien relays signal to adenlate cyclase which convers ATP to cAMP (second messengers)

• cAMP activates cytoplasmic kinases

• Kinases add phosphate groups to other enzymes turining some on and others off

• Up to 60% of drugs work through G proteins and second messengers

Selectively permeable membrane

Some molecules pass through the plasma membrane easily

Some molecules do no pass through the plasma membrane easily

Two ways substances cross the plasma membrane

Passive process/transport, Active process/ transport

Passive processes

No cellular energy ATP required

Substances move down the concentration gradient

Active Processes

Energy (ATP) required

Occurs only in living cell membranes

Passive Transport: Diffusion

Simple diffusion

Carrier and channel mediated facilitated diffusion

Osmosis

Passive Transport: Filtration

Usually across capillary walls

Gradients

A difference in a variable between one point and another

Down the gradient

Area of high concentration to an area of low concentration

Up the gradient

An area of low concentration to an area of high concentration

Filtration

Particles are driven through membrane by physical pressure

Examples of filtration

[blank] of water and small solutes through gaps in capillary walls

Allows delivery of water and nutrients to tissues

Allows removal of waste from capillaries in kidneys

Simple diffusion

Collisions cause molecules to move down or with their concentration gradients

What influences the speed of simple diffusion

Molecule size: Smaller molecules move faster

Temperature: Increased temperature increases molecule movement

What causes molecules to passively diffuse through the membrane

It is lipid soluble, or small enough to pass through membrane channels, or assisted by carrier molecule

What diffuses directly through the phospholipid bilayer

Nonpolar lipid-soluble (hydrophobic) substances

Ex: Oxygen carbon Dioxide, Fat- soluble vitamins

Carrier Mediated Facilitated Diffusion

Transmembrane integral proteins are [blank]

Transports specific polar molecules to large for channels

• Ex. sugars and amino acids

Binding of substrate causes shape change in [blank] then passage across membrane

Limited by the number of [blank] present

• [blank] are saturated when all engaged

Osmosis

Passive process

Movement of solvent across selectively permeable membrane

• Ex. Water

Occurs when water concentration differs on the two sides of membrane

How water diffuses through plasma membrane

Through the lipid bilayer

Through specific water channels called Aquaporins (AQPs)

Osmolarity

Number of osmoles per liter of solution

One osmole (osm)= 1 mole of dissolved particles

• Takes into account whether solute ionizes in water

  • 1 M glucose is 1 osm/L

  • 1 M NaCl is 2 osm/L

  • Blood plasma, tissue fluid, and intracelluler fluid are 300 millosmoles per liter (mOsm/L)