Membrane Structure & FunctionSpring 2013 - Althoff Reference: Mader & Windelspecht Ch. 5)

Lec05

• ____________________– “the boundary” between the cell’s inside workings and the world outside it.

Keys to consider: 1) ____________ for exchange between

inside and outside the cell 2) _________________ are exchanged

A Little History…

• Beginning of 20th century researchers noted lipid soluble molecules entered cells more rapidly than water soluble molecules

In ______________________________ determined phospholipid content of a cell “just enough” to form a bilayer around the cells In ______________________________ proposed proteins also part of membrane. Model they proposed was “sandwich-like”, further enhanced by Robertson in late 1950s.

A Little History…

• Robinson’s ______ _________ model. late1950s

• Singer & Nicolson __________ model, 1972.

EMBEDDED PROTEIN MOLECULES

BILAYER PHOSPHOLIPID “SANDWICH”,

INSIDE THE CELL

OUTSIDE THE CELL

PHO

SPH

OLI

PID

(similar to Mader p86 Fig. 5.1)

Components of the PLASMA MEMBRANE

• Phospholipids “bilayer”(meaning 2

layers)• “Exterior” portions are

hydrophilic (2 places)• “Interior” portion of the

bilayer is hydrophobic• Provides essential

“structure” to this portion of the cell

• Protein molecules are embedded in the plasma membrane

• Serve to stabilize and shape the plasma membrane

• Various (many) proteins perform specific functions: 1) channel 2) transport 3) cell recognition 4) receptors 5) enzymes 6) form “junctions”

Lipids Proteins

PLASMA MEMBRANE: A matrix of proteins

• Some proteins span the entire bilayer distance (__________________ proteins)

• Some proteins reach the inside surface only

Proteins

OUTSIDE

INSIDE

Fluidity of the Plasma Membrane

• At room temperature, the __________________ of the plasma membrane has the consistency of olive oil

• Result: ___________________

• _____________________ —those not attached to the cytoskeleton—can move within the fluid lipid bilayer

• This “fluidity” is critical to the _________ of proteins, particularly enzymes which speed up chemical reactions

Lipid Movement

• CHANNEL proteins – “_________________”, control passage of molecules

• CARRIER proteins – “____________” combine with a substance and move it across the membrane

• CELL RECOGNITION proteins – “_________” looking for pathogens, alert immune system

• RECEPTOR proteins – “__________”, bind with other molecules resulting in shape change that brings about cellular response

• ENZYMATIC proteins– “________”, facilitate/speed up metabolic reactions directly

• JUNCTION proteins – “___________________” form junctions between cells

Plasma Membrane PROTEINS

CHANNEL CARRIER RECOGNITION

RECEPTOR ENZYMATIC JUNCTION

When Function Goes _____• CHANNEL proteins – faulty chloride (Cl-) channel results in

cystic fibrosis (thick mucus collects in airways, pancreatic ducts, liver ducts)

• CARRIER proteins – inability to use energy transport for sodium potassium (Na+K-)transport may cause obesity for some

• CELL RECOGNITION proteins – can explain rejection of organ transplants, liked to MHC (major histocompatibility complex) glycoprotein

• RECEPTOR proteins – why some are pygmies. Membrane receptors faulty and cannot interact with growth hormone

• ENZYMATIC proteins– diarrhea: impact of cholera bacteria toxin released on enzyme adenylate cyclase, which reduces water & Na retention in large intestine

• _______________________________ – the plasma membrane is ‘choosy” about the passage of molecules into and out of the cell.

Plasma Membrane: Permeability

DIFFUSIONFACILITIATED

TRANSPORT

ACTIVE TRANSPORTEXOCYTOSISENDOCYTOSIS

Energy Not Required Energy Required

1

2

Some sugars, amino acids & ions

Lipid-soluble molecules, H20, &gases

macromoleculesmacromolecules

Some sugars& amino acids

(Mader p89 Fig. 5.4)

3

4

5

Toward _______ concentrationToward _______ concentration

Toward _______ concentration

Toward _______ of cellToward _______ of cell

Direction of moleculepassage

DIFFUSION

FACILITATED TRANSPORT

ACTIVE TRANSPORT

EXOCYTOSIS

ENDOCYTOSIS

Key process

REQUIRES ENERGY

Concentration gradientChannels or carrier AND

concentration gradient

Carrier plus energy

Vesicle fuses with plasma membrane

Vesicle formation

Requirement

DIFFUSION

FACILITATED TRANSPORT

ACTIVE TRANSPORT

EXOCYTOSIS

ENDOCYTOSIS

Key process

REQUIRES ENERGY

PROCESS OF DIFFUSION (Mader p91 Fig. 5.5)

DIFFUSION is spontaneous and ___ chemical energy is required

PROCESS OF OSMOSIS (Mader p93 Fig. 5.8)

• Must make the “____________” between cells• Permits ________________ between cells• Permits _________________ between cells• Components and construction ______ between plants

and animals• We consider these “_________________” structures

examples for plants: __________ & plasmodesmata examples for animals: __________________

_______ the Cell: EUKARYOTIC CELLSMULTICELLUAR ORGANISMS

PLANTS -- Outside

PLASMODESMATA

CELL WALL -- PRIMARY

CELL #1 CELL #2

CYTOPLASMA

ANIMAL: Extracellular Matrix

• “MESHWORK” OF _______________________

• Examples: “structural proteins” ________________ – matrix strength________________ – resilience

• Examples: “rigid packing gel” permits ________________ of nutrients,metabolites, and hormones between blood and tissue cells

OUTSIDE

INSIDE

ANIMAL: Extracellular Matrix

(Mader p99 Fig. 5.13)

Extracellular Matrix: Rigid or Flexible?

• RIGID: ______ is rock solid because the extracellular matrix includes mineral salts (i.e., calcium salts) deposited outside the cell

• FLEXIBLE: _________

Animal Cell JUNCTIONS

• _________ sheet of cells results

• Attach to ____________, within the cell via cytoplasmic plaques, intercellular filaments

• Common in heart, stomach, and bladder where ___________ must stretch

ADHESION JUNCTIONS

CELL #1 CELL #2

Animal Cell JUNCTIONS

• ____________ fastening• Plasma membrane

proteins _______ to each other

• Common in kidney where urine passes through; intestines have this type of lining to __________ ______________ from entering lining

TIGHT JUNCTIONS

CELL #1 CELL #2

Animal Cell JUNCTIONS

• Permits ______________• __________ plasma

membrane channels join• Common in the ________

muscle & _____________ (stomach)

• Permit _____________ to facilitate synchronous contraction

GAP JUNCTIONSCELL #1 CELL #2

Know Where You Are Inside or Outside the Eukaryotic Cell

RELATIVE TO THE _____________________INSIDE looking out OUTSIDE looking inCOMPONENTS

Cell wall (plants)

Nucleus

Ribosomes

Plasmodesmata (plants)

Golgi apparatus

Extracellular matrix (animals)

Adhesion junctions (aniamls)

Gap junctions (animals)

NoYes

No Yes

Know What Requires Energy & What Doesn’t Relative to _________________ of the Plasma Membrane

Energy Required Direction of passage*

Passage type

Diffusion

Endocytosis

Exocytosis

Active Transport

Facilitated Transport

No

Yes

*Toward lower concentration *Toward outside

*Toward higher concentration *Toward inside

Toward outside