UTA Cell Physiology- Exam 3 : Dr. Charles

Phospholipid Bilayer

Structure surrounding cells, with unique lipid ratio and critical fluidity features.

Flippases

Enzymes in ER aiding in asymmetric phospholipid arrangement.

Floppases

Enzymes in Golgi assisting in asymmetric phospholipid arrangement.

Glycocalyx

Carbohydrate coat regulating cell-cell recognition, movement, and adhesion—functional barrier to molecules in the ECM.

Triton X

Non-ionic detergent for gentle solubilization of membranes. (DOES NOT denature proteins)

Integral Proteins

Proteins embedded in the phospholipid bilayer, contribute to membrane mass.

Encounter intra and extracellular fluids- Transmembrane proteins

GPI Anchors

Lipid rafts enriched structures aiding in cell signaling and endocytosis.

Caveolae

Lipid raft subsets are formed by oligomers of integral membrane protein caveolin

Membrane Potential

Electrical charge near the membrane due to ion concentration differences.

K+ Leak Channels

Channels allowing K+ flow down its concentration gradient.

Nicotinic Acetylcholine Receptor

Ligand-gated cation channel permitting Na+ and K+ influx.

Acetylcholine binds- Shifts hydrophobic amino acids blocking core- Cation influx

Active Transport

Is a process using ATP to move molecules against a concentration gradient.

Secondary Active Transport

Co-transport moving substances against gradient via gradient-driven pumps.

Na+-Ca2+ Exchanger

Antiport protein using Na+ gradient to pump Ca2+ out of the cell.

Vesicular Transport

Bulk transport involving energy input to move large substances by vesicles.

Phagocytosis

Cellular uptake of large particles by engulfing and digesting.

Only a few cell types perform this.

Macropinocytosis

Uptake of extracellular fluids by most cells through cellular drinking.

Clathrin-Mediated Endocytosis

Process where receptors on PM bring substances into the cell in bulk quantities.

LDL Receptors

Receptors binding cholesterol from blood for internalization.

Two structural features critical to function of Phospholipid bilayer

1. The amphipathic nature of phospholipids establishes the membrane as a barrier between aqueous environments.

2. Bilayers of phospholipids exist as viscous fluids, not solids.

Before you can study a protein what must happen?

Must isolate it from the other cell contents/proteins.

* Solubilize the membrane (destroy bilayer; disrupt h-phobic interactions)

Detergents

Intercalate into membranes and solubilize lipids.

Single hydrocarbon tail.

SDS

Ionic- bind and disrupt hydrophobic protein regions; ideal for denaturing proteins

Peripheral Proteins

Associate with the membrane indirectly

attach to integral proteins on only one side of the bilayer.

Movement of proteins through the bilayer is restricted by

Plasma membrane domains

Tight juntions between epithelial cells lead to _ and _ domains

Apical

Basolateral

What specialized lipid domains restrict protein movement?

Lipid rafts

What is enriched in GPI anchors and transmembrane proteins?

Cell signaling, movement, endocytosis.

Caveolin

interacts with cholesterol and cytoplasmic protein cabin

Where are caveolae and Cavolin implicated in?

Endocytosis

Cell signaling

Lipid transport

Mechanical stress

Carrier proteins

Selectively bind to transport specific molecules

Binding- Conformational change in protein- transport.

Example includes glucose transporter

Facilitated diffusion

Movement of specific molecules across cell membranes through protein channels

Channel proteins

Form pores through the membrane that allows the passage of specific molecules.

(regulated by size, not permanently open- extracellular singal opens them)

Diffusion force

Favors K+ traveling down its concentration gradient

When opposing forces are equal, K+ is at

Electrochemical equilibrium

facilitated diffusion always permits molecule flow _ a concentration gradient

Down

symport

A membrane transport process that carries two substances in the same direction across the membrane.

Antiport

A membrane transport process that carries one substance in one direction and another in the opposite direction.

Na+- Ca2+ exchanger

Antiport, uses Na+ gradient to pump Ca2+ out of the cell

Na+-H+ Exchanger

Antiport, uses Na+ to pump H+ out of the cell

Vesicular transport

Bulk transport, involves energy input to transport large substances across the plasma membrane by a vesicle.

Process of phagocytosis

1. Forms large extension called pseudopodium

2. Surround particle, enclosing it in a phagosome

3. Internalized, contents digested after fusing with a lysosome.

Process of macropinocytosis

1. forms large extension called lamellipodium

2. Surrounds particle, enclosing it in an endosome

3. Internalized, contents digested after fusing with lysosome.

Cells are not bags of enzymes, but are organized into

Three dimensions

Organization is carried out by the

cytoskeleton

Eukaryotic cells must be able to:

1. Adopt a variety of shapes

2. Organize interior components

3. Interact mechanically with the environment

4. Carry out coordinated movements

What is the cytoskeleton

An intricate network of protein filaments that extends throughout the cytoplasm.

The cytoplasm- what does it do?

Acts as the bones and muscles of the cell

The cytoplasm is made of protein filaments (3 types)

1. Intermediate- fibrous proteins

2. Microtubules- Globular tubulin

3. Actin filaments- globular actin

Actin Filaments

The most abundant, smallest component of the cytoskeleton.

Function of Actin Filaments

cell movement, maintain cell shape, internal support, cell division

Actin proteins are

monomers in two twisted filaments (microfilaments)

Association with the PM- actin filaments and actin-binding proteins form the

Cell cortex beneath the PM.

3D network determines cell shape and is invovled in cell activities.

Some cross-linked actin filaments act as

stress fibers.

Anchor cell and exert tension against substratum = cell movement, growth

What is the best characteristic of a cell surface extension that contains actin filaments that permit extension and retraction?

Microvilli

_ and _ are exploratory structures

Filipodia and Lamellipodia

myosin

superfamily of molecular motor proteins

Actin-myosin in Non-muscle

small-scale contractile assemblies in other cells.

Actin filaments are interdigitated by bipolar myosin II filaments.

Two examples of Actin-mmyosin in non-muscle cells:

Stress fibers

Adhesion belts

Adhesion belts

Contraction changes shape of epithelial sheets into tubes.

Regulation of myosin II is controlled by

Phosphorylation (indirectly controlled by Ca2+)

Unconventional myosins

generate force and contribute to motility in non-muscle cells

Myosin I

single head binds to actin; tail binds to substrate

Link actin to PM in microvilli

Bind to vesicle or organelle -> transport along actin filament

Myosin V

Two-headed dimer transports cargo along actin filaments.

Crucial in neurons for macromolecule and organelle transport.

**all myosins travel towards plus end of actin except myosin VI**

Microtubles

Hollow tubes of tubulin proteins extend from centrosome to the periphery.

Creates track for trafficking vesicles, organelles, etc.

Microtubles form

cilia and flagella

Dimers of a- and beta tubulin proteins

noncovalent interactions

structurally polar.

Plus end=

*Beta tubulin*

Minus end=

a- tubulin

Polarity is crucial to growth and function of

microtubules

In animal cells, most microtubules extend outward from

centrosome

act as microtubule-organizing center.

Simpler extensions of microtubules seen during mitosis to form

mitotic spindle

Assembly and disassembly into mitotic spindle highly altered in what type of cells?

Cancer cells

Dynamic instability targeted by chemotherapeutic drugs.

y-tubulin

forms a ring with eight other proteins to serve as nucleation sites.

In differentiated cells, dynamic instability is often suppressed by _ __ _ that stabilized tubulin proteins.

Microtubule-associated proteins

Neurons

microtubules don't extend from centrosomes.

Stabilized in cytoplasm by MAP2 and Tau

Some microtubule-associated proteins are _ _ that help transport vesicles, organelles

motor proteins

Kinesins

Move towards plus end of microtubule

Dyneins

move towards minus end

Both kinesins and Dyneins use

ATP hydrolysis

Kinesins are a family of

45 motor proteins

Kenesin I

have N-terminal motor domains- move along plus end.

Some C-terminal motor domains - move towards the minus end.

Some have motor domains in the center- Depolymerize microtubules

Cytoplasmic dynes

Contains globular ATP-binding motor domains - minus end.

axonemal dyne powers beating of cilia and flagella

Cilia

Are hairlike structures that use whiplike movements to propel fluid over their surface or move singles cells.

Flagella

are longer than cilia and are designed to propel entire cells. Use regular waves along their length

Intermediate filaments

Distribute force to prevent mechanical shearing of cell

Four classes of Intermediate filaments

1. Keratin filaments (type I and II; epithelium)

2. Vimentin and vimentin-related filaments (type III; connective tissue, muscle, glia)

3. Neurofilaments (type IV; neurons)

4. Nuclear Lamins (type V)

are the most diverse class of intermediate filaments

Keratins

Span cell, distributing mechanical force to prevent tearing.

Importance seen in genetic disease

Epidermolysis bullosa simplex

Nuclear lamina

is a meshwork of lamin filaments that form a 2D structure in inner nuclear membrane. Disassembles and reforms with every cell division

extracellular matrix (ECM)

Most animal cells are embedded in ECM that binds cells and tissues together.

Components of the ECM include

1. Fibrous proteins (collagen)

2. Matrix polysaccharides

3. Adhesion Proteins

Fibrous Proteins

The major structural protein in ECM is Collagen. (provides tensile strength)

More than 40 different proteins in the collagen family.

Fibrous Protein- Collagen structure

3 alpha-helical polypeptide chains wound tightly into rope-like triple helix

Each collagen peptide consists of

Gly-X-Y repeats.

Gly is in every 3rd position

X is often proline

Y is often hydroxyproline

Gly in a collagen polypeptide is found in

every third position

X in collagen is often

proline

Y in collagen is often

hydroxyproline

Connective tissue cells make and secrete a precursor protein called

procollagen

Extracellular procollagen proteinases

cleave extensions after exocytosis