ch. 5 membrane transport and cell signaling

what is the fluid mosaic

where the membrane is a flexible mosaic containing protein molecules in a fluid bilayer

selectively permeable

regulates the cell's moleculaar traffic

• lets certain things in and some things out.

3 things that contribute to the fluidity of the membrane?

1. movement of phospholipids

2. type of fatty acid

3. cholesterol within the animal cell membrane

movement of phospholipids (2 types)

can be:

• lateral movement (side by side)

• flip flop (up and down)

type of fatty acids

1. unsaturated hydrocarbon tails

   • lots of bends = lots of space = very fluid

2. saturated hydrocarbon tails

   • less space/bending = less fluid (thick/viscous)

function of cholesterol

1. temperature buffer - make sure cell doesn't freeze/melt

2. provides stability - makes sure cell has structual support

   • in relationship to the changes outside the cell

membran proteins (3 types)

1. Integral proteins

2. Peripheral proteins

3. Integrins

Integral proteins (2 types and definition)

• proteins that are in the membrane

  1. transmembrane proteins

  2. non-transmembrane proteins

transmembrane proteins

a protein that penetrates both layers

non-transmembrane proteins

proteins penetrated in only one layer

preipheral proteins

proteins not embedded into the membrane at all

• beside it instead.

integrins

• 2 proteins located between two cells and bind to both ECM

  • they are attached to microfilaments

Passive transports (3 types)

1. Diffusion

2. Osmosis

3. facilitated diffusion

Diffusion

• particles diffuse from high concentration to low concentration. (concentration gradient)

  • molecules have the tendency to spread out evenly into the available space

  • its is passive because it requires no energy

osmosis

• diffusion of water across a selectively permeable membrane

  • diffuses across a membrane from a region of lower solute concentration to a region of higher solute concentration

tonicity

ability of a solution to cause a cell to gain or lose water

Isotonic solution

• cell and outside solution have the same solute concentration

  • no water movement

Hypertonic solution

• solution outside the cell has a greater solute concentration than inside

  • the cell loses water (it moves out)

    • can cause the cell to shrivel

Hypotonic solution

• solution outside the cell has a lower solute concentration than inside

  • the cell gains water (moves in)

    • can cause the cell to burst

In a plant cell..

1. a swelled plant cell is..

2. a shriveled plance cell is..

1. Turgid

2. Plasmolyzed

Osmoregulation

the control of water balance

e.g. a protist has a contractile protein to expell excess water

facilitated diffusion

• passive transport aided by transport proteins

transport proteins

1. channel proteins

2. carrier proteins

active transport

• uses energy (ATP) to move solutes against their gradients (low to high)

  • performed by specific proteins embedded in the membrane

  • e.g sodium potassium pump

Bulk transport

• large molecules that cross the membrane in bulk by vesicles

  • polysaccharides and proteins

  • REQUIRES ENERGY

Exocytosis

• transports vesicles that migrate to the membrane and fuse with it to release the contents

  • secretory cells use this process to export hormornes.

Endocytosis

• cells take in macromolecules by forming vesicles with the plasma membrane

3 types of endocytosis

1. phagocytosis

2. pinocytosis

3. receptor-mediated endocytosis

Phagocytosis

• cellular eating (solids in)

pinocytosis

• cellular drinking (liquids in)

  • molecules get taken into a vesicle when liquid goes in

receptor-mediated endocytosis

• the binding of ligands to receptors that trigger a vesicle to form.

  • allows for the cell to obtain bulk quantities of specific substances even if they are not concentrated.

genetic condition linked to receptor-mediated endocytosis

• familial hypercholesterolemia

• presence of high levels of cholesterol

  • missing LDL receptors/defective LDL receptors

  • cholesterol(LDL) will not be able to link therefore left in the blood and cause blockages.

6 major functions of membrane proteins

1. transport

2. enyzmatic activity

3. signal transduction

4. cell-cell recognition

5. intercellular joining

6. attatchment to the cytoskeleton and ECM

carbs in cell-cell recognition

• located on the plasma membrane and are indicators.

  • can vary species to species, individuals, one cell to another.

cell-cell communication

• process where cells receive and send signals to coordinate activities for growth, development, and maintain normal function

local signaling

• cell junctions (gap junctions and plasmodesmata) connect cells directly to e/o's cytoplasm

• can also be messenger molecules (growth factor and neurotransmitter molecules)

long distance signaling

• where plants and animals use hormornes to signal

  • endocrine signaling

the three stages of cell signaling

1. reception

2. transduction]

3. response

reception

• the binding between a ligand and receptor is very specific

  • most receptors are proteins

    • change in shape initiates transduction

3 types of membrane receptors

1. G-protein

2. ligand gated ion channels

G protein-coupled receptor (GPCR)

• receptor that works with the help of a G protein

  • the protein acts as an on and off switch

    • if GDP is bound to the PROTEIN (not receptor) it is inactive

    • GTP makes it active

GPCR diseases

cholera, whooping cough, botulism.

ligan-gated ion channel

• receptor that acts as a gate

  • a ligand binds to the receptor which opens the gate to allow specific ions through the channel

    • Na+ or Ca2+

      • important for the nervous system

Transduction

• single transductions has multiple steps (are like dominoes)

  • multistep pathways can amplify a signal which makes a larger cellular response

    • a receptor activates a protein, then activates another and another, and so on till the protein produced activates the response.

    • each step changes the protein's shape.

phosphorylation

• protein kinases (enzymes) that traansfer phosphates from ATP to a protein

  • like adding

Dephosphorylation

• protein phosphatases (enzymes) that remove the phosphate from proteins

  • taking away/subtracting

phosphorylation and dephosphorylation act as

a molecular switch

• turns activities on and off.

  • phosphorylation cascade

    • adding/removing of phosphates makes the response stronger

Nuclear and Cytoplasmic responses

• response may occur in the cytoplasm or action in the nucleus

  • signaling pathways activates a transcription factor that turns on a gene