Cell Membrane Functions and Structure - General Biology | BIOL 1001, Study notes of Biology

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Chapter 5 - Part II

Cell Membrane Structure

& Function

Biol 1001 Spring 2012

Energy Required Transport



Require energy (ATP) to transport

substances across membrane



Establishes concentration gradients

necessary for movement of substances



Types

 (^) Active transport  Endocytosis  Exocytosis

Active Transport

 Membrane proteins use energy from ATP  Movement of molecules & ions across membrane against concentration gradient  Movement from low concentration to high concentration  Used to restore concentration gradient after ions move into or out of cell

Where does energy come from?

 Energy-carrying molecule= ATP  ATP donates energy to transport proteins  (^) Energy comes from breaking bond of last phosphate group ( ATP  ADP ) http://www.zymesllc.com/knowledge-center/coenzyme-q10/what-does-coq10-do/coq10-is-required-to-produce-energy-atp/

Active Transport Proteins

 Span width of membrane  Specialized carrier proteins  Possess 2 active binding sites  1 st^ site – binds a particular molecule or ion  (^) Located on protein inside or outside of membrane  2 nd^ site – binds energy carrier molecule  (^) Located on protein inside membrane only  Often called “Pumps”  (^) Pump substances uphill against gradient  Low concentration to high concentration

ATP binding site recognition site ATP P ADP Ca2+ (extracellular fluid) (cytoplasm) ATP Transport protein binds ATP & Ca2+ Energy from ATP changes protein shape & moves ion across membrane Protein releases ion, ADP & P then closes 1 2 3

Active Transport of Ca

2+

Out of Cell

Ca 2+ move against the concentration gradient! Fig 5-

Endocytosis

 Engulfment of materials by the plasma membrane & transported into cell by vesicles  Movement of molecules too large to pass through membrane  Types (based on material to be transported)  Pinocytosis  Receptor-mediated endocytosis  Phagocytosis

Pinocytosis (“cell-drinking”)

 Moves liquids into cell  Process:  (^) Small dimple forms in cell membrane  (^) Extracellular liquid becomes surrounded by membrane  (^) Vesicle containing liquid buds off into cytoplasm (extracellular fluid) (cytoplasm) 1 2 3 Fig 5-

Receptor-Mediated Endocytosis



Moves specific molecules & complexes of

molecules into cell

 (^) Molecule must be able to react with receptor  (^) Ex: Packets of proteins & cholesterol 

Uses specialized receptor proteins

 Located in coated pits on plasma membrane  (^) Molecule binds with protein  (^) Pit deepens & membrane pinches off as coated vesicle  (^) Molecules carried into cytoplasm of cell

(cytoplasm) molecule (^) (extracellular fluid) receptor Receptor proteins in Receptors & pit deepens. Coated pit region forms & released into cytoplasm. Fig 5-

Phagocytosis (“cell-eating”)

 Moves large particles into cell  (^) Including whole microorganisms  Portions of membrane extend out & surround particle to form vesicle (= food vacuole)  (^) Examples:  (^) Amoebas  (^) Extend membrane out as pseudopodia (“false feet”)  (^) Pseudopodia fuse around prey to form food vacuole  (^) White blood cells  (^) Engulf & destroy foreign particles (e.g. bacteria)

food particle pseudopods (extracellular fluid) (cytoplasm) around particle around particle Food vacuole in cytoplasm Fig 5-

Exocytosis

 Reverse of endocytosis  Moves materials out of cell  Undigested particles & waste  (^) Products made in cell (e.g. hormones)  Process:  Vesicle carries contents to plasma membrane  Vesicle’s membrane fuses with plasma membrane  (^) Contents released out into the extracellular fluid

• Fig 5-

Energy Required Transport Summary



Movement of substances in or out of cell



Energy required= ATP



3 Types

 (^) Active Transport  (^) Movement of molecules & ions against concentration gradient via embedded proteins  (^) Endocytosis  Movement of large materials into cell via vesicles  (^) Phinocytosis – movement of fluids into cell  (^) Receptor-mediated endocytosis– movement of  (^) Phagocytosis – movement of large particles  (^) Exocytosis  Movement of large materials out of cell via vesicles

Is this pinocytosis, endocytosis, phagocytosis or exocytosis? Phagocytosis

Is this pinocytosis, endocytosis, phagocytosis or exocytosis? Endocytosis

Is this pinocytosis, endocytosis, phagocytosis or exocytosis? Pinocytosis Extracellular fluid cytoplasm

Is this pinocytosis, endocytosis, phagocytosis or exocytosis? Exocytosis

Cell Connections

 Requires specialized structures on plasma membrane  Hold cells together  (^) Avenue for communication  4 Types  (^) Desmosomes  (^) Tight junctions  (^) Gap junctions  (^) Plasmodesmata Found only in animal cells Found only in plant cells

Desmosomes

 Complex of proteins linked to intermediate filaments of cytoskeleton  Attach cells together  Found in tissues that must be resistant to tearing  Ex: skin, intestine, bladder  Very strong & flexible  Animal cells only http://www.cytochemistry.net/cell-biology/intermediate_filaments.htm

desmosome small intestine plasma membranes protein filaments hold cells together cells lining small intestine protein filaments In cytoplasm

Desmosome

Tight Junctions



Involve attachment proteins embedded in

plasma membranes

 (^) Proteins adhere together between cells  (^) Proteins bond together tightly 

Create a leakproof barrier between cells

 (^) Found in tissues that contain a lot of water  (^) Ex: skin, blood vessels, bladder 

Animal cells only

http://www.udel.edu/biology/Wags/histopage/empage/ebv/ebv.htm

urinary bladder plasma membranes cells lining bladder Proteins seal cells together

Tight Junctions

Gap Junctions



Involved in communication between cells



Channels of proteins that connect adjacent cells



Allow molecules to pass between cells

 (^) Hormones, nutrients, ions  (^) Electrical signals 

Very important in embryonic development



Animal cells only