The Cell and Plasma Membrane

http://www.youtube.com/watch?v=cj8dDTHGJBYhttp://www.youtube.com/watch?v=cj8dDTHGJBY

Prokaryotes• Smallest Cells • Lack a nucleus – DNA is located in an area called

the nucleoid• Contain plasmids – small circular pieces of DNA

Eukaryotes• Consists of: Plasma membrane• Barrier that surrounds the

cytoplasm of the cell

Organelles • Internal structures that

carry out specialized functions• Bounded by a membrane

(exception ribosome, centriole)

Cytosol• Liquid portion of the cell

Examples of Cells

Amoeba Proteus

Plant Stem

Red Blood Cell

Nerve Cell

Bacteria

Plant and Animal Cell

Nucleus • Command centre of the cell

• Contains DNA blueprints for making proteins

• Surrounded by nuclear envoleope – Protects DNA from

chemical reactions • Nucelolus – Area of chromatin

(uncoiled DNA strands) that produces ribosomes

Ribosomes • Assembled inside

nucleus • Made up of RNA and

proteins • Two Types – Free floating – found in

cytoplasm – Attached to ER

• Ribosomes make proteins

Endoplasmic Reticulum • Continuous compartment

that folds repeatedly into flattened sacs and tubes Rough ER– Contains ribosomes

• Synthesis of proteins

– Once synthesized, proteins fold and take shape inside ER

Smooth ER– Contains no ribosomes – Synthesis of lipids – Transports vesicles to plamsa

membrane or Golgi body

Golgi Bodies• Folded membrane (looks

like stack of pancakes) • Completion of proteins and

lipids making them fully functional

• use inside or outside of cell

Mitochondria • Double bound

membrane organelle• Powerhouse of cell • Two compartments– Mitochondrial matrix– Intermembrane space

• Contain their own DNA and ribosomes– Synthesize ATP

Vesicles • Transportation/destruction • Peroxisome – break down

fatty acids, detoxify alcohol• Vacuoles– Dispose of waste, debris and

toxic materials– Keep turgor pressure inside

plant cell• Lysosomes – fuse with

vacuole to dispose of worn out cell components (use of enzymes)

Cytoskeleton• Made up of many protein

filaments– Gives shape to cell– Organizes organelles– Move cell structures

• Include – Microtubules

• form tracks that allow organelles to move

– Intermediate filaments• anchor organelles into regions of

cell• Support nuclear envelope and cell

membrane

– Actin filaments • Movement of membrane

Centrosomes • Assembles and co-

ordinates activity of spindle fibres when the cell divides

• Contains centrioles

Cilia, Flagella, Pseudopods• Organized array of microtubules• Flagella

– Whiplike structure – Propels cells (sperm)

• Cilia– Hair like structure – Sweeping action moves particles

(lining of airway)• Pseudopod (false feet)

– Lobe formations – Amoeba

• Prokaryotes – Contain pili – hollow appendages that

stick to other cells to swap information

Cell Wall (Plant Cells)

• Located around plasma membrane

• Consists of cellulose fibres

• Protects supports and gives shape to the cell

• Waxy cuticle – Limits water loss on

hot/dry days

Plastids (Plant Cells)• Chloroplasts– Double membrane bound

organelle– Stroma – semifluid interior,

contains enzymes and DNA– Specialize in photosynthesis – Contain chlorophyll

Plasma Membranehttp://www.johnkyrk.com/cellmembrane.html

• Transports raw materials into the cell • Transport finished product and wastes out of cell • Prevent entry of unwanted matter into cell • Prevent matter needed to perform cellular

functions inside cell

Plasma Membrane • Described by the Fluid Mosaic Model as:• Composed of a phospholipid bilayer• Semi-permeable – regulates substances in and out

of cell with the help of transport proteins

Phospholipids

• Hydrophilic Head– Phosphate group– Polar group

• Hydrophobic Tail– Fatty acids

• Align themselves in aqueous solution

Fluidity

• Cholesterol allows cells to function in a wide range of temperatures

• High temperature – Maintains rigidity in oily membrane

• Low temperature– Keeps membrane fluid/flexible – Prevents from freezing

Membrane Protein : Integral/Peripheral

• Integral Membrane Proteins (transmembrane)– Exposed to aqueous environment on both sides of the

membrane – Transport, enzymatic activity, triggering signals,

attachment/recognition• Peripheral Membrane Proteins – Located on surface of a membrane – No interaction with hydrophobic core – Eg. Cytoskeleton

Passive Membrane Transport

• No chemical energy required• Diffusion– Net movement of a substance from a region of high

concentration to a region of low concentration– Dynamic equilibrium between cells is met

• Molecule still randomly move through membrane but concentration remains same

• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/how_diffusion_works.html• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/diffusion_through_cell_membranes.html

Simple Diffusion (Passive Transport)• Substances move across a membrane

unassisted• Size and charge affect the rate of diffusion

across the membrane

Facilitated Diffusion

• Diffusion of larger molecules with the help of a transport protein (integral membrane protein)

• Stops when equilibrium is reached• Two types of Transport Proteins – Channel proteins– Carrier proteins

Facilitated Diffusion

• Channel Proteins– Form hydrophilic pathways in the membrane – Water and certain ions can pass– Voltage-gated channels • Open or closed by changes in voltage across the

membrane or by binding molecules• Eg. Muscle contractions

Facilitated Diffusion • Carrier Proteins – Form pathways

through the membrane

– Bind to a specific solute (glucose, amino acid)

– Carrier protein changes shape allowing solute to move from one side of the membrane to the other

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/how_facilitated_diffusion_works.html

Simple vs Facilitated

• Simple Diffusion – Rate of diffusion

increases as difference in concentration gradient increases

• Facilitated Diffusion – Maximum rate is

reached but limited by number of transport protein in membrane

Osmosis

• Passive diffusion of water across a membrane via aquaporins • Water always diffuses from an area of low solute

concentration (high water concentration) to an area of greater solute concentration (low water concentration)

• Three Solutions (Cell) – Hypotonic

• Solute concentration is high in cell (swells)

– Hypertonic• Solute concentration is low in cell (shrinks)

– Isotonic • Solute and water concentration is equal both in and outside cell

• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/animation_-_osmosis.html

Osmosis

Active Membrane Transport

• Substance carried across a membrane from an area of low concentration to an area of high concentration

• Use of pump• ATP used as energy source • Two Types – Primary Active Transport– Secondary Active Transport

Primary Active Transport

• Pumps that moves positively charged ions across membranes (H⁺. Ca²⁺, Na⁺, K⁺)– ATP is hydrolyzed– Phosphate group attaches to pump allowing ion to bind to protein

transporter– Protein transporter undergoes a folding change exposing ion to

opposite side of membrane– Ion is released to side of higher concentration– Phosphate group is released

• This creates an electrochemical gradient– Effect of voltage and difference in ion concentration– Stored potential energy

• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/primary_active_transport.html

Primary Active Transport

Secondary Active Tranport • http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/cotransport__symport_and_antiport_.html

• Uses concentration gradient of an ion as its energy source• This gradient was already established by primary pump. • Transport solute across membrane• Two ways

– Symport• Solute moves through channel in the same direction as ion

– Antiport• Solute moves in opposite direction as ion

Exocytosis and Endocytosis

• Vesicles are used to transport• ATP is required• Exocytosis– Transport of proteins and waste material from

cytosol to exterior of cell • Endocytosis– Transport proteins and large molecules into cytosol

of the cell.

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis%20and%20Exocytosis