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Copyright 2010, John Wiley & Sons, Inc.

Chapter 3

Cells




Cell Structure

� Plasma membrane

� Cytoplasm: cytosol + organelles

� Nucleus




Generalized View of Cell Structure




Cell Membrane

� Phospholipid bilayer

� Cholesterol

� Proteins (integral and peripheral)� Attached carbohydrates (glycolipids and

gycoproteins)




Plasma Membrane: Chemistry and

Structure




Membrane Function

� Barrier between inside and outside of cell

� Controls entry of materials: transport

� Receives chemical and mechanical signals

� Transmits signals between intra- and extra-

cellular spaces

� Note variety of proteins in Figure 3-2.




Terminology: Body Fluid Pools

� Intracellular (ICF)

± Within cells: 2/3 of total

� Extracellular (ECF):

± Between cells = Interstitial

± In blood vessels = Plasma

± In lymphatic vessels = Lymphatic




Terminology: Solutions

� Solvent: the liquid doing the dissolving ± Usually water

� Solute: the dissolved material (particles orgas)

� Concentration ± Amount of solute in a given amount of solvent

� Concentration gradient ±

Difference in concentration between 2 areas of solution




Principle of Diffusion




Passive Transport: Simple Diffusion

� Requirements for simple diffusion ± Concentration gradient of solute present

± Solute can diffuse across a membrane if membrane is present

� Pathways of simple diffusion:

± Pass across lipid bilayer if lipid-soluble (O2, CO2,N2, fatty acids, steroids, fat-soluble vitamins), or if polar molecules (H2O, urea)

± Pass through ion channels (which may be gated:gates open and close) if ions such as K+, Ca2+, Cl




Simple Diffusion




Facilitated Diffusion� Requires a carrier in membrane but not ATP

� Solute goes down concentration gradient

� Maximum transport speed depends on

number of carriers ± insulin increases number of carriers for glucose in

plasma membrane




Facilitated Diffusion




Osmosis�

Diffusion of water across selectivelypermeable membrane:

± Permeable to solvent

± Impermeable to solute

� Types of solutions surrounding human RBCs

± Isotonic: solution outside RBC has same

concentration of solute as RBC: 0.9% NaCl

± Hypotonic: solution outside of RBC has lowerconcentration: 0% NaCl hemolysis

± Hypertonic: solution outside of RBC has higher

concentration: 4% NaCl crenation




Osmosis




Active Transport� Requires a carrier (called a pump)

� Requires energy (ATP)

� Can transport up a concentration gradient

� Critical for moving important ions

� Major active transport in most cells is sodium-

potassium (Na+/K+) pump



Copyright 2010, John Wiley & Sons, Inc.Copyright 2009 John Wiley & Sons, Inc. 19

Active TransportSolutes are transported across plasma membranes with the use of energy,from an area of lower concentration to an area of higher concentration

Example: Sodium-potassium pump

1

3 Na+

K+

gradient

Cytosol

1

3 Na+ expelled

3 Na+

ADPP

P

2 K+

imported

K+

gradient

Na+

gradientNa+/K+ ATPase

Extracellular fluid

Cytosol

2K+

ATP2 3 4




Transport in Vesicles

� Requires energy (ATP)

� Involves small membrane sac

� Endocytosis: importing materials into cell

± Phagocytosis: ingestion of particles such as

bacteria into white blood cells (WBCs)

± Pinocytosis: ingestion of fluid

� Exocytosis: exporting materials




� Transport Across the Plasma Membrane

Transport Across the Plasma

Membrane

Interactions Animation

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Cell Organelles: Table 3.2

� Cytoskeleton

� Flagella, cilia & centrioles

� Endoplasmic reticulum

� Golgi apparatus

� Mitochondrion

� Nucleus, nucleolus, nuclear envelope

� Vesicles, e.g. lysosome




Cytoplasm

� Cell contents

� Includes organelles and cytosol

� Excludes nucleus




Cytoskeleton

� Maintains shape of

cell

� Positions organelles

� Changes cell shape

� Includes:

microfilments,

intermediate

filaments,

microtubules




Centrosome

� Structure:

± Two centrioles arranged perpendicular to each

other

� Composed of microtubules: 9 clusters of 3 (triplets)

± Pericentriolar material

� Composed of tubulin that grows the mitotic spindle

�

Function: moves chromosomes to ends of cellduring cell division




Centrosome




Cilia and Flagella

� Specialized for motion

� Flagellum: single tail like structure on sperm

± Propels sperm forward in reproductive tract

� Cilia: in groups

± Found in respiratory system: move mucus




Ribosomes

� Made within the nucleus (in nucleolus)

� Sites of protein synthesis (on E.R. or freely

within cytoplasm)

� Consist of ribosomal RNA (rRNA) + proteins

� Contain large and small subunits

� Can be attached to endoplasmic reticulum or

free in cytosol




Endoplasmic Reticulum (E.R.)�

Structure: network of folded membranes� Functions: synthesis, intracellular transport

� Types of E.R.

±Rough E.R.: studded with ribosomes (sites of protein synthesis)

± Smooth E.R. lacks ribosomes. Functions:

� lipid synthesis

� release of glucose in liver cells into bloodstream

� drug detoxification (especially in liver cells)

� storage and release of Ca2+ in muscle cells (where

smooth E.R. is known as sarcoplasmic reticulum or SR)




Endoplasmic Reticulum (E.R.)




� Structure:

± Flattened membranes (cisterns) with bulging

edges (like stacks of pita bread)

� Functions:

± Modify proteins glycoproteins and

lipoproteins that:

�

Become parts of plasma membranes� Are stored in lysosomes, or

� Are exported by exocytosis

Golgi Complex




Golgi Complex




Small Bodies� Lysosomes: contain digestive enzymes

± Help in final processes of digestion within cells

± Carry out autophagy (destruction of worn out parts of

cell) and death of old cells (autolysis)

± Tay-Sachs: hereditary disorder; one missing lysosomal

enzyme leads to nerve destruction

� Peroxisomes: detoxify; abundant in liver

� Proteasomes: digest unneeded or faulty proteins

±Faulty proteins accumulate in brain cells in persons withParkinson or Alzheimer disease.




Mitochondria

� Structure:

± Sausage-shaped with many folded membranes

(cristae) and liquid matrix containing enzymes

±

Have some DNA, ribosomes (can make proteins)� Function:

± Nutrient energy is released and trapped in ATP; so

known as power houses of cell

± Chemical reactions require oxygen

� Abundant in muscle, liver, and kidney cells

± These cells require much ATP




Mitochondria

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