Chapter 3: Cell Biology

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I. Fxns of a cell • Cell

– the basic unit of all living things (the smallest part of a living organism in our case humans)

• Shared Characteristics – Plasma Membrane

• Outer boundary of the cell though which the cell interacts with its external environment

– Nucleus • Directs activities of the cell

– Cytoplasm • Most cell activities occur here

– Organelles • Perform specific fxns in cell

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I. Fxns of a cell 4 major fxns of cells A. Cell metabolism & e+ use:

– Metabolic rxns in the cell e+ is released to accomplish cell activities & maintain Body Temp.

B. Synthesis of Molecules – Can prod proteins, nucleic acids,

lipids – Cell’s fxn & characteristics are

determined by the molecules they prod

C. Communication – Cells prod & respond to chemical &

e+ signals wh/ allows them to communicate w/each other

– * Neuron to a muscle = contraction or relaxation

D. Reproduction & inheritance – Cell holds the genome. It

determines structure & fxnl characteristics of that cell.

– Cells can prod new cells – Gametes transmit genetic info.

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III. Plasma Membrane

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III. Plasma Membrane • Outer most component of the

cell • Fxns as a boundary to

separate inside from outside of the cell (intra vs extra cellular)

• Encloses and supports the cell’s contents

• Attaches the cell to the extracellular environment or to other cells

• Cell’s ability to recognize & communicate with each other occurs via the plasma membrane

• Determines what moves into ot out of the cell (therefore the contents inside the cell can be different from what is outside).

• Membrane potential: electrical charge difference across the PM resulting from the cell’s regulation of movement into and out of the cell

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Make-up: • 45-50% Lipids • 45-50% Proteins • 4-8% Carbohydrates

III. P

lasm

a M

embr

ane

• Terminology – Intracellular: (Intra- Inside) inside the cell – Extracellular: (Extra- Outside) outside of the cell – Intercellular: (Inter- Between) from 1 cell to another – Glycoproteins: carb’s + proteins – Glycolipids: Carb’s + Lipids – Membrane Potential: result of uneven distribution of ions on

the inside verses the outside of the cell • Glycocalyx:

– Collection of glycoproteins, glycolipids, and carb’s that lies on the outer surface of the plasma membrane

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IV. Membrane Lipids

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IV. M

embr

ane

Lipi

ds

• Phospholipids (PL’s): – Predominant lipid in membrane – Bipolar:

• Hydrophilic “head” is water loving and polar and faces both surfaces (inner & outer)

• Hydrophobic “tail” is water hating and non-polar and crowd together between the heads

• Cholesterol – Makes up 1/3 of the membrane

and lie btwn PL’s – Helps to limit PL’s mvmt

providing stability for the PM – It is also bipolar and the “tail” is

embedded in head while the ring is embedded in the tails

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IV. Membrane Lipids

• *Fluid Mosaic Model* – The lipid bilayer is mobile with things floating

w/in it – Consequences of this: a) Important for molecule distribution in the

membrane b) Slight damage can be repaired because the

PL’s will move to cover it c) It enables two different membranes to fuse

with each other

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V. Membrane Proteins A. Marker Molecules B. Attachment Proteins C. Transport Proteins D. Receptor Proteins E. Enzymes

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V. Membrane Proteins (MP) • Many fxns of the plasma membrane are determined by

the combination of membrane proteins present. • The ability of these proteins to fxn properly is

determined by their 3-D shape • There are 2 major types:

1. Integral/Intrinsic • (Transmembrane) contain hydrophobic and hydrophilic

regions to match the phospholipids characteristics & location 2. Peripheral/Extrinsic

• Surface proteins on inner or outer surface. • Can be bound to an integral protein or the phospholipids head

• There are 5 major classes of MP’s

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5 major classes of Membrane proteins

I. Marker molecules

II. Attachment Proteins

III. Transport Proteins

IV. Receptor Proteins

V. Enzymes

Channel

Proteins

Carrier

Proteins

ATP powered

pump

Non-gated C

hannel

Gated

Channel

Voltage-gated channel

Ligand-gated channel

Antiporter

Symporter

Uniporter

A B C

a b a b c

i ii

Receptors linked to channel proteins

Receptors linked to

G-proteins

A B

Membrane Proteins: I. Marker Molecules

• Glycoproteins or glycolipids that allow for cells to identify other cells or other molecules

• Important because cells aren’t isolated and must function as a whole for normal body function.

• May be integral or peripheral proteins

• Ex/ immune cells

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Membrane Proteins: II. Attachment Proteins

• Integral proteins that may attach to intracellular molecules.

• Integrins can also function in cellular communication.

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Membrane Proteins: III. Transport Proteins

All exhibit 3 characteristics 1. Specificity

– Each binds to & transports only 1 types of molecule/ion

2. Competition – Closely related substances

may bind to the same binding site & the one w/ greater [ ] or higher affinity is more readily moved across the PM

3. Saturation – Movement is limited by the #

of transport proteins rate will eventually plateau because the # of proteins are going at their maximum rate AP1 Chapter 3

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Membrane Proteins: III. Transport Proteins

A. Channel Proteins • Form passageways through the

plasma membranes that have both hydrophobic and hydrophilic regions.

B. Carrier Proteins • Move larger ions or molecules

across the membrane, when bound it changes shape to allow it to move from one side of the membrane to the other then return to its original shape to work again.

C. ATP-powered pumps • Moves ions or molecules across

the membrane using ATP.

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Membrane Proteins: III. Transport Proteins

A. Channel Proteins a. Non-gated Channels

• Always open responsible for the permeability of the plasma membrane when the cell membrane at rest.

b. Gated Channels • Can be opened or closed i. Ligand Gated

– Small molecules must bind in order to open or close the channel

ii. Voltage Gated – Change in voltage across the

plasma membrane causes the gate to open

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Membrane Proteins: III. Transport Proteins

B. Carrier Proteins a. Uniporter

• Movement of 1 ion or molecule across the plasma membrane.

b. Symporter • Movement of 2 ions or molecules in

the same direction (into the cell or out of the cell).

c. Antiporter • Movement of 2 ions or molecules in

opposite directions (one in and one out or vise versa).

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Membrane Proteins: III. Transport Proteins

C. Sodium-Potassium Pump • These have 2 binding sites.

One is for the molecule to be moved the other is for ATP

• Breakdown of ATP releases e+ ∆ing shape of the “pump” protein which moves the molecule across the membrane

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Membrane Proteins: IV. Receptor Proteins

• Proteins or glycoproteins in the plasma membrane that have an exposed receptor site on the outer cell surface which can attach to specific chemical signals.

• Many are part of an intercellular communication system that coordinates cell activities.

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Membrane Proteins: IV. Receptor Proteins

A. Receptor linked to channel proteins

– These help form ligand-gated channels & when bound it changes the channels shape to move ions

B. Receptors linked to G-protein complexes

– Uses a second messenger system, binding of the receptor externally causes to the cell internally

• 3 ways α can stimulate a cellular response

1. Intracellular chemical signals

2. Opening channels in the plasma membrane

3. Activation of enzymes associated with the plasma membrane

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Membrane Proteins: V. Enzymes

• These may work on the inner or outer surface of the plasma membrane.

• Some are always active but others are activated by things like GPCR’s

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VI. Movement through the plasma membrane

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V. Mvmt thru the PM • Inside of the cell:

– Enzymes other proteins, glycogen, high potassium concentration • Outside of the cell:

– High concentration of sodium, calcium, & chloride • The cell has to be able to bring in nutrients inside and get waste

products out without changing the cell’s volume, because too much can cause the cell the rupture (causing cell death) or to shrivel (also causing cell death).

• Movement 1. Molecules that are lipid soluble or very small water soluble

molecules will freely go across the plasma membrane. 2. Large lipid soluble molecules and water soluble molecules can’t

pass through the plasma membrane and may need to use transport proteins.

3. Larger water soluble molecules or whole cells may be moved by vesicles.

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Membrane transport mechanisms

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A. Passive Transport Mechanisms • No energy required to

move molecules from one side of the membrane to another

B. Active Transport Mechanisms • Energy required to move

molecules from one side of the membrane to another

Membrane transport mechanisms

Passive Transport Mechanisms A. Diffusion B. Osmosis C. Facilitated Diffusion

Active Transport Mechanisms A. Active Transport B. Secondary Active

Transport C. Vesicular Transport

a. Endocytosis b. Exocytosis

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Passive Transport Mechanisms A. Diffusion:

– Movement of solutes from an area of high concentration to an area of low concentration

– Concentration gradient: concentration difference between 2 points divided by the distance between the 2 points,

– Rate of Diffusion 1. Magnitude of the concentration gradient 2. Temperature of the solution 3. Size of the diffusion molecules 4. Viscosity of the solvent

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Passive Transport Mechanisms B. Osmosis

– Diffusion of water across a selectively permeable membrane

– Will allow water but not all solutes with in the water

– Important because it can influence a cell’s function when water moves.

– Osmotic Pressure: • Force required to prevent

water movement across a selectively permeable barrier via osmosis

1) Isosmotic 2) Hyperosmotic 3) Hyposmotic

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Concentration of solutions

Passive Transport Mechanisms B. Osmosis

• Tonicity: refers to the cell’s shape remaining constant b/c it maintains it’s internal pressure

1. Isotonic sol’n: no net mvmt of H2O, cell doesn’t ∆ shape 2. Hypertonic sol’n: mvmt out of cell b/c sol’n has a greater [ ] of

solute thus a higher osmotic pressure (crenation) 3. Hypotonic sol’n: mvmt into cell b/c sol’n has a lower [ ] of

solute thus a lower osmotic pressure (Lysis)

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Passive Transport Mechanisms C. Facilitated Diffusion

– Amino acids & glucose go into the cell and area going out of the cell can’t occur via direct diffusion because they are too big. Thus there is

– Mediated transport (facilitated diffusion): • Process by which transport proteins assist the movement

of water soluble molecules or electrically charged molecules or ions across the plasma membrane.

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Active Transport Mechanisms

A. Active Transport • also a type of mediated

transport. Requires energy provided by ATP movement dependent on the number of pumps and availability of ATP.

• Important because it can move things against their concentration gradients.

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Active Transport Mechanisms

B. Secondary Active Transport

• Passive transport of 1 molecule with its concentration gradient helps to energize the carrier so that it can transport the second molecule against its concentration gradient.

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Active Transport Mechanisms C. Vesicular Transport • Movement of larger

volumes of substances across the plasma membrane through the formation and release of vesicles requiring ATP.

• BUT…the specificity seen in others doesn’t occur in this process. a. Endocytosis

i. Pinocytosis ii. Phagocytosis iii. Receptor mediated

endocytosis b. Exocytosis

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Active transport mechanisms a) Endocytosis: uptake

of material into the cell.

• 3 types: i. Pinocytosis

• Molecules dissolved in liquid

ii. Phagocytosis • Cells and solid

particles

iii. Receptor mediated endocytosis

• Specificity for substances

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Pin

ocyt

osis

P

hago

cyto

sis

Rec

epto

r-m

edia

ted

Active Transport Mechanisms b. Exocytosis

– Materials manufactured by the cell are packaged in secretory vesicles that fuse w/the PM & release their contents outside of the cell

– ATP req’d – Proteins & other water

soluble substances

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VII. Cytoplasm

The material outside the nucleus and inside of the plasma membrane

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VII. Cytoplasm

1. Fluid Portion • Anatomy:

– H2O w/dissolved ions & molecules; colloid w/many suspended molecules espicially proteins

• Physiology: – Contains enz’s

that catalyze decomposition & synthesis rxns, ATP is also prod’d in glycolysis rxns

3. Cytoplasmic Inclusions

• Anatomy: – Collections of

molecules manufactured or ingested by cell and may be membrane bound

• Physiology – Fxn is dependent

on the molecules – Ex: energy storage lipids&glycogen

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(1/2 cytosol/1/2 organelles) 3 parts to cytoplasm

2. Cytoskeleton • Supports cell &

holds nucleus & organelles in place

• Responsible for mvmt in & of the cell

• Made up of 3 groups of proteins:

a) Microtubules b) Microfilaments c) Intermediate

filaments

VII. Cytoplasm • 2. Cytoskeleton

• Made up of 3 groups of proteins: a) Microtubules

• Provide support & structure to cytoplasm

• Involved in cell division & transport of intracellular materials

• Form essential components of organelles (centrioles, spindle fibers, cilia, & flagellum)

b) Actin Filaments • Provide structure to cytoplasm

& mechanical support for microvilli

• Responsible for cell mvmts c) Intermediate filaments

• Protein Fibers • Provide strength to cells

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VIII. The Nucleus & Cytoplasmic Organelles

A. Nucleus B. Cytoplasmic

Organelles: A. Ribosomes B. Endoplasmic Reticulum C. Golgi Apparatus D. Secretory Vesicles E. Lysosome

G. Peroxisomes H. Proteosomes I. Mitochondria J. Centrioles & Spindle Fibers K. Cilia & Flagella L. Microvilli

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• Organelles: structures w/in cells that are specialized for a particular fxn. • Number & types within each cell are related to the specific structure &

function of the cell • Largest organelle Nucleus

• (all others are considered cytoplasmic organelles)

VIII. The Nucleus & Cytoplasmic Organelles A. Nucleus

• Large membrane bound structure usually centrally located – Shape & # of lobules vary dependent on cell

type (may be multiple or spit out of cell) – 3 Major structures of the nucleus:

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IX. The N

ucleus & C

ytoplasmic O

rganelles A

. Nucleus

• 3 Major structures of the nucleus

1. Nuclear Envelope – Double membrane enclosing

the nucleus that separates the nucleus from the cytoplasm, also uses nuclear pores to regulate mvmt in/out of the nucleus

2. Chromatin – Thin strands of DNA wound

around histones (proteins) that regulate protein synthesis thus also regulating the chemical rxns in the cell

3. Nucleolus – 1 or more dense bodies

consisting of ribosomal RNA , 10 stretches of DNA called nuclear organizer regions that contain the rRNA templates, & proteins that serve as the assembly site for ribosomal subunits 41

IX. The Nucleus & Cytoplasmic Organelles B. Ribosomes

• rRNA & proteins make-up both the large & small subunits of ribosomes

• Site of protein synthesis • 2 categories: 1. Free: mainly prod proteins that

will be used inside the cell 2. Bound: mainly prod proteins

that will be excreted from the cell

C. Endoplasmic Reticulum • Series of membranes

continuous w/ the nuclear envelope distributed throughout the cell

• 2 major types: – Rough ER: ribosomes attached

fxns in protein synthesis & transport of those to the golgi

– Smooth: no ribosomes fxns in manufacture of lipids & carb’s; detoxifies harmful chemicals; can store Ca2+

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IX. The Nucleus & Cytoplasmic Organelles

E. Golgi Apparatus (GA)

• membrane bound sack from the ER that goes to the GA for processing

F. Secretory Vesicle • Membrane bound sac that

pinches off of the GA that carries the finalized proteins & lipids to the cell surface for secretion

• These can accumulate in the cell until proper signal is received to initiate its release

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D. Transport Vesicle

• Flattened membrane sacs stacked on each other modifies, packages, & distributes proteins & lipids prod’d by RER & SER for secretion or internal use

• Can concentrate, or chemically modifies by adding carbs or lipids making glycoproteins or glycolipids

IX. The Nucleus & Cytoplasmic Organelles F. Lysosome • Membrane bound sac

pinched off of GA carries digestive enz’s that can break down NA, polysaccharides, lipids, thus old cell parts & phagocytized bacteria

G. Peroxisome • Membrane bound vesicle

1 site of fatty acid & AA degradation byproduct is H2O2 using catalase brksdwn to H2O + O2

• High # in liver & kidney cells

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IX. The Nucleus & Cytoplasmic Organelles H. Proteasome • Tube-like protein in the

cytoplasm as proteins enter the cell they are enzymatically degraded in the cytoplasm

I. Mitochondria • Dynamic structure

enclosed by a double membrane. Inner projections are called cristae. Major site of ATP-synthesis when O2 is available.

• #/cell based on cell fxn

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IX. The Nucleus & Cytoplasmic Organelles J. Centrioles • Pair of cylindrical

organelles in centrosome made-up of microtubules

• Center for microtubule formation

• Determine polarity of the cell during division

• For basal bodies of cilia & flagellum

K. Cilia • Short hair-like Extensions of

the PM using microtubules to hold their shape

• Fxnally in humans it moves materials over cell surface

• Basal Body: located at base of cilia

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IX. The Nucleus & Cytoplasmic Organelles L. Flagellum • Long Hair-like extensions

of the PM using microtubules to hold their shape.

• Responsible for the mvmt of sperm

M. Microvilli • Short extension of the PM

containing microfilaments • Increase surface area of

the PM for absorption or secretion.

• May fxn as a modified sensory receptor (hair cells in ear)

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