Cells: The Living Unitsdrjerrycronin.weebly.com/uploads/5/9/7/4/5974564/...3.1 Cells: The Living...

PowerPoint® Lecture Slides

prepared by

Karen Dunbar Kareiva

Ivy Tech Community College© Annie Leibovitz/Contact Press Images

Chapter 3 Part A

Cells:

The Living

Units

© 2017 Pearson Education, Inc.

Why This Matters

• Understanding the structure of the body’s cells

explains why the permeability of the plasma

membrane can affect treatment



Video: Why This Matters

3.1 Cells: The Living Units

• Cell theory

– A cell is the structural and functional unit of life

– How well the entire organism functions depends

on individual and combined activities of all of its

cells

– Structure and function are complementary

• Biochemical functions of cells are dictated by shape of

cell and specific subcellular structures

– Continuity of life has cellular basis

• Cells can arise only from other preexisting cells



• Cell diversity

– Over 200 different types of human cells

– Types differ in size, shape, and subcellular

components; these differences lead to

differences in functions


Figure 3.1 Cell diversity.

Erythrocytes

Fibroblasts

Epithelial cells

Skeletal

muscle

cell

Smooth

muscle cells

Nerve cell

Macrophage

Fat cell

Sperm

Cell of reproduction

Cell that stores

nutrients

Cells that connect body parts, form linings,

or transport gases

Cells that move organs and body parts

Cell that gathers information and controls

body functions

Cell that fights

disease



• Generalized cell

– All cells have some common structures and

functions

– Human cells have three basic parts:

1. Plasma membrane: flexible outer boundary

2. Cytoplasm: intracellular fluid containing organelles

3. Nucleus: DNA containing control center


Figure 3.2 Structure of the generalized cell.

Chromatin

Smooth endoplasmicreticulum

Nucleolus

Mitochondrion

Lysosome

Centrioles

Centrosomematrix

Peroxisome

Secretion beingreleased from cellby exocytosis

Golgi apparatus

Ribosomes

Roughendoplasmicreticulum

Nuclear envelope

Nucleus

Plasmamembrane

Cytoplasm

Cytoskeletalelements

• Microtubule

• Intermediatefilaments


Extracellular Materials

• Substances found outside cells

• Classes of extracellular materials include:

– Extracellular fluids (body fluids), such as:

• Interstitial fluid: cells are submersed (bathed) in this

fluid

• Blood plasma: fluid of the blood

• Cerebrospinal fluid: fluid surrounding nervous system

organs

– Cellular secretions (e.g., saliva, mucus)

– Extracellular matrix: substance that acts as glue

to hold cells together


Part 1 – Plasma Membrane

• Acts as an active barrier separating

intracellular fluid (ICF) from extracellular

fluid (ECF)

• Plays dynamic role in cellular activity by

controlling what enters and what leaves cell

• Also known as the “cell membrane”


3.2 Structure of Plasma Membrane

• Consists of membrane lipids that form a

flexible lipid bilayer

• Specialized membrane proteins float through

this fluid membrane, resulting in constantly

changing patterns

– Referred to as fluid mosaic (made up of many

pieces) pattern

• Surface sugars form glycocalyx

• Membrane structures help to hold cells together

through cell junctions


Figure 3.3 The plasma membrane.

Extracellular fluid(watery environmentoutside cell)

Cholesterol

Glycolipid GlycoproteinPolar head of phospholipid molecule

Nonpolar tail of phospholipid moleculeGlycocalyx

(carbohydrates)

Lipid bilayer

containing proteins

Outward-facing

layer of

phospholipids

Inward-facing layer

of phospholipids

Filament of cytoskeleton

Peripheral proteins

Integral proteins

Cytoplasm (watery environmentinside cell)

Functions of the

Plasma Membrane:

• Mechanical barrier: Separates two

of the body’s fluid compartments.

• Selective permeability: Determines

manner in which substances enteror exit the cell.

• Electrochemical gradient:

Generates and helps to maintain

the electrochemical gradient requiredfor muscle and neuron function.

• Communication: Allows cell-to-cell recognition

(e.g., of egg by sperm) and interaction.

• Cell signaling: Plasma membrane proteins

interact with specific chemical messengersand relay messages to the cell interior.


Animation: Membrane Structure


Membrane Lipids

• Lipid bilayer is made up of:

– 75% phospholipids, which consist of two parts:

• Phosphate heads: are polar (charged), so are

hydrophilic (water-loving)

• Fatty acid tails: are nonpolar (no charge), so are

hydrophobic (water-hating)

– 5% glycolipids

• Lipids with sugar groups on outer membrane surface

– 20% cholesterol

• Increases membrane stability


Membrane Proteins

• Allow cell communication with environment

• Make up about half the mass of plasma

membrane

• Most have specialized membrane functions

• Some float freely, and some are tethered to

intracellular structures

• Two types:

– Integral proteins; peripheral proteins


Membrane Proteins (cont.)

• Integral proteins

– Firmly inserted into membrane

– Most are transmembrane proteins (span

membrane)

– Have both hydrophobic and hydrophilic regions

• Hydrophobic areas interact with lipid tails

• Hydrophilic areas interact with water

– Function as transport proteins (channels and

carriers), enzymes, or receptors


Membrane Proteins (cont.)

• Peripheral proteins

– Loosely attached to integral proteins

– Include filaments on intracellular surface used for

plasma membrane support

– Function as:

• Enzymes

• Motor proteins for shape change during cell division

and muscle contraction

• Cell-to-cell connections


Figure 3.4 Membrane proteins perform many tasks.

• A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute.

• Some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane.

• A membrane protein exposed to the outside of the cell may have a binding site that fits the shape of a specific chemical messenger, such as a hormone.

• When bound, the chemical messengermay cause a change in shape in theprotein that initiates a chain of chemicalreactions in the cell.

• Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may anchor to membrane proteins, which helps maintain cell shape and fix the location of certain membrane proteins.

• Others play a role in cell movement or bind adjacent cells together.

• A membrane protein may be an enzyme with its active site exposed to substancesin the adjacent solution.

• A team of several enzymes in a membrane may catalyze sequential steps of ametabolic pathway as indicated (left toright) here.

• Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions.

• Some membrane proteins (cell adhesion molecules or CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cellinteractions.

• Some glycoproteins (proteins bonded to short chains of sugars which help to makeup the glycocalyx) serve as identificationtags that are specifically recognized by other cells.

Intercellular joining

Cell-cell recognitionAttachment to the cytoskeletonand extracellular matrix

Receptors for signal transduction

Transport Enzymatic activity

Glycoprotein

CAMs

Enzymes

ATP

Signal

Receptor


Figure 3.4a Membrane proteins perform many tasks.

Transport

• A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute.

• Some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane.

ATP


Animation: Transport Proteins


Figure 3.4b Membrane proteins perform many tasks.

Receptors for signal transduction

• A membrane protein exposed to the outside of the cell may have a binding site that fits the shape of a specific chemical messenger, such as a hormone.

• When bound, the chemical messengermay cause a change in shape in theprotein that initiates a chain of chemicalreactions in the cell.

Signal

Receptor


Animation: Receptor Proteins


Figure 3.4c Membrane proteins perform many tasks.

• Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may anchor to membrane proteins, which helps maintain cell shape and fix the location of certain membrane proteins.

• Others play a role in cell movement or bind

adjacent cells together.

Attachment to the cytoskeletonand extracellular matrix


Animation: Structural Proteins


Figure 3.4d Membrane proteins perform many tasks.

Enzymatic activity

• A membrane protein may be an enzyme

with its active site exposed to substances

in the adjacent solution. • A team of several enzymes in a membrane

may catalyze sequential steps of ametabolic pathway as indicated (left toright) here.

Enzymes


Animation: Enzymes


Figure 3.4e Membrane proteins perform many tasks.

Intercellular joining

• Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions.

• Some membrane proteins (cell adhesion molecules or CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cellinteractions.

CAMs


Figure 3.4f Membrane proteins perform many tasks.

Cell-cell recognition

• Some glycoproteins (proteins bonded to short chains of sugars which help to makeup the glycocalyx) serve as identificationtags that are specifically recognized by other cells.

Glycoprotein


Glycocalyx

• Consists of sugars (carbohydrates) sticking out

of cell surface

– Some sugars are attached to lipids (glycolipids)

and some to proteins (glycoproteins)

• Every cell type has different patterns of this

“sugar coating”

– Functions as specific biological markers for cell-

to-cell recognition

– Allows immune system to recognize “self” vs.

“nonself”


Clinical – Homeostatic Imbalance 3.1

• Glycocalyx of some cancer cells can change so

rapidly that the immune system cannot recognize

the cell as being damaged.

• Mutated cell is not destroyed by immune system so

it is able to replicate


Cell Junctions

• Some cells are “free” (not bound to any other

cells)

– Examples: blood cells, sperm cells

• Most cells are bound together to form tissues

and organs

• Three ways cells can be bound to each other

– Tight junctions

– Desmosomes

– Gap junctions


Cell Junctions (cont.)

• Tight junctions

– Integral proteins on adjacent cells fuse to form

an impermeable junction that encircles whole

cell

– Prevent fluids and most molecules from moving

in between cells

– Where might these be useful in body?


Figure 3.5a Cell junctions.

Interlocking

junctional

proteins

Intercellular

space

Basement membrane

Microvilli

Intercellular

space

Plasma membranes

of adjacent cells

Tight junctions: Impermeable

junctions that form continuous

seals around the cells prevent

molecules from passing through

the intercellular space.© 2017 Pearson Education, Inc.


• Desmosomes

– Rivet-like cell junction formed when linker

proteins (cadherins) of neighboring cells interlock

like the teeth of a zipper

– Linker protein is anchored to its cell through

thickened “button-like” areas on inside of plasma

membrane called plaques

– Keratin filaments connect plaques intercellularly

for added anchoring strength

– Desmosomes allow “give” between cells,

reducing the possibility of tearing under tension

– Where might these be useful in body?© 2017 Pearson Education, Inc.

Figure 3.5b Cell junctions.

Plaque

Intercellular space

Linker

proteins

(cadherins)Intermediate

filament (keratin)

Microvilli

Intercellular

space

Plasma membranes

of adjacent cells

Desmosomes: Anchoring junctions

that bind adjacent cells together act

like molecular “Velcro” and also help

form an internal tension-reducing

network of fibers.

Basement membrane



• Gap junctions

– Transmembrane proteins (connexons) form

tunnels that allow small molecules to pass from

cell to cell

– Used to spread ions, simple sugars, or other

small molecules between cells

– Allows electrical signals to be passed quickly

from one cell to next cell

• Used in cardiac and smooth muscle cells


Figure 3.5c Cell junctions.

Intercellular

space

Channel

between cells

(formed by

connexons)

Basement membrane

Microvilli

Intercellular

space

Plasma membranes

of adjacent cells

Gap junctions: Communicating

junctions that allow ions and small

molecules to pass are particularly

important for communication in

heart cells and embryonic cells.© 2017 Pearson Education, Inc.

How do substances move across the plasma

membrane?

• Plasma membranes are selectively permeable

– Some molecules pass through easily; some do

not

• Two ways substances cross membrane

– Passive processes: no energy required

– Active processes: energy (ATP) required


3.3 Passive Membrane Transport

• Passive transport requires no energy

• Two types of passive transport

– Diffusion

• Simple diffusion

• Carrier- and channel-mediated facilitated diffusion

• Osmosis

– Filtration

• Type of transport that usually occurs across capillary

walls


Diffusion

• Collisions between molecules in areas of high

concentration cause them to be scattered into

areas with less concentration

– Difference is called concentration gradient

– Diffusion is movement of molecules down their

concentration gradients (from high to low)

• Energy is not required

• Speed of diffusion is influenced by size of

molecule and temperature


Figure 3.6 Diffusion.

Dye pellet Diffusion occurring Dye evenly distributed


Diffusion (cont.)

• Molecules have natural drive to diffuse down

concentration gradients that exist between

extracellular and intracellular areas

• Plasma membranes stop diffusion and create

concentration gradients by acting as selectively

permeable barriers



• If plasma membrane is severely damaged,

substances diffuse freely into and out of cell,

compromising concentration gradients

• Example: burn patients lose precious fluids,

proteins, and ions that weep from damaged

cells


Diffusion (cont.)

• Nonpolar, hydrophobic lipid core of plasma

membrane blocks diffusion of most molecules

• Molecules that are able to passively diffuse

through membrane include:

– Lipid-soluble and nonpolar substances

– Very small molecules that can pass through

membrane or membrane channels

– Larger molecules assisted by carrier molecules


Diffusion (cont.)

• Simple diffusion

– Nonpolar lipid-soluble (hydrophobic) substances

diffuse directly through phospholipid bilayer

– Examples: oxygen, carbon dioxide, fat-soluble

vitamins


Animation: Diffusion


Figure 3.7a Diffusion through the plasma membrane.

Extracellular fluid

Lipid-

soluble

solutes

Cytoplasm

Simple diffusion

of fat-soluble

molecules directly

through the

phospholipid bilayer© 2017 Pearson Education, Inc.

Diffusion (cont.)

• Facilitated diffusion

– Certain hydrophobic molecules (e.g., glucose,

amino acids, and ions) are transported passively

down their concentration gradient by:

• Carrier-mediated facilitated diffusion

– Substances bind to protein carriers

• Channel-mediated facilitated diffusion

– Substances move through water-filled channels


Diffusion (cont.)

• Carrier-mediated facilitated diffusion

– Carriers are transmembrane integral proteins

– Carriers transport specific polar molecules, such

as sugars and amino acids, that are too large for

membrane channels

• Example of specificity: glucose carriers will carry only

glucose molecules, nothing else

– Binding of molecule causes carrier to change

shape, moving molecule in process

– Binding is limited by number of carriers present

• Carriers are saturated when all are bound to

molecules and are busy transporting© 2017 Pearson Education, Inc.

Figure 3.7b Diffusion through the plasma membrane.

Lipid-insoluble solutes

(such as sugars or

amino acids)

Shape

change

releases

solutes

Carrier-mediated facilitated

diffusion via protein carrier

specific for one chemical; binding

of substrate causes transport

protein to change shape© 2017 Pearson Education, Inc.

Diffusion (cont.)

• Channel-mediated facilitated diffusion

– Channels with aqueous-filled cores are formed by

transmembrane proteins

– Channels transport molecules such as ions or water

(osmosis) down their concentration gradient

• Specificity based on pore size and/or charge

• Water channels are called aquaporins

– Two types:

• Leakage channels

– Always open

• Gated channels

– Controlled by chemical or electrical signals


Figure 3.7c Diffusion through the plasma membrane.

Small lipid-

insoluble

solutes

Channel-mediated

facilitated diffusion

through a channel

protein; mostly ions

selected on basis of

size and charge© 2017 Pearson Education, Inc.

Diffusion (cont.)

• Osmosis

– Movement of solvent, such as water, across a

selectively permeable membrane

– Water diffuses through plasma membranes

• Through lipid bilayer (even though water is polar, it is

so small that some molecules can sneak past

nonpolar phospholipid tails)

• Through specific water channels called aquaporins

(AQPs)

– Flow occurs when water (or other solvent)

concentration is different on the two sides of a

membrane© 2017 Pearson Education, Inc.

Figure 3.7d Diffusion through the plasma membrane.

Water

molecules

Lipid

bilayer

Aquaporin

Osmosis, diffusion of

a solvent such as water

through a specific

channel protein

(aquaporin) or through

the lipid bilayer© 2017 Pearson Education, Inc.

Diffusion (cont.)

• Osmolarity: measure of total concentration of

solute particles

• Water concentration varies with number of

solute particles because solute particles

displace water molecules

– When solute concentration goes up, water

concentration goes down, and vice versa

• Water moves by osmosis from areas of low

solute (high water) concentration to high areas

of solute (low water) concentration


Diffusion (cont.)

• When solutions of different osmolarity are

separated by a membrane permeable to all

molecules, both solutes and water cross

membrane until equilibrium is reached

– Equilibrium: Same concentration of solutes and

water molecules on both sides, with equal

volume on both sides


Figure 3.8a Influence of membrane permeability on diffusion and osmosis.

Membrane permeable to both solutes and water

Solute and water molecules move down their concentration gradients inopposite directions. Fluid volume remains the same in both compartments.

Leftcompartment:

Solution withlower osmolarity

Rightcompartment:

Solution with greater osmolarity

Both solutions have thesame osmolarity: volumeunchanged

Solutemolecules(sugar)

Freelypermeablemembrane

Solute

H2O


Diffusion (cont.)

• When solutions of different osmolarity are

separated by a membrane that is permeable

only to water, not solutes, osmosis will occur

until equilibrium is reached

– Same concentration of solutes and water

molecules on both sides, with unequal volumes

on both sides


Figure 3.8b Influence of membrane permeability on diffusion and osmosis.

Membrane permeable to water, impermeable to solutes

Solute molecules are prevented from moving but water moves by osmosis.Volume increases in the compartment with the higher osmolarity.

H2O

Leftcompartment

Rightcompartment

Solutemolecules(sugar)

Selectivelypermeablemembrane

Both solutions have identicalosmolarity, but volume of thesolution on the right is greaterbecause only water is free to move


Diffusion (cont.)

• Movement of water causes pressures:

– Hydrostatic pressure: pressure of water inside

cell pushing on membrane

– Osmotic pressure: tendency of water to move

into cell by osmosis

• The more solutes inside a cell, the higher the osmotic

pressure


Animation: Osmosis


Diffusion (cont.)

• A living cell has limits to how much water can enter

it

• Water can also leave a cell, causing cell to shrink

• Change in cell volume can disrupt cell function,

especially in neurons


Diffusion (cont.)

• Tonicity

– Ability of a solution to change the shape or tone

of cells by altering the cells’ internal water

volume

• Isotonic solution has same osmolarity as inside the

cell, so volume remains unchanged

• Hypertonic solution has higher osmolarity than

inside cell, so water flows out of cell, resulting in cell

shrinking

– Shrinking is referred to as crenation

• Hypotonic solution has lower osmolarity than inside

cell, so water flows into cell, resulting in cell swelling

– Can lead to cell bursting, referred to as lysing© 2017 Pearson Education, Inc.

Figure 3.9 The effect of solutions of varying tonicities on living red blood cells.

Isotonic solutions Hypertonic solutions Hypotonic solutions

Cells retain their normal size andshape in isotonic solutions (same

solute/water concentration asinside cells; water moves in

and out).

Cells lose water by osmosis andshrink in a hypertonic solution

(contains a higher concentrationof nonpenetrating solutes thanare present inside the cells).

Cells take on water by osmosisuntil they become bloated and

burst (lyse) in a hypotonicsolution (contains a lower

concentration of nonpenetratingsolutes than are present

inside cells).



• Intravenous solutions of different tonicities can

be given to patients suffering different ailments

– Isotonic solutions are most commonly given

when blood volume needs to be increased

quickly

– Hypertonic solutions are given to edematous

(swollen) patients to pull water back into blood

– Hypotonic solutions should not be given because

they can result in dangerous lysing of red and

white blood cells


Cells: The Living Unitsdrjerrycronin.weebly.com/uploads/5/9/7/4/5974564/...3.1 Cells: The Living...

Documents

Transcript of Cells: The Living Unitsdrjerrycronin.weebly.com/uploads/5/9/7/4/5974564/...3.1 Cells: The Living...