The CellAP Biology

1. All organisms are made up of cells

2. The cell is the basic unit of structure and function in all organisms

3. All cells come from pre-existing cells

The Cell Theory

Underlying the diversity of life is a striking unity

Activities of lifeMost everything you think of a whole organism needing to do, must be done at the cellular level…

reproductiongrowth & developmentenergy utilizationresponse to the environmenthomeostasis

Eukaryoteanimal cellsEukaryoteanimal cells

Eukaryoteplant cellsEukaryoteplant cells

Prokaryotebacteria cells

Prokaryotebacteria cells

Types of Cells

• Specialized structures• specialized functions

• cilia or flagella for locomotion

• Containers• partition cell into compartments• create different local environments

• separate pH, or concentration of materials

• distinct & incompatible functions• lysosome & its digestive enzymes

• Membranes as sites for chemical reactions• unique combinations of lipids &

proteins • embedded enzymes & reaction

centers• chloroplasts & mitochondria

Organellesmitochondria

chloroplast

Golgi

ER

•What jobs do cells have to do?•building proteins•proteins control every cell function

•make energy• for daily life• for growth

•build more cells•growth• reproduction• repair

DNADNA

Why study protein production?

cellscells

proteinsproteins

organismorganism

Building Proteins• Organelles involved• nucleus• ribosomes• endoplasmic reticulum

(ER)• Golgi apparatus• vesicles

nucleus ribosome ERGolgiapparatus

vesicles

The Protein Assembly Line

DNA

RNA

ribosomes

endoplasmicreticulum

vesicle

Golgi apparatus

vesicle

proteinon its way!

protein finishedprotein

Making Proteins

TO:

TO:

TO:

TO:

nucleusTO:

proteins

transportvesicle

Golgiapparatus

vesicle

smooth ER

rough ER

nuclear porenucleus

ribosome

cellmembrane protein secreted

cytoplasm

Making proteins

Putting it together…

Cells gotta live! • What jobs do cells have to do?• make proteins• proteins control every cell function

• make energy• for daily life• for growth

• build more cells• growth• reproduction• repair

ATP

Cells need power!

•Making energy• take in food & digest it• take in oxygen (O2)•make ATP• remove waste

ATP

Lysosomes• Function • little “stomach” of the cell• digests macromolecules

• “clean up crew” of the cell• cleans up broken down organelles

• Structure• vesicles of digestive enzymes

only in animal cellsonly in animal cells

Christian de Duve

1960 | 1974

Where old organellesgo to die!

Lysosomal enzymes • Lysosomal enzymes work best at pH 5• organelle creates custom pH• how? • proteins in lysosomal membrane

pump H+ ions from the cytosol into lysosome

• why? • enzymes are very sensitive

to pH• why? • enzymes are proteins —

pH affects structure• why is this an adaptation: digestive enzymes which function at pH

different from cytosol?• digestive enzymes won’t function well if some leak into cytosol =

don’t want to digest yourself!

But sometimes cells need to die…

• Lysosomes can be used to kill cells when they are supposed to be destroyed• some cells have to die for proper

development in an organism• apoptosis • “auto-destruct” process • lysosomes break open & kill cell

• ex: tadpole tail gets re-absorbed when it turns into a frog• ex: loss of webbing between your

fingers during fetal development • ex: self-destruct of cancerous cell

Fetal development

15 weeks

6 weeks

syndactyly

When things go wrong…

• Diseases of lysosomes are often fatal• digestive enzyme not working in lysosome• picks up biomolecules, but can’t digest one• lysosomes fill up with undigested material

• grow larger & larger until disrupts cell & organ function • lysosomal storage diseases• more than 40 known diseases

• example:Tay-Sachs diseasebuild up undigested fat in brain cells

From food to making Energy• Cells must convert incoming energy to forms that they can

use for work• mitochondria:

from glucose to ATP• chloroplasts:

from sunlight to ATP & carbohydrates• ATP = immediate energy• carbohydrates = stored energy

+

ATP

ATP

Mitochondria & Chloroplasts• Important to see the similarities• transform energy• generate ATP

• double membranes = 2 membranes• semi-autonomous organelles• move, change shape, divide

• internal ribosomes, DNA & enzymes

Lynn MargulisU of M, Amherst

Membrane-bound Enzymes

glucose + oxygen carbon + water + energydioxide

C6H12O6 6O2 6CO2 6H2O ATP+ + +

Membrane-bound Enzymes

+ water + energy glucose + oxygencarbondioxide

6CO2 6H2O C6H12O6 6O2lightenergy + ++

Mitochondria are everywhere!!animal cellsanimal cells plant cellsplant cells

Cells gotta live! • What jobs do cells have to do?• building proteins• proteins control

every cell function • make energy• for daily life• for growth

• build more cells• growth• reproduction• repair

Cytoskeleton

• Function• structural support • maintains shape of cell• provides anchorage for organelles• protein fibers• microfilaments, intermediate

filaments, microtubules• motility• cell locomotion• cilia, flagella, etc.

• regulation • organizes structures

& activities of cell

actin microtubule nuclei

Cytoskeleton

Centrioles • Cell division• in animal cells, pair of centrioles

organize microtubules • guide chromosomes in mitosis

2007-2008

Cell Size

Limits to cell size• Lower limit• smallest bacteria• mycoplasmas• 0.1 to 1.0 micron (µm =

micrometer)• most bacteria• 1-10 microns

• Upper limit • eukaryotic cells • 10-100 microns

micron = micrometer = 1/1,000,000 meter diameter of human hair = ~20 microns

What limits cell size?

• Surface to volume ratio• as cell gets bigger

its volume increases faster than its surface area• smaller objects

have greaterratio of surface area to volume 6:1 ~1:1 6:1s:v

Limits to cell size

• Metabolic requirements set upper limit• in large cell, cannot move material in

& out of cell fast enough to support life

CHO

CHO

aa

aa

CH

CO2

NH3aa

O2

CH

What’s the solution?

What process is this?

O2

O2

aa

CHO

aa

CH

O2

aa

CHO

CH

aa

O2

CO2

NH3

NH3

CO2

CO2

NH3

How to get bigger?• Become multicellular (cell divides)

O2

CHO

CHO

aa

aa

CH

CO2

NH3aa

O2

CH

But what challenges do you have to solve now?

aa

CO2

CO2

CO2

CO2

CO2

CO2 CO2

CO2

CO2

CO2

NH3

NH3 NH3

NH3

NH3

NH3

NH3NH3

O2

aa

CH

aa

CHO

O2

Phospholipid Cholesterol

Membraneproteins

Cell membrane• Exchange structure• plasma membrane functions as selective

barrier• allows passage of O2 & nutrients IN• allows passage of products & wastes OUT

Cell Membrane

Overview• Cell membrane separates living cell from nonliving surroundings• thin barrier = 8nm thick

• Controls traffic in & out of the cell• selectively permeable• allows some substances to cross more

easily than others• hydrophobic vs hydrophilic

• Made of phospholipids, proteins & other macromolecules

Phospholipids

Fatty acid

Phosphate

• Fatty acid tails• hydrophobic

• Phosphate group head • hydrophilic

• Arranged as a bilayer

Structure and function relationship

Phospholipid bilayer

polarhydrophilicheads

nonpolarhydrophobictails

polarhydrophilicheads

More than lipids…

• In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer

Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer

Extracellular fluid

Cholesterol

Cytoplasm

Glycolipid

Transmembraneproteins

Filaments ofcytoskeleton

Peripheralprotein

Glycoprotein

Phospholipids

Membrane fat composition varies• Fat composition affects flexibility• membrane must be fluid & flexible• about as fluid as thick salad oil

• % unsaturated fatty acids in phospholipids• keep membrane less viscous• cold-adapted organisms, like winter wheat • increase % in autumn

• cholesterol in membrane

Membrane Proteins• Proteins determine membrane’s specific functions• cell membrane & organelle membranes

each have unique collections of proteins

• Membrane proteins:• peripheral proteins

• loosely bound to surface of membrane• cell surface identity marker (antigens)

• integral proteins • penetrate lipid bilayer, usually across whole

membrane

• transmembrane protein

• transport proteins• channels, permeases (pumps)

Classes of amino acidsWhat do these amino acids have in common?What do these amino acids have in common?

nonpolar & hydrophobicnonpolar & hydrophobic

Classes of amino acidsWhat do these amino acids have in common?What do these amino acids have in common?

polar & hydrophilicpolar & hydrophilic

Protein’s domains anchor molecule• Within membrane• nonpolar amino acids • hydrophobic • anchors protein

into membrane

• On outer surfaces of membrane• polar amino acids • hydrophilic• extend into

extracellular fluid & into cytosol

Polar areasof protein

Nonpolar areas of protein

NH2

H+

COOH

Cytoplasm

Retinalchromophore

Nonpolar(hydrophobic)a-helices in thecell membrane H+

Porin monomer

b-pleated sheets

Bacterialoutermembrane

proton pump channel in photosynthetic bacteria

water channel in bacteria

function through conformational change = shape change

function through conformational change = shape change

Examples

Many Functions of Membrane Proteins

Outside

Plasmamembrane

InsideTransporter Cell surface

receptorEnzymeactivity

Cell surface identity marker

Attachment to thecytoskeleton

Cell adhesion

Membrane carbohydrates

• Play a key role in cell-cell recognition• ability of a cell to distinguish

one cell from another• antigens

• important in organ & tissue development• basis for rejection of

foreign cells by immune system

Movement across the Cell Membrane

Diffusion• 2nd Law of Thermodynamics

governs biological systems• universe tends towards disorder

(entropy)

Diffusion movement from high low concentration

Diffusion movement from high low concentration

Diffusion• Move from HIGH to LOW concentration• “passive transport”• no energy needed

diffusion osmosis

movement of water

Diffusion across cell membrane• Cell membrane is the boundary between

inside & outside…• separates cell from its environment

INfoodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O

OUTwasteammoniasaltsCO2

H2O products

cell needs materials in & products or waste out

IN

OUT

Can it be an impenetrable boundary?NO!

Diffusion through phospholipid bilayer• What molecules can get through directly?

• fats & other lipids

inside cell

outside cell

lipid

salt

aa H2Osugar

NH3

What molecules can NOT get through directly?

polar molecules H2O

ions salts, ammonia

large molecules starches, proteins

Channels through cell membrane

• Membrane becomes semi-permeable with protein channels • specific channels allow specific material

across cell membrane

inside cell

outside cell

sugaraaH2O

saltNH3

Facilitated Diffusion• Diffusion through protein channels• channels move specific molecules across

cell membrane• no energy needed

“The Doorman”“The Doorman”

open channel = fast transport

facilitated = with help

high

low

Active Transport

“The Bouncer”“The Bouncer”

conformational change

• Cells may need to move molecules against concentration gradient• shape change transports solute from

one side of membrane to other • protein “pump”• “costs” energy = ATP

ATP

low

high

symportantiport

Active transport•Many models & mechanisms

ATP ATP

video

Getting through cell membrane• Passive Transport• Simple diffusion

• diffusion of nonpolar, hydrophobic molecules• lipids• high low concentration gradient

• Facilitated transport• diffusion of polar, hydrophilic molecules• through a protein channel

• high low concentration gradient

• Active transport• diffusion against concentration gradient

• low high

• uses a protein pump• requires ATP

ATP

Transport summary

simplediffusion

facilitateddiffusion

activetransport

ATP

How about large molecules?

• Moving large molecules into & out of cell• through vesicles & vacuoles• endocytosis• phagocytosis = “cellular eating”• pinocytosis = “cellular drinking”

• exocytosis

exocytosis

Endocytosis

phagocytosis

pinocytosis

receptor-mediated endocytosis

fuse with lysosome for digestion

non-specificprocess

triggered bymolecular signal

2007-2008

The Special Case of Water

Movement of water across the cell membrane

Osmosis is diffusion of water

• Water is very important to life, so we talk about water separately

• Diffusion of water from high concentration of water to low concentration of water• across a

semi-permeable membrane

Concentration of water• Direction of osmosis is determined by

comparing total solute concentrations• Hypertonic - more solute, less water

• Hypotonic - less solute, more water

• Isotonic - equal solute, equal water

hypotonic hypertonic

water

net movement of water

freshwater balanced saltwater

Managing water balance• Cell survival depends on balancing water

uptake & loss

Managing water balance

• Isotonic• animal cell immersed in

mild salt solution• example:

blood cells in blood plasma• problem: none• no net movement of water• flows across membrane

equally, in both directions

• volume of cell is stablebalanced

Managing water balance

• Hypotonic• a cell in fresh water

• example: Paramecium

• problem: gains water, swells & can burst• water continually enters

Paramecium cell

• solution: contractile vacuole • pumps water out of cell

• ATP

• plant cells• turgid

freshwater

ATP

Water regulation

• Contractile vacuole in Paramecium

Managing water balance

• Hypertonic• a cell in salt water• example: shellfish• problem: lose water &

die• solution: take up water

or pump out salt• plant cells• plasmolysis = wilt

saltwatervideo

Aquaporins• Water moves rapidly into & out of cells• evidence that there were water channels

1991 | 2003

Peter AgreJohn Hopkins

Roderick MacKinnonRockefeller

Cell (compared to beaker) hypertonic or hypotonic

Beaker (compared to cell) hypertonic or hypotonic

Which way does the water flow? in or out of cell

.05 M .03 M

Osmosis…

Gradients (ATP Synthase)

Cotransport (Symport and Antiport)

Bozeman, Cell Communication

Bozeman, Signal Transduction Pathways

Cell Signals (DNA Learning Center)